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InfoMagic Standards 1994 January
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InfoMagic Standards - January 1994.iso
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ccitt
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1988
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8_1_03.tro
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1991-12-22
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.rs
.\" Troff code generated by TPS Convert from ITU Original Files
.\" Not Copyright (~c) 1991
.\"
.\" Assumes tbl, eqn, MS macros, and lots of luck.
.TA 1c 2c 3c 4c 5c 6c 7c 8c
.ds CH
.ds CF
.EQ
delim @@
.EN
.nr LL 40.5P
.nr ll 40.5P
.nr HM 3P
.nr FM 6P
.nr PO 4P
.nr PD 9p
.po 4P
.rs
\v'|.5i'
.LP
\fBMONTAGE:\ \ \ \fR Fin de la Rec. V.23 en t\*\|ete de cette page
.sp 2P
.LP
\v'13P'
\fBRecommendation\ V.24\fR
.RT
.sp 2P
.ce 1000
\fBLIST\ OF\ \fR \fBDEFINITIONS\ FOR\ INTERCHANGE\ CIRCUITS\ BETWEEN\fR
.EF '% Fascicle\ VIII.1\ \(em\ Rec.\ V.24''
.OF '''Fascicle\ VIII.1\ \(em\ Rec.\ V.24 %'
.ce 0
.sp 1P
.ce 1000
\fBDATA\ TERMINAL\ EQUIPMENT\ (DTE)\ AND\ DATA\ CIRCUIT\(hyTERMINATING\fR \|
\fBEQUIPMENT\ (DCE)\fR
.ce 0
.sp 1P
.ce 1000
\fI(Geneva, 1964, amended at Mar del Plata, 1968,\fR
.sp 9p
.RT
.ce 0
.sp 1P
.ce 1000
\fIGeneva, 1972, 1976 and 1980, Malaga\(hyTorremolinos, 1984\fR \fIand
at Melbourne, 1988)\fR
.ce 0
.sp 1P
.LP
\fB1\fR \fBScope\fR
.sp 1P
.RT
.PP
1.1
This Recommendation applies to the interconnecting circuits
being called
interchange circuits
at the
interface between DTE and DCE
for the transfer of binary data, control and timing signals and
analogue signals as appropriate. This Recommendation also applies to both
sides of separate intermediate equipment, which may be inserted between
these two
classes of equipment (see Figure\ 1/V.24).
.sp 9p
.RT
.LP
.rs
.sp 19P
.ad r
\fBFigure 1/V.24, (M), p.\fR
.sp 1P
.RT
.ad b
.RT
.LP
.bp
.PP
Electrical characteristics for interchange circuits are detailed in appropriate
Recommendations for electrical characteristics, or in certain
special cases, in Recommendations for DCE.
.PP
In any type of practical equipment a selection will be made from the range
of interchange circuits defined in this Recommendation, as appropriate.
.PP
The actual interchange circuits to be used in a particular DCE are
those indicated in the appropriate Recommendation.
.PP
The required interchange circuits specified in the DCE Recommendations
which make reference to this Recommendation apply only to the DCE side
of the interface. Only those circuits necessary to assure satisfactory
operation of
the application the DTE is intending to support need be controlled or monitored
by the DTE. (See note to \(sc\ 3.4 for proper handling of unimplemented
circuits).
.PP
The usage and operational requirements of the interchange circuits and
the interaction between them are recommended in \(sc\ 4. For proper operation
of
the DCE it is important that the guidelines in \(sc\ 4 are observed.
.RT
.PP
1.2
The DCE may include signal converters, timing generators, pulse
regenerators, and control circuitry, together with equipment to provide
other functions such as error control, automatic calling and automatic
answering.
Some of this equipment may be separate intermediate equipment or it may be
located in the DTE.
.PP
1.3
The range of interchange circuits defined in this
Recommendation is applicable, for example:
.LP
a)
to synchronous and asynchronous data communications;
.LP
b)
to data transmission on leased line service, either 2\(hywire
or 4\(hywire, either point\(hyto\(hypoint or multipoint operation;
.LP
c)
to data transmission on switched network service, either
2\(hywire or 4\(hywire;
.LP
d)
where short interconnecting cables are used between DTE
and DCE. An explanation of short cables is given in \(sc\ 2
below.
.PP
1.4
A DTE interface conforming to this Recommendation may also be
used for attachment to a Public Data Network (PDN). For these cases,
additional information on interchange circuit implementation and operational
requirements may be recorded in Series\ X Recommendations.
.sp 2P
.LP
\fB2\fR \fBLine of demarcation\fR
.sp 1P
.RT
.PP
The interface between DTE and DCE is located at a connector, which is the
interchange point between these two classes of equipment. Separate
connectors may be provided for the interchange circuits associated with the
signal\(hyconversion or similar equipment and those associated with the
parallel automatic calling equipment. For mechanical characteristics of
the interface
refer to ISO\ 2110 or ISO\ 4902 as appropriate.
.PP
The connector(s) will not necessarily be physically attached to the
DCE and may be mounted in a fixed position near the DTE.
.PP
An interconnecting cable or cables will normally be provided with the DTE.
The use of short cables is recommended. Their length should be limited
solely by the load capacitance and other electrical characteristics specified
in the relevant Recommendation on electrical characteristics.
.RT
.sp 2P
.LP
\fB3\fR \fBDefinitions of interchange circuits\fR
.sp 1P
.RT
.sp 1P
.LP
3.1
\fI100\ series\fR \ \(em\ \fIGeneral application\fR
.sp 9p
.RT
.PP
A list of these interchange circuits is presented in tabular form in Table\
1/V.24.
.RT
.sp 1P
.LP
\fICircuit\ 102\ \(em\ \fR \fISignal ground or common return\fR
.sp 9p
.RT
.PP
This conductor establishes the signal common return for unbalanced interchange
circuits with electrical characteristics according to
Recommendation\ V.28 and the d.c. reference potential for interchange circuits
according to Recommendations\ V.10, V.11 and V.35.
.PP
Within the DCE, this circuit shall be brought to one point, and it
shall be possible to connect this point to protective ground or earth by
means of a metallic strap within the equipment. This metallic strap can
be connected or removed at installation, as may be required to meet applicable
safety
regulations or to minimize the introduction of noise into electronic circuitry.
Caution should be exercised to prevent the establishment of ground loops
carrying high currents.
.bp
.RT
.ce
\fBH.T. [T1.24]\fR
.ce
TABLE\ 1/V.24
.ce
\fB100\(hyseries interchange circuits by category\fR
.ps 9
.vs 11
.nr VS 11
.nr PS 9
.TS
center box;
cw(30p) | cw(96p) | cw(12p) | cw(18p) sw(12p) | cw(18p) sw(12p) | cw(18p) sw(12p) , ^ | ^ | ^ | c | c | c | c | c | c.
Interchange circuit number Interchange circuit name Ground Data Control Timing
From DCE To DCE From DCE To DCE From DCE To DCE
_
.T&
cw(30p) | cw(96p) | cw(12p) | cw(18p) | cw(12p) | cw(18p) | cw(12p) | cw(18p) | cw(12p) .
1 2 3 4 5 6 7 8 9
_
.T&
lw(30p) | lw(96p) | cw(12p) | lw(18p) | lw(12p) | lw(18p) | lw(12p) | lw(18p) | lw(12p) .
102 T{
Signal ground or common return
T} X
.T&
lw(30p) | lw(96p) | cw(12p) | lw(18p) | lw(12p) | lw(18p) | lw(12p) | lw(18p) | lw(12p) .
102a DTE common return X
.T&
lw(30p) | lw(96p) | cw(12p) | lw(18p) | lw(12p) | lw(18p) | lw(12p) | lw(18p) | lw(12p) .
102b DCE common return X
.T&
lw(30p) | lw(96p) | cw(12p) | lw(18p) | lw(12p) | lw(18p) | lw(12p) | lw(18p) | lw(12p) .
102c Common return X
.T&
lw(30p) | lw(96p) | cw(12p) | lw(18p) | cw(12p) | lw(18p) | lw(12p) | lw(18p) | lw(12p) .
103 Transmitted data X
.T&
lw(30p) | lw(96p) | cw(12p) | cw(18p) | cw(12p) | lw(18p) | lw(12p) | lw(18p) | lw(12p) .
104 Received data X
.T&
lw(30p) | lw(96p) | cw(12p) | cw(18p) | cw(12p) | lw(18p) | cw(12p) | lw(18p) | lw(12p) .
105 Request to send X
.T&
lw(30p) | lw(96p) | cw(12p) | cw(18p) | cw(12p) | cw(18p) | cw(12p) | lw(18p) | lw(12p) .
106 Ready for sending X
.T&
lw(30p) | lw(96p) | cw(12p) | cw(18p) | cw(12p) | cw(18p) | cw(12p) | lw(18p) | lw(12p) .
107 Data set ready X
.T&
lw(30p) | lw(96p) | cw(12p) | cw(18p) | cw(12p) | cw(18p) | cw(12p) | lw(18p) | lw(12p) .
108/1 Connect data set to line X
.T&
lw(30p) | lw(96p) | cw(12p) | cw(18p) | cw(12p) | cw(18p) | cw(12p) | lw(18p) | lw(12p) .
108/2 Data terminal ready X
.T&
lw(30p) | lw(96p) | cw(12p) | cw(18p) | cw(12p) | cw(18p) | cw(12p) | lw(18p) | lw(12p) .
109 T{
Data channel received line signal detector
T} X
.T&
lw(30p) | lw(96p) | cw(12p) | cw(18p) | cw(12p) | cw(18p) | cw(12p) | lw(18p) | lw(12p) .
110 Data signal quality detector X
.T&
lw(30p) | lw(96p) | cw(12p) | cw(18p) | cw(12p) | cw(18p) | cw(12p) | lw(18p) | lw(12p) .
111 T{
Data signal rate selector (DTE)
T} X
.T&
lw(30p) | lw(96p) | cw(12p) | cw(18p) | cw(12p) | cw(18p) | cw(12p) | lw(18p) | lw(12p) .
112 T{
Data signal rate selector (DCE)
T} X
.T&
lw(30p) | lw(96p) | cw(12p) | cw(18p) | cw(12p) | cw(18p) | cw(12p) | lw(18p) | cw(12p) .
113 T{
Transmitter signal element timing
(DTE)
T} X
.T&
lw(30p) | lw(96p) | cw(12p) | cw(18p) | cw(12p) | cw(18p) | cw(12p) | cw(18p) | cw(12p) .
114 T{
Transmitter signal element timing
(DCE)
T} X
.T&
lw(30p) | lw(96p) | cw(12p) | cw(18p) | cw(12p) | cw(18p) | cw(12p) | cw(18p) | cw(12p) .
115 T{
Receiver signal element timing
(DCE)
T} X
.T&
lw(30p) | lw(96p) | cw(12p) | cw(18p) | cw(12p) | cw(18p) | cw(12p) | cw(18p) | cw(12p) .
116/1 T{
Back\(hyup switching in direct mode
T} X
.T&
lw(30p) | lw(96p) | cw(12p) | cw(18p) | cw(12p) | cw(18p) | cw(12p) | cw(18p) | cw(12p) .
116/2 T{
Back\(hyup switching in authorized mode
T} X
.T&
lw(30p) | lw(96p) | cw(12p) | cw(18p) | cw(12p) | cw(18p) | cw(12p) | cw(18p) | cw(12p) .
117 Standby indicator X
.T&
lw(30p) | lw(96p) | cw(12p) | cw(18p) | cw(12p) | cw(18p) | cw(12p) | cw(18p) | cw(12p) .
118 T{
Transmitted backward channel data
T} X
.T&
lw(30p) | lw(96p) | cw(12p) | cw(18p) | cw(12p) | cw(18p) | cw(12p) | cw(18p) | cw(12p) .
119 T{
Received backward channel data
T} X
.T&
lw(30p) | lw(96p) | cw(12p) | cw(18p) | cw(12p) | cw(18p) | cw(12p) | cw(18p) | cw(12p) .
120 T{
Transmit backward channel line signal
T} X
.T&
lw(30p) | lw(96p) | cw(12p) | cw(18p) | cw(12p) | cw(18p) | cw(12p) | cw(18p) | cw(12p) .
121 Backward channel ready X
.T&
lw(30p) | lw(96p) | cw(12p) | cw(18p) | cw(12p) | cw(18p) | cw(12p) | cw(18p) | cw(12p) .
122 T{
Backward channel received line signal detector
T} X
.T&
lw(30p) | lw(96p) | cw(12p) | cw(18p) | cw(12p) | cw(18p) | cw(12p) | cw(18p) | cw(12p) .
123 T{
Backward channel signal quality detector
T} X
.T&
lw(30p) | lw(96p) | cw(12p) | cw(18p) | cw(12p) | cw(18p) | cw(12p) | cw(18p) | cw(12p) .
124 Select frequency groups X
.T&
lw(30p) | lw(96p) | cw(12p) | cw(18p) | cw(12p) | cw(18p) | cw(12p) | cw(18p) | cw(12p) .
125 Calling indicator X
.T&
lw(30p) | lw(96p) | cw(12p) | cw(18p) | cw(12p) | cw(18p) | cw(12p) | cw(18p) | cw(12p) .
126 Select transmit frequency X
.T&
lw(30p) | lw(96p) | cw(12p) | cw(18p) | cw(12p) | cw(18p) | cw(12p) | cw(18p) | cw(12p) .
127 Select receive frequency X
.T&
lw(30p) | lw(96p) | cw(12p) | cw(18p) | cw(12p) | cw(18p) | cw(12p) | cw(18p) | cw(12p) .
128 T{
Receiver signal element timing
(DTE)
T} X
.T&
lw(30p) | lw(96p) | cw(12p) | cw(18p) | cw(12p) | cw(18p) | cw(12p) | cw(18p) | cw(12p) .
129 Request to receive X
.T&
lw(30p) | lw(96p) | cw(12p) | cw(18p) | cw(12p) | cw(18p) | cw(12p) | cw(18p) | cw(12p) .
130 Transmit backward tone X
.T&
lw(30p) | lw(96p) | cw(12p) | cw(18p) | cw(12p) | cw(18p) | cw(12p) | cw(18p) | cw(12p) .
131 Received character timing X
.T&
lw(30p) | lw(96p) | cw(12p) | cw(18p) | cw(12p) | cw(18p) | cw(12p) | cw(18p) | cw(12p) .
132 Return to non\(hydata mode X
.T&
lw(30p) | lw(96p) | cw(12p) | cw(18p) | cw(12p) | cw(18p) | cw(12p) | cw(18p) | cw(12p) .
133 Ready for receiving X
.T&
lw(30p) | lw(96p) | cw(12p) | cw(18p) | cw(12p) | cw(18p) | cw(12p) | cw(18p) | cw(12p) .
134 Received data present X
.T&
lw(30p) | lw(96p) | cw(12p) | cw(18p) | cw(12p) | cw(18p) | cw(12p) | cw(18p) | cw(12p) .
136 New signal X
.T&
lw(30p) | lw(96p) | cw(12p) | cw(18p) | cw(12p) | cw(18p) | cw(12p) | cw(18p) | cw(12p) .
140 Loopback/Maintenance test X
.T&
lw(30p) | lw(96p) | cw(12p) | cw(18p) | cw(12p) | cw(18p) | cw(12p) | cw(18p) | cw(12p) .
141 Local loopback X
.T&
lw(30p) | lw(96p) | cw(12p) | cw(18p) | cw(12p) | cw(18p) | cw(12p) | cw(18p) | cw(12p) .
142 Test indicator X
.T&
lw(30p) | lw(96p) | cw(12p) | cw(18p) | cw(12p) | cw(18p) | cw(12p) | cw(18p) | cw(12p) .
191 Transmitted voice answer X
.T&
lw(30p) | lw(96p) | cw(12p) | cw(18p) | cw(12p) | cw(18p) | cw(12p) | cw(18p) | cw(12p) .
192 Received voice answer X
_
.TE
.nr PS 9
.RT
.ad r
\fBTableau 1/V.24 [T1.24], p. 2\fR
.sp 1P
.RT
.ad b
.RT
.LP
.bp
.sp 1P
.LP
\fICircuit\ 102a\ \(em\ \fR \fIDTE common return\fR
.sp 9p
.RT
.PP
This conductor is connected to the DTE circuit common return and is used
as the reference potential for the unbalanced Recommendation\ V.10\(hytype
interchange circuit receivers within the DCE.
.RT
.sp 1P
.LP
\fICircuit\ 102b\ \(em\ \fR \fIDCE common return\fR
.sp 9p
.RT
.PP
This conductor is connected to the DCE circuit common return and is used
as the reference potential for the unbalanced Recommendation\ V.10\(hytype
interchange circuit receivers within the DTE.
.PP
\fINote\fR \ \(em\ Where a mixture of Recommendations\ V.10 and V.11
circuits is used in the same interface, separate provision must be made
for the Recommendation\ V.10 common return circuits\ 102a and 102b, and
for a d.c.
reference potential conductor circuit\ 102, or protective ground connection,
as required.
.RT
.sp 1P
.LP
\fICircuit\ 102c\ \(em\ \fR \fICommon return\fR
.sp 9p
.RT
.PP
This conductor establishes the signal common return for
single\(hycurrent interchange circuits controlled by contact closure with
electrical characteristics according to Recommendation\ V.31, in cases
where a common return is used.
.PP
Within the equipment containing the signal source of the interchange circuit,
this conductor must be isolated from signal ground and protective
ground, irrespective of whether it is located within the DCE or within the
DTE.
.RT
.sp 1P
.LP
\fICircuit\ 103\ \(em\ \fR \fITransmitted data\fR
.sp 9p
.RT
.PP
Direction:\ To DCE
.PP
The data signals originated by the DTE:
.RT
.LP
1)
to be transmitted via a data
channel to one or more remote data stations,
.LP
2)
to be passed to the DCE for
maintenance test purposes under control of the DTE, or
.LP
3)
for the programming or control of
serial automatic
calling DCEs
,
.LP
are transferred on this circuit to the DCE.
.sp 1P
.LP
\fICircuit\ 104\ \(em\ \fR \fIReceived data\fR
.sp 9p
.RT
.PP
Direction:\ From DCE
.PP
The data signals generated by the DCE:
.RT
.LP
1)
in response to data channel
line signals received from a remote data station,
.LP
2)
in response to the DTE
maintenance test signals, or
.LP
3)
in response to (or as an echo of) programming or control
signals from the DTE where a serial automatic calling facility is
implemented in the DCE,
.LP
are transferred on this circuit to the DTE.
.PP
\fINote\fR \ \(em\ The reception conditions for maintenance test signals
are specified with circuit\ 107.
.sp 1P
.LP
\fICircuit\ 105\ \(em\ \fR \fIRequest to send\fR
.sp 9p
.RT
.PP
Direction:\ To DCE
.PP
Signals on this circuit control the data channel transmit function of the DCE.
.PP
The ON condition causes the DCE to assume the data channel transmit
mode.
.PP
The OFF condition causes the DCE to assume the data channel
non\(hytransmit mode, when all data transferred on circuit\ 103 have been
transmitted.
.bp
.RT
.sp 1P
.LP
\fICircuit\ 106\ \(em\ \fR \fIReady for sending\fR
.sp 9p
.RT
.PP
Direction:\ From DCE
.PP
Signals on this circuit indicate whether the DCE is prepared to
accept data signals for transmission on the data channel or for maintenance
test purposes under control of the DTE.
.PP
The ON condition indicates that the DCE is prepared to accept
data signals from the DTE.
.PP
The OFF condition indicates that the DCE is not prepared to accept
data signals from the DTE.
.RT
.sp 1P
.LP
\fICircuit\ 107\ \(em\ \fR \fIData set ready\fR
.sp 9p
.RT
.PP
Direction:\ From DCE
.PP
Signals on this circuit indicate whether the DCE is ready to
operate.
.PP
The ON condition, where circuit 142 is OFF or is not implemented,
indicates that the signal converter or similar equipment is connected to the
line and that the DCE is ready to exchange further control signals with
the DTE to initiate transfer of data.
.PP
The ON condition, in conjunction with the ON condition of circuit 142,
indicates that the DCE is prepared to exchange data signals with the DTE
for
maintenance test purposes.
.PP
The OFF condition, in conjunction with the ON condition on
circuit\ 106, indicates that the DCE is ready to exchange data signals
associated with the programming or control of serial automatic calling
DCEs.
.PP
The OFF condition, in conjunction with the OFF condition on
circuit\ 106, indicates:
.RT
.LP
1)
that the DCE is not ready to operate in the data transfer
phase,
.LP
2)
that the DCE has detected a fault condition (which
may be network or DCE dependent) which has lasted longer than
some fixed period of time, such period of time being network
dependent, or
.LP
3)
in switched network operation, that the DCE has detected
a disconnect indication from the remote station or from the
network.
.PP
The OFF condition, in conjunction with the ON condition on circuit 142,
indicates that the DCE is involved in tests from the network or remote
station.
.sp 1P
.LP
\fICircuit\ 108/1\ \(em\ \fR \fIConnect data set to line\fR
.sp 9p
.RT
.PP
Direction:\ To DCE
.PP
Signals on this circuit control switching of the signal\(hyconverter or
similar equipment to or from the line.
.PP
The ON condition on this circuit, except as noted below, causes the
DCE to connect the signal\(hyconverter or similar equipment to the line and to
maintain this connection.
.PP
The ON condition on this circuit may also be used to initiate a direct
call facility for automatic calling DCEs.
.PP
The OFF condition on this circuit, except as noted below, causes the DCE
to remove the signal\(hyconverter or similar equipment from the line, when
the transmission to the line of all data previously transferred on circuit\
103
and/or circuit\ 118 has been completed.
.PP
The OFF condition on this circuit may also be used to direct the DCE to
abort or to clear a direct call facility operation (see
Recommendation\ V.25\|\fIbis\fR ).
.RT
.sp 1P
.LP
\fICircuit\ 108/2\ \(em\ \fR \fIData terminal ready\fR
.sp 9p
.RT
.PP
Direction:\ To DCE
.PP
Signals on this circuit control switching of the signal\(hyconverter or
similar equipment to or from the line.
.PP
The ON condition, indicating that the DTE is ready to operate,
prepares the DCE to connect the signal\(hyconversion or similar equipment
to the line and maintains this connection after it has been established
by
supplementary means.
.PP
The DTE is permitted to present the ON condition on circuit\ 108/2
whenever it is ready to transmit or receive data.
.bp
.PP
The OFF condition causes the DCE to remove the signal\(hyconverter or
similar equipment from the line, when the transmission to line of all data
previously transferred on circuit\ 103 and/or circuit\ 118 has been
completed.
.PP
The OFF condition of this circuit may also be used to direct the DCE to
abort or to clear a serial automatic calling operation (see
Recommendation\ V.25\|\fIbis\fR ).
.RT
.sp 1P
.LP
\fICircuit\ 109\ \(em\ \fR \fIData channel received line signal detector\fR
.sp 9p
.RT
.PP
Direction:\ From\ DCE
.PP
Signals on this circuit indicate whether the received data channel
line signal is within appropriate limits, as specified in the relevant
Recommendation for DCE.
.PP
Circuit 109 may also be in the ON condition during the exchange of
data signals between the DCE and the DTE, associated with the programming
or control of serial automatic calling DCEs.
.PP
The OFF condition indicates that the received signal is not within
appropriate limits.
.RT
.sp 1P
.LP
\fICircuit\ 110\ \(em\ \fR \fIData signal quality detector\fR
.sp 9p
.RT
.PP
Direction:\ From\ DCE
.PP
Signals on this circuit indicate whether there is a reasonable
probability of an error in the data received on the data channel. The signal
quality indicated conforms to the relevant DCE Recommendation.
.PP
The ON condition indicates that there is no reason to believe
that an error has occurred.
.PP
The OFF condition indicates that there is a reasonable probability
of an error.
.RT
.sp 1P
.LP
\fICircuit\ 111\ \(em\ \fR \fIData signalling rate selector\fR (DTE source)
.sp 9p
.RT
.PP
Direction:\ To\ DCE
.PP
Signals on this circuit are used to select one of the two data
signalling rates of a dual rate synchronous DCE, or to select one of the two
ranges of data signalling rates of a dual range asynchronous DCE.
.PP
The ON condition selects the higher rate or range of rates.
.PP
The OFF condition selects the lower rate or range of
rates.
.RT
.sp 1P
.LP
\fICircuit\ 112\ \(em\ \fR \fIData signalling rate selector\fR (DCE source)
.sp 9p
.RT
.PP
Direction:\ From\ DCE
.PP
Signals on this circuit are used to select one of the two data
signalling rates or ranges of rates in the DTE to coincide with the data
signalling rate or range of rates in use in a dual rate synchronous or dual
range asynchronous DCE.
.PP
The ON condition selects the higher rate or range of rates.
.PP
The OFF condition selects the lower rate or range of rates.
.RT
.sp 1P
.LP
\fICircuit\ 113\ \(em\ \fR \fITransmitter signal element timing\fR (DTE source)
.sp 9p
.RT
.PP
Direction:\ To\ DCE
.PP
Signals on this circuit provide the DCE with signal element timing
information.
.PP
The condition on this circuit shall be ON and OFF for nominally equal periods
of time and the transition from ON to OFF condition shall nominally
indicate the centre of each signal element on circuit\ 103.
.RT
.sp 1P
.LP
\fICircuit\ 114\ \(em\ \fR \fITransmitter signal element timing\fR (DCE source)
.sp 9p
.RT
.PP
Direction:\ From\ DCE
.PP
Signals on this circuit provide the DTE with signal element timing
information.
.PP
The condition on this circuit shall be ON and OFF for nominally
equal periods of time. The DTE shall present a data signal on circuit\ 103 in
which the transitions between signal elements nominally occur at the time of
the transitions from OFF to ON condition of circuit\ 114.
.bp
.RT
.sp 1P
.LP
\fICircuit\ 115\ \(em\ \fR \fIReceiver signal element timing\fR (DCE source)
.sp 9p
.RT
.PP
Direction:\ From\ DCE
.PP
Signals on this circuit provide the DTE with signal element timing
information.
.PP
The condition of this circuit shall be ON and OFF for nominally equal periods
of time, and a transition from ON to OFF condition shall nominally
indicate the centre of each signal element on circuit\ 104.
.RT
.sp 1P
.LP
\fICircuit\ 116/1\ \(em\ \fR \fIBack\(hyup swtiching in direct mode\fR
.sp 9p
.RT
.PP
Direction:\ To the DCE
.PP
Signals on this circuit control switching of the DCE between normal
and standby facilities.
.PP
The ON condition causes the DCE to connect to the standby facility.
.PP
The OFF condition causes the DCE to disconnect from the standby
facility, when the transmission to line of all data previously transferred
on circuit\ 103 has been completed, and the DCE then reconnects to the normal
facility.
.RT
.sp 1P
.LP
\fICircuit\ 116/2\ \(em\ \fR \fIBack\(hyup switching in authorized mode\fR
.sp 9p
.RT
.PP
Direction:\ To\ the DCE
.PP
Signals on this circuit control switching of the DCE between normal
and standby facilities.
.PP
The ON condition indicates that the DTE is ready to switch from the
normal to the standby facility and prepares the DCE to switch to the standby
facility when necessary.
.PP
The OFF condition causes the DCE to disconnect from the standby
facility, when the transmission to line of all data previously transferred
on circuit\ 103 has been completed, and the DCE then reconnects to the
normal
facility.
.RT
.sp 1P
.LP
\fICircuit\ 117\ \(em\ \fR \fIStandby indicator\fR
.sp 9p
.RT
.PP
Direction:\ From\ DCE
.PP
Signals on this circuit indicate whether the DCE is conditioned to
operate in its standby mode with the predetermined facilities replaced
by their reserves.
.PP
The ON condition indicates that the DCE is conditioned to operate in its
standby mode.
.PP
The OFF condition indicates that the DCE is conditioned to operate in its
normal mode.
.RT
.sp 1P
.LP
\fICircuit\ 118\ \(em\ \fR \fITransmitted backward channel data\fR
.sp 9p
.RT
.PP
Direction:\ To DCE
.PP
This circuit is equivalent to circuit\ 103, except that it is used to transmit
data via the backward channel.
.RT
.sp 1P
.LP
\fICircuit\ 119\ \(em\ \fR \fIReceived backward channel data\fR
.sp 9p
.RT
.PP
Direction:\ From DCE
.PP
This circuit is equivalent to circuit\ 104, except that it is used for
data received on the backward channel.
.RT
.sp 1P
.LP
\fICircuit\ 120\ \(em\ \fR \fITransmit backward channel line signal\fR
.sp 9p
.RT
.PP
Direction:\ To DCE
.PP
This circuit is equivalent to circuit\ 105, except that it is used to control
the backward channel transmit function of the DCE.
.PP
The ON condition causes the DCE to assume the backward channel
transmit mode.
.PP
The OFF condition causes the DCE to assume the backward channel
non\(hytransmit mode, when all data transferred on circuit\ 118 have been
transmitted to line.
.bp
.RT
.sp 1P
.LP
\fICircuit\ 121\ \(em\ \fR \fIBackward channel ready\fR
.sp 9p
.RT
.PP
Direction:\ From DCE
.PP
This circuit is equivalent to circuit\ 106, except that it is used to indicate
whether the DCE is conditioned to transmit data on the backward
channel.
.PP
The ON condition indicates that the DCE is conditioned to transmit
data on the backward channel.
.PP
The OFF condition indicates that the DCE is not conditioned to
transmit data on the backward channel.
.RT
.sp 1P
.LP
\fICircuit\ 122\ \(em\ \fR \fIBackward channel received line signal detector\fR
.sp 9p
.RT
.PP
Direction:\ From DCE
.PP
This circuit is equivalent to circuit\ 109, except that it is used to indicate
whether the received backward channel line signal is within
appropriate limits, as specified in the relevant Recommendation for DCE.
.RT
.sp 1P
.LP
\fICircuit\ 123\ \(em\ \fR \fIBackward channel signal quality detector\fR
.sp 9p
.RT
.PP
Direction:\ From DCE
.PP
This circuit is equivalent to circuit\ 110, except that it is used to indicate
the signal quality of the received backward channel line
signal.
.RT
.sp 1P
.LP
\fICircuit\ 124\ \(em\ \fR \fISelect frequency groups\fR
.sp 9p
.RT
.PP
Direction:\ To DCE
.PP
Signals on this circuit are used to select the desired frequency
groups available in the DCE.
.PP
The ON condition causes the DCE to use all frequency groups to
represent data signals.
.PP
The OFF condition causes the DCE to use a specified reduced number of frequency
groups to represent data signals.
.RT
.sp 1P
.LP
\fICircuit\ 125\ \(em\ \fR \fICalling indicator\fR
.sp 9p
.RT
.PP
Direction:\ From DCE
.PP
Signals on this circuit indicate whether a calling signal is being
received by the DCE.
.PP
The ON condition indicates that a calling signal is being received.
.PP
The OFF condition indicates that no calling signal is being received, and
this condition may also appear during interruptions of a pulse\(hymodulated
calling signal.
.RT
.sp 1P
.LP
\fICircuit\ 126\ \(em\ \fR \fISelect transmit frequency\fR
.sp 9p
.RT
.PP
Direction:\ To DCE
.PP
Signals on this circuit are used to select the required transmit
frequency of the DCE.
.PP
The ON condition selects the higher transmit frequency.
.PP
The OFF condition selects the lower transmit frequency.
.RT
.sp 1P
.LP
\fICircuit\ 127\ \(em\ \fR \fISelect receive frequency\fR
.sp 9p
.RT
.PP
Direction:\ To DCE
.PP
Signals on this circuit are used to select the required receive
frequency of the DCE.
.PP
The ON condition selects the lower receive frequency.
.PP
The OFF condition selects the higher receive frequency.
.bp
.RT
.sp 1P
.LP
\fICircuit\ 128\ \(em\ \fR \fIReceiver signal element timing\fR (DTE source)
.sp 9p
.RT
.PP
Direction:\ To DCE
.PP
Signals on this circuit provide the DCE with signal element timing
information.
.PP
The condition on this circuit shall be ON and OFF for nominally equal periods
of time. The DCE shall present a data signal on circuit\ 104 in which
the transitions between signal elements nominally occur at the time of the
transitions from OFF to ON condition of the signal on circuit\ 128.
.RT
.sp 1P
.LP
\fICircuit\ 129\ \(em\ \fR \fIRequest to receive\fR
.sp 9p
.RT
.PP
Direction:\ To DCE
.PP
Signals on this circuit are used to control the receive function of
the DCE.
.PP
The ON condition causes the DCE to assume the receive mode.
.PP
The OFF condition causes the DCE to assume the non\(hyreceive mode.
.RT
.sp 1P
.LP
\fICircuit\ 130\ \(em\ \fR \fITransmit backward tone\fR
.sp 9p
.RT
.PP
Direction:\ To DCE
.PP
Signals on this circuit control the transmission of a backward channel tone.
.PP
The ON condition causes the DCE to transmit a backward channel tone.
.PP
The OFF condition causes the DCE to stop the transmission of a
backward channel tone.
.RT
.sp 1P
.LP
\fICircuit\ 131\ \(em\ \fR \fIReceived character timing\fR
.sp 9p
.RT
.PP
Direction:\ From DCE
.PP
Signals on this circuit provide the DTE with character timing
information, as specified in the relevant Recommendation for DCE.
.RT
.sp 1P
.LP
\fICircuit\ 132\ \(em\ \fR \fIReturn to non\(hydata mode\fR
.sp 9p
.RT
.PP
Direction:\ To DCE
.PP
Signals on this circuit are used to restore the non\(hydata mode provided
with the DCE, without releasing the line connection to the remote station.
.PP
The ON condition causes the DCE to restore the non\(hydata mode. When the
non\(hydata mode has been established, this circuit must be turned OFF.
.RT
.sp 1P
.LP
\fICircuit\ 133\ \(em\ \fR \fIReady for receiving\fR
.sp 9p
.RT
.PP
Direction:\ To DCE
.PP
Signals on this circuit control the transfer of data on circuit\ 104, indicating
whether the DTE is capable of accepting a given amount of data
(e.g.\ a block of data), specified in the appropriate Recommendation for
an intermediate function, for example, error control.
.PP
The ON condition must be maintained whenever the DTE is capable of
accepting data, and causes the intermediate equipment or DCE to transfer the
received data to the DTE.
.PP
The OFF condition indicates that the DTE is not able to accept data, and
causes the intermediate equipment or DCE to retain the data.
.RT
.sp 1P
.LP
\fICircuit\ 134\ \(em\ \fR \fIReceived data present\fR
.sp 9p
.RT
.PP
Direction:\ From DCE
.PP
Signals on this circuit are used to separate information messages from
supervisory messages, transferred on circuit\ 104, as specified in the
appropriate Recommendation for intermediate equipment, e.g.\ error control
equipment.
.PP
The ON condition indicates the data which represent information
messages.
.PP
The OFF condition shall be maintained at all other times.
.bp
.RT
.sp 1P
.LP
\fICircuit\ 136\ \(em\ \fR \fINew signal\fR
.sp 9p
.RT
.PP
Direction:\ To DCE
.PP
Signals on this circuit are used to control the response times of the DCE
receiver.
.PP
The ON condition of circuit 136 instructs the DCE receiver to prepare itself
to detect rapidly the disappearance of the line signal (e.g.,\ by
disabling the response time circuitry associated with circuit\ 109). After
the received line signal falls below the threshold of the received line
signal
detector, the DCE will:
.RT
.LP
1)
turn OFF circuit 109, and
.LP
2)
prepare itself to detect rapidly the appearance
of a new line signal (e.g., by resetting the receiver timing
recovery circuitry).
.PP
Once turned ON, circuit 136 may be turned OFF after one unit
interval and must be turned OFF after circuit\ 109 is turned OFF. Circuit\ 136
shall be OFF at all other times.
.sp 1P
.LP
\fICircuit\ 140\ \(em\ \fR \fILoopback/Maintenance test\fR
.sp 9p
.RT
.PP
Direction:\ To DCE
.PP
Signals on this circuit are used to initiate and release loopback or other
maintenance test conditions in\ DCEs.
.PP
The ON condition causes initiation of the maintenance test condition.
.PP
The OFF condition causes release of the maintenance test
condition.
.RT
.sp 1P
.LP
\fICircuit\ 141\ \(em\ \fR \fILocal loopback\fR
.sp 9p
.RT
.PP
Direction:\ To DCE
.PP
Signals on this circuit are used to control the loop 3 test condition in
the local DCE.
.PP
The ON condition of circuit 141 causes the establishment of the loop 3
test condition in the local DCE.
.PP
The OFF condition of circuit 141 causes the release of the loop 3 test
condition in the local DCE.
.RT
.sp 1P
.LP
\fICircuit\ 142\ \(em\ \fR \fITest indicator\fR
.sp 9p
.RT
.PP
Direction:\ From DCE
.PP
Signals on this circuit indicate whether a maintenance condition
exists.
.PP
The ON condition indicates that a maintenance condition exists in the DCE,
precluding reception or transmission of data signals from or to a remote
DTE.
.PP
The OFF condition indicates that the DCE is not in a maintenance test condition.
.RT
.sp 1P
.LP
\fICircuit\ 191\ \(em\ \fR \fITransmitted voice answer\fR
.sp 9p
.RT
.PP
Direction:\ To DCE
.PP
Signals generated by a voice answer unit in the DTE are transferred on
this circuit to the DCE.
.PP
The electrical characteristics of this analogue interchange circuit
are part of the appropriate DCE Recommendation.
.RT
.sp 1P
.LP
\fICircuit\ 192\ \(em\ \fR \fIReceived voice answer\fR
.sp 9p
.RT
.PP
Direction:\ From DCE
.PP
Received voice signals, generated by a voice answering unit at the
remote DTE, are transferred on this circuit to the DTE.
.PP
The electrical characteristics of this analogue interchange circuit
are part of the appropriate DCE Recommendation.
.bp
.RT
.sp 1P
.LP
3.2
\fI200\(hyseries\ \(em\ \fR \fISpecifically for parallel automatic calling\fR
.sp 9p
.RT
.PP
A list of these interchange circuits is presented in tabular form in Table\
2/V.24.
.PP
For parallel automatic calling procedures, refer to
Recommendation\ V.25 for the general switched telephone network and
Recommendation\ S.16\ [1] for the telex network.
.RT
.LP
.sp 1
.ce
\fBH.T. [T2.24]\fR
.ce
TABLE\ 2/V.24
.ce
\fB200\(hyseries interchange circuits specifically for
.ce
automatic calling\fR
.ps 9
.vs 11
.nr VS 11
.nr PS 9
.TS
center box;
cw(36p) | cw(120p) | cw(36p) | cw(36p) .
Interchange circuit number Interchange circuit name From DCE To DCE
_
.T&
cw(36p) | lw(120p) | cw(36p) | cw(36p) .
201 T{
Signal ground or common return
T} X X
.T&
cw(36p) | lw(120p) | cw(36p) | cw(36p) .
202 Call request X
.T&
cw(36p) | lw(120p) | cw(36p) | cw(36p) .
203 Data line occupied X
.T&
cw(36p) | lw(120p) | cw(36p) | cw(36p) .
204 Distant station connected X
.T&
cw(36p) | lw(120p) | cw(36p) | cw(36p) .
205 Abandon call X
.T&
cw(36p) | lw(120p) | cw(36p) | cw(36p) .
206 Digit signal (2\u0\d) X
.T&
cw(36p) | lw(120p) | cw(36p) | cw(36p) .
207 Digit signal (2\u1\d) X
.T&
cw(36p) | lw(120p) | cw(36p) | cw(36p) .
208 Digit signal (2\u2\d) X
.T&
cw(36p) | lw(120p) | cw(36p) | cw(36p) .
209 Digit signal (2\u3\d) X
.T&
cw(36p) | lw(120p) | cw(36p) | cw(36p) .
210 Present next digit X
.T&
cw(36p) | lw(120p) | cw(36p) | cw(36p) .
211 Digit present X
.T&
cw(36p) | lw(120p) | cw(36p) | cw(36p) .
213 Power indication X
_
.TE
.nr PS 9
.RT
.ad r
\fBTableau 2/V.24 [T2.24], p.\fR
.sp 1P
.RT
.ad b
.RT
.LP
.sp 3
.sp 1P
.LP
\fICircuit\ 201\ \(em\ Signal ground or common return\fR
.sp 9p
.RT
.PP
This conductor establishes the signal common reference potential
for all 200\(hyseries interchange circuits. Within the parallel automatic
calling equipment this circuit shall be brought to one point, and it shall
be possible to connect this point to protective ground or earth by means
of a metallic
strap within the equipment. This metallic strap can be connected or removed
at installation as may be required to meet applicable regulations or to
minimize the introduction of noise into electronic circuitry. Caution should
be
exercised to prevent the establishment of ground loops carrying high
currents.
.RT
.sp 1P
.LP
\fICircuit\ 202\ \(em\ \fR \fICall request\fR
.sp 9p
.RT
.PP
Direction:\ To DCE
.PP
Signals on this circuit are used to condition the
parallel
automatic calling equipment
to originate a call and to switch the
automatic calling equipment to or from the line.
.PP
The ON condition causes the DCE to condition the
parallel
automatic calling
equipment to originate a call and to connect this
equipment to the line.
.PP
The OFF condition causes the automatic calling equipment to be
removed from the line and indicates that the DTE has released the automatic
calling equipment.
.bp
.RT
.sp 1P
.LP
\fICircuit\ 203\ \(em\ \fR \fIData line occupied\fR
.sp 9p
.RT
.PP
Direction:\ From DCE
.PP
Signals on this circuit indicate whether or not the associated
line is in use (e.g. for automatic calling, data transmission or voice
communication, test procedures).
.PP
The ON condition indicates that the line is in use.
.PP
The OFF condition indicates that the line is not in use, and
that the DTE may originate a call.
.RT
.sp 1P
.LP
\fICircuit\ 204\ \(em\ \fR \fIDistant station connected\fR
.sp 9p
.RT
.PP
Direction:\ From DCE
.PP
Signals on this circuit indicate whether a connection has been
established to a remote data station (or telex station).
.PP
The ON condition indicates the receipt of a signal from a remote DCE signalling
that a connection to that equipment has been established.
.PP
The OFF condition shall be maintained at all other times.
.RT
.sp 1P
.LP
\fICircuit\ 205\ \(em\ \fR \fIAbandon call\fR
.sp 9p
.RT
.PP
Direction:\ From DCE
.PP
Signals on this circuit indicate whether a preset time has elapsed
between successive events in the calling procedure.
.PP
The ON condition indicates that the call should be abandoned.
.PP
The OFF condition indicates that call origination can proceed.
.RT
.sp 1P
.LP
\fIDigit signal circuits\fR \fI:\fR
.sp 9p
.RT
.PP
Circuit\ 206\ \(em\ Digit signal (2\u0\d)
.PP
Circuit\ 207\ \(em\ Digit signal (2\u1\d)
.PP
Circuit\ 208\ \(em\ Digit signal (2\u2\d)
.PP
Circuit\ 209\ \(em\ Digit signal (2\u3\d)
\v'2p'
.PP
Direction:\ To DCE
.PP
On these circuits the DTE presents the code combinations shown in
Table\ 3/V.24, being the digits of the data station (or telex station) to be
called and the delimiting control characters.
.RT
.ce
\fBH.T. [T3.24]\fR
.ce
TABLE\ 3/V.24
.ps 9
.vs 11
.nr VS 11
.nr PS 9
.TS
center box;
cw(60p) | cw(96p) .
Information Binary states
_
.TE
.TS
lw(60p) | cw(24p) | cw(24p) | cw(24p) | cw(24p) .
209 208 207 206
.T&
cw(60p) | cw(24p) | cw(24p) | cw(24p) | cw(24p) .
Digit 1 0 0 0 1
.T&
cw(60p) | cw(24p) | cw(24p) | cw(24p) | cw(24p) .
Digit 2 0 0 1 0
.T&
cw(60p) | cw(24p) | cw(24p) | cw(24p) | cw(24p) .
Digit 3 0 0 1 1
.T&
cw(60p) | cw(24p) | cw(24p) | cw(24p) | cw(24p) .
Digit 4 0 1 0 0
.T&
cw(60p) | cw(24p) | cw(24p) | cw(24p) | cw(24p) .
Digit 5 0 1 0 1
.T&
cw(60p) | cw(24p) | cw(24p) | cw(24p) | cw(24p) .
Digit 6 0 1 1 0
.T&
cw(60p) | cw(24p) | cw(24p) | cw(24p) | cw(24p) .
Digit 7 0 1 1 1
.T&
cw(60p) | cw(24p) | cw(24p) | cw(24p) | cw(24p) .
Digit 8 1 0 0 0
.T&
cw(60p) | cw(24p) | cw(24p) | cw(24p) | cw(24p) .
Digit 9 1 0 0 1
.T&
cw(60p) | cw(24p) | cw(24p) | cw(24p) | cw(24p) .
Digit 0 0 0 0 0
.T&
cw(60p) | cw(24p) | cw(24p) | cw(24p) | cw(24p) .
Control character EON 1 1 0 0
.T&
cw(60p) | cw(24p) | cw(24p) | cw(24p) | cw(24p) .
Control character SEP 1 1 0 1
_
.TE
.nr PS 9
.RT
.ad r
\fBTableau 3/V.24 [T3.24], p.\fR
.sp 1P
.RT
.ad b
.RT
.LP
.bp
.PP
The control character EON (end of number) causes the DCE to take appropriate
action to await an answer from the called data station.
.PP
The control character SEP (separation) indicates the need for a pause between
successive digits or in front of the digit series, and causes the
parallel automatic calling equipment to insert the appropriate time interval.
.PP
The code combinations listed above are intended to apply only to
equipment using Recommendations\ V.25 and S.16\ [1].
.RT
.sp 1P
.LP
\fICircuit\ 210\ \(em\ \fR \fIPresent next digit\fR
.sp 9p
.RT
.PP
Direction:\ From DCE
.PP
Signals on this circuit indicate whether the parallel automatic
calling equipment is ready to accept the next code combination.
.PP
The ON condition indicates that the automatic calling equipment
is ready to accept the next code combination.
.PP
The OFF condition indicates that the automatic calling equipment
is not ready to accept signals on the digit signal circuits.
.RT
.sp 1P
.LP
\fICircuit\ 211\ \(em\ \fR \fIDigit present\fR
.sp 9p
.RT
.PP
Direction:\ To DCE
.PP
Signals on this circuit control the reading of the code combination
presented on the digit signal circuits.
.PP
The ON condition causes the automatic calling equipment to read
the code combination presented on the digit signal circuits.
.PP
The OFF condition on this circuit prevents the automatic calling
equipment from reading a code combination on the digit signal circuits.
.RT
.sp 1P
.LP
\fICircuit\ 213\ \(em\ \fR \fIPower indication\fR
.sp 9p
.RT
.PP
Direction:\ From DCE
.PP
Signals on this circuit indicate whether power is available within the
parallel automatic calling equipment.
.PP
The ON condition indicates that power is available within the
automatic calling equipment.
.PP
The OFF condition indicates that power is not available within the
automatic calling equipment.
.RT
.sp 1P
.LP
3.3
\fICircuit failures (electrical)\fR
.sp 9p
.RT
.PP
The following interchange circuits, where implemented, shall be
used to detect either a power\(hyoff condition in the equipment connected
through the interface or the disconnection of the interconnecting cable:
.RT
.LP
Circuit 105
\ \(em\ Request to send
.LP
Circuit 107
\ \(em\ Data set ready
.LP
Circuit 108/1\ \(em\ Connect data set to line
.LP
Circuit 108/2\ \(em\ Data terminal ready
.LP
Circuit 120
\ \(em\ Transmit backward channel line signal
.LP
Circuit 202
\ \(em\ Call request
.LP
Circuit 213
\ \(em\ Power indication
.PP
The criteria used to determine a failure condition shall be
specified in the appropriate Recommendation for electrical characteristics.
.PP
The receiver for these circuits shall interpret the power\(hyoff
condition or the disconnection of the interconnecting cable as an OFF condition
on these circuits.
.bp
.RT
.sp 1P
.LP
3.4
\fIOptional circuits\fR
.sp 9p
.RT
.PP
In some modem Recommendations optional facilities are defined
which require control from the DTE via optional (non\(hyessential) circuits.
Additional optional facilities may exist in DCEs also requiring control via
interchange circuits defined in this Recommendation.
.PP
The DCE should provide means to disable an option, when necessary, in case
the DTE is not equipped with circuitry to control this option.
.PP
In case the DCE does not provide an option, proper operation of the
DTE should not rely on any specific response from the DCE when the DTE
activates the control circuit related to that option.
.PP
\fINote\fR \ \(em\ DTEs may be in existence which do not comply with the
above requirements. Therefore, for an interim period, DCEs not providing
a certain
option may provide means to respond to the DTE invocation of that option
in the proper way. Especially, this may be the case for simplex or duplex
DCEs not
providing a carrier switch option (continuous carrier operation) but still
responding with circuit\ 106 to circuit\ 105.
.PP
For an interim period of time, receiver circuits may be provided in a DTE
or a DCE for which no generator is provided in the complementary equipment.
Therefore, in cases where a receiver is not connected to a generator, it
is
suggested that means be provided in the equipment where the receiver is
located to inhibit or disregard any possible false triggering of this receiver.
.RT
.sp 2P
.LP
\fB4\fR \fBOperational requirements\fR
.sp 1P
.RT
.PP
In the following, operational requirements are given for the usage of interchange
circuits. It also explains in further detail the required
correlation between interchange circuits, where implemented.
.RT
.sp 1P
.LP
4.1
\fIData circuits\fR
.sp 9p
.RT
.PP
It is evident that proper data transmission may be impaired when
the required condition is not present on an implemented control interchange
circuit. Therefore, the DTE shall not transfer, on circuit\ 103, data which
is for transmission to line or for maintenance purposes unless an ON condition
is present on all of the following four circuits, where implemented: circuit\
105, circuit\ 106, circuit\ 107 and circuit\ 108/1 or\ 108/2.
.PP
The DTE may transfer, on circuit 103, data which is for the
programming or control of serial automatic calling DCEs when an ON condition
is present on circuits\ 106 and\ 108/2, and an OFF condition is present
on
circuit\ 107. In this situation, the condition of circuit\ 105 need not be
considered, and may be ON for DTE convenience.
.PP
All data transferred on circuit\ 103 during the time an
ON condition is present on all of the above four circuits, where implemented,
shall be transmitted by the DCE.
.PP
Refer also to \(sc\(sc\ 4.4 and 4.5 below for further explanation.
.PP
The DTE shall not transfer data on circuit\ 118 unless an
ON condition is present on all of the following four circuits, where
implemented: circuit\ 120, circuit\ 121, circuit\ 107 and circuit\ 108/1
or\ 108/2.
.PP
All data transferred on circuit\ 118 during the time an
ON condition is present on all of the above four circuits, where implemented,
shall be transmitted by the DCE.
.RT
.sp 1P
.LP
4.2
\fIIdle periods\fR
.sp 9p
.RT
.PP
During intervals when circuit\ 105 and circuit\ 106 are in the
ON condition and no data are available for transmission, the DTE may
transmit binary\ 1 condition, reversals or other sequences to maintain timing
synchronizing, e.g. SYN coded characters, idle characters according to
the data link control procedure used, etc.
.PP
Specific requirements, where applicable, are stated in the appropriate
DCE Recommendations.
.bp
.RT
.sp 1P
.LP
4.3
\fIClamping\fR
.sp 9p
.RT
.PP
4.3.1
In all applications the DCE shall hold, where
implemented:
.LP
a)
circuit\ 104 in the binary\ 1 condition when circuit\ 109
is in the OFF condition, and
.LP
b)
circuit\ 119 in the binary\ 1 condition when circuit\ 122
is in the OFF condition.
.PP
4.3.2
In addition a DCE constrained to half\(hyduplex operation on a
2\(hywire line shall also hold, where implemented:
.LP
a)
circuit\ 104 in the binary\ 1 condition and circuit\ 109 in the OFF condition
when circuit\ 105 is in the ON condition, and for a
short time interval (to be specified in Recommendations for DCE)
following the ON to OFF transition on circuit\ 105; and
.LP
b)
circuit\ 119 in the binary\ 1 condition and circuit\ 122 in the OFF condition,
when circuit\ 120 is in the ON condition, and for a
short time interval (to be specified in Recommendations for
DCE) following the ON to OFF transition on circuit\ 120.
.sp 2P
.LP
4.4
\fIOperation of circuits 107, 108/1 and 108/2\fR
.sp 1P
.RT
.sp 1P
.LP
4.4.1
\fIIn switched and leased line operations\fR
.sp 9p
.RT
.PP
Signals on circuit 107 are to be considered as responses to signals which
initiate connection to line, e.g.\ circuit\ 108/1. However, the
conditioning of a data channel, such as equalization and clamp removal,
cannot be expected to have been completed when circuit 107 is turned ON.
.PP
A wiring option shall be provided within the DCE to select either
circuit\ 108/1 or circuit\ 108/2 operation.
.PP
Under certain test conditions, both the DTE and the DCE may exercise some
of the interchange circuits. Thus, when circuits\ 107,
108/1 or\ 108/2 are both OFF, the DTE is to ignore the conditions on all
other interchange circuits from the DCE, except those on circuit\ 125 and
the timing circuits, and the DCE is to ignore the conditions on all other
interchange
circuits from the DTE.
.PP
During the maintenance phases specified in Recommendation V.54, when the
DTE is not involved in the test, circuit\ 142 is in the ON condition and
circuit\ 107 is in the OFF condition. Circuit\ 107 shall not respond to
circuits\ 108/1 or\ 108/2. When the DTE is involved in the test, circuit\
142 is in the ON condition and circuit\ 107 shall respond to circuit\ 108/1
or\ 108/2.
.RT
.sp 1P
.LP
4.4.2
\fIIn leased line operations\fR
.sp 9p
.RT
.PP
Where circuit 108 is not implemented in the DTE, the condition on this
circuit is assumed to be permanently ON.
.PP
Where circuit 108 is implemented in the DTE, it shall be implemented as
circuit\ 108/1.
.RT
.sp 1P
.LP
4.4.3
\fIIn switched line operations\fR
.sp 9p
.RT
.PP
When the DCE is conditioned for automatic answering of calls,
answering of incoming calls occurs only in response to a combination of the
calling signal and an ON condition of circuit\ 108/1 or\ 108/2.
.PP
The OFF condition of circuit 108/1 or 108/2 shall not disable the
operation of circuit\ 125.
.PP
When circuit 108/2 is in the ON condition and circuit 107 is in the
OFF condition, the DTE may communicate with serial automatic calling DCEs on
circuits\ 103 and\ 104. This state is recognized by an ON condition on
circuit\ 106.
.PP
When circuit 108/1 or 108/2 is turned OFF, it shall not be turned ON again
until circuit\ 107 is turned OFF.
.PP
In the case where the DCE turns circuit 107 OFF first, the DTE shall consider
the call aborted and shall proceed as described below:
.RT
.LP
1)
In the case of circuit 108/1, the DTE shall turn this
circuit OFF with minimal delay and shall hold the circuit in
the OFF condition for a minimum of 500\ ms. After that period of
time, the DTE may turn circuit\ 108/1 back ON either to initiate
a new direct call or to respond to an incoming call signalled
by circuit\ 125 coming ON.
.LP
The DCE shall not answer an incoming call or initiate a
new call until circuit\ 108/1 has first been turned OFF and
then back ON again.
.bp
.LP
2)
In the case of circuit 108/2, the DTE shall turn this
circuit OFF with minimal delay and shall hold the circuit in the
OFF condition for a minimum of 500\ ms. After that period of
time, the DTE may turn circuit\ 108/2 back ON either to initiate
a new serial automatic calling procedure or to signal the DCE
that it is prepared to accept an incoming call.
.LP
The DCE shall answer an incoming call or initiate a new
call until circuit\ 108/2 has been turned OFF and then back ON
again or after a minimum delay (provisional value 2\ s).
.sp 1P
.LP
4.5
\fIInterrelationship of circuits 103, 105 and 106\fR
.sp 9p
.RT
.PP
The DTE signals its intent to transmit data by turning ON
circuit\ 105. It is then the responsibility of the DCE to enter the transmit
mode, i.e.\ be prepared to transmit data, and also to alert the remote
DCE and condition it to receive data. The means by which a DCE enters the
transmit mode and alerts and conditions the remote DCE are described in
the appropriate DCE Recommendation.
.PP
When the transmitting DCE turns circuit 106 ON with circuit 107 in
the ON condition, the DTE is permitted to transfer data across the interface
on circuit\ 103. By turning ON circuit\ 106 with circuit\ 107 ON, it is implied
that all data transferred across the interface prior to the time that any
one of the four circuits (105, 106, 107 and 108/1 or\ 108/2) is again turned
OFF,
will be transferred to the line; however, the ON condition of circuit\ 106 is
not necessarily a guarantee that the remote DCE is in the receive mode.
(Depending on the complexity and sophistication of the transmitting signal
converter, there may be a delay ranging from less than a millisecond up to
several seconds between the time a bit is transferred across the interface
until the time a signal element representing this bit is transmitted on the
line.)
.PP
When the transmitting DCE turns circuit 106 ON, with circuit 107 in
the OFF condition, the DTE is permitted to transfer programming or control
signals to a serial automatic calling DCE across the interface on
circuit\ 103.
.PP
During data transfer, the DTE shall not turn circuit 105 OFF before
the end of the last bit (data bit or stop element) is transferred across the
interface on circuit\ 103. Similarly, in certain duplex switched network
applications where circuit\ 105 is not implemented (see the specific DCE
Recommendations), this requirement applies equally when circuit\ 108/1
or 108/2 is turned OFF to terminate a switched network call.
.PP
Where circuit 105 is provided, the ON and OFF conditions on
circuit\ 106 during the data transfer phase (i.e.\ circuit\ 107 ON) shall be
responses to the ON and OFF conditions on circuit\ 105. Circuit\ 106 may,
however, be turned OFF during the data transfer and test phases independent
of the condition of circuit\ 105 to signal the DTE to interrupt the transfer
of
data on circuit\ 103, transmitted data, for a finite period of time (e.g.,\
for DCE flow control purposes or DCE/DCE resynchronization). It should
be noted
that data presented on circuit\ 103 after circuit\ 106 turns OFF may be
disregarded by the DCE. It should also be noted that circuit\ 106 may be
turned back ON again at any time, provided that circuit\ 105 is ON at that
time. For
the appropriate response times of circuit\ 106, and for the operation of
circuit\ 106 when circuit\ 105 is not provided, refer to the relevant
Recommendation for the DCE.
.PP
For serial automatic calling DCEs, the ON and OFF conditions on
circuit\ 106 outside the data transfer phase (i.e.\ circuit\ 107 OFF) shall be
dependent on the interface state during the automatic call set\(hyup and
associated procedures. The transitions on circuit\ 106 for this application
shall be as detailed in Recommendation\ V.25\|\fIbis\fR .
.PP
When circuit 105 and circuit 106 are both OFF, the DTE shall maintain a
binary\ 1 condition on circuit\ 103. When circuit 105 is turned OFF it
shall
not be turned ON again until circuit\ 106 is turned OFF by the DCE.
.PP
\fINote\fR \ \(em\ These conditions also apply to the relationship between
circuits\ 120, 121 and\ 118.
.RT
.sp 1P
.LP
4.6
\fITiming circuits\fR
.sp 9p
.RT
.PP
It is desirable that the transfer of timing information across the interface
shall not be restricted to periods when actual transmission of
data is in progress; however, during intervals when timing information
is not transferred across the interface, the circuit involved should be
held in the
OFF condition. The following conditions apply:
.bp
.RT
.sp 1P
.LP
4.6.1
\fICircuit\ 113\ \(em\ Transmitter signal element timing\fR (DTE source)
.sp 9p
.RT
.PP
Where circuit\ 113 is used, the DTE shall transfer timing
information across the interface on this circuit at all times that the
timing source in the DTE is capable of generating this information, e.g.
when the DTE is in a power\(hyon condition.
.RT
.sp 1P
.LP
4.6.2
\fICircuit\ 114\ \(em\ Transmitter signal element timing\fR (DCE source)
.sp 9p
.RT
.PP
Where circuit\ 114 is used, the DCE shall transfer timing
information across the interface on this circuit at all times that the
timing source in the DCE is capable of generating this information, e.g.
when the
DCE is in a power\(hyon condition. It is recognized that a DCE which derives
power from the central office battery over the local telephone loop is in a
power\(hyoff condition when disconnected from the loop, i.e. on\(hyhook.
.RT
.sp 1P
.LP
4.6.3
\fICircuit\ 115\ \(em\ Receiver signal element timing\fR (DCE source)
.sp 9p
.RT
.PP
Where circuit\ 115 is used, the DCE shall transfer timing
information across the interface on this circuit at all times that the
timing source is capable of generating this information.
.PP
It is recognized that a DCE which derives power from the serving
central office via the local telephone loop, is in a power\(hyoff condition
with timing sources stopped, when the DCE is disconnected from the line.
It is also recognized that some timing sources will not continue to run
indefinitely without a driving (external synchronization) signal.
.PP
Accuracy and stability of this signal as defined in the DCE
Recommendations are required only when circuit\ 109 is ON. Drift during
the OFF condition of circuit\ 109 is acceptable; however, resynchronization
of the
signal on circuit\ 115 must be accomplished as rapidly as possible following
the turning ON of circuit\ 109 for the next transmission as indicated in
the
relevant DCE Recommendation.
.RT
.sp 1P
.LP
4.7
\fICircuit\ 125\ \(em\ Calling indicator\fR
.sp 9p
.RT
.PP
The operation of circuit\ 125 shall not be impaired or disabled by any
condition on any other interchange circuit.
.RT
.sp 1P
.LP
4.8
\fIUsage of circuits 126 and 127\fR
.sp 9p
.RT
.PP
Originally, these circuits were defined for operational control of a 2\(hywire,
frequency\(hydivided duplex DCE, such as the Recommendation\ V.21\(hytype
modem. Transmitter and receiver control were separated, so that local
testing of both data channels might be performed as national Administrations
required.
.PP
The modem according to Recommendation\ V.21 does not require separate
operational control by the DTE of circuits\ 126 and 127 since it selects
the transmit and receive frequencies according to the condition of
circuit\ 125 in switched network operation.
.PP
However, the use of circuits 126 and 127 may become necessary in
certain types of non\(hycentralized multipoint operation.
.RT
.sp 2P
.LP
4.9
\fICircuit\ 140\ \(em\ Loopback/Maintenance Test\fR
.sp 1P
.RT
.sp 1P
.LP
4.9.1
\fIUsage of circuit 140\fR
.sp 9p
.RT
.PP
Circuit 140 can be used in conjunction with coded commands on
circuit\ 103 in accordance with the provisions of Recommendation\ V.54.
.PP
In systems not including the use of circuit 103, i.e., no coded
commands, circuit\ 140 controls only the remote loopback (loop\ 2).
.PP
In systems that involve the use of circuit 103, additional maintenance
applications of circuit\ 140 are possible. These additional applications
remain for further study.
.RT
.sp 1P
.LP
4.9.2
\fIInterrelationship of circuits 105, 106 and 140\fR
.sp 9p
.RT
.PP
For automatic control of loop 2 test, circuit 106 is under the
control of circuit\ 140 and circuit 105 is disregarded by the DCE.
.bp
.RT
.sp 2P
.LP
4.10
\fIInterrelationship of circuits 202 to 211\fR
.sp 1P
.RT
.sp 1P
.LP
\fICircuit\ 202\fR
.sp 9p
.RT
.PP
Circuit\ 202 must be turned OFF between calls or call attempts and shall
not be turned ON before circuit\ 203 is turned OFF.
.RT
.sp 1P
.LP
\fICircuit\ 204\fR
.sp 9p
.RT
.PP
The ON condition of this circuit must be maintained until the DTE has released
the automatic calling equipment, i.e. until circuit\ 202 is turned OFF.
.RT
.sp 1P
.LP
\fICircuit\ 205\fR
.sp 9p
.RT
.PP
The OFF condition shall be maintained on this circuit after
circuit\ 204 comes ON.
.PP
The initial time interval starts when circuit\ 202 comes ON. Subsequent
time intervals start each time circuit\ 210 is turned OFF.
.RT
.sp 1P
.LP
\fICircuits\ 206, 207, 208 and 209\fR
.sp 9p
.RT
.PP
The conditions on these four circuits shall not change whilst
circuit\ 211 is ON.
.RT
.sp 1P
.LP
\fICircuit\ 210\fR
.sp 9p
.RT
.PP
When circuit\ 210 is turned OFF, it shall not be turned ON again
before circuit\ 211 is turned OFF.
.RT
.sp 1P
.LP
\fICircuit\ 211\fR
.sp 9p
.RT
.PP
Circuit\ 211 shall neither be turned ON when circuit\ 210 is in the OFF
condition, nor until after the DTE has presented the required code
combination on the digit signal circuits.
.PP
Circuit\ 211 shall not be turned OFF before circuit\ 210 is
turned OFF.
.RT
.sp 2P
.LP
\fBReference\fR
.sp 1P
.RT
.LP
[1]
CCITT Recommendation \fIConnection to the telex network of an automatic\fR
\fIterminal using a V.24 DCE/DTE interface\fR , Vol.\ VII, Rec.\ S.16.
\v'6p'
.sp 2P
.LP
\fBRecommendation\ V.25\fR
.RT
.sp 2P
.ce 1000
\fBAUTOMATIC\ ANSWERING\ EQUIPMENT\fR
.EF '% Fascicle\ VIII.1\ \(em\ Rec.\ V.25''
.OF '''Fascicle\ VIII.1\ \(em\ Rec.\ V.25 %'
.ce 0
.ce 1000
\fBAND/OR\ \fR \fBPARALLEL\ AUTOMATIC\ CALLING\ EQUIPMENT\fR
.ce 0
.ce 1000
\fBON\ THE\ GENERAL\ SWITCHED\ TELEPHONE\ NETWORK\fR
.ce 0
.ce 1000
\fBINCLUDING\ PROCEDURES\ FOR\ \fR \fBDISABLING\ OF\ ECHO\ CONTROL\ DEVICES\fR
.ce 0
.sp 1P
.ce 1000
\fBFOR\ BOTH\ MANUALLY\ AND\ AUTOMATICALLY\ ESTABLISHED\ CALLS\fR
.ce 0
.sp 1P
.ce 1000
\fI(Mar del Plata, 1968; amended at Geneva, 1972 and 1976,\fR
.sp 9p
.RT
.ce 0
.sp 1P
.ce 1000
\fIMalaga\(hyTorremolinos, 1984)\fR
.ce 0
.sp 1P
.LP
\fB1\fR \fBScope\fR
.sp 1P
.RT
.PP
1.1
This Recommendation is concerned with the setting\(hyup of a data connection
when automatic answering equipment and/or parallel automatic
calling equipment is used over international circuits. The automatic calling
procedures defined in this Recommendation make use of the 200\(hyseries
interchange circuits and are known as \*Qparallel\*U automatic calling.
Automatic calling procedures, which make use of only the 100\(hyseries
interchange circuits, are known as \*Qserial\*U automatic calling and are
defined in
Recommendation\ V.25\|\fIbis\fR .
.bp
.sp 9p
.RT
.PP
Automatic calling and answering equipment used within any single Administration's
area or between two Administrations by bilateral agreement is not necessarily
constrained by these proposals. In particular, the use of
2100\ Hz answering tone, as described in this Recommendation, could be
substituted by another tone when the equipment is used over circuits not
equipped with echo control devices
. Similarly, the calling tone could be omitted by bilateral agreements
but attention is drawn to \(sc\(sc\ 7 and\ 8 below.
.PP
In addition, the provisions for echo canceller disabling and for a
\*Qcalling station response\*U prior to the termination of answer tone
are optional and only applicable to
data circuit\(hyterminating equipment\ (DCE)
for
which the series\ V Recommendation specifically calls for such
provision(s).
.RT
.PP
1.2
This Recommendation describes the sequence of events involved
in establishing a connection between a
parallel automatic calling data
station
.FS
In this Recommendation, the term \*Q
data station
\*U is
synonymous with the term \*Q
terminal installation for data
transmission
\*U\ [1].
.FE
and an
automatic answering data station
for Series\ V Recommendations modems specified for general switched network
operations. The system configuration proposed is shown in Figure\ 1/V.25.
.LP
.rs
.sp 26P
.ad r
\fBFigure 1/V.25, (M), p. 5\fR
.sp 1P
.RT
.ad b
.RT
.PP
Consideration is given only to:
.LP
a)
the events which affect the interfaces between the data
terminal equipment and the
data circuit
terminating equipment
, and
.LP
b)
the events on the line during establishment of a data call.
.PP
Interactions within the data circuit\(hyterminating equipment are not considered,
since such consideration is unnecessary for purposes of
international standardization.
.LP
.sp 1
.bp
.PP
1.3
The proposed procedures are intended to be suitable for the
four types of calls, namely:
.LP
a)
parallel automatic calling data station to automatic
answering data station;
.LP
b)
manual data station to automatic answering data station;
.LP
c)
parallel automatic calling data station to manual data
station;
.LP
d)
disabling of echo suppressors in the case of manual data
stations.
.PP
1.4
The data terminal equipment is responsible for:
.LP
a)
during call establishment:
.LP
i)
ensuring that the data circuit\(hyterminating equipment is
available for operation,
.LP
ii)
providing the telephone number,
.LP
iii)
deciding to abandon the call if it is unsuccessfully
completed;
.LP
b)
after call is established:
.LP
i)
establishing identities,
.LP
ii)
exchanging such traffic as is appropriate,
.LP
iii)
initiating disconnect at calling and answering data
station.
.sp 2P
.LP
\fB2\fR \fBAbbreviations and definitions\fR
.sp 1P
.RT
.PP
The following abbreviations are used in this
Recommendation:
.RT
.LP
CT\ 104
=\ Circuit\ 104
\(em\ Received data
.LP
CT\ 105
=\ Circuit\ 105
\(em\ Request to send
.LP
CT\ 106
=\ Circuit\ 106
\(em\ Ready for sending
.LP
CT\ 107
=\ Circuit\ 107
\(em\ Data set ready
.LP
CT\ 108/1
=\ Circuit\ 108/1
\(em\ Connect data set to line
.LP
CT\ 108/2
=\ Circuit\ 108/2
\(em\ Data terminal ready
.LP
CT\ 109
=\ Circuit\ 109
\(em\ Data channel received line signal
detector
.LP
CT\ 119
=\ Circuit\ 119
\(em\ Received backward channel data
.LP
CT\ 120
=\ Circuit\ 120
\(em\ Transmit backward channel line
signal
.LP
CT\ 121
=\ Circuit\ 121
\(em\ Backward channel ready
.LP
CT\ 122
=\ Circuit\ 122
\(em\ Backward channel received line signal detector
.LP
CT\ 125
=\ Circuit\ 125
\(em\ Calling indicator
.LP
CT\ 201
=\ Circuit\ 201
\(em\ Signal ground or common return
.LP
CT\ 202
=\ Circuit\ 202
\(em\ Call request
.LP
CT\ 203
=\ Circuit\ 203
\(em\ Data line occupied
.LP
CT\ 204
=\ Circuit\ 204
\(em\ Distant station connected
.LP
CT\ 205
=\ Circuit\ 205
\(em\ Abandon call
.LP
CT\ 206
=\ Circuit\ 206
\(em\ Digit signal (2\u0\d)
.LP
CT\ 207
=\ Circuit\ 207
\(em\ Digit signal (2\u1\d)
.LP
CT\ 208
=\ Circuit\ 208
\(em\ Digit signal (2\u2\d)
.LP
CT\ 209
=\ Circuit\ 209
\(em\ Digit signal (2\u3\d)
.LP
CT\ 210
=\ Circuit\ 210
\(em\ Present next digit
.LP
CT\ 211
=\ Circuit\ 211
\(em\ Digit present
.LP
CT\ 213
=\ Circuit\ 213
\(em\ Power indication
.LP
DCE
=\ Data circuit\(hyterminating equipment
.LP
DTE
=\ Data terminal equipment
.LP
EON
=\ End\(hyof\(hynumber control character
.LP
SEP
=\ Separation control character
.bp
.PP
The following definitions apply to this Recommendation:
.sp 1P
.LP
\fBcalling tone\fR
.sp 9p
.RT
.PP
The calling tone and calling station response should not contain
power in the band 2100\ \(+-\ 250\ Hz.
.FE
The power levels of the signals specified in this Recommendation
shall conform to the levels specified in Recommendation\ V.2.
.FE
The tone transmitted from the calling end. This may be 1300\ Hz or any
tone corresponding to binary\ 1 of the DCE in use.
\u,\d\|
.RT
.sp 1P
.LP
\fBanswering tone\fR
.sp 9p
.RT
.PP
The tone transmitted from the called end.
.RT
.sp 1P
.LP
\fBstarting signal\fR
.sp 9p
.RT
.PP
Binary\ 1, synchronizing signal or equalizer training signal, as
appropriate.
.RT
.sp 1P
.LP
\fBcalling station response\fR
.sp 9p
.RT
.PP
A tone or signal transmitted from the calling DCE in response to its detection,
as defined in this Recommendation, of answering
tone.
\u,\d\|
.FS
The specification of the calling station response and the timing of its
transmission are the subject of the individual Series\ V
Recommendation for the DCE involved. The specifications in this Recommendation
cover only limitations on its transmission during call
establishment.
.FE
\u,\d\|
.RT
.sp 1P
.LP
\fBparallel automatic calling\fR
.sp 9p
.RT
.PP
A procedure by which a DTE, by use of the 200\(hyseries interchange circuits,
may instruct a DCE to perform the call establishment function. The
transmission, from DTE to DCE, of each digit to be dialled is achieved in
parallel form on interchange circuits\ 206 through\ 209.
.RT
.sp 1P
.LP
\fBserial automatic calling\fR
.sp 9p
.RT
.PP
A procedure by which a DTE, by use of the 100\(hyseries interchange circuits,
may instruct a DCE to perform the call establishment function.
The transmission, from DTE to DCE, of each digit to be dialled is achieved
in serial form on interchange circuit\ 103
(see Recommendation\ V.25\|\fIbis\fR ).
.RT
.LP
\fB3\fR \fBInterface procedures at call\(hyoriginating data station\fR
.sp 1P
.RT
.sp 2P
.LP
\fIEvent\fR
.sp 1P
.RT
.PP
3.1
DTE checks if CT 213 ON, and the following circuits OFF:
CT\ 202, CT\ 210, CT\ 205, CT\ 204, CT\ 203.
.sp 9p
.RT
.PP
3.2
DTE puts CT\ 202 ON.
.PP
3.3
DTE puts CT 108/2 ON (CT 108/2 can be placed in the ON condition at any
time up to and including event\ 3.16).
.PP
3.4
For half\(hyduplex modems, DTE puts CT\ 105 ON if the calling end
wishes to transmit first. CT\ 105 can be placed ON at any time up to and
including event\ 3.20.
.PP
3.5
Line goes \*Qoff hook\*U.
.PP
3.6
DCE puts CT\ 203 ON.
.LP
.sp 2
.bp
.PP
3.7
Telephone system puts dial tone on line
.FS
Some countries apply
the second dial tone to the line after the initial digit is transferred.
.FE
.
.PP
3.8
DCE puts CT 210 ON.
.PP
3.9
DTE presents the first or appropriate digit on CT\ 206, CT\ 207,
CT\ 208 and CT\ 209.
.PP
3.10
DTE puts CT 211 ON after digit signals have been presented.
.PP
3.11
DCE dials first digit; then takes CT\ 210 OFF.
.PP
3.12
DTE takes CT\ 211 OFF.
.PP
3.13
Events 3.8 to 3.12 are repeated (but this process may be
interrupted by SEP) until the last digit signal is presented and transferred.
Event 3.8 is then repeated but event\ 3.14 follows.
.PP
3.14
DTE presents EON on CT 206, CT 207, CT 208 and CT 209; it then
puts CT 211 ON.
.PP
3.15
DCE takes CT 210 OFF.
.PP
3.16
DTE takes CT 211 OFF and puts CT 108/2 ON, if not previously ON.
.PP
3.17
The interrupted calling tone, as shown in Figures\ 2/V.25, 3/V.25 and 4/V.25
is transmitted to line from the calling DCE.
.LP
.rs
.sp 32P
.ad r
\fBFigure 2/V.25, (M), p. 6\fR
.sp 1P
.RT
.ad b
.RT
.LP
.bp
.LP
.rs
.sp 47P
.ad r
\fBFigure 3/V.25, (M), p. 7\fR
.sp 1P
.RT
.ad b
.RT
.LP
.bp
.LP
.rs
.sp 34P
.ad r
\fBFigure 4/V.25, (M), p. 8\fR
.sp 1P
.RT
.ad b
.RT
.LP
3.18
a)
If the call is answered by a data station, then 2100\(hyHz
tone is received by the calling DCE. Echo suppressors are disabled
during coincidence of a silent period in the interrupted calling
tone (event 3.17) with 2100\ Hz answering tone. The 2100\(hyHz
answering tone must not activate CT\ 104 and CT\ 109.
.LP
b)
If the call is not answered, or is answered by a non\(hydata
station, then no 2100\ Hz is received at the calling data
station. If no answering tone is received after an elapsed
time, CT 205 comes ON. This time is measured from event\ 3.15
and selectable in the range of 10\(hy40\ seconds. The DTE must
respond by turning CT 202 OFF.
.PP
3.19
When a 2100\(hyHz answer tone has been recognized by the DCE for a
period of 100 to 600\ ms, the interrupted calling tone is discontinued by the
DCE as shown in Figures\ 2/V.25, 3/V.25 and\ 4/V.25. The DCE transfers
control of the connection to the telephone line from CT\ 202 to CT\ 108/2.
.PP
The DCE may, as shown in Figures 3/V.25 and 4/V.25, transmit the calling
station response following the detection of a continuation of the
2100\(hyHz answer tone for a period of at least 400\ ms after the transmission
of the calling tone is terminated. As indicated in Figure\ 4/V.25, the
required
duration (\(>="\ 1\ s) of the continuous 2100\(hyHz period, which must
follow the
termination of the calling tone, is longer if the answer tone includes phase
reversals to disable echo cancellers.
.bp
.PP
For some DCEs requiring extended training sequences, the associated Series\
V Recommendation may specify that CT\ 107 be put ON at some later time,
during the handshake sequence, which is more consistent with the specification
in Recommendation\ V.24 of CT\ 107.
.FE
3.20
The DCE examines the line to determine the end of the 2100\(hyHz
answering tone. The DCE detects an absence of the 2100\(hyHz tone for 75\
\(+-\ 20\ ms, and then puts CT\ 107 ON:
.LP
i)
If CT 105 is ON, the starting signal is put on the line.
After its delay as specified in the appropriate Series\ V
Recommendation, CT\ 106 comes ON and the DTE can then
transmit data.
.LP
ii)
If CT 105 is OFF, the incoming starting signal is
recognized and after its delay as specified in the appropriate Series\ V
Recommendation, the DCE puts CT\ 109 ON to allow the examination
of CT 104 by the DTE.
.LP
iii)
For the duplex modem case, where CT 105 is not used, the starting signal
is put on the line after CT\ 107 is put ON. The
DCE then puts ON CT\ 109 and CT\ 106 after a delay as specified
in the appropriate Series\ V Recommendation.
.PP
\fINote\fR \ \(em\ There may be an interim period during which certain
existing V.21\ modems may not be able to provide the silent period between
the end of the answering tone and the application of the starting signal.
In this case, the use of a selective answering tone detector (see \(sc\
11 below) will be essential.
.PP
3.21
The DCE turns ON CT 204. The DTE then may turn OFF CT\ 202
without disconnecting the call.
.PP
\fINote\ 1\fR \ \(em\ After event 3.19, both CT 202 and CT 108/2 must be
turned OFF to disconnect. The ON of CT\ 205 is an indication to DTE disconnect.
.PP
\fINote\ 2\fR \ \(em\ Where CT 105 or CT 120 is not implemented, the timing of
CT\ 106 or CT\ 121 shall be related to CT\ 107 and CT\ 109 respectively.
.RT
.LP
\fB4\fR \fBInterface procedure at answering data station\fR
.sp 1P
.RT
.sp 2P
.LP
\fIEvent\fR
.sp 1P
.RT
.PP
4.1
Ringing received on line. DCE puts CT 125 ON.
.sp 9p
.RT
.LP
4.2
a)
If CT 108/2 is ON, DCE goes \*Qoff hook\*U.
.LP
b)
If CT 108/1 or CT 108/2 is OFF, the DCE waits for CT 108/1 or CT\ 108/2
to come ON, and then goes \*Qoff hook\*U. If CT 108/1 or CT 108/2 does
not turn ON, then the call is not answered.
.PP
4.3
The DCE goes \*Qoff hook\*U, maintains silence on the line for a
period between 1.8 and 2.5\ s, then transmits 2100\(hyHz
.FS
The 2100\(hyHz
tolerance will be \(+-\|15\ Hz in accordance with Recommendation\ G.164\ [2].
.FE
answer tone for a period, as shown in Figures\ 2/V.25 and\ 3/V.25. Where it is
intended to disable network
echo cancellers
\ [3] as well as
echo
suppressors
\ [2], reversals (180\(de)
.FS
The reversal in phase shall be
accomplished such that the phase is within 180\ \(+-\ 10\ degrees in 1\
ms and that
the amplitude of the 2100\(hyHz tone is not more than 3\ dB below its steady
state value for more than\ 400\ \(*ms.
.FE
in the phase of the 2100\(hyHz tone
shall be introduced, as indicated in Figure\ 4/V.25, at intervals of 425 to
475\ ms. The 2100\(hyHz answer tone, with continued reversals in its phase,
shall continue for 3.3\ \(+-\ 0.7\ s unless a calling station response
is received, in
which case the 2100\(hyHz tone may be discontinued after detection of the
response for 100\ ms.
.PP
For the very special application in which an
automatically
answering modem
is permanently dedicated to receive calls only from
acoustically coupled originating stations, the modem may, optionally, extend
the duration of the answer tone to ten seconds to compensate for operator
reaction time in placing the telephone handset on the
acoustic coupler
. All other timeouts remain the same and the protocol is as defined in
\(sc\ 6. Use of the extended answer tone is restricted expressly to this
unique
application.
.PP
4.4
At the end of the 2100\(hyHz transmission, the DCE shall not
transmit (i.e.\ provide a silent period) for 75\ \(+-\ 20\ ms. The DCE
puts CT\ 107 ON after this silent period.
.LP
.sp 1
.bp
.sp 2P
.LP
\fB5\fR \fBProposed line procedures\fR
.sp 1P
.RT
.PP
The line procedures outlined consider the half\(hyduplex case of the Series\
V Recommendations modems. For reasons of simplicity, the same timing of
line signals will be used for duplex modems (including modems with backward
channel).
.PP
Systems which operate in the half\(hyduplex mode and which employ
automatic calling equipment shall determine by prearrangement which of
the two data stations \(em\ calling or answering\ \(em shall first transmit
to the other
upon the establishment of the data connection. As indicated in \(sc\ 3
above, the DTE at the data station which is to transmit first must put
CT\ 105 ON, at the appropriate point in the call establishment sequence.
For correct operation, it is necessary that the longer response times of
CT\ 106 and CT\ 109 as specified in the appropriate Series\ V Recommendation
are used during call
establishment.
.PP
Figures 2/V.25, 3/V.25 and 4/V.25 show the timing of line signals
when automatic calling and automatic answering are employed. The sequence of
operation is as follows:
.PP
After the DCE has dialled the digits of the directory number for the automatic
answering data station, followed by the EON character, the DCE sends the
calling tone to the answering data station. The calling tone consists of
a series of interrupted bursts of binary\ 1 signal or 1300\ Hz, ON for
a duration of not less than 0.5\ s and not more than 0.7\ s and OFF for
a duration of not
less than 1.5\ s and not more than 2.0\ s.
.PP
1.8 to 2.5 s after the answering data station is connected to the line
(i.e., CT\ 125 and CT\ 108 are ON), it sends a continuous 2100\(hyHz answering
tone for a duration of not more than 4.0\ s. If it is intended to disable
network
echo cancellers as well as echo suppressors, the answering station reverses
the phase of the tone at intervals of 425 to 475\ ms (see Figure\ 4/V.25).
.PP
The answering tone propagates towards the calling data station and,
during the course of one or two interruptions between bursts of calling
tone, causes any echo suppressors on the circuit to disable. If the phase
reversals are included in the signal, any echo cancellers in the circuit
would also be
disabled. The answering tone is recognized by the calling data station for a
period of between\ 100\ ms and 600\ ms after its arrival. The calling station
discontinues the calling tone and may transmit a calling station response.
The answering station, after detecting the calling station response, may
discontinue transmission of the tone. The answering station shall provide a
silent interval of 75\ +\ 20\ ms in its transmitted output following the
discontinuance of the 2100\(hyHz tone.
.RT
.PP
The calling data station recognizes the end of the answering 2100\(hyHz
tone for a period of 75\ \(+-\ 20\ ms. At the end of this interval, the
DCE may put CT\ 107 ON. Similarly, the answering data station delays for
a period of
75\ \(+-\ 20\ ms after discontinuing the answer tone before it may put CT\ 107
ON.
.PP
To keep the echo suppressor disabled, it is necessary to ensure that following
the 75\ \(+-\ 20\ ms silent period after the transmission of the 2100\(hyHz
answering tone from the answering data station, which serves to disable the
echo suppressor or echo canceller during the silent period in the calling
tone, energy is maintained as specified in Recommendation\ G.164\ [2].
.PP
During the automatic calling and answering procedures, the echo
suppressors will be disabled and the echo cancellers will be disabled if the
required sequence is transmitted. If signal gaps, at the echo suppressor or
canceller, exceed 100\ ms at any time, e.g.\ during
modem turn\(hyaround
,
they may become re\(hyenabled. This requires that, to maintain the disabled
state of echo control devices on circuits with satellite links, the answering
data
station resume transmission after the 75\ \(+-\ 20\ ms silent period unless
a calling station response is received prior to the silent interval and
appropriately
continued.
.RT
.sp 2P
.LP
\fB6\fR \fBManual data station calling automatic answering
data station\fR
.sp 1P
.RT
.PP
The procedure for establishment of a call from a manual data
station to an automatic answering data station is similar to that from an
automatic calling data station, except that no tone is transmitted from the
calling data station until the answering data station has answered. The
manual operator dials the required number, hears 2100\ Hz returned from
the automatic answering data station and then presses his data button to
connect the data
circuit\(hyterminating equipment to the line during the period that 2100\ Hz is
being received. CT\ 107 comes ON at the time specified in event\ 3.20.
Where the calling station is acoustically coupled to the line, placement
of the telephone handset on the acoustic coupler is logically equivalent
to pressing a \*Qdata\*U
button on a permanently installed DCE.
.bp
.PP
Satisfactory disabling of echo suppressors by the answering tone,
however, will require that no speech signals from the microphone at the
calling data station enter the telecommunications circuit for a period
of at least
1\ s during the receipt of answering tone. This may be accomplished by a
handset switch or other appropriate means.
.RT
.sp 2P
.LP
\fB7\fR \fBAutomatic calling data station calling manual data\fR
\fBstation\fR
.sp 1P
.RT
.PP
An operator answering a call from an automatic calling equipment
hears an interrupted calling tone of\ 0.5 to 0.7\ s ON and\ 1.5 to 2.0\
s OFF. The data button must be depressed to connect the DCE to line. A
period of
up to\ 4.0\ s of 2100\(hyHz tone is transmitted to the calling data station to
disable echo suppressors and/or echo cancellers and to notify the calling
data station that the connection is being established. This sequence is
followed by data transmission, as required.
.RT
.sp 2P
.LP
\fB8\fR \fBDisabling of echo suppressors in the case of\fR
\fBmanual data\fR
\fBstations\fR
.sp 1P
.RT
.PP
The procedures as described in \(sc\(sc\ 6 and\ 7 above with regard to
the manually operated data stations, can obviously be used for disabling
echo
suppressors when manual switching from voice conversation to data is required,
which is the preferred principle of operation. Considering the type of
DCE
designed to be used in conjunction with manual connection set\(hyup, it will be
necessary to equip the DCE with a 2100\(hyHz answering tone generator. To avoid
modifying existing equipment at the data station which receives the answering
tone, the following procedure may replace the operation principle of \(sc\
6 above. The manual operator operates his data key after the end of the
2100\(hyHz
answering tone. The data station which is to transmit the answering tone
is to be agreed between the operators while still in the voice mode.
.PP
Care must be exercised in cases of half\(hyduplex modems where
transmission of data is started from the data station which transmits the
answering tone, to avoid mutilation of the initial data.
.RT
.PP
\fINote\fR \ \(em\ Where disabling of echo suppressors is not required in the
half\(hyduplex modem case, the 2100\(hyHz answering tone need not be transmitted.
However, the delay between CT\ 105 to CT\ 106 ON conditions should be longer
than 100\ ms in consideration of the echo suppressor suppression hangover
time.
.RT
.sp 2P
.LP
\fB9\fR \fBProtection of ordinary telephone users\fR
.sp 1P
.RT
.PP
As both automatic calling and automatic answering data stations
transmit tones to line during call establishment, a normal telephone user
who becomes inadvertently connected to one will receive tone signals for
a period of sufficient duration to indicate clearly to him that he is incorrectly
connected.
.RT
.sp 2P
.LP
\fB10\fR \fBManual selection of automatic answering, data mode and voice
mode\fR
.sp 1P
.RT
.PP
It is recognized that, at the data station, means should be
provided to allow the operator to select between automatic and manual answering
of calls. If a call is manually answered, voice mode shall be established.
Subsequent switching to the data mode shall be performed by the procedure as
specified in \(sc\ 7 above.
.PP
Selection of manual or automatic answering of subsequent calls shall be
possible after entering the data mode. As an option, automatic answering
may be arranged for all subsequent incoming calls. In this case, manual
answering may still be achieved by keeping CT\ 108/2 OFF to cause an audible
signal to
occur at the telephone instrument.
.PP
The DCE shall be disconnected from the line whenever CT\ 108/1 or
CT\ 108/2 is turned OFF, irrespective of the means employed in establishing
the connection.
.PP
Procedures for switching to the voice mode between data transmission within
the same call shall ensure that CT\ 107 is turned OFF while in the voice
mode.
.RT
.sp 2P
.LP
\fB11\fR \fB2100\(hyHz tone recognition\fR
.sp 1P
.RT
.PP
To protect the 2100\(hyHz tone detector against faulty operation
resulting from interference generated by the interrupted calling tone, the
detector may be inhibited during the ON periods of the calling tone.
.bp
.PP
Additionally, in cases where automatic calling equipment is used to
set up the call, the 2100\(hyHz detector must not respond to spurious tones
which may arise from speech or service signals during call establishment. It
is suggested that the answering tone detection be prevented when the 2100\(hyHz
signal is accompanied by any other signal of comparable level within the
ranges 350\ Hz to 1800\ Hz and 2500\ Hz to 3400\ Hz.
.PP
\fINote\fR \ \(em\ The relative inhibiting signal levels recommended for the
echo suppressor disabling tone detector of Recommendation\ G.164\ [2] are a
useful guide for 2100\(hyHz tone detector inhibiting levels.
.RT
.sp 2P
.LP
\fBReferences\fR
.sp 1P
.RT
.LP
[1]
CCITT Definition: \fITerminal installation for data transmission\fR ,
Vol.\ X (Terms and Definitions).
.LP
[2]
CCITT Recommendation \fIEcho suppressors\fR , Vol.\ III, Rec.\ G.164.
.LP
[3]
CCITT Recommendation \fIEcho cancellers\fR , Vol.\ III, Rec.\ G.165.
\v'1P'
.sp 2P
.LP
\fBRecommendation V.25\|bis
.RT
.sp 2P
.ce 1000
\fBAUTOMATIC\ CALLING\ AND/OR\ ANSWERING\ EQUIPMENT\fR
.EF '% Fascicle\ VIII.1\ \(em\ Rec.\ V.25^bis''
.OF '''Fascicle\ VIII.1\ \(em\ Rec.\ V.25^bis %'
.ce 0
.ce 1000
\fBON\ THE\ GENERAL\ SWITCHED\ TELEPHONE\ NETWORK\ (GSTN)\fR
.ce 0
.sp 1P
.ce 1000
\fBUSING\ THE\ 100\(hySERIES\ INTERCHANGE\ CIRCUITS\fR
.ce 0
.sp 1P
.ce 1000
\fI(Malaga\(hyTorremolinos, 1984; modified at Melbourne, 1988)\fR
.sp 9p
.RT
.ce 0
.sp 1P
.LP
\fB1\fR \fBScope\fR
.sp 1P
.RT
.PP
1.1
This Recommendation is concerned with the setting up of a data connection
on the general switched telephone network where the automatic
calling equipment used interfaces to the data terminal equipment via the
100\(hyseries interchange circuits.
.sp 9p
.RT
.PP
This procedure is known as
serial automatic calling
.
Procedures for parallel automatic calling are defined in
Recommendation\ V.25.
.PP
1.2
The Recommendation describes the sequence of events involved in
establishing a connection between
a\ serial automatic calling data
station
.FS
In this Recommendation, the term \*Q
data station
\*U
is synonymous with the term \*Q
terminal installation for data
transmission
\*U.
.FE
and an automatic answering data station for Series\ V
Recommen
dation\ modems specified for general switched telephone operation.
The system configuration is shown in
Figure\ 1/V.25\|\fIbis\fR .
.LP
.rs
.sp 13P
.ad r
\fBFigure\ 1/V.25\|bis, (M), p.\fR
.sp 1P
.RT
.ad b
.RT
.LP
.bp
.PP
1.3
The procedures are intended to be suitable for the following
three types of call:
.LP
a)
serial automatic calling data station to automatic answering data station;
.LP
b)
manual calling data station to automatic answering data
station;
.LP
c)
serial automatic calling data station to manual answering
data station.
.PP
It is intended that data terminal equipment designed to control
automatic calling equipment in accordance with this Recommendation will
also be suitable for use with manually controlled data circuit\(hyterminating
equipment, and also that data circuit\(hyterminating equipment incorporating
serial automatic calling equipment may be manually controlled where necessary.
.PP
1.4
The procedures described should allow automatic calling
equipment conforming to this Recommendation to interwork with automatic
answering equipment conforming to Recommendation\ V.25. Similarly, the
procedures herein described for automatic answering allow interworking with
automatic calling equipment conforming to Recommendation\ V.25.
.PP
1.5
The data terminal equipment is responsible:
.LP
a)
during call establishment:
.LP
i)
for ensuring that the data circuit\(hyterminating
equipment is available for operation,
.LP
ii)
for providing the telephone number or selecting a
telephone number pre\(hyprogrammed into the data circuit\(hyterminating
equipment,
.LP
iii)
for deciding to abandon the call if it is
unsuccessfully completed;
.LP
b)
after call establishment:
.LP
i)
for controlling data transfer,
.LP
ii)
for initiating disconnect at calling or answering
data stations.
.PP
1.6
This Recommendation deals with call establishment and clearing.
Any specific use of Recommendation\ V.24 interchange circuits herein described
only applies during these phases. The management of interchange circuits
and
the line during the data transmission phase is not part of this
Recommendation.
.PP
Details of interface procedures following the OFF to ON transition of circuit\
107 on entry of the data transmission phase can be found in the
relevant modem Recommendations.
.PP
1.7
Annex A gives guidance on the maintenance facilities which may
be associated with an automatic calling data circuit\(hyterminating equipment.
Methods for testing the automatic calling functions of the data
circuit
terminating equipment are included.
.PP
1.8
References to automatic calling in the remainder of this
Recommendation may be taken as serial automatic calling unless otherwise
stated.
.sp 2P
.LP
\fB2\fR \fBAbbreviations and definitions\fR
.sp 1P
.RT
.PP
The following abbreviations are used in this Recommendation:
.RT
.LP
DCE\ =\ Data circuit\(hyterminating equipment
.LP
DTE
\ =\ Data terminal equipment.
.PP
The following definitions apply to this Recommendation:
.sp 1P
.LP
\fBcommand\fR
.sp 9p
.RT
.PP
An instruction issued by the DTE to the DCE as part of the
automatic calling procedure.
.RT
.sp 1P
.LP
\fBindication\fR
.sp 9p
.RT
.PP
An instruction or response issued by the DCE to the DTE as part of the
automatic calling procedure.
.PP
\fINote\fR \ \(em\ In this Recommendation the terms \*Qindication\*U and
\*Qresponse\*U are not to be taken in the sense defined in Recommendation\
X.210.
.RT
.sp 1P
.LP
\fBparameter\fR
.sp 9p
.RT
.PP
A variable which may accompany Commands or Indications.
.bp
.RT
.sp 1P
.LP
\fBparallel automatic calling\fR
.sp 9p
.RT
.PP
A procedure by which a DTE, by use of the 200\(hyseries interchange circuits,
may instruct a DCE to perform the call establishment function. The
transmission, from DTE to DCE, of each digit to be dialled is achieved in
parallel form on interchange circuits\ 206 to\ 209.
.RT
.sp 1P
.LP
\fBserial automatic calling\fR
.sp 9p
.RT
.PP
A procedure by which a DTE, by use of the 100\(hyseries interchange circuits,
may instruct a DCE to perform the call establishment function. The
transmission, from DTE to DCE, of each digit to be dialled is achieved in
serial form on circuit\ 103.
.RT
.sp 2P
.LP
\fB3\fR \fBGeneral\fR
.sp 1P
.RT
.PP
3.1
The automatic calling and/or answering data stations can be
operated, according to this Recommendation, in two modes:
.sp 9p
.RT
.LP
\(em
The \*Qaddressed call and/or answer authorized by the DTE
(circuit\ 108/2)\*U mode gives at a calling data station extensive
facilities by means of instructions exchanged between the DTE
and the DCE on circuits\ 103 and\ 104. It gives an answering data
station the capacity to accept \*Qa priori\*U an incoming call.
.LP
\(em
The \*Qdirect call and/or answer controlled by the DTE
(circuit\ 108/1)\*U mode gives at a calling data station the
capacity of calling a number (or a sequence of numbers)
pre\(hyrecorded in the DCE, by means of the 108/1 control circuit.
It gives to an answering data station the capacity of accepting
incoming calls on a \*Qper call\*U basis.
.PP
3.2
Though
automatic answering data stations
as well as
automatic calling and answering data stations
may implement both modes of operation, they are configured at installation
to operate in either one or the other of the two modes.
.LP
\fB4\fR \fBAddressed call and/or answer authorized by the DTE\fR
(circuit\ 108/2)
.sp 1P
.RT
.sp 2P
.LP
4.1
\fIInterface procedure\fR
.sp 1P
.RT
.sp 1P
.LP
4.1.1
\fIInterchange circuits\fR \fIinvolved\fR
.sp 9p
.RT
.PP
The interchange circuits used in this automatic calling/answering procedure
are listed in Table\ 1/V.25\|\fIbis\fR . Their use during the automatic
calling/answering procedures is described below.
.RT
.ce
\fBH.T. [T1.25]\fR
.ce
TABLE\ 1/V.25\|\fIbis\fR
.ps 9
.vs 11
.nr VS 11
.nr PS 9
.TS
center box;
cw(114p) | cw(66p) .
Interchange circuit Direction
_
.T&
cw(24p) | cw(90p) | cw(36p) | cw(30p) .
Number Name from DCE to DCE
_
.T&
cw(24p) | lw(90p) | lw(36p) | cw(30p) .
103 Transmitted data X
.T&
cw(24p) | lw(90p) | cw(36p) | cw(30p) .
104 Received data X
.T&
cw(24p) | lw(90p) | cw(36p) | cw(30p) .
106 Ready for sending X
.T&
cw(24p) | lw(90p) | cw(36p) | cw(30p) .
107 Data set ready X
.T&
cw(24p) | lw(90p) | cw(36p) | cw(30p) .
108/2 Data terminal ready X
.T&
cw(24p) | lw(90p) | cw(36p) | cw(30p) .
125 Calling indicator X
_
.TE
.nr PS 9
.RT
.ad r
\fBTableau 1/V.25\|bis [T1.25], p.\fR
.sp 1P
.RT
.ad b
.RT
.LP
.bp
.sp 1P
.LP
4.1.1.1
\fICircuit 103 \(em Transmitted data\fR
.sp 9p
.RT
.PP
The instructions issued by the DTE during the automatic calling
procedure, known as \fIcommands\fR , are transmitted to the DCE on this
circuit.
.RT
.sp 1P
.LP
4.1.1.2
\fICircuit 104 \(em Received data\fR
.sp 9p
.RT
.PP
Responses from the DCE to DTE Commands, known as \fIindications\fR , are
transmitted to the DTE on this circuit. Optionally, circuit 104 may convey
the echo of the commands transmitted on circuit\ 103 (for further study).
.RT
.sp 1P
.LP
4.1.1.3
\fICircuit 106 \(em Ready for sending\fR
.sp 9p
.RT
.PP
The DCE shall turn circuit\ 106 ON in response to the DTEs
circuit\ 108/2 being ON.
.PP
The DCE shall turn circuit 106 OFF:
.RT
.LP
i)
on connection to line when answering tone is detected;
.LP
ii)
when the DCE aborts the call set\(hyup under the control of
DTE by turning 108/2 in the OFF condition.
.sp 1P
.LP
4.1.1.4
\fICircuit 107 \(em Data set ready\fR
.sp 9p
.RT
.PP
The DCE shall turn circuit 107 ON:
.RT
.LP
i)
at the end of the automatic call set\(hyup procedure, to
indicate to the DTE that the connection is established and the
DCE connected to line;
.LP
ii)
on completion of manual call set\(hyup procedure.
.PP
The DCE shall turn circuit 107 OFF:
.LP
i)
to indicate to the DTE that the connection has been cleared down during
the data transfer phase (to be permitted where
national regulations require it);
.LP
ii)
in response to a clear request by the DTE turning OFF
circuit\ 108/2.
.sp 1P
.LP
4.1.1.5
\fICircuit 108/2 \(em Data terminal ready\fR
.sp 9p
.RT
.PP
The DTE turns circuit 108/2 ON:
.RT
.LP
i)
to enable the DCE to set up a connection either manually or automatically;
.LP
ii)
to indicate to the DCE that it is ready to accept an
incoming call.
.PP
The DTE shall turn circuit 108/2 OFF:
.LP
i)
to instruct the DCE to clear down the connection during data transfer;
.LP
ii)
to instruct the DCE to abort the call set\(hyup procedure;
.LP
iii)
to indicate to the DCE that it is not ready to accept an incoming call.
.sp 1P
.LP
4.1.1.6
\fICircuit 125 \(em Calling indicator\fR
.sp 9p
.RT
.PP
The DCE should provide circuit 125 to indicate to the DTE an
incoming call. This incoming call will override a call request prior to
seizure of the line. The usage of circuit\ 125 in the DTE is optional.
.RT
.sp 1P
.LP
4.1.1.7
\fIOther interchange circuits\fR
.sp 9p
.RT
.PP
The state of other interchange circuits is not part of the
procedure. However, to ensure maximum compatibility with existing equipment,
the other interchange circuits provided should retain their normal function
during the automatic calling procedure.
.PP
Particularly to ensure correct operation of the DTE, the condition of circuit\
109 should follow the condition of circuit\ 106.
.PP
The DTE may choose to hold circuit 105 ON during the automatic
calling procedure, but the DCE is not required to recognize this
condition.
.bp
.RT
.sp 1P
.LP
4.1.2
\fIControl information\fR \fIformat\fR
.sp 9p
.RT
.PP
Call set\(hyup is achieved by the use of interchange circuits 106, 107
and 108 together with messages exchanged between the DTE and the DCE on
circuits\ 103 and\ 104. These messages consist of commands
or\ indications
from the DTE or DCE respectively, and may be accompanied by \fIparameters\fR
where necessary.
The\ commands/indications required for the automatic calling
procedure are outlined in Table\ 2/V.25\|\fIbis\fR and
Table\ 3/V.25\|\fIbis\fR together with their parameters.
.PP
The use of commands/indications other than one of the call request
commands (CR\(em) and the invalid indication (INV) is optional in the DTE
and DCE respectively.
.PP
The commands/indications and their parameters are described
below.
.RT
.sp 1P
.LP
4.1.2.1
\fICall request commands\fR
.sp 9p
.RT
.PP
These commands from the DTE instruct the DCE to initiate a call
set\(hyup procedure. The commands shall include a suffix to indicate the type
of call request concerned (see Table\ 3/V.25\|\fIbis\fR ) and shall be
accompanied by one or more of the following parameters:
.RT
.LP
i)
the number to be dialled. (In applications where additional
dial tones are required, separators, \*Qwait tone\*U, etc., may be
included in this number);
.LP
ii)
the identification number of the data station;
.LP
iii)
the DCE memory address which contains the number to be
dialled, this having been previously programmed;
.PP
\fINote\fR \ \(em\ Manufacturers should note that the response time to
a Call Request Command is determined by the time required to execute line
procedures (see \(sc\ 6.1).
.sp 1P
.LP
4.1.2.2
\fIProgram commands\fR
.sp 9p
.RT
.PP
These commands from the DTE instruct the DCE to enter a programming state.
The commands shall be accompanied by one or more of the following
parameters:
.RT
.LP
i)
the DCE memory address into which the number to be dialled is to be stored;
.LP
ii)
the number which is to be stored;
.LP
iii)
the identification number of the data station.
.PP
Where a DCE does not contain the programming capability, this DCE shall
reply to a program command by an \fIinvalid\fR indication.
.PP
Where a DTE is not capable of programming the DCE, it may still
initiate call attempts using the \fIcall request\fR command in the normal
way.
.RT
.sp 1P
.LP
4.1.2.3
\fIList request commands\fR
.sp 9p
.RT
.PP
These commands from the DTE instruct the DCE to list the numbers
that have been programmed in its memory with or without their status. The
commands shall include a suffix to indicate the type of list concerned. The
command may be accompanied by parameters to select items to be listed. These
parameters are for further study.
.RT
.sp 1P
.LP
4.1.2.4
\fIDisregard incoming call command\fR
.sp 9p
.RT
.PP
This command from the DTE instructs the DCE not to answer the
current incoming call which is, or has been, signalled from the DCE to the
DTE.
.RT
.sp 1P
.LP
4.1.2.5
\fIConnect incoming call command\fR
.sp 9p
.RT
.PP
This command from the DTE instructs the DCE to connect an incoming call
that has been disregarded due to a previous disregard incoming call
command.
.RT
.sp 1P
.LP
4.1.2.6
\fICall failure indication\fR
.sp 9p
.RT
.PP
This indication may be issued by the DCE in response to a \fIcall\fR \fIrequest\fR
command from the DTE and may be accompanied by a parameter stating
the reason for the failure of the call.
.bp
.PP
The following parameters indicate the possible conditions that may
result in a call failure on the GSTN:
.RT
.LP
i)
engaged tone;
.LP
ii)
number not stored;
.LP
iii)
local DCE busy, (e.g. DCE involved in an operation invoked from the front
panel);
.LP
iv)
ring tone, (the remote end was ringing but the call is
aborted on time\(hyout)
.LP
v)
abort call, (the call is aborted on time\(hyout)
.LP
vi)
answer tone not detected, (the other end was recognized as going off
hook but the V.25 answer tone was not detected);
.LP
vii)
forbidden call, (call attempts to this number are blocked by the DCE
due to national regulations) (Note);
.LP
viii)
other parameters dependent on national network
variations.
.LP
\fINote\fR \ \(em\ Procedure for clearance of forbidden call numbers
is not covered in this Recommendation.
.PP
The provision of the \fIcall failure\fR indication is optional in the DCE.
For this reason, the DTE should also be capable of recognizing call
failure by means of a time out.
.sp 1P
.LP
4.1.2.7
\fIDelayed call indication\fR
.sp 9p
.RT
.PP
This indication from the DCE may be implemented depending on
national regulations, and informs the DTE that, for example, owing to repeated
unsuccessful call attempts, call attempts to this number are blocked by
the DCE for a time given by the accompanying parameter.
.RT
.sp 1P
.LP
4.1.2.8
\fIIncoming call indication\fR
.sp 9p
.RT
.PP
This indication may be provided by the DCE to inform the DTE that a
ring tone
has been detected on the telephone line.
.PP
\fINote\fR \ \(em\ In the event of collision between an incoming call and
a call request, the incoming call will have priority.
.RT
.sp 1P
.LP
4.1.2.9
\fIValid indication\fR
.sp 9p
.RT
.PP
This indication may be provided by the DCE to acknowledge call
request, program, disregard incoming call and correct incoming call commands,
and to inform the DTE that the command has been accepted.
.RT
.sp 1P
.LP
4.1.2.10
\fIInvalid indication\fR
.sp 9p
.RT
.PP
This indication shall be provided by the DCE when it receives an
invalid command, or receives a command which it is incapable of executing
either because it does not implement the function or because the function is
invoked at a wrong time in the V.25\|\fIbis\fR process. This indication may be
accompanied by a parameter stating the reason for the invalid
situation.
.PP
The following parameters indicate the possible conditions that may
result in an invalid situation:
.RT
.LP
i)
command unknown error,
.LP
ii)
message syntax error,
.LP
iii)
parameter syntax error,
.LP
iv)
parameter value error.
.sp 1P
.LP
4.1.2.11
\fIList indications\fR
.sp 9p
.RT
.PP
A series of such indications may be provided by the DCE to list
specific items stored in its memory according to the \fIlist request\fR command
previously made by the DTE. These indications will be accompanied by one or
more of the following parameters:
.RT
.LP
i)
the DCE memory address into which the number is stored;
.LP
ii)
the number stored;
.LP
iii)
the status of this number (for further study);
.LP
iv)
the identification number of the data station.
.PP
\fINote\fR \ \(em\ When the list request command invokes edition of an
empty list, a list indication with no parameter may be issued.
.bp
.sp 1P
.LP
4.1.2.12
\fICall connecting indication\fR
.sp 9p
.RT
.PP
This indication may be provided by the DCE to inform the DTE that the connection
procedures are about to be completed.
.RT
.LP
.sp 3
.ce
\fBH.T. [T2.25]\fR
.ce
TABLE\ 2/V.25\|\fIbis\fR
.ce
\fBSet of commands and indications\fR
.ce
(Note 1)
.ps 9
.vs 11
.nr VS 11
.nr PS 9
.TS
center box;
cw(60p) | cw(36p) | cw(36p) | cw(96p) .
Command/indication DTE to DCE (command) DCE to DTE (indication) Parameters
_
.T&
lw(60p) | cw(36p) | cw(36p) | lw(96p) .
Call request X \(em Number to be dialled
.T&
lw(60p) | cw(36p) | cw(36p) | lw(96p) .
T{
\(em
Memory address of the number to be dialled
T}
.T&
lw(60p) | cw(36p) | cw(36p) | lw(96p) .
\(em Identification number
.T&
lw(60p) | cw(36p) | cw(36p) | lw(96p) .
Program X \(em Number to be dialled
.T&
lw(60p) | cw(36p) | cw(36p) | lw(96p) .
T{
\(em
Memory address for the number to be dialled
T}
.T&
lw(60p) | cw(36p) | cw(36p) | lw(96p) .
\(em Identification number
.T&
lw(60p) | cw(36p) | cw(36p) | lw(96p) .
List request X \(em (Note 2)
.T&
lw(60p) | cw(36p) | cw(36p) | lw(96p) .
Disregard incoming call X \(em None
.T&
lw(60p) | cw(36p) | cw(36p) | lw(96p) .
Connect incoming call X \(em None
.T&
lw(60p) | cw(36p) | cw(36p) | lw(96p) .
Call failure X \(em Engaged tone
.T&
lw(60p) | cw(36p) | cw(36p) | lw(96p) .
\(em Number not stored
.T&
lw(60p) | cw(36p) | cw(36p) | lw(96p) .
\(em Local DCE busy
.T&
lw(60p) | cw(36p) | cw(36p) | lw(96p) .
\(em Ring tone (time out)
.T&
lw(60p) | cw(36p) | cw(36p) | lw(96p) .
\(em Abort call (time out)
.T&
lw(60p) | cw(36p) | cw(36p) | lw(96p) .
T{
\(em
V.25 answer tone not detected
T}
.T&
lw(60p) | cw(36p) | cw(36p) | lw(96p) .
T{
\(em
Forbidden call (nationally dependent
parameters)
T}
.T&
lw(60p) | cw(36p) | cw(36p) | lw(96p) .
Delayed call X T{
\(em
Time to permissible call request
(minutes)
T}
.T&
lw(60p) | cw(36p) | cw(36p) | lw(96p) .
Incoming call X \(em None
.T&
lw(60p) | cw(36p) | cw(36p) | lw(96p) .
Valid X \(em None
.T&
lw(60p) | cw(36p) | cw(36p) | lw(96p) .
Invalid X \(em Optionally, error code
.T&
lw(60p) | cw(36p) | cw(36p) | lw(96p) .
List X \(em Memory address
.T&
lw(60p) | cw(36p) | cw(36p) | lw(96p) .
\(em Number to be dialled
.T&
lw(60p) | cw(36p) | cw(36p) | lw(96p) .
\(em Status (Note 2)
.T&
lw(60p) | cw(36p) | cw(36p) | lw(96p) .
\(em Identification number
.T&
lw(60p) | cw(36p) | cw(36p) | lw(96p) .
Call connecting X \(em
.TE
.LP
(Note 2)
\fINote\ 1\fR
\ \(em\ DTE manufacturers should note that a set of indications may
not be implemented in a DCE, and allowance for this, by use of suitable
time\(hyouts, should be made.
.LP
\fINote\ 2\fR
\ \(em\ This item is for further study.
.nr PS 9
.RT
.ad r
\fBTableau 2/V.25\|bis [T2.25], p.\fR
.sp 1P
.RT
.ad b
.RT
.LP
.sp 1
.bp
.ce
\fBH.T. [T3.25]\fR
.ce
TABLE\ 3/V.25\|\fIbis\fR
.ce
\fBEncoding of commands and indications\fR
.ps 9
.vs 11
.nr VS 11
.nr PS 9
.TS
center box;
cw(60p) | cw(30p) | cw(138p) .
Command/indication IA5 characters Parameter format
_
.T&
lw(60p) | lw(30p) | lw(18p) | lw(82p) .
Call request with:
.T&
lw(60p) | cw(30p) | lw(18p) | lw(82p) .
number provided: CRN CRN T{
Number to be dialled
XXXXX\|.\|.\|.\|.\|.\|XXXX
T}
.T&
lw(60p) | cw(30p) | lw(18p) | lw(60p) | lw(60p) .
T{
number provided with the identification number:
T} CRI CRI T{
Number to be dialled
XXXXX\|.\|.\|XXXX
;
T} T{
Identification number
YY\|.\|.\|.\|.YY
T}
.T&
lw(60p) | cw(30p) | lw(18p) | lw(82p) .
memory address provided: CRS CRS T{
Memory address
XXXXX\|.\|.\|.\|XX
T}
.T&
lw(60p) | lw(30p) | lw(18p) | lw(60p) | lw(60p) .
Program:
.T&
lw(60p) | cw(30p) | lw(18p) | lw(60p) | lw(60p) .
normal: PRN PRN T{
Memory address
XXXXX\|.\|.\|XX
;
T} T{
Number to be dialled
XXXXX\|.\|.\|.\|XXXX
T}
.T&
lw(60p) | cw(30p) | lw(18p) | lw(82p) .
identification: PRI PRI T{
identification number
XXXXX\|.\|.\|.\|.\|.\|XX
T}
.T&
lw(60p) | cw(30p) | lw(18p) | lw(82p) .
List request of:
.T&
lw(60p) | cw(30p) | lw(18p) | lw(82p) .
stored number: RLN RLN T{
For further study
ZZZ\|.\|.\|.\|.\|.\|Z
T}
.T&
lw(60p) | cw(30p) | lw(18p) | lw(82p) .
forbidden numbers: RLF RLF T{
For further study
ZZZ\|.\|.\|.\|.\|.\|Z
T}
.T&
lw(60p) | cw(30p) | lw(18p) | lw(82p) .
delayed call numbers: RLD RLD T{
For further study
ZZZ\|.\|.\|.\|.\|.\|Z
T}
.T&
lw(60p) | cw(30p) | lw(18p) | lw(82p) .
identification number: RLI RLI
.T&
lw(60p) | cw(30p) | lw(18p) | lw(82p) .
Disregard incoming call: DIC DIC
.T&
lw(60p) | cw(30p) | lw(18p) | lw(82p) .
Connect incoming call: CIC CIC
.T&
lw(60p) | cw(30p) | lw(18p) | lw(82p) .
Call failure indication: CFI CFI Failure type XX
.T&
lw(60p) | cw(30p) | lw(18p) | lw(82p) .
Delayed call: DLC DLC T{
Time duration (in minutes)
XXX\|.\|.\|.\|XX
T}
.T&
lw(60p) | cw(30p) | lw(18p) | lw(82p) .
Incoming call: INC INC
.T&
lw(60p) | cw(30p) | lw(18p) | lw(82p) .
Valid: VAL VAL
.T&
lw(60p) | cw(30p) | lw(18p) | lw(82p) .
Invalid: INV INV Optionally, error type XX
.TE
.TS
lw(60p) | lw(30p) | lw(18p) | lw(44p) | lw(38p) | lw(38p) .
List of:
.T&
lw(60p) | lw(30p) | lw(18p) | lw(44p) | lw(38p) | lw(38p) .
Memory address Number to be dialled Status (for further study)
.T&
lw(60p) | cw(30p) | lw(18p) | lw(44p) | lw(38p) | lw(38p) .
stored numbers: LSN LSN XXXX\|.\|.\|XX ; YYYY\|.\|.\|YYY ; ZZZZ (Note)
.T&
lw(60p) | cw(30p) | lw(18p) | lw(44p) | lw(38p) | lw(38p) .
forbidden numbers: LSF LSF XXXX\|.\|.\|XX ; YYYY\|.\|.\|YYY ; ZZZZ (Note)
.T&
lw(60p) | cw(30p) | lw(18p) | lw(44p) | lw(38p) | lw(38p) .
delayed call numbers: LSD LSD XXXX\|.\|.\|XX ; YYYY\|.\|.\|YYY ; ZZZZ (Note)
.T&
lw(60p) | cw(30p) | lw(18p) | lw(120p) .
identification number: LSI LSI T{
Identification number
XXXX\|.\|.\|.\|.\|XX (Note)
T}
.T&
lw(60p) | cw(30p) | lw(18p) | lw(120p) .
Call connecting: CNX CNX ZZZ\|.\|.\|.\|.\|Z (for further study)
.TE
.LP
\fINote\fR
\ \(em\ When the list request command invokes edition of an empty list, a list indication with no parameter may be issued.
.nr PS 9
.RT
.ad r
\fBTableau 3/V.25\|bis {T3.25], p.\fR
.sp 1P
.RT
.ad b
.RT
.LP
.bp
.sp 1P
.LP
4.1.3
\fIFormat for commands and indications\fR
.sp 9p
.RT
.PP
Commands and indications may be encoded in the formats specified
below, according to application.
.RT
.sp 1P
.LP
4.1.3.1
\fIAsynchronous operation\fR
.sp 9p
.RT
.PP
The format for asynchronous operation shall be as shown in
Figure\ 2/V.25\|\fIbis\fR .
.RT
.LP
.rs
.sp 10P
.ad r
\fBFigure\ 2/V.25\|bis, (M), p.\fR
.sp 1P
.RT
.ad b
.RT
.PP
In this mode of operation, the character format shall be one start element
followed by 8\(hybit data units and one\(hyunit stop element. The 8\(hybit
data units are formed by a 7\(hybit IA5\ character in accordance with
Recommendation\ T.50 together with an even parity unit in accordance with
Recommendation\ V.4.
.PP
Where the DCE operating rate is variable, the transmision rate for
commands and parameters should be the maximum data rate permitted by the
modem Recommendation, i.e.:\ 300, 600, 1200 and\ 2400 bit/s.
.PP
\fINote\fR \ \(em\ These bit rates are the minimum which should be provided.
The addition of other bit rates is for further study.
.PP
Depending on the application, characters may or may not be echoed by the
DCE (for further study).
.RT
.sp 1P
.LP
4.1.3.2
\fISynchronous character oriented operation\fR
.sp 9p
.RT
.PP
The format for synchronous character oriented operation shall be in accordance
with ISO\ 1745, and shall be as shown in Figure\ 3/V.25\|\fIbis\fR .
.RT
.LP
.rs
.sp 6P
.ad r
\fBFigure\ 3/V.25\|bis, (M), p.\fR
.sp 1P
.RT
.ad b
.RT
.PP
Generally the command/indication is terminated by ETX. However,
when a succession of indications is transmitted (e.g.\ succession of LSN
indications), ETB should be used instead of ETX with all but the last
indication of the succession, to indicate that other indications are
coming.
.PP
In this mode of operation, consecutive 8\(hybit data units are used.
The 8\(hybit data units are formed by a 7\(hybit IA5 character in accordance
with
Recommendation\ T.50 with an odd parity bit in accordance with
Recommendation\ V.4.
.PP
The bit rate used for the data transfer shall apply.
.bp
.RT
.sp 1P
.LP
4.1.3.3
\fISynchronous bit oriented operation\fR
.sp 9p
.RT
.PP
HDLC (High Level Data Link Control) format shall be used for
synchronous bit oriented operation, and shall be as shown in
Figure\ 4/V.25\|\fIbis\fR .
.RT
.LP
.rs
.sp 6P
.ad r
\fBFigure 4/V.25\|bis, (M), p.\fR
.sp 1P
.RT
.ad b
.RT
.PP
The message is the information field of a UI frame transmitted
with the global address. Generally the P/F bit
is set to\ 1. Consequently, the A and C\ fields are generally as
follows:
.LP
A\ =\ 11111111
C\ =\ 11001000
.LP
C\
LSB\ \ \ MSB
.PP
However, when a succession of indications is transmitted
(e.g.\ succession of LSN indications), the P/F bit should be set to\ 0,
i.e.\ the control field is changed to:
.LP
C\ =\ 11000000
.LP
C\
LSB\ \ \ MSB
.LP
with all but the last indication of the succession, to indicate that other
indications are coming.
.PP
The introduction of other addresses is for further study.
.PP
Within the message, consecutive 8\(hybit data units are used and
submitted to the HDLC framing (zero insertion). The 8\(hybit data units
are formed by a 7\(hybit IA5 character in accordance with Recommendation\
T.50 together with an eighth bit set indifferently either to \*Qone\*U
or \*Qzero\*U, or the odd parity. No parity checking will be done on reception.
.PP
The transmission mode and the bit rate used for the data transfer
shall apply.
.RT
.sp 1P
.LP
4.1.4
\fIMessage format and encoding\fR
.sp 9p
.RT
.PP
The message format shall comprise:
.RT
.LP
i)
a three\(hycharacter command/indication (see
Table\ 3/V.25\|\fIbis\fR );
.LP
ii)
one or more parameters separated by \*Q;\*U characters
(see Tables\ 4/V.25\|\fIbis\fR and 5/V.25\|\fIbis\fR ); these parameters
may include \*Q\|\*U
and \*Q.\*U as presentation characters (see Table\ 6/V.25\|\fIbis\fR ).
.PP
A detailed description of the
command/indication syntax
is contained in Table\ 6/V.25\|\fIbis\fR . A general presentation of this
syntax is
offered in Appendix\ I.
.sp 1P
.LP
4.1.5
\fICommand/indication exchange protocol\fR
.sp 9p
.RT
.PP
The exchange of commands and indications between the DTE and the
DCE can be regarded as asynchronous and balanced.
.RT
.PP
4.1.5.1
The following basic rules apply:
.sp 9p
.RT
.LP
\(em
Every command is to be followed by, at least, one indication or by circuit\
107 going ON in the case of successful call.
.LP
\(em
Several indications may be issued by the DCE one after the
other, either of the same nature or of a different nature.
.LP
\(em
The issue by the DTE of new commands other than DIC prior to the reception
of the indication to the previous command may abort the execution of this
previous command and should therefore be avoided.
.bp
.ce
\fBH.T. [T4.25]\fR
.ce
TABLE\ 4/V.25\|\fIbis\fR
.ce
\fBParameter enconding\fR
.ce
(Number to be dialled)
.ps 9
.vs 11
.nr VS 11
.nr PS 9
.TS
center box;
cw(90p) | cw(42p) .
T{
Alphabet for number to be dialled
T} IA5 coding
_
.T&
cw(90p) | cw(42p) .
0 0
.T&
cw(90p) | cw(42p) .
1 1
.T&
cw(90p) | cw(42p) .
2 2
.T&
cw(90p) | cw(42p) .
3 3
.T&
cw(90p) | cw(42p) .
4 4
.T&
cw(90p) | cw(42p) .
5 5
.T&
cw(90p) | cw(42p) .
6 6
.T&
cw(90p) | cw(42p) .
7 7
.T&
cw(90p) | cw(42p) .
8 8
.T&
cw(90p) | cw(42p) .
9 9
.T&
lw(90p) | cw(42p) .
Wait tone :
.T&
lw(90p) | cw(42p) .
Pause (Note 1) <
.T&
lw(90p) | cw(42p) .
Separator 3 (Note 2) =
.T&
lw(90p) | cw(42p) .
Separator 4 (Note 2) >
.T&
lw(90p) | cw(42p) .
T{
Dialling to be continued in pulse mode (Note\ 4)
T} P
.T&
lw(90p) | cw(42p) .
T{
Dialling to be continued in DTMF mode (Note\ 4)
T} T
.T&
lw(90p) | cw(42p) .
Flash (Notes 3 and 4) &
.TE
.LP
\fINote\ 1\fR
\ \(em\ Usage and duration of this parameter are a national matter.
.LP
\fINote\ 2\fR
\ \(em\ For national use.
.LP
\fINote\ 3\fR
\ \(em\ The flash duration is a national matter.
.LP
\fINote\ 4\fR
\ \(em\ Optionally accepted parameter.
.nr PS 9
.RT
.ad r
\fBTableau 4/V.25\|bis, {T4.25], p. 16\fR
.sp 1P
.RT
.ad b
.RT
.ce
\fBH.T. [T5.25]\fR
.ce
TABLE\ 5/V.25\|\fIbis\fR
.ce
\fBParameter encoding\fR
.ce
(Failure and error types)
.ps 9
.vs 11
.nr VS 11
.nr PS 9
.TS
center box;
cw(90p) | cw(42p) .
Parameter IA5 coding
_
.T&
lw(90p) | cw(42p) .
Engaged tone ET
.T&
lw(90p) | cw(42p) .
Number not stored NS
.T&
lw(90p) | cw(42p) .
Local DCE busy CB
.T&
lw(90p) | cw(42p) .
Ring tone RT
.T&
lw(90p) | cw(42p) .
Abort call AB
.T&
lw(90p) | cw(42p) .
Answer tone not detected NT
.T&
lw(90p) | cw(42p) .
Forbidden call FC
.T&
lw(90p) | cw(42p) .
T{
Command unknown/Unexpected error
T} CU
.T&
lw(90p) | cw(42p) .
Message syntax error MS
.T&
lw(90p) | cw(42p) .
Parameter syntax error PS
.T&
lw(90p) | cw(42p) .
Parameter value error PV
_
.TE
.nr PS 9
.RT
.ad r
\fBTableau 5/V.25\|bis, {T5.25], p. 17\fR
.sp 1P
.RT
.ad b
.RT
.LP
.bp
.ce
\fBH.T. [T6.25]\fR
.ce
TABLE\ 6/V.25\|\fIbis\fR
.ce
\fBDetailed description of the V.25\|bis
.ce
command/indication syntax\fR
.ps 9
.vs 11
.nr VS 11
.nr PS 9
.TS
center box;
lw(228p) .
description language:
.T&
lw(228p) .
a | b denotes the set (a, b)
.T&
lw(228p) .
a b denotes the set (ab)
.T&
lw(228p) .
T{
a*
denotes the set (e, a, aa, aaa, .\|.\|.\|)
T}
.T&
lw(228p) .
(e = empty)
.T&
lw(228p) .
description:
.T&
lw(228p) .
T{
message
=
command | indication
T}
.T&
lw(228p) .
T{
command
=
CR
\(ulcommand | PR
\(ulcommand | RL
\(ulcommand |
DIC
\(ulcommand | CIC
\(ulcommand |
T}
.T&
lw(228p) .
T{
indication
=
LS
\(ulindication | CFI
\(ulindication |
DLC
\(ulindication | INC
\(ulindication |
VAL
\(ulindication | INV
\(ulindication | CNX
\(ulindication |
T}
.T&
lw(228p) .
T{
CR
\(ulcommand
=
CRN
\(ulcommand | CRI
\(ulcommand |
CRS
\(ulcommand
T}
.T&
lw(228p) .
T{
PR
\(ulcommand
=
PRN
\(ulcommand | PRI
\(ulcommand
T}
.T&
lw(228p) .
T{
RL
\(ulcommand
=
RLN
\(ulcommand | RLF
\(ulcommand | RLD
\(ulcommand |
RLI
\(ulcommand
T}
.T&
lw(228p) .
T{
LS
\(ulindication
=
LSN
\(ulindication | LSF
\(ulindication |
LSD
\(ulindication | LSI
\(ulindication
T}
.T&
lw(228p) .
T{
CRN
\(ulcommand
=
`CRN` number
T}
.T&
lw(228p) .
T{
CRI
\(ulcommand
=
`CRI` number delimiter identification
T}
.T&
lw(228p) .
T{
CRS
\(ulcommand
=
`CRS` address
T}
.T&
lw(228p) .
T{
PRN
\(ulcommand
=
`PRN` address delimiter number
T}
.T&
lw(228p) .
T{
PRI
\(ulcommand
=
`PRI` identification
T}
.T&
lw(228p) .
T{
RLN
\(ulcommand
=
`RLN` | (`RLN` RL
\(ulparameter)
T}
.T&
lw(228p) .
T{
RLF
\(ulcommand
=
`RLF` | (`RLF` RL
\(ulparameter)
T}
.T&
lw(228p) .
T{
RLD
\(ulcommand
=
`RLD` | (`RLD` RL
\(ulparameter)
T}
.T&
lw(228p) .
RLI \(ulcommand = `RLI`
.T&
lw(228p) .
DIC \(ulcommand = `DIC`
.T&
lw(228p) .
CIC \(ulcommand = `CIC`
.T&
lw(228p) .
T{
LSN
\(ulindication
=
(`LSN` address delimiter number) |
(`LSN` address delimiter number delimiter status) | `LSN`
T}
.T&
lw(228p) .
T{
LSF
\(ulindication
=
(`LSF` address delimiter number) |
(`LSF` address delimiter number delimiter status) | `LSF`
T}
.T&
lw(228p) .
T{
LSD
\(ulindication
=
(`LSD` address delimiter number) |
(`LSD` address delimiter number delimiter status) | `LSD`
T}
.T&
lw(228p) .
T{
LSI
\(ulindication
=
`LSI` identification | `LSI`
T}
.T&
lw(228p) .
T{
CFI
\(ulindication
=
`CFI` failure
\(ultype
T}
.T&
lw(228p) .
T{
DLC
\(ulindication
=
`DLC` time
\(ulduration
T}
.T&
lw(228p) .
INC \(ulindication = `INC`
.T&
lw(228p) .
VAL \(ulindication = `VAL`
.T&
lw(228p) .
T{
INV
\(ulindication
=
`INV` | (`INV` error
\(ultype)
T}
.T&
lw(228p) .
T{
CNX
\(ulindication
=
`CNX` | (`CNX` CNX
\(ulparameter)
T}
.T&
lw(228p) .
T{
number
=
presentation* (digit | special)
(digit | special | presentation)*
T}
.T&
lw(228p) .
T{
identification
=
presentation* digit (digit |
presentation)*
T}
.T&
lw(228p) .
T{
address
=
presentation* digit (digit | presentation)*
T}
.T&
lw(228p) .
T{
failure
\(ultype
=
presentation* (`ET` | `NS` | `CB` | `RT` |
`AB` | `NT` | `FC`)
T}
.T&
lw(228p) .
T{
RL
\(ulparameter
=
to be defined *****
T}
.T&
lw(228p) .
T{
time
\(ulduration
=
presentation* digit (digit |
presentation)*
T}
.T&
lw(228p) .
T{
error
\(ultype
=
presentation* (`MS` | `CU` | `PS` |
`PV`)
T}
.T&
lw(228p) .
status = to be defined *****
.T&
lw(228p) .
T{
CNX
\(ulparameter
=
to be defined *****
T}
.T&
lw(228p) .
T{
digit
=
`0` | `1` | `2` | `3` | `4` | `5` | `6` |
`7` | `8` | `9`
T}
.T&
lw(228p) .
T{
special
=
`&` | `:` | `>` | `<` | `=` | `P` | `T`
T}
.T&
lw(228p) .
presentation = `\ ` | `.`
.T&
lw(228p) .
delimiter = `;`
_
.TE
.nr PS 9
.RT
.ad r
\fBTableau 6/V.25\|bis, {T6.25], p. 18\fR
.sp 1P
.RT
.ad b
.RT
.LP
.bp
.sp 1P
.LP
4.1.5.2
\fIErroneous command/indication\fR
.sp 9p
.RT
.LP
\(em
Whenever a command/indication is detected with a level\ II
framing error
(incorrect framing, parity or FCS,
see \(sc\ 4.1.3), this command/indication is disregarded.
.LP
\(em
Whenever a DCE detects an error in the message of a command
or receive a command which cannot be executed,
it acknowledges negatively this command by issuing an \fIinvalid\fR
indication (INV). The letters within opcodes for commands and
indications shall be upper case letters. Optionally, DCEs are
allowed to accept the presence of corresponding lower case
letters in place of specified upper case letters within the
three letter opcode of a command.
.sp 1P
.LP
4.1.5.3
\fICommand/indication succession\fR
.sp 9p
.RT
.PP
Table 7/V.25\|\fIbis\fR lists for all the commands defined:
.RT
.LP
\(em
the state of the interface in which the command may be
issued,
.LP
\(em
the state to which the interface moves after the issue of the command,
.LP
\(em
the indications pertinent to that command,
.LP
\(em
the state to which the interface moves after the issue of the indication,
.LP
\(em
the consequence of this indication for the action initiated by the command.
.PP
\fINote\fR \ \(em\ The state diagram of the interface is shown in
Figure\ 5/V.25\|\fIbis\fR . In addition an SDL description of the message
exchange, as per the Z.100 serie Recommendations, is offered in Annex\
B.
.LP
.sp 2
.ce
\fBH.T. [T7.25]\fR
.ce
TABLE\ 7/V.25\|\fIbis\fR
.ce
\fBCommands, indications and their consequences\fR
.ps 9
.vs 11
.nr VS 11
.nr PS 9
.TS
center box;
cw(66p) | cw(24p) | cw(24p) | cw(30p) | cw(24p) | cw(60p) .
DTE command From state To state DCE response To state Consequence
_
.T&
lw(66p) | cw(24p) | cw(24p) | cw(30p) | cw(24p) | lw(60p) .
Call Request (CR \(ul) 3 NC VAL/CFI 4/3 Failed
.T&
lw(66p) | cw(24p) | cw(24p) | cw(30p) | cw(24p) | lw(60p) .
VAL/CNX 4/5 Accepted
.T&
lw(66p) | cw(24p) | cw(24p) | cw(30p) | cw(24p) | lw(60p) .
VAL/INC 4/10 Aborted
.T&
lw(66p) | cw(24p) | cw(24p) | cw(30p) | cw(24p) | lw(60p) .
VAL \(ul 4/10 Aborted
.T&
lw(66p) | cw(24p) | cw(24p) | cw(30p) | cw(24p) | lw(60p) .
VAL/DLC 4/3 Failed
_
.T&
lw(66p) | cw(24p) | cw(24p) | cw(30p) | cw(24p) | lw(60p) .
Program (PR \(ul)\|\ua\d\u)\d 3/10/14 NC VAL NC Accepted
.T&
lw(66p) | cw(24p) | cw(24p) | cw(30p) | cw(24p) | lw(60p) .
CNX(10) 11 Aborted
_
.T&
lw(66p) | cw(24p) | cw(24p) | cw(30p) | cw(24p) | lw(60p) .
T{
List Request (RL
\(ul)\|\ua\d\u)\d
T} 3/10/14 NC LS \(ul NC Accepted
.T&
lw(66p) | cw(24p) | cw(24p) | cw(30p) | cw(24p) | lw(60p) .
CNX(10) 11 Aborted
_
.T&
lw(66p) | cw(24p) | cw(24p) | cw(30p) | cw(24p) | lw(60p) .
Disregard Incoming Call (DIC) 10 NC VAL 14 Incoming call not accepted
_
.T&
lw(66p) | cw(24p) | cw(24p) | cw(30p) | cw(24p) | lw(60p) .
Connect Incoming Call (CIC) 14 NC VAL/CNX 11 Incoming call accepted
.T&
lw(66p) | cw(24p) | cw(24p) | cw(30p) | cw(24p) | lw(60p) .
VAL 3 Incoming call not accepted
_
.T&
lw(66p) | cw(24p) | cw(24p) | cw(30p) | cw(24p) | lw(60p) .
Any command X NC INV NC Failed
.TE
.LP
NC\ No change
.LP
\ua\d\u)\d
Reception of INC \(em circuit 125 turning ON or OFF and/or the issue of DIC \(em does not interfere with Program and List commands and their
responses.
.nr PS 9
.RT
.ad r
\fBTableau 7/V.25\|bis, {T7.25], p.\fR
.sp 1P
.RT
.ad b
.RT
.LP
.bp
.LP
.rs
.sp 45P
.ad r
\fBFigure 5/V.25\|bis, (N), p.\fR
.sp 1P
.RT
.ad b
.RT
.LP
.bp
.sp 1P
.LP
4.2
\fIInterface procedures at the calling data station\fR
.sp 9p
.RT
.PP
The DTE/DCE interface procedure for automatic calling and answering is
shown in the state diagram in Figure\ 5/V.25\|\fIbis\fR .
.PP
The call set\(hyup procedure is as follows:
.RT
.LP
\(em
When the DTE is not ready to answer an incoming call or to
enter the dialogue with the DCE, the interface is in state\ 1,
\fIDTE not ready\fR .
.LP
\(em
Prior to entering the dialogue with the DCE, the DTE shall
signal 108/2\ =\ ON and the interface is then in state\ 2,
\fIDTE ready\fR .
.LP
\(em
The DCE signals to the DTE that it is ready to enter the
dialogue with the DTE by signalling 106\ =\ ON, state\ 3,
\fIDTE\(hyDCE dialogue\fR . In this state, the DTE can issue commands
and the DCE may issue indications.
.LP
\(em
To initiate a call set\(hyup, the DTE shall issue a \fIcall\fR \fIrequest\fR
command which should be acknowledged by the DCE either
with an invalid or a valid indication. In the latter case the
interface moves to state\ 4, call establishment.
If the \fIcall request\fR command contains a PSTN (public switched
telephone network) number, the DCE shall proceed with the call
set\(hyup procedure. If it contains a DCE memory address, the DCE
shall use its stored number.
.LP
\(em
The DCE remains in state\ 4 during the dialling process.
.LP
\(em
If the call is established and the answering tone is detected
(see \(sc\ 6.1), a call connecting indication should be issued by
the DCE, the interface moves to state\ 5, \fIanswer tone\fR \fIdetected\fR
, and circuit\ 106 is turned OFF.
.LP
\(em
If the call fails, the DCE may issue a \fIcall failure\fR or a
delayed call indication while in state\ 4 and return to state\ 3.
During transmission of a calling station identification and the
subsequent disconnection from the line following a call failure,
the DCE may turn circuit\ 106 OFF and return to state\ 2, when it
is not capable of handling new commands from the DTE.
.LP
\(em
On completion of the line procedures (see \(sc\ 6.1), circuit\ 107
is turned ON and the interface moves to state\ 6, \fIcall\fR \fIconnected\fR
. From this state the DTE may enter the \fIdata\fR \fItransfer\fR phase,
state\ 12, in the normal manner.
.LP
\(em
While the DCE is in state 3 or state 4, prior to going \fIoff\fR
\fIhook\fR , an incoming call shall be signalled to the DTE using
circuit\ 125 and/or using the \fIincoming call\fR indication. The
interface then moves to state\ 10, \fIincoming call accepting\fR . If
in this state the DTE wishes not to answer the incoming call, it
may issue a \fIdisregard incoming call\fR command. In this case the
interface will move to state\ 14 and allow exchange of
indications and commands other than \fIcall request\fR . The
collision of a call request with an incoming call before the
latter has been detected is for further study.
.LP
\(em
The DTE may clear a call or call attempt at any time by
turning circuit 108/2 OFF, state\ 7, \fIclearing by DTE\fR . The
interface will then move to state\ 1 or\ 8 for circuit\ 125 OFF or
ON respectively.
.sp 1P
.LP
4.3
\fIInterface procedures at the answering data station\fR
.sp 9p
.RT
.PP
The DTE/DCE interface procedure for automatic calling and answering is
shown in the state diagram in Figure\ 5/V.25\|\fIbis\fR . The procedure
is as
follows:
.RT
.LP
\(em
When the DTE is not ready to answer an incoming call or to
enter the dialogue with the DCE, the interface is in state\ 1,
\fIDTE not ready\fR .
.LP
\(em
Prior to entering the dialogue with the DCE, the DTE shall
signal 108/2\ =\ ON and the interface is then in state\ 2,
\fIDTE ready\fR .
.LP
\(em
The DCE signals to the DTE that it is ready to enter the
dialogue with the DTE by signalling 106\ =\ ON, state\ 3, \fIDTE\(hyDCE\fR
\fIdialogue\fR . In this state the DTE can issue commands and the DCE
may issue indications.
.LP
\(em
An incoming call is indicated to the DTE using circuit\ 125
and/or with an \fIincoming call\fR indication, and by this means the
interface will move from state\ 3 or\ 4 to state\ 10, \fIincoming\fR
\fIcall accepting\fR . (In the case of state\ 4, the incoming call
may only be detected prior to the DCE going \fIoff hook\fR .)
.LP
\(em
If an incoming call occurs when the DTE is in state\ 1, \fIDTE\fR
\fInot ready\fR , the DCE moves to state\ 8, \fIincoming call\fR . The DTE
may then turn circuit\ 108/2 ON, in response to this call or in
order to enter the dialogue with the DCE. The interface thus
moves to state\ 9, \fIincoming call recognized\fR . The DCE will
respond by turning circuit\ 106 ON and thus also in this case the
interface moves to state\ 10.
.bp
.LP
\(em
While in state\ 10, the DTE may reject the incoming call by
turning circuit\ 108/2 OFF or issue a \fIdisregard incoming call\fR
command which should be acknowledged by the DCE either with an
invalid or valid indication. In the latter case, the interface
will move to state\ 14 and allow exchange of indications and
commands other than \fIcall request\fR . If no \fIdisregard incoming\fR
\fIcall\fR command has been issued within a period determined by
national regulations, or when this command is reset by a
subsequent \fIconnect incoming call\fR command which should be
acknowledged by the DCE either with an invalid or a valid
indication, the DCE shall accept the incoming call, may issue a
Call Connecting indication and move to state\ 11, \fIincoming call\fR
\fIaccepted\fR turning circuit\ 106 OFF, and from there to state\ 13,
\fIline seized\fR , by turning circuit\ 125 OFF.
.LP
\fR
.LP
\(em
Simple DCEs, having no programming capabilities, have in the past, been
provided which do not respond to the DIC and CIC
commands.
.LP
\(em
In this case the DCE will connect the incoming call
immediately or after a predetermined period dependent on
national regulations, thus moving directly from state\ 9,
\fIincoming call recognized\fR to state\ 13, \fIline seized\fR .
.LP
\(em
On completion of the line procedures (see \(sc\ 6.1), circuit 107
is turned ON and the interface moves to state\ 6, \fIcall\fR \fIconnected\fR
. From this state the DTE may enter the \fIdata\fR \fItransfer\fR phase,
state\ 12 in the normal manner.
.sp 2P
.LP
\fB5\fR \fBDirect call\fR \fB and/or\fR
\fBanswer controlled by the\fR
\fBDTE\fR (circuit 108/1)
.sp 1P
.RT
.PP
The \fIdirect call\fR operating mode provides the DTE with the facility
of setting up a call on the PSTN to a predefined data station, without
a
message exchange between the DTE and the DCE. The PSTN number to be called
(or sequence of PSTN numbers) is recorded in the DCE. This Recommendation
does not cover the method for recording the number in the DCE.
.RT
.sp 1P
.LP
5.1
\fIInterchange circuits involved\fR
.sp 9p
.RT
.PP
The interchange circuits used in this automatic calling/answering procedure
are listed in Table\ 8/V.25\|\fIbis\fR .
.RT
.ce
\fBH.T. [T8.25]\fR
.ce
TABLE\ 8/V.25\|\fIbis\fR
.ps 9
.vs 11
.nr VS 11
.nr PS 9
.TS
center box;
cw(114p) | cw(66p) .
Interchange circuit Direction
_
.T&
cw(24p) | cw(90p) | cw(36p) | cw(30p) .
Number Name from DCE to DCE
_
.T&
cw(24p) | lw(90p) | cw(36p) | lw(30p) .
107 Data set ready X
.T&
cw(24p) | lw(90p) | cw(36p) | cw(30p) .
108/1 Connect data set to line X
.T&
cw(24p) | lw(90p) | cw(36p) | cw(30p) .
125 Calling indicator X
_
.TE
.nr PS 9
.RT
.ad r
\fBTableau 8/V.25\|bis, [T8.25], p.\fR
.sp 1P
.RT
.ad b
.RT
.LP
.sp 1
.sp 1P
.LP
5.1.1
\fICircuit 107 \(em Data set ready\fR
.sp 9p
.RT
.PP
The DCE shall turn circuit 107 ON:
.RT
.LP
i)
at the end of the automatic call set\(hyup procedure, to
indicate to the DTE that the connection is established and the
DCE connected to line;
.LP
ii)
on completion of manual call set\(hyup procedure.
.PP
The DCE shall turn circuit\ 107 OFF:
.LP
i)
to indicate to the DTE that the connection has been cleared down during
the data transfer phase (to be permitted where
national regulations require it);
.LP
ii)
in response to a clear request by the DTE turning OFF
circuit\ 108/1 while in the data transfer state.
.bp
.sp 1P
.LP
5.1.2
\fICircuit 108/1 \(em Connect data set to line\fR
.sp 9p
.RT
.PP
The DTE shall turn circuit\ 108/1 ON:
.RT
.LP
i)
to instruct the DCE to seize the line, dial the pre\(hyrecorded number
and execute the connection procedure on the PSTN as
the caller party;
.LP
ii)
to instruct the DCE to seize the line and execute the
connection procedure on the PSTN as the called party if
circuit\ 125 is in the ON condition.
.PP
The DTE shall turn circuit\ 108/1 OFF:
.LP
i)
to instruct the DCE to clear down the connection during data transfer;
.LP
ii)
to instruct the DCE to abort the call set\(hyup procedure;
.LP
iii)
to indicate to the DCE that it is not ready to accept an incoming call.
.sp 1P
.LP
5.1.3
\fICircuit 125 \(em Calling indicator\fR
.sp 9p
.RT
.PP
The DCE shall provide circuit 125.
.RT
.sp 1P
.LP
5.2
\fIInterface procedure at the calling data station\fR
.sp 9p
.RT
.PP
The state diagram shown in Figure\ 6/V.25\|\fIbis\fR displays the allowed
transitions between the different interface states. The call set\(hyup
appears on the left side of Figure\ 6/V.25\|\fIbis\fR and proceeds as follows:
.RT
.LP
\(em
The DTE, whenever it wishes to initiate a call, checks that
circuit\ 125 is in the OFF condition, then turns ON
circuit\ 108/1. A timer (T1) is started on the transition from
state\ 1, \fIidle\fR to state\ 2.
.LP
\(em
The DCE turns ON circuit 107 when it has recognized the
successful establishment of the call, thus moving to state\ 3,
\fIdata transfer\fR .
.LP
\(em
If the first call attempt is unsuccessful, the DCE may make
further attempts according to its programming and national
regulations. During this period, the interface remains in
state\ 2.
.LP
\(em
When in state 1, the DCE will turn circuit 125 ON whenever an
incoming call occurs, and the interface moves to state\ 5,
\fIincoming call\fR . State\ 6, \fIincoming call accepted\fR , is reached
when the DTE turns ON circuit\ 108/1 to accept the call, which in
turn leads to state\ 7, \fIanswering station connecting\fR . The DCE
may abort the incoming call by turning OFF circuit\ 108/1 when in
state\ 7, and return to state\ 1.
.LP
\(em
When in state\ 2, the DCE will turn circuit\ 125 ON whenever an
incoming call has been detected prior to the DCE seizing the
line. The interface then moves to state\ 6 as incoming calls have
priority over call set\(hyup attempts. The DCE should remain
in state\ 6 for at least 100\ ms (this value is for further study)
before entering state\ 7, to allow the DTE to recognize the ON
condition on circuit\ 125.
.LP
\(em
While in state 2, the DTE can abort the call attempt by
turning OFF circuit 108/1. This may be done if timer T1
expires with circuit 107 remaining in the OFF condition.
.PP
\fINote\fR \ \(em\ Timeout T1 could range from 1 to 5\ minutes depending
on the programming of the DCE and national regulations.
.sp 1P
.LP
5.3
\fIInterface procedure at the answering data station\fR
.sp 9p
.RT
.PP
This mode provides the DTE with the facility of accepting an
incoming call on a \*Qper call\*U basis.
.PP
This operating mode is shown on the right hand side of the state
diagram shown in Figure\ 6/V.25\|\fIbis\fR and proceeds as follows:
.RT
.LP
\(em
The DCE turns ON circuit 125 whenever it detects a ringing
signal on the line and moves from state\ 1, \fIidle\fR , to state\ 5,
\fIincoming call\fR .
.LP
\(em
If the DTE does not want to accept the call, it may hold
circuit\ 108/1 in the OFF condition. After the end of the ringing
signal, the interface returns to state\ 1.
.LP
\(em
If the DTE wishes to accept the call, it turns circuit\ 108/1
ON, and moves from state\ 5, \fIincoming call\fR , to state\ 6,
\fIincoming call accepted\fR , and then to state\ 7, \fIanswering\fR \fIstation
connecting\fR .
.LP
\(em
In state\ 7, \fIanswering station connecting\fR , the DCE accepts
the call as detailed in \(sc\ 6. While in this state the DTE may
abort the connection by turning OFF circuit\ 108/1.
.LP
\(em
On completion of the connection procedure, the DCE turns ON
circuit\ 107, moving then from state\ 7, \fIanswering station\fR \fIconnecting\fR
, to state\ 3, \fIdata transfer\fR .bp
.LP
.
.LP
.rs
.sp 32P
.ad r
\fBFigure 6/V.25\|bis, (MC), p.\fR
.sp 1P
.RT
.ad b
.RT
.sp 2P
.LP
\fB6\fR \fBLine procedures\fR
.sp 1P
.RT
.sp 1P
.LP
6.1
\fILine procedure at the calling DCE\fR
.sp 9p
.RT
.LP
\(em
Whenever the DCE has received the \fIcall request\fR (see
Figure\ 5/V.25\|\fIbis\fR and Figure\ 6/V.25\|\fIbis\fR ), the DCE seizes the
line by going \fIoff hook\fR .
.LP
\(em
Dialling may proceed when dial tone has been detected, or,
where national regulations permit this, after a fixed time
delay. The value of this delay will be dependent on the national
network.
.LP
\(em
On completion of dialling, or, where possible, on recognizing
the other end going off hook, a calling tone as specified in
Recommendation\ V.25 is transmitted.
.LP
\(em
During interruptions of the calling tone, the DCE monitors
the line in order to detect call progress tones from the network
and/or the answering tone, as specified in Recommendation\ V.25
provided by the remote DCE. If no answering tone is detected
within a time\(hyout, the DCE may go on hook and may issue an
appropriate \fIcall failure\fR indication. It may slso issue \fIcall\fR
\fIfailure\fR indication on recognition of specific signalling tones
from the network.
.LP
\(em
When the answering tone has been recognized by the DCE as
detailed in Recommendation\ V.25, the DCE should issue a call
connecting indication and then turn circuit\ 106 to the OFF
condition.
.LP
\(em
All other actions including the turning ON of circuit 107 and
the completion of the connection procedure, are as detailed
in Recommendation\ V.25.
.bp
.PP
The policy for handling unsuccessful calls may be dependent on the national
networks. In this respect, a first level action by the call
originating data station, which could involve blocking, by either the DCE or
the DTE, of call attempts is not part of this Recommendation.
.PP
A second level action, which could permit the Administrations to trace
erroneous calls when a subscriber complains, should be, where required
by the Administration, implemented in the following way:
.RT
.sp 1P
.LP
6.1.1
\fICalling station identification\fR (where required by the
Administration)
.sp 9p
.RT
.PP
To enable the Administrations to have means to trace the originator of
erroneous calls, an identification message has to be transmitted on the
line by the call originating data station.
.RT
.sp 1P
.LP
6.1.1.1
\fICriteria for transmission of identification information\fR
.sp 9p
.RT
.PP
The calling station identification information should be
transmitted after the transmission of the calling tone when:
.RT
.LP
\(em
the answering tone is not received within a time interval T2
from the end of the last digit dialled, or
.LP
\(em
the answering tone is not received within a time interval T3
from detection of the remote end by DCE going \fIoff hook\fR .
.PP
The choice of time outs T2 and T3 and their durations is
dependent on national regulations.
.PP
Whenever the DCE enters the transmission of the identification
information on the line, it will defer the execution of any \fIclearing
request\fR made by the DTE which puts circuit\ 108 in the OFF\ condition
until the
transmission of this identification information is completed.
.PP
The complete identification information should be transmitted
successively 3 times or more.
.RT
.sp 1P
.LP
6.1.1.2
\fIModulation method\fR
.sp 9p
.RT
.PP
The identification signal should be asynchronously frequency
modulated with the frequencies 1300\ Hz (mark) and 2100\ Hz (space) in
such a way that it is possible to receive this signal with a modem according
to
Recommendation\ V.23.
.PP
The modulation rate should be 1200 bauds. In cases where this rate
cannot be realized, a modulation rate of 300\ bauds should be used.
.RT
.sp 1P
.LP
6.1.1.3
\fIFormat of identification information\fR
.sp 9p
.RT
.PP
The identification information should be encoded according to
International Alphabet No.\ 5 with one start bit, one stop bit and an even
parity bit according to Recommendations\ T.50 and\ V.4. The first digits
of the identification number should contain the country code of the subscriber's
telephone number.
.RT
.sp 1P
.LP
6.1.1.4
\fIImplementation\fR
.sp 9p
.RT
.PP
In addition to the contents of this Recommendation, the regulations of
the national Administrations must also be complied with. The additional
requirements may be:
.RT
.LP
\(em
the use of the CRI command with or without the identification number;
.LP
\(em
generation and storage of the identification number;
.LP
\(em
complete structure and content of the identification number (except the
first two digits);
.LP
\(em
recording and detection of the identification information.
.sp 1P
.LP
6.2
\fILine procedure at the answering DCE\fR
.sp 9p
.RT
.LP
\(em
When ringing is received on the line, the DCE turns ON
circuit\ 125 and where implemented, issues an \fIincoming call\fR
indication if circuits\ 108/2 and\ 106 are in the ON condition.
.LP
\(em
If circuit 108/1 or circuit 108/2 is OFF, the DCE waits for
circuit\ 108 to be turned ON.
.LP
\(em
If circuit 108/2 is ON, and the \fIdisregard incoming call\fR command
is not received within a period of time determined by
national regulations, the DCE may issue, where implemented, a
call connecting indication and then goes off hook.
.LP
\(em
When circuit 108/1 is ON, the DCE goes \fIoff hook\fR after a
period of time determined by national regulations.
.bp
.LP
\(em
If circuit 108 is not turned ON, then the call is not
answered.
.LP
\(em
Whenever the DCE goes \fIoff hook\fR , it turns OFF circuit\ 106
if not already OFF.
.LP
\(em
After going \fIoff hook\fR , the DCE completes the connection
procedure and turns circuit\ 107 ON, as detailed in
Recommendation\ V.25.
.sp 2P
.LP
\fB7\fR \fBManual calling and answering\fR
.sp 1P
.RT
.PP
The operational procedures for manual calling to an automatic
answering data station, and automatic calling to a manual answering data
station, are the same as detailed in Recommendation\ V.25, \(sc\(sc\ 6
and\ 7, with the exception that circuit\ 106 has to be turned OFF before
turning ON circuit\ 107, in the mode \fIaddressed call and/or answer authorized
by the DTE\fR .
.PP
Where the answering data station is expected to have a manual
answering mode, this may be indicated to the calling DCE. The method for
doing this is for further study.
.RT
.ce 1000
ANNEX\ A
.ce 0
.ce 1000
(to Recommendation V.25\|\fIbis\fR )
.sp 9p
.RT
.ce 0
.ce 1000
\fBTest facilities\fR
.sp 1P
.RT
.ce 0
.LP
\fIGuidance on maintenance facilities\fR
.sp 1P
.RT
.PP
This annex contains information on test facilities thought to be
desirable in relation to implementations of Recommendation\ V.25\|\fIbis\fR
automatic calling procedures.
.PP
The adoption of such procedures and especially the provision of
centralized maintenance facilities by Administrations may not be assumed.
.PP
In order to enable a fault to be located in either the DTE or the DCE,
the DTE should not be involved in the test. The test may be initiated,
e.g.\ by pressing a button on the DCE, whereas indication of the test result
may be presented, e.g.\ by means of a visual indicator.
.PP
The actual test consists of two stages: a DCE self\(hytest and a test in
cooperation with a maintenance centre. In which order these two stages
are
activated is not specified in this Recommendation. The test of the modem
part of the DCE will not be part of this Recommendation, but should be
performed
separately according to Recommendation\ V.54.
.RT
.sp 1P
.LP
A.1
\fIDCE self\(hytest stage\fR
.sp 9p
.RT
.PP
In this stage, the DCE will test as many functions and hardware as reasonably
possible.
.PP
The test should comprise a loop at the DTE\(hyDCE interface similar to
Recommendation\ V.54 loop\ 2 including all circuits normally exercised
during the call set\(hyup and clear phase. Further parts of the test depend
on the DCE
implementation, e.g.\ in case of a microprocessor\(hybased design a functional
test of the CPU, RAM and ROM would be appropriate.
.RT
.sp 1P
.LP
A.2
\fIDCE test with maintenance centre\fR
.sp 9p
.RT
.PP
In this stage, the procedure is as follows:
.RT
.PP
A.2.1
The user sets up manually a call with the maintenance
centre\ (MC).
.PP
A.2.2
On answering the call, the MC will send an answering tone of
appropriate length to ensure detection by the DCE.
.PP
A.2.3
As soon as the answering tone is detected, the DCE should be
connected with the line.
.PP
A.2.4
After detecting the end of the answering tone, the DCE starts
sending the dialling digits\ 1, 2, 3, 4, 5, 6, 7, 8, 9,\ 0 in accordance
with the regulations of the Administration involved.
.PP
\fINote\fR \ \(em\ They shall have the same spacing as during the automatic
call set\(hyup.
.bp
.PP
A.2.5
In case not all numbers are detected faultlessly, the MC will
send a 2100\ Hz tone for 0.4\ \(+-\ 0.1\ s indicating a negative test result
and
disconnect from the line.
.PP
A.2.6
On detecting the 2100 Hz tone, the DCE will end the test
procedure and indicate a negative test result.
.PP
A.2.7
If all numbers are received correctly, the MC will send a 1300 Hz tone
for 0.4\ \(+-\ 0.1\ s and start sending towards the DCE signalling tone
to be
defined by the Administration involved.
.PP
A.2.8
At the end of this sequence, a 2100\ Hz tone will be sent for
0.4\ \(+-\ 0.1\ s and the MC will disconnect.
.PP
A.2.9
The DCE receiving the 2100 Hz tone will give a positive or
negative indication depending on the test result and end the procedure.
.PP
\fINote\fR \ \(em\ For pulse dialling, the open contact shall be coded
by a 2100 Hz tone and the closed contact by no signal at all.
\v'1P'
.ce 1000
ANNEX\ B
.ce 0
.ce 1000
(to Recommendation V.25\|\fIbis\fR )
.sp 9p
.RT
.ce 0
.ce 1000
\fBSDL Description of the addressed call \(em 108/2 Response Mode\fR
.sp 1P
.RT
.ce 0
.PP
This Annex provides an SDL description, as per the Z.100 serie
Recommendations, of the message exchanges specified in the present
Recommendation for the addressed call \(em 108/2 response mode. This part
of the automatic calling procedure is specified in \(sc\ 4 and Figure\
5/V.25\|\fIbis\fR , which have to be taken as the master in case of any
ambiguity.
.sp 1P
.RT
.PP
The process described hereafter in Figure\ B\(hy2/V.25\|\fIbis\fR the
key of which is Figure\ B\(hy1/V.25\|\fIbis\fR , is invoked when the DCE
enters state\ 3 \*QDTE\(hyDCE dialogue\*U, or state\ 10 \*QIncoming call
accepting\*U. It is terminated
when the DCE enters state\ 5 \*QAnswer tone detected\*U, or state\ 11 \*QIncoming
call accepted\*U.
.LP
.rs
.sp 20P
.ad r
\fBFigure B\(hy1/V.25\|bis, (N), p.\fR
.sp 1P
.RT
.ad b
.RT
.LP
.bp
.LP
.rs
.sp 47P
.ad r
\fBFigure B\(hy2/V.25\|bis, (N), p.\fR
.sp 1P
.RT
.ad b
.RT
.LP
.bp
.ce 1000
APPENDIX\ I
.ce 0
.ce 1000
(to Recommendation V.25\|\fIbis\fR )
.sp 9p
.RT
.ce 0
.ce 1000
\fBGeneral description of the\fR
\fBV.25\|bis command/indication
syntax\fR
.sp 1P
.RT
.ce 0
.PP
The following table is a general presentation of the V.25\|\fIbis\fR message
syntax which is offered for guidance in the development of any
application where harmonization with Recommendation\ V.25\|\fIbis\fR is sought
(Detailed description of the V.25\|\fIbis\fR syntax is presented in
Table\ 6/V.25\|\fIbis\fR ).
.sp 1P
.RT
.ce
\fBH.T. [T9.25]\fR
.ce
TABLE\ I\(hy1/V.25\|\fIbis\fR
.ce
\fBGeneral description of the V.25\|bis message
.ce
syntax\fR
.ps 9
.vs 11
.nr VS 11
.nr PS 9
.TS
center box;
lw(228p) .
description language:
.T&
lw(228p) .
a | b denotes the set (a, b)
.T&
lw(228p) .
a b denotes the set (ab)
.T&
lw(228p) .
T{
a*
denotes the set (e, a, aa, aaa, .\|.\|.\|)
T}
.T&
lw(228p) .
(e = empty)
.T&
lw(228p) .
description:
.T&
lw(228p) .
T{
message
=
(opcode) | (opcode parameter
\(ullist)
T}
.T&
lw(228p) .
opcode = letter letter letter
.T&
lw(228p) .
T{
parameter list
=
parameter (delimiter
parameter)*
T}
.T&
lw(228p) .
T{
parameter
=
(letter | digit | special | presentation)
(letter | digit | special | presentation)*
T}
.T&
lw(228p) .
T{
letter
=
`A` | `B` | `C` | `D` | `E` | `F` | `G` |
`H` | `I` | `J` | `K` | `L` | `M` | `N` |
`O` | `P` | `Q` | `R` | `S` | `T` | `U` |
`V` | `W` | `X` | `Y` | `Z`
T}
.T&
lw(228p) .
T{
digit
=
`0` | `1` | `2` | `3` | `4` | `5` | `6` |
`7` | `8` | `9`
T}
.T&
lw(228p) .
T{
special
=
`&` | `:` | `>` | `<` | `=` | `P` | `T`
T}
.T&
lw(228p) .
presentation = `\ ` | `.`
.T&
lw(228p) .
T{
delimiter
=
`;`
T}
.TE
.LP
\fINote\fR
\ \(em\ The syntax of the parameters depends on the message and should be
specified in the message description.
.nr PS 9
.RT
.ad r
\fBTableau I\(hy1/V.25\|bis [T9.25], p.\fR
.sp 1P
.RT
.ad b
.RT
.LP
.rs
.sp 20P
.ad r
BLANC
.ad b
.RT
.sp 2P
.LP
\fBMONTAGE:\ \ \fR Rec. V.26 sur le reste de cette page
.sp 1P
.RT
.LP
.bp