1、 International Telecommunication Union ITU-T Y.2175TELECOMMUNICATION STANDARDIZATION SECTOR OF ITU (11/2008) SERIES Y: GLOBAL INFORMATION INFRASTRUCTURE, INTERNET PROTOCOL ASPECTS AND NEXT-GENERATION NETWORKS Next Generation Networks Quality of Service and performance Centralized RACF architecture f
2、or MPLS core networks Recommendation ITU-T Y.2175 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
3、Interfaces and 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 capabil
4、ities and resource 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
5、architecture models 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
6、 Y.2400Y.2499 Network 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. Rec. ITU-T Y.2175 (11/2008) i Recommendation ITU-T Y.2175 Centralized RACF architecture for MPLS core
7、 networks Summary The architectural structure of a centralized resource admission and control functions (RACF) is considered in Recommendation ITU-T Y.2175. RACF is comprised of a transport resource control functional entity (TRC-FE) and a policy decision functional entity (PD-FE). This Recommendati
8、on defines an architecture, which considers a centralized RACF resulting from a centralized TRC-FE, specifies supporting requirements, and describes the resource reservation process for this specific architecture. Source Recommendation ITU-T Y.2175 was approved on 13 November 2008 by ITU-T Study Gro
9、up 13 (2009-2012) under Recommendation ITU-T A.8 procedure. ii Rec. ITU-T Y.2175 (11/2008) FOREWORD The International Telecommunication Union (ITU) is the United Nations specialized agency in the field of telecommunications, information and communication technologies (ICTs). The ITU Telecommunicatio
10、n 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 (WT
11、SA), 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 fall
12、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 Reco
13、mmendation 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 such
14、 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 Recommend
15、ation 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 approva
16、l 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 this may not represent the latest information and are therefore strongly urged to consult the TSB pat
17、ent 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-T Y.2175 (11/2008) iii CONTENTS Page 1 Scope 1 2 References. 1 4 Abbreviations and acronyms 1 5 Ce
18、ntralized RACF architecture. 2 6 Required functions 3 6.1 Resizing established LSP . 3 6.2 Mapping flow to the LSP . 3 6.3 Resource and topology monitoring of the MPLS network. 4 6.4 Required functions in the TRC-FE . 4 6.5 Required functions in the TRE-FE. 4 6.6 Requirements for Rc and Rn 5 7 Resou
19、rce control procedure in the MPLS network. 9 7.1 Resource and admission control in MPLS network . 10 7.2 Procedure for aggregate bandwidth adjustment . 11 8 Security considerations. 13 Appendix I End-to-end control scenario in the centralized RACF architecture. 14 Bibliography. 17 Rec. ITU-T Y.2175
20、(11/2008) 1 Recommendation ITU-T Y.2175 Centralized RACF architecture for MPLS core networks 1 Scope ITU-T Y.2111 defines the general requirements for resource and admission control functions for next generation networks (NGNs). These requirements are independent of the underlying transport technolo
21、gy. Multiprotocol label switching (MPLS) is considered to be a key transport technology in core networks. In particular, networks which use MPLS with traffic engineering (MPLS-TE) capabilities provide significant assurance that the delivery of the desired quality of service (QoS) for a variety of se
22、rvices and applications will occur. Resource and admission control functions (RACF) are used to control the flow of traffic from access networks into the MPLS core ITU-T Y.2111. A centralized architectural structure of one RACF functional entity, the transport resource control functional entity (TRC
23、-FE), is considered in this Recommendation. In this architectural arrangement, MPLS transport resource is monitored and controlled by the centralized control entity. This Recommendation defines the centralized architecture for the TRC-FE and specifies supporting requirements. 2 References The follow
24、ing 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; users of this Recomm
25、endation 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 Recommendation does not g
26、ive it, as a stand-alone document, the status of a Recommendation. ITU-T Y.2012 Recommendation ITU-T Y.2012 (2006), Functional requirements and architecture of the NGN release 1. ITU-T Y.2111 Recommendation ITU-T Y.2111 (2006), Resource and admission control functions in next generation networks. IE
27、TF RFC 3814 IETF RFC 3814 (2004), Multiprotocol Label Switching (MPLS) Forwarding Equivalence Class To Next Hop Label Forwarding Entry (FEC-To-NHLFE) Management Information Base (MIB). 3 Definitions The definitions for the terms used in this Recommendation can be found in ITU-T Y.2111. 4 Abbreviatio
28、ns and acronyms This Recommendation uses the following abbreviations. CAC Connection Admission Control E-LSP EXP inferred LSP FEC Forwarding Equivalence Class FTN FEC-To-NHLFE LER Label Edge Router 2 Rec. ITU-T Y.2175 (11/2008) L-LSP Label inferred LSP LSP Label Switching Path LSR Label Switching Ro
29、uter MPLS MultiProtocol Label Switching NHLFE Next Hop Label Forwarding Entry NMS Network Management System OAM Operation, Administration and Maintenance OSS Operations and Support System PD-FE Policy Decision Functional Entity PE-FE Policy Enforcement Functional Entity QoS Quality of Service RACF R
30、esource and Admission Control Functions RIR Resource Initiation Request TE Traffic Engineering TRC-FE Transport Resource Control Functional Entity TRE-FE Transport Resource Enforcement Functional Entity 5 Centralized RACF architecture Reference point RnRc + RnLERCore RACFLERLERLSRLSRLSRLSRLERTRC-FEA
31、ccess RACFService Control FunctionsNACFAccess Network Core NetworkTRC-FELER: Label Edge Router . The transport node has a relationship with the TRC-FE through Rc and Rn reference point.LSR: Label Switching Router . The transport node is part of MPLS core and has a relationship with the TRC-FE throug
32、h the Rn reference point.TRC-FE: Transport Resource Control Functional Entity. This functional element is part of RACF and is centralized.Figure 1 Centralized RACF architecture Rec. ITU-T Y.2175 (11/2008) 3 Figure 1 describes the centralized RACF architecture for the MPLS-based core network. In the
33、architecture, the access network aggregates the data traffic to the core network. The edge nodes of the core network are connected by pre-provisioned LSPs or TE tunnels. At the edge of the core network, the traffic of multiple flows is aggregated into these pre-provisioned LSPs or tunnels. This Reco
34、mmendation considers the case where the RACF of the MPLS network is centralized. The RACF is comprised of a TRC-FE and a PD-FE. In the centralized architecture, the TRC-FE is located in the centralized control entity, monitors the resource status of the network, and adjusts the bandwidth of the LSP.
35、 The LER and LSR are responsible for the role of the TRE-FE in enforcing aggregate bandwidth. The TRC-FE interacts with the LERs through the Rc and Rn reference points and also interacts with the LSR through the Rn reference point. The TRC-FE collects the network resource and status information thro
36、ugh the Rc reference point to the LER. The TRC-FE adjusts the LSP bandwidth through the Rn reference point to the LER and LSR. The Rn reference point is also used for the TRC-FE to update the flow to the LSP mapping in the LER. The admission decision is made by the RACF based on the available bandwi
37、dth of the pre-provisioned LSP tunnels in the core. The RACF determines the mapping of the individual flow to the pre-provisioned LSP. The QoS can be monitored at the LSP level. The RACF monitors the network resource in the LSP and adjusts the bandwidth of the established LSP. The number of admissio
38、n requests in the core network is high. The resource checking between the PD-FE and the TRC-FE for connection admission control needs to process the high number of resource requests. In the centralized architecture, by placing the TRC-FE and PD-FE in the centralized entity, the call level admission
39、decision (especially for the resource check between the TRC-FE and the PD-FE) can be done efficiently. An example of an end-to-end control scenario in the centralized architecture is described in Appendix I. 6 Required functions ITU-T Y.2111 defines the control of transport independent aspects. This
40、 Recommendation describes the aspects that are specific to the MPLS transport. The TRC-FE and the TRE-FE are the functional entities responsible for the MPLS-specific resource control. This clause describes the required functions of the two functional entities the TRC-FE and the TRE-FE and the corre
41、sponding reference points Rc and Rn. 6.1 Resizing established LSP It is recommended that the TRC-FE request the LSP resource adjustment based on the resource status of the MPLS network or the rejection ratio of the admission request. The resizing operation does not occur on every admission decision
42、of the PD-FE. It is required that the TRC-FE adjust the bandwidth of an established LSP by (1) changing the bandwidth configuration of the LERs and LSRs or by (2) instructing the ingress LER to initiate path-coupled signalling. In the first case, the TRC-FE instructs the LERs and LSRs along the LSP
43、to modify the bandwidth of the LSP. In the second case, the TRC-FE instructs the ingress LER to initiate the path-coupled signalling e.g., aggregate RSVP-TE b-IETF RFC 4804 and clause 7.2. 6.2 Mapping flow to the LSP It is recommended that the flows be mapped into an LSP tunnel at the edge of the LS
44、P network. Flow-to-LSP mapping is controlled by the TRC-FE. Flow-to-LSP mapping occurs at the ingress LER as defined in IETF RFC 3814. The FTN (forwarding equivalence class to next hop label forwarding entry (FEC-To-NHLFE) table defines the mapping rule from the data flow to the LSP. In the IPv4 cas
45、e, the mapping rule is defined by IP classifier consisting of combination of 5-tuple (source address, destination address, source port, destination port, and protocol) and the DSCP. 4 Rec. ITU-T Y.2175 (11/2008) The TRC-FE maintains the LSP/TE tunnel information. Upon receiving resource request from
46、 the PD-FE, the TRC-FE selects the right LSP/TE tunnel that can best provide the desired priority and QoS, instructs the TRE-FE updating the FTN table to map the media flow into that LSP/TE tunnel, and sends the response to the PD-FE with success. Mapping of flow to the LSP is enforced by the TRE-FE
47、 at the ingress LER based on the FTN table which is created and maintained in the TRE-FE under the instruction of the TRC-FE. The TRC-FE controls the FTN table at the ingress LER. The mapping control operation does not have to occur on every PD-FE admission decision. A mapping rule can be pre-provis
48、ioned based on network policy or set up dynamically per resource request. 6.3 Resource and topology monitoring of the MPLS network The bandwidth adjustment of the established LSP occurs based on the resource status of the network. The resource status is recommended to be obtained from the management
49、 system or from embedded OAM capability of the transport equipment. The TRC-FE is required to collect the basic performance parameters per LSP i.e., number of sent packets, number of bytes sent, and number of dropped packets for an LSP tunnel. It is recommended that the TRC-FE collect the topology derived from the hop list i.e., the LSP route hop b-IETF RFC 3812. It is optional that the TRC-FE monitor the network status using the MPLS OAM functions defined in b-ITU-T Y.1711. The OAM function provides the connectivity veri
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