1、INTERNATIONAL TELECOMMUNICATION UNION ITU-T TELECOMMUNICATION STANDARDIZATION SECTOR OF ITU BROADBAND ISDN Q.211 O (07/94) B-ISDN ATM ADAPTATION LAYER - SERVICE SPECIFIC CONNECTION ORIENTED PROTOCOL (SSCOP) ITU-T Recommendation Q.211 O (Previously “CCIlT Recommendation”) ITU-T RECflN*Q.ZLLO 7Y Y8625
2、91 0596111 8TL = FOREWORD The ITU-T (Telecommunication Standardization Sector) is a permanent organ of the International Telecommunication Union (ITLJ). The ITU-T is responsible for studying technical, operating and tariff questions and issuing Recommen- dations on them with a view to standardizing
3、telecommunications on a worldwide basis The World Telecommunication Standardization Conference (WTSC), which meets every four years, etablishes the topics for study by the ITU-T Study Groups which, in their turn, produce Recommendations on these topics. The approval of Recommendations by the Members
4、 of the ITU-T is covered by the procedure laid down in WTSC Resolution No. 1 (Helsinki, March 1-12, 1993). ITU-T Recommendation 4.2110 was prepared by IT-T Study Group 11 (1993-1996) and was approved under the WTSC Resolution No. 1 procedure on the 29th of July 1994. NOTE In this Recommendation, the
5、 expression “Administration” is used for conciseness to indicate both a telecommunication administration and a recognized operating agency. O ITU 1995 All rights reserved. No part of this publication may be reproduced or utilized in any form or by any means, electronic or mechanical, including photo
6、copying and microfilm, without permission in wrhing from the ITU. CONTENTS Scope Normative references . Abbreviations . General Functions of the SSCOP . Elements for layer to layer communication 6.1 6.2 6.3 . Signals between SSCOP and SSCF, and SSCOP and SSCS layer management State transition diagra
7、m for sequences of signals . Protocol elements for peer-to-peer communications Signals between SSCOP and CPCS 7.1 SSCOP PDUs . 7.2 SSCOP PDU formats 7.3 States of SSCOP protocol entity . 7.4 SSCOP state variables 7.5 SSCOP PDU parameters . 7.6 SSCOP timers . 7.7 SSCOP parameters 7.8 SSCOP credit and
8、 flow control . Specification of SSCOP . 8.1 Overview 8.2 SDL diagrams . Annex A . Management error indications Annex B . Protocol implementation conformance statement (PICS) proforma to Recommendation 4.21 10 . B.l General Bi2 Abbreviations and special symbols . B.3 Instructions for completing the
9、PICS proforma B.4 Global statement of conformance . B.5 SSCOP-4.2110 Appendix I - Concepts and terminology . Appendix II - Examples of SSCOP operation Appendix III . Summary of buffer and state variable management Appendix IV -Default window size for SSCOP Page 1 1 1 3 4 5 5 7 7 9 9 11 16 17 18 19 2
10、0 21 22 22 24 78 79 79 79 79 80 80 83 85 93 95 Recommendation Q.2110 (07/94) 1 SUMMARY The intent of this Recommendation is to provide a new protocol specification that can be used in the B-ISDN ATM Adaptation Layer (AAL). This protocol, called the Service Specific Connection Oriented Protocol (SSCO
11、P), provides assured data delivery between AAL connection endpoints. The ATM Adaptation layer (AAL) is defined as enhancing the services provided by the ATM layer to support the functions required by the next higher layer. Different AALS support various protocols to suit the different needs of a ran
12、ge of AAL service users. One particular type of AAL service user is the signalling entity wishing to communicate with a peer entity. The signalling AAL (SAAL) comprises AAL functions necessary to support such a signalling entity. The structure of the SAAL is defined in Recommendation 4.2100. The SSC
13、OP has been defined to provide functions required in the SAAL. The SAAL is a combination of two sublayers: a common part and a service specific part. The common part protocol is defined in Recommendation 1.363. The service specific part is also known as the Service Specific Convergence Sublayer (SSC
14、S). In the SAAL, the SSCS itself is functionally divided into the SSCOP and an Service Specific Coordination Function (SSCF) which maps the services provided by the SSCOP to the needs of the user of the SAAL. This structure allows a common connection oriented protocol with error recovery (the SSCOP)
15、 to provide a generic reliable data transfer service for different AAL interfaces defined by the SSCF. Two such SSCFs, one for signalling at the User Network Interface (UNI) and one for signalling at the Network to Network Interface (NNI), have been defined in Recommendations 4.2130 and 4.2140, resp
16、ectively. It is also possible to define additional SSCFs over the common SSCOP to provide different AAL services. The SSCOP is a peer-to-peer protocol which provides the following functions: - - - flowcontrol; - connection control; - - - - - status reporting. transfer of user data with sequence inte
17、grity; error correction by selective retransmission; error reporting to layer management; connection maintenance in the prolonged absence of data transfer; local data retrieval by the user; error detection of protocol control information; and This Recommendation descrbes for SSCOP the necessary elem
18、ents for layer to layer communication, the elements for peer-to-peer communication, a detailed protocol specification, and examples of SSCOP operation. Keywords AAL ATM Adaptation Layer ATM Asynchronous Transfer Mode B-ISDN Broadband Integrated Services Network “-I Network Node Interface SAAL Signal
19、ling AAL SSCF Service Specific Coordination Function SSCOP SSCS Service Specific Convergence Sublayer UNI User to Network Interface Service Specific Connection Oriented Protocol Il Recommendation Q.2110 (07/94) ITU-T RECNN*Q-ZLLO 94 W 4862593 0596114 500 M Recommendation Q.2110 B-ISDN ATM ADAPTATION
20、 LAYER - SERVICE SPECIFIC CONNECTION ORIENTED PROTOCOL (SSCOP) (Geneva, 1994) 1 Scope This Recommendation describes the Service Specific Connection Oriented Protocol (SSCOP). This Recommendation specifies the peer-to-peer protocol for the transfer of information and control between any pair of SSCOP
21、 entities, the interactions between the SSCOP and an SSCF, the interactions between the SSCOP and the AAL Common Part, and the interactions between the SSCOP and the AAL management plane. Recommendation 4.2100 8 describes how this Recommendation is related to the SSCF for signalling at the UNI, Reco
22、mmendation 4.2130 9, and to the SSCF for signalling at the “I, Recommendation 4.2140 lo. 2 Normative 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 e
23、ditions indicated were valid. All Recommendations 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 v
24、alid IT-T Recommendation is published. CCIT Recommendation X.200, Reference model of open systems interconnection for CCITT applications. CCIT Recommendation X.210,OSI layer service conventions. ITU-T Recommendation I. 150, B-ISDN Asynchronous Transfer Mode Functional Characteristics. ITU-T Recommen
25、dation 1.361, B-ISDN ATM Layer Specification. ITU-T Recommendation Q.293 1, B-ISDN access signalling system DSS2 (Digital Subscriber Signalling System No. 2). IT-T Recommendation 4.704, Signalling Network Functions and Messages. ITU-T Recommendation 1.363, B-ISDN ATM Adaptation Layer (AAL) Specijcat
26、ion. ITU-T Recommendation Q.2 100, B-ISDN Signalling ATM Adaptation Layer (SAAL) overview description. ITU-T Recommendation Q.2130, B-ISDN Signalling ATM Adaptation Layer - Service Specific Coordination Function for support of signalling at the user-to-network interface (SSCF at UNI). IT-T Recommend
27、ation 4.2 140, B-ISDN Signalling ATM Adaptation Layer - Service Specific Coordination Function for Signalling at the Network Node Interface (SSCF at “1). 3 Abbreviations AA ATM Adaptation AAL ATM Adaptation Layer ATM Asynchronous Transfer Mode Recommendation Q.2110 (07/94) 1 B-ISDN BGAK BGN BGRET BR
28、 CPCS END ENDAK ER ERAK ID LM MAA MaxCC MaxPD MaxSTAT MD MSB MTP Mu NNI os1 PAD PCI PD PDU PICS PL POLL QOS R RN RS RSAK Rsvd S SAAL SAP SAR SD SDL SDU SN SSCF SSCOP sscs Broadband Integrated Services Digital Network Begin Acknowledge (PDU) Begin (PDU) Begin Reject (PDU) Buffer Release Common Part C
29、onvergence Sublayer End (PDU) End Acknowledge (PDU) Error Recovery (PDU) Error Recovery Acknowledge (PDU) Interface Data Layer Management Management ATM Adaptation Maximum Connection Control (Count) Maximum Poil Data (Count) Maximum STAT (Count) Management Data (PDU) Most Significant Bit Message Tra
30、nsfer Part Message Unit Network Node Interface Open Systems Interconnection Padding Protocol Control Information POLL Data Protocol Data Unit Protocol Implementation Conformance Statement Pad Length Poll (PDU) Quality of Service Reserved (field) Retrieval Number Resynchronization (PDU) Resynchroniza
31、tion Acknowledge (PDU) Reserved (field) Source (field) Signalling ATM Adaptation Layer Service Access Point Segmentation And Reassembly Sequenced Data (PDU) Specification and Description Language Service Data Unit Sequence Number Service Specific Coordination Function Service Specific Connection Ori
32、ented Protocol Service Specific Convergence Sublayer 2 Recommendation Q.2110 (07194) ITU-T RECMN*Q.ZLLO 94 m 4862591 059b11b 383 m Service Specific Coordination Fviction (SSCF) STAT Solicited Status (PDU) UD Unnumbered Data (PDU) UNI User Network Interface -* _-_ Peer-tchPeer PDUs (Note 2) USTAT Uns
33、olicited Status (PDU) uu User-to-User AAL Functions VR Receiver state Variable Peer-to-Peer PDUs Protocol (CP-AAL) VT Transmitter state Variable 4 General The Service Specific Connection Oriented Protocol (SSCOP) resides in the Service Specific Convergence Sublayer (SSCS) of the ATM Adaptation Layer
34、 (AAL). Figure 1 illustrates the structure of the AAL. SSCOP is used to transfer variable length Service Data Units (SDUs) between users of SSCOP. Seruce specific Convergence Sublayer AAL Functions Signals I Service Specific Peer-to-Peer PDUS 1 Connection Orientei NOTES 1 The figure represents the a
35、llocation of functions and is not extended to illustrate sub-layers as defined by OS1 modeling principles. The Common Part AAL jointly consists of the CPCS and SAR protocols. 2 A particular SSCF may include a protocol for the exchange of PDUs. FIGURE UQ.2110 AAL Structure Recommendation Q.2110 (07/9
36、4) 3 - ITU-T RECMN+Q.2110 94 48b2591 059bLL7 2LT SSCOP provides its service to a Service Specific Coordination Function (SSCF). The SSCF maps the service of SSCOP to the needs of the AAL user. The SSCFs are specified in other Recommendations. SSCOP utilizes the service of the CPCS (Common Part Conve
37、rgence Sublayer) and SAR protocols which provide an unassured information transfer and a mechanism for detecting corruption of SSCOP Protocol Data Units (PDUs). The CPCS and SAR protocols are specified in Recommendation 1.363 171. As shown in Figure 1, the AAL is functionally divided into the common
38、 part and the Service Specific Convergence Sublayer (SSCS). The SSCS is specific to the needs of the particular service application and in some cases may be functionally null. The SSCOP can operate over different AAL Common Part Protocols and may be used by different SSCFs; the SSCF is specific to t
39、he needs of the service application. The Common Part protocols are specified in Recommendation 1.363 7. One currently defined use of SSCOP is within the signalling AAL (SAAL). The purpose of the SAAL is to convey information between layer 3 entities across the UNI and “I using Asynchronous Transfer
40、Mode (ATM) virtual channels. Other uses of SSCOP are for further study. The definition of the SAAL takes into consideration the principles and terminology of Recommendations X.200 i and X.210 2 - The reference model and layer service conventions for Open Systems Interconnection (OSI). NOTES 1 The ph
41、ysical layer is currently defined in Recommendations 1.150 3 and 1.361 4. Layer 3 is defined in Recommendations Q.2931 5 for the UNI and Recommendation 4.704 6 for the NNI. References should be made to these Recommendations for the complete definition of the protocols and procedures across the B-ISD
42、N UNI and ”I, respectively. 2 The term “layer 3” is used to indicate the layer above the SAAL, the user of the SAAL services. This Recommendation specifies: a) b) the peer-to-peer protocol for the transfer of information and control between any pair of SSCOP entities: the interactions between the SS
43、COP and an SSCF; c) d) the interactions between the SSCOP and the AAL Common Part; the interactions between the SSCOP and the AAL management plane. 5 Functions of the SSCOP The SSCOP performs the following functions. a) Sequence integrity This function preserves the order of SSCOP SDUs that were sub
44、mitted for transfer by SSCOP. Error Correction by Selective Retransmission Through a sequencing mechanism, the receiving SSCOP entity can detect missing SSCOP SDUs. This function corrects sequence errors through retransmission. b) c) Flow Control This function allows an SSCOP receiver to control the
45、 rate at which the peer SSCOP transmitter entity may send information. Error Reporting to Layer Management This function indicates to layer management errors which have occurred. d) e) Keep Alive This function verifies that the two peer SSCOP entities participating in a connection are remaining in a
46、 link connection established state even in the case of a prolonged absence of data transfer. f) Local Data Retrieval This function allows the local SSCOP user to retrieve in-sequence SDUs which have not yet been released by the SSCOP entity. 4 Recommendation Q.2110 (07/94) Connection Control This fu
47、nction performs the establishment, release, and resynchronization of an SSCOP connection. It also allows the transmission of variable length user-to-user information without a guarantee of delivery. Transfer of User-Data This function is used for the conveyance of user data between users of the SSCO
48、P. SSCOP supports both assured and unassured data transfer. Protocol Error Detection and Recovery This function detects and recovers from errors in the operation of the protocol. Status Reporting This function allows the transmitter and receiver peer entities to exchange status information. Request
49、Indication Response Generic Name 6 Elements for layer to layer communication Confirmation This clause defines the signals and state transition diagram for sequences of signals between SSCOP and the SSCF. The term ?signai? is used instead of ?primitive? in order to reflect the fact that between SSCF and SSCOP there is no service access point defined. AA-RELEASE 6.1 The following repertoire of AA-signals between SSCF and SSCOP, and MAA-signals between the SSCS layer management and SSCOP, is defined (see Table 1): . Signais between SSCOP a
