1、ITUgT RECMN*Q-725 93 = 4862571 0585865 553 INTERNATIONAL TELECOMMUN CATION UN ION ITU-T TELECOMMUNICATION STANDARDIZATION SECTOR OF ITU Q.725 (03/93) SPECIFICATIONS OF SIGNALLING SYSTEM No. 7 SIGNALLING SYSTEM NO. 7 - SIGNALLING PERFORMANCE IN THE TELEPHONE APPLICATION ITU-T Recommendation Q.725 (Pr
2、eviously “CCIlT Recommendation”) FOREWORD The ITU Telecommunication Standardization Sector (ITU-T) is a permanent organ of the Intemational Telecom- munication Union. The ITU-T is responsible for studying technical, operating and tariff questions and issuing Recommendations on them with a view to st
3、andardizing telecommunications on a worldwide basis. The World Telecommunication Standardization Conference (WTSC), which meets every four years, established the topics for study by the ITU-T Study Groups which, in their turn, produce Recommendations on these topics. ITU-T Recommendation 4725 was re
4、vised 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 CCIT ceased to exist as of 28 February 1993. In its place, the ITU Telecommunication Stand
5、ardization 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 Similarly, in this reform process, the CCIR and the IFRB have been replaced by the Radiocommunication Sector.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 in the text to references containing the acronyms
6、“CCIT. 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 recognized operating agency. In this Recommendation, the
7、 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 microfilm, without permission in writing from the ITU. _
8、 m . m CONTENTS 1 Introduction 2 3 Unavailability of a signalling route set . 4 Labelling potential 5 Cross-office transfer time . 5.1 Functional reference points and transfer time components 5.2 Definitions 5.3 Queueing delay . 5.4 Estimates for message transfer time . 5.5 Answer delay 5.6 Referenc
9、es . Unsuccessful calls due to signalling malfunction Delays due to data base queries Recommendation Q.725 (0-3) Page 1 1 1 1 1 1 2 2 8 8 8 8 i ITU-T RECMN*Qm25 93 = 48b259L 0585868 2b2 Recommendation Q.725 SIGNALLING SYSTEM NO. 7 - SIGNALLING PERFORMANCE IN THE TELEPHONE APPLICATION (Geneva, 1980;
10、modified at Helsinki, 1993) 1 Introduction This Recommendation gives the requirements of the telephone application of Signalling System No. 7 (SS No. 7). In Recommendation 4.706. the Message Transfer Part (MTP) performance is described. The MTP is the basis of the telephone application of SS No. 7 a
11、nd provision of a signalling network to serve the telephone service must take account of the performance of the Message Transfer Part and the requirements of the telephone application. For example, taking account of the message transfer times detailed in Recommendation 4.706 the signalling Hypotheti
12、cal Reference Connection (4.709) and the requirements for message transfer times between two telephone exchanges, a figure may be derived for the total permissible number of signalling links in signalling relations in tandem for a particular call. See also Recommendation Q.709. 2 Unsuccessful calls
13、due to signalling malfunction The proportion of calls that are unsuccessful due to signalling malfunction should be less than 1 in lo5. By means of error detection (see Recommendation Q.703) as well as transmission fault indication (see Recommen- dations G.732 11 and G.733 2), it is ensured that, ov
14、erall, not more than one error in lo8 of all signal units transmitted is accepted and will cause false operation. Unsuccessful calls may be caused by undetected errors, loss of messages or messages delivered out of sequence (during emergency situations within the signalling network) and may result i
15、n: - incomplete call Set-up; - - misrouted calls (e.g. connection of wrong numbers); calls routed correctly but mishandled (e.g. false clearing). 3 The overall unavailability of a signalling route set causing the unavailability of a signalling relation should not exceed a total of 10 minutes per yea
16、r. NOTE - The availability of a signalling route set within a signalling network may be enhanced by replication of signalling links. signalling paths and signalling routes. Unavailability of a signalling route set 4 Labelling potential The label of the Telephone User Part of SS No. 7 provides the po
17、tential to identify 16384 signalling points and up to 4096 speech circuits for each signalling relation. 5 Cross-office transfer time 5.1 Functional reference points and transfer time components Delays concerning data base query functions are not included at this time. The delays corresponding to th
18、ose functions are for further study. Figure 1 shows the time components associated with the handling and transfer of a TUP message at a transit exchange. Recommendation Q.725 (0-3) 1 ITU-T RECMN*Q.725 93 48b259L 0585869 IT9 W T, Crossdice transfer time Tmr MTP receivhg tie a) Tm MTPsendhgtimea) a) T
19、hu Telephone USM Part handing time The definitions of these times are given in Recommendation 4.706. FIGURE 1/Q.725 Functional diagram of the cross-office transfer time 5.2 Definitions For the purposes of this Recommendation, the following definitions apply. cross-office transfer time, Tcu: T, is th
20、e period which starts when the last bit of the signal unit leaves the incoming 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 Thu. It also includes the queueing delay in the absence of
21、 disturbances but not the additional queueing delay caused by retransmission. It does not include the data channel propagation time. user handling time, Thu: Th, is the period which starts when the last bit of the message has entered the Telephone User Part and ends when the last bit of the derived
22、message has left the Telephone User Part. 5.3 Queueing delay The formulae for the queueing delays are described in 4.YQ.706. The queuing delay does not include the data channel propagation time. The telephone trafic model assumed is given in Table 1, from which the proportion of signal messages may
23、be obtained as shown in Table 2. Using Table 2, examples of queueing delays are calculated as shown in Figures 2 to 5, where one call attempt per second per 64 kbit/s signalling data link may yield 0.00577 Erlang of the traffic loading of each channel. These values, based on a mean message length of
24、 15 bytes, apply only for configurations where no User Part other than the TUP uses the links of the SP in consideration. If the load on these links is mixed with messages of significantly different length (e.g. from other User Parts), or if long delay links are used, then the increase in outgoing l
25、ink delay (Tod) as shown in 4.3.414.706 will have to be taken into account. 2 Recommendation Q.725 (0393) ITU-T RECMN*Q.725 93 = 48b2591 0585870 910 Length (bits) Messages per call in both directions Percent Mean message length (T,) Sending procedure Type of call 176 152 128 112 104 Total 0.45 0.5 0
26、.45 2.0 2.9 6.3 7.1 7.9 7.1 31.7 46.0 100 117.2 bits Messages per call kl k2 Percent calls 1 .O32 1.107 12-digit IAM 6-digit IAM 3-digit SAM 1-digit SAM Address complete k3 Others 1.239 Length (bits) 176 152 128 112 112 104 TABLE UQ.725 Traffic model En-bloc AW SB CC AB 30 10 5 5 1 1 1 O 1 1 O O 3s
27、2 3 O Overlap AW SB CC AB 30 10 5 5 1 1 1 1 O 1 3 3 O O 1 1 O O 3s 2 3 2 AW Answered SB CC Circuit congestion AB Abortive IAM Initiai address message SAM Subsequent address message NOTE - The assumptions used in this model are chosen for illustrative purposes, and should not be considered to be typi
28、cal. Subscriber busy and not answered TABLE 2/Q.725 Proportion of messages Recommendation Q.725 (03/93) 3 4 ITU-T RECMN*Q=725 73 = 48b2591 0585871 857 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.; Traffc loaang of MSU (a) CalVS FIGURE UQ.725 Mean totai queueing delay of each channel of traffic - Basic error corre
29、ction method Recommendation 4.725 (0393) ITU-T RECMN*Q-725 93 m 4862593 0585872 793 m ms 16 14 12 6 10 .- 6 Y 18 !i U m6 4 2 O 0.1 02 0.3 0.4 O5 0.6 0.7 0.8 T1157590W3 Traffic loang of MCU (a) FIGURE 3/Q. 725 Stanbrd deviation of qwieing delay of each channel of traffic - Basic error correction meth
30、od Recommendation Q.725 (03/93) 5 6 ITU-T RECMNaQ.725 93 4862591 0585873 b2T I I I I Tm= 1 .a31 ms (1 17.2 bits and 64 kbitls) if = 0.75 ms (48 bits and 64 kWs) I I l I I -JO Eriangs 0.1 0.2 0.3 0.4 0.5 Traffic Ming of MU (a) Calus I I O 20 40 60 80 100 T1157600-93/404 Equivdent call rate FIGURE 414
31、.725 Mean total queueing delay of each channel of traffic - Preventive cyclic retransmission error correction method Recommendation Q.725 (0393) ITU-T RECMNtQ.725 93 4862591 0565874 566 l I I I 1 Tm= 1 .31 Tr = 0.75 ks (48 bits and 64 kbitls) (1 17.2 bitt and 64 kbvs) 1 1 l I I Pu = 4 x 1 O3 ! “O 0.
32、1 0.2 0.3 0.4 0.5 0.6 Traffic loacing d MSU (a) T115761093/do5 FIGURE 514.725 Standard deviation of queueing delay of each channel of traffk - Preventive cyclic retransmission error correction method Recommendation 4.725 (03/93) 7 ITU-T RECMN*Q.725 93 486259L 0585875 4T2 Exchange call attempt loadin
33、g Normal +15% +30% 5.4 The figures in Table 3 are related to a signalling bit rate of 64 kbi/s. Estimates for message transfer time T, (ms) i) Mean 95% 110 220 165 330 275 550 TABLE 3/Q.725 Cross-office transfer time Teu Normal +15% +30% Message type 180 360 270 540 450 900 Simple (e.g. answer) Proc
34、essing intensive (e.g. IAM) I I a) Provisionai values. 5.5 Answer delay As a consequence of correction by retransmission, not more than one in 104 signals should be delayed more than 300 ms as a long-term average. This requirement refers to each signalling link. This requirement is laid down in orde
35、r to ensure satisfactory answer delays. Further study is required to determine if this value is sufficient if satellite working is used. These values, based on a mean message length of 15 bytes, apply only for configurations where no other MTP Users, generating longer messages or higher dynamic load
36、s than the Tup, use the links of the signalling point in consideration. If the load on the links is mixed with messages of significantly different lengths (e.g. from other User Farts) then the increase in the outgoing delay Tod as shown in 5/Q.706, has to be taken into consideration. If satellite li
37、nks are used in this case, the relevant increase is shown in 3/Q.706. 5.6 Delays relating to data base query functions have not been included. These delays are for further study, but information relating to these delays can be found in 7/Q.709. Delays due to data base queries References i 21 CCITT Recommendation G.732 Characteristics of primary PCM multiplex equipment operating at 2048 kbids. CCITT Recommendation G.733 Characteristics of primary PCM multiplex equipment Operating at 1.544 kbids. 8 Recommendation Q.725 (03/93)
