1、 International Telecommunication Union ITU-T Y.1418TELECOMMUNICATION STANDARDIZATION SECTOR OF ITU (02/2008) SERIES Y: GLOBAL INFORMATION INFRASTRUCTURE, INTERNET PROTOCOL ASPECTS AND NEXT-GENERATION NETWORKS Internet protocol aspects Interworking Pseudowire layer network Recommendation ITU-T Y.1418
2、 ITU-T Y-SERIES RECOMMENDATIONS GLOBAL INFORMATION INFRASTRUCTURE, INTERNET PROTOCOL ASPECTS AND NEXT-GENERATION NETWORKS GLOBAL INFORMATION INFRASTRUCTURE General Y.100Y.199 Services, applications and middleware Y.200Y.299 Network aspects Y.300Y.399 Interfaces and protocols Y.400Y.499 Numbering, ad
3、dressing and naming Y.500Y.599 Operation, administration and maintenance Y.600Y.699 Security Y.700Y.799 Performances Y.800Y.899 INTERNET PROTOCOL ASPECTS General Y.1000Y.1099 Services and applications Y.1100Y.1199 Architecture, access, network capabilities and resource management Y.1200Y.1299 Transp
4、ort Y.1300Y.1399 Interworking Y.1400Y.1499 Quality of service and network performance Y.1500Y.1599 Signalling Y.1600Y.1699 Operation, administration and maintenance Y.1700Y.1799 Charging Y.1800Y.1899 NEXT GENERATION NETWORKS Frameworks and functional architecture models Y.2000Y.2099 Quality of Servi
5、ce and performance Y.2100Y.2199 Service aspects: Service capabilities and service architecture Y.2200Y.2249 Service aspects: Interoperability of services and networks in NGN Y.2250Y.2299 Numbering, naming and addressing Y.2300Y.2399 Network management Y.2400Y.2499 Network control architectures and p
6、rotocols Y.2500Y.2599 Security Y.2700Y.2799 Generalized mobility Y.2800Y.2899 For further details, please refer to the list of ITU-T Recommendations. Rec. ITU-T Y.1418 (02/2008) i Recommendation ITU-T Y.1418 Pseudowire layer network Summary Recommendation ITU-T Y.1418 defines a layer network that fa
7、cilitates the transport of arbitrary client services over arbitrary server networks, including concatenations of several server networks of different technologies. It describes the encapsulation format. Source Recommendation ITU-T Y.1418 was approved on 29 February 2008 by ITU-T Study Group 13 (2005
8、-2008) under Recommendation ITU-T A.8 procedure. Keywords Client/server, interworking, multi-segment pseudowire, network interworking, pseudowire, user plane. ii Rec. ITU-T Y.1418 (02/2008) FOREWORD The International Telecommunication Union (ITU) is the United Nations specialized agency in the field
9、 of telecommunications, information and communication technologies (ICTs). 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 Recommendations on them with a view to standardizin
10、g 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 approval of ITU-T Recommendations is covered b
11、y 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 “Administration“ is used for conciseness to indicate b
12、oth 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 with the Recommendation is achieved when
13、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 required of any party. INTELLECTUAL PROPERTY
14、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 Intellectual Property Rights, whether asserted by
15、 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 implement this Recommendation. However, implementers are cautioned that th
16、is 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 2009 All rights reserved. No part of this publication may be reproduced, by any means whatsoever, without the prior written permission of ITU. Rec. ITU
17、-T Y.1418 (02/2008) iii CONTENTS Page 1 Scope 1 2 References. 1 3 Definitions 2 3.1 Terms defined elsewhere 2 3.2 Terms defined in this Recommendation. 2 4 Abbreviations and acronyms 2 5 Conventions 3 6 Multi-segment pseudowires 3 6.1 Reference architecture for multi-segment transport using pseudowi
18、res 3 6.2 Advantages of the PW layer. 5 6.3 Terminating and stitching IWFs. 5 6.4 PW encapsulation format . 5 7 General capabilities 6 7.1 User plane capabilities 6 7.2 Control and management plane capabilities. 6 8 The PW encapsulation format 7 8.1 Usage and compatibility. 7 8.2 Server layer packet
19、 . 8 9 Security considerations. 8 Appendix I Compatibility with existing encapsulations. 9 I.1 Encapsulations compatible with this Recommendation. 9 I.2 Encapsulations not compatible with this Recommendation. 9 Appendix II Guidance for use of PWs with specific server networks 10 II.1 MPLS 10 II.2 Et
20、hernet. 10 II.3 IP. 11 II.4 PDH/SDH/OTN using GFP 11 Bibliography. 12 Rec. ITU-T Y.1418 (02/2008) 1 Recommendation ITU-T Y.1418 Pseudowire layer network 1 Scope This Recommendation describes a layer network that facilitates the transport of arbitrary client services over arbitrary server networks. A
21、n example of client services include ATM, frame relay, low-rate TDM, and Ethernet. An example of server layers include MPLS, Ethernet, IP, and PDH/SDH/OTN using the generic framing procedure (GFP). The layer network is called the pseudowire (PW) layer and is suitable for both single and multi-segmen
22、t transport. This Recommendation does not preclude the use of other adaptations, and in many cases alternative mechanisms are preferable. This Recommendation is not intended to redefine the behaviour of the protocols specified in the normatively referenced IETF RFCs. In the event of discrepancies be
23、tween protocols in this Recommendation and the normative RFCs, the IETF RFC is the authoritative source. 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 public
24、ation, 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 the Recommendations and other references listed below. A list of the
25、 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. ITU-T G.805 Recommendation ITU-T G.805 (2000), Generic functional architecture of transport networks. ITU
26、-T X.84 Recommendation ITU-T X.84 (2004), Support of frame relay services over MPLS core networks. ITU-T Y.1401 Recommendation ITU-T Y.1401 (2008), Principles of interworking. ITU-T Y.1411 Recommendation ITU-T Y.1411 (2003), ATM-MPLS network interworking Cell mode user plane interworking. ITU-T Y.14
27、12 Recommendation ITU-T Y.1412 (2003), ATM-MPLS network interworking Frame mode user plane interworking. ITU-T Y.1413 Recommendation ITU-T Y.1413 (2004), TDM-MPLS network interworking User plane interworking. ITU-T Y.1414 Recommendation ITU-T Y.1414 (2004), Voice services MPLS network interworking.
28、ITU-T Y.1415 Recommendation ITU-T Y.1415 (2005), Ethernet-MPLS network interworking User plane interworking. ITU-T Y.1452 Recommendation ITU-T Y.1452 (2006), Voice trunking over IP networks. ITU-T Y.1453 Recommendation ITU-T Y.1453 (2006), TDM-IP Interworking User plane interworking. 2 Rec. ITU-T Y.
29、1418 (02/2008) IETF RFC 3550 IETF RFC 3550 (2003), RTP: A Transport Protocol for Real-Time Applications . IETF RFC 4385 IETF RFC 4385 (2006), Pseudowire Emulation Edge-to-Edge (PWE3) Control Word for Use over an MPLS PSN . 3 Definitions 3.1 Terms defined elsewhere This Recommendation uses the follow
30、ing terms defined elsewhere: 3.1.1 interworking: See ITU-T Y.1411. 3.1.2 characteristic information (CI): See ITU-T G.805. 3.2 Terms defined in this Recommendation This Recommendation defines the following terms: 3.2.1 multi-segment transport: Transport of a client service over more than one server
31、network trail. 3.2.2 pseudowire: A layer network used to emulate the behaviour of another layer network. 3.2.3 stitching IWF: The stitching IWF is a composite transport processing function that recovers the pseudowire characteristic information (PW CI) from a first server layer network, updates the
32、PW label and re-encapsulates the PW CI into characteristic information (CI) of a second server layer network. Note that the client of the PW is not recovered. 3.2.4 terminating IWF: The terminating IWF is a composite transport processing function that encapsulates/decapsulates the client service cha
33、racteristic information (CI) ITU-T G.805 to/from the server layer CI. 4 Abbreviations and acronyms This Recommendation uses the following abbreviations and acronyms: CAL Common Adaptation Layer CI Characteristic Information CW Control Word DA Destination Address FCS Frame Check Sequence GFP Generic
34、Framing Procedure IP Internet Protocol IWF Interworking Function LAN Local Area Network LSP Label Switched Path MPLS Multiprotocol Label Switching MTU Maximum Transport Unit OAM Operations, Administration and Maintenance OTN Optical Transport Network Rec. ITU-T Y.1418 (02/2008) 3 PDU Protocol Data U
35、nit PW Pseudowire QoS Quality of Service RTP Real Time Protocol TDM Time Division Multiplexing VLAN Virtual LAN 5 Conventions For brevity, all functional diagrams in this Recommendation assume connection-oriented networks, and thus follow the diagrammatic conventions of ITU-T G.805. When either the
36、client network, or server network, or both, are connectionless networks, similar diagrams with the necessary changes apply. In addition, when discussing the encapsulation of a client protocol data unit (PDU) into a server packet in this Recommendation, the pre-pending of server-layer headers will be
37、 consistently mentioned. It is recognized that certain server layer encapsulations additionally involve appending of trailers. 6 Multi-segment pseudowires 6.1 Reference architecture for multi-segment transport using pseudowires Initial work on client-server interworking focused on client information
38、 being carried over a single-server network. However, there are many scenarios where it is desirable to traverse multiple concatenated server networks, and in order to facilitate this interworking, the pseudowire (PW) layer network is introduced. Figure 6-1 depicts the general topology for multi-seg
39、ment pseudowires, depicting the native service, transport segments, the multi-segment path, the terminating and stitching IWFs. The native service is the client of the PW layer network. Note that pseudowire is an implementation of common adaptation layer (CAL) as described in ITU-T Y.1401. Figure 6-
40、1 Multi-segment interworking topology In this Recommendation, for the multi-segment case, the PW label may be modified by the interworking function. This is in contrast to the single segment cases. The generic adaptation specified by the PW layer network is used for transport over a single transport
41、 segment when there is no well-established adaptation, and whenever multi-segment transport is required. Use of the PW layer is not universally recommended, as many client and server networks have well-established efficient adaptations. 4 Rec. ITU-T Y.1418 (02/2008) Multi-segment transport is the tr
42、ansport of a native service over the concatenation of multiple server networks. One case where multi-segment transport must be employed involves native service end-points connected to server networks based on differing technologies. Present interworking Recommendations are specific to the server net
43、work technology, and thus the client information can not be carried across such concatenated server networks without client-specific processing between each pair of server networks. Figure 6-2 is a functional diagram, following the diagrammatic conventions of ITU-T G.805, for a case where it is requ
44、ired to traverse three server networks of different technologies. nativePW / clientPW_TTserver1 / PWserver1_TTserver1T-IWFS-IWFnativeS-IWFPW / clientserver3 / PWserver3server3_TTPW_TTT-IWFserver2PW trailFigure 6-2 Functional diagram for multi-segment interworking for the multi-technology case A seco
45、nd case where multi-segment transport is employed is when native service end-points connect to server networks in different administrative domains. In this case, the terminating IWFs will in general not have mutual visibility as internal topologies may not be advertised outside their respective admi
46、nistrative domains. Figure 6-3 is a functional diagram showing the traversal of two server networks belonging to different administrative domains. nativePW / clientPW_TTserver / PWserver_TTT-IWFS-IWFnativeS-IWFPW / clientserver / PWserver_TTPW_TTT-IWFadministrative domain boundaryFigure 6-3 Function
47、al diagram for multi-segment interworking for the multi-domain case Rec. ITU-T Y.1418 (02/2008) 5 Multi-segment transport may also be used even when there is single-technology reachability and both terminal IWFs are in a single administrative domain. For example, in Appendix I of ITU-T Y.1415 a full
48、 mesh of interworking LSPs is required to provide a multipoint Ethernet service. If the full mesh is prohibitive from a resource point of view, then a partial mesh may be used if multi-segment transport is supported. 6.2 Advantages of the PW layer The introduction of an intermediate layer network en
49、ables the use of stitching IWFs that operate without knowledge of the native service type, and do not need specific processing functionality to handle different types. For real-time native services, such as TDM, use of the intermediate layer avoids exposure of the native service between server networks, which would introduce additional packetization delay and clock degradation. Introduction of an intermediate layer enables use of PW layer OAM. The PW encapsulation described below features an associated c
