1、CCITT THE INTERNATIONAL TELEGRAPH AND TELEPHONE CONSULTATIVE COMMITTEE TELEPHONE NETWORK AND ISDN QUALITY OF SERVICE, NETWORK MANAGEMENT AND TRAFFIC ENGINEERING E.712 (1 0/92) _- = - CCITT RECMN*E.732 92 = 4862593 0576535 274 = INTERNATIONAL TELECOMMUNICATION UNION USER PLANE TRAFFIC MODELLING Recom
2、mendation E.712 CCITT RECMN*E-7L2 92 m 486259L 0576536 LOO m FOREWORD The CCITT (the International Telegraph and Telephone Consultative Committee) is a permanent organ of the International Telecommunication Union (RU). CCITT is responsible for studying technical, operating and tariff questions and i
3、ssuing 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 approval of Recommendations by the members
4、of CCITT between Plenary Assemblies is covered by the procedure laid down in CCITT Resolution No. 2 (Melbourne, 1988). Recommendation E.712 was prepared by Study Group II and was approved under the Resolution No. 2 procedure on the 30th of October 1992. CCIIT NOTES 1) telecommunication administratio
5、n 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 ITU 1993 All rights reserved. No part of this publication may be reproduce
6、d or utilized in any form or by any means, electronic or mechanical, including photocopying and microfilm, without permission in writing from the ITU. - - _ r CCITT RECMN*E=712 92 = 4862593 0576517 047 Recommendation E.712 USER PLANE TRAFFIC MODELLING (1 992) 1 Introduction In Recommendation E.711 t
7、he user demand is characterized by means of his call demands and by the description of each type of call demand. On the basis of the information provided by this user characterization, Recommendation E.712 derives the values of the traffic parameters required for dimensioning the 1 to 3 layer resour
8、ces of ISDN user plane. The resources involved by the user plane traffic are: - - - mnkgroups. customer accesses (Basic, Primary and their multiplexes): B- and D-channels; resources of ISDN Exchanges: switching networks, packet handlers, etc.; 2 General approach In ISDN, call demands with different
9、connection characteristics can be offered to the same group of resources. Depending on the kind of resources, dimensioning may require to separately characterize the traffic components corresponding to call demands with some different connection characteristics. First, there is a distinction of two
10、main traffic components according to the connection characteristic information transfer mode. Each of these two components (circuit switched and packet switched) may be further split up into new components, according to the other connection characteristics of their call demands. Thus, the approach f
11、or the modelling of the traffic offered to a group of resources is: - - to identify the call demands which make use of this group of resources; to identify the connection characteristics which imply the split up of the traffic due to these call demands into traffic components; to describe and quanti
12、fy these traffic components by means of a set of parameters derived from those defined in Recommendation E.7 11. - This approach will be followed in 0 3 to model the circuit switched traffic and in 0 4 for the packet switched traffic. 3 Modelling of circuit switched traffic 3.1 Observations on the c
13、oncept of group of resoiirces In the first implementations of the ISDN, the number of channels or circuits reserved per call will be the same for both directions of the information flow. This number is given for each call by the direction in which the information transfer rate is higher. In this sit
14、uation, the B-channels of an ISDN access or the channels (slots) of a trunk group are referred here as a group of resources, with independence of the direction of the information flow. Recommendation E.712 (10/92) 1 CCITT RECMN*E-712 92 4862571 0576518 T83 In further implementations of the ISDN, whe
15、n the connection characteristic Symmetry” of the call pattern takes the values unidirectional or bidirectional asymmetric, the number of channels reserved per call may be different in each direction of the information flow. In this situation, the channels carrying each direction of the information f
16、low have to be separately dimensioned (the final dimensioning being given by the direction in which the required number of channels is higher). Thus, the channels of each direction should be considered, in the context of this Recommendation, as a different group of resources. 3.2 Identijcution of cu
17、ll demands using a group of resources To identify the call demands using a group of resources the following connection characteristics should be considered: - communication configuration: This characteristic, in the wide sense considered in Recommen- dation E.711, d 2.2, defines the position of the
18、endpoints involved in the communication; this, together with the routing strategy, determines if a certain group of resources may be used by a call demand. - information transfer capability; - establishment of communication; - information transfer rate. The last three characteristics should be consi
19、dered since different groups of resources may be provided for call demands with certain values of these connection characteristics (e.g. resources only used for single channel connections or only traffic on demand). 3.3 Split up into trafJic components When call demands with different connection cha
20、racteristics share the same group of resources, different components of the offered traffic have to be separately characterized. For circuit switched traffic these components are distinguished according to the following criteria: the number of resources required per call: the connection characterist
21、ics of the call demand determining this number are: a) - the information transfer rate: in the first situation of 0 3.1, it is the rate in the direction in which the rate is higher; in the second situation, it is the rate in the direction under consideration. When this rate is n x 64 kbit/s, ii B-ch
22、annels of the ISDN access or n channels of a trunk group are required for each call; the communication configuration: in multipoint connections several resources of the same group can be required by a call, depending on the place where the information is split; Figure 1E.712 gives two examples of a
23、three points communication; if the information transfer rate is it x U4 kbit/s, II resources are required in each trunk group in example a), while in example b), 2 x ti resources are required in the trunk group between the local exchange A and the transit exchange, and n resources in each of the oth
24、er two trunk groups; - b) the existence of any restriction on the allocation of several resources for the same call; time-slot sequence integrity (TSSI) is required for ti x 64 kbit/s communications when the values of the information transfer capability is unrestricted or 8 kHz structured; one techn
25、ique to obtain this integrity is to allocate the ti channels (slots) on the same PCM primary multiplex, or even to assure that the n channels are contiguous; traffic components with different restrictions in the allocation should be distinguished; call routing: it is related to the general call rout
26、ing strategy and to the connection characteristic “communication configuration” of the call demand, which defines the position of the end-points involved in the communication. Traffic components offered to the considered group of resources in a fust choice have to be distinguished from those which o
27、nly are offered if overflow from previous groups. Among the last ones, components for which the previous choices are different have also to be distinguished; c) 2 Recommendation E.712 (10/92) - i - CCITT RECMN*E*732 92 m 4Bb2593 0576539 9LT m a) Information is sw-up in the transit exchange LE B O C
28、LE TE O c 91 LE b) Information is sfl-up in the local exchange A LE Localexchange TE Transit exchange FIGURE 1E.712 Two examples of implementation of a three-points communication d) procedure for the establishment of the communication: for those resources sharing traffic of call demuids with differe
29、nt values of this connection characteristic, the traffic components on reservation and on demmd have to be separately characterized; e) ,my characteristic which could motivate a different priority or protection treatment: a different treatment (e.g. by means of service protection methods) of differe
30、nt traffic components can be motivated by some of the above-mentioned criteria, e.g. single slot versus multi-slot calls, first choice traffic versus overflow traffic, or cadis on demand versus reserved calls. In addition, other characteristics can also motivate a different priority or protection tr
31、eatment, e.g. traffic components with different GS objectives (corresponding to different values of the general attributekonnection characteristic Quality of Service“). Service protection methods may also be applied between traffic components corresponding to different services or to the two Set-up
32、directions of two-way trunk groups, even although these traffic components have the srune GOS objectives and the same values of the other above-mentioned characteristics. The reason for this protection is to avoid that the overload of traffic component can deteriorate the GOS of the other ones. In a
33、ll the cases in which a different priority or protection treatment between traffic components may be required, each of these traffic coinponents has to be separately characterized. The identification of other criteria, as e.g. different supplementary services, which could motivate a further distinct
34、ion of traffic components is for further study. 3.4 Purmeters describing euch trc component Once the different traffic components offered to a group of resources have been distinguished according to criteria of 0 3.3, each component has to be characterized. Recommendation E.712 (10/92) 3 Note - In c
35、ase of alternative routing, the dimensioning of a trunk group does not only require the characterization of the traffic components which in a first or subsequent choice can be offered to the considered trunk group, but also the characterization of all the other components offered to the network clus
36、ter to which the trunk group belongs. Each traffic component is characterized by: - the relevant connection characteristics of the component: they are the same which, according to 3.3, can motivate a separate characterization of the component, i.e. number of required resources per call, restrictions
37、 on the allocation of resources, call routing, establishment of the communication and GOS objective; the value and the generating process of the traffic offered by the component: the generating process is for further study; nevertheless in a first step it may be considered pure chance traffic, from
38、the point of view of the call arrival process when it is offered to the first choice resources. The value of the traffic offered is discussed in 0 3.5; additional traffic parameters related to certain traffic components: e.g. in case of reservation traffic, the quantification of some parameters rela
39、ted to the reservation time (interval between the reservation request and the start of the reserved time) and to the reserved time is required. A description of these parameters requires further study. Additional traffic parameters may also be required to describe some supplementary services. These
40、parameters are also for further study. - - 3.5 Qicantcation of trafic ofleered The traffic offered to a group of resources due to the traffic component m is given by: where: - - - Xtn is the arrival rate of call demands of the traffic component In; hin is the mean holding time of the resources per c
41、all demand of the traffic component m, din is the number of resources required per call demand of the traffic component m. Aft, describes the traffic offered from the point of view of number of simultaneous call, while Airl describes the traffic offered from the point of view of number of resources
42、simultaneously busy. In case of traffic offered to first choice resources, Aftti may be considered pure chance traffic, while AiTl has to be considered batch traffic with batch size equal to di,l. Thus, neither Am alone nor A, alone fully describe the traffic process. Any one of them needs to be com
43、plemented with the value of dril. From the user characterization made in Recommendation E.711, the vdue of Ain (and thus Atrz = Ai, . dtJ cCm be obtained as follows. 3.5.1 ISDN accesses For the B-channels of the ISDN accesses of a CPE, is given by: A!, = rc(ij,k) . Recommendation E.712 (10/92) - CCI
44、TT RECNN*E.7%2 92 4862591 0576521 578 - fm(ij) is a factor which Les the value 1 or O depending on whether the cas of the types ij belong or not to the traffic component rn; - h(ij,k) is the mean total holding time of the B-channels per call demand of type (ij,k). The rates rc(ij,k) must refer to th
45、e reference period. The definition of the reference period is for further study. h(ij,k) has to include the holding time of the B-channels due to all the attempts of the call demand. Number of Uncompleted call attempts per completed and per uncompleted call demand has to be estimated, as well as the
46、 holding time per uncompleted and per completed call attempt. These parcmeters are derived from the call variables defined iii 6 2.3.1 of Recommendation E.711. In the case of resources of ISDN exchanges or trunk groups, the first step is to identify the users which can offer traftic to the group of
47、resources. As two or more users are involved in a call demand, two criteria can be followed to identify the user which offers traffic to these resources: - to assume that the user which offers traffic to the group of resources, among the ones involved in a call demand, is chosen according to a posit
48、ion criteria, as, e.g. the closest one to the group of resources. This criterion is more usual when the closest user can be clearly identified, as e.g. for a trunk group connecting a local aid a transit exchange, in which the closest user is the one of the mentioned local exchange. With this assumpt
49、ion, the traffic offered to the group of resources is derived from the originating and terminating call demands of the closest users; - to assume that the user which offers traffic to the group of resources, among the ones involved in a call demnrid, is the one which originates the call. This criterion may be practical, e.g. for evaluating the traffic offered to a trunk group connecting two local exchanges. This traffic is derived, following this criterion, from the originating call demands of the users of both exchanges. Once the population of users
