1、ITU-T RECMN*Q-766 93 4862593 0588530 475 = INTERNATIONAL TELECOMMUNICATION UNION ITU-T TELECOMMUNICATION STANDARDIZATION SECTOR OF ITU Q.766 (03/93) SPECIFICATIONS OF SIGNALLING SYSTEM No. 7 ISDN USER PART PERFORMANCE OBJECTIVES IN THE INTEGRATED SERVICES DIGITAL NETWORK APPLICATION ITU-T Recommenda
2、tion Q.766 (Previously “CCITT Recommendation”) ITU-T RECMN*Q.766 93 48b2593 0588533 301 FOREWORD The ITU Telecommunication Standardization Sector (ITU-T) is a permanent organ of the International Telecom- munication Union. The -T is responsible for studying technical, operating and tariff questions
3、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 years, established the topics for study by the -T Study Groups which, in their turn, produce Recommendations
4、 on these topics. ITU-T Recommendation 4.766 was revised by the ITU-T Study Group XI (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
5、 1993. In its place, the IT Telecommunication 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 Similarly, in this reform process, the CCIR and the IFRB have been replaced by the Radiocommunication Sector.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
6、 in the text to references containing the acronyms %Ci”, 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 recogn
7、ized operating agency. In this Recommendation, 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 microf
8、ilm, without permission in writing from the ITU. ITU-T RECHNxQ.7bb 93 4b259L 0568512 246 D CONTENTS Introduction Signalling availability 2.1 2.2 Signalling network availability . Signalling route set availability Signalling dependability . 3 .i General 3.2 Probability of signalling malfunction . Sig
9、nalling delay 4.1 Functional reference points and transfer time components 4.2 Delays . 4.3 Answer delay 4.4 Influence of new ISDN applications on performance . Signalling system limitations . 5.1 Labelling potential 5.2 Number of ISDN call identities at a signalling point References . Recommendatio
10、n Q.766 (03D3) Page 1 1 1 1 1 1 2 2 2 2 3 3 3 3 4 4 i ITU-T RECMNUQ.766 93 W 4862591 0588513 184 Recommendation 4.766 PERFORMANCE OBJECTIVES IN THE INTEGRATED SERVICES DIGITAL NETWORK APPLICATION (Malaga-Torremolinos 1984; modified at Helsinki, 1993) 1 Introduction This Recommendation gives the requ
11、irements of the Integrated Services Digital Network (ISDN) application call control service supported by Signalling System No. 7 (SS No. 7). The MTP supports the ISDN application of Signalling System No. 7. In Recommendation 4.706, the Message Transfer Part (MTP) performance is described. The provis
12、ion of a signalling network to support the ISDN application must take account of the performance of the MTP and the requirements of the ISDN application. For example, taking account of the message transfer times in Recommendation Q.706 and the requirements for message transfer times between twoISDN
13、exchanges, a figure may be derived for the total permissible number of signalling links in tandem for a particular call. The Recommendations E.721 3 and 1.352 4 also relate to ISDN performance. 2 Signalling availability 2.1 Signalling route set availability The availability of a signalling route set
14、 is determined by the availability of the individual components of the signalling network (signalling links and the signalling points) and by the structure of a signalling network. The availability of a signalling route set (according to 1. VQ.709) should not be less than 0.99998. This corresponds t
15、o a total downtime for a user signalling relation of ten minutes per year maximum. 2.2 Signalling network availability The availability of the signalling network should be sufficiently high as to meet the signalling route set downtime objectives stated in 2.1. The signalling network architecture sel
16、ected will strongly influence the availability. In general, the greater the number of link sets in tandem in a signalling route set the more redundant signalling paths that will be needed to meet the availability objective for the signalling route set or user signalling relation. 3 Signalling depend
17、ability 3.1 General The ISDN application is different from other applications, such as telephony and data, in that there may be multiple paths involved for any given ISDN call. There may be several circuits (e.g. telephone conferencing) for either telephony or data and non-circuit related connection
18、s for access to data bases or for terminal-to-terminal control. This diverse set of uses may require closer control of the signalling network resources than might be required for other more simple applications. 3.1.1 Probability of false operation By means of error detection (see Recommendation 4.70
19、3) as well as transmission fault indication (see Recommendations G.732 i and G.733 2), it is ensured that, overall, not more than one in lo* of all signal units transmitted is accepted that, due to errors, will cause false operation. Recommendation Q.766 (03/93) 1 3.2 Probability of signalling malfu
20、nction Tmr Th“ Tms 4 - - - misrouted calls (e.g. connection of wrong numbers); calls routed correctly but mishandled (e.g. false clearing); inability to access a data base. Considering the above conditions and the performance for the MTP, no more than 2 in id (provisional value) of all ISDN calls sh
21、ould be unsuccessful due to signalling malfunction. NOTE - No more than 1 in 105 of ail ISDN circuit connections should be unsuccessful due to signalling malfunction. 4 Signalling delay 4.1 Functional reference points and transfer time components Figure 1 shows the time components associated with th
22、e handling and transfer of ISUP messages at a transit exchange. FIGURE 1fQ.766 Transit exchange cross-Hice transfer time components 4.2 Delays T, and Tm are defined in 4.3.UQ.706. 4.2.1 cross-office transfer time, T, TC, is the period which starts when the last bit of the signal unit leaves the inco
23、ming signalling data link and ends when the last bit of the signal unit enters the outgoing signalling data link for the first time. It includes the user handling time Th,. It also includes the queuing delay in the absence of disturbances but not the additional queuing delay caused by retransmission
24、. It does not include the data channel propagation time. 4.2.2 user handling th!, Thu Th, is the period which starts when the last bit of the message has entered the upper layer functions and ends when the last bit of the derived message has left the upper layer functions. 4.2.3 The figures in Table
25、 1 are the objectives for the cross-office transfer time TC, for the ISDN signalling points in the signalling network. These figures are related to a signalling bit rate of 64 kbit/s. Objectives for cross-office transfer time, T, 2 Recommendation Q.766 (03/93) ITU-T RECMN*Q*7bb 93 4862591 0588515 T5
26、7 Exchange call attempt loading Normal +15% +30% TABLE VQ.766 Transit exchange cross-office transfer time, Tcy*) Tal (ms) Mean 95% 110 220 165 330 275 550 Message type Processing intensive (e.g. IAM) Simple (e.g. answer) Normal 180 360 +15% 270 540 +30% 450 900 Delays concerning data base query func
27、tions are not included at this time. The delays corresponding to those unctions are for further study. A processing intensive message is one that arrives at an exchange and requires detailed examination (and possibly modification) before it is transmitted to the next exchange. A simple message is on
28、e that requires little or no examination or modification (typically only label translation) before it is transmitted to the next exchange. 4.3 Answer delay As a consequence of correction by retransmission, not more than one in 104 signais should be delayed more than 300 ms as a long-term average. Th
29、is requirement refers to each signalling link. This requirement is laid down in order to ensure satisfactory answer delays. Further study is required to determine if this value is sufficient if satellite working is used. 4.4 Influence of new ISDN applications on performance Delays relating to data b
30、ase query functions have not been included. These delays, and the relationship between them are for further study, but information relating to these delays can be found in 7/Q.709. If the load on the links is mixed with messages of significantly different lengths (e.g. from other User Parts) then th
31、e increase in the outgoing link delay Tr,d as shown in WQ.706, has to be taken into consideration. If satellite links are used in this case, the relevant increase is shown in 3/Q.706. 5 Signalling system limitations 5.1 Labelling potential 5.1.1 Signalling points The label of the SS No. 7 for the IS
32、DN application provides the potential to identify 16 384 signalling points. 5.1.2 There may be up to 4096 circuits (4096 channels in each direction) for each user signalling relation. Number of circuits in a user signalling relation Recommendation Q.766 (03/93) 3 ITU-T RECHN*Qm7bb 93 = 48b259L 05885
33、Lb 993 9 5.1.3 Number of SCCP comections in a user signaing reiation There may be up to 224 SCCP connections available at an ISDN signalling point. All of these may be available for any given user signalling relation, but must be shared over all signalling relations. 5.2 Number of ISDN call identiti
34、es at a signalling point There may be up to 224 (value for further study) simultaneous ISDN calls at a signalling point with the 224 call identities available. The use of ISDN call identities is for further study. References 4 CC Recommendation Characteristics of primury PCM multiplex equipment oper
35、ating at 2048 kbit/s, Rec. G.732. CCi“ Recommendation Characteristics of primary PCM multiplex equipment operating at 1544 kbit/s, Rec. G.733. CCi“ Recommendation Network GOS parameters and target values for circuit-switched services in the evolving Ism, Rec. E.72 1. CCi“ Recommendation Network performance objectives for connection processing delays in an ISDN, Rec. 1.352. Recommendation Q.766 (0-3)
