1、ITU-T RECMN*E.724 9b m 48b2591 Ob17379 97T m INTERNATIONAL TELECOMMUNICATION UNION ITU-T TELECOMMUNICATION STANDARDIZATION SECTOR OF ITU E.724 (02/96) TELEPHONE NETWORK AND ISDN QUALITY OF SERVICE, NETWORK MANAGEMENT AND TRAFFIC ENGINEERING GOS PARAMETERS AND TARGET GOS OBJECTIVES FOR IN SERVICES IT
2、U-T Recommendation E.724 (Previously “CCITT Recommendation“) ITU-T RECRN*E.?ZY 9b 4862571 0617380 691 FOREWORD The IT-T (Telecommunication Standardization Sector) is a permanent organ of the International Telecommunication Union (ITU). The ITU-T is responsible for studying technical, operating and t
3、ariff questions and issuing Recommen- dations on them with a view to standardizing telecommunications on a worldwide basis. The World Telecommunication Standardization Conference (WTSC), which meets every four years, establishes the topics for study by the -T Study Groups which, in their turn, produ
4、ce Recommendations on these topics. The approval of Recommendations by the Members of the ITU-T is covered by the procedure laid down in WTSC Resolution No. 1 (Helsinki, March 1-12, 1993). ITU-T Recommendation E.724 was prepared by IT-T Study Group 2 (1993-1996) and was approved under the WTSC Resol
5、ution No. 1 procedure on the 19th of February 1996. NOTE In this Recommendation, the expression “Administration” is used for conciseness to indicate both a telecommunication administration and a recognized operating agency. O ITU 1996 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. 1 2 3 4 5 6 7 8 9 ITU-T RECMN*E.24 b 4862593 Ob37381 528 TABLE OF CONTENTS Scope References Definitions Abbreviations . General . 5.1 Intelligent net
7、work overview 5.2 Performance assessment methodology . Service analysis 6.1 General 6.2 Representative service definitions 6.3 User-perceptible GOS criteria 6.4 User expectation data Reference topologies Target GOS objectives (provisional values) Delay objectives for networks Delay objectives for si
8、ngle services Blocking objectives for IN seniices History 8.1 8.2 8.3 Bibliography Page 1 1 1 2 2 2 2 3 3 3 3 4 4 8 8 9 9 9 9 Recommendation E.724 (OU96) i SUMMARY To ensure the effective deployment of Intelligent Network I capabilities, performance objectives must be established to serve as a basis
9、 for traffk engineering and related network planning. This Recommendation defines performance parameters for a range of IN services and provides corresponding Grade of Service (GOS) performance objectives. Currently only one such objective, namely incremental post-selection delay is addressed. For t
10、he successful introduction of new service capabilities provided by intelligent networks, network planning and engineering should be based on the fundamental requirement of providing acceptable service to the end user. Reasonable grade of service performance objectives have been developed by understa
11、nding user expectations and typical implementations of representative IN services. The Recommendation introduces the notion of service classes that are defined on the basis of end user requirements. Performance requirements during periods of network congestion are for further study. ii Recommendatio
12、n E.724 (02/96) ITU-T RECMN*E.724 9b = 4862591 0617383 3T0 Recommendation E.724 GOS PARAMETERS AND TARGET GOS OBJECTIVES FOR IN SERVICES (Geneva, 1996) 1 Scope This Recommendation is limited in scope to cover Capability Set 1 (3-1). Extensions to cover further evolution of IN concepts are for furthe
13、r study. Before using this Recommendation for applications other than CS-1, the user should check that it is appropriate to do so. Appropriate performance objectives in the IN environment should carefully balance user expectations and technology capabilities. The latter are largely influenced by fac
14、tors such as reference connections, signalling message flows, nodal processing times and queueing delays associated with particular servicedeployment scenarios. Expectations of the end user in an IN environment are based on assessments of typical user tolerance to various delays and categories of un
15、availability - again for particular services or service classes. 2 References The following Recommendations and other references contain provisions which, through reference in this text, constitute provisions of this Recommendation. At the time of publication, the editions indicated are valid. All R
16、ecommendations and other references are subject to revision; all users of this Recommendation are therefore encouraged to investigate the possibility of applying the most recent edition of the Recommendations and other references listed below. A list of currently valid ITU-T Recommendations is regul
17、arly published. Recommendations Q.1202,Q.1211,Q.1214,Q.1218,Q.1219, E.492, E.721, E.723, E.733, Q.706,Q.716 and Q.766. 3 Definitions For the purposes of this Recommendation, the following definitions apply: 3.1 comparable calk A call which does not invoke IN services and which is selected by the net
18、work operator as being similar in user expectation, with respect to the post-selection delay, to the call(s) invoking the IN service(s) under consideration. Where there are no calls with similar user expectation, the network operator may select an average call as the comparable call. 3.2 incremental
19、 post-selection delay: This parameter is the increase in the post-selection delay (as defined in Recommendation E.721) when IN services are invoked on a call. For calls involving the setting up of voice connection paths beyond the usual expectation for a call type (for example, as the result of a ca
20、ll forwarding action triggered by the called number) the IN processing delay includes any extra delay in setting up such a path. Calculation of this value for calls involving a user interaction with the IN service logic is for further study. 3.3 IN services: Services implemented using IN structured
21、networks. Recommendation E.724 (OY96) 1 ITU-T RECMN*E.24 9b m 4862591 Ob17384 237 = 4 Abbreviations For the purposes of this Recommendation, the following abbreviations are used: CPE Customer Premises Equipment CS-1 Capability Set 1 GOS Grade of Service IN Intelligent Network IP Intelligent Peripher
22、al ISDN Integrated Services Digital Network SCP Service Control Point SDP Service Data Point SSP Service Switching Point STP Signalling Transfer Point UPT Universal Personal Telecommunication 5 General 5.1 Intelligent network overview In the development of this Recommendation, use has been made of t
23、he definitions of intelligent network concepts (including concepts relating to capability set 1) which are contained in the Q.1200-Series of Recommendations. In particular, Recommendations Q.1201,Q.1211, Q.1214, Q.1218 and 4.1219 are noted. The intelligent network architecture is based primarily on
24、a network concept for the support of supplementary services provided in combination with bearer services, teleservices, broadband interactive services and broadband distribution services. CS- 1 services and features described in Recommendation 4.1214 have been analysed in establishing service catego
25、ries and in determining the grade of service targets given in clause 8. From the performance assessment standpoint, a service type will be characterized by the associated combination(s) of IN transactions and circuit and signalling connections involved in the invocation of the service. 5.2 Performan
26、ce assessment methodology The GOS targets of clause 8 have been determined based on background studies using network models incorporating representative services and features to provide information on achievable performance (as perceived by the end user) in typical intelligent network environments.
27、On the one hand, a bottom-up approach was used to assess end-to-end delays perceptible to end user by utilizing Recommendations in the E.700- and Q.700-Series which contain delay objectives for signalling links, Signalling Transfer Points (STP), signalling relay points, Service Switching Points (SSP
28、) and Service Control Points (SCP) - in conjunction with appropriate reference connections (see clause 7). In particular, Recommendations E.723, E.733,Q.706, 4.7 16 and 4.766 have been used. This bottom-up approach was complemented by a top-down assessment based on user performance expectations - wh
29、ich are discussed more fully in 6.3. In the former approach, distinct call types have differing associated topological reference connections; from the top-down perspective, they have differing user expectations. Performance objectives for service switching points, signalling transfer points, service
30、 control points, intelligent Peripherals (E) and Service Data Points (SDP) are for further study. 2 Recommendation E.724 (02/96) ITU-T RECMN*E.724 96 4862571 Oh37385 173 6 Service analysis 6.1 General This Recommendation can be viewed as extending Recommendation E.721, which takes into account only
31、a limited penetration of IN services (such as the freephone and credit card calling services which require simple interaction with a database). With the increasing penetration of IN services that require database look-up for number translation andlor other call screening purposes, new reference conn
32、ection models that include the database query-response aspects are needed (see clause 7). 6.2 Representative service definitions As an example, Universal Personal Telecommunication (UPT) is an important application which will support a whole class of databasedependent services. UPT will be providing
33、 personal mobility management functions, and it is generally recognized that the evolving IN architecture is well suited for supporting these UPT functions. In this context, IN resource allocation will depend on optimizing the location of databases as part of overall UPT information-sharing strategi
34、es. UPT deployment in an IN environment therefore provides valuable insight into the broad issue of IN resource allocation and dimensioning and the consequent impact on performance parameters like post-selection delay and answer signal delay seen by the end user. In addition to the UPT services just
35、 described, a range of CS-1 services and features have been examined. (Further study is required to classify these services and features into categories which may need to be separately specified in clause 8.) 6.3 User-perceptible GOS criteria In setting traffic standards for IN, the existing standar
36、ds for basic telephony and Integrated Services Digital Network (ISDN) provide a useful structure, with extensions required to address the new network realities introduced with IN. The following subclauses discuss the issues which have led to the GOS criteria provided in clause 8. 6.3.1 Importance of
37、 post-selection delay As switching technology has advanced, post-selection delays have decreased dramatically. With the wide deployment of SS No. 7, delays are less than with tone signalling and users come to expect quicker call setup. With the introduction of IN services, post-selection delays incr
38、ease. Time is required to send and process the messages for service logic. If the delays become too long, users will become dissatisfied and may even believe that there has been some kind of network failure. Therefore, it is particularly important to set standards for post-selection delays in IN. 6.
39、3.2 Separate network and service objectives For a network operator, it is important to ensure that the service to the users achieves at least a certain minimum level of quality. Therefore, it is appropriate to establish a GOS standard for the average post-selection delay averaged over all calls in t
40、he network. With the intelligent network, any given call may invoke more than one IN service. The designer of an IN service may not be the network provider and hence the designer may not know the total network GOS level. To assist service design, standards should provide additional targets directed
41、to the GOS of the specific service. Therefore, when possible, standards should provide GOS targets relevant to individual service classes, in addition to targets for total network GOS. Note also that there may be some services, such as non-call related messaging, for which individual- service GOS ob
42、jectives are appropriate, yet these services will not be included in the GOS objectives for networks. Recommendation E.724 (02J96) 3 6.3.3 Target values GOS standards may be defined for different purposes. Existing GOS standards have been selected, and networks engineered, to assure a network operat
43、or that performance is acceptable, considering the limitations imposed by technology. With the introduction of IN and with the rapidly evolving technology, it may be desirable, in some cases, to select more stringent design targets to provide a greater level of user satisfaction. In these situations
44、, thresholds should identify the delay under which user satisfaction does not significantly increase. Clause 8 identifies, for service design and network planning purposes, the threshold of mean delays under which end user satisfaction does not significantly change. 6.3.4 User-based target As IN ser
45、vices are introduced into the network, end users may not be aware of the new requirements for processing of the service logic. They may well be unaware that any IN service is invoked at all (for example, when a call is redirected to an alternate location to follow another user). Therefore, some limi
46、t is appropriate to minimize the total post-selection delay. Such a limit should be based on the end users GS requirements as typically established in a testing or hiai environment. To provide GOS targets useful in designing a new service, reliance must be on testing data rather than on user experie
47、nce with the actual service. 6.3.5 Incremental delay for processing IN services Existing standards for regular telephony and ISDN provide a good basis for engineering even in IN structured networks. The extra complexity and performance issues in IN can be addressed with GOS targets specifying the ap
48、propriate additional requirements. Considering the discussion of the previous subclauses, it is useful to set objectives for the increment in post-selection delay attributable to the processing of IN services. This allows development of GOS targets for service classes and the forecasting of the tota
49、l expected post-selection delay based on the expected mix of invoked services. 6.4 User expectation data Data derived from laboratory investigation of users expectation of post-selection delay has been used to derive the targets specified in clause 8. These results show that instead of a single GOS target, several different ones are required. The following subclauses outline the reasons for this. 6.4.1 Allowance for connection type As reflected in Recommendation E.721, GOS objectives for ISDN, users will allow extra delay when calls are perceived to involve setup over a greater
