1、 International Telecommunication Union ITU-T G.8110/Y.1370TELECOMMUNICATION STANDARDIZATION SECTOR OF ITU (01/2005) SERIES G: TRANSMISSION SYSTEMS AND MEDIA, DIGITAL SYSTEMS AND NETWORKS Ethernet over Transport aspects MPLS over Transport aspects SERIES Y: GLOBAL INFORMATION INFRASTRUCTURE, INTERNET
2、 PROTOCOL ASPECTS AND NEXT-GENERATION NETWORKS Internet protocol aspects Transport MPLS layer network architecture ITU-T Recommendation G.8110/Y.1370 ITU-T G-SERIES RECOMMENDATIONS TRANSMISSION SYSTEMS AND MEDIA, DIGITAL SYSTEMS AND NETWORKS INTERNATIONAL TELEPHONE CONNECTIONS AND CIRCUITS G.100G.19
3、9 GENERAL CHARACTERISTICS COMMON TO ALL ANALOGUE CARRIER-TRANSMISSION SYSTEMS G.200G.299 INDIVIDUAL CHARACTERISTICS OF INTERNATIONAL CARRIER TELEPHONE SYSTEMS ON METALLIC LINES G.300G.399 GENERAL CHARACTERISTICS OF INTERNATIONAL CARRIER TELEPHONE SYSTEMS ON RADIO-RELAY OR SATELLITE LINKS AND INTERCO
4、NNECTION WITH METALLIC LINES G.400G.449 COORDINATION OF RADIOTELEPHONY AND LINE TELEPHONY G.450G.499 TRANSMISSION MEDIA CHARACTERISTICS G.600G.699 DIGITAL TERMINAL EQUIPMENTS G.700G.799 DIGITAL NETWORKS G.800G.899 DIGITAL SECTIONS AND DIGITAL LINE SYSTEM G.900G.999 QUALITY OF SERVICE AND PERFORMANCE
5、 GENERIC AND USER-RELATED ASPECTS G.1000G.1999 TRANSMISSION MEDIA CHARACTERISTICS G.6000G.6999 DATA OVER TRANSPORT GENERIC ASPECTS G.7000G.7999 ETHERNET OVER TRANSPORT ASPECTS G.8000G.8999 General aspects G.8000G.8099 MPLS over Transport aspects G.8100G.8199 Quality and availability targets G.8200G.
6、8299 For further details, please refer to the list of ITU-T Recommendations. ITU-T Rec. G.8110/Y.1370 (01/2005) i ITU-T Recommendation G.8110/Y.1370 MPLS layer network architecture Summary This Recommendation describes the functional architecture of MPLS networks using the modelling methodology desc
7、ribed in ITU-T Recs G.805 and G.809. The MPLS network functionality is described from a network level viewpoint, taking into account MPLS network layering, definition of characteristic information, client/server associations, networking topology and layer network functionality. The functional archit
8、ecture of the server networks used by the MPLS network is not within the scope of this Recommendation. Such architectures are described in other ITU-T Recommendations or IETF RFCs. This Recommendation is based on IETF RFCs 3031, 3032, 3270 and 3443. Source ITU-T Recommendation G.8110/Y.1370 was appr
9、oved on 13 January 2005 by ITU-T Study Group 15 (2005-2008) under the ITU-T Recommendation A.8 procedure. ii ITU-T Rec. G.8110/Y.1370 (01/2005) FOREWORD The International Telecommunication Union (ITU) is the United Nations specialized agency in the field of telecommunications. The ITU Telecommunicat
10、ion 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 on a worldwide basis. The World Telecommunication Standardization Assembly (
11、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 down in WTSA Resolution 1. In some areas of information technology which fal
12、l 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 both a telecommunication administration and a recognized operating agency. Compliance with this Re
13、commendation 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 all of these mandatory provisions are met. The words “shall“ or some other obligatory language su
14、ch 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 RIGHTS ITU draws attention to the possibility that the practice or implementation of this Recomme
15、ndation 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 Recommendation development process. As of the date of appro
16、val 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 the latest information and are therefore strongly urged to consult the TSB p
17、atent database. ITU 2005 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. G.8110/Y.1370 (01/2005) iii CONTENTS Page 1 Scope 1 2 References. 1 3 Definitions 1 4 Abbreviations 4 5 Conventions 5 6 Transp
18、ort functional architecture of MPLS networks 5 6.1 General . 5 6.2 MPLS network layered structure 5 7 MPLS shim header functional architecture description based on ITU-T Rec. G.809 7 7.1 MPLS layer network. 7 7.2 MPLS layer network partitioning. 12 7.3 MPLS label behaviour 15 7.4 Penultimate Hop Pop
19、ping (PHP) 20 7.5 LSP Tunnels . 23 8 MPLS shim header based functional architecture based on ITU-T Rec. G.805. 25 8.1 MPLS Layer network . 25 8.2 MPLS layer network partitioning. 30 8.3 MPLS subnetwork behaviour. 30 8.4 Penultimate Hop Popping (PHP) 31 8.5 LSP tunnels. 31 9 MPLS hierarchies . 31 9.1
20、 G.809 MPLS hierarchies 31 9.2 G.805 MPLS hierarchies 32 9.3 Heterogeneous MPLS hierarchies 33 10 Server/client associations 36 10.1 MPLS/client adaptation 36 10.2 Non-MPLS Server/MPLS adaptation. 38 11 MPLS network control . 38 12 MPLS survivability techniques. 38 12.1 Protection techniques 38 12.2
21、 Network restoration 38 13 MPLS and support of the Diff-Serv architecture 38 13.1 Reference diagrams for uniform, pipe and short pipe models 40 13.2 MPLS TTL behaviour 43 13.3 MPLS EXP behaviour 47 13.4 LSP merging and Diff-Serv support. 52 iv ITU-T Rec. G.8110/Y.1370 (01/2005) Page Annex A Function
22、al model for fragmentation of packets in an MPLS network 53 Annex B Reserved label processing 54 Annex C G.809 to G.805 translation. 57 Annex D MPLS and IP multiplexing 57 Appendix I Functional model for describing the use of ECMP in MPLS networks 59 ITU-T Rec. G.8110/Y.1370 (01/2005) 1 ITU-T Recomm
23、endation G.8110/Y.1370 MPLS layer network architecture 1 Scope This Recommendation describes the functional architecture of MPLS bearer plane networks using the modelling methodology described in ITU-T Recs G.805 and G.809. The MPLS network functionality is described from a network level viewpoint,
24、taking into account an MPLS network layered structure, client characteristic information, client/server associations, networking topology, and layer network functionality providing MPLS signal transmission, multiplexing, supervision, performance and survivability. The basis for this first version of
25、 the Recommendation is the MPLS specification in IETF RFCs 3031, 3032, 3270 and 3443. MPLS OAM as specified in ITU-T Recs Y.1711, Y.1712 and Y.1713 is not described in this version. It will be added along with other MPLS OAM under development in the IETF in the next version of this Recommendation. 2
26、 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 other references are subject to revision
27、; 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 reference to a document within this Rec
28、ommendation does not give it, as a stand-alone document, the status of a Recommendation. ITU-T Recommendation G.805 (2000), Generic functional architecture of transport networks. ITU-T Recommendation G.809 (2003), Functional architecture of connectionless layer networks. ITU-T Recommendation Y.1711
29、(2004), Operation MPLS flow termination source (MPLS_FT_So); MPLS flow termination sink (MPLS_FT_Sk); MPLS network flow (NF); MPLS link flow (LF); MPLS flow domain flow (FDF); MPLS flow domain (FD); MPLS link. 8 ITU-T Rec. G.8110/Y.1370 (01/2005) Figure 3/G.8110/Y.1370 MPLS layer network example The
30、 MPLS layer network may be employed recursively to describe an MPLS hierarchy, implemented as a label stack. This is described by the use of sub-layering. A transport network based on MPLS can be decomposed into a number of independent transport sublayer networks with a client/server association bet
31、ween adjacent sublayer networks. An example of MPLS sublayers and their structure and the adaptation functions is shown in Figure 4. This convention is used in this Recommendation. The label stack is related to the MPLS sublayers in such a way that the bottom of the stack is associated with the MPLS
32、 sublayer at the top of the diagram (where the client is not MPLS), whilst the top of the stack is associated with the MPLS sublayer at the bottom of the diagram. ITU-T Rec. G.8110/Y.1370 (01/2005) 9 Figure 4/G.8110/Y.1370 Example of MPLS hierarchy illustrated using sub-layering 10 ITU-T Rec. G.8110
33、/Y.1370 (01/2005) MPLS allows for the creation of an arbitrary depth of sublayers, or label stacks. An example is shown in Figure 5. Figure 5/G.8110/Y.1370 Example of MPLS stack depths ITU-T Rec. G.8110/Y.1370 (01/2005) 11 7.1.1 MPLS topological components The MPLS topological components are: MPLS l
34、ayer network; MPLS flow domain; MPLS link; MPLS access group. The MPLS layer network is partitioned into a number of MPLS Flow Domains interconnected by MPLS links. 7.1.1.1 MPLS layer network The MPLS layer network is defined by the complete set of MPLS access groups that may be associated for the p
35、urpose of transferring information. The information transferred is characteristic of the MPLS layer network and is termed MPLS characteristic information. The associations of the MPLS flow terminations (that form a connectionless trail) in the MPLS layer network are defined on a per traffic unit bas
36、is, which is the MPLS_CI traffic unit. The topology of the MPLS layer network is described by MPLS access groups, MPLS flow domains and the MPLS flow point pool links between them. The structures within the MPLS layer network and its server and client layer networks are described by the components b
37、elow. 7.1.1.2 MPLS flow domain An MPLS flow domain is defined by the set of MPLS flow points that are available for the purpose of transferring information. MPLS_CI traffic unit transfers, across the MPLS flow domain, that correspond to a particular association between ingress and egress MPLS flow p
38、oints, need not be present at all times. In general, MPLS flow domains may be partitioned into smaller flow domains interconnected by MPLS flow point pool links. The matrix is a special case of an MPLS flow domain that cannot be further partitioned. Unless otherwise explicitly stated, the descriptio
39、n of flow domains in this Recommendation is at the matrix level. 7.1.1.3 MPLS flow point pool link An MPLS flow point pool link consists of a subset of the MPLS flow points at the edge of one MPLS flow domain or MPLS access group that are associated with a corresponding subset of MPLS flow points at
40、 the edge of another MPLS flow domain or MPLS access group for the purpose of transferring MPLS characteristic information. The MPLS flow point pool link (FPP link) represents the topological relationship and available capacity between a pair of MPLS flow domains, or an MPLS flow domain and an MPLS
41、access group, or a pair of MPLS access groups. Multiple MPLS flow point pool links may exist between any given MPLS flow domain and MPLS access group or pair of MPLS flow domains or MPLS access groups. MPLS flow point pool links are established at the timescale of the MPLS server layer network. 7.1.
42、1.4 MPLS access group An MPLS access group is a group of co-located MPLS flow termination functions that are connected to the same MPLS flow domain or MPLS flow point pool link. 7.1.2 MPLS transport entities The MPLS transport entities are: MPLS link flow; MPLS flow domain flow; MPLS network flow; M
43、PLS connectionless trail. 12 ITU-T Rec. G.8110/Y.1370 (01/2005) 7.1.3 MPLS transport processing functions The MPLS transport processing functions are: MPLS flow termination function; MPLS to client layer network adaptation functions. 7.1.3.1 MPLS flow termination The MPLS_FT_So function inserts the
44、8-bit TTL field in the MPLS_CI traffic unit. The MPLS_CI traffic unit is output via the MPLS TFP. The MPLS_FT_Sk terminates and processes the 8-bit TTL field as described in 13.2. Note that a flow termination is associated with one LSP instance. 7.1.3.2 MPLS to client layer network adaptation functi
45、ons The MPLS/client adaptation functions are described in clause 10. 7.1.4 MPLS reference points The MPLS reference points (Figure 3) are: MPLS Access Point (AP); MPLS Termination Flow Point (TFP); MPLS Flow Point (FP); MPLS Flow Point Pool (FPP); MPLS Termination Flow Point Pool (TFPP). 7.1.4.1 MPL
46、S access point An MPLS Access Point (MPLS AP) represents the binding between an MPLS flow termination function and one or more MPLS/client, or MPLS/MPLS adaptation functions. 7.1.4.2 MPLS termination flow point An MPLS Termination Flow Point (MPLS TFP) connects an MPLS Flow Termination (MPLS FT) fun
47、ction with an MPLS Link. 7.1.4.3 MPLS flow point An MPLS link connects to an MPLS flow domain or another MPLS link via an MPLS flow point. This flow point is provided through the Server/MPLS, or MPLS/MPLS adaptation function. 7.1.4.4 MPLS flow point pool A group of MPLS flow points is referred to as
48、 MPLS Flow Point Pool (FPP). An FPP has the same properties as its flow points. 7.1.4.5 MPLS termination flow point pool A group of MPLS termination flow points is referred to as MPLS Termination Flow Point Pool (TFPP). A TFPP has the same properties as its termination flow points. 7.2 MPLS layer ne
49、twork partitioning MPLS layer network partitioning can be represented in a single layer network by means of a geometric translation of the MPLS hierarchy. This is illustrated in Figure 6. Figure 6 a) illustrates an example of an MPLS hierarchy only the source functions are shown. The MPLS TFPs can be shown at the same horizontal level in a diagram by means of a simple translation as shown in Figure 6 b). This can be extended to represent a label stack of arbitrary depth. The result of this ITU-T Rec.
