1、INTERNATIONAL TELECOMMUNICATION UNION)45G134 6 TELECOMMUNICATIONSTANDARDIZATION SECTOROF ITU$!4!G0G0#/-5.)#!4)/./6%2G0G04(%G0G04%,%0(/.%G0G0.%47/2+G0G0“)43G0G00%2G0G03%#/.$G0G0$50,%8G0G0-/$%-34!.$!2$):%$G0G0 amended at Malaga- Torremolinos, 1984; and at Melbourne, 1988)1 Introduction1.1 This modem i
2、s intended for use on connections on General Switched Telephone Networks (GSTNs), and onpoint-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 frequenc
3、y 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.1.2 Recognizing the wide range of application, this Recommendation provides for three alternative configurations.The
4、 choice of alternative is a matter for the Administration concerned. The facilities given by the alternatives are:Alternative A1200 bit/s synchronous600 bit/s synchronous (optional)Alternative B1200 bit/s synchronous 600 bit/s synchronous (optional)as in Alternative A1200 bit/s start-stop600 bit/s s
5、tart-stop (optional)Alternative C1200 bit/s synchronous 600 bit/s synchronous (optional)1200 bit/s start-stop600 bit/s start-stop (optional)as in Alternative BAn asynchronous mode having capability of handling 1200 bit/s start-stop and asynchronous data at up to300 bit/s.The selection of the asynchr
6、onous mode is made during the handshaking sequence (see 6). This givescompatibility between Alternative B and Alternative C.Note - The possibility of transmitting low speed anisochronous data in Alternatives A and B is left for furtherstudy.2 Fascicle VIII.1 - V.222 Line signals2.1 Carrier and guard
7、 tone frequenciesThe carrier frequencies shall be 1200 0.5 Hz for the low channel and 2400 1 Hz for the high channel. Aguard tone of 1800 Hz 20 Hz, to be transmitted only when the modem is transmitting in the high channel, may bedisabled as a national option. An alternative guard tone of 550 20 Hz m
8、ay be incorporated as a national option. Thequestion of international calls between countries requiring different guard tones is left for further study.2.2 Data and guard tone line signal levelsThe 1800-Hz guard tone shall be at a level of 6 1 dB below the level of the data power in the high channel
9、.The level of the optional 550 Hz tone is for further study. The total power transmitted to line shall be in accordance withRecommendation V.2 and shall be the same for transmission in either channel. Because of the 1800-Hz guard tone, thepower level of data signals in the high channel will be appro
10、ximately 1 dB lower than data signals in the low channel.2.3 Fixed compromise equalizerFixed compromise equalization shall be incorporated in the modem. Such equalization shall be equally sharedbetween transmitter and receiver. The characteristics of the equalizer shall be the responsibility of each
11、 Administrationto recommend nationally. The possibility of producing compromise characteristics for international implementation isfor further study.2.4 Spectrum and group-delay characteristicAfter making allowance for the nominal specified compromise equalizer characteristic, the transmitted linesi
12、gnal shall have a frequency spectrum equivalent to the square root of a raised cosine shaping with a 75% roll-off andwithin the limits of Figure 1/V.22. Similarly, the group delay of the transmitter output shall be within 150microseconds over the frequency range 900 Hz-1500 Hz (low channel) and 2100
13、 Hz-2700 Hz (high channel). Thesefigures are provisional.FIGURE 1/V.22Amplitude limits for transmitted line signal (unequalized)Fascicle VIII.1 - V.22 32.5 Modulation2.5.1 Data signalling ratesAlternatives A and B: The data signalling rate transmitted to line shall be 1200 bit/s or 600 bit/s 0.01% w
14、ith amodulation 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. InMode 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 r
15、ate shall be 1223 2 bit/s with a modulation rate of 611.5 1 baud.2.5.2 Encoding of data bits2.5.2.1 1200 bits per secondThe data stream to be transmitted shall be divided into groups of 2 consecutive bits (dibits). Each dibit shall beencoded as a phase change relative to the phase of the preceding s
16、ignal element (see Table 1/V.22). At the receiver, thedibits shall be decoded and the bits reassembled in correct order. The left-hand digit of the dibit is the one occurring firstin the data stream as it enters the modulator portion of the modem after the scrambler.TABLE 1/V.22Note - The phase chan
17、ge is the actual on-line phase shift in the transition region from the centre of onesignalling element to the centre of the following signalling element.2.5.2.2 600 bits per secondEach bit shall be encoded as a phase change relative to the phase of the preceding signal element(see Table 1/V.22).2.6
18、Received signal frequency toleranceNoting that the frequency tolerance of the transmitter carriers is 1 Hz or less, and assuming a maximum shiftof 6 Hz in the connection, the receiver shall be able to accept errors of at least 7 Hz in the received frequencies.3 Interchange circuits3.1 Table of inter
19、change circuits (Note 1 of Table 2/V.22)Essential and optional interchange circuits are listed in Table 2/V.22.Dibit values(1200 bit/s)Bit values(600 bit/s)Phase change(Modes i, ii, iii, iv)Phase change(Mode v)000111100-1-+ 900+ 270+ 180+ 270+ 180+ 9004 Fascicle VIII.1 - V.22TABLE 2/V.22Interchange
20、circuits (Note 1)Note 1 - All essential interchange circuits and any others which are provided shall comply with the functional and operationalrequirements of Recommendation V.24. All interchange circuits provided shall be properly terminated in the data terminal equipmentand in the data circuit-ter
21、minating 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 callingmodem. The general switched telephone network (GSTN) constant c
22、arrier handshake is such that no calling tone will be emitted bythe 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
23、 in 4.1, 4.2 and 4.3 is provided in themodem. 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 DTEsoperating in an asynchronous mode do not have
24、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 DTEsoperating in an asynchronous mode do not terminate this circuit.Note 7 - This circuit is for use with the general switched telephone netw
25、ork only.Interchange circuitNotesNo. Description102103104105106107108/1108/2109111113114115125140141142Signal ground or common returnTransmitted dataReceived dataRequest to sendReady for sendingData set readyConnect data set to lineData terminal readyData channel received line signal detectorData si
26、gnalling rate selector (DTE source)Transmitter signal element timing (DTE source)Transmitter signal element timing (DCE source)Receiver signal element timing (DCE source)Calling indicatorLoopback/maintenance testLocal loopbackTest indicatorNote 2Note 3Note 3Note 4Note 5Note 6Note 6Note 7Fascicle VII
27、I.1 - V.22 53.2 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 foroperating sequences.TABLE 3/V.22ConstantcarrierControlled carrierCircuit 106OFF to ONON to OFF 2 ms 2 ms210 to 275 ms 2 ms
28、Circuit 109OFF to ONON to OFF105 to 205 ms10 to 24 ms105 to 205 ms10 to 24 ms3.3 Circuit 109 thresholdsHigh channel threshold:greater than -43 dBm circuit 109 ONless than -48 dBm circuit 109 OFFLow channel threshold:greater than -43 dBm circuit 109 ONless than -48 dBm circuit 109 OFFThe condition of
29、 circuit 109 between the ON and OFF levels is not specified, except that the signal detectorshall exhibit a hysteresis action such that the level at which the OFF to ON transition occurs shall be at least 2 dB greaterthan for the ON to OFF transition.Circuit 109 thresholds are specified at the input
30、 to the modem excluding the effects of the compromiseequalizer.Circuit 109 shall not respond to the 1800-Hz or 550-Hz guard tones, or the 2100-Hz (nominal) answer toneduring the handshake sequence.Administrations are permitted to change these thresholds where transmission conditions are known.3.4 Ci
31、rcuit 111 and data rate controlData 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 shallselect 600 bit/s operation.3.5 Electrical characteristics of
32、 interchange circuitsUse of electrical characteristics conforming to Recommendation V.28 is recommended together with theconnector and pin assignment plan specified by ISO 2110.Note - Manufacturers may wish to note that the long-term objective is to replace electrical characteristicsspecified in Rec
33、ommendation V.28, and that Study Group XVII has agreed that the work shall proceed to develop amore efficient, all-balanced, interface for the V-Series application which minimizes the number of interchange circuits.6 Fascicle VIII.1 - V.223.6 Fault condition of interchange circuits(See Recommendatio
34、ns 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 The DCE should interpret a fault condition on circuits 105 and 108 as an OFF condition using failure detectiont
35、ype 1.3.6.3 All other circuits not referred to above may use failure detection type 0 or 1.4 Modes of operation over the DTE/DCE interface4.1 Alternative AThe modem can be configured for the following modes of operation:Mode i) 1200 bit/s 0.01% synchronousMode iii) 600 bit/s 0.01% synchronous (optio
36、nal).In these modes of operation, the modem shall accept synchronous data from the DTE on circuit 103 undercontrol of circuit 113 or circuit 114. The data shall then be scrambled in accordance with 5 and then passed to themodulator for encoding in accordance with 2.5.2.In addition to standard V.24 t
37、ransmitter timing arrangements, the modem shall provide capabilities to derivetransmit signal element timing from receiver signal element timing.4.2 Alternative BThe modem can be configured for the following modes of operation:Mode i) 1200 bit/s 0.01% synchronousMode ii) 1200 bit/s start-stop 8, 9,
38、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 characteroptionalThe 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 a
39、t a nominalrate of 1200 or 600 bits per second. The start-stop data to be transmitted shall be converted, in conformity withRecommendation V.14, to a synchronous data stream suitable for transmission in accordance with 4.1Demodulated data shall be decoded in accordance with 2.5.2, then descrambled i
40、n accordance with 5 andthen passed to the converter in conformity with Recommendation V.14 for regaining the data stream of start-stopcharacters.The intracharacter signalling rate provided to the DTE over circuit 104 shall be in the ranges given inTable 4/V.22 when operating in the basic or in the e
41、xtended signalling rate ranges, respectively.Fascicle VIII.1 - V.22 7TABLE 4/V.22Intracharacter signalling rate range4.3 Alternative CThe modem can be configured for the following modes of operation.Mode i) 1200 bit/s 0.01% synchronousMode ii) 1200 bit/s start-stop 8, 9, 10 or 11 bits per character(
42、Mode iii) 600 bit/s 0.01% synchronous optional (Mode iv) 600 bit/s start-stop 8, 9, 10 or 11 bits per characteroptionalMode v) An asynchronous mode having capability of handling 1200 bit/s start-stop and anisochronous data atup to 300 bit/s.Modes i) to iv) are as given in Alternative B.4.3.1 Basic m
43、odesIn Alternative C, the modem shall incorporate Modes i), ii), iii) and iv) given in Alternative B, plus Mode v), inwhich the modem transmitter sends data at a rate always greater than the input data rate, and thus disables the receiverbuffer. The GSTN handshaking sequence allows automatic selecti
44、on of Modes ii) or v). Modes i), iii) and iv) must beselected at installation. On leased circuits there is no automatic mode selection. The line encoding for specific dibitvalues is described in Table 1/V.22.4.3.2 TransmitterIn Mode v), the modem shall accept a data stream of start-stop characters f
45、rom the DTE at a nominal rate of a 0to 300 bit/s or 1200 bit/s automatically. The transmitter buffer that converts incoming data to a synchronous data streamat 1205 bit/s or 1223 bit/s shall:a) start its asynchronous bit counter on either data transition,b) always transmit the last bit received over
46、 circuit 103 after the bit counter has elapsed,c) 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 introduceddistortion of 25% at 300 bit/s (and 12.5% at 150 bit
47、/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) at1200 bit/s asynchronous, two adjacent character formats, e.g. 9- and 10-bit character, can be handled automatically. Asin Altern
48、ative B, the modem shall derive its line signal clock from internal clock circuits, or alternatively, from receiversignal element timing, as an installation option.Data rateSignalling rate rangeBasic Extended600 bit/s1200 bit/s600 to 606 bit/s1200 to 1212 bit/s600 to 614 bit/s1200 to 1227 bit/s8 Fas
49、cicle VIII.1 - V.224.3.3 Basic signalling rate rangeIn 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/s1223 bit/s line rate 0 to 305 bit/s and 1190 to 1221 bit/sSelection of line rate is made in the transmitter by installer option and automatically detected in the receiver.5 Scrambler and descrambler5.1 ScramblerA self synchronizing scrambler having the generating polynomial 1 x-14 x-17shall be included i
