CEPT T GSI 02-05 E-1987 Quality of Service《服务质量》.pdf

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1、CEPT T/GSI*02-05 E = 2326434 000543Y 7 0 02-05 Page 1 E Recommendation T/GSI 02-05 (Nice 1985, revised by correspondence, June 1987) QUALITY OF SERVICE IN THE ISDN Recommendation proposed by the Special Group Integration (GSI) Revised text of the Recommendation adopted by the “Telecommunications Com

2、mission: “The European Conference of Postal and Telecommunications Administrations, considering - that the quality of service offered by the ISDN needs to be defined with view to bearer services and Teleservices in voice and non-voice communications, recommends - that European Administrations wishin

3、g to provide ISDN services apply this Recommendation which covers: 1. the general description of quality of service in the ISDN and its distinction from the networks technical 2. quality of Service parameters and their definitions.” performance ; Nore. The allocation of numerical values to the vario

4、us parameters and the relationship between these parameters and the corresponding parameters describing the networks technical performance need further study. Edition of October 31, 1987 CEPT T/GSI*02-05 E m 2326434 0005435 9 m T/GSI 02-05 E Page 2 1. GENERAL DISTINCTION BETWEEN QUALITY OF SERVICE A

5、ND NETWORK PERFORMANCE AS APPLIED TO ISDN The proposed structure is based upon a distinction between user observed Quality of Service and Network Performance from the network providers point of view. Bearer- and Teleservices as defined in Recommendations T/GSI 02-01,02-02 and 02-03 are the objects w

6、hich Administrations offer to their customers. A major attribute of these services is the set of Quality of Service (QoS) parameters which a particular service offers. These parameters are user oriented, and they take into account the elements involved in a particular service as given in Figure 2 of

7、 Recommendation T/GSI 02-02. A typical user is not concerned with how a particular service is provided or with any aspects of the systems internal design. However, he is interested in comparing one service with another in terms of certain universal, user oriented performance concerns which apply to

8、any end-to-end service. Therefore, from a users point of view, Quality of Service is best expressed by parameters which i) focus on user-perceivable effects, rather than their causes within the network, ii) do not depend, in their definition, on assumptions about the networks internal design, iii) t

9、ake into account all aspects of the service from the users point of view, i.e. technical, commercial, ergonomic factors. Another reason to describe Quality of Service standards in network independent terms is to create a common language understandable to the user in defining his demands for Quality

10、of Service against the Administration. On the other hand, Bearer- and Teleservices are supported by a range of connection types which involve network elements. Therefore, the performance of the connections is characterized by a set of Network Performance (NP) parameters. The purpose of defining Netw

11、ork Performance in qualitative and quan- titative terms is to provide information on - system development, - network planning (dimensioning of trunks and switching means) both nationally and internationally, - operation and maintenance, for the provider. The user oriented parameters provide a valuab

12、le framework for network design, but they are not directly usable in specifying performance requirements for particular connections. Similarly, the Network Perfor- mance parameters ultimately determine the (user observed) Quality of Service but they do not describe that quality in a way that is mean

13、ingful to users. Both types of parameters are needed, and their values must be quantitatively related if the ISDN is to be effective in serving its users. In describing the QoS of Teleservices the performance of the Terminal Equipment (TE) has to be taken into account. For a Teleservice there should

14、 be a complete mapping between the QoS of the Teleservice and the performance of the customer equipment including the terminal and the overall (end-to-end) Network Performance of the connection type supporting this service. For a Bearer service there should be a mapping between the QoS of the Bearer

15、 service and the overall (end-to-end) Network Performance of the connection type supporting this service. Figure 1 (T/GSI 02-05) illustrates the scope of QoS and NP. Edition of October 31, 1987 CEPT T/GSI*02-05 E m 232b414 00054Lb O TIOSI 02-05 E Page 3 Customer equipment Performance Tele- I Bearer

16、Services services Attributes T/GSI 02-03 Quality of Service 2. Attributes T/GSI 02-02 11 Quality of Service ISDN connections I Attributes assigned to connection types T/GSI 03-04 Figure 1 (T/GSI 02-05). equipment U QUALITY OF SERVICE PARAMETERS For the definition of parameters for quality of the ser

17、vice in the ISDN, concept of Bearer services and Teleservices as defined in Recommendation T/GSI 02-01 need to be borne in mind. In particular there is a difference between the kinds of parameters which would describe the quality of service of a Bearer Service and that a Teleservice. This is because

18、 the point of observation of, or access point to, the service is different in each case. Figure 1 (T/GSI 02-05) above illustrates this point. In the case of Teleservices the interface between the user and the service provider may be a man-machine interface. In the case of Bearer services this interf

19、ace corresponds to the S/T reference points. As a result some of the parameters for describing the QoS of a Teleservice will be different than those which describe the QoS of a Bearer service. Based on the concepts given above it is appropriate that the Quality of Service parameters for ISDN should

20、be expressed in system and network independent but user oriented terms. This leads first of all to generic Quality of Service parameters which are applicable to all kinds of telecommunication services offered on an ISDN. This approach is fully in line with the general QoS studies in CEFT Working Gro

21、up “Services and Facilities”. (See Note.) Edition of October 31, 1987 - CEPT T/GSI*02-05 E 2326414 0005417 2 W T/GSI 02-05 Page 4 Table 1 (T/GSI 02-05) lists these generic QoS parameters and their definitions are contained in section 3. below. For individual bearer or teleservices (or groups of thes

22、e) detailed QoS parameters will need to be specified. In some cases where the same parameter is applicable to different services it may be the case that different values of this parameter may apply. Note. This work on QoS in WG SF is expected to lead to a CEPT series Recommendation T/SF on QoS categ

23、ories for all types of telecommunication services. Generic parameters (examples) 1. Time to establish call 2. End-to-end information transfer time 3. Time to release call 4. Quality accuracy of reproduction of information 5. Correctness of call establishment 6. Loss of information transfer probabili

24、ty 7. Correctness of call release 8. Loss of service frequency 9. Loss of service duration Table 1 (T/GSI 02-05). Examples of Generic QoS parameters. 3. DEFINITIONS OF GENERIC QOS PARAMETERS 1. Time to establish call. The time interval between the start of a call attempt and an indication that the c

25、all has been established or cannot be established. This figure does not include time intervals depending on human factors. 2. End-to-end information transfer time. The time interval between the start of transmission of information to the network by a terminal and the start of receipt of that informa

26、tion by a receiving terminal. 3. Time to release call. The time interval between the clearing terminal transmitting the clear request signal to the network and the call being cleared or the clearing terminal receiving a network indication confirming that the call has been cleared. 4. Quality accurac

27、y of reproduction of information. A measure of the quality of the received information relative to the transmitted information during the information transfer phase of a call. 5. Correctness of call establishment. The probability that a call is established to the address specified by correctly trans

28、mitted call establishment information and does not fail due to network (customer or public) congestion and/or malfunction. Nofe. Further elaboration is required to cover call attempts which fail due to called customer network or terminal busy. 6. Loss of information transfer probability. The ratio o

29、f total information transfer samples which fall below a minimum level of specification to total information samples while the call is in progress. Note. Further elaboration may be required. 7. Correctness of call release. The probability that an established call is released in accordance with the sp

30、ecified procedures. 8. Loss of service frequency. Loss of service frequency is expressed as a maximum frequency of occurrence (N times per year) or as a mean time between failures of service. 9. Loss of service duration. The time interval between the detection of service loss by the Administration,

31、or the reporting of a service loss by the user, and the time at which the full service is restored. This figure could be expressed as a mean or 95% maximum value. Note to 8 and 9. A user has lost service if the function of the requested service is not provided for a certain number of consecutive tri

32、als over a specified time period. Loss of service can be total or partial, e.g. local calls can be made but not longer distance calls, or could entail the premature release of an existing call. Failure can be caused either accidentally or deliberately by Administration staff, or by network or terminal equipment failure. Edition o1 4 O ktober 31. 1987