1、 International Telecommunication Union ITU-T G.998.1TELECOMMUNICATION STANDARDIZATION SECTOR OF ITU (01/2005) SERIES G: TRANSMISSION SYSTEMS AND MEDIA, DIGITAL SYSTEMS AND NETWORKS Digital sections and digital line system Access networks ATM-based multi-pair bonding ITU-T Recommendation G.998.1 ITU-
2、T G-SERIES RECOMMENDATIONS TRANSMISSION SYSTEMS AND MEDIA, DIGITAL SYSTEMS AND NETWORKS INTERNATIONAL TELEPHONE CONNECTIONS AND CIRCUITS G.100G.199 GENERAL CHARACTERISTICS COMMON TO ALL ANALOGUE CARRIER-TRANSMISSION SYSTEMS G.200G.299 INDIVIDUAL CHARACTERISTICS OF INTERNATIONAL CARRIER TELEPHONE SYS
3、TEMS ON METALLIC LINES G.300G.399 GENERAL CHARACTERISTICS OF INTERNATIONAL CARRIER TELEPHONE SYSTEMS ON RADIO-RELAY OR SATELLITE LINKS AND INTERCONNECTION WITH METALLIC LINES G.400G.449 COORDINATION OF RADIOTELEPHONY AND LINE TELEPHONY G.450G.499 TRANSMISSION MEDIA CHARACTERISTICS G.600G.699 DIGITAL
4、 TERMINAL EQUIPMENTS G.700G.799 DIGITAL NETWORKS G.800G.899 DIGITAL SECTIONS AND DIGITAL LINE SYSTEM G.900G.999 General G.900G.909 Parameters for optical fibre cable systems G.910G.919 Digital sections at hierarchical bit rates based on a bit rate of 2048 kbit/s G.920G.929 Digital line transmission
5、systems on cable at non-hierarchical bit rates G.930G.939 Digital line systems provided by FDM transmission bearers G.940G.949 Digital line systems G.950G.959 Digital section and digital transmission systems for customer access to ISDN G.960G.969 Optical fibre submarine cable systems G.970G.979 Opti
6、cal line systems for local and access networks G.980G.989 Acess networks G.990G.999 QUALITY OF SERVICE AND PERFORMANCE GENERIC AND USER-RELATED ASPECTS G.1000G.1999 TRANSMISSION MEDIA CHARACTERISTICS G.6000G.6999 DIGITAL TERMINAL EQUIPMENTS G.7000G.7999 DIGITAL NETWORKS G.8000G.8999 For further deta
7、ils, please refer to the list of ITU-T Recommendations. ITU-T Rec. G.998.1 (01/2005) i ITU-T Recommendation G.998.1 ATM-based multi-pair bonding Summary This Recommendation describes a method for bonding of multiple digital subscriber lines (DSL) to transport ATM streams. The specifications of this
8、Recommendation provide a complete description of startup, operational, and contingency modes of operation which allows for interoperability between vendors. This Recommendation includes the following types of requirements, recommendations, and information for defined DSL systems, including: higher-l
9、ayer transport-independent requirements; higher-layer transport-dependent, e.g., ATM, requirements. Source ITU-T Recommendation G.998.1 was approved on 13 January 2005 by ITU-T Study Group 15 (2005-2008) under the ITU-T Recommendation A.8 procedure. ii ITU-T Rec. G.998.1 (01/2005) FOREWORD The Inter
10、national Telecommunication Union (ITU) is the United Nations specialized agency in the field of telecommunications. The ITU Telecommunication Standardization Sector (ITU-T) is a permanent organ of ITU. ITU-T is responsible for studying technical, operating and tariff questions and issuing Recommenda
11、tions on them with a view to standardizing telecommunications on a worldwide basis. The World Telecommunication Standardization Assembly (WTSA), which meets every four years, establishes the topics for study by the ITU-T study groups which, in turn, produce Recommendations on these topics. The appro
12、val of ITU-T Recommendations is covered by the procedure laid down in WTSA Resolution 1. In some areas of information technology which fall within ITU-Ts purview, the necessary standards are prepared on a collaborative basis with ISO and IEC. NOTE In this Recommendation, the expression “Administrati
13、on“ is used for conciseness to indicate both a telecommunication administration and a recognized operating agency. Compliance with this Recommendation is voluntary. However, the Recommendation may contain certain mandatory provisions (to ensure e.g. interoperability or applicability) and compliance
14、with the Recommendation is achieved when all of these mandatory provisions are met. The words “shall“ or some other obligatory language such as “must“ and the negative equivalents are used to express requirements. The use of such words does not suggest that compliance with the Recommendation is requ
15、ired of any party. INTELLECTUAL PROPERTY RIGHTS ITU draws attention to the possibility that the practice or implementation of this Recommendation may involve the use of a claimed Intellectual Property Right. ITU takes no position concerning the evidence, validity or applicability of claimed Intellec
16、tual Property Rights, whether asserted by ITU members or others outside of the Recommendation development process. As of the date of approval of this Recommendation, ITU had received notice of intellectual property, protected by patents, which may be required to implement this Recommendation. Howeve
17、r, implementors are cautioned that this may not represent the latest information and are therefore strongly urged to consult the TSB patent database. ITU 2005 All rights reserved. No part of this publication may be reproduced, by any means whatsoever, without the prior written permission of ITU. ITU
18、-T Rec. G.998.1 (01/2005) iii CONTENTS Page 1 Scope 1 2 References. 1 3 Definitions 2 4 Abbreviations and acronyms 2 5 Overview 4 6 Mode of operation. 5 6.1 Sequencing payload traffic. 5 6.2 Bonding Group ID (GID) and Management Entity (ME) 5 6.3 Autonomous Status Messages (ASMs) 6 6.4 Link eligibil
19、ity and link activation . 6 6.5 Measurement of bonding group differential delay . 8 6.6 Compensation of differential delay by the CPE transmitting entity. 8 7 Reference models 9 7.1 User plane protocol reference model 9 7.2 Bonding sublayer in layer reference model 10 7.3 Functional reference model
20、10 8 Cell header formats. 11 8.1 Autonomous Status Messages (ASM) 11 8.2 Idle and unassigned cells 11 8.3 OAM and ATM payload cells 11 8.4 HEC errors 11 9 Bonding group internal control protocol 11 9.1 Types of control message . 11 10 Initialization 18 11 External management . 20 11.1 OAM interface
21、primitives. 20 11.2 OAM channel between NMS and bonding entity 21 11.3 Cell rate adjustment 21 11.4 MIB elements . 22 Appendix I Optional initialization procedure facilitating spectral optimization 23 Appendix II Sample initialization for the ATM bonding protocol . 24 Appendix III Link status state
22、machine 26 Appendix IV Example of algorithm to derive the end-to-end delay. 27 BIBLIOGRAPHY 28 ITU-T Rec. G.998.1 (01/2005) 1 ITU-T Recommendation G.998.1 ATM-based multi-pair bonding 1 Scope The purpose of this Recommendation is to assist manufacturers, providers, and users of products on how to us
23、e multiple DSL lines to carry a single ATM payload stream. In order to satisfy this purpose, requirements and guidelines are provided. This Recommendation is written to satisfy the following bonding objectives: 1) bonding shall support dynamic removal and restoration of pairs without human intervent
24、ion; 2) bonding shall support disparate data rates, up to a ratio of 4-to-1 (fastest to slowest), amongst its pairs; 3) the protocol shall allow bonding of 2-32 pairs; 4) the protocol shall permit bonding of randomly assigned ports on an access node; 5) the protocol shall be PHY independent; 6) the
25、protocol shall incur a maximum overall one-way bonding delay of 2 ms. In order for implementations compliant to this Recommendation to be interoperable between vendors, an initialization procedure, a payload tagging method, and OAM capability are provided. The applications supported within this Reco
26、mmendation relate to bonding of multiple DSL loops to deliver ATM payload beyond the rate/reach capability of a single DSL loop. Each ATM TPS-TC (assuming multiple bearer channels) shall operate in an independent bonded group. As described within this Recommendation, the customer premises equipment
27、(CPE) represents the User-Network Interface (UNI) to the ATM network. 2 References The following ITU-T 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 were
28、valid. All Recommendations and other references are subject to revision; 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 the currently valid ITU-T Recommendati
29、ons is regularly published. The reference to a document within this Recommendation does not give it, as a stand-alone document, the status of a Recommendation 1 ITU-T Recommendation G.992.3 (2005), Asymmetric digital subscriber line transceivers2 (ADSL2). 2 ITU-T Recommendation G.994.1 (2003), Hands
30、hake procedures for digital subscriber line (DSL) transceivers. 3 ITU-T Recommendation G.997.1 (2003), Physical layer management for digital subscriber line (DSL) transceivers. 4 ITU-T Recommendation I.363.5 (1996), B-ISDN ATM Adaptation Layer specification: Type 5 AAL. 2 ITU-T Rec. G.998.1 (01/2005
31、) 3 Definitions This Recommendation defines the following terms: 3.1 carrier: An organization that provides telecommunications services to customer installations. 3.2 central office: In this Recommendation, the telephone building that is the origin of the outside loop plant. 3.3 customer installatio
32、n: All cabling and equipment on the customer side of the network interface. 3.4 customer premises equipment: Telecommunications equipment located at the customer installation on the customer side of the network interface. For the purposes of this Recommendation, it is defined as multiple receivers t
33、hat aggregate traffic from multiple lines into one ATM stream. 3.5 downstream: The direction of transmission from the carrier central office to the customer installation. 3.6 Inverse Multiplexing over ATM (IMA): IMA is used in this Recommendation to refer to ATM Forum specifications, not the bonding
34、 method of this Recommendation. 3.7 loop: A communication path between the distributing frame in a carrier central office and the network interface at a customer location. 3.8 network: All equipment and facilities, including loop plant, located on the carrier side of the network interface. 3.9 netwo
35、rk interface: The physical demarcation point between carrier network loop facilities and the CI. 3.10 pair: Two insulated conductors. 3.11 showtime: A mode of operation of DSL modems that corresponds to transmission of live user data. It follows as a last step after all initialization and retraining
36、 procedures. 3.12 upstream: The direction of transmission from the customer installation to the carrier Central Office. 4 Abbreviations and acronyms This Recommendation uses the following abbreviations: AAL 5 ATM Adaptation Layer 5 ADSL Asymmetric Digital Subscriber Line ANSI American National Stand
37、ards Institute ASM Autonomous Status Message ATM Asynchronous Transfer Mode ATM-TC ATM Transmission Convergence (sublayer) CAC Connection Admission Control CI Customer Installation (see definition) CLP Cell Loss Priority CO Central Office (see definition) CPE Customer Premises Equipment (see definit
38、ion) ITU-T Rec. G.998.1 (01/2005) 3 CRC Cyclic Redundancy Check DS Downstream DSL Digital Subscriber Line FE Far End GID Group Identifier GFC Generic Flow Control HEC Header Error Control ICP IMA Control Protocol (cell) IMA Inverse Multiplexing over ATM (see definition) ITU-T International Telecommu
39、nication Union Telecommunication Standardization Sector ME Management Entity MIB Management Information Base ms Millisecond NE Near End NI Network Interface (see definition) NMS Network Management System OAM Operations, Administration and Maintenance PHY Physical layer PMD Physical Media Dependent (
40、sublayer) PMS-TC Physical Media-Specific Transmission Convergence (sublayer) PTI Payload Type Identifier Rx Receive SAR Segmentation And Reassembly SID Sequence Index SNMP Simple Network Management Protocol TPS-TC Transport Protocol Specific Transmission Convergence (sublayer) TU-C Transceiver Unit
41、Central office end. Sometimes combined with another letter; e.g., ATU-C for a central office ADSL transceiver TU-R Transceiver Unit Remote terminal end. Sometimes combined with another letter; e.g., ATU-R for a remote ADSL transceiver Tx Transmit UNI User-Network Interface US Upstream UTOPIA Univers
42、al Test and Operations PHY Interface for ATM VC Virtual Channel VCI VC Identifier VP Virtual Path 4 ITU-T Rec. G.998.1 (01/2005) VPI VP Identifier 5 Overview An illustration of the bonding system for transport of an ATM payload across several DSL lines with disparate data rates is provided in Figure
43、 1 below. In traditional inverse multiplexing over ATM (IMA) as specified in the ATM Forum document, Inverse Multiplexing for ATM (IMA) Specification, Version 1.1 B1, it is assumed that all bonded links operate at the same nominal rate. The original cells are not modified, and control (ICP) cells ar
44、e inserted for OAM communication between the two ends. In this Recommendation, each cell is tagged with a Sequence ID (SID). The transmitter may place any cell on any link, and the receiver can reassemble the original sequence. Figure 1/G.998.1 Status message flow. Each transmission direction is tre
45、ated independently A bonding group is defined as a bidirectional ATM stream transported by multiple bidirectional bearers across multiple physical media in both upstream and downstream directions.1A single bonding group cannot span multiple CPE entities or CO-side access nodes. As a consequence, the
46、 control channel is also a bidirectional ATM stream, consisting of ATM messages called Autonomous Status Messages (ASMs). The content and sequence of these messages defines a control protocol between the two bonding entities in both directions. Some implementations may support multiple bearers on ea
47、ch physical link. Different bearers on the same line shall never be bonded together into the same group. The control protocol communicates the status of each link in the bonding group. The way a bonding group is defined at startup, maintained during operation, and put out of service is discussed bel
48、ow. The underlying bit rate of the individual links within a bonded group may be freely and independently changed by their respective PHY layers.2It is the responsibility of the transmitter not to overrun PHY transmit buffers, nor add delay created by excess buffering (by either carefully controllin
49、g the PHY bit rate itself, by allowing the PHY bit rate to “float“ and then honoring back pressure, or by monitoring instantaneous bit rate and rate shaping its transmissions, matching multiplex ordering to rates, etc.). _ 1It should be noted that the upstream and downstream rates may be different. 2Resultant changes in bit rate are subject to constraints of buffer size, number of lines, and differential delay. The 4-to-1 ratio is not a hard limit, and may be violated provided these other constraints are satisfied
