1、 ITu-T RECMN*E.OII 93 4b259L 0593455 2LT INTERNATIONAL TELECOMMUNICATION UNION ITU-T TELECOMMUNICATION STANDARDIZATION SECTOR OF ITU TELEPHONE NETWORK AND ISDN OPERATION, NUMBERING, ROUTING AND MOBILE SERVICE E.301 (03/93) IMPACT OF NON-VOICE APPLICATIONS ON THE TELEPHONE NETWORK ITU-T Recommendatio
2、n E.301 (Previously “CCITT Recommendation”) FOREWORD The ITU Telecommunication Standardization Sector (ITU-T) is a permanent organ of the International Telecom- munication Union. The ITU-T is responsible for studying technical, operating and tariff questions and issuing Recommendations on them with
3、a view to standardizing telecommunications on a worldwide basis. The World Telecommunication Standardization Conference (WTSC), which meets every four years, established the topics for study by the ITU-T Study Groups which, in their turn, produce Recommendations on these topics. ITU-T Recommendation
4、 E.301 was revised by the ITU-T Study Group II (1988-1993) and was approved by the WTSC (Helsinki, March 1-12, 1993). NOTES 1 As a consequence of a reform process within the International Telecommunication Union (ITU), the CCITT ceased to exist as of 28 February 1993. In its place, the ITU Telecommu
5、nication Standardization Sector (ITU-T) was created as of 1 March 1993. Similarly, in this reform process, the CCIR and the IFRB have been replaced by the Radiocommunication Sector. In order not to delay publication of this Recommendation, no change has been made in the text to references containing
6、 the acronyms “CCITT, CCIR or IFRB” or their associated entities such as Plenary Assembly, Secretariat, etc. Future editions of this Recommendation will contain the proper terminology related to the new ITU structure. 2 telecommunication administration and a recognized operating agency. In this Reco
7、mmendation, the expression “Administration” is used for conciseness to indicate both a O ITU 1994 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
8、from the ITU. ITU-T RECMNUE.301 93 = 48b2591 0593457 O92 1 2 3 4 5 6 7 8 9 10 CONTENTS Introduction Scope Related Recommendations . Category 1 applications 4.1 Voice . 4.2 Non-voice . 4.3 Mixed Signalling and transmission considerations for Category 1 applications . 5.2 Transmission . 5.1 Signal int
9、erference 5.3 Potential solutions . DCME for Category 1 applications 6.1 Speech quality considerations . 6.2 Impact of DLC on blocking performance . 6.3 Other considerations . 6.4 Tandem DCME connections . Category 2 applications Signalling, dialling and routing considerations for Category 2 applica
10、tions . 8.1 Signalling considerations 8.2 Dialling and numbering considerations 8.3 Routing considerations . Network architecture considerations 9.1 Overlay networks 9.2 Integrated networks Recommendation history Annex A . Teletraffic characteristics of non-voice traffic A.1 Mean call duration A.2 2
11、4-hour traffic profile . Annex B . Annex C . Annex D Annex E . Recommendation E.301 (03/93) Page 1 1 2 2 2 2 3 3 3 3 3 4 4 5 5 6 6 7 7 7 8 8 8 8 8 8 8 8 11 12 13 14 i ITU-T RECMN*E.301 93 4862591 0591c158 T29 = Recommendation E.301 IMPACT OF NON-VOICE APPLICATIONS ON THE TELEPHONE NETWORK (Modjied a
12、t Helsinki, 1993) 1 Introduction recognizing that true Integrated Service Digital Networks (ISDNs) as described in the I-Series Recommendations, will evolve from Public Switched Telephone Networks (PSTNs); that this evolutionary process is already well under way in that digital capabilities are bein
13、g introduced in PSTNs all over the world, in place of analogue facilities; that although the realization of true ISDNs worldwide is unlikely to occur for many years, the introduction of digital capabilities nevertheless provides the opportunity for Administrations to improve the quality of existing
14、services and simultaneously also offer new “ISDN-like” services; and that these same digital capabilities may also introduce network elements that may adversely impact service quality in ways not yet fully understood; this Recommendation provides an analysis of some of the problems which may be enco
15、untered in the existing telephone network during the PSTN to ISDN transition period. Further, this Recommendation also described network control and routing procedures that can be used to provide high levels of service quality for all services until a comprehensive ISDN can be achieved. 2 Scope From
16、 a network capabilities point of view, it is convenient to separate the various types of traffic that PSTNs may be expected to carry into the following two broad categories. Category 1 applications are those traffic streams that can be carried over analogue networks but will henceforth be carried on
17、 digital facilities in order to realize the quality improvements inherent in digital transmission. Examples of such applications include data and facsimile with further details contained in section 4. Category 2 applications are primarily those traffic streams that inherently require digital facilit
18、ies and in addition may require further network actions to accommodate requirements peculiar to the particular traffic stream. Examples of such applications include switched digital services with fuller details given in clause 7. However, there may be cases where an Administration may choose to trea
19、t an application normally considered to be of Category 1 as a Category 2 application. For example, an Administration providing switched transit service may choose to provide special treatment to transit calls. Within this framework, the scope of this Recommendation is as follows: This Recornmendatio
20、n only deals with PSTNs which are evolving, by the introduction of digital capabilities, towards ISDNs. Clauses 4, 5 and 6 deal with Category 1 applications. Clauses 7, 8 and 9 deal with Category 2 applications. CSPDNs and PSPDNs, which are based on the X.121 numbering plan, and the interworking bet
21、ween these networks and PSTNs is outside the scope of this Recommendation. Finally, it should be noted that this Recommendation does not consider Packet Circuit Multiplication Equipment (PCME) technology. The impact of this technology on the issues discussed here are for further study. Recommendatio
22、n E.301 (03/93) 1 ITU-T RECNN*Em30L 93 H 4862593 0593459 9b5 H 3 Related Recommendations The following Recommendations cover related topics in the evolution of PSTNs towards ISDN: - - - - - - - - Rec. E. 164 Numbering plan for the ISDN era; Rec. E.171 International telephone routing plan; Rec. E. i
23、72 ISDN routing plan; Rec. (3.721 32 kbids Adaptive Difserential Pulse Code Modulation (ADPCM); Rec. G.726 Adaptive pulse code modulation for 40, 32, 24, 16 kbit/s(ADPCM); Rec. G.727 5, 4-, 3-, 2- bits sample, embedded ADPCM; Rec. G.728 16 kbith low-delay CELP (LD-CELP) speech coding algorithm; Rec.
24、 G.763 Digital circuit multiplication equipment using 32 kbit/s ADPCM and digital speech interpolation; - Rec. (3.766 Facsimile demodulation and remodulation in DCME; - Rec. P.84 Subjective listening test method for evaluating digital circuit multiplication and packetized voice systems. 4 Category 1
25、 applications In this clause we consider three types of Category 1 applications classified as the following. 4.1 Voice Voice traffic is mainly composed of speech conversation. Because of the rapid deployment of Digital Circuit Multiplication Equipment (DCME) which utilizes speech interpolation and c
26、ompression to efficiently utilize digital facilities, increasing volumes of non-voice traffic can cause problems that can affect the performance of voice traffic. 4.2 Non-voice Voice-band traffic which is not speech. Example applications for which the present telephone network is capable of providin
27、g bearer services include: - data (analogue coded); - facsimile: - scrambled speech; - phototelegraphy; - Voice Frequency (VF) telegraphy. VF telegraphy is not widely carried on PSTNs. Furthermore, phototelegraphy calls use telephone circuits removed from normal service, as set out in Recommendation
28、 E.320. Therefore, for calls on the PSTN, only Voice-Band Data (VBD) and facsimile services are considered below. Between these two non-voice applications, probably the most common type is facsimile. In fact, for certain traffic streams the majority of the traffic is facsimile. At the same time facs
29、imile traffic is growing at several times the rate of voice traffic. Special considerations may need to be given to the suitability of the telephone network to carry these services because of their particular characteristics which differ from those of voice traffic in the following ways: the transmi
30、ssion of some of these services is characterized by a continuous power loading, compared to the syllabic bursts found in speech; a) 2 Recommendation E.301 (03/93) ITU-T RECIN*E.301 93 M 4862591 0593460 687 b) non-voice traffic often has a 24-hour traffic profile different from voice traffic; this is
31、 especially true for international routes, where time zone differences result in the peaks of voice and non-voice traffic occurring at different times (see Annex A for some typical traffic profiles); c) mean call holding times are often significantly shorter than voice traffic. 4.3 Mixed Traffic whi
32、ch has both voice and non-voice transmission. An example of one such service would be videotelephony. 5 Signalling and transmission considerations for Category 1 applications The increasing presence of non-voice traffic in Category 1 applications may result in signalling and transmission problems. 5
33、.1 Signal interference Non-voice service signals can interfere with telephone circuit signalling systems and vice versa. Data or facsimile signals can interfere with signalling systems which use in-band line signalling such as Signalling Systems No. 4, No. 5 and RI. Thus such non-voice calls should
34、use the standardized systems set out in the Series-V and -T Recommendations since these are designed to prevent interference with the standard signalling systems, either by avoiding the particular signalling frequencies or by operating the guard circuit of the signalling receiver. Despite the safegu
35、ards mentioned above, it may sometimes happen that the signalling receiver is momentarily operated by the carried service signal. In this case the splitting device in the signalling receiver will operate and cause a short discontinuity in the received service signal. 5.2 Transmission 5.2.1 Interfere
36、nce to transmission systems If the proportion of non-voice calls is large, it can increase the overall power loading in a transmission assembly (group or supergroup). This can cause distortion in the group of signals and/or the operation of power limiters which can adversely affect other calls or se
37、rvices in the same transmission assembly. 5.2.2 Interference by transmission systems It may be the case that ordinary speech channels do not provide an adequate transmission path for some types of non-voice service, resulting in an unacceptable error performance, or in the worst case not allowing an
38、y service at all. For example, echo suppressors may not allow the transmission of duplex data unless the tone-disabling signal is first applied and immediately followed by the service signal. Some types of transmission systems do not support higher speed data transmission. For example, the 32 kbids
39、ADPCM algorithm in Recommendation G.726 supports VBD traffic only up to 4800 bids and the 40 kbit/s algorithm in G.726 supports VBD rates up to 9600 bids with 14 400 bids supported only for non-tandem connections. Also the LD-CELP algorithm in G.728 supports VBD only up to 2400 bids. 5.3 Potential s
40、olutions If the transmission of non-voice services on the telephone network is found to cause problems due to the issues discussed in 5.2.1 and 5.2.2, the Administrations concerned should take the following actions: Recommendation E.301 (03/93) 3 5.3.1 which recognize the need to provide for non-voi
41、ce services within prescribed Quality of Service parameters. It should be established for each bilateral relationship what commercial and regulatory arrangements exist 5.3.2 can be taken: If it is decided by the Administration concerned that certain services must be supported, then two approaches a)
42、 only transmission systems allowing suitable performance for non-voice services are used; b) separate routings are established for the whole or part of the networks, where unsuitable transmission would otherwise occur. 5.3.3 methods for achieving this: In case b) above, it is necessary to know when
43、subscribers are initiating non-voice calls. There are two i) the subscriber line is known to be one originating only non-voice calls, e.g. it is a facsimile terminal; ii) the subscriber sends some form of service indication to the network, identifying a non-voice call request (e.g. Recommendation E.
44、 13 1). If these indications are directly available at the exchange where the separate routing is selected, then path selection need only combine this indication with the dialled digits. In other cases it is necessary for a suitable signalling system to be employed to carry this indication forward t
45、o the special selection point. This may be done using signalling systems including special call categories. In particular, a call category “data call” is provided in Signalling Systems R2, No. 6 and No. 7, also No. 5 by bilateral agreement. The separate routing may be continued throughout the networ
46、k using either “path of entry” indications at the exchanges concerned or the special call category signals within the signalling system (see Recommendation E. 172). 6 DCME for Category 1 applications As mentioned in 4.1, in order to economize on the provision of international voice channels, interna
47、tional digital transmission systems are increasingly being deployed with speech interpolation systems such as DCME. Information on speech interpolation systems can be found in Supplement 2 of Fascicle VI.1. Circuit gains are realized by speech compression and by exploiting the silent period normally
48、 existing during speech conversations. DCME equipment uses Low Rate Encoding (LRE) for non-voice signals and a combination of LRE and Variable Bit Rate Encoding (VBR) for speech signals (see Recommendation P.84, Blue Book for a definition of LRE and VBR). In the absence of VBD traffic, circuit gains
49、 of 4: 1 are achievable. Annex B shows a functional view of a typical DCME configuration. 6.1 Speech quaiity considerations Continuous non-voice service signals will cause the continuous operation of the speech detectors and give rise to permanent association of the telephone circuit to the transmission channel. This in turn increases the probability of noticeable speech clipping due to freeze-out where no channel is available. Thus the quality of speech on parallel voice calls can be affected, resulting in a need to reduce the gain advantage of the speech interpolation system. LRE and
