\fIMalaga\(hyTorremolinos, 1984 and Melbourne, 1988)\fR
.ce 0
.sp 1P
.PP
On leased circuits, considering that there exist and will
come into being other modems with features designed to meet the requirements
of the Administrations and users, this Recommendation in no way restricts
the use of any other modems.
.sp 1P
.RT
.PP
The only group reference pilot frequency which can be used in
conjunction with this modem is 104.08\ kHz.
.bp
.sp 2P
.LP
\fB1\fR \fBScope\fR
.sp 1P
.RT
.LP
.PP
The family of modems covered by this Recommendation should be
applicable to the following uses:
.RT
.LP
a)
transmission of data between customers on leased circuits;
.LP
b)
transmission of a multiplex aggregate bit stream for public
data networks;
.LP
c)
extension of a PCM channel at 64\ kbit/s over analogue
facilities;
.LP
d)
transmission of a common channel signalling system for
telephony and/or public data networks;
.LP
e)
extension of Single\(hyChannel\(hyPer\(hyCarrier (SCPC) circuit
from a satellite earth station;
.LP
f
)
transmission of a multiplex aggregate bit stream for
telegraph and data signals.
.PP
Principal recommended characteristics to be used for simultaneous both\(hyway
synchronous operation are the following:
.LP
.sp 2P
.LP
\fB2\fR \fBData signalling rates\fR
.sp 1P
.RT
.sp 1P
.LP
2.1
\fIApplication\ a)\fR
.sp 9p
.RT
.PP
The recommended data signalling rate (equals the customer
signalling rate) for international use is synchronous at 48\ kbit/s. For
certain national applications or with bilateral agreement between Administrations,
the following data signalling rates are applicable: 56, 64 and 72\ kbit/s.
.RT
.sp 1P
.LP
2.2
\fIApplications\ b), c) and d)\fR
.sp 9p
.RT
.PP
For these applications, the recommended data signalling rate is
synchronous at 64\ kbit/s.
.PP
For those
synchronous networks
requiring the end\(hyto\(hyend
transmission of both the 8\ kHz and 64\ kHz timing together with the data at
64\ kbit/s, a data signalling rate of 72\ kbit/s on the line is
suggested.
.PP
The corresponding data format should be obtained by inserting one
extra bit\ E just before the first bit of each octet of the 64\ kbit/s data
stream. The bits\ E convey alignment and
housekeeping information
,
according to the pattern shown in Figure\ 1/V.36.
.RT
.LP
.rs
.sp 3P
.ad r
\fBFigure 1/V.36. p.\fR
.sp 1P
.RT
.ad b
.RT
.PP
The use of the
housekeeping bits
H is determined with
bilateral agreement between Administrations. When not used, these bits
should be assigned the value\ 1. A framing strategy is not specified in
this
Recommendation.
.PP
When the transmission of the 8\ kHz timing is not required, the data
signalling rate on the line may be 64\ kbit/s.
.RT
.sp 1P
.LP
2.3
\fIApplication\ e)\fR
.sp 9p
.RT
.PP
The recommended data signalling rate (equals the customer
signalling rate) for international use is synchronous at 48\ kbit/s. For
certain national applications or with bilateral agreement between Administrations
the data signalling rate of 56\ kbit/s is applicable.
.RT
.LP
.sp 1P
.LP
2.4
\fIApplication\ f\fR \fI)\fR
.sp 9p
.RT
.PP
The recommended data signalling rate is synchronous at
64\ kbit/s.
.RT
.PP
2.5
The permitted tolerance for all the data signalling rates
mentioned above is \(+-\|5\ \(mu\ 10
\s6\(em5
.PS 10
\ bit/s.
.sp 9p
.RT
.PP
\fINote\fR \ \(em\ There are equipments in service which will only work
successfully with a maximum tolerance of the data signalling rate of
\(+-\|1\ bit/s.
.sp 2P
.LP
\fB3\fR \fBScrambler/descrambler\fR
.sp 1P
.RT
.PP
In order to be
bit sequence independent
and to avoid high amplitude spectral components on the line, the data should
be scrambled and
descrambled by means of the logical arrangements described in Appendix\ I.
.bp
.RT
.sp 2P
.LP
\fB4\fR \fBBaseband signal\fR
.sp 1P
.RT
.PP
\fB\fI\fR The equivalent
baseband
signal shaping process is based
upon the binary coded partial response pulse, often referred to as class\ IV,
whose time and spectral function are defined by:
\v'6p'
.RT
.sp 1P
.ce 1000
\fIg\fR (\fIt\fR ) =
@ {2 } over {\(*p } @ \(mu
$$3osin
@ {\(*p } over {\fIT\|\fR } @
\fIt\fR $$3u
@ left ( {\fIt\|\fR } over {\fIT\|\fR } right ) @
$$2x2 \(em 1
$$3e
.ce 0
.sp 1P
.LP
.sp 1
.LP
and
\v'6p'
.sp 1P
.ce 1000
\fIG\fR (
\fIf\fR ) = \
$$6O2 \fIT j\fR sin 2 \(*p \fIT f\fR $$6U0
$$6E\|
@ pile { {, 2!
\fIf\fR left | \(= {1 } over {2 \fIT\fR } } above { , right | \fIf\fR
left | > {1 } over {2 \fIT\fR } } }
.ce 0
.sp 1P
.LP
.sp 1
.LP
respectively, where 1/\fIT\fR denotes the data signalling rate.
.PP
This shaping process should be effected in such a way that the
decoding can be achieved by full wave rectification of the demodulated line
signal.
.PP
The reference to equivalent baseband signals recognizes that the modem
implementation may be such that the binary signal at the input and output
of
the modem is converted to and from the line signal without appearing as an
actual baseband signal.
.RT
.sp 2P
.LP
\fB5\fR \fBLine signal in 60\(hy108\ kHz band\fR (at the line output of
the modem)
.sp 1P
.RT
.PP
5.1
In the 60\(hy108\ kHz band the line signal should correspond to a single
sideband signal with its carrier frequency at 100\ kHz\ \(+-\ 2\ Hz.
.sp 9p
.RT
.LP
.PP
5.2
The relationship between the binary signals at the real or
hypothetical output of the scrambler and the transmitted line signal states
shall be in accordance with the amplitude modulation case of
Recommendation\ V.1, i.e.,\ tone ON for binary\ 1 and tone OFF for binary\ 0.
.PP
In a practical case this means that the voltage or no voltage
conditions which will result from the full wave rectification of the
demodulated line signal will correspond with the binary\ 1 and binary\
0 signals respectively at the output of the
scrambler
.
.PP
5.3
The amplitude of the theoretical line signal spectrum,
corresponding to binary symbol\ 1 appearing at the output of the scrambler,
is to be sinusoidal, with zeros and maxima at the frequencies listed below:
.LP
.ce
\fBH.T. [T1.36]\fR
.ps 9
.vs 11
.nr VS 11
.nr PS 9
.TS
center box;
cw(60p) | cw(60p) | cw(60p) .
T{
Data signalling rate
(kbit/s)
T} Zeros at (kHz) Maxima at (kHz)
_
.T&
cw(60p) | cw(60p) | cw(60p) .
64 68 and 100 84
.T&
cw(60p) | cw(60p) | cw(60p) .
48 76 and 100 88
.T&
cw(60p) | cw(60p) | cw(60p) .
56 72 and 100 86
.T&
cw(60p) | cw(60p) | cw(60p) .
72 64 and 100 82
_
.TE
.nr PS 9
.RT
.ad r
\fBTable [T1.36], p.\fR
.sp 1P
.RT
.ad b
.RT
.PP
5.4
In the 60\(hy108\ kHz band, amplitude distortion of the real
spectrum relative to the theoretical spectrum as defined under \(sc\ 5.3\
above is not to exceed \(+-\|1\ dB; the group delay distortion is not to
exceed
8\ microseconds. These two requirements are to be met for each frequency
band centred on one of the maxima mentioned in \(sc\ 5.3 and whose width
is equal to 80% of the frequency band used.
.bp
.LP
.PP
5.5
The nominal level of the line data signal should be \(em6\ dBm0. The actual
level should be within \(+-\|1\ dB of the nominal level.
.PP
5.6
A pilot carrier at the same frequency as the modulated carrier at the transmitter
and with a level of \(em9\ \(+-\ 0.5\ dB relative to the actual level
mentioned under \(sc\ 5.5\ above, should be added to the line signal. The
relative phase between the modulated carrier and the pilot carrier at the
transmitter
should be time invariant.
.sp 2P
.LP
\fB6\fR \fBGroup reference pilot\fR
.sp 1P
.RT
.PP
6.1
Provision should be made for facilitating the injection of a
group reference pilot of 104.08\ kHz from a source external to the modem.
.sp 9p
.RT
.PP
6.2
The protection of the group reference pilot should conform to
Recommendation\ H.52\ [1].
.sp 2P
.LP
\fB7\fR \fBVoice channel\fR
.sp 1P
.RT
.PP
7.1\fR
The service speech channel is an integral part of the
applications\ a) and e) of this system and is used on an optional basis. The
channel corresponds to channel\ 1 of a 12\(hychannel SSB\(hyAM system in the
104\(hy108\ kHz band (virtual carrier at 108\ kHz). It can transmit continuous
voice at a mean level of maximum \(em15\ dBm0 or pulsed signalling tones
according to the individual specifications.
.sp 9p
.RT
.PP
To avoid overloading of the system by peak signals a limiter shall be used
with cut\(hyoff levels above +3\ dBm0.
.PP
To avoid stability problems the channel shall be connected to 4\(hywire
equipment only.
.PP
For operator\(hyto\(hyoperator signalling Recommendation\ Q.1\ [2] shall be
followed, but instead of 500/20\ Hz a non\(hyinterrupted tone of 2280\
Hz at a level of \(em10\ dBm0 shall be used.
.PP
For other signalling purposes [application\ e)] the R1 or R2 inband
signalling, described in Recommendations\ Q.322\ [3], Q.323\ [4] and Q.454\
[5],
Q.455\ [6] respectively, is preferred.
.PP
The transmit filter shall be such that any frequency applied to the
transmit input terminals at a level of \(em15\ dBm0 will not cause a level
exceeding:
.RT
.LP
a)
\(em73\ dBm0p in the adjacent group,
.LP
b)
\(em61\ dBm0 in the vicinity (\(+-\|25\ Hz) of the pilot 104.08\ kHz,
.LP
c)
\(em55\ dBm0 in the data band between 64 and 101\ kHz,
.LP
d)
the values specified in Recommendation\ Q.414\ [7] to protect
the nearest low level signalling path.
.PP
The voice band is sufficiently protected if the same filter is
used in the receive direction of the channel. The attenuation/frequency
characteristic, measured between the voice\(hyfrequency input and the group
band output or the group band input and the voice\(hyfrequency output,
with respect to the value at 800\ Hz is limited by:
.LP
\(em1\ dB over the 300\(hy3400\ Hz band,
.LP
+2\ dB between 540 and 2280\ Hz.
.PP
7.2
The voice channel is inapplicable to applications\ b), c), d)
and\ f
). It is used on an optional basis for applications\ a) and\ e).
.PP
\fINote\fR \ \(em\ When the modem is installed at the repeater station,
the voice channel should be extended to the renter's premises.
.sp 2P
.LP
\fB8\fR \fBAdjacent channel interference\fR
.sp 1P
.RT
.PP
In the bands 36\(hy60 kHz and 108\(hy132 kHz, the adjacent channel
interference should conform to Recommendation\ H.52\ [1].
.RT
.sp 2P
.LP
\fB9\fR \fBLine characteristics\fR
.sp 1P
.RT
.PP
The modem is intended to operate satisfactorily over
group
links
according to reference\ [8] at data signalling rates of 48 up to
64\ kbit/s.
.PP
For group links, comprising more than three group sections, or where a
data signalling rate of 72\ kbit/s is required, the characteristics given
in reference\ [8] are not adequate.
.bp
.PP
Furthermore, compliance of a group link with reference\ [8] does not
necessarily guarantee proper operation of the modem, nor does noncompliance
imply improper operation.
.PP
In Annex A a method is presented to calculate the suitability of a
group link for data transmission using a modem according to this
Recommendation.
.PP
When an automatic adaptive equalizer is included in the modem, proper operation
over a circuit of similar construction as the
hypothetical
reference circuit
as specified in reference\ [9] will be possible at data
signalling rates up to 64\ kbits.
.PP
\fINote 1\fR \ \(em\ Reference\ [9] specifies a maximum number of\ 8
through\(hygroup filters
, but this figure is subject to further study
and possible amendment.
.PP
\fINote 2\fR \ \(em\ The modem may allow operation at 72 kbit/s over a
circuit having a maximum of 5\ through\(hygroup filters. This value is
left for further
study.
.RT
.LP
\fB10\fR \fBInterface\fR
.sp 1P
.RT
.sp 2P
.LP
10.1
\fIInterface for applications a), e) and f\fR \fI) indicated in\fR
\fI\(sc\ 1\fR
.sp 1P
.RT
.sp 1P
.LP
10.1.1
\fIList of\fR
\fIinterchange circuits\fR (See Table 1/V.36)
.sp 9p
.RT
.LP
.ce
\fBH.T. [T2.36]\fR
.ce
TABLE\ 1/V.36
.ps 9
.vs 11
.nr VS 11
.nr PS 9
.TS
center box;
cw(168p) | cw(60p) .
T{
Interchange circuit (see Note 1)
T} Remark
_
.T&
lw(24p) | lw(144p) | cw(60p) .
102 T{
Signal ground or commun return
T} See Note 2
.T&
lw(24p) | lw(144p) | cw(60p) .
102a DTE common return See Note 3
.T&
lw(24p) | lw(144p) | cw(60p) .
102b DCE common return See Note 3
_
.T&
lw(24p) | lw(144p) | cw(60p) .
103 Transmitted data
.T&
lw(24p) | lw(144p) | cw(60p) .
104 Received data
_
.T&
lw(24p) | lw(144p) | cw(60p) .
105 Request to send
.T&
lw(24p) | lw(144p) | cw(60p) .
106 Ready for sending
.T&
lw(24p) | lw(144p) | cw(60p) .
107 Data set ready
.T&
lw(24p) | lw(144p) | cw(60p) .
109 T{
Data channel received line signal detector
T}
_
.T&
lw(24p) | lw(144p) | cw(60p) .
113 T{
Trasmitter signal element timing (DTE source)
T}
.T&
lw(24p) | lw(144p) | cw(60p) .
114 T{
Trasmitter signal element timing (DCE source)
T}
.T&
lw(24p) | lw(144p) | cw(60p) .
115 T{
Receiver signal element timing (DCE source)
T}
_
.T&
lw(24p) | lw(144p) | cw(60p) .
140 Loopback/Maintenance test See Note 2
.T&
lw(24p) | lw(144p) | cw(60p) .
141 Local loopback See Note 2
.T&
lw(24p) | lw(144p) | cw(60p) .
142 Test indicator See Note 2
.TE
.LP
\fINote\ 1\fR
\ \(em\ When the modem is installed at the repeater station, this interface should appear at the customer's premises without restrictions regarding the
data signalling rate and the provision of the voice channel. The method to
achieve this is subject to national regulations.
.LP
\ \(em\ Equipment may be in service that does not implement these circuits.
.LP
\ \(em\ Interchange circuits 102a and 102b are required where the electrical characteristics defined in Recommendation\ V.10 are used.
.sp 1P
.RT
.ad b
.RT
.LP
.bp
.sp 1P
.LP
10.1.2
\fIElectrical characteristics\fR
.sp 9p
.RT
.PP
Use of electrical characteristics conforming to Recommendation\ V.10 and/or\
V.11 is recommended together with the use of the connector and pin
assignment plan specified by ISO\ 4902.
.RT
.LP
i)
Concerning circuits 103, 104, 113, 114 and 115, both the
generators and the receivers shall be in accordance with
Recommendation\ V.11.
.LP
ii)
In the case of circuits 105, 106, 107 and 109, generators
shall comply with Recommendation\ V.10 or alternatively
Recommendation\ V.11. The receivers shall comply with
Recommendation\ V.10, category\ 1 or V.11 without
termination.
.LP
iii)
In the case of all other circuits, Recommendation V.10
applies with receivers configured as specified by
Recommendation\ V.10 for category\ 2.
.PP
\fINote\fR \ \(em\ For an interim period the connector and
contact\(hyassignment plan specified in ISO\ 2593 and commonly referred
to as the \*QV.35 interface\*U may optionally be used. In this case electrical
characteristics may be either V.11 for circuits\ 103, 104, 113, 114 and\ 115
together with V.10 (receivers configured as specified in category\ 2) for all
other circuits, or V.35 Appendix\ II together with V.28 respectively.
.sp 1P
.LP
10.2
\fIInterface for applications b), c) and d) indicated in \(sc\ 1\fR
.sp 9p
.RT
.PP
For applications b), c) and d) the interface may comply with the
functional requirements given in reference\ [10] for the 64\ kbit/s interface.
In these cases, the electrical characteristics may comply with reference\
[11].
.PP
If an end\(hyto\(hyend transmission of the 8\ kHz timing signal is not
used, an 8\ kHz timing signal across the interface will not be supplied
nor utilized by the modem.
.PP
Alternatively the interface according to \(sc\ 10.1 may be used for
these applications.
.RT
.sp 2P
.LP
\fB11\fR \fBThreshold and \fR \fBresponse time of circuit\fR \fB109\fR
.sp 1P
.RT
.sp 1P
.LP
\fI\fR
11.1
\fIThreshold\fR
.sp 9p
.RT
.PP
For a data line signal level greater than \(em13 dBm0, circuit 109 is ON.
For data line signal level less than \(em18\ dBm0, circuit\ 109 is OFF.
.PP
\fINote\fR \ \(em\ The corresponding levels for the pilot carrier are \(em22
dBm0 and \(em27\ dBm0 respectively.
.PP
The condition of circuit 109 for levels between the above levels is
not specified, except that the signal detector shall exhibit a hysteresis
action such that the level at which the OFF to ON transition occurs is
at least 2\ dB greater than that for the ON to OFF transition. To measure
the thresholds of the detector, a modulated data signal with its pilot
carrier at the level
specified in \(sc\ 5.6 should be used.
.RT
.sp 1P
.LP
11.2
\fIResponse time\fR
.sp 9p
.RT
.PP
From OFF to ON: 15 ms to 150 ms,
.PP
From ON to OFF: \ 5 ms to \ 15 ms.
.PP
The response times of circuit 109 are the time intervals between the appearance
or disappearance of the line signal at the reception input terminal of
the modem and the occurrence of the corresponding ON or OFF condition on
circuit\ 109.
.PP
The line signal level should be within the range from 3 dB above the actual
threshold of the line signal detector at reception and the maximum
permissible level of the signal at reception.
.RT
.LP
.sp 2P
.LP
\fB12\fR \fBError performance\fR
.sp 1P
.RT
.PP
12.1
For a hypothetical reference circuit, 2500\ km in length, with characteristics
in accordance with Recommendation\ H.14\ [8], and with not more than two
through\(hygroup connection equipments, the performance objective in
terms of error rate should be not worse than 1\ error per 10\u7\d\ bits
transmitted. This is based on an assumed Gaussian noise power of 4\ pW per
km/per 4\ kHz band psophometrically weighted (this figure corresponds to
4\ pW0p/km).
.bp
.sp 9p
.RT
.sp 2P
.LP
\fB13\fR \fBAdditional information for the designer\fR
.sp 1P
.RT
.sp 1P
.LP
13.1
\fIInput level variation\fR
.sp 9p
.RT
.PP
The step\(hychange in the input level is, under normal conditions,
smaller than \(+-\|0.1\ dB. The gradual input level change is smaller than
\(+-\|6\ dB
and includes the tolerance of the transmitter output level.
.RT
.sp 1P
.LP
13.2
\fIInterference from adjacent group bands\fR
.sp 9p
.RT
.PP
A sinusoidal signal of +10\ dBm0 in the frequency bands of 36\(hy60\ kHz
and 108\(hy132\ kHz can appear together with the data line signal at the
input of the receiver.
\v'1P'
.RT
.LP
.ce 1000
ANNEX\ A
.ce 0
.ce 1000
(to Recommendation V.36)
.sp 9p
.RT
.ce 0
.ce 1000
\fBLine characteristics\fR
.sp 1P
.RT
.ce 0
.PP
For proper operation of the modem, the line characteristic of a
The interchange circuit table is valid for the main channel or the subchannel
interfaces.
.RT
.ce
\fBH.T. [T6.37]\fR
.ce
TABLE\ 6/V.37
.ps 9
.vs 11
.nr VS 11
.nr PS 9
.TS
center box;
cw(168p) | cw(60p) .
T{
Interchange circuit (see Note 1)
T} Remark
_
.T&
lw(24p) | lw(144p) | cw(60p) .
102 T{
Signal ground or common return
T} See Note 2
.T&
lw(24p) | lw(144p) | cw(60p) .
102a DTE commun return See Note 3
.T&
lw(24p) | lw(144p) | cw(60p) .
102b DCE common return See Note 3
_
.T&
lw(24p) | lw(144p) | cw(60p) .
103 Transmitted data
.T&
lw(24p) | lw(144p) | cw(60p) .
104 Received data
_
.T&
lw(24p) | lw(144p) | cw(60p) .
105 Request to send See Note 4
.T&
lw(24p) | lw(144p) | cw(60p) .
106 Ready for sending See Notes 4 and 5
.T&
lw(24p) | lw(144p) | cw(60p) .
107 Data set ready
.T&
lw(24p) | lw(144p) | cw(60p) .
109 T{
Data channel received line signal detector
T}
_
.T&
lw(24p) | lw(144p) | cw(60p) .
113 T{
Transmitter signal element timing
(DTE source)
T} See Note 4
.T&
lw(24p) | lw(144p) | cw(60p) .
114 T{
Transmitter signal element timing
(DCE source)
T}
.T&
lw(24p) | lw(144p) | cw(60p) .
115 T{
Receiver signal element timing
(DCE source)
T}
.T&
lw(24p) | lw(144p) | cw(60p) .
128 T{
Receiver signal element timing
(DTE source)
T}
_
.T&
lw(24p) | lw(144p) | cw(60p) .
140 Loop\(hyback/Maintenance test
.T&
lw(24p) | lw(144p) | cw(60p) .
141 Local loop\(hyback See Note 4
.T&
lw(24p) | lw(144p) | cw(60p) .
142 Test indicator See Note 6
.TE
.LP
\fINote\ 1\fR
\ \(em\ When the modem is installed at the repeater station, this interface should appear at the customer's premises without restrictions regarding the
data signalling rate and the provision of the voice channel. The method to
achieve this is subject to national regulations.
.LP
\fINote\ 2\fR
\ \(em\ The provision of this conductor is optional.
.LP
\fINote\ 3\fR
\ \(em\ Interchange circuits 102a and 102b are required where the
electrical characteristics defined in Recommendation\ V.10 are used.
.LP
\fINote\ 4\fR
\ \(em\ Not essential in subchannel.
.LP
\fINote\ 5\fR
\ \(em\ During the synchronization process of the main modem, the OFF
condition of circuit 106 is signalled at all port interface.
.LP
\fINote\ 6\fR
\ \(em\ Circuit 142 is present on all ports of the multiplexer, but may be activated on an individual port basis for individual port tests. All are
activated simultaneously for entire modem test.
.nr PS 9
.RT
.ad r
\fBTableau\ 6/V.37 [T6.37] et Remarques, p. 10\fR
.sp 1P
.RT
.ad b
.RT
.sp 1P
.LP
13.2
\fIElectrical characteristics\fR
.sp 9p
.RT
.PP
Use of electrical characteristics conforming to
Recommendation\ V.10 and/or V.11 is recommended together with the use of
the connector and pin assignment plan specified by ISO\ 4902.
.RT
.LP
i)
Concerning circuits 103, 104, 113, 114 and 115, both the
generators and the receivers shall be in accordance with
Recommendation\ V.11.
.LP
ii)
In the case of circuits 105, 106, 107 and 109, generators
shall comply with Recommendation\ V.10 or alternatively
Recommendation\ V.11. The receivers shall comply with
Recommendation\ V.10,
category\ 1, or\ V.11 without
termination.
.LP
iii)
In the case of all other circuits, Recommendation V.10
applies, with receivers configured as specified by
Recommendation\ V.10 for category\ 2.
.bp
.PP
\fINote\fR \ \(em\ For an interim period the connector and
contact\(hyassignment plan specified in ISO\ 2593 and commonly referred
to as the \*QV.35 interface\*U may optionally be used. In this case electrical
characteristics may be either V.11 for circuits\ 103, 104, 113, 114 and\ 115
together with V.10 (receivers configured as specified in category\ 2) for all
other circuits, or V.35 Appendix\ II together with V.28 respectively.
.LP
.sp 2P
.LP
\fB14\fR \fBOptional PCM interface alternative\fR
.sp 1P
.RT
.PP
The recommended data signalling rate is synchronous at 64 kbit/s.
.PP
For those synchronous networks requiring the end\(hyto\(hyend transmission
of both the 8\ kHz and 64\ kHz timing together with the data at 64\ kbit/s,
an
internal data signalling rate of 72\ kbit/s is suggested.
.PP
The corresponding data format shall be obtained by inserting one extra
bit\ (E) just before the first bit of each octet of the 64\ kbit/s data
stream.
.PP
The bits E convey
alignment and housekeeping information
,
according to the pattern shown in
Figure\ 1/V.37.
.RT
.LP
.rs
.sp 3P
.ad r
\fBFigure 1/V.37, p.\fR
.sp 1P
.RT
.ad b
.RT
.PP
The use of the
housekeeping bits
H is determined with
bilateral agreement between Administrations. When not used these bits should
be assigned the value\ 1. A framing strategy is not specified in this
Recommmendation.
.PP
When the transmission of the 8\ kHz timing is not required, the data
signalling rate may be 64\ kbit/s.
.PP
The interfaces shall comply with the functional requirements given in Recommendation\
G.703\ [4] for the 64\ kbit/s interface. The electrical
characteristics may comply with reference\ [5].
.PP
If an end\(hyto\(hyend transmission of an 8 kHz timing signal is not used,
an 8\ kHz timing across the interface will not be supplied nor utilized
by the modem.
.RT
.sp 2P
.LP
\fB15\fR \fBThreshold and \fR \fBresponse times of circuit\fR \fB 109\fR
.sp 1P
.RT
.sp 1P
.LP
15.1
\fIThreshold\fR
.sp 9p
.RT
.PP
For a data line signal level greater than \(em13 dBm0, circuit 109 is ON.
For a data line signal level less than \(em18\ dBm0, circuit\ 109 is OFF.
.PP
\fINote\fR \ \(em\ The corresponding levels for the pilot carrier are \(em22
dBm0 and\ \(em27\ dBm0 respectively.
.PP
The condition of circuit 109 for levels between the above levels is
not specified, except that the signal detector shall exhibit a hysteresis
action such that the level at which the\ OFF to\ ON transition occurs is at
least 2\ dB greater than that for the\ ON to\ OFF transition. To measure the
thresholds of the detector, a modulated data signal with its carrier and
timing pilots at the levels specified in \(sc\(sc\ 6.5 and\ 6.6 above should
be used.
.RT
.sp 1P
.LP
15.2
\fIResponse times\fR
.sp 9p
.RT
.PP
ON to OFF: 15 to 50 ms.
.PP
OFF to ON:
.RT
.LP
1)
For initial equalization, circuit 109 must be ON prior to
user data appearing on circuit\ 104.
.bp
.LP
2)
For re\(hyequalization during data transfer, circuit 109 will
be maintained in the ON condition. During this period,
circuit\ 104 may be clamped to the binary\ 1 condition.
.LP
3)
After a line signal interruption that lasts more than the ON
to\ OFF response time:
.LP
a)
when no new equalization is needed, the exact figure
is under study;
.LP
b)
when a new equalization is needed, circuit 109 must
be ON prior to user data appearing in circuit\ 104.
.PP
The response times of circuit 109 are the time intervals between the appearance
or disappearance of the line signal at the reception input
terminals of the modem and the occurrence of the corresponding\ ON or\ OFF
condition on circuit\ 109.
.PP
The line signal level should be within the range from 3\ dB above the actual
threshold of the line signal detector at reception and the maximum
permissible level of the signal at reception.
.RT
.sp 2P
.LP
\fB16\fR \fBResponse times of circuit 106\fR
.sp 1P
.RT
.PP
ON to OFF response time less than or equal to 2 ms
.PP
OFF to ON response time less than or equal to 2 ms.
.RT
.sp 2P
.LP
\fB17\fR \fBEqualizer\fR
.sp 1P
.RT
.PP
An
automatic adaptive equalizer
shall be provided in the
receiver.
.PP
The receiver shall incorporate a means of detecting loss of
equalization and initiating a synchronizing signal sequence in its associated
local transmitter.
.PP
The receiver shall incorporate a means of detecting a synchronizing
signal sequence from the remote transmitter and initiating a synchronizing
signal sequence in its associated local transmitter, which may be initiated
at any time during the reception of the synchronizing signal sequence.
.PP
Either modem can initiate the synchronizing signal sequence. The
synchronizing signal is initiated when the receiver has detected a loss of
equalization. Having initiated a
synchronizing signal
, the modem
expects a synchronizing signal from the remote transmitter.
.PP
If the modem does not receive a synchronizing signal from the remote transmitter
within a time interval equal to the maximum expected two\(hyway
propagation delay plus twice the synchronizing signal detection time, it
transmits another synchronizing signal.
.PP
If the modem fails to synchronize on the received signal sequence, it transmits
another synchronizing signal.
.PP
If a modem receives a synchronizing signal when it has not initiated a
synchronizing signal and the receiver properly synchronizes, it returns
only one synchronizing sequence.
.RT
.sp 2P
.LP
\fB18\fR \fBAdditional information for the designer\fR
.sp 1P
.RT
.sp 1P
.LP
18.1
\fIInput level variation\fR
.sp 9p
.RT
.PP
The step\(hychange in the input level is, under normal conditions,
smaller than \(+-\|0.1\ dB. The gradual input level change is smaller than
\(+-\|6\ dB
and includes the tolerance of the transmitter output level.
.RT
.sp 1P
.LP
18.2
\fIInterference from adjacent group bands\fR
.sp 9p
.RT
.PP
A sinusoidal signal of +10 dBm0 in the frequency bands of
36\(hy60\ kHz and 108\(hy132\ kHz can appear together with the data line
signal at
the input of the receiver.
.bp
.RT
.LP
.ce 1000
APPENDIX\ I
.ce 0
.ce 1000
(to Recommendation V.37)
.sp 9p
.RT
.ce 0
.ce 1000
\fBScrambling process\fR
.sp 1P
.RT
.ce 0
.LP
I.1
\fIDefinitions\fR
.sp 1P
.RT
.sp 1P
.LP
I.1.1
\fBapplied data bit\fR
.sp 9p
.RT
.PP
The data bit which has been applied to the scrambler but has not affected
the transmission at the time of consideration.
.RT
.sp 1P
.LP
I.1.2
\fBnext transmitted bit\fR
.sp 9p
.RT
.PP
The bit which will be transmitted as a result of scrambling the
applied data bit.
.RT
.sp 1P
.LP
I.1.3
\fBearlier transmitted bits\fR
.sp 9p
.RT
.PP
Those bits which have been transmitted earlier than the next
transmitted bit. They are numbered sequentially in reverse time order,
i.e.\ the first earlier transmitted bit is that immediately preceding the
next
transmitted bit.
.RT
.LP
.sp 1P
.LP
I.1.4
\fBadverse state\fR
.sp 9p
.RT
.PP
The presence of any one of certain repetitive patterns in the
earlier transmitted bits.
.RT
.sp 1P
.LP
I.2
\fIScrambling process\fR
.sp 9p
.RT
.PP
The binary value of the next transmitted bit shall be such as to
produce odd parity when considered together with the twentieth and third
earlier transmitted bits and the applied data bit unless an adverse state is
apparent, in which case the binary value of the next transmitted bit shall
be such as to produce even instead of odd parity.
.PP
An adverse state shall be apparent only if the binary values of the
\fIp\fR \s6th
.PS 10
and (
\fIp\fR \ +\ 8)
\s6th
.PS 10
earlier transmitted bits have not differed from one another when \fIp\fR
represents all the integers from\ 1 to\ \fIq\fR inclusive. The value of
\fIq\fR shall be such that, for
\fIp\fR \ =\ (\fIq\fR \ +\ 1), the \fIp\fR \s6th
.PS 10
and
(
\fIp\fR \ +\ 8)
\s6th
.PS 10
earlier transmitted bits had opposite
binary
values and \fIq\fR \ =\ (31\ +\ 32\ \fIr\fR ), \fIr\fR being 0 or any positive
integer.
.RT
.PP
At the time of commencement, i.e. when no earlier bits have been
transmitted, an arbitrary 20\(hybit pattern may be assumed to represent the
earlier transmitted bits. At this time also it may be assumed that the
.PP
\fIp\fR \s6th
.PS 10
and (
\fIp\fR \ +\ 8)
\s6th
.PS 10
earlier transmitted bits have had
the same binary value when \fIp\fR represents all the integers up to any
arbitrary value. Similar assumptions may be made for the descrambling process
at
commencement.
.RT
.PP
\fINote\ 1\fR \ \(em\ From this it can be seen that received data cannot
necessarily be descrambled correctly until at least 20\ bits have been
correctly received and any pair of these bits, separated from each other
by seven other bits have differed in binary value from one another.
.PP
\fINote\ 2\fR \ \(em\ It is not possible to devise a satisfactory test
pattern to check the operation of the
Adverse State Detector (ASD)
because of the large number of possible states in which the 20\ state
shift register
can be at the commencement of testing. For those modems in which it is
possible to bypass the scrambler and the descrambler and to strap the scrambler
to
function as a descrambler, the following method may be used. A\ 1\|:\|1 test
pattern is transmitted with the ASD of the scrambler bypassed. If the ASD of
the descrambler is functioning correctly the descrambled test pattern will
contain a single element error every 32\ bits, i.e.\ 180\|000\ errors per
minute
for a modem operating at 96\ kbit/s indicates that the descrambler is
.PP
functioning correctly. The operation of the ASD of the scrambler may be
checked in a similar manner with the
scrambler
strapped as a
descrambler
and the descrambler bypassed.
.RT
.PP
I.3
Figure I\(hy1/V.37 is given as an indication only, since with another
technique this logical arrangement might take another form.
.bp
.sp 9p
.RT
.LP
.rs
.sp 41P
.ad r
\fBFigure\ I\(hy1/V.37, p.12\fR
.sp 1P
.RT
.ad b
.RT
.sp 2P
.LP
\fBReferences\fR
.sp 1P
.RT
.LP
[1]
CCITT Recommendation \fICharacteristics of group links for the\fR
\fItransmission of wide\(hyspectrum signals\fR , Vol.\ III, Fascicle\ III.4,
Rec.\ H.14, \(sc\ 2.
.LP
[2]
CCITT Recommendation \fITransmission of wide\(hyspectrum signals (data,\fR
\fIfacsimile, etc.) on wideband group links\fR , Vol.\ III, Fascicle\ III.4,
Rec.\ H.52.
.LP
[3]
CCITT Recommendation \fICharacteristics of group links for the\fR
\fItransmission of wide\(hyspectrum signals\fR , Vol.\ III, Fascicle\ III.4,