1、 INTERNATIONAL TELECOMMUNICATION UNION ITU-T Q.115.1TELECOMMUNICATION STANDARDIZATION SECTOR OF ITU (12/2002) SERIES Q: SWITCHING AND SIGNALLING Clauses applicable to ITU-T standard systems Logic and protocols for the control of signal processing network elements and functions Logic for the control
2、of echo control devices and functions ITU-T Recommendation Q.115.1 ITU-T Q-SERIES RECOMMENDATIONS SWITCHING AND SIGNALLING SIGNALLING IN THE INTERNATIONAL MANUAL SERVICE Q.1Q.3 INTERNATIONAL AUTOMATIC AND SEMI-AUTOMATIC WORKING Q.4Q.59 FUNCTIONS AND INFORMATION FLOWS FOR SERVICES IN THE ISDN Q.60Q.9
3、9 CLAUSES APPLICABLE TO ITU-T STANDARD SYSTEMS Q.100Q.119 General clauses Q.100Q.109 Transmission clauses for signalling Q.110Q.114 Logic and protocols for the control of signal processing network elements and functions Q.115 Abnormal conditions Q.116Q.119 SPECIFICATIONS OF SIGNALLING SYSTEM No. 4 Q
4、.120Q.139 SPECIFICATIONS OF SIGNALLING SYSTEM No. 5 Q.140Q.199 SPECIFICATIONS OF SIGNALLING SYSTEM No. 6 Q.250Q.309 SPECIFICATIONS OF SIGNALLING SYSTEM R1 Q.310Q.399 SPECIFICATIONS OF SIGNALLING SYSTEM R2 Q.400Q.499 DIGITAL EXCHANGES Q.500Q.599 INTERWORKING OF SIGNALLING SYSTEMS Q.600Q.699 SPECIFICA
5、TIONS OF SIGNALLING SYSTEM No. 7 Q.700Q.799 Q3 INTERFACE Q.800Q.849 DIGITAL SUBSCRIBER SIGNALLING SYSTEM No. 1 Q.850Q.999 PUBLIC LAND MOBILE NETWORK Q.1000Q.1099 INTERWORKING WITH SATELLITE MOBILE SYSTEMS Q.1100Q.1199 INTELLIGENT NETWORK Q.1200Q.1699 SIGNALLING REQUIREMENTS AND PROTOCOLS FOR IMT-200
6、0 Q.1700Q.1799 SPECIFICATIONS OF SIGNALLING RELATED TO BEARER INDEPENDENT CALL CONTROL (BICC) Q.1900Q.1999 BROADBAND ISDN Q.2000Q.2999 For further details, please refer to the list of ITU-T Recommendations. ITU-T Rec. Q.115.1 (12/2002) i ITU-T Recommendation Q.115.1 Logic for the control of echo con
7、trol devices and functions Summary Echo is a common problem in long distance (propagation delay) telephony, and echo control devices are deployed to eliminate the effects of it. The call/bearer control entities involved in a telephony connection must use consistent logical procedures to analyse the
8、available information related to echo control requirements in order to optimize the locations at which echo control devices are provided in the connection. This Recommendation defines the information and logical procedures employed within call/bearer control entities to optimise echo control device
9、placement. The information elements and logic defined in this Recommendation are applicable to basic telephony calls, and to calls using supplementary services and Intelligent Networking features, in both narrow-band and broadband networks using circuit switched or packet bearer technology, and shou
10、ld be applied regardless of the particular signalling systems that convey information between the call/bearer control entities involved in a connection. This Recommendation is a revision of the ITU-T Rec. Q.115 (12/1999) and incorporates the contents of Implementors Guide (12/2000) for ITU-T Rec. Q.
11、115 (12/1999). Source ITU-T Recommendation Q.115.1 (2002) was revised from ITU-T. Rec. Q.115 (1999) by ITU-T Study Group 11 (2001-2004) and approved under the WTSA Resolution 1 procedure on 29 December 2002. ii ITU-T Rec. Q.115.1 (12/2002) FOREWORD The International Telecommunication Union (ITU) is
12、the United Nations specialized agency in the field of telecommunications. The ITU Telecommunication Standardization Sector (ITU-T) is a permanent organ of ITU. ITU-T is responsible for studying technical, operating and tariff questions and issuing Recommendations on them with a view to standardizing
13、 telecommunications on a worldwide basis. The World Telecommunication Standardization Assembly (WTSA), which meets every four years, establishes the topics for study by the ITU-T study groups which, in turn, produce Recommendations on these topics. The approval of ITU-T Recommendations is covered by
14、 the procedure laid down in WTSA Resolution 1. In some areas of information technology which fall within ITU-Ts purview, the necessary standards are prepared on a collaborative basis with ISO and IEC. NOTE In this Recommendation, the expression “Administration“ is used for conciseness to indicate bo
15、th a telecommunication administration and a recognized operating agency. INTELLECTUAL PROPERTY RIGHTS ITU draws attention to the possibility that the practice or implementation of this Recommendation may involve the use of a claimed Intellectual Property Right. ITU takes no position concerning the e
16、vidence, validity or applicability of claimed Intellectual Property Rights, whether asserted by ITU members or others outside of the Recommendation development process. As of the date of approval of this Recommendation, ITU had not received notice of intellectual property, protected by patents, whic
17、h may be required to implement this Recommendation. However, implementors are cautioned that this may not represent the latest information and are therefore strongly urged to consult the TSB patent database. ITU 2003 All rights reserved. No part of this publication may be reproduced, by any means wh
18、atsoever, without the prior written permission of ITU. ITU-T Rec. Q.115.1 (12/2002) iii CONTENTS Page 1 Scope 1 2 References. 2 2.1 Normative references 2 2.2 Informative references 2 3 Terms and definitions . 2 4 Abbreviations 4 5 Bearer capabilities for which echo control is required . 5 6 Arrange
19、ments of echo control devices with respect to signalling 6 7 Operation without signals. 6 8 Considerations for the need of ECDs . 7 8.1 Information taken into consideration 7 8.2 Propagation delay counter, call history information 8 9 Functions of an exchange initiating echo control. 8 10 Unavailabi
20、lity of echo control devices . 9 11 Placement of echo control devices in the network . 9 12 Handling of echo control devices in the case of different bearer capabilities 9 13 Other considerations . 10 Annex A Echo control logic 10 A.1 General principles and definitions 10 A.2 Abstract model 11 A.3 S
21、DL diagrams. 20 Appendix I Transmission of echo control information elements via signalling systems . 45 ITU-T Rec. Q.115.1 (12/2002) 1 ITU-T Recommendation Q.115.1 Logic for the control of echo control devices and functions 1 Scope The propagation delay in transport networks affects both computer c
22、ommunication 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 achieve transmission objectives on long connections (refer to 3.10), it is necessary to take into
23、 account the effects of echo. A general discussion of echo considerations is given in ITU-T Rec. G.131 6. The characteristics of terminal half-echo control devices are given in ITU-T Rec. G.164 1. The characteristics of echo cancellers are given in ITU-T Recs G.165 2 and G.168 14. In order to achiev
24、e optimum echo control for each call, it is necessary to control both echo suppressors and echo cancellers (realized as a standalone device or as a function of a signal processing network element). This can be carried out at call/bearer control entities only if sufficient information is available to
25、 coordinate an overall control 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 call bearer control entities, is given particular attention. Self-contained contro
26、l action, such as tone disablement of echo suppressors and echo cancellers for data transmission, is not within the scope of this Recommendation. The target to be reached by the use of echo control logic is: to optimize the location of provision/insertion of Echo Control Devices/Functions (ECD). The
27、 echo control logic should select an ECD as near to the echo source (hybrid or terminal 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 insertion/p
28、rovision of ECD in the connection in the forward and in the backward direction. The delay time counter procedures require the addition of transmission delay values, 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 le
29、ast 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 call), the call/bearer control entity having knowledge about this change is responsible to initiate the echo control logic procedures for
30、this new configuration. Echo control logic is independent of the signalling systems/protocols involved, but the optimal placement may depend on the capability of the signalling systems used for the call set up. Echo control logic described in this Recommendation is backward compatible with the logic
31、 described in ITU-T Rec. Q.115 (12/99). For new versions of signalling systems/protocols, it is necessary to define parameters and messages to transmit the echo control information and requests as specified in Annex A. It is outside the scope of this Recommendation to determine when signalling messa
32、ges are initiated. 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, IN and hybrid networks. The term hybrid networks in this context stands for any combination of PSTN, ISDN, Mobile- and Pa
33、cket-Network. 2 ITU-T Rec. Q.115.1 (12/2002) NOTE Echo control devices (realized as standalone device or as a function of a signal processing device) controlled by the logic described in this Recommendation are designed to eliminate echo of a voice/audio signal. These Echo Control Devices/Functions
34、are provided by the network. The technique used in these Echo Control Devices/Functions to eliminate the echo is beyond the scope of this Recommendation. 2 References The following ITU-T Recommendations and other references contain provisions which, through reference in this text, constitute provisi
35、ons of this Recommendation. At the time of publication, the editions indicated were valid. All Recommendations and other references are subject to revision; users of this Recommendation are therefore encouraged to investigate the possibility of applying the most recent edition of the Recommendations
36、 and other references listed below. A list of the currently valid ITU-T Recommendations is regularly published. The reference to a document within this Recommendation does not give it, as a stand-alone document, the status of a Recommendation. 2.1 Normative references 3 ITU-T Recommendation I.230 (1
37、988), Definition of bearer service categories. 4 ITU-T Recommendation G.172 (1988), Transmission plan aspects of international conference calls. 5 ITU-T Recommendation G.173 (1993), Transmission planning aspects of the speech service in digital public land mobile networks. 6 ITU-T Recommendation G.1
38、31 (1996), Control of talker echo. 7 ITU-T Recommendation E.220 (1996), Interconnection of public land mobile networks (PLMN). 9 ITU-T Recommendation Z.100 (2002), Specification and description language (SDL). 2.2 Informative references 1 ITU-T Recommendation G.164 (1988), Echo suppressors. 2 ITU-T
39、Recommendation G.165 (1993), Echo cancellers. 14 ITU-T Recommendation G.168 (2002), Digital network echo cancellers. 8 ITU-T Recommendation Q.764 (1993), ISDN user part signalling procedures. 10 ITU-T Recommendation Q.271 (1988), General. 11 ITU-T Recommendation Q.724 (1988), Telephone user part sig
40、nalling procedures. 12 ITU-T Recommendation Q.112 (1988), Signal levels and signal receiver sensitivity. 13 ITU-T Recommendation Q.2764 (1999), Signalling System No. 7 B-ISDN User Part B-ISUP Basic call procedures. 3 Terms and definitions 3.1 Subsequent discussion of control measures will refer to t
41、he standard terminal half-echo suppressor specified in ITU-T Rec. G.164 1 and the echo cancellers specified in ITU-T Recs G.165 2 and G.168 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 canceller
42、s. 3.2 Two means of introducing ECDs are considered as acceptable. These are the use of permanently associated echo control devices, and the use of echo control devices inserted from a common pool. ITU-T Rec. Q.115.1 (12/2002) 3 3.3 With respect to control of permanently associated ECDs, control act
43、ions 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 inserted ECD is controlled in order to enable or disable it. 3.5 With respect to ECD provided in B-ISDN exchanges, the term “ECD“ denote
44、s echo cancellers only, as echo suppressors should not be used. 3.6 Information to assist in the placement of echo control 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 contr
45、ol device (see 3.11) are enabled at a single exchange. 3.8 long circuit: is considered as one which, if used by itself, would require echo control. 3.9 short circuit: is considered as one which, if used by itself, would not require echo control. 3.10 long connection: is a connection that requires ec
46、ho control. A long connection may consist of several circuits in tandem. These circuits may or may not be long circuits, 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
47、 information carried in signalling (see 8.2). 3.11 incoming echo control device (IECD): is a device cancelling the echo returned from the destination network with reference to the direction in which the call is set up. 3.12 outgoing echo control device (OECD): is a device cancelling the echo returne
48、d from the network of origin with reference to the direction in which the call is set up. 3.13 Two types of 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 Re
49、commendation. Any exchange in a network can be of Type 1. 3.13.2 exchange Type 2: cannot invoke echo logic 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 system/protocol to the other. 3.14 echo control initiating exchange: is the first exchange that recognizes the need to apply echo control procedures. 3.15 propagation delay initiating exchange: is the exchange that initiates t
