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IMPORT
R:\\ART\\W INTERNATIONAL TELECOMMUNICATION UNION
MF\\ITU.WM
F \*
mergeforma
t
CCITT V.32 bis
THE INTERNATIONAL
TELEGRAPH AND TELEPHONE
CONSULTATIVE COMMITTEE
DATA COMMUNICATION
OVER THE TELEPHONE NETWORK
A DUPLEX MODEM OPERATING AT
DATA SIGNALLING RATES OF UP TO
14 400 bit/s FOR USE ON THE
GENERAL
SWITCHED TELEPHONE NETWORK AND
ON LEASED POINT-TO-POINT 2-WIRE
TELEPHONE-TYPE CIRCUITS
Recommendation V.32 bis
IMPORT Geneva, 1991
R:\\ART\\
WMF\\CCIT
TRUF.WMF
\*
mergeform
at
Printed in Switzerland
FOREWORD
The CCITT (the International Telegraph and Telephone Consultative
Committee) is a permanent organ of the International Telecommunication Union
(ITU). CCITT is responsible for studying technical, operating and tariff
questions and issuing Recommendations on them with a view to standardizing
telecommunications on a worldwide basis.
The Plenary Assembly of CCITT which meets every four years, establishes
the topics for study and approves Recommendations prepared by its Study Groups.
The approval of Recommendations by the members of CCITT between Plenary
Assemblies is covered by the procedure laid down in CCITT Resolution No. 2
(Melbourne, 1988).
Recommendation V.32 bis was prepared by Study Group XVII and was approved
under the Resolution No. 2 procedure on the 22 of February 1991.
___________________
CCITT NOTE
In this Recommendation, the expression "Administration" is used for
conciseness to indicate both a telecommunication Administration and a recognized
private operating agency.
F ITU 1991
All rights reserved. No part of this publication may be reproduced or utilized in
any form or by any means, electronic or mechanical, including photocopying and
microfilm, without permission in writing from the ITU.
PAGE BLANCHE
Recommendation V.32 bis
Recommendation V.32 bis
A DUPLEX MODEM OPERATING AT DATA SIGNALLING RATES OF UP TO
14 400 bit/s FOR USE ON THE GENERAL SWITCHED TELEPHONE
NETWORK AND ON LEASED POINT-TO-POINT 2-WIRE
TELEPHONE -TYPE CIRCUITS
1 Introduction
This modem is intended for use on connections on general switched
telephone networks (GSTNs) and on point-to-point 2-wire leased telephone-type
circuits. The principal characteristics of the modem are as follows:
a) duplex mode of operation on GSTN and point-to-point 2-wire leased
circuits;
b) channel separation by echo cancellation techniques;
c) quadrature amplitude modulation for each channel with synchronous line
transmission at 2400 symbols/s;
d) the following synchronous data signalling rates shall be implemented in
the modem:
ù 14 400 bit/s trellis coded,
ù 12 000 bit/s trellis coded,
ù 9600 bit/s trellis coded,
ù 7200 bit/s trellis coded,
ù 4800 bit/s uncoded;
e) compatibility with Recommendation V.32 modems at 9600 and 4800 bit/s;
f) exchange of rate sequences during start-up to establish the data
signalling rate;
g) a procedure to change the data signalling rate without retraining.
Note 1 ù On international GSTN connections that utilize circuits that are
in accord with Recommen-dation G.235 (16-channel terminal equipments), it may be
necessary to employ a greater degree of equalization within the modem than would
be required for use on most national GSTN connections.
Note 2 ù The transmit and receive rates in each modem shall be the same.
The possibility of asymmetric working remains for further study.
2 Line signals
2.1 Carrier frequency and modulation rate
The carrier frequency is to be 1800 ▒ 1 Hz. The receiver must be able to
operate with a maximum received frequency offset of up to ▒ 7 Hz.
The modulation rate shall be 2400 symbols/s ▒ 0.01%.
2.2 Transmitted spectrum
The transmitted power level must conform to Recommendation V.2. With
continuous binary ones applied to the input of the scrambler, the transmitted
energy density at 600 Hz and 3000 Hz shall be attenuated 4.5 ▒ 2.5 dB with
respect to the maximum energy density between 600 Hz and 3 000 Hz.
styleref head_footRecommendation V.32
bis PAGE9
2.3 Coding
2.3.1 Signal element coding for 14 400 bit/s
At 14 400 bits per second, the scrambled data stream to be transmitted is
divided into groups of six consecutive data bits. The first two bits in time Q1n
and Q2n in each group, where the subscript n designates the sequence number of
the group, are first differentially encoded into Y1n and Y2n according to
Table 1/V.32 bis. The two differentially encoded bits Y1n and Y2n are used as
input to a systematic convolutional encoder which generates a redundant bit Y0n
(see Figure 1/V.32 bis). This redundant bit and the six information-carrying bits
Y1n, Y2n, Q3n, Q4n, Q5n, Q6n are then mapped into the coordinates f the signal
element to be transmitted according to the signal space diagram shown in Figure 2
1/V.32 bis.
include 32b-T04ETABLE 1/V.32 bis
Differential quadrant coding with trellis coding
Inputs Previous outputs Outputs
Q1n Q2n Y1n-1 Y2n-1 Y1n Y2n
0 0 0 0 0 0
0 0 0 1 0 1
0 0 1 0 1 0
0 0 1
PAGE8 styleref head_footRecommendation V.32 bis
1 1 1
0 1 0 0 0 1
0 1 0 1 0 0
0 1 1 0 1 1
0 1 1 1 1 0
1 0 0 0 1 0
styleref head_footRecommendation V.32
bis PAGE9
1 0 0 1 1 1
1 0 1 0 0 1
1 0 1 1 0 0
1 1 0 0 1 1
1 1 0 1 1 0
1 1 1
PAGE8 styleref head_footRecommendation V.32 bis
0 0 0
1 1 1 1 0 1
2.3.2 Signal element coding for 12 000 bit/s
At 12 000 bits per second, the scrambled data stream to be transmitted is
divided into groups of five consecutive data bits. The first two bits in time Q1n
and Q2n in each group, where the subscript n designates the sequence number of
the group, are first differentially encoded into Y1n and Y2n according to
Table 1/V.32 bis. The two differentially encoded bits Y1n and Y2n are used as
input to a systematic convolutional encoder which generates a redundant bit Y0n
(see Figure 1/V.32 bis). This redundant bit and the five information-carrying
bits Y1n, Y2n, Q3n, Q4n, Q5n, are then mapped into the coordinates of t e signal
element to be transmitted according to the signal space diagram shown in Figure 2
2/V.32 bis.
styleref head_footRecommendation V.32
bis PAGE9
Figure 1/V.32 bis
Figure 2-1/V.32 bis
Figure 2-2/V.32 bis
2.3.3 Signal element coding for 9600 bit/s
At 9600 bits per second, the scrambled data stream to be transmitted is
divided into groups of four consecutive data bits. The first two bits in time Q1n
and Q2n in each group, where the subscript n designates the sequence number of
the group, are first differentially encoded into Y1n and Y2n according to
Table 1/V.32 bis. The two differentially encoded bits Y1n and Y2n are used as
input to a systematic convolutional encoder which generates a redundant bit Y0n
(see Figure 1/V.32 bis). This redundant bit and the four information-carrying
bits Y1n, Y2n, Q3n, Q4n, are then mapped into the coordinates of the signal
element to be transmitted according to the signal space diagram shown in Figure 2
3/V.32 bis.
2.3.4 Signal element coding for 7200 bit/s
At 7200 bits per second, the scrambled data stream to be transmitted is
divided into groups of three consecutive data bits. The first two bits in time
Q1n and Q2n in each group, where the subscript n designates the sequence number
of the group, are first differentially encoded into Y1n and Y2n according to
Table 1/V.32 bis. The two differentially encoded bits Y1n and Y2n are used as
input to a systematic convolutional encoder which generates a redundant bit Y0n
(see Figure 1/V.32 bis). This redundant bit and the three information-carrying
bits Y1n, Y2n, Q3n, are then mapped into the coordinates of the signal element to
be transmitt d according to the signal space diagram shown in Figure 2-
4/V.32 bis.
PAGE8 styleref head_footRecommendation V.32 bis
Figure 2-3/V.32 bis
Figure 2-4/V.32 bis
2.3.5 Signal element coding for 4800 bit/s
At 4800 bits per second, the scrambled data stream to be transmitted is
divided into groups of two consecutive data bits. The two bits Q1n and Q2n, where
Q1n is first in time, where the subscript n designates the sequence number of the
group, are first differentially encoded into Y1n and Y2n according to
Table 2/V.32 bis. The two differentially encoded bits Y1n and Y2n are then mapped
into the coordinates of the signal element to be transmitted according to the
signal space diagram shown in Figure 2-5/V.32 bis.
include 32b-T05ETABLE 2/V.32 bis
Differential quadrant coding for 4800 bit/s
Inputs Previous Phase Outputs Signal state
outputs quadrant for
Q1n Q2n Y1n-1 Y2n-1 change Y1n Y2n 4800 bit/s
0 0 0 0 +90░ 0 1 B
0 0 0 1 1 1 C
0
styleref head_footRecommendation V.32
bis PAGE9
0 1 0 0 0 A
0 0 1 1 1 0 D
0 1 0 0 0░ 0 0 A
0 1 0 1 0 1 B
0 1
PAGE8 styleref head_footRecommendation V.32 bis
1 0 1 0 D
0 1 1 1 1 1 C
1 0 0 0 +180░ 1 1 C
1 0 0 1 1 0 D
1 0 1
styleref head_footRecommendation V.32
bis PAGE9
0 0 1 B
1 0 1 1 0 0 A
1 1 0 0 +270░ 1 0 D
1 1 0 1 0 0 A
1 1 1 0
PAGE8 styleref head_footRecommendation V.32 bis
1 1 C
1 1 1 1 0 1 B
Figure 2-5/V.32 bis
3 DTE interface
When a standardized physical interface for the interchange circuits is not
present, the equivalent functionality of the circuits must still be provided (see
Table 3/V.32 bis).
include 32b-t06eTABLE 3/V.32 bis
Interchange circuit
No. Description
102 Signal ground or common return
103 Transmitted data
104 Received data
105 Request to send
styleref head_footRecommendation V.32
bis PAGE9
106 Ready for sending
107 Data set ready
108/1 or Connect data set to line Note 1
108/2 Data terminal ready Note 1
109 Data channel received line signal detector
113 Transmitter signal element timing (DTE source) Note 2
114 Transmitter signal element timing (DCE source) Note 3
115 Receiver signal element timing (DCE source) Note 3
125 Calling indicator
140 Loopback/maintenance
141 Local loopback
PAGE8 styleref head_footRecommendation V.32 bis
142 Test indicator
Note 1 ù This circuit shall be capable of operation as circuit 108/1 or
circuit 108/2 depending on its use. Operation of circuits 107 and 108/1
shall be in accordance with S 4.4 of Recommendation V.24.
Note 2 ù When the modem is not operating in a synchronous mode at the
interface, any signals on this circuit shall be disregarded. Many DTEs
operating in an asynchronous mode do not have a generator connected to this
circuit.
Note 3 ù When the modem is not operating in a synchronous mode at the
interface, this circuit shall be clamped to the OFF condition. Many DTEs
operating in an asynchronous mode do not terminate this circuit.
3.1 Synchronous interfacing
The modems shall accept synchronous data from the DTE on circuit 103 (see
Recommendation V.24) under control of circuit 113 or 114. The modem shall pass
synchronous data to the DTE on circuit 104 under the control of circuit 115. The
modem shall provide to the DTE, a clock on circuit 114 for transmit-data timing,
and a clock on circuit 115 for receive-data timing. The transmit-data timing may,
however, originate in the DTE and be transferred to the modem via circuit 113. In
some applications, it may be necessary to slave the transmitter timing to the
receiver timing inside the modem.
After the start-up and retrain sequences, circuit 106 must follow the
state of circuit 105 within 2 ms.
OFF to ON and ON to OFF transitions of circuit 109 should occur solely in
accordance with the operating sequences defined in S 5. Thresholds and response
times are inapplicable because a line signal detector cannot be expected to
distinguish wanted received signals from unwanted talker echos.
styleref head_footRecommendation V.32
bis PAGE9
3.2 Asynchronous character-mode interfacing
The modulation process operates synchronously. However, the modem may be
associated with an asynchronous to synchronous conversion entity interfacing to
the DTE in an asynchronous (or start-stop character) mode. The protocol for
conversion shall be in accordance with Recommendations V.14 or V.42. Other
facilities such as data compression may also be employed.
3.3 Electrical characteristics of interchange circuits
When a standardized physical interface is provided, the electrical
characteristics conforming to Recommendation V.28 will normally be used.
Alternatively, the electrical characteristics conforming to Recommendations V.10
and V.11 may be used. The connector and pole assignments specified by ISO 2110,
corresponding to the electrical characteristics provided, shall be used.
3.4 Fault condition on interchange circuits
The DTE shall interpret a fault condition on circuit 107 as an OFF
condition using failure detection type 1.
The DCE shall interpret a fault condition on circuits 105 and 108 as an
OFF condition using failure detection type 1.
All other circuits not referred to may use failure detection types 0 or 1.
Note ù See S 7 of Recommendation V.28 and S 11 of Recommendation V.10.
4 Scrambler and descrambler
A self-sychronizing scrambler/descrambler shall be included in the modem.
Each transmission direction uses a different scrambler. The method of allocating
the scramblers is described in S 4.1. According to the direction of transmission,
the generating polynomial is:
Call mode modem generating polynomial: (GPC) = 1 + xù18 + xù23, or
Answer mode modem generating polynomial: (GPA) = 1 + xù5 + xù23
At the transmitter, the scrambler shall effectively divide the message
data sequence by the generating polynomial. The coefficients of the quotients of
this division, taken in descending order, form the data sequence which shall
appear at the output of the scrambler. At the receiver, the received data
sequence shall be multiplied by the scrambler generating polynomial to recover
the message sequence.
4.1 Scrambler/descrambler allocation
On the general switched telephone network, the modem at the calling data
station (call mode) shall use the scrambler with the GPC generating polynomial
and the descrambler with the GPA generating polynomial. The modem at the
answering data station (answer mode) shall use the scrambler with the GPA
generating polynomial and the descrambler with the GPC generating polynomial. On
point-to-point leased circuits or when calls are established on the GSTN by
operators, call mode/answer mode designation will be by bilateral agreement
between Administrations or users and the scrambler/descrambler allocation will be
the same as used on the GSTN.
5 Operating procedures
5.1 Recommendation V.25 automatic answering sequence
The Recommendation V.25 automatic answering sequence shall be transmitted
from the answer mode modem on GSTN connections. The transmission of the sequence
may be omitted on point-to-point leased circuits. In this event, the modem shall
initiate transmission as in the retrain procedure specified in S 7.
PAGE8 styleref head_footRecommendation V.32 bis
5.2 Receiver conditioning signal
The receiver conditioning signal shall be used in the start-up and retrain
procedures defined in SS 6 and 7 below. The signal consists of three segments:
5.2.1 Segment 1, denoted by S in Figures 3/V.32 bis and 4/V.32 bis consists of
alternations between states A and B as shown in Figure 2-5/V.32 bis, for a
duration of 256 symbol intervals.
Figure 3/V.32 bis
5.2.2 Segment 2, denoted by eq \o(S,\s\up5(-)) in Figures 3/V.32 bis and
4/V.32 bis consists of alternations between states C and D as shown in Figu e 2-
5/V.32 bis, for a duration of 16 symbol intervals.
Note ù The transition from segment 1 to segment 2 provides a well-defined
event in the signal that may be used for generating a time reference in the
receiver.
styleref head_footRecommendation V.32
bis PAGE9
Figure 4/V.32 bis
5.2.3 Segment 3, denoted by TRN in Figures 3/V.32 bis and 4/V.32 bis, is a
sequence derived by scrambling binary ones at a data rate of 4800 bit/s with the
scrambler defined in S 4. During the transmission of this segment, the
differential quadrant encoding shall be disabled. The initial state of the
scrambler shall be all zeros, and a binary one applied to the input for the
duration of segment 3. Successive dibits are encoded onto transmitted signal
states.
The first 256 transmitted signal states are determined from the state of
the first bit occurring (in time) in each dibit. When this bit is ZERO, signal
state A is transmitted; when this bit is ONE, signal state C is transmitted.
Depending on whether the modem is in call or answer mode, the scrambler output
patterns and corresponding signal states will then begin as below, where the bits
and the signal states are shown in time sequence from left to right.
Call mode modem:
eq \a\al(GPC:, ) eq
\a\ac\co15\hs4(11,11,11,11,11,11,11,11,11,00,00,01,11,11,11,C,C,C,C,C,C,C,C,C,A,A
,A,C,C,C)
Answer mode modem:
eq \a\al(GPA:, ) eq
\a\ac\co15\hs4(11,11,10,00,00,11,11,10,00,00,11,10,01,11,11,C,C,C,A,A,C,C,C,A,A,C
,C,A,C,C)
Immediately after 256 such symbols, successive scrambled dibits are
encoded onto transmitted signal states in accordance with Table 4/V.32 bis
directly without differential encoding for the remainder of segment 3. The
duration of segment 3 shall be at least 1280 and not exceed 8192 symbol
intervals.
Segment 3 is intended for training the adaptive equaliser in the receiving
modem and the echo canceller in the transmitting modem.
include 32b-T01ETABLE 4/V.32 bis
Encoding for TRN segment
after the first 256 symbols
Dibit Signal state
00 A
01 B
11 C
10 D
5.3 Rate signal
The rate signal shall be us d in the start-up, retrain, and rate re-
negotiating procedures.
The rate signal consists of a whole number of repeated 16-bit binary
sequences, as defined in Table 5/V.32 bis, scrambled and transmitted at
4800 bit/s with dibits differentially encoded as in Table 2/V.32 bis. In the
start-up and retrain procedures (see SS 6 and 7), the differential encoder shall
be initialized using the final symbol of the transmitted TRN segment.
In the rate renegotiation procedure (see S 8), the differential encoder
shall be initialized using the final symbol of the transmitted preamble and the
scrambler shall be initialized to all zeros.
The first two bits and each successive dibit of the rate sequence shall be
encoded to form the transmitted signal states.
include 32b-T02ETABLE 5/V.32 bis
Coding of the rate signal
B B B B B B B B B B B B BB
0 1 2 3 4 5 6 7 8 9 10 11 1213
B B B
14 15
PAGE8 styleref head_footRecommendation V.32 bis
0 B B B
1 2 3 ╖ ╖
╖
0 0 0 0 1 - - 1 1 - - 1 -0
0 1 0 0 0 0
B0-B3, B7, B11, B15For synchronizing on a rate signal
B4 = 1 (Note 1)
B8 = 1 (Note 1)
B5 1 denotes that operation at 4800 bit/s rate is
enabled
B6 1 denotes that operation at 9600 bit/s rate is
enabled
B9 1 denotes that operation at 7200 bit/s rate is
enabled
B10 1 denotes that operation at 12 000 bit/s rate is
enabled
B12 1 denotes that operation at 14 400 bit/s rate is
enabled
B13, B14 = 0, 0 (Note 2)
Note 1 ù When B4 or B8 is set to zero, in a transmitted or received
rate signal, then interworking can proceed only in accordance with
Recommendation V.32.
Note 2 ù B13 and B14 shall be set to zero when transmitting and
ignored during the reception of a rate signal; they are reserved for
future definition by the CCITT and must not be used by manufacturers.
Note 3 ù B4-B6, B9-B10, B12 set to zero calls for a GSTN cleardown.
5.3.1 Detecting a rate signal
styleref head_footRecommendation V.32
bis PAGE9
The minimum requirement for detection is the receipt of two consecutive
identical 16-bit sequences each with bits B0-B3, B7, B11 and B15 conforming to
Table 5/V.32 bis.
5.3.2 Ending the rate signal
In order to mark the end of transmission of any rate signal other then R1
(see Figure 3/V.32 bis), the modem shall first complete the transmission of the
current 16-bit rate sequence, and then transmit one 16-bit sequence E, coded as
shown in Table 6/V.32 bis.
include 32b-T03ETABLE 6/V.32 bis
Coding of sequence E
B B B B B B B B B B B B BB
0 1 2 3 4 5 6 7 8 9 10 11 1213
B B
14 15
1 1 1 1 1 - - 1 1 - - 1 -0
PAGE8 styleref head_footRecommendation V.32 bis
0 1
B4-B12 as in Table 5/V.32 bis except the only data rate to be indicated
shall relate to the transmission of scrambled binary ones immediately following
signal E.
styleref head_footRecommendation V.32
bis PAGE9
6 Start-up procedure
The procedure for achieving synchronism between the calling modem and the
answering modem on international GSTN connections is shown in Figure 3/V.32 bis.
the procedure includes the estimating of round-trip delay from each modem, the
training of echo cancellers and receivers initially with half-duplex
transmissions, and the exchanging of rate signals for automatic bit-rate and mode
selection.
6.1 Call mode modem
After receiving the answer tone for a period of at least 1 s as specified
in Recommendation V.25, the modem shall be connected to line (see Note 1 below)
and shall condition the scrambler and descrambler in accordance with S 4.1.
The modem shall repetively transmit carrier state A as shown n Figure 2-
5/V.32 bis.
The modem shall be conditioned to detect (see Note 2 below) one of two
incoming tones at frequencies 600 ▒ 7 Hz and 3000 ▒ 7 Hz, and subsequently to
detect a phase reversal in that tone.
On detection of one such phase reversal, the modem shall be conditioned to
detect a second phase reversal in the same tone, start a counter/timer and change
to repetively transmitting state C as shown in Figure 2-5/V.32 bis. The time
delay between the reception of this phase reversal at the line terminals and the
transmitted AA to CC transition appearing at the line terminals shall be 64 ▒ 2
symbol periods.
On detection of a second phase reversal in the same incoming tone, the
modem shall stop the counter/timer and cease transmitting.
When the modem detects an incoming S sequence (see S 5.2), it shall
proceed to train its receiver, and then seek to detect at least two consecutive
identical 16-bit rate sequences as defined in Table 5/V.32 bis.
On detection of the rate signal (R1), the modem shall transmit an S
sequence for a period NT already estimated by the counter/timer.
After this period has expired (see Note 3 below), the modem shall transmit
the receiver conditioning signal as defined in S 5.2, starting with an S sequence
for 256 symbol intervals.
Transmission of the TRN segment of the receiver conditioning signal may be
extended in order to ensure a satisfactory level of echo cancellation (see Note 4
below).
After the TRN segment, the modem shall apply an ON condition to circuit
107 and transmit a rate signal (R2) in accordance with S 5.3 to indicate the
currently available data rates. R2 shall exclude rates not appearing in the
previously received rate signal R1. It is recommended that R2 take also account
of the likely receiver performance with the particular GSTN connection. If it
appears that satisfactory performance cannot be attained at any of the available
data rates, then R2 should be used to call for a GSTN cleardown in accordance
with Table 5/V.32 bis.
Transmission of R2 shall continue until an incoming rate signal R3 is
detected. The modem shall then, after completing its current 16-bit rate
sequence, transmit a single 16-bit sequence E in accordance with S 5.3.2
indicating the data rate called for in R3. If, however, R3 is calling for GSTN
cleardown in accordance with Table 5/V.32 bis, then the call modem shall
disconnect from line and effect a cleardown.
The modem shall then transmit continuous scrambled binary ones at the data
rate called for in R3. If trellis coding is to be used, the initial states of the
delay elements of the convolution encoder shown in Figure 1/V.32 bis shall be set
to zero.
On detecting an incoming 16-bit E sequence as defined in S 5.3.2, the
modem shall condition itself to receive data at the rate indicated by the
incoming E sequence. After a delay of 128 symbol intervals, it shall apply an ON
condition to circuit 109, and unclamp circuit 104.
The modem shall then enable circuit 106 to respond to the condition of
circuit 105 and be ready to transmit data.
6.2 Answer mode modem
On connection to line, the modem shall condition the scrambler and
descrambler in accordance with S 4.1, and transmit the Recommendation V.25 answer
sequence. Means, defined in Recommendation V.25, of disabling network cancellers
and/or truncating the answer tone may be employed.
After the Recommendation V.25 answer sequence, the modem shall transmit
alternate carrier states A and C as shown in Figure 2-5/V.32 bis.
After alternate states A and C have been transmitted for an even number of
symbol intervals greater than or equal to 128 and an incoming tone has been
detected at 1800 ▒ 7 Hz for 64 symbol periods (see Note 5 below), the modem shall
be conditioned to detect a phase reversal in the incoming tone, start a
PAGE8 styleref head_footRecommendation V.32 bis
counter/timer, and change to transmitting alternate carrier states C and A for an
even number of symbol intervals.
On detecting a phase reversal in the incoming tone, the modem shall stop
the counter/timer and, after transmitting a state A, revert to transmitting
alternate states A and C. The time delay between the reception of this phase
reversal at the line terminals and the transmitted CA to AC transition appearing
at the line terminals shall be 64 ▒ 2 symbol periods.
When an amplitude drop is detected in the incoming tone, the modem shall
cease transmitting for a period of 16 symbol intervals and then (see Note 3
below) transmit the receiver conditioning signal as defined in S 5.2.
Transmission of the TRN segment of the receiver conditioning signal may be
extended in order to ensure a satisfactory level of echo cancellation (see Note 4
below).
After the TRN segment, the modem shall transmit a rate signal (R1) in
accordance with S 5.3 to indicate the data rates currently available in the
answer modem and associated DTE.
On detection of an incoming S sequence, the modem shall cease
transmitting.
The modem shall wait for a period MT already estimated by the
counter/timer and then, if an incoming S sequence persists, or when an S sequence
reappears (see Note 3 below), the modem shall proceed to train its receiver.
After training its receiver, the modem shall seek to detect at least two
consecutive identical incoming 16-bit rate sequences as defined in S 5.3.
On detection of a rate signal (R2), the modem shall apply an ON condition
to circuit 107 and transmit a second receiver conditioning signal as defined in
S 5.2.
After the TRN segment, the modem shall transmit a second rate signal (R3)
in order to indicate the data rate to be used by both modems. The data rate
selected by R3 shall be within those indicated by R2. It is recommended that R3
take also account of the likely performance of the answer modem receiver with the
particular GSTN connection established. If R2 is calling for a GSTN cleardown
(see Table 5/V.32 bis) and/or if it appears that satisfactory performance cannot
be attained by the answer modem at any of the available data rates, then R3
should call for a GSTN cleardown, in accordance with Table 5/V.32 bis (see Note 6
below).
When the modem detects an incoming 16-bit E sequence as defined in
S 5.3.2, it shall condition itself to receive data at the rate indicated by the
E sequence.
The modem shall complete the current 16-bit rate sequence and then
transmit a single 16-bit E sequence indicating the data rate to be used in the
subsequent transmission of scrambled binary ones. If trellis coding is to be
used, then the initial states of the delay elements of the convolution encoder
shown in Figure 1/V.32 bis shall be set to zero.
The modem shall transmit scrambled binary ones for 128 symbol intervals,
then enable circuit 106 to respond to the condition of circuit 105 and be ready
to transmit data.
The modem shall also apply an ON condition to circuit 109 and unclamp
circuit 104.
styleref head_footRecommendation V.32
bis PAGE9
Notes to S 6
Note 1 ù Once an incoming tone is detected at 600 ▒ 7 Hz or 3000 ▒ 7 Hz,
the calling modem may proceed with the start-up sequence even if no 2100 Hz tone
has been detected.
Note 2 ù In some cases, the incoming tones may be preceded by a special
pattern which may last up to 3100 ms.
Note 3 ù The TRN segment in the receiver conditioning signal is suitable
for training the echo canceller in the transmitting modem. Alternatively, it is
acceptable to precede the receiver conditioning signal by a sequence which can be
used specially for training the echo canceller, but which need not be defined in
detail in the Recommendation. The echo cancellation sequence (if used) must
maintain energy transmitted to line to hold network echo control devices disabled
(as required). In order to avoid confusion with Segments 1 or 2 of the receiver
conditioning signal defined in S 5.2, the echo cancellation sequence shall
produce a transmitted signal such that the sum of its power in the three 200 Hz
bands centred at 600 Hz, 1800 Hz and 3000 Hz is at least 1 dB less than its power
in the remaining bandwidth. This applies for the relative power averaged over any
6 ms time interval. The duration of this signal must not exceed 8192 symbol
intervals.
Note 4 ù Manufacturers are cautioned that a period of 650 ms is needed for
training any network echo cancellers conforming to Recommendation G.165, that may
be encountered on GSTN connections.
Note 5 ù The answering modem may disconnect from the line if the
1800 ▒ 7 Hz tone is not detected following transmission of the segment AC.
However, to assure compatibility with manual originating data stations, it shall
not disconnect for at least 3 seconds after the segment AC has been transmitted.
Note 6 ù If R3 is calling for a GSTN cleardown, the modem shall repeat the
transmission of signal R3 for not less than 64 symbol intervals before clearing
the connection.
7 Retrain procedure
A retrain may be initiated during data transmission if either modem
incorporates a means of detecting unsatisfactory signal reception.
Figure 4a)/V.32 bis shows a retrain event initiated by the calling modem and
Figure 4b)/V.32 bis shows a retrain event initiated by the answering modem. The
procedure is as follows:
7.1 Call mode modem
Following detection of unsatisfactory signal reception or detection of one
of two tones at frequencies 600 ▒ 7 Hz and 3000 ▒ 7 Hz for more than 128 symbol
intervals, the modem shall turn OFF circuit 106, clamp circuit 104 to binary one
and repetively transmit carrier state A as shown in Figure 2-5/V.32 bis. It shall
then proceed in accordance with S 6.1 beginning with the third paragraph.
7.2 Answer mode modem
Following detection of unsatisfactory signal reception or detection of a
tone of frequency 1800 ▒ 7 Hz for more than 128 symbol intervals the modem shall
turn OFF circuit 106, clamp circuit 104 to binary one and transmit alternate
carrier states A and C for an even number of symbol intervals not less than 128.
It shall then proceed in accordance with S 6.2 beginning with the third
paragraph.
7.3 Operation of circuits 107 and 109 during retrain procedure
Circuit 107 shall be maintained in the ON condition during the retrain
procedure.
Circuit 109 shall be maintained in the ON condition except that the OFF
condition may optionally be applied if transmission of the AA segment in the call
modem or of the first AC segment in the answer modem continues for a period
exceeding 45 seconds. If the retrain procedure is subsequently completed, the ON
condition shall be re-applied to circuit 109 at the time that circuit 104 is
unclamped.
PAGE8 styleref head_footRecommendation V.32 bis
8 Rate renegotiating procedure
The following procedure shall be provided to enable modems to change their
data signalling rate without retraining. Either modem may transmit a proposal for
a desired data signalling rate. The proposal comprises a preamble followed by a
rate code.
The preamble transmitted by the call mode modem consists of signal AA for
a period of 56T followed by signal CC for a period 8T. The preamble transmitted
by the answer mode modem consists of signal AC for a period 56T followed by
signal CA for a period 8T.
The rate signal is as defined in S 5.3. The initial state of the scrambler
shall be all zeros and the differential encoder shall be initialized using the
final symbol of the transmitted preamble.
The rate renegotiating procedure is shown in Figure 5/V.32 bis.
Figure 5a)/V.32 bis shows the procedure as initiated by the calling modem; Figure
5b)/V.32 bis shows the procedure as initiated by the answering modem.
8.1 Initiating procedure
Rate renegotiation may be initiated at any time during data transmission.
When a data signalling rate change is desired, the initiating modem shall
turn circuit 106 OFF and transmit the appropriate preamble followed by a rate
signal R4. R4 shall indicate the desired rate in the initiating modem and all
lower data signalling rates at which the initiating modem is enabled to operate.
Following detection of the preamble (this might occur during the
transmission of a preamble if both modems initiate the procedure almost
simultaneously), the initiating modem shall clamp circuit 104 to binary one and
condition its receiver to detect rate signal R5.
On detection of rate signal R5, the initiating modem shall condition its
receiver to detect sequence E. Then, when R4 has been transmitted for a minimum
of 64T, it shall complete the current 16-bit rate signal R4 and transmit sequence
E in accordance with S 5.3.2 indicating the highest data signalling rate common
to R4 and R5 (see Notes 1, 2 below). The initiating modem shall then transmit
scrambled binary ones at this data signalling rate for 24T. The initial state of
the convolutional encoder delay elements shall be zero. The initiating modem
shall then enable circuit 106 to respond to the condition of circuit 105 and be
ready to transmit data (see Note 3 below).
On detecting sequence E, the initiating modem shall condition itself to
receive data at the highest data signalling rate common to both R4 and R5 and,
after a delay of 24T, shall unclamp circuit 104.
8.2 Responding procedure
A modem shall be conditioned to detect an incoming preamble at any time
while receiving data.
When a preamble is detected, the responding modem shall clamp circuit 104
to binary one and shall condition its receiver to detect rate signal R4. On
detection of R4, the responding modem shall turn circuit 106 OFF and shall
transmit the appropriate preamble.
Following the transmission of the preamble, the responding modem shall
begin transmitting signal R5. R5 shall indicate the desired rate in the
responding modem and all lower data signalling rates at which the responding
modem is enabled to operate irrespective of the rates indicated in R4 (see
Note 2 below).
After R5 has been transmitted for a period of 64T, the responding modem
shall transmit sequence E in accordance with S 5.3.2 indicating the highest
signalling rate common to R4 and R5 (see Note 2 below). The modem shall then
transmit scrambled binary ones at this data signalling rate for 24T. The initial
state of the convolutional encoder delay elements shall be zero. The responding
modem shall then enable circuit 106 to respond to the condition of the
circuit 105 and be ready to transmit data.
On detecting sequence E, the responding modem shall condition itself to
receive data at the highest data signalling rate common to both R4 and R5 and,
after a delay of 24T, it shall unclamp circuit 104.
styleref head_footRecommendation V.32
bis PAGE9
Figure 5/V.32 bis
Notes to S 8
Note 1 ù If the highest data signalling rate indicated in R5 is less than
the desired rate requested in R4, this may be either because line conditions do
not permit the responding modem to operate currently at the desired rate or
because this rate has been disabled in the responding modem. Both possibilities
should be taken into account in determining the desirability of further rate
renegotiation.
Note 2 ù If R4 or R5 is calling for a GSTN cleardown in accordance with
Table 5/V.32 bis or R4 and R5 have no rates in common, the modem shall complete
the renegotiation procedure by repeating the transmission of sequence E for not
less than 64T before clearing the connection.
Note 3 ù If an attempt by the initiating modem to complete the rate
renegotiation procedures is unsuccessful, it might be that the responding modem
is a V.32 type modem that uses B4 for other purposes. The initiating modem should
take this into consideration before attempting further rate renegotiation
procedures.
9 Testing facilities
Test loops 2 and 3 as defined in Recommendation V.54 shall be provided.
Provision for test loop 2 shall be as specified for point-to-point circuits.
ANNEX A
(to Recommendation V.32 bis)
Considering that there is a need for some V.32/V.32 bis modems to include
the capability of interworking with V.22 and V.22 bis modems, the following start
up procedures are recommended. A modem which includes this optional capability
will be referred to as an automode modem.
A.1 Definition of terms used
ANS The 2100 Hz answer tone defined in Recommendation V.25;
USB1 Unscrambled binary ones modulated by an answering modem as defined
in Recommen-dation V.22 bis;
SB1 Scrambled binary ones modulated as defined in
Recommendation V.22 bis;
S1 Unscrambled double dibit 00 and 11 modulated as defined in
Recommendation V.22 bis;
AA See Figures 4/V.32 and 3/V.32 bis;
AC See Figures 4/V.32 and 3/V.32 bis.
A.2 Interworking of duplex modems
Modems conforming with Recommendations V.22 (operating at 1200 bit/s
only), V.22 bis, V.32 and V.32 bis could interwork with a dedicated automode
modem implementing a procedure for sensing the capabilities of a remote modem and
employing the appropriate modulation scheme.
The procedure can follow two courses. The calling modem makes a decision
as to whether its signal AA was detected by the answering modem during the V.25
answer sequence. If the decision indicates that signal AA was detected, the
course followed is as depicted in Figure A-1/V.32 bis. Otherwise the course
followed is as depicted in Figures A-2/V.32 bis and A-3/V.32 bis. Interworking
with calling V.22 bis or V.22 modems is as depicted in Figure A-4/V.32 bis.
PAGE8 styleref head_footRecommendation V.32 bis
A.2.1 Operation of the calling automode modem
On connection to line, the calling modem shall initially remain silent and
shall condition its receiver to detect any of three signals: AC, USB1, ANS.
A.2.1.1 If signal AC is detected, the modem shall begin transmission of
signal AA and continue as defined in S 6.1 of this Recommendation.
A.2.1.2 If signal USB1 is detected, the modem shall start a timer.
When the elapsed time exceeds Tc, where Tc > 3100 ms, if signal USB1 is
again detected, the modem shall first transmit signal S1 in the low band then
begin transmitting signal SB1 and then continue with Recommendation V.22 bis
beginning at S 6.3.1.1.1c) of Recommendation /V.22 bis (see Note 1). If at any
time signal AC is detected, the modem shall continue as defined in S 6.1 of this
Recommendation.
A.2.1.3 If signal ANS is detected for a period of at least 1 second, the modem
shall begin transmission of signal AA, condition its receiver to prepare to
detect either signal USB1 or signal AC, and start a timer to measure the duration
of the remaining answer tone.
On the detection of the end of signal ANS, the timer is stopped. The timer
value shall not include the 75 ms silent period defined in Recommendation V.25.
If, following the 75 ms silent period, signal AC is detected, the modem
shall continue with the V.32 or V.32 bis training sequence beginning at S 6.1 of
this Recommendation. When signal USB1 is detected for 155 ▒ 10 ms (see Note 2),
subsequent procedures shall depend on the duration of signal ANS measured by the
timer. If the duration was greater than 800 ms, the modem shall first stop
transmitting AA, then, after 456 ms silent period, shall transmit signal S1 in
the low band then begin transmitting signal SB1 and then continue with
Recommendation V.22 bis beginning at S 6.3.1.1.1c) of Recommendation V.22 bis.
Otherwise, the modem shall proceed in accordance with S A.2.1.2.
A.2.2 Operation of the answering automode modem
On connection to line, the answering modem shall transmit the V.25 answer
sequence and condition its receiver to detect signal AA.
If signal AA is detected at any time during the transmission of the V.25
answer sequence, the modem shall continue as defined in S 6.2 of this
Recommendation at the second paragraph.
If signal AA is not detected during the transmission of the V.25 answer
sequence, the modem shall begin transmitting signal USB1, condition its receiver
to detect in the low band either of the two signals S1, SB1 and start a timer.
If either of the two signals S1, SB1 are detected in the low band, the
modem shall continue as defined in Recommendation V.22 bis beginning at
S 6.3.1.1.2b). Otherwise, when the elapsed time exceeds Ta, where
Ta = 3000 ▒ 50 ms (see Note 3), the modem shall proceed as defined in S 6.2 of
this Recommendation beginning at the second paragraph.
Note 1 ù There may be implementations of V.22 bis modems that terminate
the transmission of USB1 before the elapsed time exceeds Tc because
Recommendation V.22 bis does not specify a minimum timeout duration. These
implementations may not interwork with this procedure.
Note 2 ù There is a small possibility that some GSTN signalling systems
could produce brief interruptions in transmission during a period in which signal
AA may be inhibiting the effect of the 1800 Hz Rec. V.22 bis/V.22 guard tone
transmitted with signal USB1.
Note 3 ù The transmission of USB1 for this maximum duration is recommended
in order to avoid signal AC being received and possibly misinterpreted as a loss
of carrier by some implementations of V.22 bis modems. Some implementation
of 1984 and 1988 V.32 modems might be sensitive to more than 294 ms of USB1 (see
S 6, Note 2 of this Recommendation).
styleref head_footRecommendation V.32
bis PAGE9
Figure A-1/V.32 bis
Figure A-2/V.32 bis
Figure A-3/V.32 bis
Figure A-4/V.32 bis
PAGE8 styleref head_footRecommendation V.32 bis
