1、CCITT RECMN*I*2LL (REV*L) 93 m 4862593 0580539 374 m INTERNATIONAL TELECOMMUN CATION UNION ITU-T TELECOMMUNICATION STANDARDIZATION SECTOR OF ITU INTEGRATED SERVICES DIGITAL NETWORK (ISDN) SERVICE CAPABILITIES 1.21 1 (03/93) B-ISDN SERVICE ASPECTS ITU-T Recommendation 1.21 1 (Previously “CCITT Recomm
2、endation“) CCITT RECMNtI-211 (REV*1) 93 m 4862591 0580520 0b FOREWORD The ITU Telecommunication Standardization Sector (ITU-T) is a permanent organ of the International Telecom- munication Union. The -T is responsible for studying technical, operating and tariff questions and issuing Recommendations
3、 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, produce Recommendations on these topics. ITU-T
4、Recommendation 1.211 was revisd by the ITU-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 proce-ss within the International Telecommunication Union (ITU), the CCIT ceased to exist as of 28 February 1993. In its place, t
5、he IT Telecommunication Standardization Sector (-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 Similarly, in this reform process, the CCIR and the IFRB have been replaced by the Radiocommunication Sector.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 change has been made in the text to reference
6、s containing the acronyms “CC, CCIR or IFRB” 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 administration and a recognized operating agency. In
7、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 photocopying and microfilm, without permission in
8、writing from the ITU. CONTENTS Introduction 1 Classification of broadband ISDN services . 1.1 General . 1.2 Service ciasses 1.3 Definition of service classes 1.4 Identification of possible broadband services . 2 General network aspects of broadband services 2.1 2.2 2.3 2.4 2.5 2.6 2.7 2.8 2.9 2.10 G
9、eneral . Multimedia aspects . Quality of service (QOS) aspects . Service bit rate aspects Service timing/synchronization aspects . Simultaneous service capabilities Connectionless data service aspects . interworking aspects . Signalling aspects . Service aspects of virtual path connection (VET) and
10、virtual channel connection (VCO . 3 Video services and dig aspect . 3.1 General . 3.2 ATM network impacts on video coding . 3.3 Video service interworking and coding aspect . 3.4 Cell loss resilience and coding aspects 3.5 3.6 Constant bit ra ii) to provide some considerations on the means to descri
11、be services based on the description method as defmed m Recommendation I. 130; iii) to give a basis for the definition of the network capabilities required by B-ISDN. The service concepts considered in this Recommendation are in accordance with uI.210. The Recommendation takes into account some of t
12、he known and relevant aspects of the B-ISDN including: - capabilities to increase flexibility to both user and network ope- including independent call and connection control; the quality of service implications of information beiig structured and transported in cells; capabilities for flexible bandw
13、idth allocation; capabilities for the provision of service timing infmation; - - - - the overall interface capabilities. The Recommendation ais0 gives guidance on video ding aspects taking into account the characteristics of the ATM based network and recommends a common approach to video coding for
14、all visual services including botb interactive and distribution type services. ii Recommendation 1.211 (Os/92) CCITT RECMN*I-ZLL (REV*L) 93 m Y8b253L 0580523 8T5 m Recommendation I311 B-ISDN SERVICE ASPECTS (Geneva, 1991; revised in Helsinki, 1993) 1 Classification of broadband ISDN services 1.1 Gen
15、eral This subclause describes the classification of broadband services, the definition of those service classes, and gives examples of services in each service class proposed to be supported by the B-ISDN. This classification does not take into account the location or the implementation of the funct
16、ions either in the network or in the terminals. This classification is primarily from the point of view of the network and not from the user point of view. Depending on their communication functions and applications, the services to be supported by the B-ISDN may be internationally standardized and
17、offered by the Administration as bearer services or teleservices. 1.2 Service classes Depending on the different forms of the future broadband communication and their applications, two main service categories have been identified: interactive services and distribution services. The interactive servi
18、ces are subdivided into three classes of services, viz., the conversational services, the messaging services, and the retrieval services. The distribution services are represented by the class of distribution services without user individual presentation control and the class of distribution service
19、s with user individual presentation control (see Figure 1). Distribution senkes Il I FIGURE 1L.211 Classincation of broadband services Recommendation 1.211 (OW92) 1 CCITT RECNN*I.ZLL (REVtL) 93 = 48b259L 058052Y 73L 1.3 Dennition of service classes conversational services: Conversational services in
20、 general provide the means for bidirectional communication with real-time (no storeand-forward) end-to-end information transfer from user to user or between user and host (eng. for data procasing). The flow of the user information may be bidirectional symmetric, bidirectional asymmetric and in some
21、specific cases (e.g. such as video surveillance), the flow of information may be unidirectional. The information is generated by the sending user or users, and is dedicated to one or more of the communication partners at the receiving site. Examples of broadband Conversational services are videotele
22、phony, video conference and high speed data transmission. messaging services: Messaging services offer user-to-user communication between individual users via storage units with store-and-forward, mailbox andor message handling (e.g. information editing, processing and conversion) functions. Example
23、s of broadband messaging services are message handling services and mad services for moving pictures (films), high resolution images and audio information. retrieval services: The user of retrieval services can retrieve information stored in information centres provided for public use. This informat
24、ion will be sent to the user on his demand only. The information can be retrieved on an individual basis. Moreover, the time at which an information sequence is to start is under the control of the user, Examples are broadband retrieval services for film, high resolution image, audio information, an
25、d archivai information. distribution services without user individual presentation control: These services include broadcast services. They provide a continuous flow of information which is distributed from a central source to an unlimited number of authorized receivers connected to the network. The
26、 user can access this flow of information without the ability to determine at which instant the distribution of a string of information will be started. The user cannot control the start and order of the presentation of the broadcased information. Depending on the point of time of the users access,
27、the information will not be presented from the beginning. Examples are broadcast services for television and audio programmes. distribution services with user individual presentation control: Services of this class also distribute information Ennn a central source to a large number of users. However
28、, the information is provided as a sequence of information entities (e.g. frames) with cyclical repetition. So, the user has the ability of individual access to the cyclical distributed information and can control start and order of presentation. Due to the cyclical repetition, the information entit
29、ies selected by the user will always be presented from the beginning. One example of such a service is fuli channel broadcast videography. 1.4 Identification of possible broadband services Table 1 contains examples of possible services, their applications and some possible attribute values describin
30、g the main characteristics of the services. The identification and full specification of specific services for standardization can only be completed after a thorough examination of the needs of users by e.g. market research. The full specifkation of such services should be based on the application o
31、f appropriate description methodology. 2 General network aspects of broadband services 2.1 General The purpose of this subclause is to give guidance concerning some of the important aspects which need to be taken into account when supporting and developing services for the B-ISDN. 2 Recommendation 1
32、.211 (oaf92) CCITT RECMN*I-ZLL (REV*L) 93 48b2591 0580525 b7B TABLE 1D.211 Possible broadband services in ISDN“) Service classes TYP of information Examples of broadband services Some possible atibute values 9, Applications Conversa- tional services Moving pictures (video) and sound Broadbandb). C)
33、video-telephony - Demandreservdpermanent - Bidirectional symmeid bidirectional asymmetric - (Value for information transfer rate is under study) - Point-to-pointhnultipoint Communication for the transfer of voice (sound), moving pictures, and video scanned still images and documents between two loca
34、tions (person-to-person) c) - Tele-education - telsshopping - tele-advertising Multipoint communication for the transfer of voice (sound), moving pictures, and video scanned stili images and documents between two or more locations (person-to-group, - Tele-education - Tele-shopping - Tele-advertising
35、 group-to-group)c) Broadbandb).) videoconference - Demandheservdpermanent - Point-to-point/multipoint - Bidirectional symmeic/ bidirectional asymmetric Video-surveillance - Buildingsecurity - Traffcmonitoriag - Demandheservdpermanent - Point-to-point/multipoint - Bidirectional symmetric/ unidirectio
36、nal - TV signal transfer - Video/audio dialogue - Contribution of information - emandheserved/permanent - Point-to-point/multipoint - Bidirectional symmetric/ Video/audio information transmission service Multiple sound- programme signals bidirectional a - - control of interworking situations; - simp
37、licity for the network operator; commonality of terminal and network components. The B-ISDN provides independent call and connection control facilities which should be exploited to help achieve the above objectives. The B-ISDN will make it possible, within a single cai1 associated with a specific se
38、rvice, to establish a number of connections which may each be associated with a specific information type. The B-ISDN will enable the addition and/or deletion of optional information types during a cal. Recommendation U11 (08/92) 5 CCITT RECMN*I-ZLL (REV*L) 93 m 48b259L O580528 387 It is recommeoded
39、 therefore that the development of multimedia services proceeds on the basis of the following PIinCipies: - - that a limited set of srandardized information types be developed; that the association of services and standardized information types be conmlled, but in a flexible manner. 2.3 Quaiity ofse
40、rvice (QOS) aspects 2.3.1 General Rinciples of quality of service (QOS) and network performance Ovp) and their reiationship with each other are described in Recommendation 1.350. A merbod of identifymg QOS and Np paramem is given in Annex AiI.350. Further enhancement of the methodology and the defin
41、ition of individual parameters for B-ISDN are. for further study. 23.2 QOS indication and negotiation QS is negotiated during the caU set up phase and possibly during a call. It is for further study whether specific QOS parameter values will be expcitiy indicated (e.g. by a specinc cell loss ratio v
42、alue) or implicitiy associated with specific service requests (e.g. a standardized service wiil by defdtion include the specification of all relevant QS parameters). For several reasons, including network operation, interworking and service development, a limited number of specific QOS will be stau-
43、. Additidy, for some services there may be a need for an explicit cell loss priority (CLP) indication on a cell by cell basis as a meaos of managing cell loss during periods of network congestion. This allows a user to use two levels of cell loss ratios for ATM coIIlKction. However, if this indicato
44、r is used it will be necessary duhg the caU set up phase to indicate the intended incidence of use of this indicator. This is necessary to facilitate appropriate network resource allocation and usagdnetwork parameter control. Further details on the use of CLP bit are in Recommendation 1.371. 2.4 Ser
45、vice bit rate aspects 2.4.1 Generd The issue of service bit rates and associated user assurances is very much related to suitable aocation of network resources. The objectives should include - - - - - Constant bit rate (CBR) services support of service bit rate requirements; simplicity of service bi
46、t rate expressions; efficient utilization of network resources; exploitation of the inherent variable bit rate capabiity of ATM, ind use of network resources during lightly loaded periods. 2.4.2 Constant bit rates are expressed by a number of parameters, relate to be traffic characteristics describe
47、d in Recommendation 1.37 1. Constant service bit rates are negotiated at cail set up time for on demand services and that the necessary network resources are fully allocated at this stage for the duration of the call. Changes to bit rates during a ca may be negotiated via signalling and details are.
48、 for further study. Service bit rates for permanent and semi-permanent connections may be the transfer capacity for signalling and OAM cells; the ATM Adaptation Layer overheads. 2.45 Maximum service bit rate supported by the 622.080 Mbit/s interface The transfer capability at the user network interf
49、ace is 622.080 Mbits with a payload capacity of 599.040 Mbit/s. With the ATM cell format of a 5 octet header and 48 octet information field, the maximum rate available from the interface ftom all celi information fields is 542.526 MbiVs. The maximum service bit rate which can be supported on this interface may be equal to or less than 542.526 Mbids. The actual maximum service bit rate is for furtber study. The following factors, if applicable, will affect the actuai maximum service bit rate; - - - the service delay and buffering requirements; the transfer capacity f
