1、CCITT 9ECMNtI.350 (REV*:L) 73 I 4862571 0580b10 028 I INTERNATIONAL TELECOMMUNICATION UNION ITU-T TELECOMMUNICATION STANDARDIZATION SECTOR OF ITU 1.350 (03/93) INTEGRATED SERVICES DIGITAL NETWORK (ISDN) OVERALL NETWORK ASPECTS AND FUNCTIONS GENERAL ASPECTS OF QUALITY OF SERVICE AND NETWORK PERFORMAN
2、CE IN DIGITAL NETWORKS, INCLUDING ISDNs ITU-T Recommendation 1.350 (Previously “CCITT Recommendation”) FOREWORD The U Telecommunication Standardization Sector (J3V-T) is a permanent organ of the International Telecom- munication Union. The ITU-T is responsible for studying technical, operating and t
3、ariff questions and issuing 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 aini, prod
4、uce Recommendations on these topics. ITU-T Recommendation 1.350 was revised by the IT-T Study Group XVIII (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 (), the CCITT ceased to exist
5、 as of 28 February 1993. In its place, the IT 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 Similarly, in this reform process, the CCIR and the IFRB have been replaced by the Radiocommunication Sector.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 ch
6、ange has been made in the text to references containing the acronyms “CCITT, CCIR or IFRl3” 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 admini
7、smation and a recognized operating agency. In this Recommendation, the expression “Administration is used for conciseness to indicate both a O IT 1993 Ail rights reserved. No part of this publication may be reproduced or utilized in any form or by any means, electronic or mechanical, including photo
8、copying and microfilm, without permission in writing from the ITU. CCITT RECMN*I.350 (REV*L) 93 I 4862571 0580b12 7TO M 1 1.1 2 3 3.4 4 CONTENTS . General Purpose of Recommendation Purpose of QOS and Np . 2.1 General . 2.2 Purpose of QOS 2.3 Purpose of NP . 1.2 Description of Quaiity of Service (QOS
9、) and Network Performance (NP) Principles for the development of QOS and NP parameters and values . 3.1 General principles . 3.3 Np principles primary and derived performance parameters 3.2 QOS principles . Generic performance parameters Annex A . Method of identifying parameters 3 x 3 matrix approa
10、ch for network perf0 nnance Description of the basic communication functions . Description of the performance . A . 1 A.2 A.3 A.4 AS The matrix approach . 3 x 3 matrix approach for QOS . Annex B - Relationship between generic and possible specific QOS and NP parameters Page 1 1 1 1 1 2 2 2 2 4 5 5 5
11、 6 6 6 7 7 8 8 Recommendation 1.350 (0383) i CCITT RECMN*I.350 (REVU11 93 m 4862591 0580613 837 H Recommendation I350 GENERAL ASPECTS OF QUALITY OF SERVICE AND NETWORK PERFORMANCE IN DIGITAL NETWORKS, INCLUDING ISDNs (Melbourne, 1988: revised Helsinki, 1993) 1 General 1.1 Purpose of Recommendation T
12、his Recommendation has been developed to: - - provide descriptions of Quality of Service and network performance; illustrate how the Quaiity of Service and the network performance concepts are applied in digitai networks, including ISDNs; describe the features of, and the relationship between these
13、concepts; indicate and classify performance concerns for which parameters may be needed; - - - identify generic performance parameters. The generic term “performance” refers to Quality of Service and network performance as they are defined in 1.2. 1.2 Description of Quality of Service (QOS) and Netw
14、ork Performance (NP) 1.2.1 QOS is defined in Recommendation E.800 as follows: “Collective effect of service performances which determine the degree of satisfaction of a user of the service”. Description of Quality of Service The note of Recommendation E.800 underlines that the QOS is characterized b
15、y to the combined aspects of: - - service support and service operability performance; and servability and service integrity performance. The definition of Quality of Service in Recommenation E.80 is a wide one encompassing many areas of work, including subjective customer satisfaction. However, wit
16、hin this Recommendation the aspects of Quality of Service that are covered are restricted to the identification of parameters that can be directly observed and measured at the point at which the service is accessed by the user. Other types of QOS parameters which are subjective in nature, i.e. depen
17、d upon user actions or subjective opinions, will not be specified in the I-Series Recommendations on QOS. 1.2.2 Description of network performance Network performance is measured in terms of parameters which are meaningful to the network provider and are used for the purposes of system design, confi
18、guration, operation and maintenance. NP is defined independently of terminai performance and user actions. 2 Purpose of QOS and NP 2.1 General Bearer services and teleservices as described in the 1.20-Series Recommendations are the objects which network and service providers offer to their customers
19、. A major attribute of these services is the set of QOS parameters which a particular service offers. These parameters are user-oriented and take into account the elements involved in a particular service as given in Figure 2h.211. Recommendation 1.350 (0303) 1 CCITT RECMN*I*350 (REV*L) 93 48b259L 0
20、580bL4 773 = Bearer services and teleservices are supported by a range of connection types, each of which comprises severai connection elements. The performance of the connection types is characterized by a set of NP parameters. These parameters are network oriented. Figure 1 illustrates how the con
21、cepts of QOS and NP are applied in the ISDN environment. 2.2 Purpose of QOS A typical user is not concerned with how a particular service is provided, or with any of the aspects of the networks internai design. However, he is interested in comparing one service with another in terms of certain unive
22、rsal, user- oriented performance concerns which apply to any end-to-end service. Therefore from a users point of view, Quality of Service is best expressed by parameters which: - focus on user-perceivable effects, rather than their causes within the network; - do not depend, in their definition, on
23、assumptions about the network internal design; - take into account all aspects of the service from the users point of view which can be objectively measured at the service access point; - may be assured to a user at the service access point by the service providerb); - are described in network indep
24、endent terms and create a common language understandable by both the user and the service provider. As networks evolve, providers should maintain the Quality of Service of bearer services provided to users within acceptable limits, and where possible, should make Quality of Service improvements. The
25、 Quality of Service perceived by users should not be perceptibly degraded by network evolution. 2.3 PurposeofNP A network provider is concerned with the efficiency and effectiveness of the network, in providing services to customers. Therefore from a network providers point of view, NP is best expre
26、ssed by parameters which provide information for: - system development; - network planning, both nationally and internationally; - operation and maintenance. 3 Principles for the development of QOS and NP parameters and values 3.1 General principles 3.1.1 Distinction between QOS and NP The user-orie
27、nted QOS parameters provide a valuable framework for network design, but they are not necessarily usable in specifying performance requirements for particular connections. Similarly, the NP parameters ultimately determine the (user observed) QOS, but they do not necessarily describe that quality in
28、a way that is meaningful to users. Both types of parameters are needed, and their values must be quantitatively related if a network is to be effective in serving its users. The definition of QS and NP parameters should make mapping of values clear in cases where there is not a simple one-to-one rel
29、ationship between them. 2 Recommendation 1.350 (03/93) CCITT RECMN*I-350 REV*L) 93 m 48b259L 0580bL5 bOT I- l- ;a I Recommendation 1.350 (03/93) 3 CCITT RECMNUI.350 (REVaL) 93 m 48b259L 0580636 54b m Table 1 shows some of the characteristics which distinguish QOS and NP. Quality of service User orie
30、nted TABLE 1fi.350 Network performance Provider oriented Service attribute Focus on user-observable effects Between (at) service access points Connection element atbibute Focus on planning, development (design), operations and maintenance End-to-end or network connection elements capabilities 3.1.2
31、Due to separating QOS and NP, a number of general points should be noted when considering the development of parameters: - the definition of QOS parameters should be clearly based on events and states observable at service access points and independent of the network processes and events which suppo
32、rt the service; the definition of NP parameters should be clearly based on events and states observable at connection element boundaries, e.g. protocol specific interface signals; the use of events and states in the definition of parameters should provide for measurements at the boundaries identifie
33、d above. Such measurements should be verifiable in accordance with generally accepted statistical techniques. Measurability of QOS and NP parameter values - - 3.1.3 Multiple network provider environments It should be recognized in the development of parameter values that services may be provided by
34、multiple providers. In such an environment different levels of QOS may be supported. Therefore, in practice, users may experience a variety of ranges of QOS. It is thus important to establish minimum performance levels for each service and for connection elements providing international connections.
35、 3.2 QOS principles For the definition of parameters for QOS in the ISDN, the concept of bearer services and teleservices needs to be borne in mind. In particular, there is a difference between the kinds of parameters which would describe the QOS of a bearer service and that of a teleservice, since
36、the point of observation of, or access to, the service is different in each case. Figure 1 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 interface corresponds to the S or
37、 T reference points. As a result, some of the parameters for describing the QOS of a teleservice will be different from those which describe the QOS of a bearer service. In describing the QOS of teleservicess, the performance of the terminal equipment (TE) has to be taken into account. For a teleser
38、vice, there should be a mapping between the QOS of the teleservice and the performance of the customer equipment including the terminal and the overall (end-to-end) NP of the connection elements supporting this service. For a bearer service there should be mapping between the QOS of the bearer servi
39、ce and the overall (end-to-end) IW of connection elements supporting this service. 4 Recommendation 1.350 (03/93) CCITT RECMN*I-350 (REV*%) 93 48b259L 0580bL7 482 3.3 NP principles When developing NP parameters the following points should be borne in mind: - NP parameters must be measurable at the b
40、oundary of the network connection element(s) to which they are applied. The definitions should not be based on assumptions about either the internal characteristics of a network (or portions thereof), or the internai causes of impairments observed at the boundaries; the division of a network portion
41、 into sub-components should only be done if they must be specified separately in order to ensure satisfactory end-to-end performance or, where appropriate, to derive fair and reasonable allocations among providers. No network provider should bear a disproportionate cost in establishing and operating
42、 a service. - 3.4 3.4.1 3.4.2 Primary and derived performance parameters Description - Primary pevormance parameter A parameter or a measure of a parameter determined on the basis of direct observations of events at services access points or connection element boundaries. - Derived perjiormunce paru
43、meter A parameter or a measure of a parameter determined on the basis of observed values of one or more relevant primary performance parameters and decision thresholds for each relevant primary performance parameter. Relationship between primary and derived performance parameters A number of event t
44、ypes can be directly observed at service access points or connection element boundaries. Examples of such events are: the layer 3 protocol state transition associated with the transfer of a SETUP message or a DISCONNECT message across a connection element boundary; the correct receipt of an informat
45、ion bit (or a specified number of information bits) at an interface. - - Parameters related to the time interval between specific events and the frequency of events can be measured. These directly measurable parameters or primary performance parameters describe the QOS (at service access points) or
46、the NP (at connection element boundaries) during periods when the service or connection is available. Derived performance parameters describe performance based on events which are defined as occurring when the value of a function of a primary performance parameter(s) crosses a particular threshold.
47、These derived threshold events identifj the transitions between the available and the unavailable states. Parameters related to the time interval between these derived threshold events and their frequency can be identified, These derived performance parameters describe the QOS and the NP for all tim
48、e intervals; i.e. during periods when the service or connection is available or unavailable. NOTE - primary performance parameters are measured for all time intervals, since the transitions between available and unavailable states depend upon the value of these parameters. However, the values of pri
49、mary performance parameters would not be specified for a service or connection in the unavailable state. 4 Generic performance parameters Nine generic primary performance parameters are listed below. These have been developed as a result of the matrix approach described in Annex A. These parameters may be used in developing specific QOS and NP parameters: - access speed: - access accuracy; - access dependability; - information transfer speed; Recommendation 1.350 (03/93) 5 CCITT RECMN*I.350 (REV*II) 93 48b259L 0580618 319 = - information transfer accuracy; - information tr
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