ITU-T I 370-1991 Congestion Management for the ISDN Frame Relaying Bearer Service (Study Group XVIII) 13 pp《ISDN帧中续承载业务拥塞管理 研究组18 13pp》.pdf
《ITU-T I 370-1991 Congestion Management for the ISDN Frame Relaying Bearer Service (Study Group XVIII) 13 pp《ISDN帧中续承载业务拥塞管理 研究组18 13pp》.pdf》由会员分享,可在线阅读,更多相关《ITU-T I 370-1991 Congestion Management for the ISDN Frame Relaying Bearer Service (Study Group XVIII) 13 pp《ISDN帧中续承载业务拥塞管理 研究组18 13pp》.pdf(13页珍藏版)》请在麦多课文档分享上搜索。
1、48b2591 0561415 9 INTERNATIONAL TELECOMMUN CATION UN ION CCITT THE INTERNATIONAL TELEGRAPH AND TELEPHONE CONS U LTATIV E COM M ITTE E INTEGRATED SERVICES DIGITAL NETWORK (ISDN) OVERALL NETVVORK ASPECTS AND FUNCTIONS, IS DN US ER-N ETWORK INTER FACES 1.370 CONGESTION MANAGEMENT FOR THE ISDN FRAME REL
2、AYING BEARER SERVICE Recommendation 1.370 Geneva, 1991 4862593 O563436 O INTERNATIONAL TELECOMMUNICATIO CCITT TH E INTERNATIONAL TELEGRAPH AND TELEPHONE CON SU LTATIVE C OMM ITTE E INTEGRATED SERVICES DIGITAL NETWORK (ISDN) OVERALL NETWORK ASPECTS AND FUNCTIONS, ISDN USER-NETWORK INTERFACES C 1.370
3、CONGESTION MANAGEMENT FOR THE ISDN FRAME RELAYING BEARER SERVICE Recommendation 1.370 I Geneva, 1991 FOREWORD The CCITT (the International Telegraph and Telephone Consultative Committee) is a permanent organ of the International Telecommunication Union (ITU). CCI is responsible for studying technica
4、l, operating and tariff questions and issuing Recommendations on them with a view to standardizing telecommunications on a worldwide basis. The Plenary Assembly of CCITT which meets every four years, establishes the topics for study and approves Recommendations prepared by its Study Groups. The appr
5、oval of Recommendations by the members of CC between Plenary Assemblies is covered by the procedure laid down in CCIT Resolution No. 2 (Melbourne, 1988). Recommendation 1.370 was prepared by Study Group XWI and was approved under the Resolution No. 2 procedure on the 25th of October 1991. CC NOTES 1
6、) telecommunication Administration and a recognized private operating agency. 2) In this Recommendation, the expression “Administration” is used for conciseness to indicate both a A list of abbreviations used in this Recommendation can be found in Annex A. O IT 1991 All rights reserved. No part of t
7、his publication may be reproduced or utilized in any form or by any means, electronic or mechanical, including photocopying and microfilm, without permission in writing from the ITU. 4862593 0563438 4 R Recommendation 1.370 CONGESTION MANAGEMENT FOR THE ISDN FRAME RELAYING BEARER SERVICE 1 Congestio
8、n management principles 1.1 Scope This Recommendation describes U-plane based congestion management strategy and mechanisms for ISDN frame relay bearer services. It covers both network and end user mechanisms and responsibilities to avoid or recover from periods of congestion. C-plane procedures at
9、the user network interface other than clearing or not accepting calls are not recommended. Procedures, objectives and requirements for C-plane congestion management between networks are for further study. Special provisions for the treatment of continuous bit stream oriented (CBO) traffk is outside
10、the scope of the Recommendation. This strategy is intended to operate for access channel rates up to 2048 kbit/s. 1.2 Definitions access rate The data rate of the user access channel , B or H). The speed of the access channel determines how much data (maximum rate) the end user can inject into the n
11、etwork. committed burst size, Bc The maximum committed amount of data a user may offer to the network during a time interval Tc. Bc is negotiated at call Set-up. excess burst size, Be The maximum ailowed amount of data by which a user can exceed Bc during a time interval Tc. This data (Be) is delive
12、red in general with a lower probability than Bc. Be is negotiated at cal Set-up. committed rate measurement interval, Tc The time interval during which the user is ailowed to send only the committed amount of data (Bc) and the excess amount of data (Be). Tc is computed. committed information rate (C
13、IR) The information transfer rate which the network is committed to transfer under normal conditions. The rate is averaged over a minimum increment of time Tc. CIR is negotiated at call Set-up. forward explicit congestion notification (FECN) See Recommendation Q.922 for the full definition. Recommen
14、dation 1,370 1 4Bb2591 0561419 b = backward explicit congestion notification (BECN) See Recommendation Q.922 for the full definition. consolidated link layer management message (CLLM) See Recommendation Q.922 for the full definition. discard eligibiity indicator This indicates that a frame should be
15、 discarded in preference to other frames in a congestion situation, when frames must be discarded to ensure safe network operation and maintain the committed level of service within the network. fairness An attempt by the network to maintain the committed call parameters which the end user negotiate
16、d at call setup time. An example of this would be first discarding the frames in excess of the committed information rate (CIR) and refusing to allow new call setups to occur prior to discarding committed data traffic. offered load Refers to the frames offered to the network, by an end user, to be d
17、elivered to the selected destination. The information rate offered to the network could exceed the negotiated class of service parameters. congestion management Includes network engineering, OAM procedures to detect the onset of congestion, and real time mechanisms to prevent or recover from congest
18、ion. Congestion management includes but is not limited to congestion control, congestion avoidance and congestion recovery as defined below. congestion control Refers to real-time mechanisms to prevent and recover from congestion during periods of coincidental peak trafk demands or network overload
19、(e.g., resource failures). Congestion control includes both congestion avoidance and congestion recovery mechanisms. congestion avoidance Congestion avoidance procedures refer to procedures initiated at or prior to point A (see Figures 1D.370 and 2D.370) to prevent congestion from progressing to poi
20、nt B. Congestion avoidance procedures operate around point A and within the regions of mild congestion and severe congestion as shown in Figures 1D.370 and 2D.370. congestion recovery Congestion recovery refers to procedures initiated to prevent congestion from severely degrading the end user percei
21、ved quality of service(s) delivered by the network. These procedures are typically initiated when the network has begun to discard frames due to congestion. Congestion recovery procedures operate around point B and within the region of severe congestion as shown in Figures 1D.370 and 2D.370. ingress
22、 node The node that supports the source user-network interface (UNI). 2 Recommendation 1.370 egress node The node that supports the destination user-network interface (UNI). 1.3 Objectives of congestion management The primary objectives of congestion control mechanisms are to maintain, with a very h
23、igh probability, specified quality of service (e.g. throughput, delay, frame loss) for each virtual call or permanent virtual circuit. Congestion in the U-plane of a frame relay bearer service occurs when traffk, arriving at a resource (e.g. memory, bandwidth, processor), exceeds the network enginee
24、red level. It can also occur for other reasons (e.g. equipment failure). The impact of network congestion is performance degradation in terms of throughput and delay. Two levels of congestion in terms of impact on class of service, are defined. Point A is the point beyond which the transit delay in
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