ITU-T E 720-1993 ISDN Grade of Service Concept《综合业务数字网(ISDN)服务等级(GOS)概念》.pdf

1、INTERNATIONAL TELECOMMUNICATION UNION)45G134 % TELECOMMUNICATIONSTANDARDIZATION SECTOROF ITU4%,%0(/.%G0G0.%47/2+G0G0!.$G0G0)3$.15!,)49G0G0/ these GOS parameters may be expressed as probability of blocking, probability of delay, etc. Blocking anddelay are caused by the fact that the traffic handling

2、capacity of a network/network component is finite and that thedemand traffic is stochastic by nature.The users of telecommunication services can experience the effects of GOS parameters depending on theirperception of events such as:1) failure of a call demand or excessive delay to satisfy a call de

3、mand;2) failure of call attempts or excessive delay to satisfy call attempts;3) failure of automatic re-attempts or excessive delay to satisfy automatic re-attempts.Events of the first class are always perceived by the user. Events of the other two classes may be perceived bythe user depending on th

4、e capability of the terminal equipment to transmit signalling information to the calling user.In all three classes the ability to distinguish GOS depends on having distinct indications of called userconditions and network conditions.GOS may be distinguished as the user GOS, network GOS and network c

5、omponent GOS as shown inFigure 1/E.720. User GOS relates to user call demands. Network GOS relates to any call attempts including both usergenerated call attempts and terminal generated automatic reattempts. Network component GOS relates to bids for theutilization of a specific network component inc

6、luding both bids generated by call attempts and bids generated by callattempts and bids generated by internal retrials in the network. Parameters related to user GOS and network componentGOS are for further study.Recommendation E.721 defines network GOS parameters based on any call attempt. Subseque

7、ntRecommendations in the E.720 Series will define other GOS parameters. Recommendations in the E.740 series willdefine traffic measurement and performance monitoring requirements.User GOS performance effects and other traffic-independent, user-perceived effects such as availability andservice integr

8、ity contribute to Quality of Service (QOS). Network GOS parameters and their values provideinformation on the traffic aspects of the QOS.3 Principles to select ISDN GOS parameters3.1 ISDN traffic characteristicsISDN has many characteristics different from the existing dedicated networks such as Publ

9、ic SwitchedTelephone Network (PSTN), Circuit Switched Public Data Network (CSPDN), Packet Switched Public Data Network(PSPDN), etc. The following characteristics are taken into account when defining GOS parameters for ISDN: ISDN provides integrated access to a wide variety of telecommunication servi

10、ces through a small set ofstandardized user-network interfaces. Services have heterogeneous traffic demand profiles and diverse performance requirements. The traffic streams generated by user demands for bearer services and teleservices utilize layer 1, 2 and 3resources. The configuration and implem

11、entation of a users terminal and its man-machine interface may vary fromone service to another service and one user to another user.2 Fascicle II.3 - Rec. E.720 Out-of-band signalling and call control capability, based on D-channel and Signalling System No. 7 (S.S.No. 7) are provided.3.2 Parameter s

12、election principlesThe GOS parameters defined in the E.720 series of Recommendations applies to the first phase of ISDN. Thedefinitions of these parameters may be expanded or additional GOS parameters defined to accomodate future evolutionof ISDN architecture and services. Considering the above char

13、acteristics in ISDN, the following principles arerecommended for selecting GOS parameters in ISDN:i) A minimum common set of GOS parameters is defined for attempts on layers 1, 2 and 3 such attemptsbelonging to different services may or may not share the same out-of-band call set-up and releaseproce

14、dures. (See Note.)ii) The GOS parameters are defined and specified in such a way that the GOS can be derived at well-definedreference points (traffic significant points).iii) The GOS parameters should be specified with reference to traffic load conditions in the sense ofRecommendation E.500.iv) Bloc

15、king GOS parameters may in the future need to take account of repetitions due to network status, butare presently based on lost-call-cleared assumptions.v) GOS parameters related to the user plane information transfer phase are for further study.Fascicle II.3 - Rec. E.720 3Note To assess the perform

16、ance directly perceived by a user, other additional parameters which are specific tothe users terminal equipment may also be necessary.3.3 GOS standard setting principlesGOS standard setting principles will take into account the current standards for voice and data services so thatwhen the user migrates from a dedicated network to the ISDN, the user does not encounter a marked undesirablecontrast.