1、 INTERNATIONAL TELECOMMUNICATION UNION ITU-T Series QTELECOMMUNICATION STANDARDIZATION SECTOR OF ITU Supplement 46(09/2003) SERIES Q: SWITCHING AND SIGNALLING Technical Report TRQ.2830: ATM-MPLS network interworking signalling requirements ITU-T Q-series Recommendations Supplement 46 ITU-T Q-SERIES
2、RECOMMENDATIONS SWITCHING AND SIGNALLING SIGNALLING IN THE INTERNATIONAL MANUAL SERVICE Q.1Q.3 INTERNATIONAL AUTOMATIC AND SEMI-AUTOMATIC WORKING Q.4Q.59 FUNCTIONS AND INFORMATION FLOWS FOR SERVICES IN THE ISDN Q.60Q.99 CLAUSES APPLICABLE TO ITU-T STANDARD SYSTEMS Q.100Q.119 SPECIFICATIONS OF SIGNAL
3、LING SYSTEMS No. 4, 5, 6, R1 AND R2 Q.120Q.499 DIGITAL EXCHANGES Q.500Q.599 INTERWORKING OF SIGNALLING SYSTEMS Q.600Q.699 SPECIFICATIONS OF SIGNALLING SYSTEM No. 7 Q.700Q.799 Q3 INTERFACE Q.800Q.849 DIGITAL SUBSCRIBER SIGNALLING SYSTEM No. 1 Q.850Q.999 PUBLIC LAND MOBILE NETWORK Q.1000Q.1099 INTERWO
4、RKING WITH SATELLITE MOBILE SYSTEMS Q.1100Q.1199 INTELLIGENT NETWORK Q.1200Q.1699 SIGNALLING REQUIREMENTS AND PROTOCOLS FOR IMT-2000 Q.1700Q.1799 SPECIFICATIONS OF SIGNALLING RELATED TO BEARER INDEPENDENT CALL CONTROL (BICC) Q.1900Q.1999 BROADBAND ISDN Q.2000Q.2999 For further details, please refer
5、to the list of ITU-T Recommendations. Q series Supplement 46 (09/2003) i Supplement 46 to ITU-T Q-series Recommendations Technical Report TRQ.2830: ATM-MPLS network interworking signalling requirements Summary This Supplement provides the signalling requirements to enable ATM services to be provided
6、 over an MPLS network in a network interworking environment. Source Supplement 46 to ITU-T Q-series Recommendations was agreed by ITU-T Study Group 11 (2001-2004) on 12 September 2003. ii Q series Supplement 46 (09/2003) FOREWORD The International Telecommunication Union (ITU) is the United Nations
7、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 Recommendations on them with a view to standardizing telecommunications
8、 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 by the procedure laid
9、 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 publication, the expression “Administration“ is used for conciseness to indicate both a telecommunication
10、 administration and a recognized operating agency. Compliance with this publication is voluntary. However, the publication may contain certain mandatory provisions (to ensure e.g. interoperability or applicability) and compliance with the publication is achieved when all of these mandatory provision
11、s 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 publication is required of any party. INTELLECTUAL PROPERTY RIGHTS ITU draws attention to the p
12、ossibility that the practice or implementation of this publication 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 others outside of the
13、publication development process. As of the date of approval of this publication, ITU had not received notice of intellectual property, protected by patents, which may be required to implement this publication. However, implementors are cautioned that this may not represent the latest information and
14、 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. Q series Supplement 46 (09/2003) iii CONTENTS Page 1 Scope 1 2 References. 1 3 Definiti
15、ons 1 4 Abbreviations 2 5 Role of ATM signalling 2 6 Relationship between ATM connection and MPLS LSP . 3 6.1 Encapsulating ATM connections . 4 7 Signalling information requirements 5 7.1 Negotiation . 6 8 Signalling information flows 6 8.1 Signalling procedures overview . 6 8.2 Signalling objects .
16、 7 8.3 Successful ATM connection establishment information flows 8 8.4 Unsuccessful ATM connection establishment information flows 11 8.5 ATM connection release information flows. 12 Q series Supplement 46 (09/2003) 1 Supplement 46 to ITU-T Q-series Recommendations Technical Report TRQ.2830: ATM-MPL
17、S network interworking signalling requirements 1 Scope MPLS has the potential to consolidate service provider networks and services, for example, ATM, Frame Relay (FR), circuit emulation, voice and IP services, over a single common core infrastructure. This Supplement provides a general overview of
18、ATM-MPLS network interworking and defines the signalling architecture and requirements. The scope is indicated in Figure 1. Q.SUPP.46_F01LSPMPLSATMATMIWFLSRATMATM network MPLS network ATM networkMPLSScope of this SupplementATM user 1ATM user 2ATMuser 3ATM user 4ATMIWFMPLSFigure 1 Reference network a
19、rchitecture for ATM-MPLS network interworking and scope of this Supplement Initially, point-to-point and point-to-multi-point ATM connections are covered. Other connection types are for further study. For point-to-multi-point connections it is assumed that the replication point is at or beyond the s
20、ucceeding IWF. 2 References 1 IETF RFC 3031 (2001), Multiprotocol Label Switching Architecture. 2 ATM Forum Specification af-aic-0178.000 (2001), ATM-MPLS Network Interworking Version 1.0. 3 ITU-T Recommendation Y.1411 (2003), ATM-MPLS network interworking Cell mode user plane interworking. 4 ITU-T
21、Recommendation Y.1412 (2003), ATM-MPLS network interworking Frame Mode User plane interworking. 3 Definitions This Supplement defines the following terms: 3.1 signalling objects: The description of one of the characteristics of an ATM call/connection or of an MPLS LSP. 3.2 cell concatenation: See IT
22、U-T Rec. Y.1411 3. 3.3 interworking: See ITU-T Rec. Y.1411 3. 2 Q series Supplement 46 (09/2003) 3.4 preceding IWF: The IWF initiating the establishment of an ATM VCC or VPC within an interworking LSP. 3.5 succeeding IWF: The IWF receiving a request to establish an ATM VCC or VPC within an interwork
23、ing LSP. 3.6 forward LSP: A transport or interworking LSP carrying the traffic in the forward call direction from the preceding IWF to the succeeding IWF. 3.7 backward LSP: A transport or interworking LSP carrying the traffic in the backward call direction from the succeeding IWF to the preceding IW
24、F. 3.8 Transport LSP: See ITU-T Rec. Y.1411 3. 3.9 Interworking LSP: See ITU-T Rec. Y.1411 3. 4 Abbreviations This Supplement uses the following abbreviations: ATM Asynchronous Transfer Mode FR Frame Relay I-LSP Interworking LSP IWF Interworking Function LSP Label Switched Path MPLS Multi-Protocol L
25、abel Switching PDU Protocol Data Unit SDU Service Data Unit T-LSP Transport LSP VCC Virtual Channel Connection VCI Virtual Channel Identifier VCL Virtual Channel Link VPC Virtual Path Connection VPI Virtual Path Identifier VPL Virtual Path Link 5 Role of ATM signalling Figure 1 provides the referenc
26、e architecture for ATM-MPLS network interworking. The Transport MPLS Label Switched Paths (LSPs) connect pairs of Interworking Functions (IWF). For each Transport LSP, one of the IWFs acts as a source of data flow and the other acts as a sink. From an ATM signalling perspective, the MPLS network and
27、 Transport LSPs can be considered as an abstraction of a physical link established between two ATM nodes. Figure 2 captures this view. In the ATM-MPLS network interworking configuration addressed by this Supplement, the role of ATM signalling is to establish interworking LSPs between IWFs during ATM
28、 VCC or VPC establishment and to perform related signalling functions. Q series Supplement 46 (09/2003) 3 Q.SUPP.46_F02Transmission direction I-LSPs carrying user information within T-LSPIWFI-LSPs carrying user information within T-LSPIWFATM nodeATM nodePhysical linkATM nodeATM nodeNetwork node with
29、 IWFNetwork node with IWFATM nodeATM nodeTransport LSPMPLS networkATMMPLSMPLSATMI-LSPs carrying sig. signalling messages, and/or routing and management messages. The signalling channel of a Transport LSP is used to setup and control interworking LSPs within the transport LSP. Q.SUPP.46_F04Interworki
30、ng-LSPRouting control channelSignalling channelLayer management channelBackward Transport LSPPrecedingIWF Forward Transport LSPMPLS networkSucceedingIWFATMnode ATMnodeFigure 4 Transport LSPs and their potential nested LSPs 6.1 Encapsulating ATM connections Cell and frame are two encapsulation modes
31、identified in ITU-T Recs Y.1411 3 and Y.1412 4 respectively. ITU-T Rec. Y.1411 defines two encapsulation formats for cell mode. One format allows for one VCC or VPC to be encapsulated into one interworking LSP (One-to-one mode), and the other allows cells belonging to one or more VCCs or VPCs to be
32、encapsulated into one interworking LSP (N-to-one mode). ITU-T Rec. Y.1412 defines two encapsulation formats. One allows for encapsulation of AAL5 PDUs and the other allows for encapsulation of AAL5 SDUs. Detailed procedures for these encapsulation formats are provided in 3 and 4. Q series Supplement
33、 46 (09/2003) 5 7 Signalling information requirements At the preceding IWF, the ATM VPC/VCCs are encapsulated into an interworking LSP according to procedures described in 3 and 4. An overview of the user plane encapsulation characteristics to be associated between VPC/VCC and an interworking LSP, s
34、ummarized from 3 and 4, is shown in Figure 5. Q.SUPP.46_F05ATM virtual path connection (VPC)/Virtual channel connection (VCC)Cell modeFrame modeI-LSP identification (i.e. label value)Call-related characteristicsVPL/VCL identification (VPI, VCI)ATM traffic characteristicsOther ATM VPC/VCC characteris
35、ticsEncapsulation characteristics and I-LSP label valueATM VPL/VCL identification (VPI, VCI)Encapsulation modesOne-to-oneN-to-oneAAL 5 PDUAAL 5 SDUForwardBackwardMPLS Interworking LSP (I-LSP)LSP identification (fwd Encapsulation mode: cell (One-to-one or N-to-one): single cell; concatenated cells. F
36、rame AAL 5 PDU: Fragmented or Not fragmented. AAL 5 SDU. 6 Q series Supplement 46 (09/2003) Forward and backward maximum number of cells that can be received; VPI/VCI or VCI values in both One-to-one and N-to-one modes; Presence or absence of the Common interworking indicators field 3: Whether or no
37、t the sequence number field is used; Whether or not the length field is used; In the case of N-to-one cell mode, whether or not the control field is used. Selection of an interworking LSP: Use existing interworking LSP (i.e., preprovisioned for the One-to-one or N-to-one modes and for subsequent VPC
38、/VCCs in the N-to-one mode signal only the VPI/VCI and the interworking LSP label used. Set-up interworking LSP on demand (i.e., for the One-to-one mode or for the first VPC/VCC in the N-to-one mode). Both cases are required. NOTE Some of the encapsulation formats in the user plane dont carry the VP
39、I/VCI values. 7.1 Negotiation It is required to negotiate the encapsulation mode from the options in clause 7. 8 Signalling information flows 8.1 Signalling procedures overview The signalling messages sent by the preceding IWF may be carried in the forward transport LSP. Similarly, the signalling me
40、ssages sent by the succeeding IWF may be carried in the backward transport LSP. The signalling procedures to set up an ATM VPC or VCC across MPLS network include: Reception of request from the preceding ATM node to establish a VCC or VPC by the preceding IWF; Initiation of the request by preceding I
41、WF for establishment of a pair of Interworking LSPs between preceding and succeeding IWFs in forward and backward directions; Progression of the establishment of the ATM VPCs or VCCs by the succeeding IWF towards the called user; Establishment of a pair of Interworking LSPs between preceding and suc
42、ceeding IWFs in forward and backward directions after confirmation by succeeding IWF. Clauses 8.3 through 8.5 illustrate, through the information flows, the establishment (successful and unsuccessful) and release of an ATM connection (VCC or VPC) when it passes over an MPLS network. These flows are
43、intended to be protocol independent. To achieve this, the flows between the preceding IWF (X) and succeeding IWF (Y) in the MPLS network contain options to allow for different methods of MPLS label distribution. To draw a parallel with MPLS architecture as defined in RFC 3031, the label assignment m
44、ethod allows both “downstream on demand“ or “unsolicited downstream“ assignment. Call-related signalling information following connection set-up is conveyed transparently across the MPLS network. Q series Supplement 46 (09/2003) 7 8.2 Signalling objects The signalling objects used in the signalling
45、information flows are described as follows: 8.2.1 Call reference Circuit independent information identifying a particular call. 8.2.2 Bearer characteristics Information sent in the forward direction to indicate a requested ATM bearer service to be provided by the network. 8.2.3 Called party end poin
46、t address Uniquely defines the end point address of the called party. 8.2.4 Calling party end point address Uniquely defines the end point address of the calling party. 8.2.5 Connection identifier Identifies the ATM connection within a call between peer signalling entities. 8.2.6 ATM traffic charact
47、eristics The set of parameters that capture the traffic characteristics requested from the network for an ATM connection. 8.2.7 Quality of service characteristics The set of parameters that capture the QoS characteristics requested from the network for an ATM connection. 8.2.8 User information Infor
48、mation generated by one of the ATM end points and transferred transparently through the network between the requesting and terminating ATM endpoints. 8.2.9 Failure reason Information sent in either the forward or the backward direction indicating where and why the call failed. 8.2.10 Release reason
49、Information sent in either the forward or the backward direction indicating where and why the call was released. 8.2.11 Optional additional LSP parameters Additional bearer parameters related to the LSP between the two interworking nodes. 8 Q series Supplement 46 (09/2003) 8.3 Successful ATM connection establishment information flows Q.SUPP.46_F06AXYB21ATM node73 813 12410 9ATM nodeRequesting ATM endpointPreceding IWF Succeeding IWF Addressed
