1、 INTERNATIONAL TELECOMMUNICATION UNION ITU-T Y.1411TELECOMMUNICATION STANDARDIZATION SECTOR OF ITU (02/2003) SERIES Y: GLOBAL INFORMATION INFRASTRUCTURE AND INTERNET PROTOCOL ASPECTS Internet protocol aspects Interworking ATM-MPLS network interworking Cell mode user plane interworking ITU-T Recommen
2、dation Y.1411 ITU-T Y-SERIES RECOMMENDATIONS GLOBAL INFORMATION INFRASTRUCTURE AND INTERNET PROTOCOL ASPECTS 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, addressing and
3、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 Transport Y.1300Y.1
4、399 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 For further details, please refer to the list of ITU-T Recommendations. ITU-T Rec. Y.1411 (02/2003) i ITU-T Recom
5、mendation Y.1411 ATM-MPLS network interworking Cell mode user plane interworking Summary This Recommendation addresses required functions of network interworking between ATM networks and MPLS networks specifically the user plane interworking mechanisms and procedures. One of the key aspects of netwo
6、rk interworking is to provide network support for ATM services during the evolution of networks. Details of the interworking model and required interworking functions are described. Source ITU-T Recommendation Y.1411 was prepared by ITU-T Study Group 13 (2001-2004) and approved under the WTSA Resolu
7、tion 1 procedure on 22 February 2003. Keywords ATM, MPLS, interworking, network, user plane. ii ITU-T Rec. Y.1411 (02/2003) FOREWORD The International Telecommunication Union (ITU) is the United Nations specialized agency in the field of telecommunications. The ITU Telecommunication Standardization
8、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 standardizing telecommunications on a worldwide basis. The World Telecommunication Standardization Assembly (WTSA), which meets e
9、very 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 by the procedure laid down in WTSA Resolution 1. In some areas of information technology which fall within ITU-Ts purv
10、iew, 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 both a telecommunication administration and a recognized operating agency. INTELLECTUAL PROPERTY RIGHTS ITU draws atte
11、ntion 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 ITU members or other
12、s 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, implementors are cautioned that this may not represent
13、the latest information and are therefore strongly urged to consult the TSB patent database. ITU 2003 All rights reserved. No part of this publication may be reproduced, by any means whatsoever, without the prior written permission of ITU. ITU-T Rec. Y.1411 (02/2003) iii CONTENTS Page 1 Scope 1 2 Ref
14、erences. 1 3 Definitions 2 4 Abbreviations 2 5 ATM-MPLS interworking 4 6 General requirements 4 6.1 User plane requirements. 4 6.2 Control plane aspects 5 6.3 Management plane aspects. 6 6.4 Traffic Management aspects. 7 7 Methods of ATM transport over MPLS . 8 7.1 One-to-one mode 8 7.2 N-to-one mod
15、e 8 7.3 Functional group considerations for ATM-MPLS Network interworking. 10 8 One-to-one mode encapsulation . 12 8.1 Transport label 12 8.2 Interworking label 12 8.3 Common interworking indicators. 13 8.4 ATM-MPLS interworking specific header. 13 8.5 ATM payload 13 8.6 Encapsulation . 13 9 N-to-on
16、e mode encapsulation. 15 9.1 Transport label 15 9.2 Interworking label 15 9.3 Common interworking indicators. 16 9.4 ATM-MPLS interworking specific header. 16 9.5 ATM payload 16 9.6 Encapsulation . 16 10 OAM and RM cell treatment 19 10.1 ATM-to-MPLS direction 19 10.2 MPLS-to-ATM direction 19 iv ITU-
17、T Rec. Y.1411 (02/2003) Introduction There is a need to focus on required functions of network interworking between ATM networks and MPLS networks specifically the user plane interworking mechanisms and procedures. One of the key aspects of network interworking is to provide network support for ATM
18、services during the evolution of networks. ITU-T Rec. Y.1411 (02/2003) 1 ITU-T Recommendation Y.1411 ATM-MPLS network interworking Cell mode user plane interworking 1 Scope This Recommendation focuses on required functions for network interworking between ATM and MPLS, specifically the user plane in
19、terworking mechanisms and procedures for cell mode transport. In particular it specifies a list of requirements, interworking scenarios and interworking encapsulation format and semantics for ATM-MPLS cell mode network interworking. This Recommendation enables transport of ATM Permanent Virtual Conn
20、ections (PVC) or Switched Virtual Connections (SVC) over an MPLS network. The encapsulation allows ATM Virtual Channel Connections (VCCs) or Virtual Path Connections (VPCs) to be carried within MPLS Label Switched Paths (LSPs). The scope includes support of all AAL types as well as OAM and RM cells,
21、 and the ability to encapsulate one or multiple ATM cells in a single MPLS Frame. 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 ind
22、icated 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 currently valid ITU-T
23、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. 1 ITU-T Recommendation I.510 (1993), Definitions and general principles for ISDN interworking. 2 IETF RFC 3031 (2001), Multiprot
24、ocol label switching architecture. 3 ITU-T Recommendation I.610 (1999), B-ISDN operation and maintenance principles and functions. 4 ITU-T Recommendation I.610 (1999)/Cor.1 (2000), B-ISDN operation and maintenance principles and functions Corrigendum 1. 5 ITU-T Recommendation I.610 (1999)/Amd.1 (200
25、0), B-ISDN operation and maintenance principles and functions Amendment 1. 6 ITU-T Recommendation Y.1710 (2002), Requirements for Operation 2) N ATM connections to an interworking LSP, refered to as N-to-one mode. The one-to-one mode specifies an encapsulation method that maps one ATM VCC or one ATM
26、 VPC to one interworking LSP. For VCCs, the VPI/VCI is not included. For VPCs, the VPI is not included. Cells from one VCC or one VPC may be concatenated. The N-to-one mode specifies an encapsulation method that maps one or more ATM VCCs (or one or more ATM VPCs) to one interworking LSP. For both VC
27、Cs and VPCs, the VPI/VCI is always included. Cells from one or more VCCs (or one or more VPCs) may be concatenated. This Recommendation defines only the encapsulation of ATM cells that use the NNI format 15. The encapsulation of ATM cells that use the UNI format which includes the GFC field is for f
28、urther study. 6 General requirements 6.1 User plane requirements For transparent transfer of ATM-related services in the transfer (user) plane, the following items are required: a) the ability to multiplex multiple ATM connections (i.e., VPCs and/or VCCs) into interworking LSPs; b) support for the t
29、raffic contracts and the QoS commitments made to the ATM connections; c) the ability to transparently carry all AAL types; d) the ability to transparently carry all OAM cells, including the support for proper operation of OAM PM cells; e) transport of Resource Management (RM) cells; ITU-T Rec. Y.141
30、1 (02/2003) 5 f) transport of Cell Loss Priority (CLP) indication and Payload Type Indication (PTI) information from the ATM cell header; g) the ability to encapsulate an ATM single cell or concatenated ATM cells into one MPLS frame; h) maintaining sequence integrity for all VCCs and VPCs between th
31、e IWFs; i) support of ATM point-to-point and ATM point-to-multipoint connection; j) support of unidirectional ATM connection; k) support of bidirectional point-to-point ATM connections with symmetric or asymmetric bandwidth. Figure 2 shows the network reference model and protocol layers for ATM-MPLS
32、 user plane interworking. Y.1411_F02Physical Physical PhysicalATM IWF MPLSMPLS LSPIWFATMPhysicalATMPhysical PhysicalIWFATMATMIWFLink LayerAALUpper LayersVC/VP VC/VPLink Layer Link LayerPhysicalATMAALUpper LayersPhysicalLink LayerMPLSLSPStacksMPLSLSPStacksMPLSLSPStacksMPLSLSPStacksFigure 2/Y.1411 Net
33、work reference model and protocol layers for ATM-MPLS user plane interworking 6.2 Control plane aspects For transparent transfer of ATM-related services, the following items are to be signalled or provisioned: a) exchange of interworking label(s) between IWFs; b) correlation of interworking labels f
34、or one or more bidirectional connections per interworking LSP. Mechanisms are to be defined; c) operation in one-to-one or N-to-one mode; d) maximum number of concatenated cells for a given interworking LSP between IWFs; e) indication of cell encapsulation modes as either single or concatenated; f)
35、presence of common interworking indicators field; g) support of the connection types Switched Virtual Connection (SVC) and Soft Permanent Virtual Connection (SPVC); 6 ITU-T Rec. Y.1411 (02/2003) h) support of ATM point-to-point and ATM point-to-multipoint connections; i) support of bidirectional ATM
36、 point-to-point connections with symmetric or asymmetric bandwidth; j) the transparent transport of ATM signalling protocols (e.g., DSS2, B-ISUP, ATM-F UNI, ATM-F PNNI, ATM-F AINI), ATM routing protocols (e.g., ATM-F PNNI) and ATM management protocols (e.g., ATM-F ILMI), which control the ATM connec
37、tions across the MPLS, network; k) the ability to control the MPLS interworking LSPs via ATM control protocols by the IWFs for ATM SVCs and ATM Soft-PVCs; l) the control of MPLS Transport LSPs or interworking LSPs via MPLS control protocols by the IWFs; m) a mechanism to associate the two transport
38、LSPs, one for each direction, to act as a logical ATM port to ATM signalling and routing, capable of carrying ATM connections between two IWFs. 6.3 Management plane aspects ATM OAM cells carry performance, defect, and protection switching information for VCCs and VPCs on an end-to-end and per segmen
39、t basis to support the ATM management plane 3, 4 and 5. OAM functionality in MPLS networks and OAM mechanism for MPLS networks can be found in ITU-T Recs Y.1710 6 and Y.1711 7. For transparent transfer of ATM-related services in the management plane, the interworking function should support transpar
40、ent transfer or mapping of performance, defect, and protection switching information between MPLS OAM flows and ATM OAM cells. As a minimum, the interworking function shall transfer ATM OAM information through the MPLS core network by encapsulating OAM cells in MPLS packets. The encapsulation mechan
41、ism supports the ordered delivery of OAM cells in respect to cell flow of that connection. Where end-to-end OAM is required, the interworking function may have to correlate the MPLS OAM information with the ATM OAM. This aspect of OAM interworking with MPLS is outside the scope of this Recommendatio
42、n. Figure 3 shows functional representation of ATM-MPLS management plane. ITU-T Rec. Y.1411 (02/2003) 7 Y.1411_F03ATMIWF MPLSMPLS management ATMIWFATM management ATM management IWFIWFAIS,RDI,CC,LB,FPMFDI,BDI,CV,LB,PFDI,BDI,CV,LB,PAIS,RDI,CC,LB,FPMAISCCLBCVPAlarm Indication SignalContinuity Check Loo
43、p BackConnectivity VerificationP flowsRDIFPMFDIBDIRemote Defect IndicationForward Performance MonitoringForward Defect IndicatorBackward Defect IndicationFigure 3/Y.1411 Functional representation of ATM-MPLS management plane interworking 6.4 Traffic Management aspects In ATM, a number of different A
44、TM Transfer Capabilities (ATC) 8, 9 and Quality of Service (QoS) classes 10 are defined. A combination of an ATC and an associated QoS class is intended to support an ATM layer service model. When a transport LSP is used to carry multiple ATM connections with different combinations of ATC and QoS cl
45、asses, the transport LSP shall be capable of providing the required QoS for all ATM connections. In a MPLS network that does not support QoS differentiation on a per packet basis, the LSP shall meet the most stringent QoS requirements of the ATM connections transported by the LSP. 6.4.1 Use of Diffe
46、rentiated Services for ATM-MPLS interworking If the MPLS network supports Differentiated Services (DiffServ) Behaviour Aggregates defined in 16, MPLS packets can be treated with different priorities on a Per Hop Behaviour (PHB). In this case, two different types of LSPs are defined 11, which can bot
47、h be used for the transport LSP: Label-Only-Inferred-PSC LSPs (L-LSP); EXP-Inferred-PSC LSPs (E-LSP). If a L-LSP is used as a transport LSP, the PHB scheduling class (PSC) 17 of each packet is inferred from the label without any other information (e.g., regardless of the EXP field value). In that ca
48、se, the LSP shall meet the most stringent QoS requirements of the ATM connections transported by the LSP. If an E-LSP is used as a transport LSP, the EXP field of the transport label is used to determine the PHB to be applied to each packet, i.e., different packets in one LSP may receive a different
49、 QoS. The 3-bit EXP field of the transport label can represent eight different combinations of Per Hop Behaviour (PHB) and drop precedence levels. The mapping of the PHB to EXP fields is either explicitly signalled at label set-up or relies on a pre-configured mapping. The mapping between ATM QoS classes and MPLS PHB is for further study. 8 ITU-T Rec. Y.1411 (02/2003) 6.4.2 Connection admission control for the IWF Virtual connections (VPCs, VCCs, LSPs) have to be managed on both ATM and MPLS sides of the IWF. The IWF b
