that Recommendation X.29 defines procedures for a packet mode DTE to control
the PAD and for interworking between\ PADs;
.PP
(c)
that Recommendation X.3 defines the Packet
Assembly/Disassembly (PAD) facility in a public data network;
.PP
(d)
that the logical control links for packet\(hyswitched data transmission
services are defined in Recommendation\ X.92;
.PP
(e)
the need for defining an international Recommendation
for the exchange of control information between a start\(hystop mode DTE and
a\ PAD;
.PP
(f
)
that DTEs operating in the start\(hystop mode will
send and receive network call control information and user information
in the form of characters according to Recommendation\ T.50 or the \fIbreak\fR
signal;
.PP
(g)
that the necessary elements for an interface
Recommendation should be defined independently as:
.LP
1)
procedures for the establishment of a national access
information path between a start\(hystop mode DTE and a\ PAD,
.LP
2)
procedures for character interchange and service
initialization between a start\(hystop mode DTE and a\ PAD,
.LP
3)
procedures for the exchange of control information between a start\(hystop
mode DTE and a\ PAD,
.LP
4)
procedures for the exchange of user data between a
start\(hystop mode DTE and a\ PAD.
.sp 1P
.LP
\fIunanimously declares\fR
.sp 9p
.RT
.PP
that start\(hystop mode DTE accessing the PAD should operate in
accordance with this Recommendation.
.LP
\fB1\fR \fBProcedures for the establishment of a \fR \fBnational access
information path between a start\(hystop mode DTE and a PAD\fR
.sp 1P
.RT
.sp 2P
.LP
1.1
\fIAccess via a public switched telephone network or leased lines\fR
\fIwith V\(hySeries interfaces\fR
.sp 1P
.RT
.sp 1P
.LP
1.1.1
\fIDTE/DCE interface\fR
.sp 9p
.RT
.PP
The access information path will be provided by the use of modems standardized
for use in the public switched telephone network or leased line
operating:
.RT
.LP
i)
at rates up to 300 bit/s in accordance with
Recommendation\ V.21; or
.LP
ii)
at the rate of 1200 bit/s in accordance with
Recommendation\ V.22 alternative\ B, mode ii) or V.22\|\fIbis\fR mode\
4, and at the rates of 2400\ bit/s in accordance with
Recommendation\ V.22\|\fIbis\fR mode\ 2, on the public switched
telephone network or 2\(hywire leased circuit, or at the rates up
to 1200\ bit/s in accordance with Recommendation\ V.23 without
backward channel on 4\(hywire leased circuits; or
.LP
iii)
at the rate of 75/1200 bit/s (for the signal
received by the DTE and 75\ bit/s for the signal sent by the DTE
on the backward channel) in accordance with
Recommendation\ V.23.
.PP
The particular
interchange circuits
provided, and their
operation, shall be in accordance with the relevant modem Recommendations,
and clamping of circuit\ 104 shall be implemented in accordance with
Recommendation\ V.24, \(sc\ 4.3.
.bp
.PP
At rates of up to 300 bit/s or at 1200 bit/s or 2400 bit/s:
.RT
.LP
a)
on the telephone network, the modem shall be set up for
channel operation in accordance with Recommendation\ V.21, or
with Recommendation\ V.22, or with Recommendation\ V.22\|\fIbis\fR ; or
.LP
b)
on leased lines (2\(hywire), the channel operation will be
determined by the same rule, the modem at the DTE side being
considered as the one making the telephone call.
.PP
At the rate of 75/1200 bit/s: the modem shall be set up for
channel operation in accordance with Recommendation\ V.23.
.PP
\fINote\ 1\fR \ \(em\ The interface requirements for other data signalling
rates are for further study.
.PP
\fINote\ 2\fR \ \(em\ In some networks, references to modem characteristics do
not apply (e.g. for leased lines).
.RT
.sp 1P
.LP
1.1.2
\fIElectrical characteristics\fR
.sp 9p
.RT
.PP
The electrical characteristics of the DTE/DCE interface shall be in accordance
with Recommendation\ V.28.
.RT
.sp 2P
.LP
1.1.3
\fIProcedure for setting up and disconnecting the\fR
\fIaccess information path\fR
.sp 1P
.RT
.sp 1P
.LP
1.1.3.1
\fISetting up the access information path by the DTE\fR
.sp 9p
.RT
.PP
The access information path shall be established in accordance with Recommendation\
V.25 for a
manual data station
calling an
automatic answering station
.
.PP
The mechanism for echo suppressor disablement may not be implemented in
some national networks where the access information path does not include
echo suppressors.
.PP
Subsequent to the completion of the above, both the DTE and DCE shall transmit
binary\ 1 on circuits\ 103 and\ 104.
.RT
.LP
.sp 1P
.LP
1.1.3.2
\fIDisconnecting the access information path by the DTE\fR
.sp 9p
.RT
.PP
The access information path shall be disconnected by:
.RT
.LP
i)
reversion of the data circuit to the voice mode, or
.LP
ii)
the DTE turning circuit 108/1 or 108/2 OFF for a period
greater than\ Z. The value of\ Z is for further study.
.sp 1P
.LP
1.1.3.3
\fISetting up the access information path by the PAD\fR
.sp 9p
.RT
.PP
The procedure for the PAD to establish an access information path shall
be in accordance with Recommendation\ V.25 as far as it is perceived by
the DTE.
.RT
.sp 1P
.LP
1.1.3.4
\fIDisconnecting the access information path by the PAD\fR
.sp 9p
.RT
.PP
\fR \fI\fR
Disconnection by the PAD will be indicated by the DCE turning
circuits\ 106 and 109\ OFF, while circuit\ 108 is\ ON.
.PP
\fINote\fR \ \(em\ Access information path clear indication to the DTE is not
signalled by circuit 107\ OFF. Not all DTEs allow circuit\ 107 to be turned
OFF if circuit\ 108 has not been turned OFF previously.
.RT
.LP
1.2
\fIAccess via a public switched data network or via leased lines\fR \fIwith
X\(hySeries interfaces\fR
.sp 1P
.RT
.LP
.sp 2P
.LP
1.2.1
\fIDTE/DCE interface designed for start\(hystop transmission\fR
\fIservices on public data networks\fR \fI(Recommendation\ X.20)\fR
.sp 1P
.RT
.sp 1P
.LP
1.2.1.1
\fIPhysical characteristics\fR
.sp 9p
.RT
.PP
The physical characteristics of the DTE/DCE interface are defined in \(sc\
2 of Recommendation\ X.20.
.bp
.RT
.sp 1P
.LP
1.2.1.2
\fIProcedures for setting up and disconnecting the access\fR
\fIinformation path (call control)\fR
.sp 9p
.RT
.PP
The procedures and formats for call control of the public
circuit\(hyswitched data network are described in \(sc\(sc\ 3 and\ 4 of
Recommendation\ X.20. The procedures for setting up a virtual call in a
packet\(hyswitched network are those given in \(sc\(sc\ 2, 3 and\ 4 of this
Recommendation. The use of Recommendation\ X.20 procedures to establish a
virtual call via a PAD is for further study.
.RT
.sp 1P
.LP
1.2.2
\fIDTE/DCE interface designed for operation on telephone type\fR \fInetworks\fR
\fI(Recommendation\ X.20\|bis)\fR
.sp 9p
.RT
.PP
In the case of DTEs with interfaces designed for operation on
telephone type networks (V\(hySeries interfaces), the access information
path will be established by the use of DCEs standardized for start\(hystop
transmission
services on public data networks according to Recommendation\ X.20\|\fIbis\fR .
.RT
.LP
.sp 1P
.LP
1.2.2.1
\fICharacteristics of interchange circuits\fR
.sp 9p
.RT
.PP
The characteristics of the interchange circuits are described in
\(sc\ 2 of Recommendation\ X.20\|\fIbis\fR .
.RT
.sp 1P
.LP
1.2.2.2
\fIOperational requirements\fR
.sp 9p
.RT
.PP
The requirements for the operation of the interchange circuits 106, 107,
108, 109 and\ 125 are described in \(sc\ 3 of Recommendation\ X.20\|\fIbis\fR
.
.RT
.sp 1P
.LP
1.2.2.3
\fIOperational requirements for disconnecting the access\fR
\fIinformation path by the DTE\fR
.sp 9p
.RT
.PP
The access information path shall be disconnected either
.RT
.LP
\fImanually\fR by depressing the clearing key of the DCE, or
.LP
\fIautomatically\fR by the DTE turning OFF circuit 108/1 or 108/2 for a
period longer than 210\ ms.
.sp 1P
.LP
1.2.2.4
\fIIndication of disconnection by the PAD\fR
.sp 9p
.RT
.PP
Disconnection by the PAD, i.e. DCE clearing, will be indicated by the DCE
by turning OFF circuits\ 106 and\ 109. The DTE should then perform clear
confirmation by turning OFF circuit\ 108.
.RT
.LP
.sp 1P
.LP
1.2.2.5
\fISetting up the access information path by the PAD\fR
.sp 9p
.RT
.PP
The procedure for the PAD to establish an access information path is for
further study.
.RT
.sp 1P
.LP
1.2.2.6
\fIOperational constraints for maintaining the access\fR
\fIinformation path during information transfer\fR
.sp 9p
.RT
.PP
The transmission of a
\fIbreak\fR signal
longer than 200\ ms may cause clearing in a public switched data network.
Therefore, the transmission of a \fIbreak\fR signal in either direction
should either be avoided or the timer of the circuit generating a \fIbreak\fR
signal should be adjusted to generate a
signal length considerably shorter than 200\ ms (see also \(sc\ 3.1.2).
.RT
.sp 2P
.LP
\fB2\fR \fBProcedures for \fR \fBcharacter interchange and service\fR
\fBinitialization between a start\(hystop mode DTE and a PAD\fR
.sp 1P
.RT
.sp 1P
.LP
2.1
\fIFormat of characters used in the exchange of control information\fR
\fIbetween start\(hystop mode DTE and a PAD\fR \v'3p'
.sp 9p
.RT
.LP
.PP
2.1.1
The start\(hystop mode DTE shall generate and be capable of
receiving characters in accordance with International Alphabet No.\ 5 as
described in Recommendation\ T.50. The general structure of characters shall
be in accordance with Recommendation\ X.4 except that the transmitted stop
bits shall be as specified in \(sc\ 2.1.2. The character
format specified below applies to the procedures described in \(sc\(sc\
2 and\ 3.
.bp
.PP
2.1.2
The PAD will transmit and expect to receive 8\(hybit characters.
.PP
When the value of parameter 21 is set to 0, whenever the PAD has to interpret
a received character for a specific action different from or
additional to the transfer of this data character to the remote DTE, it will
only inspect the first seven bits and will not take account of the eighth
bit (the last bit preceding the stop element).
.PP
When the value of parameter 21 is set to 1, the PAD will treat the
8th\ bit of the characters received from the start\(hystop DTE as a parity
bit and check this bit against the type of parity [even, odd, space (\*Q0\*U)
or mark
(\*Q1\*U)] used between the PAD and the start\(hystop mode DTE.
.PP
When the value of parameter 21 is set to 2, the PAD will replace the 8th\
bit of the characters to be sent to the start\(hystop mode DTE with the
bit
that corresponds to the type of parity used between the PAD and the start\(hystop
mode DTE.
.PP
When the value of parameter 21 is set to 3, the PAD will both check
the parity bit for characters received from the start\(hystop mode DTE and
generate the parity bit for characters to be sent to the start\(hystop
mode DTE, as described for values 1 and 2.
.PP
Whenever the PAD generates characters (e.g.\ \fIPAD service\fR signals),
they will be transmitted by the PAD with even parity if parameter 21 is
set to 0, and with the type of parity (even, odd, space or mark) used between
the PAD and the start\(hystop mode DTE if parameter 21 is set to 1, 2 or
3 or if the
parity is determined by alternate means.
.PP
When the value of parameter 21 is set to 1 or 3, if the PAD detects a parity
error in the characters received from the start\(hystop mode DTE, the PAD
will:
.RT
.LP
\(em
if parameter 2 is set to 0 (no echo), and parameter\ 6 is set to\ 0 (no
service signals), reset the virtual circuit;
.LP
\(em
if parameter 2 is set to 1 (echo) and parameter\ 6 is set to\ 0 (no service
signals), discard and not echo the character in error and transmit the
character 0/7 (BEL) to the start\(hystop mode DTE;
.LP
\(em
if parameter 2 is set to 1 (echo) and parameter\ 6 is set to\ 1 or greater
(service signals) discard and not echo the character in error and
transmit the character 0/7 (BEL) to the start\(hystop mode DTE; the PAD
may also transmit the parity error \fIPAD service\fR signal. The action
of the PAD when
parameter\ 2 is set to\ 0 (no echo) and parameter\ 6 is set to\ 1 or greater
(service signal) is for further study.
.PP
The PAD will accept characters which have a single stop element
and will transmit characters with at least two stop elements if the start\(hystop
mode DTE is operating at 110\ bit/s. If the PAD is operating at any other
speed, the PAD will transmit and accept
characters with a single stop element.
.sp 1P
.LP
2.2
\fIProcedures for initialization\fR
.sp 9p
.RT
.PP
The references to states in the following procedures correspond to the
state diagrams, see Figures\ 1/X.28, 2/X.28 and\ 3/X.28.
.RT
.sp 1P
.LP
2.2.1
\fIActive link (state 1)\fR
.sp 9p
.RT
.PP
After the access information path has been established, the
start\(hystop mode DTE and the PAD exchange binary\ 1 across the start\(hystop
mode
DTE/DCE interface and the interface is in the \fIactive link\fR state.
.RT
.LP
.sp 1P
.LP
2.2.2
\fIService request (state 2)\fR
.sp 9p
.RT
.PP
If the interface is in the \fIactive link\fR state, the DTE shall
transmit a sequence of characters to indicate \fIservice request\fR and to
initialize the PAD. The \fIservice request\fR signal enables the PAD to
detect the data rate, the code and, optionally, the parity
used by the DTE and to select the \fIinitial profile\fR of the PAD.
The parameters of CCITT \fIstandard profiles\fR are summarized in Table\
1/X.28.
.PP
The format of the \fIservice request\fR signal to be transmitted by the
DTE is given in \(sc\ 3.5.16 below.
.PP
Some networks may allow state 2 to be bypassed. In case the start\(hystop
mode DTE is connected to the PAD by a leased line or if the access information
path is set up by the PAD, the PAD either knows the speed, code, and initial
profile, required for the start\(hystop mode DTE or uses a default value. The
default value is network dependent. In case the access information path is
set up by the start\(hystop mode DTE, the access method chosen may be uniquely
dedicated to a single combination of speed, code and initial profile.
.bp
.RT
.LP
.rs
.sp 47P
.ad r
\fBFigure\ 1a/X.28, p. 1\fR
.sp 1P
.RT
.ad b
.RT
.LP
.bp
.LP
.rs
.sp 47P
.ad r
\fBFigure\ 1b/X.28, p. 2\fR
.sp 1P
.RT
.ad b
.RT
.LP
.bp
.LP
.rs
.sp 47P
.ad r
\fBFigure\ 2a/X.28, p. 3\fR
.sp 1P
.RT
.ad b
.RT
.LP
.bp
.LP
.rs
.sp 47P
.ad r
\fBFigure\ 2b/X.28, p. 4\fR
.sp 1P
.RT
.ad b
.RT
.LP
.bp
.LP
.rs
.sp 27P
.ad r
\fBFigure\ 3/X.28, p. 5\fR
.sp 1P
.RT
.ad b
.RT
.sp 1P
.LP
2.2.3
\fIDTE waiting (state 3A)\fR
.sp 9p
.RT
.PP
Following the transmission of the \fIservice request\fR signal the DTE
shall transmit binary\ 1 and the interface will be in the \fIDTE waiting\fR
state.
.PP
When the value of parameter 6 is set to 0, the interface will directly
enter the \fIPAD waiting\fR state following receipt of a valid \fIservice
request\fR signal.
.RT
.sp 1P
.LP
2.2.4
\fIService ready (state 4)\fR
.sp 9p
.RT
.PP
When parameter 6 is not set to 0 the interface will enter the
\fIservice ready\fR state when the PAD transmits a \fIPAD identification
PAD\fR
\fIservice\fR signal after receiving a \fIservice request\fR signal. If
the \fIPAD\fR
\fIidentification PAD service\fR signal is not received within V\ seconds,
the DTE should retransmit the \fIservice request\fR signal. Following transmission
of the \fIservice request\fR signal W\ times the user should report a fault
to the
appropriate point. The values of\ V and\ W are for further study.
.PP
The standard format of the \fIPAD identification PAD service\fR signal
is given in \(sc\ 3.5.18 below.
.RT
.sp 1P
.LP
2.2.5
\fIFault condition\fR
.sp 9p
.RT
.PP
If a valid \fIservice request\fR signal is not received by the PAD
within Y\ seconds after the transmission of binary\ 1, it will perform PAD
clearing by disconnecting the access information path.
.PP
The value of Y is for further study.
.PP
\fINote\fR \ \(em\ Some networks may allow states 2 to 4 to be bypassed. In
this case the condition described under \(sc\ 2.2.4 does not apply.
.bp
.RT
.ce
\fBH.T. [1T1.28]\fR
.ce
TABLE\ 1/X.28
.ce
\fBPAD parameter settings\fR
.ce
The parameter references and values relate to Recommendation X.3
.ce
(see Note 1)
.ps 9
.vs 11
.nr VS 11
.nr PS 9
.TS
center box;
cw(36p) | cw(54p) | cw(72p) sw(66p) , ^ | ^ | c | c.
T{
Parameter reference number
(see Note 3)
T} Parameter description T{
Parameter setting for CCITT standard profile
(see Note 2)
T}
T{
Transparent standard profile
(see Note 4)
T} T{
Simple standard profile
(see Note 4)
T}
_
.T&
cw(36p) | lw(54p) | lw(72p) | lw(66p) .
\ 1 PAD recall using a character T{
Set to \fInot possible\fR
(value 0)
T} T{
Set to \fIpossible\fR
(value 1)
T}
_
.T&
cw(36p) | lw(54p) | lw(72p) | lw(66p) .
\ 2 Echo T{
Set to \fIno echo\fR
(value 0)
T} T{
Set to \fIecho\fR
(value 1)
T}
_
.T&
cw(36p) | lw(54p) | lw(72p) | lw(66p) .
\ 3 T{
Selection of \fIdata forwarding\fR
signal
T} T{
Set to \fIno data forwarding signal\fR
(value 0)
T} T{
Set to \fIall characters in columns 0 and 1 and character 7/15 (DEL)\fR
of International Alphabet No.\ 5 (value 126)
T}
_
.T&
cw(36p) | lw(54p) | lw(72p) | lw(66p) .
\ 4 T{
Selection of \fIidle timer delay\fR
T} T{
Set to \fIone second\fR
(value 20)
T} T{
Set to \fIno time out\fR
(value 0)
T}
_
.T&
cw(36p) | lw(54p) | lw(72p) | lw(66p) .
\ 5 Ancillary device T{
Set to \fIno use of X\(hyON and X\(hyOFF\fR
(value 0)
T} T{
Set to \fIuse of X\(hyON and X\(hyOFF\fR
(value 1)
T}
_
.T&
cw(36p) | lw(54p) | lw(72p) | lw(66p) .
\ 6 T{
Control of \fIPAD service\fR
signals and \fIPAD command\fR
signals
T} T{
Set to \fIno service signals sent to the\fR
start\(hystop mode DTE
(value 0)
T} T{
Set to \fIservice signals are sent\fR
(value\ 1)
T}
_
.T&
cw(36p) | lw(54p) | lw(72p) | lw(66p) .
\ 7 T{
Selection of operation of PAD on receipt of \fIbreak\fR
signal from the
start\(hystop mode DTE
T} T{
Set to \fIreset\fR
(value 2)
T} T{
Set to \fIreset\fR
(value 2)
T}
_
.T&
cw(36p) | lw(54p) | lw(72p) | lw(66p) .
\ 8 Discard output T{
Set to \fInormal data delivery\fR
(value\ 0)
T} T{
Set to \fInormal data delivery\fR
(value\ 0)
T}
_
.T&
cw(36p) | lw(54p) | lw(72p) | lw(66p) .
\ 9 T{
Padding after carriage return (CR)
T} T{
Set to \fIno padding after CR\fR
(value\ 0)
(see Note 5)
T} T{
Set to \fIno padding after CR\fR
(value\ 0)
(see Note 5)
T}
_
.T&
cw(36p) | lw(54p) | lw(72p) | lw(66p) .
10 Line folding T{
Set to \fIno line folding\fR
(value 0)
T} T{
Set to \fIno line folding\fR
(value 0)
T}
_
.T&
cw(36p) | lw(54p) | lw(72p) | lw(66p) .
11 (read only) T{
Binary speed of start\(hystop mode DTE
T} Indicate speed of DTE Indicate speed of DTE
_
.T&
cw(36p) | lw(54p) | lw(72p) | lw(66p) .
12 T{
Flow control of the PAD by the start\(hystop mode DTE
T} T{
Set to \fIno use of X\(hyON and X\(hyOFF\fR
(value 0)
T} T{
Set to \fIuse of X\(hyON and X\(hyOFF\fR
(value 1)
T}
_
.T&
cw(36p) | lw(54p) | lw(72p) | lw(66p) .
13 (see Note 6) T{
Linefeed insertion after carriage return
T} T{
Set to \fIno linefeed insertion\fR
(value 0)
T} T{
Set to \fIno linefeed insertion\fR
(value 0)
T}
_
.T&
cw(36p) | lw(54p) | lw(72p) | lw(66p) .
14 (see Note 6) Linefeed padding T{
Set to \fIno linefeed after LF\fR
(value\ 0)
T} T{
Set to \fIno linefeed after LF\fR
(value\ 0)
T}
_
.T&
cw(36p) | lw(54p) | lw(72p) | lw(66p) .
15 (see Notes 6 and 7) Editing T{
Set to no editing in \fIdata transfer\fR
state (value 0)
T} T{
Set to no editing in \fIdata transfer\fR
state
(value 0)
T}
_
.TE
.nr PS 9
.RT
.ad r
\fBTableau 1/X.28 [1T1.28], p. 6\fR
.sp 1P
.RT
.ad b
.RT
.LP
.bp
.ce
\fBH.T. [2T1.28]\fR
.ce
TABLE\ 1/X.28\ \fI(cont.)\fR
.ps 9
.vs 11
.nr VS 11
.nr PS 9
.TS
center box;
cw(36p) | cw(54p) | cw(72p) sw(66p) , ^ | ^ | c | c.
T{
Parameter reference number
(see Note 3)
T} Parameter description T{
Parameter setting for CCITT standard profile
(see Note 2)
T}
T{
Transparent standard profile
(see Note 4)
T} T{
Simple standard profile
(see Note 4)
T}
_
.T&
cw(36p) | lw(54p) | lw(72p) | lw(66p) .
16 (see Note 6) Character delete T{
Set to character 7/15 (DEL)
(value\ 127)
T} T{
Set to character 7/15 (DEL)
(value\ 127)
T}
_
.T&
cw(36p) | lw(54p) | lw(72p) | lw(66p) .
17 (see Note 6) Line delete T{
Set to character 1/8 (CAN)
(value\ 24)
T} T{
Set to character 1/8 (CAN)
(value\ 24)
T}
_
.T&
cw(36p) | lw(54p) | lw(72p) | lw(66p) .
18 (see Note 6) Line display T{
Set to character 1/2 (DC2)
(value\ 18)
T} T{
Set to character 1/2 (DC2)
(value\ 18)
T}
_
.T&
cw(36p) | lw(54p) | lw(72p) | lw(66p) .
19 (see Notes 6 and 7) T{
Editing \fIPAD service\fR
signals
T} T{
Set to editing \fIPAD service\fR
signals for printing terminals
(value 1)
T} T{
Set to editing \fIPAD service\fR
signals for printing terminals
(value 1)
T}
_
.T&
cw(36p) | lw(54p) | lw(72p) | lw(66p) .
20 (see Notes 6 and 8) Echo mask T{
Set to echo all characters (value 0)
T} T{
Set to echo all characters (value 0)
T}
_
.T&
cw(36p) | lw(54p) | lw(72p) | lw(66p) .
21 (see Notes 6 and 9) Parity Treatment T{
Set to no parity detection or generation (value 0)
T} T{
Set to no parity detection or generation
(value 0)
T}
_
.T&
cw(36p) | lw(54p) | lw(72p) | lw(66p) .
22 (see Note 6) Page Wait T{
Set to page wait disabled (value 0)
T} T{
Set to page wait disabled (value 0)
\fINote\ 1\fR
\ \(em\ All parameters standardized by CCITT are listed in Table\ 1/X.3
including those which provide additional user facilities listed in
Recommendation\ X.2.
.parag
\fINote\ 2\fR
\ \(em\ In the case of a leased circuit access, the appropriate profile
parameter values are specified at subscription time. In the case of access from public telephone networks or circuit switched public data networks, the
definition of other CCITT standard profiles is for further study.
.parag
\fINote\ 3\fR
\ \(em\ Parameter reference 0 is not used to define a PAD parameter.
Specific use of the decimal value\ 0 in PAD messages to permit the existence of parameters not defined by CCITT is provided in Recommendation\ X.29. A similar use of this value in Recommendation\ X.28 is for further study.
.parag
\fINote\ 4\fR
\ \(em\ The procedures for selecting \fItransparent standard\fR
profile or
\fIsimple standard\fR
profile by the start\(hystop mode DTE are currently defined by using the \fIservice request\fR
signal or \fIstandard profile selection PAD command\fR
signal.
.parag
\fINote\ 5\fR
\ \(em\ There will be no padding except that \fIPAD service\fR
signals will
obtain a number of padding characters according to the data transmission rate of the start\(hystop mode DTE.
.parag
\fINote\ 6\fR
\ \(em\ Parameter which provides additional user facilities available in
some countries for international and national services (see
Recommendation\ X.3). The implementation of this parameter in a PAD is a matter for national determination. When implemented, the values appropriate when a
\fIstandard\fR
profile is selected are given in this table.
.parag
\fINote\ 7\fR
\ \(em\ Editing functions apply during the \fIPAD command\fR
state irrespective of the value of parameter\ 15. The default values of selectable values of
parameters\ 16, 17, 18 and\ 19 apply for the functions.
.parag
\fINote\ 8\fR
\ \(em\ This parameter does not apply if parameter\ 2 is set to\ 0.
.parag
\fINote\ 9\fR
\ \(em\ Characters generated by the PAD itself (e.g. \fIPAD service\fR
signals) have even parity when parameter\ 21 is set to zero unless the
parity is set by alternate means.
.parag
T}
_
.TE
.nr PS 9
.RT
.ad r
\fBTableau 1/X.28 [2T1.28], p. 7\fR
.sp 1P
.RT
.ad b
.RT
.LP
.bp
.LP
\fB3\fR \fBProcedures for the exchange of control information between\fR
\fBa start\(hystop mode DTE and a PAD\fR
.sp 1P
.RT
.sp 2P
.LP
3.1
\fIGeneral\fR
.sp 1P
.RT
.sp 1P
.LP
3.1.1
\fIPAD command signals\fR \fIand \fR \fIPAD service signals\fR
.sp 9p
.RT
.PP
The operation of the PAD depends on the current values of internal PAD
variables which are known as PAD parameters. Initially PAD parameter values
depend on the initial standard profile applicable at the time of sending
a
service request signal or by previous arrangement with the Administration.
The parameter values for the transparent and simple standard profile
are given in Table\ 1/X.28.
.PP
\fIPAD command\fR \| signals (direction DTE to PAD) are provided
for:
.RT
.LP
a)
the establishment and clearing of a virtual call (see \(sc\ 3.2 below);
.LP
b)
the selection of a set of preset values of PAD parameters
known as a \fIstandard\fR profile, either CCITT or network defined
(see \(sc\ 3.3.1 below);
.LP
c)
the selection of individual PAD parameter values (see
\(sc\ 3.3.2 below);
.LP
d)
requesting the current values of PAD parameters to be
transmitted by the PAD to the DTE (see \(sc\ 3.4 below);
.LP
e)
sending of an interrupt;
.LP
f
)
requesting the status of the circuit (see \(sc 3.7
below);
.LP
g)
resetting the virtual call.
.PP
\fIPAD service\fR signals (direction PAD to DTE) are provided
to:
.LP
a)
transmit \fIcall progress\fR signals to the calling DTE;
.LP
b)
acknowledge \fIPAD command\fR signals;
.LP
c)
transmit information regarding the operation of the PAD to the start\(hystop
mode DTE.
.LP
.PP
The formats of \fIPAD command\fR \| signals and the standard formats of
\fIPAD service\fR \| signals are given in \(sc\ 3.5 below. Some networks
may also support the extended dialogue mode for \fIPAD command\fR signals
and \fIPAD service\fR signals as defined in \(sc\ 3.5 and \(sc\ 5 below.
Some networks may also support additional
\fIPAD command\fR signals and \fIPAD service\fR signals as defined in \(sc\
5 below.
.PP
The information content of \fIPAD command\fR \| signals and \fIPAD service\fR
\| signals are summarized in Annex\ A.
.RT
.sp 1P
.LP
3.1.2
\fIBreak signal\fR
.sp 9p
.RT
.PP
The \fIbreak\fR \| signal is provided to allow the start\(hystop mode DTE
to signal to the PAD without loss of character transparency. The \fIbreak\fR
signal
can also be transmitted by the PAD to the start\(hystop mode DTE.
.PP
The \fIbreak\fR \| signal is defined as the transmission of binary 0 for
more than 135\ ms. The maximum permitted duration shall depend upon the
type of access information path used (see, for example, \(sc\ 1.2.2.6 above).
.PP
A \fIbreak\fR \| signal shall be separated from any following start\(hystop
character or other \fIbreak\fR \| signal by the transmission of binary\
1 for more
than 100\ ms.
.RT
.sp 1P
.LP
3.1.3
\fIPrompt PAD service signal\fR
.sp 9p
.RT
.PP
If parameter 6 is set to 5 on entering the \fIPAD waiting\fR \| state or
\fIwaiting for command\fR \| state, the PAD will indicate its readiness
to receive a \fIPAD command\fR signal by transmitting the \fIprompt PAD
service\fR signal.
.PP
If the value of parameter 6 is set to 0 or 1, the PAD will not
transmit the \fIprompt PAD service\fR signal to the start\(hystop mode DTE.
.PP
If the value of parameter 6 is set to 5, a \fIPAD command\fR signal
transmitted before the \fIprompt PAD service\fR signal has been received from
the PAD will be ignored.
.PP
If the value of parameter 6 is set to any of the values 8\(hy15, the
availability and format of a \fIprompt PAD service\fR signal is network
dependent.
.PP
The standard format of the \fIprompt PAD service\fR signal is given in
\(sc\ 3.5.23.
.bp
.RT
.sp 1P
.LP
3.2
\fIProcedures for virtual call control\fR
.sp 9p
.RT
.PP
Figure 1/X.28 (Sequence of events at the interface) shows the
procedures at the DTE/DCE interface during call establishment, data transfer
and call clearing. Figure 2/X.28 shows the state diagram.
.PP
For details on the action expected of the start\(hystop mode DTE
following receipt of a \fIPAD service\fR signal, refer to Recommendation\ X.96.
.RT
.sp 2P
.LP
3.2.1
\fICall establishment\fR
.sp 1P
.RT
.sp 1P
.LP
3.2.1.1
\fIPAD waiting (state 5)\fR
.sp 9p
.RT
.PP
Following the transmission of a \fIPAD service\fR signal the interface
will be in the \fIPAD waiting\fR state unless a virtual call is established
or is being established. During the \fIPAD waiting\fR state the PAD will
transmit
binary\ 1.
.PP
If parameter 2 is set to 1, all characters are echoed.
.PP
\fINote\fR \ \(em\ In some networks the \fIactive link\fR \| state will
either lead
directly to the \fIPAD waiting\fR \| state, the \fIservice ready\fR state
or the
\fIconnection in progress\fR state.
.RT
.sp 1P
.LP
3.2.1.2
\fINetwork user identification (NUI)\fR
.sp 9p
.RT
.PP
When required, for security, billing and/or network management
purposes the network user shall transmit a \fInetwork user identification\fR
signal. Some Administrations may not implement a \fInetwork user identification\fR
signal. When implemented, the \fInetwork user identification\fR signal
will be
defined in the \fIfacility request\fR block of a \fIselection PAD command\fR
signal.
.PP
The format of the \fIfacility request\fR \| block is defined in \(sc\ 3.5.15.1.
.PP
The information content of the \fInetwork user identification\fR \| signal
is network dependent.
.PP
When \fInetwork user identification\fR \| is not used and the calling DTE
is not identified by other means, the \fIreverse charging\fR facility will
be
used.
.RT
.sp 1P
.LP
3.2.1.3
\fIPAD command (state 6)\fR
.sp 9p
.RT
.PP
The DTE may transmit a \fIPAD command\fR \| signal when the interface is
in the \fIPAD waiting\fR \| state (state\ 5) and enters the \fIPAD command\fR
state at
the start of a \fIPAD command\fR signal.
.PP
The DTE may also transmit \fIPAD command\fR \| signals after escaping from
the \fIdata transfer\fR state or the \fIconnection in progress\fR state
(see \(sc\ 4.9.1 below).
.PP
If parameter 2 is set to 1, characters in \fIPAD command\fR \| signals
are echoed, except the characters following the character\ P in a \fIselection
PAD\fR \fI\fR \fIcommand\fR signal, which are not echoed. If parameter\
20 is implemented, the set of characters to be echoed is determined by
the value of parameter\ 20.
.PP
If parameter 6 is not set to 0, the PAD will ignore all characters
received from the DTE following the receipt of a \fIPAD command\fR signal
until the associated \fIPAD service\fR signal or sequence of \fIPAD service\fR
signals has been transmitted to the DTE by the PAD.
.PP
If parameter 6 is set to 0, the PAD will not transmit a \fIPAD\fR
\fIservice\fR signal. Therefore it is for the user to define the way in which
information regarding the completion of the connection is signalled to the
start\(hystop mode\ DTE.
.PP
The DTE may request the establishment of a virtual call by
transmitting a \fIselection PAD command\fR signal.
.PP
The DTE may edit \fIPAD command\fR \| signals before they are actioned by
the PAD by using the procedures in \(sc\ 3.6 below.
.PP
The formats of \fIPAD command\fR \| signals are given in \(sc\ 3.5 below. A
summary of
\fIPAD command\fR \| signals
is given in Table\ 2/X.28.
.RT
.sp 1P
.LP
3.2.1.4
\fIDTE waiting (state 3B)\fR
.sp 9p
.RT
.PP
Following the transmission of a \fIPAD command\fR \| signal the DTE will
transmit binary\ 1 and the interface will be in the \fIDTE waiting\fR
state.
.bp
.RT
.ce
\fBH.T. [T2.28]\fR
.ce
TABLE\ 2/X.28
.ce
\fBSummary of PAD command signals\fR
.ps 9
.vs 11
.nr VS 11
.nr PS 9
.TS
center box;
cw(120p) | cw(36p) | cw(36p) | cw(36p) .
PAD command signals T{
Valid before virtual call set\(hyup
T} T{
Valid after escaping from \fIdata transfer\fR
state
T} T{
Valid after escaping from \fIconnection\(hyin\(hyprogress\fR
state
T}
_
.T&
lw(120p) | cw(36p) | cw(36p) | cw(36p) .
Selection (\(sc 3.2.1.3) X
.T&
lw(120p) | cw(36p) | cw(36p) | cw(36p) .
T{
Profile selection (\(sc\(sc 3.3.1 and 4.9.2.5)
T} X X
.T&
lw(120p) | cw(36p) | cw(36p) | cw(36p) .
T{
Set (\(sc\(sc 3.3.2 and 4.9.2.5)
T} X X
.T&
lw(120p) | cw(36p) | cw(36p) | cw(36p) .
T{
Set and read (\(sc\(sc 3.3.2 and 4.9.2.5)
T} X X
.T&
lw(120p) | cw(36p) | cw(36p) | cw(36p) .
T{
Read (\(sc\(sc 3.4 and 4.9.2.5)
T} X X
.T&
lw(120p) | cw(36p) | cw(36p) | cw(36p) .
T{
Clear request (\(sc\(sc 3.2.1.5, 3.2.2.1\|a) and 4.9.2.1)
T} X X
.T&
lw(120p) | cw(36p) | cw(36p) | cw(36p) .
T{
Status (\(sc\(sc 3.7 and 4.9.2.2)
T} X X
.T&
lw(120p) | cw(36p) | cw(36p) | cw(36p) .
Reset (\(sc 4.9.2.3) X
.T&
lw(120p) | cw(36p) | cw(36p) | cw(36p) .
Interrupt (\(sc 4.9.2.4) X
.T&
lw(120p) | cw(36p) | cw(36p) | cw(36p) .
T{
Remote set and read (\(sc\(sc 3.3.4)
T} X
.T&
lw(120p) | cw(36p) | cw(36p) | cw(36p) .
Remote read (\(sc 3.4.2) X
.T&
lw(120p) | cw(36p) | cw(36p) | cw(36p) .
T{
Invitation to clear (\(sc 3.2.2)
T} X
.T&
lw(120p) | cw(36p) | cw(36p) | cw(36p) .
T{
\fIExtended dialogue mode\fR
T}
.T&
lw(120p) | cw(36p) | cw(36p) | cw(36p) .
Break (\(sc 5.1) X
.T&
lw(120p) | cw(36p) | cw(36p) | cw(36p) .
Help (\(sc 5.4) X\fR X
.T&
lw(120p) | cw(36p) | cw(36p) | cw(36p) .
Language (\(sc 5.3) X X
.T&
lw(120p) | cw(36p) | cw(36p) | cw(36p) .
NUI on (\(sc 5.2) X
.T&
lw(120p) | cw(36p) | cw(36p) | cw(36p) .
NUI off (\(sc 5.2) X
_
.TE
.nr PS 9
.RT
.ad r
\fBTable 2/X.28 [T2.28], p.\fR
.sp 1P
.RT
.ad b
.RT
.sp 1P
.LP
.sp 2
3.2.1.5
\fIConnection\(hyin\(hyprogress (state 7)\fR
.sp 9p
.RT
.PP
If parameter 6 is not set to 0, on receipt of a valid \fIselection\fR \fIPAD
command\fR \| signal the PAD will transmit an \fIacknowledgement PAD service\fR
signal followed by binary\ 1 and the interface will enter the
\fIconnection\(hyin\(hyprogress\fR state. The interface will enter the
\fIPAD service\fR
\fIsignals\fR state as necessary and the PAD will transmit the \fIconnected
PAD\fR
\fIservice\fR signal or a \fIclear indication PAD service\fR signal to
the DTE. During this period the PAD will not accept any \fIPAD command\fR
signals. Characters
are not echoed.
.PP
If the value of parameter 6 is 0, the PAD will not transmit \fIPAD\fR
\fIservice\fR \| signals to the start\(hystop mode DTE. Following the receipt
of a valid \fIselection PAD command\fR signal, the interface shall remain
in the \fI\fR
\fIconnection\(hyin\(hyprogress\fR state until the virtual call has been
established.
.PP
In some networks, during the \fIconnection in progress\fR state, the
start\(hystop mode DTE may escape from that state by transmitting a \fIPAD
recall\fR signal to the PAD. On detection of the \fIPAD recall\fR signal,
the interface will enter the \fIwaiting for command\fR state.
.PP
If parameter 1 is set to 1, the PAD will recognize the character\ 1/0 (DLE)
as the \fIPAD recall\fR signal from the start\(hystop mode DTE.
.PP
If parameter 1 is set to a decimal value from 32 to 126, the PAD will recognize
the binary representation of the decimal value as the \fIPAD recall\fR
signal from the start\(hystop mode DTE.
.PP
If parameter 7 is set to 8, the \fIbreak\fR signal may be used as the
\fIPAD recall\fR signal from the \fIconnection in progress\fR state, allowing
for
escape from the \fIconnection in progress\fR state without loss of character
transparency.
.bp
.PP
If parameter 6 is set to 5, the \fIprompt PAD service\fR will be
transmitted by the PAD. At this time, the PAD may accept the \fIclear request\fR
\fIPAD command\fR signal or another suitable command to be determined by
further
study.
.PP
On receipt of the next character from the start\(hystop mode DTE, the PAD
will act in accordance with one of the following conditions:
.RT
.LP
a)
if the character received is the \fIPAD recall\fR character or
the \fIPAD command\fR signal delimiter [characters 2/11 (+) or 0/13
(CR)] the interface will return to the \fIconnection in progress\fR
state and no action will be taken with the character;
.LP
b)
if the character received is in columns 2 to 7 of
International Alphabet No.\ 5, excluding the characters\ 2/0 (SP),
2/11\ (+) [see \(sc\ 3.2.1.5.1 a) above], 7/15 (DEL) and the \fIPAD\fR
\fIrecall\fR character, the interface will enter the \fIPAD command\fR
state, and the character will be placed in the editing buffer.
Characters\ 2/0 (SP) and 7/15 (DEL) will be ignored;
.LP
c)
if the character is not covered above, for example editing
character sin columns\ 2 to\ 7 and characters in columns\ 0 and\ 1
of IA5, the action by the PAD is for further study.
.PP
If the first character of a \fIPAD command\fR signal is not received within
P seconds of the interface entering the \fIwaiting for command\fR state
from the \fIconnection in progress\fR state, the PAD will transmit an \fIerror
PAD\fR
\fIservice\fR signal, when parameter\ 6 is not set to\ 0. The interface
will then
enter the \fIconnection in progress\fR state, irrespective of the value of
parameter\ 6. The value of P is for further study but will not be less than
60\|s.
.PP
If the \fIPAD command\fR signal delimiter is not received within Q\ seconds
of the interface entering the \fIPAD command\fR state from the \fIconnection
in\fR
\fIprogress\fR state, or an invalid \fIPAD command\fR signal is received,
the PAD will transmit an \fIerror PAD service\fR signal, when parameter\
6 is not set to\ 0,
indicating that an error has occurred. The interface will then enter the
\fIconnection in progress\fR state, irrespective of the value of parameter\
6. The value of\ Q is for further study but will not be less than 60\|s.
.PP
If a valid \fIclear request PAD command\fR signal is received the
procedure will be as described in \(sc\ 3.2.2.1\ a).
.RT
.sp 1P
.LP
3.2.1.6
\fIPAD service signals (state 8)\fR
.sp 9p
.RT
.PP
Following receipt by the DTE of a \fIPAD service\fR \| signal or a
sequence of \fIPAD service\fR \| signals (in the case of call set\(hyup)
in response
to a previously transmitted \fIPAD command\fR signal, the interface will be in
either:
.RT
.LP
a)
a \fIPAD waiting\fR state (state 5) if no virtual call is in
progress, or
.LP
b)
a \fIdata transfer\fR state (state 9) if a virtual call is in
progress.
.PP
Any \fIPAD service\fR \| signal arising from events within the packet
network will not be transmitted until any \fIPAD service\fR signal outstanding
from a previously received \fIPAD command\fR signal has been transmitted.
.PP
\fIPAD service\fR \| signals will not be transmitted if the value of
parameter\ 6 is set to\ 0 and the \fIPAD service\fR signals state will be
bypassed.
.PP
The standard format of \fIPAD service\fR signals is defined in \(sc\ 3.5
below.
.PP
A summary of \fIPAD service\fR \| signals is given in Annex\ A.
.RT
.sp 1P
.LP
3.2.1.7
\fIIncoming calls\fR
.sp 9p
.RT
.PP
The PAD will indicate \fIincoming call\fR \| to the start\(hystop mode
DTE only if the DTE/DCE interface is in the \fIPAD waiting\fR state (state\
5). In any other case the PAD will only indicate incoming call if:
.RT
.LP
a)
the PAD knows the speed and code of the start\(hystop mode DTE by previous
agreement, or a default value is applicable;
.LP
b)
the PAD waiting state (state 5) is reached by the setting
up of an access information path within X\ seconds.
.PP
The value of X is for further study, but should not exceed 120
s.
.PP
The PAD will transmit to the start\(hystop mode DTE an \fIincoming call\fR
\fIPAD service\fR \| signal.
.PP
The PAD will not expect a response to the \fIincoming call PAD\fR
\fIservice\fR \| signal from the start\(hystop mode DTE and will consider
the interface to enter at once the \fIdata transfer\fR state (state\ 9).
.PP
The standard format of the \fIincoming call PAD service\fR \| signal is
given in \(sc\ 3.5.22 below.
.bp
.RT
.sp 2P
.LP
3.2.2
\fIClearing\fR
.sp 1P
.RT
.sp 1P
.LP
3.2.2.1
\fIClearing by the start\(hystop mode DTE\fR
.sp 9p
.RT
.sp 1P
.LP
3.2.2.1.1
\fIClearing by the local PAD\fR
.sp 9p
.RT
.PP
DTE clearing of the PAD to which the DTE is connected shall be
indicated by either:
.RT
.LP
a)
transmitting a \fIclear request PAD command\fR \| signal after
escaping from the \fIdata transfer\fR state during a virtual
call (see \(sc\ 4.9 below). The format of a \fIclear request PAD\fR \fIcommand\fR
signal is given in \(sc\ 3.5.8 below. The PAD will
transmit a \fIclear confirmation PAD service\fR signal within
B\ seconds. The value of\ B is for further study. The standard
format of the \fIclear confirmation PAD service\fR signal is given
in \(sc\ 3.5.9 below. The interface will enter the \fIPAD waiting\fR state
and the DTE will be allowed to make a follow\(hyon call; or
.LP
b)
disconnecting the access information path.
.sp 1P
.LP
3.2.2.1.2
\fIClearing of the remote PAD\fR
.sp 9p
.RT
.PP
\fINote\fR \ \(em\ This is an optional function which will not be supported
on all PADs.
.PP
DTE clearing of a remote PAD shall be indicated by transmitting an
\fIinvitation to clear PAD command\fR signal after escaping from the data
transfer state during a virtual call (see \(sc\ 4.9 below). The format
of an \fIinvitation to\fR \fIclear PAD command\fR signal is given in \(sc\
3.5.8 below. The PAD to which the DTE issuing the invitation to clear is
connected will transmit a \fIclear indication\fR \fIPAD service\fR signal
to that DTE once indication of clearing has been received
.PP
from the remote PAD. The format of the clear indication PAD service signal
is given in \(sc\ 3.5.17 below. The interface will enter the PAD waiting
state and the DTE will be allowed to make a follow\(hyon call or disconnect
the access
information path.
.RT
.sp 1P
.LP
3.2.3
\fIUnsuccessful calls\fR
.sp 9p
.RT
.PP
If a call is unsuccessful for any reason, the PAD will indicate the reason
to the start\(hystop mode DTE by means of a \fIclear indication PAD service\fR
signal. If parameter\ 6 is set to\ 0, a \fIPAD service\fR signal is not
transmitted.
.PP
After transmission of the \fIclear indication PAD service\fR signal the
PAD will be in the \fIPAD waiting\fR state.
.RT
.sp 2P
.LP
3.2.3.1
\fIFault conditions\fR
.sp 1P
.RT
.sp 1P
.LP
3.2.3.1.1
\fIFailure to receive a PAD command signal\fR
.sp 9p
.RT
.PP
If the first character of a \fIPAD command\fR \| signal is not received
within T\ seconds of the interface entering the \fIPAD waiting\fR state,
the PAD
will perform PAD clearing in accordance with \(sc\ 3.2.2.2 above. The value
of\ T is for further study.
.PP
This restriction does not apply to a DTE which accesses the PAD by a leased
line.
.PP
If following the first character of a \fIPAD command\fR \| signal a \fIPAD\fR
\fIcommand\fR \| signal delimiter is not received within S\ seconds, the
PAD will
.PP
transmit an \fIerror PAD service\fR signal, if parameter\ 6 is not set to\ 0,
indicating that an error has occurred (see \(sc\ 3.5.19 below) and the
interface
will return to the \fIPAD waiting\fR state. The value of\ S is for further
study
but will not be less than\ 60\ s.
.PP
If the PAD receives an unrecognized \fIPAD command\fR \| signal it will
transmit an \fIerror PAD service\fR \| signal, if parameter\ 6 is not set
to\ 0,
indicating that an error has occurred and the interface will return to the
\fIPAD waiting\fR state.
.PP
The operation of the PAD when parameter 6 is set to 0 is for further study.
.RT
.sp 1P
.LP
3.2.3.1.2
\fIFailure to establish a virtual call\fR
.sp 9p
.RT
.PP
If the interface enters the \fIPAD waiting\fR state more than N times after
setting up the access information path without a virtual call being
established, the PAD will disconnect the access information path. This
restriction does not apply to DTEs which access the PAD by leased lines.
.PP
The value of N is for further study.
.bp
.RT
.LP
.sp 1P
.LP
3.2.3.1.3
\fIInvalid clear request PAD command signal\fR
.sp 9p
.RT
.PP
If the PAD receives a \fIclear request PAD command\fR \| signal while the
interface is in the \fIPAD waiting\fR \| state, the PAD will transmit a
\fIclear\fR
\fIindication PAD service\fR signal (local procedure error) if parameter\ 6
is not set to\ 0 and the interface will return to the \fIPAD waiting\fR state.
The standard format of the relevant \fIclear indication PAD service\fR
signal is
given in \(sc\ 3.5.17\|e) below.
.RT
.sp 1P
.LP
3.2.3.1.4
\fIInvalid facility request\fR
.sp 9p
.RT
.PP
If the PAD receives an invalid facility request code the PAD will perform
PAD clearing in accordance with \(sc\(sc\ 3.2.2.1.1 or 3.2.2.1.2 above.
.RT
.sp 1P
.LP
3.2.3.2
\fIFailure of the access information path\fR
.sp 9p
.RT
.PP
If the access information path is disconnected for any reason, the call
attempt or virtual call will be cleared by the PAD.
.RT
.sp 1P
.LP
3.2.4
\fIData transfer\fR
.sp 9p
.RT
.PP
The procedures for data transfer are given in \(sc\ 4 below.
.RT
.LP
.sp 1P
.LP
3.2.5
\fICalled DTE reselection\fR
.sp 9p
.RT
.PP
The called DTE reselection is provided as default condition by the PAD.
The start\(hystop mode DTE is able to prevent the called DTE reselection
by including the \fIcalled DTE reselection prevention facility\fR in the
\fIselection\fR \fIPAD command\fR signal.
.PP
On receipt of a \fIreselection PAD\fR \| message the PAD will, if
parameter\ 6 is not set to\ 0 and the \fIcalled DTE reselection prevention\fR
\fIfacility\fR has not been requested in the \fIselection PAD command\fR
signal, send a \fIreselection PAD service\fR signal to the start\(hystop
mode DTE.
.PP
The standard format of the \fIreselection PAD service\fR
signal is given in \(sc\ 3.5.29. The interface will enter \fIconnection in\fR
\fIprogress\fR state, and the PAD will act as described in \(sc\ 3.2.1.5 above.
.PP
\fINote\fR \ \(em\ Some networks may not implement this procedure.
.RT
.sp 1P
.LP
3.3
\fIProcedures for setting or changing the values of PAD\fR
\fIparameters\fR
.sp 9p
.RT
.PP
The procedures described in \(sc\(sc\ 3.3.1 and\ 3.3.2 give details for
setting or changing the
values of PAD parameters
by the start\(hystop mode DTE connected to that PAD. These procedures may
be used before the \fIselection\fR \fIPAD command\fR signal is sent and
also after escaping from the \fIdata transfer\fR state.
.PP
The procedures described in \(sc 3.3.3 below refer to the PAD behaviour
about the current values of PAD parameters in the case of call clearing.
.PP
The procedures described in \(sc\ 3.3.4 give details for setting or
changing the values of remote PAD parameters by a start\(hystop mode DTE. These
precedures may only be used after escaping the \fIdata transfer\fR state.
.PP
\fINote\fR \ \(em\ The procedure for setting or changing parameters in
a remote PAD is optional and may not be supported by many PADs.
.RT
.sp 1P
.LP
3.3.1
\fISelection of a \fR \fIstandard profile\fR \fIby the start\(hystop\fR
\fImode DTE\fR
.sp 9p
.RT
.PP
The start\(hystop mode DTE may select a set of defined values of PAD parameters
known as a \fIstandard profile\fR [see \(sc\ 3.1.1\ b) above] by sending
the \fIprofile selection PAD command\fR signal which includes a
profile
identifier
. This procedure is additional to the selecting of an \fIinitial\fR \fIstandard
profile\fR by transmitting the \fIservice request\fR signal. The start\(hystop
mode DTE may select a set of parameter values as an initial profile at
subscription time by agreement with the Administration.
.PP
The format of the \fIprofile selection PAD command\fR \| signal is
given in \(sc\ 3.5.5 below.
.PP
A list of the parameter values associated with the \fItransparent\fR \|
and \fIsimple standard profiles\fR \| is given in Table\ 1/X.28. Other
CCITT \fIstandard\fR \fIprofiles\fR , all corresponding parameter values
and their identifiers are
subjects for further study.
.PP
When parameter 6 is not set to 0, the PAD will acknowledge the
\fIprofile selection PAD command\fR \| signal by sending an \fIacknowledgement\fR
\fIPAD service\fR signal to the start\(hystop mode DTE.
.PP
The standard format of the \fIacknowledgement PAD service\fR \| signal is
defined in \(sc\ 3.5.3 below.
.bp
.RT
.sp 1P
.LP
3.3.2
\fIProcedures for setting or changing one or several parameters\fR
\fIby the start\(hystop mode DTE\fR
.sp 9p
.RT
.PP
The start\(hystop mode DTE may change the values of one or several
parameters by sending a \fIset\fR or \fIset and read PAD command\fR signal
including
the parameter reference(s) and value(s). The format of \fIPAD command\fR
signals is defined in \(sc\ 3.5 below.
.PP
When parameter 6 is not set to 0, the PAD will respond to a valid
\fIset and read PAD command\fR \| signal by transmitting a \fIparameter
value PAD\fR
\fIservice\fR signal, showing the newly set parameter values. The PAD will
respond to a valid \fIset PAD command\fR signal by transmitting an \fIacknowledgement
PAD\fR \fIservice\fR signal. If at least one of the requested PAD parameters
is invalid, the PAD will send a \fIparameter value PAD\fR \fIservice\fR
signal to the start\(hystop
mode DTE to identify the invalid parameters. In this case the valid parameters
will be accepted and invoked. Valid parameter references and values are
given in Table\ 1/X.3.
.PP
The format of the \fIparameter value PAD service\fR \| signal is defined
in \(sc\ 3.5.14 below.
.PP
When parameter 6 is set to 0, the PAD will accept and invoke valid
parameters without advising the start\(hystop mode DTE of any invalid parameters
or parameter values.
.PP
If the function of a character is duplicated by the selection of
parameter values by use of the \fIset\fR or \fIset and read PAD command\fR
signal, the PAD will consider these parameter changes as valid, and will
respond as
described above. After these changes are invoked, when the PAD receives from
the start\(hystop mode DTE the character with the duplicated function, the PAD
will perform the function of the character that has the highest priority
among the functions that are duplicated. The priority assignment of the
functions is as follows:
.RT
.LP
(Highest)
1)
PAD recall character (parameter 1)
.LP
2)
PAD command signal delimiter
.LP
3)
X\(hyON, X\(hyOFF (parameters 12 and 22)
.LP
4)
Line Display (parameter 18)
.LP
5)
Character delete (parameter 16)
.LP
6)
Line delete (parameter 17)
.LP
(Lowest)
7)
Data forwarding character (parameter 31).
.sp 1P
.LP
3.3.3
\fIPAD procedures regarding the current values of PAD\fR
\fIparameters\fR
.sp 9p
.RT
.PP
The following situations are considered:
.RT
.LP
i)
\fICall establishment phase\fR
.LP
In any case if a \fIclear\fR \| condition, without disconnecting the
access information path, occurs prior to the virtual call being
set up, the current values of PAD parameters are left as
they are.
.LP
ii)
\fIClear after call set up\fR
.LP
In the case where a \fIclear\fR \| condition, without
disconnecting the access information path, occurs after set up of the virtual
call, the PAD will reset the parameters to the values specified
in the \fIinitial profile\fR .
.sp 1P
.LP
3.3.4
\fIProcedures for setting or changing one or several parameters\fR
\fIof a remote PAD by the start\(hystop mode DTE\fR
.sp 9p
.RT
.PP
\fINote\fR \ \(em\ The function of being able to set or change parameters
in the remote PAD is optional and may not be supported by many PADs.
.PP
The start\(hystop mode DTE may change the values of one or several
parameters in a remote PAD by sending a remote \fIset and read PAD command\fR
signal
including the parameter reference(s) and value(s). The format of \fIPAD
command\fR signals is defined in \(sc\ 3.5 below.
.PP
When parameter 6 is not set to 0, the PAD will, in response to a valid
remote \fIset and read PAD command\fR signal from the local DTE and following
receipt
of a \fIparameter indication PAD\fR message from the remote PAD, transmit
a remote parameter value PAD service signal to the local DTE showing the
newly set
parameter values in the remote PAD.
.RT
.sp 1P
.LP
3.4
\fIProcedures for reading the values of one or several parameters\fR
\fIby the start\(hystop mode DTE\fR
.sp 9p
.RT
.PP
This procedure may be used when parameter 6 is not set to 0.
The PAD will ignore a \fIread PAD command\fR signal or a \fIremote read
PAD command\fR \fIsignal\fR if parameter\ 6 is set to\ 0.
.bp
.RT
.LP
.sp 1P
.LP
3.4.1
\fITo read local PAD parameter values\fR
.sp 9p
.RT
.PP
The start\(hystop mode DTE may enquire about the current values of one
or several PAD parameters by sending the \fIread PAD command\fR signal
and the
references of the required parameters before the \fIselection PAD command\fR
signal is sent and also after escaping from the \fIdata transfer\fR state.
The format of the \fIread PAD command\fR signal is defined in \(sc\ 3.5.4
below.
.PP
The PAD will respond by sending a \fIparameter value PAD service\fR \|
signal containing the requested parameter values. The standard format of the
\fIparameter value PAD service\fR signal is defined in \(sc\ 3.5.14 below.
.RT
.sp 1P
.LP
3.4.2
\fITo read remote PAD parameter values\fR
.sp 9p
.RT
.PP
The procedures used by the start\(hystop mode DTE to enquire about the
current values of the remote PAD are similar to those in \(sc\ 3.4.1 above.
In this case the remote \fIread PAD command\fR signal and \fIremote parameter
value PAD\fR
signal are used, and the procedure may only be used after escaping from the
\fIdata transfer\fR state.
.RT
.sp 1P
.LP
3.5
\fIFormats of \fR \fIPAD command signals\fR \fIand \fR \fIPAD service\fR
\fIsignals\fR
.sp 9p
.RT
.PP
All characters in columns 2 to 7 of International Alphabet No. 5, excluding
the characters 2/0\ (SP), 7/15\ (DEL), 2/11\ (+) and the characters
assigned to perform editing functions will be recognized by the PAD as
forming part of a \fIPAD command\fR signal. The PAD will always recognize
the characters
0/13\ (CR) and 2/11\ (+) as the \fIPAD command signal delimiter\fR . The
\fIPAD command\fR \fIsignal delimiter\fR is not part of the command. Characters
2/0\ (SP) and
7/15\ (DEL) are not considered as part of a \fIPAD command\fR signal and those
characters will be ignored by the PAD if no other function is assigned
to these characters. Characters from columns\ 0 to\ 7 may be assigned to
perform editing functions and in this case the PAD will operate in accordance
with \(sc\ 3.6 below. Unassigned characters in columns\ 0 and\ 1 will be
ignored by the PAD.
.PP
\fIPAD command\fR \| signals are defined in upper case characters in this
Recommendation; however, in addition, lower case characters are acceptable.
For an interim period, some networks may consider \fIPAD command\fR signals
containing lower case characters as invalid.
.PP
All \fIPAD command\fR \| signals shall be terminated with the \fIPAD command\fR
\fIsignal delimiter\fR .
.PP
If the low order 4 bits or parameter 6 are set to a value of 1 or\ 5, \fIPAD
service\fR signals will be sent in the standard format, as described below.
If the low order 4\ bits of parameter\ 6 are set to one of the values\
8 to\ 15
\fIPAD service\fR signals are sent in a network dependent format.
.PP
If the high order 4\ bits of parameter\ 6 are not all zero, the PAD will
operate in the extended dialogue mode. The extended dialogue mode provides
additional natural language text in \fIPAD service\fR signals. It provides
a \fIhelp\fR \fIPAD command\fR signal for requesting explanatory information
on \fIPAD command\fR signals, PAD parameters, standard profiles,\ etc.
In the following definitions of standard formats for \fIPAD service\fR
signals, the extended text, where shown, is to be sent only when the PAD
is in the extended dialogue mode. In some
networks the extended dialogue mode information may be provided in different
languages. Additional \fIPAD command\fR signals may be provided as defined in
\(sc\ 5. Some networks may also provide the additional \fIPAD command\fR
signals while the PAD is not in extended dialogue mode.
.PP
\fINote\fR \ \(em\ The text for service signals in languages other than
English is for further study. See Annex\ C.
.PP
Some networks may not permit the free use of character 2/0 (SP)
anywhere in the command when operating in the extended dialogue mode. In
particular this character may not be permitted within keywords. In addition,
at least one such character may be required as a separator between keywords
or
between keywords and numeric values.
.PP
\fIPAD service\fR \| signals, other than the \fIacknowledgement\fR , \fIprompt\fR
,
\fIcharacter deleted, line deleted\fR and \fIpage wait PAD service\fR signals
(see
\(sc\(sc\ 3.5.2, 3.5.23, 3.5.24, 3.5.25 and 3.5.26) will commence with and be
followed by the \fIformat effector\fR .
.RT
.sp 1P
.LP
3.5.1
\fIFormat of the \fR \fIPAD command signal delimiter\fR
.sp 9p
.RT
.PP
The character 0/13 (CR) or character 2/11 (+) may be sent as a
delimiter.
.RT
.sp 1P
.LP
3.5.2
\fIFormat of the \fR \fIformat effector\fR
.sp 9p
.RT
.PP
The characters 0/13 (CR) 0/10 (LF) will be sent by the PAD followed by,
when parameter\ 9 is set to\ 0, two padding characters if the start\(hystop
mode DTE operates at a data rate of 110\ bit/s and four padding characters
if the
start\(hystop mode DTE operates at 200\ bit/s, 300\ bit/s, 1200\ bit/s or
75/1200\ bit/s.
.bp
.PP
If parameter 9 is not set to 0, then the number of padding characters transmitted
after the character 0/10\ (LF) will be equal to the current value of that
parameter.
.PP
The format of the padding characters is given in \(sc\ 3.5.20
below.
.PP
\fINote\fR \ \(em\ The term \*Qformat effector\*U is used here slightly
differently than in Recommendation\ T.50.
.RT
.sp 1P
.LP
3.5.3
\fIStandard format of the \fR \fIacknowledgement PAD service\fR
\fIsignal\fR
.sp 9p
.RT
.PP
The \fIformat effector\fR \| will be sent.
.RT
.sp 1P
.LP
3.5.4
\fIFormat of \fR \fIread PAD command signal\fR
.sp 9p
.RT
.PP
3.5.4.1
To read parameters of the local PAD to which the requesting DTE is connected,
the characters 5/0 (P) 4/1 (A) 5/2 (R) 3/15 (?) shall be sent
followed by the decimal reference of the parameter to be read.
.PP
Characters of International Alphabet No. 5 will be sent to
represent both the parameter reference and parameter value, e.g.\ decimal
value\ 12 would be sent as characters 3/1\ (1) and 3/2\ (2).
.PP
If no parameter reference number is indicated in the \fIread PAD\fR
\fIcommand\fR \| signal then it applies implicitly to all parameters.
.PP
When more than one parameter is required to be read by sending the
\fIread PAD command\fR \| signal, the character 2/12\ (,) shall be sent
between the
decimal references of the parameters.
.PP
Example: PAR? 1, 3, 5
.PP
The format required to read national parameters is for further
study.
.RT
.PP
3.5.4.2
If reading of remote PAD parameters is supported by the local
PAD, the characters 5/2 (R) 5/0 (P) 4/1 (A) 5/2 (R) 3/15 (?) shall be sent
followed by the reference of the parameter to be read.
.sp 9p
.RT
.PP
Characters of International Alphabet No.\ 5 will be sent to
represent both the parameter reference and parameter value, e.g.\ decimal
value\ 12 would be sent as characters\ 3/1 (1) and 3/2\ (2).
.PP
If no parameter reference number is indicated in the \fIremote read PAD\fR
\fIcommand\fR signal then it applies implicitly to all parameters.
.PP
When more than one parameter is required to be read by sending the
\fIremote read PAD command\fR signal, the character 2/12 (,) shall be sent
between the decimal references of the parameters.
.PP
Example: RPAR ? 1, 3, 5
.RT
.sp 1P
.LP
3.5.5
\fIFormat of \fR \fIprofile selection PAD command signal\fR
.sp 9p
.RT
.PP
The characters 5/0 (P) 5/2 (R) 4/15 (O) 4/6 (F) shall be sent
followed by a
profile identifier
. A profile identifier will consist of one or more alphanumeric characters.
The profile identifiers 90\(hy99 are reserved for CCITT defined profiles
as defined in Tables\ 3/X.28. In addition, some
networks may also assign other profile identifiers to CCITT defined
profiles.
.RT
.LP
.ce
\fBH.T. [T3.28]\fR
.ce
TABLE\ 3/X.28
.ce
\fBCCITT standard profile identifiers\fR
.ps 9
.vs 11
.nr VS 11
.nr PS 9
.TS
center box;
cw(54p) | cw(78p) .
Profile identifier CCITT standard profile
_
.T&
cw(54p) | lw(78p) .
90 Simple standard profile
_
.T&
cw(54p) | lw(78p) .
91 Transparent standard profile
_
.T&
cw(54p) | lw(78p) .
92 to 99 Reserved for future use
_
.TE
.nr PS 9
.RT
.ad r
\fBTable 3/X.28 [T3.28], p.\fR
.sp 1P
.RT
.ad b
.RT
.LP
.bp
.sp 1P
.LP
3.5.6
\fIFormat of set PAD command signal and the set and read PAD\fR
\fIcommand signal\fR
.sp 9p
.RT
.PP
3.5.6.1
To set or set and read parameters in the local PAD to which the
DTE is connected:
.PP
The
\fIset PAD command\fR \| signal
will consist of the
characters
5/3\ (S) 4/5\ (E) 5/4\ (T) followed by the decimal reference of the parameter
to be set, followed by character\ 3/10\ (:) and the parameter value required.
.PP
The
\fIset and read PAD command\fR \| signal
will consist of the
characters 5/3 (S) 4/5 (E) 5/4 (T) 3/15 (?) followed by the decimal reference
of the parameter to be set and read, followed by the character 3/10 (:)
and the parameter value required.
.PP
If more than one parameter is to be set or set and read by the \fIset\fR
\fIand read PAD\fR \fIcommand\fR \| signal, the character 2/12\ (,) shall
be sent between a parameter
value and the next parameter reference.
.PP
Example: SET 2:0, 3:2, 9:4
.PP
The format required to set national parameters is for further
study.
.RT
.sp 1P
.LP
3.5.6.2
\fITo set and read parameter in the remote PAD\fR
.sp 9p
.RT
.PP
The local PAD may optionally support the setting and reading of the remote
PAD parameters.
.PP
The \fIremote set and read PAD command\fR signal will consist of the
characters 5/2 (R) 5/3 (S) 4/5 (E) 5/4 (T) 3.15 (?) followed by the decimal
reference of the parameter to set and read, followed by the character\
3/10 (:) and the parameter value required.
.PP
If more than one parameter is to be set and read by the \fIremote set and\fR
\fIread PAD command\fR signal, the character 2/12 (,) shall be sent between
a
parameter value and the next parameter reference.
.PP
Example: RSET 2:0, 3:2, 9:4
.RT
.sp 1P
.LP
3.5.7
\fIStandard format of the \fR \fIreset PAD service signal\fR
.sp 9p
.RT
.PP
The \fIreset PAD service\fR signal consists of the following
elements:
.RT
.LP
<reset PAD service signal> ::= <RESET> <cause> <diagnostic>
