1、INTERNATIONAL TELECOMMUNICATION UNION CCITT THE INTERNATIONAL TELEGRAPH AND TELEPHONE CONSULTATIVE COMMITTEE TELEPHONE NETWORK AND ISDN OPERATION, NUMBERING, ROUTING AND MOBILE SERVICE E.170 (1 0/92) TRAFFIC ROUTING Recommendation E.170 CCITT RECMN*EmL70 92 4862593 0576787 222 FOREWORD The CCITT (th
2、e Ititertiatioiid Telegraph and Telephone CoiisulLtive Committee) is a pennaiieiit organ of tlie Internatioual Telecnmunication Union (ITU). CCITT is responsible for studying technical, operating and tariff questions and issuing Recommendations o11 them with a view to standardizing telecoininuiiicat
3、ious on a worldwide basis. The Plenary Assembly of CCITT which meets every four years, establishes the topics for study aid approves Recoinineudatiotis prepared by its Study Groups. The approval of Recommendations by the members of CCITT between Plenary Assemblies is covered by the procedure laid do
4、wn in CCITT Resolution No. 2 (Melbourne, 1988). Recomineiidatioii E.170 was revised by Study Group II and was approved under the Resolution No. 2 procedure on the 30th of October 1992. CCIT NOTES 1) telecoinmunication administration and a recognized private operating agency. In this Recommendation,
5、the expression “Administration” is used for conciseness to indicate both a 2) A list of abbreviations used in this Recomendatioii cai be found in Annex A. O ITU 1993 All rights reserved. No part of this publication may be reproduced or utilized in any form or by .my means, electronic or inechxiicai,
6、 iiicludiiig photocopying and microfilm, without permission in writing from the ITU. - - - - - - -_ _ CCITT RECflN*E.370 92 4862593 O576788 369 9 Recommendation E.170 TRAFFIC ROTING (revised 1992) 1 Introduction 1.1 Objective o.ftr S2 indicates that congestion has occurred further downstream, e.g. o
7、n outgoing trunks from D. The choice of action at Exchange A is subject to bilateral agreement. 4 Recommendation E.170 (10/92) - - CCITT RECflN*E.L70 92 4862591 057b792 b9T Traffic stream to a particular destination (e.g. area code) In the exainple of Figure 4E.170, a call from A to D is routed via
8、C because the circuit group B-D is congested (Sl-indicator) aid a call from A to F is routed via E because the circuit group D-F is congested (S2-indicator) A 13% Four outgoing b B 3% rotdingpatterns b C 42% to the destination b D 16% 100% - Originating Terminating exchange exchange TOo202220-91 Abt
9、e - Blockiiig Goni to D activates signal S1 to A. Blocking Goni Dto F activates signal S2 to k FiGURE 4E.170 Adiniiiistratioiis inay wish to consider the increase in signalling load and the number of call Set-up operations resulting froin the use of these signals. If the increase is unacceptable, ad
10、tninistrations may restrict the number of recautiiigs or litnit the signalling capability to fewer exchanges. Finally, cue must he taken to avoid circular routings which return the call to the point at which blocking previously occurred during the call Set-up. 4.3 Loud diciring All routing scheines
11、result in the sharing of traffic load between network elements. Routing schemes can however he developed to ensure that crdl attempts are offered to route choices according to a preplanned distribution. Figure 5E. 170 illustrates this application of load shnring which can be made available as a soft
12、ware function of SPC exchanges. The system works by distributing the call attempts to a particular destination in a fixed ratio between the specified outgoing routing patterns. Note -. Fach outgoing routing pattern (A, B, C, D) may include alternative routing options. FIGURE 5E.170 Recommendation E.
13、170 (10/92) 5 CCITT RECMN*E-L70 92 4862593 0576793 526 4.4 Dytiumic routing 4.4.1 Exmnple of state-dependent routing A centralized routing processor is employed to select optimum routing patterns on the basis of the actual occupancy levels of the circuit groups and exchanges iii the tietwork which a
14、re monitored on a periodical basis (e.& 10 s), see Figure 6E.170. In addition, qualitative traffic parameters may also be taken into consideration in the detennination of the optimal routing pattern. This routing technique inherently incorporates fundamental principles of network maiiagemetit in det
15、enninirig routing patterns. These include: - avoiding occupied circuit groups: - - tiot using overloaded exchanges for transit: in overload circuinstaices, restriction of routing direct connections. Exchanges v., TO203550-93 Data links“. FIGURE 6E.170 4.4.2 Exumple of time-dependent roi&g For each o
16、riginating and terminating exchange pair, a particular route pattern is planned depending on the time of day ,and day of week, see Figure 7E.170. A weekday, for example, can be divided into different time periods, with each the period resulting in different route patterns being defined to route traf
17、fic streams between the same pair of exchanges. This type of routing takes advantge of idle circuit capacity in other possible routes between the originatiiig and terminating exchanges which may exist due to non-coincident busy periods. Crankback may be utilized to identify dowristrenm blocking on t
18、he second link of each two-link alternative path. - C AB, ACB, AD0 6 Recommendation E.170 (10192) T0203560-93 FIGW 7E.170 4.4.3 Example of event-dependent routing Choice 1 2 In a fully connected network, calls between each originating and terminating exchange pair try the direct route with a two-lin
19、k alternative path selected dynamically. Whilst calls are successfully routed on a two-link path, that alternative will be retained. Otherwise a new two-link alternative path will be selected. This updating, for example, could be at r,andom or weighted by the success of previous calls. A to B route
20、pattern Current After cai1 failure AB AB AEB ACB This type of routing scheme routes traffic away from congested links by retaining routing choices where calls are successful. It is simple, adapts quickly to chcanging traffic patterns and requires only local information. i 5 n History First published in 1988 (Blue Book). Revised in 1992. ANNEX A (to Recommendation E. 170) Alphabetical list of abbreviations used in this Recommendation AAR Autoinatic alternative routing ARR Automatic rerouting ISC Iiiteniutioaal switching centre SPC Stored program controlled 8 Recommendation E.170 (10/92)
