1、INTERNATIONAL TELECOMMUNICATION UNION ITU=T TELECOMMUNICATION STANDARDIZATION SECTOR OF ITU Q.115 (I 2/1999) SERIES Q: SWITCHING AND SIGNALLING Clauses applicable to ITU-T standard systems - Control of echo suppressors Logic for the control of echo control devices ITU-T Recommendation Q. I 15 (Forme
2、rly CCIlT Recommendation) STD-ITU-T RECMN Q-115-ENGL 1999 4662571 0685747 506 ITU-T Q-SERIES RECOMMENDATIONS SWITCHING AND SIGNALLING SIGNALLING IN THE INTERNATIONAL MANUAL SERVICE FUNCTIONS AND INFORMATION FLOWS FOR SERVICES IN THE 1SDN INTERNATIONAL AUTOMATIC AND SEMI-AUTOMATIC WORKING CLAUSES APP
3、LICABLE TO ITU-T STANDARD SYSTEMS General clauses Transmission clauses for signalling Control of echo suppressors Abnormal conditions SPECIFICATIONS OF SIGNALLING SYSTEMS No. 4 AND No. 5 SPECIFICATIONS OF SIGNALLING SYSTEM No. 6 SPECIFICATIONS OF SIGNALLING SYSTEM R1 SPECIFICATIONS OF SIGNALLING SYS
4、TEM R2 DIGITAL EXCHANGES INTERWORKING OF SIGNALLING SYSTEMS SPECIFICATIONS OF SIGNALLING SYSTEM No. 7 DIGITAL SUBSCRIBER SIGNALLMG SYSTEM No. 1 PUBLIC LAND MOBILE NETWORK INTERWORKING WITH SATELLITE MOBILE SYSTEMS INTELLIGENT NETWORK BROADBAND ISDN SIGNALLING REQUIREMENTS AND PROTOCOLS FOR 1MT-2000
5、Q. 14.3 Q.4-Q.59 Q.60-Q.99 Q.lOO-Q.119 Q. 1 0-Q. I09 Q.110-Q.114 Q.115 Q.116-Q.119 Q. 120-4.249 4.250-4.309 4.3 104.399 Q.40O-Q.499 Q.50O-Q.599 Q.60O-Q.699 4.700-4.849 Q.85-Q.999 Q. 1000-Q. 1099 Q.1100-Q.1199 Q. 1200-Q. 1699 Q. 1700-4.1799 4.2000-4.2999 For further details, please refer to the list
6、of ITU-T Recommendntions. STD*ITU-T RECMN Q=LLS-ENGL 1999 48b2591 0685748 442 ITU-T Recommendation Q.i 15 Logic for the control of echo control devices Summary Echo is a common problem in long distance (propagation delay) telephony, and echo control devices are deployed to eliminate the effects of i
7、t. The switching centres involved in a telephony connection must use consistent logical procedures to analyse the available information related to echo control requirements in order to optimize the locations at which echo control devices are provided in the connection. This ITU-T Recommendation defi
8、nes the information and logical procedures employed within switching centres to optimize echo control device placement. The information elements and logic defined in this ITU-T Recommendation are applicable to basic telephony calls, and to calls using supplementary services and Intelligent Networkin
9、g features, in both narrow-band and broadband networks, and should be applied regardless of the particular signalling systems that convey information between the switching centres involved in a connection. Source ITU-T Recommendation Q.115 was revised by ITU-T Study Group 11 (1997-2000) and approved
10、 under the WTSC Resolution 1 procedure on 3 December 1999. STD-ITU-T RECMN Q*LLS-ENGL L999 W 4862591 Ob85749 389 FOREWORD The International Telecommunication Union (ITU) is the United Nations specialized agency in the field of telecommunications. The ITU Telecommunication Standardization Sector (ITU
11、-T) is a permanent organ of IT. ITU-T is responsible for studying technical, operating and tariff questions and issuing Recommendations on them with a view to standardizing telecommunications on a worldwide basis. The World Telecommunication Standardization Conference (WTSC), which meets every four
12、years, establishes the topics for study by the ITU-T study groups which, in turn, produce Recommendations on these The approval of IT-T Recommendations is covered by the procedure laid down in WTSC Resolution I. In some areas of information technology which fall within IT-Ts purview, the necessary s
13、tandards are prepared on a collaborative basis with IS0 and IEC. topics. NOTE In this Recommendation, the expression “Administration“ is used for conciseness to indicate both a telecommunication administration and a recognized operating agency. INTELLECTUAL PROPERTY RIGHTS IT draws attention to the
14、possibility that the practice or implementation of this Recommendation may involve the use of a claimed Intellectual Property Right. IT takes no position concerning the evidence? validity or applicability of claimed Intellectual Property Rights, whether asserted by ITU members or others outside of t
15、he Recommendation development process. As of the date of approval of this Recommendation? ITU had not received notice of intellectual property, protected by patents, which may be required to implement this Recommendation. However, implementors are cautioned that this may not represent the latest inf
16、omation and are therefore strongly urged to consult the TSB patent database. o ITU 2001 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 fiom the I
17、TU. 1 2 3 4 5 6 7 8 8.1 8.2 9 10 11 12 13 STD-ITU-T RECMN Q-LLS-ENGL 1999 m 4862593 Ob85750 OTO M CONTENTS Scope References Terms and definitions . Abbreviations . Bearer capabilities for which echo control is required . Arrangements of echo control devices with respect to signalling Operation witho
18、ut signals . Considerations for the need of ECDs . Information taken into consideration Propagation delay counter, call history information Functions of an exchange initiating echo control . Unavailability of echo control devices . Placement of echo control devices in the network . Handling of echo
19、control devices in the case of different bearer capabilities Other considerations . Annex A . Echo control logic . General principles and definitions A . 1 A.l.l General principles . A.1.2 Definitions . A.2 Abstract model A.2.1 General description . A.2.2 Signalling systedprotocol A.2.3 Interworking
20、 A.2.4 Special network nodes . A.2.5 Echo control logic . A.3 SDL diagrams . Appendix I - Transmission of echo control information elements via signalling systems . Page 1 2 2 4 6 6 7 7 7 8 8 9 9 10 10 10 10 10 11 11 11 14 16 16 17 17 42 ITU-T Recommendation Q.115 Logic for the control of echo contr
21、ol devices 1 Scope The propagation delay in telecommunication networks affects both computer communication protocols and audiovisual communication between humans. The most noted effect is the echo problem for telephony which depends heavily on the propagation delay of the connection. In order to ach
22、ieve transmission objectives on long connections (refer to 3.10), it is necessary to take into account the effects of echo. A general discussion of echo considerations is given in ITU-T Recommendation G.131 6. The Characteristics of terminal half-echo control devices are given in ITU-T Recommendatio
23、n G.164 i. The characteristics of echo cancellers are given in ITU-T Recommendations G.165 2 and G.168 14. In order to achieve optimum echo control for each call, it is necessary to control both echo suppressors and echo cancellers. This can be carried out at switching centres only if sufficient inf
24、ormation is available to coordinate an overall controi action. Logical means to obtain pertinent information and the switching considerations governing its practicable use are detailed below. Control based on the transfer of signals between switching centres is given particular attention. Self-conta
25、ined control action such as tone disablement of echo suppressors and echo cancellers for data transmission is not within the scope of this ITU-T Recommendation. The target to be reached by the use of echo control logic is: - to optimize the location of provisiodinsertion of Echo Control Devices (ECD
26、). The echo control logic should select an ECD as near to the echo source (hybrid or terminai equipment) as possible. The ECD should be close enough to the source of echo so that its echo control tail length is sufficient to cancel any echo that may be present; to provide information about the inser
27、tiodprovision of ECD in the connection in the forward and in the backward direction. Where it is appropriate to extend the echo control methods and logic into national networks, this is subject to national guidelines. The delay time counter procedures require the addition of transmission delay value
28、s, beginning at the origin of a call and ending at the destination of it. These values could only be representative, if the whole or at least most of the delay of the connection is considered. If the configuration of a call is changed after the call Set-up (e.g. a new leg is added to a conference ca
29、ll), the exchange having knowledge about this change is responsible to initiate the echo control logic procedures for this new configuration. Echo control logic, i.e. the set of echo control logic procedures, covers the needs of echo control not only in the PSTN but also in the N-ISDN, B-ISDN, PLMN
30、and IN. It is also capable of adaptation to the changing requirements in connections supporting services such as call forwarding and multiparty calls. It is independent of the signalling systemsprotocols involved, but the optimal placement may depend on the capability of the signalling systems. Echo
31、 control logic described in this ITU-T Recommendation is compatible with the logic described in previous versions. For new versions of signalling systemsprotocols it is necessary to define parameters and messages to transmit the echo control information and requests as specified in Annex A. - STD-IT
32、U-T RECMN 4-LIS-ENGL L999 W 4Bb259L 0685752 973 It is outside the scope of this ITU-T Recommendation to determine when signalling messages are initiated. 2 References The following ITU Recommendations and other references contain provisions which, through reference in this text, constitute provision
33、s of this Recommendation. At the time of publication, the editions indicated were valid. All Recommendations and other references are subject to revision; all users of this Recommendation are therefore encouraged to investigate the possibility of applying the most recent edition of the Recommendatio
34、ns and other references listed below. A list of the currently valid ITU-T Recommendations is regularly published. CCITT Recommendation G. 164 (1 988), Echo suppressors. ITU-T Recommendation G. 165 (1 993), Echo cancellers. CCITT Recommendation 1.230 (1 988), Depnition of bearer service categories. C
35、CITT Recommendation G. 172 (1988), Transmission plan aspects of international conference calls. ITU-T Recommendation G. 173 (1 993), Transmission planning aspects of the speech service in digital public land mobile networks. CCITT Recommendation G. 13 1 (1 988), Stability and echo. CCITT Recommendat
36、ion E.220 (1 992), Interconnection of public land mobile nefworks (PLMN). ITU-T Recommendation 4.764 (1 993), ISDN user part signalling procedures. ITU-T Recommendation Z. 1 O0 (1 993), CCIT SpeciJcation and description language CCITT Recommendation 4.271 (1 988), Continuity check of the speech path
37、: General. CCITT Recommendation 4.724 (1 988), Telephone user part signalling procedures. CCITT Recommendation Q. 1 12 (1 988), Signal levels and signal receiver sensitivity. ITU-T Recommendation Q.2764 (1 999, Signalling System No. 7 B-ISDN User Part B-ISUP - Basic call procedures. ITU-T Recommenda
38、tion G. 168 (1 997), Digital network echo cancellers. (SDL). Terms and definitions Subsequent discussion of control measures will refer to the standard terminal half-echo suppressor specified in ITU-T Recommendation G.164 i and the echo cancellers specified in ITU-T Recommendations G.165 2 and G.168
39、 14. The terms “echo suppressor“ and “echo canceller“ will be used to denote these devices. The term “ECD“ will comprise both echo suppressors and echo cancellers. 3.2 Two means of introducing ECDs are considered as acceptable. These are the use of permanently associated echo control devices, and th
40、e use of echo control devices inserted from a common pool. 3.3 With respect to control of permanently associated ECDs, control actions are said to enable or disable. 3.4 With respect to echo control devices provided from pools, control actions are concerned with inserting or not inserting. An insert
41、ed ECD is controlled in order to enable or disable it. STD-ITU-T RECMN QILLS-ENGL 1999 m 48b2591 Ob85753 BOT 3.5 With respect to ECD provided in B-ISDN exchanges, the term “ECD“ denotes echo cancellers only, as echo suppressors should not be used. 3.6 Information to assist in the placement of echo c
42、ontrol devices is communicated between exchanges by ITU-compliant signalling. 3.7 Full ECD describes the situation where both an outgoing echo control device and an incoming echo control device (see 3.1 1) are enabled at a single exchange. 3.8 A long circuit is considered as one which, if used by it
43、self, would require echo control. 3.9 A short circuit is considered as one which, if used by itself, would not require echo control. 3.10 A long connection is a connection that requires echo control. A long connection may consist of several circuits in tandem. These circuits may or may not be long c
44、ircuits, but their total propagation delay is such that echo control is required. If not detected at call Set-up time, the total propagation delay is calculated during call set-up based on information carried in signalling (see 8.2). 3.11 An incoming echo control device (IECD) is a device cancelling
45、 the echo returned from the destination network with reference to the direction in which the call is set up. 3.12 An outgoing echo control device (OECD) is a device cancelling the echo returned from the network of origin with reference to the direction in which the call is set up. 3.13 Two types of
46、exchanges are defined: 3.13.1 exchange Type 1 invokes echo control logic procedures for all calls of the bearer capability “speech or 3.1 kHz audio“. These procedures are described in this ITU-T Recommendation. Any exchange in a network can be of Type 1. 3.13.2 exchange Type 2 cannot invoke echo log
47、ic control procedures. The received echo control information is passed unchanged (in both directions). In case of interworking the echo control information is mapped from one signalling systemprotocol to the other. 3.14 An echo control initiating exchange is the first exchange that recognizes the ne
48、ed to apply echo control procedures. 3.15 The propagation delay initiating exchange is the exchange that initiates the propagation delay determination procedure; e.g. a typical case is the originating local exchange. 3.16 The propagation delay terminating exchange is the exchange that terminates the
49、 propagation delay determination procedure; e.g. typically the local destination exchange. 3.17 Node of the Intelligent Network (IN) is a node which belongs temporarily or permanently to the IN, e.g. a) an SSP is normally considered to be a node of the PSTN/N-, B-ISDN, but when connecting a Specialized Resource Function (SRF) for the user interaction it is considered to be a node of the IN; and an SCP is considered to be a permanent node of the IN. b) - STD-ITU-T RECMN Q.LL5-ENGL Lqqq W 48b2591 Ob85754 746 4 Abbreviations This ITLJ-T Recommendation uses
