1、CCITT RECMN*I-233 92 4862593 0572987 425 INTERNATIONAL TELECOMMUNICATION UNION CCITT THE INTERNATIONAL TELEGRAPH AND TELEPHONE CONSULTATIVE COMMITTEE INTEGRATED SERVICES DIGITAL NETWORK (ISDN) GENERAL STRUCTURE AND SERVICE CAPABILITIES 1.233 FRAME MODE BEARER SERVICES Recommendation 1.233 I Geneva,
2、1992 CCITT RECMN*I-233 92 = 48b2591 0572988 361 INTERNATIONAL TELECOMMUN ICAT CCITT ON UNION THE INTERNATIONAL TELEGRAPH AND TELEPHONE CON SU LTATIVE COM M ITTE E INTEGRATED SERVICES DIGITAL NETWORK (ISDN) GENERAL STRUCTURE AND SERVICE CAPABILITIES 1.233 FRAME MODE BEARER SERVICES Recommendation 1.2
3、33 FOREWORD The CCITT (the International Telegraph and Telephone Consultative Committee) is a permanent organ of the International Telecommunication Union (ITU). CCITT is responsible for studying technical, operating and tariff questions and issuing Recommendations on them with a view to standardizi
4、ng telecommunications on a worldwide basis. The Plenary Assembly of CCI?T which meets every four years, establishes the topics for study ahd approves Recommendations prepared by its Study Groups. The approval of Recommendations by the members of CCITT between Plenary Assemblies is covered by the pro
5、cedure laid down in CCITT Resolution No. 2 (Melbourne, 1988). Recommendation 1.233 was prepared by Study Group XVIII and was approved under the Resolution No. 2 procedure on the 25th of October 199 1. I CCIT NOTES 1) telecommunication Administration and a recognized private operating agency. 2) In t
6、his Recommendation, the expression “Administration” is used for conciseness to indicate both a A list of abbreviations used in this Recommendation can be found in Annex E and C. O ITU 1992 Ail rights reserved. No part of this publication may be reproduced or utilized in any form or by any means, ele
7、ctronic or mechanical, including photocopying and microfilm, without permission in writing from the ITU. CCITT RECMN*I.233 92 = 4862591 0572990 TIT Recommendation 1.233 FRAME MODE BEARER SERVICES Recommendation 1.210 describes the principles for defining telecommunication services supported by an IS
8、DN including the concept of bearer services, teleservices and supplementary services. It also provides the means for the definition and description of such services. A recommended set of bearer service categories is defined in Recommendation 1.230. The purpose of this Recommendation is to describe a
9、 recommended set of frame mode bearer services (FWBS), to describe individual frame mode bearer services and to recommend their provision in an ISDN. Bearer services are described by prose definitions and descriptions, by attributes and their values and by dynamic descriptions following the descript
10、ion method given in Recommendation 1.130. The application of the attribute technique and the definition of those attributes and attribute values is given in Recommendation I. 140. The following set of frame mode bearer services is currently identified 1.233.1 ISDN frame relay in bearer service 1.233
11、.2 ISDN fiame switching bearer service. Recommendation 1.233 1 CCITT RECMNaI.233 92 m 4862593 0572993 956 m Recommendation 1.233.1 ISDN FRAME RELAYING BEARER SERVICE 1 Introduction Recommendation 1.210 describes the principles for defining telecommunication services supported by an ISDN including th
12、e concept of bearer services, teleservices and supplementary services. It also provides the means for the definition and description of such services. The purpose of this Recommendation is to describe the frame relaying bearer service and to recommend the method of its provision in an ISDN. The defi
13、nition and description of this service form the basis to define the network capabilities required for the support of the service in an ISDN. According to Recommendation 1.210 a stage 1 service description uses three steps: prose description, static description and dynamic description. These steps be
14、gin in O$ 1,8 and 9 respectively. 2 Definition The frame relaying bearer service provides the bidirectional transfer of service data units (SDU) from one S or T reference point to another with the order preserved. The service data units are routed through the network by appropriate layer 2 PDUs on t
15、he basis of an attached label. This label is a logical identifier with local significance termed DLCI (data link connection identifier) in the protocol description. The user network interface structure at the S or T reference point allows for the establishment of multiple virtual calls and/or perman
16、ent virtual circuits to many destinations. This service is generally available on the following ISDN access arrangements: point-to-multipoint (passive bus) and point-to-point (NT2). It is a requirement of this service description to show how the OS1 network layer service could be supported. 3 Descri
17、ption 3.1 General description The frame relaying bearer service has the following characteristics: 1) All C-plane procedures, if needed, are performed in a logically separate manner using protocol procedures that are integrated across all ISDN telecommunication services. The U-plane procedures at la
18、yer 1 are based on Recommendations 1.430D.431. Layer 2 procedures are based on the core functions of Recommendation Q.922 (see O 3.1.1). These layer 2 core functions aow for the statistical multiplexing of user information flows immediately above layer 1 functions. This bearer service provides the b
19、idirectional transfer of service data units (frames) from one S or T reference point to another with the order preserved. 2) This bearer service: 1) preserves the order ot SDUs transmitted at one S or T reference point when they are delivered at the other end; Note - Since the network does not suppo
20、rt any procedure above the core functions of Recommendation Q.922, sequence numbers are not kept by the network. Networks should be implemented in such a way that, in principle, frame order is preserved. detects transmission, format and operational errors (e.g. frames with unknown label); 2) 2 Recom
21、mendation 1.233.1 CCITT RECMN*I.233 92 = 48b2591 0572992 892 3) 4) The functions above are based on the core functions of Recommendation Q.922. It provides service quality 1) throughput; 2) access rate; 3) committed information rate; 4) committed burst size; 5) excess burst size; 6) transit delay; 7
22、) residual error rate; 8) delivered errored frames; 9) delivered duplicated frames; 10) delivered out-of-sequence frames; 11) lost frames; 12) misdelivered frames. transports frames transparently, only the label and frame check sequence CS) may be modified by the network; does not acknowledge frames
23、 (within the network). that is characterized by the values of the following parameters: 3.1.1 Corefilnctions The core functions of Recommendation Q.922 are: - frame delimiting, alignment and transparency; - frame multiplexing/demultiplexing using the address field1); - inspegion of the frame to ensu
24、re that it consists of an integer number of octets prior to zero bit insertion or following zero bit extraction; - inspection of the frame to ensure that it is neither too long nor too short (see Q 4.2.2.1.6); - detection of transmission errors; - congestion control functions. 3.2 Specific tenninolo
25、gy See Annex A. 3.3 Qiialifications Not applicable 3.4 Applications The frame mode bearer service described in this Recommendation aims to support a wide range of data applications and rates from very low to high (typically 2 Mbids). A typical application may be interconnection between local area ne
26、tworks CANS). The address field default length is 2 octets. It can be extended to 3 or 4 octets where the fial octet is optionally a control information field. Recommendation 1.233.1 3 CCITT RECMN*I.233 92 W 4862593 0572993 729 4 Procedures 4.1 Provisiodwithdrawal This bearer service is offered with
27、 several subscription options which apply separately to each ISDN number or group of ISDN numbers on the interface. For each subscription option, only one value can be selected. Subscription options for the interface are summarized below: - - - general subscription to the frame relaying bearer servi
28、ce2)* 3); subscription to the Crame relaying bearer service with user defined profile; subscription to the conveyance of sub-addresses for terminal selection and/or conveyance of NSAP addresses for support of the OS1 network layer service4); subscription to the Multiple Subscriber Number (MSN) or Di
29、rect-Dialling-In (DDI) suppkmentary services may be required for terminal selection purposes. In general, there will be a limit on the number of information channels available at the user-network - in terface: - - maximum number of total calls present (active frame relayed VCs) per interface = N; ma
30、ximum number of total calls present (active frame relayed VCs) per channel (D, B, H) = M. 4.2 Normal procedures All user-network signalling takes place using logically separate messages. On the user side of the S or T reference point, Recommendation 1.430 or 1.431 provides the layer 1 protocol for t
31、he U (user) and C (control) planes. The C-plane uses the D-channel with Recommendations Q.921 and Q.933 as the layer 2 and 3 protocols respectively. For permanent virtual circuits (PVCs), no real-time call establishment is necessary and any parameters are agreed upon at subscription time. The U-plan
32、e may use any channel (D, B or H on which the user implements the core functions of Recommendation Q.922. 4.2.1 Activatioddeactivatiodregistration Not applicable. 4.2.2 Invocation and operation terminal. Virtual call and permanent virtuai circuit procedures can be invoked and operated concurrently b
33、y a given 4.2.2.1 Virtual call procediires connection for signalling are required. Before procedures Cor originating the service are invoksd, a layer 1 physical channel and a reliable data link 2, Some networks may not require specific subscription of the frame relaying bearer service since it may b
34、e offered as a default for general ISDN subscription. 3, The address convention (e.g. address length) is agreed at subscription time. A single address convention applies per access. 4) The conveyance of NSAP addresses may be restricted if the Calling Line Identification Restriction (CLIR) or Connect
35、ed Line Identification Resiction (COLR) are used. 4 Recommendation 1.233.1 CCITT RECMN*I=233 92 m 4862593 0572994 665 m 4.2.2.1.1 Originating the service (call Set-up) The call is originated by the user requesting from the network the required bearer service, with this request including a number ide
36、ntifying the called user. Other information required for the bearer service and additional information (e.g. calling line identity) may also be included. There are three possible channel types (D, B, HJ that could be used. Moreover, there are two possible physical channel access arrangements: - dema
37、nd establishment of the channel; - semi-permanent establishment of the channel. In the first arrangement, if a physical channel is not established, or already established channels have no free capacity, another channel (if available) is established using Q.933 procedures. In the second arrangement a
38、nd also for the D-channel, no dynamic establishment procedure is required. Once a physical channel has been established either dynamically or semi-permanently then, in the virtual call case, the value of the logical identifier and the other associated parameters, as defined in 4 1, are negotiated du
39、ring the call Set-up by means of C-plane procedures. Depending on the parameters requested, the network may accept or reject the call. The user network interface structure at the S or T reference point allows for the establishment of multiple virtual calls and/or permanent virtual circuits to one or
40、 more destination(s). Since it is a requirement of this service description Co show how the OS1 network layer service could be supported, Recommendation Q.933 will be used to carry the connection establishment and release primitives and parameters for the OS1 network service. See Annex B for details
41、. 4.2.2.1.2 Indications during call Set-up If interworking takes place, an indication of such interworking is required. The user can then decide whether to proceed with the interworking or to clear the call. See 0 6 and 1,500-Series Recommendations. See also Annex B for indications specific to the s
42、upport of the OS1 network service. 4.2.2.1.3 Terminal selectiodidentijication The Multiple Subscriber Number and Direct-Dialling-In supplementary services as well as sub-addressing are methods applicable to terminal selection and identification. 4.2.2.1.4 Call notijcation Q.933 procedures are used t
43、o notify the user of incoming calls. Note - Channel negotiation allows the called user to request that a call be offered on a specific channel, D, B or H. 4.2.2.1.5 Synchronization between C-plane and U-plane In some cases there is a gap between the time a connect confirmation is received and when t
44、he actual connection is established. It may be necessary to verify the connection prior to the beginning of data transfer. This should be accomplished end-to-end in the U-plane. 4.2.2.1.6 Virtual call procedures data transfer Frame relaying data units are frames as defined in Recommendation Q.Y22. T
45、he basic bearer service provided by the network is the unacknowledged transfer of frames between S or T reference points. Recommendation 1.233.1 5 CCITT RECMN*I-233 92 W 4862591 0572995 5T1 The frame size supported by this service is determined by the following factors: a) the default maximum inform
46、ation field to be supported by all networks is 260 octets; b) ali other values are negotiated between users and networks and between networks; c) the support by networks of a negotiated value of at least 1600 octets is strongly recommended for applications such as LAN (IS0 8802-3) interconnect, to p
47、revent the need for segmentation and reassembly by the user equipment; d) when interworking with frame switching, and the D-channel is used, the maximum information field that can be used is 260 octets (N201). In particular, the frame relay default of 262 octets (N202) cannot be used without negotia
48、tion when interconnected with a frame switching network due to the two byte frame switching control field. In this case, without negotiation, the frame relay user must use the N201 (260 octet) value. Figure lh.233.1 illustrates the U-plane configuration for this service. Protocol functions up to and
49、 including layer 3 are shown. The network does not terminate the full layer 2 (Q.922) protocol. The bearer service provided at the user-network interface (S or T reference point) included in a sub-layer, supports only the core functions as defined in Q 3.1.1. This sub-layer provides a core service which is modelled in a formal way in Annex C. The sub-layer provides the delimited and unacknowledged transparent transmission of protocol data units containing a number of octets up to the maximum information field size as defined above. The protocol service data units are transmitted in
