1、 International Telecommunication Union ITU-T J.212TELECOMMUNICATION STANDARDIZATION SECTOR OF ITU (11/2006) SERIES J: CABLE NETWORKS AND TRANSMISSION OF TELEVISION, SOUND PROGRAMME AND OTHER MULTIMEDIA SIGNALS Interactive systems for digital television distribution Downstream external Physical layer
2、 interface for modular cable modem termination systems ITU-T Recommendation J.212 ITU-T Rec. J.212 (11/2006) i ITU-T Recommendation J.212 Downstream external Physical layer interface for modular cable modem termination systems Summary This Recommendation defines an interface known as the Downstream
3、External PHY Interface (DEPI) and associated protocol requirements for the transport of downstream user data between the “M-CMTS Core“ and the EQAM. It describes the characteristics of the DEPI interface, provides requirements that must be met by the M-CMTS Core and the EQAM, and also describes vari
4、ous aspects of technical issues that are involved in the implementation and deployment of a DOCSIS system using the M-CMTS architecture. Source ITU-T Recommendation J.212 was approved on 29 November 2006 by ITU-T Study Group 9 (2005-2008) under the ITU-T Recommendation A.8 procedure. ii ITU-T Rec. J
5、.212 (11/2006) FOREWORD The International 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
6、 questions and issuing Recommendations 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 Recommend
7、ations on these topics. The approval 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 Recommendat
8、ion, the expression “Administration“ 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
9、or applicability) and compliance 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 complianc
10、e with the Recommendation is required 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
11、applicability of claimed Intellectual 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 not received notice of intellectual property, protected by patents, which may be required to
12、implement this Recommendation. However, implementers are cautioned that this may not represent the latest information and are therefore strongly urged to consult the TSB patent database at http:/www.itu.int/ITU-T/ipr/. ITU 2007 All rights reserved. No part of this publication may be reproduced, by a
13、ny means whatsoever, without the prior written permission of ITU. ITU-T Rec. J.212 (11/2006) iii CONTENTS Page 1 Scope 1 2 References. 2 2.1 Normative references 2 2.2 Informative references 2 2.3 Reference acquisition . 3 3 Terms and definitions . 3 4 Abbreviations, acronyms and conventions. 6 4.1
14、Abbreviations and acronyms 6 4.2 Conventions 8 5 Technical overview. 9 5.1 System architecture 9 5.2 Bonding services model . 13 5.3 Multiple services model . 13 6 DEPI architecture 14 6.1 DEPI Data Path. 14 6.2 Networking considerations. 18 6.3 System timing considerations. 20 7 DEPI control plane
15、. 20 7.1 Topology. 21 7.2 Addressing 21 7.3 Control message format 23 7.4 Signalling 27 7.5 AVP definitions 33 8 DEPI forwarding plane. 47 8.1 L2TPv3 transport packet format. 47 8.2 DOCSIS MPT mode. 50 8.3 PSP mode 51 8.4 DEPI latency measurement (DLM) sublayer header 52 8.5 M-CMTS core output rate
16、53 Annex A DEPI MTU 54 A.1 L2TPv3 lower layer payload size. 54 A.2 Maximum frame size for DEPI 54 A.3 Path MTU discovery. 55 Annex B Parameters and constants. 55 Appendix I DEPI and DOCSIS system performance . 56 I.1 Introduction 56 I.2 Round-trip time and performance 56 iv ITU-T Rec. J.212 (11/2006
17、) Page I.3 Elements of round-trip time 56 I.4 CIN characteristics . 58 I.5 Queueing delays in network elements 59 I.6 Traffic prioritization and network delays. 60 I.7 Queue persistence in a DEPI flow 60 I.8 PSP mode 62 Appendix II Early adoption and evolving use of EQAM devices 63 II.1 EQAM develop
18、ment: Category A (no DTI). 63 II.2 EQAM development: Category B (with DTI) 64 II.3 Possible M-CMTS feature phasing 64 II.4 Optional UDP layer 65 ITU-T Rec. J.212 (11/2006) 1 ITU-T Recommendation J.212 Downstream external Physical layer interface for modular cable modem termination systems 1 Scope Th
19、is Recommendation is part of the DOCSISfamily of Recommendations that define a Modular Cable Modem Termination System (M-CMTS) architecture for head-end components that comply with DOCSIS. The DOCSIS Recommendations J.122 define the requirements for the two fundamental components that comprise a hig
20、h-speed data-over-cable system: the cable modem (CM) and the cable modem termination system (CMTS). The M-CMTS architecture was designed as an extension to the DOCSIS Recommendations to allow for flexibility and independent scaling of certain CMTS functions, and to allow operators to more efficientl
21、y use available network resources. One of the key elements of the M-CMTS architecture is the separation of the downstream physical layer QAM modulation and up-conversion functions from the CMTS, and the placement of that functionality into an “Edge-QAM“ (EQAM) device. This separation allows for the
22、development of EQAM products that support both video and DOCSIS, which in turn allows operators to use the same network resources to support multiple types of services such as data, voice and video. This Recommendation defines an interface known as the Downstream External PHY Interface (DEPI) and as
23、sociated protocol requirements for the transport of downstream user data between the “M-CMTS Core“ and the EQAM. It describes the characteristics of the DEPI interface, provides requirements that must be met by the M-CMTS Core and the EQAM, and also describes various aspects of technical issues that
24、 are involved in the implementation and deployment of a DOCSIS system using the M-CMTS architecture. Two different master clock frequency options are available within the M-CMTS architecture. The first option, a 10.24 MHz master clock is used in the Americas, Europe and other regions. The second opt
25、ion, a 9.216 MHz master clock is used in Japan. Compliance with this Recommendation requires compliance with the one or the other of these implementations, not with both. It is not required that equipment built to one option shall interoperate with equipment built to the other. A list of the documen
26、ts in the Modular CMTS Interface Recommendations family is provided below. Designation Title J.212 Downstream External PHY Interface J.211 DOCSIS Timing Interface CM-SP-ERMI Edge Resource Manager Interface, CM-SP-ERMI-I02-051209, 9 December 2005, Cable Television Laboratories, Inc. CM-SP-M-OSSI M-CM
27、TS Operations Support System Interface, CM-SP-M-OSSI-I02-051209, 9 December 2005, Cable Television Laboratories, Inc. 2 ITU-T Rec. J.212 (11/2006) 2 References 2.1 Normative references The following ITU-T Recommendations and other references contain provisions which, through reference in this text,
28、constitute provisions of this Recommendation. At the time of publication, the editions indicated were 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 t
29、he Recommendations and other references listed below. A list of the currently valid ITU-T Recommendations 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. H.222.0 ITU-T Recommendation H.222.0 (
30、2006) | ISO/IEC 13818-1:2007, Information technology Generic coding of moving pictures and associated audio information: Systems. J.83 ITU-T Recommendation J.83 (1997), Digital multi-programme systems for television, sound and data services for cable distribution. J.122 ITU-T Recommendation J.122 (2
31、002), Second-generation transmission systems for interactive cable television services IP cable modems. J.210 ITU-T Recommendation J.210 (2006), Downstream RF interface for Cable Modem Termination Systems. J.211 ITU-T Recommendation J.211 (2006), Timing interface for Cable Modem Termination Systems.
32、 IANA-PORTS IANA (2004), Port Numbers. IEEE-802.1Q IEEE Std 802.1Q-2005, IEEE Standard for Local and Metropolitan Area Networks Virtual Bridged Local Area Networks. IEEE-802.3 IEEE Std 802.3-2005, IEEE Standard for information technology Telecommunications and information exchange between systems Lo
33、cal and metropolitan area networks Specific requirements Part 3: Carrier Sense Multiple Access With Collision Detection (CSMA/CD) Access Method And Physical Layer Specification. RFC-IP IETF RFC 791 (1981), Internet Protocol DARPA Internet Program Protocol specification. RFC-L2TP-DSCP IETF RFC 3308 (
34、2002), Layer Two Tunnelling Protocol (L2TP) Differentiated Services Extension. RFC-L2TPv3 IETF RFC 3931 (2005), Layer Two Tunnelling Protocol Version 3 (L2TPv3). RFC-MTU IETF RFC 1191 (1990), Path MTU Discovery. RFC-PHBID-AF IETF RFC 2597 (1999), Assured Forwarding PHB Group. RFC-PHBID-EF IETF RFC 3
35、246 (2002), An Expedited Forwarding PHB (Per-Hop Behaviour). RFC-UDP IETF RFC 768 (1980), User Datagram Protocol. 2.2 Informative references DVB-RF ETSI EN 300 429 V1.2.1 (1998), Digital Video Broadcasting (DVB); Framing structure, channel coding and modulation for cable systems. ITU-T Rec. J.212 (1
36、1/2006) 3 ERMI Edge Resource Manager Interface, CM-SP-ERMI-I02-051209, 9 December 2005, Cable Television Laboratories, Inc. ISO 8802-2 ISO/IEC 8802-2:1998 (IEEE Std 802.2:1994) Information technology Telecommunications and information exchange between systems Local and metropolitan area networks Spe
37、cific requirements Part 2: Logical link control. MOSSI DOCSIS M-CMTS Operations Support Interface, CM-SP-M-OSSI-I02-051209, 9 December 2005, Cable Television Laboratories, Inc. RFC-DSCP-1 IETF RFC 2983 (2000), Differentiated Services and Tunnels. RFC-DSCP-2 IETF RFC 3260 (2002), New Terminology and
38、Clarifications for Diffserv. VCCV IETF draft-ietf-pwe3-vccv-12.txt, Pseudo Wire Virtual Circuit Connectivity Verification (VCCV), January 2007. 2.3 Reference acquisition Cable Television Laboratories, Inc., Internet: http:/ http:/ The Institute of Electrical and Electronics Engineers, Inc, Internet:
39、 http:/standards.ieee.org Internet Engineering Task Force (IETF), Internet: http:/www.ietf.org Internet Assigned Numbers Authority, IANA, Internet: http:/www.iana.org European Telecommunications Standards Institute, ETSI, http:/www.etsi.org 3 Terms and definitions This Recommendation defines the fol
40、lowing terms: 3.1 bonded channels: A logical channel comprising multiple individual channels. 3.2 cable modem (CM): A modulator-demodulator at subscriber locations intended for use in conveying data communications on a cable television system. 3.3 converged interconnect network: The network (general
41、ly gigabit Ethernet) that connects an M-CMTS Core to an EQAM. 3.4 customer premises equipment (CPE): Equipment at the end users premises; may be provided by the service provider. 3.5 data rate: Throughput, data transmitted in units of time usually in bits per second (bit/s). 3.6 decibels (dB): Ratio
42、 of two power levels expressed mathematically as dB = 10log10(POUT/PIN). 3.7 decibel-millivolt (dBmV): Unit of RF power expressed in decibels relative to 1 millivolt, where dBmV = 20log10(value in mV/1 mV). 3.8 downstream (DS): 1) Transmissions from CMTS to CM. This includes transmission from the M-
43、CMTS Core to the EQAM as well as the RF transmissions from the EQAM to the CM. 2) RF spectrum used to transmit signals from a cable operators headend or hub site to subscriber locations. 3.9 edge QAM modulator (EQAM): A headend or hub device that receives packets of digital video or data. It re-pack
44、etizes the video or data into an MPEG transport stream and digitally modulates the digital transport stream onto a downstream RF carrier using quadrature amplitude modulation (QAM). 4 ITU-T Rec. J.212 (11/2006) 3.10 flow: A stream of packets in DEPI used to transport data of a certain priority from
45、the M-CMTS Core to a particular QAM channel of the EQAM. In PSP operation, there can exist several flows per QAM channel. 3.11 GigE (GE): Gigabit Ethernet (1 Gbit/s). 3.12 hybrid fibre/coax (HFC) system: A broadband bidirectional shared-media transmission system using optical fibre trunks between th
46、e headend and the fibre nodes, and coaxial cable distribution from the fibre nodes to the customer locations. 3.13 Institute of Electrical and Electronics Engineers (IEEE): A voluntary organization which, among other things, sponsors standards committees and is accredited by the American National St
47、andards Institute (ANSI). 3.14 Internet Engineering Task Force (IETF): A body responsible for, among other things, developing standards used in the Internet. 3.15 Internet Protocol (IP): An Internet network-layer protocol. 3.16 L2TP access concentrator (LAC): If an L2TP Control Connection Endpoint (
48、LCCE) is being used to cross-connect an L2TP session directly to a data link, we refer to it as an L2TP Access Concentrator (LAC). An LCCE may act as both an L2TP Network Server (LNS) for some sessions and LAC for others, so these terms must only be used within the context of a given set of sessions
49、 unless the LCCE is in fact single purpose for a given topology. 3.17 L2TP attribute value pair (AVP): The L2TP variable-length concatenation of a unique Attribute (represented by an integer), a length field, and a Value containing the actual value identified by the attribute. 3.18 L2TP control connection: An L2TP control connection is a reliable control channel that is used to establish, maintain, and release individual L2TP sessions
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