1、INTERNATIONAL TELECOMMUNICATION UNION)45G134 ( TELECOMMUNICATIONSTANDARDIZATION SECTOROF ITU,).%G0G042!.3-)33)/./ amended at Melbourne, 1988)IntroductionVideoconferencing and visual telephony are new services which require greater bit rates than telephony. In thestudies in CCITT on the ISDN and on i
2、nternational interworking, 384 kbit/s is emerging as an important channelcapacity for wideband services. On this basis it is recommended that the videoconferencing and visual telephoneservices should be based on multiples of 384 kbit/s.It is noted that both the 2048 kbit/s and 1544 kbit/s primary di
3、gital levels can be expressed by the formulay + (n 384) kbit/s, where n = 5 or 4 and y = 128 or 8 kbit/s, respectively.While this Recommendation covers only frame structures for transmission at the primary digital rates, it is notintended to suggest that transmissions using other frame structures or
4、 formats at primary rates or lower are precluded.In the future, frame structure based on other multiples and/or sub-multiples of 384 kbit/s may also be considered.1 Characteristics of a 2048 kbit/s (n = 5) frame structure for use in codecs described in 1 ofRecommendation H.1201.1 General characteris
5、ticsThe multiplex structure described under 1 is suitable for use on digital paths and connections whichinterconnect video codecs for videoconferencing or visual telephony using 2048 kbit/s transmission. The connectionsmay either be direct or via higher-order digital multiplex equipment compatible w
6、ith the primary PCM multiplexequipment defined in Recommendation G.732.Some of the characteristics of this multiplex structure are identical to those in Recommendation G.704 and arecovered by cross-references to that Recommendation.The main features of the multiplex structure are that it provides: o
7、ne 64 kbit/s channel for frame alignment, alarm signals and other signals as required; one 64 kbit/s channel reserved for the transmission of the sound signal; one 32 kbit/s channel for codec-to-codec information; the option of one or two 64 kbit/s channels and/or one 32 kbit/s channel for stereopho
8、nic sound, facsimile,data, etc.; the possibility of end-to-end and subscriber-to-network signalling; the remaining capacity (between 1664 and 1888 kbit/s) is used for the encoded video signal.1.1.1 Fundamental characteristicsThe multiplex structure contains 32 time slots, each of 64 kbit/s.1.1.2 Bit
9、 rateThe nominal bit rate is 2048 kbit/s. The tolerance on this rate is 50 parts per million (ppm).1.1.3 Timing signalThe timing signal is a 2048-kHz signal from which the bit rate is derived. It should be possible to derive thetiming signal from an internal source or from the network.1.1.4 Interfac
10、esThe interfaces should comply with Recommendation G.703.2 Fascicle III.6 - Rec. H.1301.2 Frame structure and time slot allocationsThe frame structure is in accordance with Recommendation G.704, 3.3. The time slot (TS) allocations withinthe frame are given in Table 1/H.130, two options are shown acc
11、ording to whether or not the network is switched(under control of signals within the frame structure).1.3 Codec-to-codec informationThis information is transmitted in the 32 kbit/s channel corresponding to odd frames of TS2 (frame parity isgained from the multiframe alignment in the 8th bit of alter
12、nate TS2, the frames are consecutively numbered 0 to 15,forming a multiframe).The 32 kbit/s channel is structured in a multiframe and supermultiframe derived from 128 consecutive 256 bitframes. The multiframe is composed of 8 octets numbered 1, 3, 5, ., 15, each from TS2 in an odd numbered 256 bitfr
13、ame. The supermultiframe corresponds to 8 consecutive multiframes which are numbered 0, 1, 2, ., 7.The use of the bits in each octet in the odd frames is as follows: Bit 1 for clock justification, Bit 2 for buffer state, Bit 3 for coding mode identification; the 8 consecutive bits 3 of TS2 in a mult
14、iframe will carry thefollowing information:Bit 3.1 1)Codec facilities (see below)Bit 3.3 Colour transmission (1 if provided)Bit 3.5 split-screen indicator (if required)Bit 3.7 Fast update request (1 if required)Bit 3.9 Advance warning of interruption (1 if required)Bit 3.11 Sound power signal, for u
15、se with encryptedmultipoint (under study)Bit 3.13 Data distribution (1 if required)Bit 3.15 Detection of looped ports (set to 1)Bit 3.1 is used to signal the availability of certain facilities in the decoder at supermultiframe rate, as follows:Bit 3.1.0 Graphics (mode 1) (1 if provided)Bit 3.1.1 Hig
16、h-quality speech (1 if provided)Bit 3.1.2 4 x 384 kbit/s capability (see Note 1) (1 if provided)Bit 3.1.3 Encryption (1 if provided)Bit 3.1.4 System M (1 if 525-line signal beingcoded)Bit 3.1.5 Graphics (mode 2) (1 if provided)Bit 3.1.6 Spare (set to 0)Bit 3.1.7 2 x 384 kbit/s capability (see Note 1
17、) (1 if provided)_1)The notation used here should be interpreted as in the following examples: Bit 3.1 means Bit 3 (in TS2) of frame No. 1 in eachmultiframe: Bit 3.1.0 means Bit 3 (in TS2) of frame No. 1 in multiframe No. 0 of each supermultiframe.Fascicle III.6 - Rec. H.130 3TABLE 1/H.130Timeslot a
18、llocation in 32 Timeslot frame structure of Recommendation G.704Timeslot allocation(within the 256-bit frame)Bit rate(kbit/s)Non switched(i)Switched(ii)Frame alignment, network alarms, etc. as in G.704 0 0Speech information 64 1 1Codec-to-codec information 32 2 2Signalling information(subscriber-net
19、work)64 - 16Fax, data, etc. (optional) up to2 6417and/or1817and/or18Encoded video information (minimum) (i) 27 64(ii) 26 643 to 16+19 to 313 to 15+19 to 31Note 1 Frame alignment, network alarms, etc.This information is transmitted in TSO with the same rules and characteristics as recommended in Reco
20、mmendationG.704. Additionally, bit 8 in odd frames is used as a synchronization bit which is required when the codec is used withsynchronous digital networks. On receipt of this bit set to zero, the transmission clock for the encoder will be derivedfrom the incoming data stream. This bit is always s
21、et to one in the encoder.Note 2 SpeechSpeech is transmitted at 64 kbit/s in TS1. The coding law is the A- law of Recommendation G.711 or, for future applications, thelaw that will be recommended by CCITT for higher quality speech. In the case of stereophonic transmission, the second speechchannel wi
22、ll be transmitted in TS17.Note 3 Codec-to-codec informationThis information requires a capacity of 32 kbit/s and is transmitted on odd frames of TS2. The remaining 32 kbit/s capacity on theeven frames of TS2 will be used for encoded video or data transmission. The detailed use and structure of the 3
23、2 kbit/s channel forcodec-to-codec information is described in 1.3.Note 4 Signalling (subscriber-to-network)A capacity of 16 kbit/s is considered adequate for videoconference as for basic access. The methods of switched access to the ISDNat 2048 kbit/s have not yet been formulated. Option (ii) avoid
24、s any problems in this respect, by leaving the whole of TS16 (64 kbit/s)clear of video information and available for subscriber signalling and call set-up information when switched access is required. Fornon-switched access, option (i) should be used.Note 5 Facsimile, data, etc.When required, this i
25、nformation will be transmitted in TS17 and/or 18.Note 6 Encoded videoA minimum of 26 x 64 kbit/s capacity is reserved for encoded video in TS3 to 15 and 19 to 31. In addition, depending onapplications, TS2 (even frames), TS16, 17 and 18 may also be used for video, providing a maximum of 29.5 x 64 kb
26、it/s capacity; theavailable video bit-rate therefore lies between 1664 and 1888 kbit/s. Bit 4 to identify the use of time slots; the 8 consecutive bits 4 of TS2 in a multiframe will carry thefollowing information:Bit 4.1 TS2 (even) is used for video (0) or other (1)Bit 4.3 TS16 is used for video (0)
27、 or other (1)Bit 4.5 TS17 is used for video (0) or other (1)Bit 4.7 TS18 is used for video (0) or other (1)Bit 4.9 TS16, 26 to 31 are not used for video (see Note 2)Bit 4.11 Graphics transmission (1 if required)4 Fascicle III.6 - Rec. H.130Bit 4.13 Error correction (1 if required)(see Note 3)Bit 4.1
28、5 Use of time slots for video in conjunction with bit 4.9 (see Note 2) Bit 5 for multipoint conferencing; provides a 4 kbit/s message channel (transparent through the codec) fromcustomer to multipoint control unit, between control units and from customer to customer. (The messageformat and protocols
29、 are under study.)When the codec is not equipped with a message channel, bit 5 is used to signal split-screen: 1 = split-screenactive, 0 = split- screen inactive. Bit 6 free (for possible national use) (set to 0) Bit 7 free (for possible national use) Bit 8 for multiframe and supermultiframe alignme
30、nt; the values of bit 8 in each frame of the multiframe(multiframe and supermultiframe alignment patterns) should be as detailed in Table 2/H.130.Note 1 Bits 3.1.2 and 3.1.7, taken together, signal the capability of the codec to operate at various bit rates, asfollows:Note 2 Bits 4.9 and 4.15, taken
31、 together, signal the time slots available (subject to the settings of bits 4.1, 4.3,4.5 and 4.7) for video at various bit rates. The use of TS0, TS1 and TS2 (odd) is unaffected by these bits.A 2 Mbit/s codec which allows n 384 kbit/s working, will set to zero time slots other than those mentioned a
32、bove inits transmitter and ignore them in the receiver.Note 3 When set to 1, the last 64 bits of each multiframe contain the error corrector parity bits. Themultiframe then appears as follows:The conditions signalled in bits 3 and 4 can only change at supermultiframe rate. The change at the decoderw
33、ill take place at the start of the first supermultiframe following the one where the change in signalling has beendetected. This procedure can be used to improve the resistance to transmission errors.Bit 3.1.2 Bit 3.1.701010 2 Mbit/s only0 2 Mbit/s and 4 x 384 kbit/s operation1 2 Mbit/s and 2 x 384
34、kbit/s operation1 2 Mbit/s and 4, 3, and 2 x 384 kbit/s operationBit 4.9 Bit 4.15 Bit rate Time slot available for video011000112 048 kbit/s4 384 kbit/s3 384 kbit/s2 384 kbit/sTS2 (even), TS3-31TS2 (even), TS3-15 and 17-25TS2 (even), TS3-9 and 17-25TS2 (even), TS3-6 and 17-22Fascicle III.6 - Rec. H.
35、130 5Note - Undefined (reserved for possible future use in a higher level framing structure).2 Characteristics of a 1544 kbit/s (n = 4) frame structure for use with codecs described in 2 ofRecommendation H.1202.1 General characteristicsThe multiplex structure described under 2 is suitable for use on
36、 digital paths and connections whichinterconnect video codecs for videoconferencing or visual telephony using 1544 kbit/s transmission. The connectionsmay either be direct or via higher-order digital multiplex equipment compatible with the primary PCM multiplexequipment defined in Recommendation G.7
37、33.Some of the characteristics of this multiplex structure are identical to those in Recommendation G.704 and/or in 1 of this Recommendation; these are covered by cross-references to the appropriate documents.The main features of the multiplex structure are that it provides: one 8 kbit/s channel for
38、 frame alignment, alarm signals and other signals as required; one 64 kbit/s channel for the sound signal; one 32 kbit/s channel for codec-to-codec information; the option of one or two 64 kbit/s channels and/or one 32 kbit/s channel for auxiliary data services; the remaining capacity (between 1280
39、and 1440 kbit/s) is used for the encoded video signal.2.1.1 Fundamental characteristicsThe multiplex structure contains 24 time slots per frame, each of 64 kbit/s, plus one bit per frame for framealignment and signalling. The number of bits per frame is 193 and the nominal frame repetition rate is 8
40、000 Hz.6 Fascicle III.6 - Rec. H.1302.1.2 Bit rateThe nominal bit rate is 1544 kbit/s. The tolerance on this rate is 50 parts per million (ppm).2.1.3 Timing signalThe timing signal is a 1544 kHz signal from which the bit rate is derived. It should be possible to derive thetiming signal from an inter
41、nal source or from the network.2.1.4 InterfacesThe interfaces should comply with Recommendation G.703; the option of AMI or B8ZS should be provided asthe interface code. Which of the two codes is used should be determined by bilateral agreement.2.1.5 Format restrictions enforced by the networkAs ind
42、icated in Recommendation G.703, runs of more than 15 “zeros” are forbidden in some networks; also,there must be, on average, at least three “ones” in every 24 digits. Provision is made by means of a scrambling systemto ensure that forbidden patterns cannot occur.2.2 Frame structure and time slot all
43、ocationsThe basic frame structure follows Recommendation G.704. The time slots are numbered from 1 to 24, with the1st bit positioned between TS24 and TS1.2.2.1 Frame alignmentThe basic frame alignment is obtained at bit No. 1, as in Recommendation G.704, Method 2 (see 2.1.3.2). Thepattern transmitte
44、d is as shown in Table 3/H.130.TABLE 3/H.130Frame No. Frame alignment signal S-bit Signalling bit1234567891011121-0-1-0-1-0-0-0-1-1-1-0AB2.2.2 SpeechSpeech is transmitted at 64 kbit/s in TS1. The coding law is the A-law of Recommendation G.711 or, for futureapplications, the law that will be recomme
45、nded by CCITT for higher-quality speech. In the case of stereophonictransmission, the second speech channel will be transmitted in TS17.2.2.3 Codec-to-codec informationThis information is transmitted in the 32-kbit/s channel corresponding to the odd frames of TS2. The channel isstructured in multifr
46、ames of 16 frames and supermultiframes of 8 multiframes in exactly the same way as in the 2-Mbit/s version in 1. Multiframe and supermultiframe alignment are obtained from bit 8 of TS2 (odd) in the same wayas in 1.Fascicle III.6 - Rec. H.130 7The multiframe of TS2 for codec-to-codec signalling is qu
47、ite independent of the basic 12-frame multiframe ofRecommendation G.704.2.2.4 SignallingIn the future, some 1.5 Mbit/s networks will allow the use of bits A and B for signalling. This facility is notavailable on all networks.2.2.5 Facsimile, data, etc.When required, this information will be transmit
48、ted in TS16 and TS17 and TS2 (even).2.2.6 Encoded videoA minimum of 20 x 64 kbit/s capacity is reserved for encoded video in TS3-15 and 18-24; depending onapplications, TS2 (even), TS16 and 17 may also be used for video, providing a maximum of 22.5 x 64 kbit/s capacity.The available bit rate for vid
49、eo therefore lies between 1280 and 1440 kbit/s.2.3 Codec-to-codec informationThe structure of the multiframe and supermultiframe are exactly the same as in 1, except that each framecontains only 24 time slots as compared with 32 in the frames in 1.The bit allocations in TS2 (odd) are identical with 1, with the following exceptions: Bit 1 for clock justification, required for interworking with 625-line codecs; disregarded in 525-linedecoders. Bit 3.1.2 is permanently set to 1 (see Note 1) Bit
