1、 International Telecommunication Union ITU-T Y.1415TELECOMMUNICATION STANDARDIZATION SECTOR OF ITU (02/2005) SERIES Y: GLOBAL INFORMATION INFRASTRUCTURE, INTERNET PROTOCOL ASPECTS AND NEXT-GENERATION NETWORKS Internet protocol aspects Interworking Ethernet-MPLS network interworking User plane interw
2、orking ITU-T Recommendation Y.1415 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
3、protocols Y.400Y.499 Numbering, addressing 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 resou
4、rce management Y.1200Y.1299 Transport 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 mo
5、dels Y.2000Y.2099 Quality of Service 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 N
6、etwork control architectures and protocols Y.2500Y.2599 Security Y.2700Y.2799 Generalized mobility Y.2800Y.2899 For further details, please refer to the list of ITU-T Recommendations. ITU-T Rec. Y.1415 (02/2005) i ITU-T Recommendation Y.1415 Ethernet-MPLS network interworking User plane interworking
7、 Summary This Recommendation addresses the required functions for network interworking between a client Ethernet network and an MPLS server network, specifically the user plane interworking mechanisms and procedures. One of the key aspects of network interworking is to provide network support for Et
8、hernet services during the evolution of networks. Details of the interworking model and required interworking functions are described. Source ITU-T Recommendation Y.1415 was approved on 13 February 2005 by ITU-T Study Group 13 (2005-2008) under the ITU-T Recommendation A.8 procedure. Keywords Ethern
9、et, Interworking, MAC frame, MPLS, Network Interworking, user plane. ii ITU-T Rec. Y.1415 (02/2005) 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 perm
10、anent organ of ITU. ITU-T is responsible for studying technical, operating and tariff 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, establi
11、shes 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 by the procedure laid down in WTSA Resolution 1. In some areas of information technology which fall within ITU-Ts purview, the necessary stand
12、ards are prepared on a collaborative basis with ISO and IEC. NOTE In this Recommendation, 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 Reco
13、mmendation may contain certain mandatory provisions (to ensure e.g. interoperability 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 ar
14、e used to express requirements. The use of such words does not suggest that compliance 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 Int
15、ellectual Property Right. ITU takes no position concerning the evidence, validity or 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 rece
16、ived notice of intellectual property, protected by patents, which may be required to implement this Recommendation. However, 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
17、. No part of this publication may be reproduced, by any means whatsoever, without the prior written permission of ITU. ITU-T Rec. Y.1415 (02/2005) iii CONTENTS Page 1 Scope 1 2 References. 1 3 Definitions 2 4 Abbreviations 2 5 Conventions 2 6 Ethernet-MPLS interworking . 3 7 Requirements 5 7.1 User
18、plane requirements. 5 7.2 Control plane aspects 5 7.3 Management plane aspects. 5 7.4 Traffic Management aspects. 5 8 Functional group considerations for Ethernet-MPLS network interworking. 6 8.1 Transport label 6 8.2 Interworking label 6 8.3 Common interworking indicators. 6 9 Procedures 8 9.1 Enca
19、psulation . 8 9.2 Transport label 9 9.3 Interworking label 9 9.4 Common interworking indicators. 9 9.5 Processing of Ethernet frames at the ingress IWF 9 9.6 Processing of MPLS packets at the egress IWF. 9 10 Security considerations. 9 Appendix I Support of multipoint Ethernet services 10 ITU-T Rec.
20、 Y.1415 (02/2005) 1 ITU-T Recommendation Y.1415 Ethernet-MPLS network interworking User plane interworking 1 Scope This Recommendation focuses on required functions for network interworking between a client Ethernet network and an MPLS server network, specifically the user plane interworking mechani
21、sms and procedures. In particular, it specifies a list of requirements, interworking encapsulation formats and semantics and procedures for Ethernet 1 protocol data unit (PDU) interworking with MPLS. The interworking defined in this Recommendation is applicable to a point-to-point connection between
22、 two interworking functions (IWFs). 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 valid. All Recommendations and oth
23、er 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 Recommendations is regularly published. The re
24、ference to a document within this Recommendation does not give it, as a stand-alone document, the status of a Recommendation. 1 IEEE 802.3-2002, IEEE Standard for Information technology Telecommunications and Information Exchange between Systems Local and Metropolitan Area Networks Specific Requirem
25、ents Part 3: Carrier sense multiple access with collision detection (CSMA/CD) access method and physical layer specifications. 2 ITU-T Recommendation G.809 (2003), Functional architecture of connectionless layer networks. 3 ITU-T Recommendation Y.1411 (2003), ATM-MPLS network interworking Cell mode
26、user plane interworking. 4 IEEE 802.1Q-2003, IEEE standards for local and metropolitan area networks: Virtual bridged local area networks. 5 IETF RFC 3031 (2001), Multiprotocol label switching architecture. 6 ITU-T Recommendation G.8012/Y.1308 (2004), Ethernet UNI and Ethernet NNI. 7 ITU-T Recommend
27、ation G.805 (2000), Generic functional architecture of transport networks. 8 IEEE 802.1D-2004, IEEE standard for local and metropolitan area networks: Media Access Control (MAC) Bridges. 9 ITU-T Recommendation Y.1710 (2002), Requirements for Operation b) the ability to transport Ethernet frames with
28、 or without FCS (Frame Check Sequence) retention; c) maintaining Ethernet frame sequence integrity; d) support for the traffic contracts and the QoS commitments made to the Ethernet connections; e) support of bidirectional point-to-point connections between two IWFs with symmetric or asymmetric band
29、width. 7.2 Control plane aspects For transfer of Ethernet frames, the following are to be signalled or provisioned: a) exchange of Interworking label(s) between IWFs; b) correlation of Interworking labels for a bidirectional connection for each Interworking LSP. Mechanisms are to be defined; c) asso
30、ciation of each Interworking LSP label with a Transport LSP label; d) the ability of the two IWFs to exchange the MTU size that can be supported; e) the ability to indicate if FCS is retained as part of the payload of the Interworking LSP; f) presence and use of Common interworking indicators; g) th
31、e ability of the IWF to optionally inspect the user priority field of a tagged Ethernet frame 8 in order to determine the requested QoS and appropriately mark the MPLS packet. 7.3 Management plane aspects The interworking function shall support transfer of defect information from the server MPLS net
32、work to the client Ethernet network. OAM functionality in MPLS networks and OAM mechanisms for MPLS networks are specified in ITU-T Recs Y.1710 9 and Y.1711 10 respectively. The transfer of defect information is beyond the scope of this Recommendation. Requirements for OAM functions in Ethernet-base
33、d networks and Ethernet services are specified in ITU-T Rec. Y.1730 11. The user-to-user OAM and provider OAM are transported transparently when present in an Ethernet frame. For transparent transfer of Ethernet-related information in the management plane, the interworking function should support tr
34、ansfer or mapping of QoS performance parameters between Ethernet and MPLS network. Such mapping could select a Transport LSP with appropriate QoS for the Ethernet service. 7.4 Traffic Management aspects The Ethernet client layer shall only deliver traffic to the IWF that conforms to traffic contract
35、s. If the Ethernet client exceeds its traffic contract and the IWF becomes congested, data may be discarded. 6 ITU-T Rec. Y.1415 (02/2005) 8 Functional group considerations for Ethernet-MPLS network interworking Figure 8-1 provides an illustration of functional grouping for Ethernet-MPLS network int
36、erworking. Transport label Interworking label Optional common interworking indicators Ethernet frame (without preamble, optionally with FCS) Figure 8-1/Y.1415 Ethernet-MPLS interworking functional groups 8.1 Transport label The 4-octet Transport label identifies an LSP which is used to transport tra
37、ffic between two IWFs. The Transport label is a standard MPLS shim header, as specified in IETF RFC 3032 12, and is processed by LSRs as described in IETF RFC 3032 12. The S bit is set to “0“ indicating that this is not the bottom of the label stack. The setting of the EXP fields is beyond the scope
38、 of this Recommendation. The setting of the TTL fields is beyond the scope of this Recommendation. Procedures for establishment of the Transport LSP are beyond the scope of this Recommendation. Since LSPs are unidirectional and Ethernet is bidirectional, two Transport LSPs and hence, in general, two
39、 Transport labels are required for Ethernet-MPLS network interworking. 8.2 Interworking label The interworking function associates an Interworking LSP label with each Ethernet connection. The 4-octet Interworking label uniquely identifies one Interworking LSP carried inside a Transport LSP. The Inte
40、rworking label is a standard MPLS shim header, as specified in IETF RFC 3032 12. More than one Interworking LSP may be supported by one Transport LSP. The Interworking label is processed only at the ingress or the egress IWF. The S bit is set to “1“ to indicate the bottom of the label stack. The set
41、ting of the EXP field is for further study. The TTL field shall not be set to less than 2. Procedures for establishment of the Interworking LSP are beyond the scope of this Recommendation. Since LSPs are unidirectional and Ethernet is bidirectional, two Interworking LSPs and hence, in general, two I
42、nterworking labels are required for Ethernet-MPLS network interworking. 8.3 Common interworking indicators The Common interworking indicators functions are related to the Interworking LSP. For general interworking with MPLS networks, the Common interworking indicators functional group is comprised o
43、f a Control field, a Fragmentation and Length field and a Sequence number field. Use of the Common interworking indicators is optional, however, when used all fields shall be present. Figure 8-2 illustrates the structure of the Common interworking indicators. ITU-T Rec. Y.1415 (02/2005) 7 Bit 8 7 6
44、5 4 3 2 1 Control (1 octet) Fragmentation and length (1 octet) Sequence number (2 octets) NOTE Bit 8 is the most significant bit. Figure 8-2/Y.1415 Common interworking indicators functional group 8.3.1 Control field This field is not used in this Recommendation. 8.3.2 Fragmentation and Length fields
45、 These fields are not used in this Recommendation. Fragmentation field The 2-bit Fragmentation field indicates if any fragmentation of the original frame has been done to fulfil the MTU requirements. This field is not used in this Recommendation. Length field The 6-bit Length field indicates the len
46、gth of the payload in order to compensate for padding applied to the MPLS packet. This field is not used in this Recommendation. 8.3.3 Sequence number field The Sequence number field is used to check the sequence integrity of MPLS packets sent from the ingress IWF to the egress IWF. When Ethernet se
47、rvices are transported over an underlying MPLS based network, it is required that the MPLS network maintain the sequence integrity of the Ethernet frames encapsulated in the MPLS packets. Even under the normal “first in first out“ (FIFO) operation, it is possible that misordering of the packets coul
48、d occur. As an option, the Sequence number field can be set by the IWF in the Ethernet-to-MPLS direction. The Sequence number is a 2-octet field using a 16-bit, unsigned circular space. The sequence number value of “0“ is used to indicate that the sequence number check algorithm is not used. 8.3.3.1
49、 Setting the sequence numbers If the sequence number field is used, then the following procedures apply in the Ethernet-to-MPLS direction: The sequence number shall be set to 1 for the first MPLS packet transmitted on the Interworking LSP. For each subsequent MPLS packet, the sequence number shall be incremented by 1. If the value of the incremented sequence number is 65535 for the current MPLS packet, the sequence number shall be set to 1 for the following MPLS packet. If the ingress IWF does not
