1、 AMERICAN NATIONAL STANDARD FOR TELECOMMUNICATIONS ATIS-0100501.1994(R2013) Tandem Encoding Limits for 32-kbit/s ADPCM As a leading technology and solutions development organization, ATIS brings together the top global ICT companies to advance the industrys most-pressing business priorities. Through
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10、quire that action be taken periodically to reaffirm, revise, or withdraw this standard. Purchasers of American National Standards may receive current information on all standards by calling or writing the American National Standards Institute. Notice of Disclaimer Category 2: Voiceband (4 kHz) signa
11、ls that cannot be transmitted with satisfactory performance over connections containing G.726 32-kbit/s ADPCM links. These two categories apply to both PSTN and private-network connections. Criteria for satisfactory performance are application-dependent and ultimately determined by the end-user. In
12、deriving the G.726 32-kbit/s ADPCM tandem encoding limits set forth in this standard, the following criteria were used: Voice: The criterion is based on a measure called Q that captures the effect of quantizing noise on quality (see J. R. Cavanaugh in the bibliography). The criterion of Q 20 dB was
13、used; Voiceband data: Two criteria were used. Block error ratio (BLER) 102(with a block size of 103bits) and bit error ratio (BER) 105. Whether BLER or BER is more meaningful depends upon the application. For transfers of large amounts of data with retransmittal protocols, BLER is appropriate. For f
14、acsimile applications and asynchronous character transfer, BER is more meaningful. The BER is usually the more stringent criterion; Dual-tone multi frequnecy (DTMF) signals: The criterion of digit error ratio 103was used. 4.3 Tandem connecting arrangements Two ADPCM links in tandem are said to be sy
15、nchronously connected if the connecting transmission system is the equivalent of a 64-kbit/s PCM bit stream. Likewise, two ADPCM links are said to be asynchronously connected if they are connected by any other type of transmission system; in general, one which converts the signal-to-analog format at
16、 some point. The performance of two or more synchronously connected G.726 32-kbit/s ADPCM links is equivalent (except for delay) to one link if (1) the transmission of the G.726 32-kbit/s ADPCM links and the intermediate 64-kbit/s PCM links is error free4)and (2) the G.726 32-kbit/s ADPCM and interm
17、ediate 64-kbit/s PCM bit streams are not disturbed by digital signal processing. Any tandem connecting arrangement that employs PCM-modifying digital signal processing on the connecting link(s), such as that performed by digital echo cancelers or digital loss pads, will not satisfy the above constra
18、ints. If two G.726 32-kbit/s ADPCM links are connected by a 64-kbit/s transmission system that does not preserve bit integrity (i.e., it uses digital signal processing or bit-robbing, etc.) the net effect on performance will be bounded by the performance of one G.726 32-kbit/s ADPCM link and the per
19、formance of two asynchronously connected G.726 32-kbit/s ADPCM links. This effect, however, has not been well quantified; it is a subject for further study. Therefore, for purposes of this standard, this arrangement should be counted as equivalent to two asynchronously connected G.726 32-kbit/s ADPC
20、M links. 4.4 Tandem encoding limits The total number of G.726 32-kbit/s ADPCM links in connections shall be limited in order to provide the capability of quality transmission performance between end-users. These limits apply to PSTNs, private networks, and combinations thereof. The total number of a
21、synchronously connected G.726 32-kbit/s ADPCM links in these network connections shall be limited as follows: Category 1 signals: The limit is three asynchronously connected G.726 32-kbit/s ADPCM links; Category 2 signals: The limit is zero G.726 32-kbit/s ADPCM links. In some private network applic
22、ations, it may be possible to customize the network to meet the end-users specific application needs. In these cases, greater flexibility is possible, in terms of the number of G.726 32-kbit/s ADPCM links in tandem, while still satisfying the end-users needs. An example of guidelines that may be use
23、d in such cases is contained in annex A. 4.5 Allocation of end-to-end limits The allocation of the end-to-end limits presented in this standard is based on the assumption that G.726 32-kbit/s ADPCM is not deployed on the end-users side of the network interface (NI). If G.726 32-kbit/s ADPCM is deplo
24、yed on the end-users side of the NI, the overall limits should be observed in order to provide satisfactory performance. 4.5.1 National connections When a single carrier provides an end-to-end PSTN or private-network connection, the carrier shall implement the limits in clause 4.4. For connections w
25、ith both EC- and IC-provided portions, the Category 1 signal limit of three is allocated, one each for the EC, IC and EC portions. Each of the EC portions includes all components from the NI to the IC point of termination (POT). The Category 2 signal limit of zero requires that each providers portio
26、n has no G.726 32-kbit/s ADPCM links. See annex B, Functional usage guidelines, for implementation information. For both private and public switched connections, if an EC provides a G.726 32-kbit/s ADPCM-encoded signal at the EC-IC interface as a service option at the request of the IC, it will be c
27、onsidered as the ICs G.726 32-kbit/s ADPCM link. 4.5.2 International connections Typical international connections would contain a combined EC and IC network in the national extension (NI to gateway). Based on the implementation of this standard, there would be zero, one, or two asynchronously conne
28、cted G.726 32-kbit/s ADPCM links in the national extension. The allocation specified in the provisional planning rule, as described in ITU-T Recommendation G.113, allows at most one G.726 32-kbit/s ADPCM link in the national extension. However, an exception is noted that would allow at most two G.72
29、6 32-kbit/s ADPCM links with a clear indication that this is undesirable. Although the allocation of this standard allows up to a maximum of two links on the national extension of international connections, the frequency of occurrence of this maximum is expected to be low. Annex A (informative) ADPC
30、M performance effects A.1 General The impact of G.726 32-kbit/s ADPCM on the performance of a voiceband connection depends on the signal types transmitted (Category 1 or Category 2), the level and distribution of other analog impairments, the specific design of the terminal equipment and the number
31、of asynchronously connected G.726 32-kbit/s ADPCM links in the connection. This annex is provided as an aid to the reader in understanding the limits in the standard. The information in this annex was derived from evaluations of specific modems and DTMF receivers of several manufacturers and may not
32、 describe performance of all available similar hardware. A.2 References The following documents are referenced in this annex: 1 ANSI T1.508-1992, Telecommunications Network performance Loss plan for evolving digital networks 2 ITU-T Recommendation G.113, Transmission requirements. Blue Book, Volume
33、III Fascicle III.1, Melbourne, 19882)3 ITU-T Recommendation G.711, Pulse code modulation (PCM) of voice frequencies. Blue Book, Volume III Fascicle III.4, Melbourne, 19882)4 ITU-T Recommendation G.721, 32 kbit/s adaptive differential pulse code modulation (ADPCM). Red Book, Volume III Fascicle III.3
34、, Malaga-Torremolinos, 19842)5 ITU-T Recommendation G.721, 32 kbit/s adaptive differential pulse code modulation (ADPCM) (revised). Blue Book, Volume III Fascicle III.3, Melbourne, 19882) 6 ITU-T Recommendation V.17, A 2-wire modem for facsimile applications with rates up to 14400 bits per second. G
35、eneva, 19912) 7 ITU-T Recommendation V.29, 9600 bits per second modem standardized for use on point-to-point 4-wire leased telephone-type circuits. Blue Book, Volume VIII Fascicle VIII.1, Melbourne, 19882) 8 ITU-T Recommendation V.32, A family of 2-wire, duplex modems operating at data signalling ra
36、tes of up to 9600 bit/s for use on the general switched telephone network and on leased telephone-type circuits. Blue Book, Volume VIII Fascicle VIII.1, Melbourne, 19882)9 ITU-T Recommendation V.32bis, A duplex modem operating at data signalling rates of up to 14400 bits/s for use on the general swi
37、tched telephone network and on leased point-to-point 2-wire telephone type circuits. Geneva, 19912)10 ITU-T Draft Recommendation V.34, A modem operating at data signalling rates of up to 28800 bits/s for use on the general switched telephone network and on leased point-to-point 2-wire telephone-type
38、 circuits. 19942)11 Carey, M. B.; Chen, H-T; Descloux, A.; Ingle, J. F.; Park, K.I., 1982/83 end office connection study; analog voice and voiceband data characterization of the public-switched network. AT Sparrell, D., FSK Enhancements for the proposed T1Y1 ADPCM algorithm. Document T1Y1.2/86-006,
39、January 19866)13 Dimolitsas, S; Corcoran, F. L.; Onufry, M.; Suyderhoud, H. G., Evaluation of ADPCM coders for digital circuit multiplication equipment. COMSAT Technical Review, pp. 323 345, Fall 19877)14 Kalb, M., ADPCM performance impact on voiceband data. In: IEEE GLOBECOM 1985 Conference Record,
40、 New York, IEEE, December 1985, pp. 1133-11378)15 SG XVIII Report R26, Source: CCITT Secretariat, Report of the Meeting of Working Party XVIII/8 (Speech Processing). July 19862)A.3 Definitions A.3.1 quantizing distortion: The distortion introduced when an analog signal is encoded to digital format,
41、then decoded to analog format. The quantizing distortion is the difference between the original analog signal and the analog signal resulting from the decoding process. A.3.2 quantizing distortion unit (qdu): The distortion that is subjectively equivalent to the quantizing distortion introduced by a
42、n average 8-bit codec pair (A/D and D/A conversion; A-law or u-law) that complies with ITU-T Recommendation G.711 3.9)A.4 End-to-end performance criteria In determining the tandem encoding limits, it was first necessary to establish a set of criteria for judging the acceptability of end-to-end perfo
43、rmance. The voice criterion is based on a measure called Q. Various standard ITU-T recommendations have assigned values of Q to different processing techniques, including ADPCM, and have determined laws of addition for tandem devices and for combining with idle circuit noise. The ITU-T studies are b
44、ased on the 32-kbit/s ADPCM algorithm defined in the 1984 ITU-T Recommendation G.721 4 rather than that defined in the 1988 ITU-T Recommendation G.721 5. However, it has been shown that, except for the improved performance with respect to frequency-shift keying modems, the performance of the 1988 al
45、gorithm is essentially identical to that of the 1984 algorithm 12, 15. The ITU-T, in Recommendation G.113 2, has established a provisional end-to-end planning value of 14 quantizing distortion units (qdu), which corresponds to Q = 20 dB. A level of Q = 20 dB corresponds to the quantizing distortion
46、(not idle-circuit noise) of 14 asynchronously tandemmed PCM (A/D, D/A) pairs. Studies have shown that in a typical network connection, a Q of 20 dB corresponds to a modest degradation in voice transmission quality. However, as Q decreases below 20 dB, there is a rapid and marked decrease in quality.
47、 On this basis, Q = 20 dB is a reasonable planning limit and is the voice criterion for this standard. Delay also has an effect on overall transmission performance. Consider an end-to-end connection with up to three G.726 32-kbit/s ADPCM links in tandem. The additional round-trip delay consists of u
48、p to six G.726 32-kbit/s ADPCM encodingdecoding stages. As a general guide, if there are no active echo control devices in the connection, the additional round-trip delay should be less than 5 ms 1. For voiceband data, two criteria are used: block error ratio (BLER) 102(for a block size of 103bits)
49、and bit error ratio (BER) 105. Whether BLER or BER is more meaningful depends upon the application. For transfers of large amounts of data with retransmittal protocols, BLER is appropriate. For facsimile applications and asynchronous character transfer, BER is more meaningful. The BER is usually the more stringent criterion. Note that typical switched network performance is an order of magnitude better than the above limiting criteria 11. A.5 Performance criteria versus asynchronously connected G.
