1、CEPT T/CD*OL-LL*E 80 H 2326414 0003205 T O1-I1 Page 1 E Recommendation T/CD O1 -1 1 E (Brussels 1980, revised at Cannes 1983) concerning the general engineering requirements for a groupband modem according to CCIlT Recommen- dation V.36 Recommendation proposed by Working Group T/WG 10 “Data Communic
2、ations” (CD) Text of the revised Recommendation adopted by the “Telecommiiiiicatioiu” Commission, “The Conference of European Post and Telecommunications Administrations, Considering - that CCITT Recommendation V.36 describes the standardization of modems for synchronous data transmission using 60-1
3、08 kHz groupband circuits; - that CEPT Recommendation T/CD 01-01 contains the text of the specification of the general engineering requirements for data circuit terminating equipment for use on voiceband, baseband and groupband circuits; - that Working Group CD has studied the harmonization of modem
4、s under the auspices of Question CD 1. Recommends - that the attached Specification of general engineering requirements for a groupband modem according to CCITT Recommendation V.36 as contained in Annex 1 to this Recommendation should be taken into account by all CEPT Administrations when implementa
5、tion of such a piece of equipment is being planned by Administrations.” Administrations are free to stipulate additional requirements, and also which of the optional requirements, if any, are to be provided. Note I; It should be noted that this specification may be revised from time to time. Note 2;
6、 The Annex is an integral part of the Recommendation. - Edition of November 30, 1985 T/CD 01-11 E Page 3 Contents Section A . General reqriirenents 5 2 . Data signalling rates 5 4 . Modulation and coding . 5 1 . General . 5 3 . Scrambling . 5 5 . Pilot carrier . 6 6 . Group reference pilot 6 7 . Adj
7、acent channel interference 6 8 . Specific design requirements . 7 9 . Testloops 7 10 . Performance requirements . 7 Section B . Network depeident requirements . 9 2 . Line signal levels . 9 3 . Interface requirements . 9 4 . Group reference pilot input port . 11 5 . Testing and measuring requirement
8、s . 11 6 . Power supplies 11 Section C . Optional reqrirements 12 1 . General . 12 2 . Additional interface requirements 12 3 . Manual carrier phase optimisation 12 4 . Adaptive equaliser and adaptive phase optimisation . 12 6 . 100 kHz carrier 15 7 . Loss of signal alarm 15 9 . Stationalarm . 15 1
9、. General . 9 O 5 . Error rateindication 13 8 . Powerfailurealarm 15 O _ Edition of November 30. 1985 CEPT T/CD*OL-LL*E 80 m 2326434 0003207 3 m - T/CDOl-lI E Peg9 5 Section A. General requirements 1. 2. 3. 4. 4.1. 4.2. GENERAL The groupband modem described in this document is intended to form part
10、of a duplex point to point data transmission system for the transmission of unrestricted format data over a 60-108 kHz groupband circuit. The 60-108 kHz band is available for the transmission of modulated data signals. The 104-108 kHz band is reserved for the transmission of control or other suitabl
11、e signals. The principal fields of application for this modem shall be one or more of the following: (a) Transmission of a multiplex aggregate bit stream for public data networks. (b) Extension of a PCM channel at 64 kbit/s over analogue facilities. (c) Transmission of a multiplex aggregate bit stre
12、am for telegraph and data signals. (d) Transmission of data between customers on leased circuits where such circuits are extended to customers? premises by means of baseband modems or baseband extenders. (e) Transmission of a common channel signalling system for telephony and/or public data networks
13、. (0 Extension of single-channel-per-carrier (SCPC) circuit from a Satellite earth station. DATA SIGNALLING RATES The modem shall be capable of operation at one or more of the following rates: Synchronous at 48, 56, 64 and 72 kbitls. The modem shall be able to accommodate a tolerance of I50 parts pe
14、r million in the data signalling rate, SCRAMBLING The modem shall include a scrambling device in the modem transmitter and a descrambling device in the modem receiver. The operation of these devices shall be in accordance with Appendix 1 to CCIT Recommendation V.36. MODULATION AND CODING The modem t
15、ransmitter shail perform coding and modulation functions specified beIow, either in the manner stipulated below or in a manner that is equivalent to it. Coding The class 4 partial response coding shali be performed in the transmitter in such a manner that decoding can be performed by full wave recti
16、fication of the demodulated line signal. Specifically, the sequence a, at the output of the scrambler shall be coded to give a sequence b, such that b, = bn-2 0 an where 0 signifies a modulo 2 addition. The sequence b, shall be processed to yield a 3 level sequence c, where c, = b, - bn-2 according
17、to which the transmission line signal shall be modulated. Modulation In the 60-104 kHz band the line signal shall be substantially single sideband signal with its carrier frequency at 100,000 Hz f 2 Hz. The relationship between the binary signal at the output of the scrambler and the transmitted lin
18、e signal shall be in accordance with the amplitude modulation case of CCITT Recommendation V.l., i.e. tone ON for binary 1 and tone OFF for binary O. Specifically the ternary signal at the input to the modulator shall be interpreted as follows. The 2 outer levels shall correspond to the tone ON cond
19、ition and the middle level shail correspond to the tone OFF condition. CEPT T/CD*OL-LL*E rn 232b414 0003208 5 rn TICD 01-11 E Pago 6 4.3. Line signal spectrum The amplitude of the line signal spectrum corresponding to an isolated binary 1 appearing at the output of the scrambler is to be sinusoidal
20、with zeros and maxima at the frequencies specified below: Data signalling rate Zeros Maxima 48 kbit/s 76 and 100 kHz 88 kHz 56 kbit/s 72 and 100 kHz 86 kHz 64 kbitls 68 and 100 kHz 84 kHz 72 kbit/s 64 and 100 kHz 82 kHz In the 60-104 kHz band the amplitude distorsion of the real spectrum relative to
21、 the theoretical spectrum as defined above is not to exceed 1 dB; the relative group delay distorsion is not to exceed 8 ps. These 2 requirements are to be met for the frequency band centred on the maximum mentioned above and whose width is equal to 80% of the frequency band used. 5. PILOT CARRIER A
22、 pilot carrier at the same frequency as the modulated carrier at the transmitter with a level of -9 kO.5 dB relative to the actual level mentioned under paragraph B.2.2. shall be added to the line signal. The relative phase between the modulated carrier and the pilot carrier shall be time invariant.
23、 6. GROUP REFERENCE PILOT (GRP) The modem receiver is required to operate correctly irrespective of the presence or the absence of the group reference pilot which may be present in the line signal at a frequency of 104.08 kHz. The pilot, when present, will be at a level of -20 dBmO nominal. In order
24、 to protect the group reference pilot the modem transmitter shall not emit any single discrete frequency components in the vicinity of the GRF at a level in excess of that specified in Figure 1. For continuous spectrum signals, the spectral power density of signals emitted by the modem transmitter s
25、hall not exceed -70 dBmO/Hz in the band 104.08 kHz k 25 Hz. dBmO Frequency diterence from f, (pilot frequency) (Hz) Figure 1. Maximum permissible level of discrete frequency components in the vicinity of the group reference pilot. 7. ADJACENT CHANNEL INTERFERENCE In the transmit direction the power
26、outside the range 60-108 kHz shall satisfy the following requirements. The power in any 4 kHz band inside the range 12-60 kHz and 108-156 kHz shall not exceed -73 dBmOp. Edition of November 30, 1985 .h CEPT T/CD*OL-LL*E 80 m 2326414 0003209 7 m T/CD 01-11 E Page 7 8. SPECIFIC DESIGN REQUIREMENTS 8.1
27、. Line impairments The modem receiver shall take into account the need to contend with phase hits, amplitude hits, impulsive noise and a frequency offset of up to f6 Hz. 8.2. Adjacent channel interference The design shall take into account the fact that a sinusoidal signal of + 10 dBmO in the freque
28、ncy band 36-60 kHz and 108-132 kHz can appear with the data line signal at the groupband input to the modem receiver. 8.3. Propagation delay The signal propagation delay in the modem (transmit side looped to receive side) shall not exceed 2 ms. 9. TEST LOOPS Facilities shall be provided for carrying
29、 out “Local test” i.e. CCITT loop 3 and “Remote test” i.e. CCITT The establishment and the release of these test loops shall be by means of the appropriate interchange circuits defined in paragraph B 2. and/or manually operated switches. When the establishment and the release of the test loops is un
30、der the control of the interchange circuits specified in paragraph C 2. l., the protocols used shall be in accordance with CCITT Recommendation V.54. loop 2. 10. PERFORMANCE REQUIREMENTS 10.1. Line characteristics At 48, 56 and 64 kbit/s the modem is required to operate satisfactorily over a correct
31、ed groupband link comprising up to 4 groupband sections in tandem, namely, 3 Equalised through group lters (ETGF) and 4 pairs of Group translating equipment (GTE) i.e. mod-demod equipment. At 72 kbit/s the modem is required to operate satisfactorily over a groupband link comprising 2 groupband secti
32、ons in tandem, namely, one ETGF and 2 pairs of GTE. Each ETGF may have any combination of slope, sag and ripple within the template specified in Figure 2. The number of ripple cycles is to be specified later. Each pair of GTE may have any combination of slope and sag within the template specified in
33、 Figure 2. The amplitude/frequency characteristics of such a corrected groupband link wi lie within the template specified in Figure 3. 10.2. Error rates When measured over a test channel simulating 3 pairs of GTE and 2 ETGFs in tandem the performance of the modems at 48, 56 and 64 kbit/s shail be a
34、s follows: Test pattern Noise Noise bandwidth Normalised signal 23 dB. to noise ratio Error rate At 72 kbit/s the performance of the modem over a test channel simulating one pair of GTE shall be as above. 51 1 bits pseudo-random. Uniform power spectral density with Gaussian amplitude distribution. F
35、rom 40 kHz to 120 kHz. Better than 1 in 10 bits. Edition of November 30, 1985 CEPT T/CD*OL-LL*E = 2326434 0003210 3 T/CD 01-11 E Page 8 64 84 Frequency (kHz) 100 Figure 2. Group delay frequency template for (a) Group translating equipment. (b) An equalised through group filter. 68 84 Frequency (kHz)
36、 100 Figure 3. Attenuation/Frequency template for a 5 section groupband link with respect to attenuation at 84 kHz. Edition of November 30, 1985 CEPT T/CD*OL-LL*E 80 232b4L4 00032LL 5 = T/CD 01-11 E Page 9 Section B. Network dependent requirements 1. 2. 2.1. 2.2. 2.3. 2.4. 3. GENERAL This section sp
37、ecifies requirements that are related to specific fields of applications as well as the particular system configurations within which the modem is commoniy used. LINE SIGNAL LEVELS Groupband inputloutput ports The groupband input and output ports shall include line transformers. A strappable facilit
38、y shall be provided whereby the secondary of the groupband output transformer and the primary of the groupband input transformer can be connected to modem earth. The groupband input and output impedances shall be as follows. The selection of the required impedance shall be by means of a strap. 150 i
39、2 balanced. The relative level of the groupband modem output port shall be -37 dBr or -36 dBr or -33 dBr or - 26 dBr. The relative level of the groupband modem input port shall be - 30 dBr or - 14.8 dBr or - 8 dBr. The actual signal levels at these ports shall be as specified below. The return loss
40、of the line transformers in the frequency range 60-108 kHz shall not be less than 20 dB when measured against a nominal non-reactive impedance of 75 Cl or 150 Q as appropriate. 75 Q unbalanced; Transmit signal level With a random data signal the nominated value of the mean signal power of the compos
41、ite modulated data signal plus the pilot carrier in the 60-104 kHz band at the groupband output port shall be -5.5 dBmO. The actual level, taking into account environmental changes, ageing and setting up tolerances shall at all times stay within f 1 dB of the nominal level. The absolute output power
42、 level of the modulated data signal shall be adjustable in 1 dB steps over the range -45 dBm to -29 dBm. (Note that the pilot carrier is required to be added to the above data signal at a level -9.O+ 0.5 dB relative to the absolute power level mentioned above.) Receive signal levels The nominal leve
43、l of the composite modulated data signal plus the carrier pilot shall be - 5.5 dBmOf2 dB. The actual input sensitivity in terms of the absolute input power level of the modulated data signal plus the carrier pilot shall be selectable by means of a strap from the following set of values. Nominal leve
44、l Range of nominal level -35.5 dBm -37.5 dBm to -33.5 dBm -20.3 dBm -22.3 dBm to -18.3 dBm -13.5 dBm -15.5 dBm to -11.5 dBm AGC requirements The receive section of the groupband modem shall be able to accommodate a level variation of up to f 7 dB from any value within the range of nominal levels sti
45、pulated in paragraph B 2.3. INTERFACE REQUIREMENTS Three main variants of this interface exist: i) ii) A digital interface for direct connection to codirectional or contradirectional interface for accessing PCM equipment as defined in CCITT Recommendation G.703. An internal engineering interface as
46、defined in paragraph B 3.2. This interface is defined for those configurations or implementations where, for example, the modem may be an integral part of another equipment e.g. a multiplexor, or where additional but separately defined items like baseband modems or interface conversion units are int
47、egrated with groupband modems. iii) A digital modem interface. The digital modem interface is required to be externally accessible and shall be in accordance with paragraph B 3.3. Edition of November 30. 1985 CEPT T/CD*OL-LL*E m 2326434 0003232 7 m TJCD O1 -11 E Page 10 3. I. PCM equipment interface
48、 3.1.1. Electrical und functional characteristics The PCM : codirectional interface shall be in accordance with CCITT Recommendation G.703 para- graphs 5. and 9. The PCM : contradirectional interface shall be designed to allow for direct connection to a PCM interface that is in accordance with CCITT
49、 Recommendation G.703. For those synchronous networks that require the end to end 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 shall be used. The corresponding data format shall be obtained by inserting one extra bit E just before the final bit of each octet of the 64 kbit/s data stream. The bits E shall convey alignment and housekeeping information according to the following pattern. . lOH1OHlOH . The defini
