1、ITU-T RECMN*Q-706 93 = 4862591 0584995 284 INTERNATIONAL TELECOMMU N CATION UN ION ITU-T TELECOMMUNICATION STANDARDIZATION SECTOR OF ITU Q.706 (03/93) SPECIFICATIONS OF SIGNALLING SYSTEM No. 7 SIGNALLING SYSTEM NO. 7 - MESSAGE TRANSFER PART SIGNALLING PERFORMANCE ITlJ=T Recommendation Q.706 (Previou
2、sly “CCIlT Recommendation“) ITU-T RECMNUQa70b 93 = LiBb259L 0584976 IL0 W FOREWORD The ITU Telecommunication Standardization Sector (ITU-T) is a permanent organ of the International Telecom- munication Union. The ITU-T is responsible for studying technical, operating and tariff questions and issuing
3、 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 ITU-T Study Groups which, in their turn, produce Recommendations on thes
4、e topics. ITU-T Recommendation Q.706 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 (IT). the CC ceased to exist as of 28 February 1993. In it
5、s place, the ITU 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 Similarly, in this reform process, the CCIR and the IFRB have been replaced by the Radiocommunication Sector.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 in the tex
6、t to references containing the acronyms “CCIIT, 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 oper
7、ating 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 microfilm, with
8、out permission in writing from the IT. ITU-T RECMN*Q.706 93 48b2591 0584997 057 M CONTENTS Basic parameters related to MTP signalling performance Unavailability of a signalling route set . 1.3 Message transfer times 1.1 1.2 Unavoidable MTP malfunction 1.4 Signalling traffic throughput capability Sig
9、nalling traffic characteristics . 2.1 Labelling potential 2.2 Loading potential 2.3 Structure of signalling traffk Parameters related to transmission characteristics . 3.1 Application of Signalling System No . 7 to 64 kbi/s links . 3.2 Application of Signalling System No . 7 to links using lower bit
10、 rates . 3.3 Signalling link delays over terrestrial and satellite links Parameters of influence on signalling performance . 4.1 Signalling network 4.2 Queueing delays 4.3 Message transfer times 4.4 Error control . 4.5 Security arrangements 4.6 Failures . 4.7 priorities Estimates for message transfe
11、r times . 5.1 Estimate for Ta . 5.2 Calculation for Tod 5.3 Performance under adverse conditions 6.1 Adverse conditions . 6.2 Influence of adverse conditions Estimates for STP processor handling time TPh . Annex A . Computation of transmission delays Annex B . Calculation of Outgoing Link Delay (Tod
12、) . Approximative calculation of the 95% -Values of Tod . . B . 1 B.2 Calculation of the kth moments of the MSU emission time Reference . Recommendation Q.706 (03/93) Page 1 1 1 1 1 2 2 2 2 3 3 3 3 4 4 5 15 18 19 20 20 20 21 21 31 32 32 32 32 34 34 35 36 i ITU-T RECMN*Q*70b 93 48b259L 0584998 T93 IN
13、TRODUCTION The Message Transfer Part (MTP) of Signalling System No. 7 (SS No. 7) is designed as ajoint transport system for the messages of different users. The requirements of the different users have to be met by the Message Transfer Part (MTP). These requirements are not necessarily the same and
14、may differ in importance and stringency. In order to satisfy the individual requirements of each user, the MTP is designed in such a way that it meets the most stringent User Part requirements envisaged at the time of specification. To this end. the requirements of the telephone service, the data tr
15、ansmission service and the signalling network management, in particular, were investigated. It is assumed that a signalling performance which satisfies the requirements mentioned above will also meet those of future users. In the light of the above, signalling system performance is understood to be
16、the capability of the MTP to transfer messages of variable length for different users in a defined manner. In order to achieve a proper signalling performance, three groups of parameters have to be taken into account: The first group covers the objectives derived from the requirements of the differe
17、nt users. The aims are limitation of message delay, protection against all kinds of failures and guarantee of availability. The second group covers the features of the signalling traffk, such as the loading potential and the structure of the signalling Mic. The third group covers the given environme
18、ntal influences, such as the characteristics (e.g. error rate and proneness to burst) of the transmission media. The three groups of parameters are considered in the specification of the procedures to enable the MTP to transfer the messages in such a way that the signalling requirements of ail users
19、 are met and that a uniform and satisfactory overall signalling system performance is achieved. - - - 11 Recommendation Q.706 (03/93) ITU-T RECMN*Qm70b 93 4862593 O584999 92T Recommendation 4.706 SIGNALLING SYSTEM NO. 7 - MESSAGE TRANSFER PART SIGNALLING PERFORMANCE (Geneva, 1980; modified at Helsin
20、ki, 1993) 1 Basic parameters related to MTP signalling performance Signalling performance is defined by a great number of different parameters. In order to ensure a proper signalling performance for all users to be served by the common MTP, the following design objectives are established for the MTP
21、. 1.1 Unavailability of a signalling route set The unavailability of a signalling route set is determined by the unavailability of the individual components of the signalling network (signalling links and the signalling points) and by the structure of a signalling network. The unavailability of a si
22、gnalling route set should not exceed a total of 10 minutes per year. The unavailability of a signalling route set within a signalling network may be improved by replication of signalling links, signalling paths and signalling routes. 1.2 Unavoidable MTP malfunction The MTP is designed to transport m
23、essages in a correct sequence, In addition, the messages are protected against transmission errors. However, a protection against transmission errors cannot be absolute. Furthermore, missequencing and loss of messages in the MTP cannot be excluded in extreme cases. For all User Parts, the following
24、conditions are guaranteed by the MTP: a) Undetected errors On a signalling link employing a signalling data link which has the error rate characteristic as described in Recommendation 4.702 not more than one in 1Olo of all message signal units will contain an error that is undetected by the MTP. b)
25、Loss of messages Not more than one in lo7 messages will be lost due to failure in the MTP. c) Messages out-of sequence Not more than one in 1O1O messages will be delivered out-of-sequence to the User Parts due to failure in the MTP. This value also includes duplication of messages. 1.3 Message trans
26、fer times This parameter includes: - - - handling times at the signalling points (see 4.3); queueing delays including retransmission delays (see 4.2); signalling data link propagation times. 1.4 Signalling traffic throughput capabiiity Needs further study (see 2.2). Recommendation Q.706 (OW3) 1 ITU-
27、T RECMN*Q=70b 93 m 4862571 0585000 24T m 2 Signalling traffic characteristics 2.1 Labeling potential The design of Signalling System No. 7 provides the potential for labels to identify 16 384 signalling points. For each of the 16 different User Parts a number of user transactions may be identified,
28、e.g. in the case of the telephone service up to 4096 speech circuits. 2.2 Loading potential Considering that the load per signalling channel will vary according to the traffic characteristics of the service, to the user transactions served and to the number of signals in use, it is not practicable t
29、o specify a general maximum limit of user transactions that a signalling channel can handle. The maximum number of user transactions to be served must be determined for each situation, taking into account the trafk characteristics applied so that the total signalling load is held to a level which is
30、 acceptable from different points of view. With regard to signalling route set congestion (see 11.2.3/Q.704), the last method referred to in 11.2.3.1 ii) b), the congested link method of deciding when to send a Transfer Controlled message, has advantages in the case of asymmetrical load distribution
31、 within a link set. When determining the normal load of the signalling channel, account must be taken of the need to ensure a sufficient margin for peak traffk loads. The loading of a signalling channel is restricted by several factors which are itemized below. 2.2.1 Queueing delay The queueing dela
32、y in absence of disturbances is considerably influenced by the distribution of the message length and the signalling traffk load (see 4.2). 2.2.2 Security requirements The most important security arrangement is redundancy in conjunction with changeover. As load sharing is applied in normal operation
33、, the load on the individual signalling channels has to be restricted so that, in the case of changeover, the queueing delays do not exceed a reasonable limit. This requirement has to be met not only in the case of changeover to one predetermined link but also in the case of load distribution to the
34、 remaining links. 2.2.3 Capacity of sequence numbering The use of 7 bits for sequence numbering finally limits the number of signal units sent but not yet acknowledged to the value of 127. In practice this will not impose a limitation on the loading potential. 2.2.4 Signalling channels using lower b
35、it rates A loading value for a signalling channel using bit rates of less than 64 kbit/s will result in greater queueing delays than the same loading value for a 64 kbih signalling channel. 2.3 Structure of signalling trac The M“ serves different User Parts as a joint transport system for messages.
36、As a result, the structure of the signalling traffic largely depends on the types of User Parts served. It can be assumed that at least in the near future the telephone service will represent the main part of the signalling traffk also in integrated networks. It cannot be foreseen yet how the signal
37、ling traffk is influenced by the integration of existing and future services. The traffic models given in 4.2.4 have been introduced in order to consider as far as possible the characteristics and features of different services within an integrated network. If new or more stringent requirements are
38、imposed on signalling (e.g. shorter delays) as a consequence of future services, they should be met by appropriate dimensioning of the load or by improving the structure of the signalling network. 2 Recommendation Q.7 (03193) ITU-T RECMNxQ.70b 93 48b2591 058500L Lb Wire Orm) 3 Parameters related to
39、transmission characteristics Fibre Radio No special transmission requirements are envisaged for the signalling links of Signalling System No. 7. Therefore, System No. 7 provides appropriate means in order to cope with the given transmission characteristics of ordinary links. The following items indi
40、cate the actual characteristics to be expected - as determined by the responsible Study Groups - and their consequences on the specifications of the MTP. 500 1000 3.1 Application of Signalling System No. 7 to 64 kbis links 2.4 2.50 1.7 4.8 5.0 3.3 The MTP is designed to operate satisfactorily with t
41、he following transmission characteristics: a) b) a long term bit error rate of the signalling data link of less than 1od i; a medium term bit error rate of less than 10-4; 2000 5000 c) random errors and error bursts including long bursts which might occur in the digital link due to, for instance, lo
42、ss of frame alignment or octet slips in the digital link. The maximum tolerable interruption period is specified for the signai unit error rate monitor (see 10.UQ.703). 9.6 10.0 16.6 24.0 25.0 16.5 3.2 Application of Signalling System No. 7 to links using lower bit rates 10 000 15 000 Needs further
43、study. 48.0 50.0 33.0 72.0 75.0 49.5 3.3 Signalling link deiays over terrestrial and Satellite links 17 737 20000 25 o00 Data Channel Propagation Time (T,) is defined in 4.3.2.4. It depends on transmission speed, the distance between nodes, repeater spacing and the delays in the repeaters. Transmiss
44、ion speed and repeater delays depend on the type of medium used to transmit the messages. Four types of medium are considered: wire, fibre optic cable, terrestrial radio and satellite systems. (Wire systems comprise standard underground copper cables and undersea cables.) 85.1 88.7 58.5 96.0 100.0 6
45、6.0 120.0 125.0 82.5 Table 1 provides representative delay values and Figure 1 shows those results graphically for the various transmission media. TABLE UQ.706 Calculated terrestrial transmission deiays for various call distances Recommendation Q.706 (03/93) 3 600 500 400 300 278 -236 g 200 100 O IT
46、U-T RECMN*Q-706 93 D 4862591 0585002 O12 W ms Delay varies with distances of each earth station from point on the Earth over which the satellite is located. (See Annex A.) a) FIGURE 1/Q.706 Trannnission deiays using satellite and terrestrial message Ming facilities The double hop values do not take
47、into consideration any terrestrial extensions and repeaters thai may be required. Formulae for computing the transmission delays are given in Annex A along with the assumptions made. Due to the longer delay of satellite links and the longer terresirial links, the message transfer times increase (see
48、 clause 5). Therefore care must be taken in the design of signalling networks if they are to meet the overall delay performance criterion (see Recommendation Q.709). 4 Parameters of influence on signalling performance 4.1 Signalling network Signalling System No. 7 is designed for both associated and
49、 non-associated applications. The reference section in such applications is the signalling route set, irrespective of whether it is served in the associated or quasi-associated mode of operation. For every signalling route set in a signalling network, the unavailability limit indicated in 1.1 has to be observed irrespective of the number of signalling links in tandem of which it is composed. In planning SS No. 7 signalling networks to meet E.721, E.723 and 1.352 delay requirements, consideration should be given to - processing delays in SPs; - number of SPs; - numberofSTPs
