INTERNATIONAL TELECOMMUNICATION UNION
`
`)45 4
`
`TELECOMMUNICATION
`STANDARDIZATION SECTOR
`OF ITU
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`)45 4Recommendation6
`(Extract from the "LUE"OOK)
`
`Qualcomm Incorporated v. Rembrandt Wireless Techs. LP.
`IPR2020-00510
`Qualcomm Ex. 1057
`Page 1 of 16
`
`

`

`INTERNATIONAL TELECOMMUNICATION UNION
`
`)45 4
`
`TELECOMMUNICATION
`STANDARDIZATION SECTOR
`OF ITU
`
`6(cid:14)(cid:18)(cid:18)
`
`$!4!#/--5.)#!4)/.
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`)45 4Recommendation6(cid:14)(cid:18)(cid:18)
`(Extract from the "LUE"OOK)
`
`Page 1 of 16
`
`

`

`NOTES
`
`ITU-T Recommendation V.22 was published in Fascicle VIII.1 of the Blue Book. This file is an extract from
`1
`the Blue Book. While the presentation and layout of the text might be slightly different from the Blue Book version, the
`contents of the file are identical to the Blue Book version and copyright conditions remain unchanged (see below).
`
`In this Recommendation, the expression “Administration” is used for conciseness to indicate both a
`2
`telecommunication administration and a recognized operating agency.
`
`ª ITU 1988, 1993
`
`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 2 of 16
`
`

`

`Fascicle VIII.1 - V.22
`
`Recommendation V.22
`
`1200 BITS PER SECOND DUPLEX MODEM STANDARDIZED FOR USE IN THE GENERAL SWITCHED TELEPHONE
`NETWORKAND ON POINT-TO-POINT 2-WIRELEASED TELEPHONE-TYPE CIRCUITS
`
`(Geneva, 1980; amended at Malaga- Torremolinos, 1984; and at Melbourne, 1988)
`
`1
`
`Introduction
`
`This modem is intended for use on connections on General Switched Telephone Networks (GSTNs), and on
`1.1
`point-to-point circuits when suitably conditioned.
`
`The principal characteristics of this modem are as follows:
`
`a) duplex operation on 2-wire GSTN and point-to-point leased circuits,
`
`b) channel separation by frequency division,
`
`c) differential phase shift modulation for each channel with synchronous line transmission at 600 bauds
`(nominal),
`
`d) inclusion of a scrambler,
`
`e) inclusion of test facilities.
`
`Recognizing the wide range of application, this Recommendation provides for three alternative configurations.
`1.2
`The choice of alternative is a matter for the Administration concerned. The facilities given by the alternatives are:
`
`Alternative A
`
`1200 bit/s synchronous
`
` 600 bit/s synchronous (optional)
`
`Alternative B
`
`1200 bit/s synchronous
` 600 bit/s synchronous (optional)
`
`1200 bit/s start-stop
`
` 600 bit/s start-stop (optional)
`
`Alternative C
`
`1200 bit/s synchronous
` 600 bit/s synchronous (optional)
`1200 bit/s start-stop
` 600 bit/s start-stop (optional)
`
` as in Alternative A
`
`as in Alternative B
`
`An asynchronous mode having capability of handling 1200 bit/s start-stop and asynchronous data at up to
`300 bit/s.
`
`The selection of the asynchronous mode is made during the handshaking sequence (see § 6). This gives
`compatibility between Alternative B and Alternative C.
`
`Note - The possibility of transmitting low speed anisochronous data in Alternatives A and B is left for further
`
`study.
`
`Fascicle VIII.1 - V.22
`
`1
`
`Page 3 of 16
`
`(cid:254)(cid:253)(cid:252)
`(cid:254)(cid:239)(cid:253)(cid:239)(cid:252)
`

`

`2
`
`2.1
`
`Line signals
`
`Carrier and guard tone frequencies
`
`The carrier frequencies shall be 1200 ± 0.5 Hz for the low channel and 2400 ± 1 Hz for the high channel. A
`guard tone of 1800 Hz ± 20 Hz, to be transmitted only when the modem is transmitting in the high channel, may be
`disabled as a national option. An alternative guard tone of 550 ± 20 Hz may be incorporated as a national option. The
`question of international calls between countries requiring different guard tones is left for further study.
`
`2.2
`
`Data and guard tone line signal levels
`
`The 1800-Hz guard tone shall be at a level of 6 ± 1 dB below the level of the data power in the high channel.
`The level of the optional 550 Hz tone is for further study. The total power transmitted to line shall be in accordance with
`Recommendation V.2 and shall be the same for transmission in either channel. Because of the 1800-Hz guard tone, the
`power level of data signals in the high channel will be approximately 1 dB lower than data signals in the low channel.
`
`2.3
`
`Fixed compromise equalizer
`
`Fixed compromise equalization shall be incorporated in the modem. Such equalization shall be equally shared
`between transmitter and receiver. The characteristics of the equalizer shall be the responsibility of each Administration
`to recommend nationally. The possibility of producing compromise characteristics for international implementation is
`for further study.
`
`2.4
`
`Spectrum and group-delay characteristic
`
`After making allowance for the nominal specified compromise equalizer characteristic, the transmitted line
`signal shall have a frequency spectrum equivalent to the square root of a raised cosine shaping with a 75% roll-off and
`within the limits of Figure 1/V.22. Similarly, the group delay of the transmitter output shall be within ± 150
`microseconds over the frequency range 900 Hz-1500 Hz (low channel) and 2100 Hz-2700 Hz (high channel). These
`figures are provisional.
`
`FIGURE 1/V.22
`
`Amplitude limits for transmitted line signal (unequalized)
`
`2
`
`Fascicle VIII.1 - V.22
`
`Page 4 of 16
`
`

`

`2.5
`
`Modulation
`
`2.5.1
`
`Data signalling rates
`
`Alternatives A and B: The data signalling rate transmitted to line shall be 1200 bit/s or 600 bit/s ± 0.01% with a
`modulation rate of 600 baud ± 0.01%.
`
`Alternative C: In Modes i), ii), iii) and iv) (§ 4) the data signalling rates are as in Alternatives A and B. In
`Mode v), the data signalling rate transmitted to line shall be 1205 1 bit/s with a modulation rate of 602.5 ± 0.5 baud.
`Optionally in Mode v), the line rate shall be 1223 ± 2 bit/s with a modulation rate of 611.5 ± 1 baud.
`
`2.5.2
`
`Encoding of data bits
`
`2.5.2.1
`
`1200 bits per second
`
`The data stream to be transmitted shall be divided into groups of 2 consecutive bits (dibits). Each dibit shall be
`encoded as a phase change relative to the phase of the preceding signal element (see Table 1/V.22). At the receiver, the
`dibits shall be decoded and the bits reassembled in correct order. The left-hand digit of the dibit is the one occurring first
`in the data stream as it enters the modulator portion of the modem after the scrambler.
`
`TABLE 1/V.22
`
`Dibit values
`
`(1200 bit/s)
`
`Bit values
`
`(600 bit/s)
`
`Phase change
`
`(Modes i, ii, iii, iv)
`
`Phase change
`
`(Mode v)
`
`+ 90°
`
`0°
`
`+ 270°
`
`+ 180°
`
`+ 270°
`
`+ 180°
`
`+ 90°
`
`0°
`
`0 - 1 -
`
`00
`
`01
`
`11
`
`10
`
`Note - The phase change is the actual on-line phase shift in the transition region from the centre of one
`
`signalling element to the centre of the following signalling element.
`
`2.5.2.2
`
`600 bits per second
`
`Each bit shall be encoded as a phase change relative to the phase of the preceding signal element
`(see Table 1/V.22).
`
`2.6
`
`Received signal frequency tolerance
`
`Noting that the frequency tolerance of the transmitter carriers is ± 1 Hz or less, and assuming a maximum shift
`of ± 6 Hz in the connection, the receiver shall be able to accept errors of at least ± 7 Hz in the received frequencies.
`
`3
`
`3.1
`
`Interchange circuits
`
`Table of interchange circuits (Note 1 of Table 2/V.22)
`
`Essential and optional interchange circuits are listed in Table 2/V.22.
`
`Fascicle VIII.1 - V.22
`
`3
`
`Page 5 of 16
`
`

`

`TABLE 2/V.22
`
`Interchange circuits (Note 1)
`
`Interchange circuit
`
`Description
`
`No.
`
`102
`
`103
`
`104
`
`105
`
`106
`
`107
`
`Signal ground or common return
`
`Transmitted data
`
`Received data
`
`Request to send
`
`Ready for sending
`
`Data set ready
`
`108/1
`
`Connect data set to line
`
`108/2
`
`Data terminal ready
`
`109
`
`111
`
`113
`
`114
`
`115
`
`125
`
`140
`
`141
`
`142
`
`Data channel received line signal detector
`
`Data signalling rate selector (DTE source)
`
`Transmitter signal element timing (DTE source)
`
`Transmitter signal element timing (DCE source)
`
`Receiver signal element timing (DCE source)
`
`Calling indicator
`
`Loopback/maintenance test
`
`Local loopback
`
`Test indicator
`
`Notes
`
`Note 2
`
`Note 3
`
`Note 3
`
`Note 4
`
`Note 5
`
`Note 6
`
`Note 6
`
`Note 7
`
`Note 1 - All essential interchange circuits and any others which are provided shall comply with the functional and operational
`requirements of Recommendation V.24. All interchange circuits provided shall be properly terminated in the data terminal equipment
`and in the data circuit-terminating equipment in accordance with the appropriate Recommendation for electrical characteristics (see §
`3.5).
`
`Note 2 - Some automatic calling equipments are designed to emit a calling tone to line by turning ON circuit 105 to the calling
`modem. The general switched telephone network (GSTN) constant carrier handshake is such that no calling tone will be emitted by
`the V.22 modem when used with these equipments.
`
`Note 3 - This circuit shall be capable of operation as circuit 108/1 or 108/2 depending on its use.
`
`Note 4 - This circuit is optional if only the 1200 bit/s speed [modes i) and ii) as defined in §§ 4.1, 4.2 and 4.3] is provided in the
`modem. If the 600 bit/s speed [modes iii) and iv)] is also provided, this circuit is essential.
`
`Note 5 - When the modem is not operating in a synchronous mode 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 6 - When the modem is not operating in a synchronous mode, this circuit shall be clamped to the OFF condition. Many DTEs
`operating in an asynchronous mode do not terminate this circuit.
`
`Note 7 - This circuit is for use with the general switched telephone network only.
`
`4
`
`Fascicle VIII.1 - V.22
`
`Page 6 of 16
`
`

`

`3.2
`
`Circuits 106 and 109 response limes (see Table 3/V.22)
`
`Circuit 106 response times are from the application of an ON or OFF condition on circuit 105. See also § 6 for
`operating sequences.
`
`TABLE 3/V.22
`
`Constant
`carrier
`
`Controlled carrier
`
` 2 ms
`
` 2 ms
`
`210 to 275 ms
`
` 2 ms
`
`105 to 205 ms
`
`10 to 24 ms
`
`105 to 205 ms
`
`10 to 24 ms
`
`Circuit 106
`
`Circuit 109
`
`OFF to ON
`
`ON to OFF
`
`OFF to ON
`
`ON to OFF
`
`3.3
`
`Circuit 109 thresholds
`
`High channel threshold:
`greater than
`-43 dBm
`less than
`-48 dBm
`
`Low channel threshold:
`greater than
`-43 dBm
`less than
`-48 dBm
`
`circuit 109 ON
`circuit 109 OFF
`
`circuit 109 ON
`circuit 109 OFF
`
`The condition of circuit 109 between the ON and OFF 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 shall be at least 2 dB greater
`than for the ON to OFF transition.
`
`Circuit 109 thresholds are specified at the input to the modem excluding the effects of the compromise
`equalizer.
`
`Circuit 109 shall not respond to the 1800-Hz or 550-Hz guard tones, or the 2100-Hz (nominal) answer tone
`during the handshake sequence.
`
`Administrations are permitted to change these thresholds where transmission conditions are known.
`
`3.4
`
`Circuit 111 and data rate control
`
`Data rate selection may be by switch (or similar means) or by circuit 111 or a combination of both.
`
`The ON condition on circuit 111, where provided, shall select 1200 bit/s operation and the OFF condition shall
`select 600 bit/s operation.
`
`3.5
`
`Electrical characteristics of interchange circuits
`
`Use of electrical characteristics conforming to Recommendation V.28 is recommended together with the
`connector and pin assignment plan specified by ISO 2110.
`
`Note - Manufacturers may wish to note that the long-term objective is to replace electrical characteristics
`specified in Recommendation V.28, and that Study Group XVII has agreed that the work shall proceed to develop a
`more efficient, all-balanced, interface for the V-Series application which minimizes the number of interchange circuits.
`
`Fascicle VIII.1 - V.22
`
`5
`
`Page 7 of 16
`
`£
`£
`£
`

`

`3.6
`
`Fault condition of interchange circuits
`
`(See Recommendations V.28, § 7 for association of the receiver failure detection types.)
`
`3.6.1
`
`The DTE should interpret a fault condition on circuit 107 as an OFF condition using failure detection type 1.
`
`3.6.2
`type 1.
`
`The DCE should interpret a fault condition on circuits 105 and 108 as an OFF condition using failure detection
`
`3.6.3
`
`All other circuits not referred to above may use failure detection type 0 or 1.
`
`4
`
`Modes of operation over the DTE/DCE interface
`
`4.1
`
`Alternative A
`
`The modem can be configured for the following modes of operation:
`
`Mode i) 1200 bit/s ± 0.01% synchronous
`
`Mode iii) 600 bit/s ± 0.01% synchronous (optional).
`
`In these modes of operation, the modem shall accept synchronous data from the DTE on circuit 103 under
`control of circuit 113 or circuit 114. The data shall then be scrambled in accordance with § 5 and then passed to the
`modulator for encoding in accordance with § 2.5.2.
`
`In addition to standard V.24 transmitter timing arrangements, the modem shall provide capabilities to derive
`transmit signal element timing from receiver signal element timing.
`
`4.2
`
`Alternative B
`
`The modem can be configured for the following modes of operation:
`
`Mode i) 1200 bit/s ± 0.01% synchronous
`
`Mode ii) 1200 bit/s start-stop 8, 9, 10 or 11 bits per character
`
`(Mode iii) 600 bit/s ± 0.01% synchronous optional
`
`(Mode iv) 600 bit/s start-stop 8, 9, 10 or 11 bits per character
`
`optional
`
`The synchronous modes are as given in Alternative A.
`
`In the start-stop modes, the modem shall accept a data stream of start-stop characters from the DTE at a nominal
`rate of 1200 or 600 bits per second. The start-stop data to be transmitted shall be converted, in conformity with
`Recommendation V.14, to a synchronous data stream suitable for transmission in accordance with § 4.1
`
`Demodulated data shall be decoded in accordance with § 2.5.2, then descrambled in accordance with § 5 and
`then passed to the converter in conformity with Recommendation V.14 for regaining the data stream of start-stop
`characters.
`
`The intracharacter signalling rate provided to the DTE over circuit 104 shall be in the ranges given in
`Table 4/V.22 when operating in the basic or in the extended signalling rate ranges, respectively.
`
`6
`
`Fascicle VIII.1 - V.22
`
`Page 8 of 16
`
`(cid:254)(cid:253)(cid:252)
`

`

`TABLE 4/V.22
`
`Intracharacter signalling rate range
`
`Signalling rate range
`
`Data rate
`
`600 bit/s
`
`1200 bit/s
`
`Basic
`
`Extended
`
`600 to 606 bit/s
`
`600 to 614 bit/s
`
`1200 to 1212 bit/s
`
`1200 to 1227 bit/s
`
`4.3
`
`Alternative C
`
`The modem can be configured for the following modes of operation.
`
`Mode i) 1200 bit/s ± 0.01% synchronous
`
`Mode ii) 1200 bit/s start-stop 8, 9, 10 or 11 bits per character
`
`(Mode iii) 600 bit/s ± 0.01% synchronous optional
`
`(Mode iv) 600 bit/s start-stop 8, 9, 10 or 11 bits per character
`
`optional
`
`Mode v) An asynchronous mode having capability of handling 1200 bit/s start-stop and anisochronous data at
`up to 300 bit/s.
`
`Modes i) to iv) are as given in Alternative B.
`
`4.3.1
`
`Basic modes
`
`In Alternative C, the modem shall incorporate Modes i), ii), iii) and iv) given in Alternative B, plus Mode v), in
`which the modem transmitter sends data at a rate always greater than the input data rate, and thus disables the receiver
`buffer. The GSTN handshaking sequence allows automatic selection of Modes ii) or v). Modes i), iii) and iv) must be
`selected at installation. On leased circuits there is no automatic mode selection. The line encoding for specific dibit
`values is described in Table 1/V.22.
`
`4.3.2
`
`Transmitter
`
`In Mode v), the modem shall accept a data stream of start-stop characters from the DTE at a nominal rate of a 0
`to 300 bit/s or 1200 bit/s automatically. The transmitter buffer that converts incoming data to a synchronous data stream
`at 1205 bit/s or 1223 bit/s shall:
`
`a)
`
`b)
`
`c)
`
`start its asynchronous bit counter on either data transition,
`
`always transmit the last bit received over circuit 103 after the bit counter has elapsed,
`
`sample incoming data during the bit count at 1205 Hz or 1223 Hz depending upon line rate.
`
`This will assure that incoming data at 0 to 300 bit/s shall pass through the buffer with a maximum introduced
`distortion of 25% at 300 bit/s (and 12.5% at 150 bit/s), and that break signals pass through the buffer unchanged.
`
`The length and structure of incoming characters shall be the same as given in Alternative B. Within Mode v) at
`1200 bit/s asynchronous, two adjacent character formats, e.g. 9- and 10-bit character, can be handled automatically. As
`in Alternative B, the modem shall derive its line signal clock from internal clock circuits, or alternatively, from receiver
`signal element timing, as an installation option.
`
`Fascicle VIII.1 - V.22
`
`7
`
`Page 9 of 16
`
`(cid:254)(cid:253)(cid:252)
`

`

`4.3.3
`
`Basic signalling rate range
`
`In Mode v), the intracharacter signalling rate provided by the DTE on circuit 103 must be:
`
`1205 bit/s line rate
`
`0 to 301 bit/s and 1170 to 1204 bit/s
`
`1223 bit/s line rate
`
`0 to 305 bit/s and 1190 to 1221 bit/s
`
`Selection of line rate is made in the transmitter by installer option and automatically detected in the receiver.
`
`5
`
`Scrambler and descrambler
`
`5.1
`
`Scrambler
`A self synchronizing scrambler having the generating polynomial 1 ¯
` x-14¯
` x-17 shall be included in the
`modem transmitter. The message data sequence applied to the scrambler shall be effectively divided 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. The scrambler output data sequence
`
`where
`
`Ds
`
`Di
`
`.
`
`is the data sequence at the output of the scrambler
`
`is the data sequence applied to the scrambler
`
`denotes modulo 2 addition
`
`denotes binary multiplication
`
`Figure 2/V.22 shows a suitable implementation.
`
`To prevent occasional inadvertent instigation of remote loop 2 caused by scrambler lockup, circuitry shall be
`included to detect a sequence of 64 consecutive ones at the scrambler output (Ds) and, if detected, invert the next input
`to the scrambler, Di. This circuitry will not operate during handshaking or during the instigation of remote loop 2.
`
`Note 1 Marks (binary 1) and spaces (binary 0) at the V.24 interface correspond to ones and zeros, respectively, in this
`logic diagram.
`Note 2 Circuitry shall be included to detect a sequence of 64 consecutive binary ones at the scrambler output (Ds) and, if
`detected, invert the next input to the scrambler (Di).
`
`FIGURE 2/V.22
`
`Scrambler
`
`8
`
`Fascicle VIII.1 - V.22
`
`Page 10 of 16
`
`¯
`

`

`5.2
`
`Descrambler
`
`A self synchronizing descrambler having the polynomial 1 ¯
` x-14 ¯
` x-17 shall be provided in the modem
`receiver. The message data sequence produced after demodulation shall be effectively multiplied by the generating
`polynomial 1 ¯
` x-14 ¯
` x-17 to form the descrambled message. The coefficients of the recovered message sequence taken
`in descending order form the output data sequence Do, which is given by
`
`Figure 3/V.22 shows a suitable implementation.
`
`Note1 - Marks (binary 1) and spaces (binary 0) at the V.24 interface correspond to ones and zeros, respectively, in this logic
`
`diagram.
`
`Note 2 - Circuitry may be included to detect a sequence of 64 consecutive ones at the input to the descrambler (Ds) and, if
`detected, invert the next output from the descrambler,(Do).This detector should not begin operating until the handshaking
`sequence is complete. If this circuitry is included, detection of the initiation signal described in § 7.1.1 (unscrambled binary
`ones) should be performed at the point Do.
`
`FIGURE 3/V.22
`
`Descrambler
`
`6
`
`6.1
`
`Operating sequences
`
`Channel and operating mode selection
`
`On the general switched telephone network, the modem at the calling data station shall transmit in the low
`channel and receive in the high channel (call mode). The modem at the answering data station shall receive in the low
`channel and transmit in the high channel (answer mode).
`
`Where calls are established on the GSTN by operators, bilateral agreement between users on channel allocation
`will be necessary. On point-to- point leased circuits, channel allocation will be by bilateral agreement between
`Administrations or users. In these cases the method of selection of call or answer mode is a national matter.
`
`On point-to-point leased circuits, selection of Modes i) to v) will be by bilateral agreement between
`Administrations or users. The method of selection is a national matter.
`
`6.2
`
`V.25 automatic answering sequence
`
`The V.25 automatic answering sequence shall be transmitted from the answer mode modem on international
`GSTN connections. The transmission of the sequence may be omitted on point-to-point leased circuits or on national
`connections on the GSTN, where permitted by the Administration.
`
`Fascicle VIII.1 - V.22
`
`9
`
`Page 11 of 16
`
`

`

`6.3
`
`Operating sequences for Alternatives A and B
`
`6.3.1
`
`GSTN - constant carrier
`
`The means of achieving initial synchronism between the call mode modem and the answer mode modem on
`international GSTN connections is shown in Figure 4/V.22. The alternative handshake without V.25 automatic
`answering is shown in Figure 5/V.22.
`
`FIGURE 4/V.22
`
`Handshake sequence for Alternatives A and B (with V.25 auto-answering)
`
`10
`
`Fascicle VIII.1 - V.22
`
`Page 12 of 16
`
`

`

`FIGURE 5/V.22
`
`Handshake sequence for Alternatives A and B (without V.25 auto-answer sequence)
`
`6.3.1.1 Call mode modem
`
`Once the call mode modem has connected to line, it shall be conditioned to receive signals in the high channel
`and shall apply an ON condition to circuit 107 in accordance with Recommendation V.25. The modem shall remain
`silent until unscrambled binary 1 is detected for 155 ± 50 ms, and after waiting for 456 ± 10 ms shall transmit scrambled
`binary 1 in the low channel. Upon detecting scrambled binary 1 in the high channel in 270 ± 40 ms, the modem shall
`turn
`circuit 109 ON, then wait a further 765 ± 10 ms. Circuit 106 shall then respond to the condition of circuit 105 according
`to Table 3/V.22 constant carrier mode. When circuit 106 is OFF, circuit 103 shall be clamped to the binary 1 condition.
`
`Note - Manufacturers may wish to note that in certain countries, for national purposes, modems are in service
`which emit an answering tone of 2225 Hz instead of unscrambled binary 1.
`
`Fascicle VIII.1 - V.22
`
`11
`
`Page 13 of 16
`
`

`

`6.3.1.2 Answer mode modem
`
`Once the answer mode modem has connected to line and immediately following the V.25 answer sequence, the
`modem shall be conditioned to receive signals in the low channel. It shall then apply an ON condition to circuit 107 and
`transmit unscrambled binary 1. Upon detecting scrambled binary 1 or 0 in the low channel in 270 ± 40 ms, the modem
`shall transmit scrambled binary 1 in the high channel, and after waiting for 765 ± 10 ms, apply an ON condition to
`circuit 109. Circuit 106 shall then respond to the condition of circuit 105 according to Table 3/V.22, constant carrier
`mode. When circuit 106 is OFF, circuit 103 shall be clamped to the binary 1 condition.
`
`Where both modems are manually connected to line this sequence will apply irrespective of whether the call or
`answer mode modem is connected to line first.
`
`After completion of the handshake sequence, any inadvertent loss and reappearance of the received line signal
`should not cause another handshake sequence to be generated. Circuit 109 should respond with the response times given
`in Table 3/V.22.
`
`6.3.2
`
`GSTN and point-to-point leased circuits - controlled carrier
`
`Once an ON condition has been applied to circuit 105 by the DTE, the modem shall transmit a synchronizing
`signal corresponding to binary 1 applied to circuit 103. The ON condition shall be applied to circuit 106, 210 to 275 ms
`after starting to transmit the synchronizing signal. The receiving modem shall establish timing and descrambler
`synchronization and then turn circuit 109 ON in 105 to 205 ms.
`
`Each direction of transmission shall be independently controlled.
`
`Note - Controlled carrier operation on GSTN is optional. For circuits with echo suppressors, controlled carrier
`working is not recommended.
`
`6.4
`
`Operating sequence for Alternative C
`
`Refer to Figure 6/V.22.
`
`6.4.1
`
`GSTN - constant carrier
`
`6.4.1.1 Call mode modem
`
`If configured for Modes i), iii), or iv), the handshake sequence proceeds as for Alternative B. If configured for
`Mode v), the handshaking sequence shall automatically select Mode ii) or v). This sequence shall be as follows:
`
`Once the call mode modem has connected to line, it shall be conditioned to receive signals in the high channel
`and shall apply an ON condition to circuit 107 in accordance with Recommendation V.25. The modem shall remain
`silent until unscrambled binary 1 [Mode ii)] is detected for 155 ± 50 ms and after waiting for 456 ± 10 ms shall transmit
`scrambled binary 0 [Mode ii)] in the low channel. Upon detecting scrambled binary 1 [Mode ii)] in the high channel
`within 270 ± 40 ms, the modern shall turn circuit 109 ON, enter Mode ii), then wait a further 765 ± 10 ms. Upon
`detecting scrambled binary 1 [Mode v)] in the high channel in 270 ± 40 ms, the modem shall turn ON circuit 109, enter
`Mode v), then wait a further 765 ± 10 ms. Circuit 106 shall then respond to the condition of circuit 105 according to
`Table 3/V.22 constant carrier mode. When circuit 106 is OFF, circuit 103 shall be clamped to the binary 1 condition.
`
`See also the note in § 6.3.1.1.
`
`6.4.1.2 Answer mode modem, Mode v)
`
`Once the answer mode modem has connected to line and immediately following the V.25 answer sequence, the
`modem shall be conditioned to receive signals in the low channel. It shall then apply an ON condition to circuit 107 and
`transmit unscrambled binary 1 [Mode ii)].
`
`If scrambled binary 0 [Mode ii)] is detected in the low channel for 270 ± 40 ms, the modem shall enter Mode
`v), transmit scrambled binary 1 [Mode v)] in the high channel and after waiting for 765 ± 10 ms apply an ON condition
`to circuit 109.
`
`If scrambled binary 1 [Mode ii)] is detected in the low channel for 270 ± 40 ms, the modem shall enter Mode
`ii), transmit scrambled binary 1 [Mode ii)] in the high channel and after waiting for 765 ± 10 ms apply an ON condition
`to circuit 109.
`
`Circuit 106 shall respond to the condition of circuit 105 according to Table 3/V.22 constant carrier mode. When
`circuit 106 is OFF circuit 103 shall be clamped to the binary 1 condition.
`
`6.4.2
`
`GSTN and point-to-point leased circuits
`
`Controlled carrier operation as in § 6.3.2.
`
`12
`
`Fascicle VIII.1 - V.22
`
`Page 14 of 16
`
`

`

`FIGURE 6/V.22
`
`Handshake sequence for Alternative C (without V.25 auto-answer sequence)
`
`Fascicle VIII.1 - V.22
`
`13
`
`Page 15 of 16
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`

`

`7
`
`7.1
`
`Testing facilities
`
`Test loops
`
`Test loops 2 (local and remote) and 3 as defined in Recommendation V.54 shall be provided. Interface operation shall be
`as defined in Recommendation V.54. Instigation and termination sequences are not compatible with Recommendation
`V.54.
`
`7.1.1
`
`Instigation of remote loop 2
`
`Signals controlling the application of remote loop 2 may only be transmitted after the synchronizing andshake
`has been completed.
`
`As in Recommendation V.54, the modems are referred to as modem A and modem B.
`
`When modem A is instructed to instigate a remote loop 2, the modem shall transmit an initiation signal of
`unscrambled binary 1.
`
`Modem B shall detect 154-231 ms of the initiation signal, and then transmit to modem A scrambled alternate
`binary ones and zeros (reversals) at 1200 bit/s (or 600 bit/s).
`
`Modem A shall detect 231-308 ms of scrambled reversals, cease transmission of the initiation signal, and then
`transmit scrambled binary 1 at 1200 bit/s (or 600 bit/s).
`
`Modem B shall detect the loss of initiation signal and activate loop 2 within modem B.
`
`Modem A, upon receiving 231-308 ms of scrambled binary 1 shall indicate to the DTE that it may begin
`sending test messages.
`
`7.1.2
`
`Termination of remote loop 2
`
`When modem A is instructed to terminate a remote loop 2, the line signal shall be suppressed for a period of
`77 ± 10 ms, after which transmission shall be restored.
`
`Modem B detects the loss of line signal in 17 ± 7 ms and detects the reappearance of the signal within
`155 ± 50 ms, after which it returns to normal operation.
`
`7.2
`
`Self tests
`
`7.2.1
`
`Self test end-to-end
`
`Upon activation of the self-test switch an internally generated data pattern of alternate binary ones and zeros
`(reversals) at the selected bit rate shall be applied to the scrambler. An error detector, capable of identifying errors in a
`stream of reversals shall be connected to the output of the descrambler. The presence of errors shall be indicated by a
`visual indicator. All generating interchange circuits except 114 (if used), 115 and 142 shall be clamped to the binary 1 or
`OFF condition. If circuit 113 is used, the DCE shall disregard this interchange circuit and use its internal clock.
`
`7.2.2
`
`Self test with loop 3
`
`Loop 3 shall be applied to the modem as defined in Recommendation V.54. The self-test switch shall be
`activated and DCE operation shall be as in § 7.2.1.
`
`7.2.3
`
`Self test with remote loop 2
`
`The modem shall be conditioned to instigate a loop 2 at the remote modem as specified in § 7.1. The self-test
`switch shall be activated and DCE operation shall be as in § 7.2.1.
`
`It shall be possible to perform the above tests (§§ 7.2.1, 7.2.2 and 7.2.3) with or without the DTE connected to
`the modem. These tests employ an internally generated data pattern that is controlled by a switch on the DCE.
`
`During any self-test mode, interchange circuits 103, 105 and 108 will be ignored. Note that self tests do not
`7.2.4
`test asynchronous-to-synchronous converter circuits in either the transmitter or receiver.
`
`Note - Inclusion of remote loop signalling according to Recommendation V.54 is for further study.
`
`14
`
`Fascicle VIII.1 - V.22
`
`Page 16 of 16
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`