1、INTERNATIONAL TELECOMMUNICATION UNIONITU-T Y.1231TELECOMMUNICATIONSTANDARDIZATION SECTOROF ITU(11/2000)SERIES Y: GLOBAL INFORMATION INFRASTRUCTUREAND INTERNET PROTOCOL ASPECTSInternet protocol aspects Architecture, access, networkcapabilities and resource managementIP access network architectureITU-
2、T Recommendation Y.1231(Formerly CCITT Recommendation)ITU-T Y-SERIES RECOMMENDATIONSGLOBAL INFORMATION INFRASTRUCTURE AND INTERNET PROTOCOL ASPECTSGLOBAL INFORMATION INFRASTRUCTUREGeneral Y.100Y.199Services, applications and middleware Y.200Y.299Network aspects Y.300Y.399Interfaces and protocols Y.4
3、00Y.499Numbering, addressing and naming Y.500Y.599Operation, administration and maintenance Y.600Y.699Security Y.700Y.799Performances Y.800Y.899INTERNET PROTOCOL ASPECTSGeneral Y.1000Y.1099Services and applications Y.1100Y.1199Architecture, access, network capabilities and resource management Y.1200
4、Y.1299Transport Y.1300Y.1399Interworking Y.1400Y.1499Quality of service and network performance Y.1500Y.1599Signalling Y.1600Y.1699Operation, administration and maintenance Y.1700Y.1799Charging Y.1800Y.1899For further details, please refer to the list of ITU-T Recommendations.ITU-T Y.1231 (11/2000)
5、iITU-T Recommendation Y.1231IP access network architectureSummaryThis Recommendation provides the definitions of terminology regarding IP access, and thehigh-level IP network architecture and models for the IP services. It describes the access types andinterfaces to be supported by the IP access net
6、work, the IP access network capabilities andrequirements, and the IP access network functional models and possible arrangements.SourceITU-T Recommendation Y.1231 was prepared by ITU-T Study Group 13 (2001-2004) and approvedunder the WTSA Resolution 1 procedure on 24 November 2000.ii ITU-T Y.1231 (11
7、/2000)FOREWORDThe International Telecommunication Union (ITU) is the United Nations specialized agency in the field oftelecommunications. The ITU Telecommunication Standardization Sector (ITU-T) is a permanent organ ofITU. ITU-T is responsible for studying technical, operating and tariff questions a
8、nd issuing Recommendationson them with a view to standardizing telecommunications 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
9、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 standards areprepared on a collaborative basis with ISO and IEC.NOTEIn this Recommendation, the expression “
10、Administration“ is used for conciseness to indicate both atelecommunication administration and a recognized operating agency.INTELLECTUAL PROPERTY RIGHTSITU draws attention to the possibility that the practice or implementation of this Recommendation mayinvolve the use of a claimed Intellectual Prop
11、erty Right. ITU takes no position concerning the evidence,validity or applicability of claimed Intellectual Property Rights, whether asserted by ITU members or othersoutside of the Recommendation development process.As of the date of approval of this Recommendation, ITU had not received notice of in
12、tellectual property,protected by patents, which may be required to implement this Recommendation. However, implementors arecautioned that this may not represent the latest information and are therefore strongly urged to consult theTSB patent database. ITU 2001All rights reserved. No part of this pub
13、lication may be reproduced or utilized in any form or by any means,electronic or mechanical, including photocopying and microfilm, without permission in writing from ITU.ITU-T Y.1231 (11/2000) iiiCONTENTSPage1 Scope 12 References 12.1 Normative references 12.2 Informative references 23 Definitions a
14、nd abbreviations. 23.1 Definitions 23.2 Abbreviations . 24 Architectural model of IP access networks 44.1 General network architecture of IP network. 44.2 IP access network reference model 55 Examples of functional models of IP Access Network 65.1 Use of PPP 65.1.1 PPP tunnelling aggregation . 75.1.
15、2 PPP terminated aggregation 85.2 Use of Ethernet . 96 Examples of access types and interfaces in IP access network 107 Examples of functional requirements for IP Access 10Appendix I Examples of IP mapping mechanisms. 10I.1 IP over PPP over ATM. 10I.2 IP over ATM. 11I.3 IP over Frame Relay. 11I.4 IP
16、 over PPP over PHY 11I.5 IP over Ethernet 12I.6 IP over PPP over Ethernet 12Appendix II An example of functional model of CATV access. 13ITU-T Y.1231 (11/2000) 1ITU-T Recommendation Y.1231IP access network architecture1ScopeThis Recommendation defines the functional IP Access Network architecture an
17、d the functions andrequirements above the transport access functions defined in ITU-T Y.1001. The functionalrequirements for the Access Network Transport are defined for the handling and transport of digitalbearer signals defined in ITU-T G.902.This Recommendation describes: the definitions of termi
18、nology regarding IP access; the high-level IP network architecture and models for the IP services; the access types and interfaces to be supported by the IP access network; the IP access network capabilities and requirements; and the IP access network functional models and possible arrangements.The
19、functional view of IP access network is independent of the access network transport functionsdescribed in ITU-T Y.1001.2 ReferencesThe following ITU-T Recommendations and other references contain provisions which, throughreferences in this text, constitute provisions of this Recommendation. At the t
20、ime of publication, theeditions indicated were valid. All Recommendations and other references are subject to revision; allusers of this Recommendation are therefore encouraged to investigate the possibility of applying themost recent edition of the Recommendations and other references listed below.
21、 A list of the currentlyvalid ITU-T Recommendations is regularly published.NOTE A reference to a document within this Recommendation does not give it, as a stand-alone document,the status of a Recommendation.2.1 Normative references1 ITU-T Q.922 (1992), ISDN data link layer specification for frame m
22、ode bearer services.2 ITU-T I.363.5 (1996), B-ISDN ATM Adaptation Layer specification: Type 5 AAL.3 ITU-T I.414 (1997), Overview of Recommendations on Layer 1 for ISDN and B-ISDNcustomer accesses.4 ITU-T G.902 (1995), Framework Recommendation on functional Access Networks (AN) Architecture and funct
23、ions, access types, management and service node aspects.5 ITU-T Y.1001 (2000), IP framework A framework of convergence of telecommunicationsnetwork and IP network technologies.6 ITU-T Y.1401 (2000), General requirements for interworking with Internet Protocol (IP)-based networks.7 ISO/IEC 8802-2:199
24、8, Information technology Telecommunications and informationexchange between systems Local and metropolitan area networks Specificrequirements Part 2: Logical link control.2 ITU-T Y.1231 (11/2000)2.2 Informative references8 IEEE Std 802.2 (1998), Logical link control (802.2).9 IEEE Std 802.3 (1998),
25、 CSMA/CD access method (802.3).10 Data-Over-Cable Service Interface Specifications, Cable Modem to Customer PremiseEquipment Interface Specification, SP-CMCI-I03-991115, Cable Television Laboratories,Inc.11 IETF RFC 894 (1984), A Standard for the Transmission of IP Datagrams over EthernetNetworks.12
26、 IETF RFC 1042 (1988), A Standard for the Transmission of IP Datagrams over IEEE 802Networks.13 IETF RFC 1334 (1992), Password Authentication Protocols.14 IETF RFC 2684 (1999), Multiprotocol Encapsulation over ATM Adaptation Layer 5.15 IETF RFC 1661 (1994), The Point-to-Point Protocol (PPP).16 IETF
27、RFC 1662 (1994), PPP in HDLC-like Framing.17 IETF RFC 1994 (1996), PPP Challenge Handshake Authentication Protocol (CHAP).18 IETF RFC 2138 (1997), Remote Authentication Dial In User Services (RADIUS).19 IETF RFC 2225 (1998), Classical IP and ARP over ATM.20 IETF RFC 2364 (1998), PPP over AAL5.21 IET
28、F RFC 2427 (1998), Multiprotocol Interconnect over Frame Relay.22 IETF RFC 2661 (1999), Layer Two Tunnelling Protocol (L2TP).23 IETF RFC 2516 (1999), A Method for Transmitting PPP Over Ethernet (PPPoE).3 Definitions and abbreviations3.1 DefinitionsThis Recommendation defines the following terms:3.1.
29、1 IP access network: An implementation comprising network entities to provide the requiredaccess capabilities between an “IP user“ and an “IP service provider“ for the provision of IP services.“IP user“ and “IP service provider“ are logical entities which terminate the IP layer and/or IP relatedfunc
30、tions, and may also include lower layer functions, and may also include lower layer functions.3.1.2 IP core network: IP service providers network, including one or more IP service providers.3.2 AbbreviationsThis Recommendation uses the following abbreviations:AAA Authentication, Authorization and Ac
31、countingAF Access FunctionARP Address Resolution ProtocolATM Asynchronous Transfer ModeCHAP Challenge Handshake Authentication ProtocolCMCI Cable Modem to CPE InterfaceITU-T Y.1231 (11/2000) 3CMTS Cable Modem Termination SystemCPE Customer Premises EquipmentCPN Customer Premises NetworkDHCP Dynamic
32、Host Configuration ProtocolDIX Digital Intel XeroxDOCSIS Data-Over-Cable Service Interface SpecificationsEF Edge FunctionFR Frame RelayHFC Hybrid Fibre and CoaxIP Internet ProtocolIPSEC Internet Protocol SecurityISDN Integrated Services Digital NetworkIWF InterWorking FunctionLAN Local Area NetworkL
33、LC Logical Link ControlL2TP Layer 2 Tunnelling ProtocolMAC Medium Access ControlMPLS Multiprotocol Label SwitchingNAT Network Address TranslationNSI Network Side InterfaceNT Network TerminationPAP Password Authentication ProtocolPC Personal ComputerPCI Peripheral Component InterfacePHY Physical Laye
34、rPON Passive Optical NetworkPPP Point-to-Point ProtocolPSTN Public Switched Telephone NetworkRADIUS Remote Access Dial In User ServicesRFI Radio Frequency InterfaceRP Reference PointSNMP Simple Network Management ProtocolTE Terminal EquipmentTEL TelephoneTFTP Trivial File Transfer ProtocolUDP User D
35、atagram ProtocolVCI Virtual Channel Identifier4 ITU-T Y.1231 (11/2000)VPI Virtual Path IdentifierWAN Wide Area Network4 Architectural model of IP access networks4.1 General network architecture of IP networkFigure 1a shows a general network architecture of IP network. In Figure 1a, the lines between
36、various rectangles and ellipses represent connections that are bidirectional, that may be asymmetricalin bit rate, and that may be of differing media in the two directions. The reference points (RP)illustrated are logical separation between the functions and may not correspond to physical interfaces
37、in certain network implementations. In certain network implementations, access and core networksmay not be separable.T1317460-00TETEPCTETEPCTELRP RP RP RPCPNCPNTELIP AccessNetworkIP CoreNetworkIP AccessNetworkFigure 1a/Y.1231 General network architecture of IP networkFigure 1b shows an example of re
38、lationship between IP network and PSTN/ISDN. In Figure 1b,some connections and InterWorking Function (IWF) between IP Access/Core network andPSTN/ISDN are shown as an example, but not all PSTN/ISDN connections may be necessary. Adefinition of IWF is described in ITU-T Y.1401 6.ITU-T Y.1231 (11/2000)
39、 5T1317470-00TETEPCTETEPCTELRP RP RP RPCPNCPNTELIWFTETEPCTELCPNIWFIWFNTIP AccessNetworkIP CoreNetworkIP AccessNetworkPSTN/ISDNFigure 1b/Y.1231 An example of relationship between IP network and PSTN/ISDN4.2 IP access network reference modelFigure 2 shows an example of IP access network reference mode
40、l. In some cases, the IP accessFunction (IP-AF) can be distributed within the IP Access Network. Examples of the IP-AF aredescribed in clause 7.The functional requirements for the Access Network Transport are defined for the handling andtransport of digital bearer signals defined in ITU-T G.902 4.Th
41、e functional view of IP access network is independent of the access network transport functionsdescribed in ITU-T Y.1001 5.T1317480-00RP RPCPNRPAccess Network Transport FunctionIP Access FunctionIP Access Network System Managementfor management interfaceIP Access NetworkIP Core NetworkIP Service Pro
42、vider 3IP Service Provider 2IP Service Provider 1Figure 2/Y.1231 IP Access Network architecture example6 ITU-T Y.1231 (11/2000)5 Examples of functional models of IP Access Network5.1 Use of PPPIn this clause, PPP is shown as an example for protocol used to carry IP over access network. PPP isa widel
43、y used protocol for dial-up IP access and ADSL access. PPP termination point in the networkside interacts with AAA (Authentication, Authorization and Accounting) server (e.g. RADIUSserver) and provides AAA functions.Figures 3a and 3b provide the following two options regarding PPP termination point
44、in the networkside:1) PPP tunnelling aggregation (PPP is terminated by IP service provider); and2) PPP terminated aggregation (PPP is terminated by the IP access function).T1317490-00IP User IP Access Function IP Service ProviderPPPTerminationFunctionPPPTerminationFunctionAAAClientFunctionAAAServerF
45、unctionFigure 3a/Y.1231 PPP tunnelling aggregationT1317500-00IP User IP Access FunctionIP Service ProviderPPPPPPAAAClientAAAServerFigure 3b/Y.1231 PPP terminated aggregationITU-T Y.1231 (11/2000) 75.1.1 PPP tunnelling aggregationThis clause gives some examples of protocol stacks for the PPP tunnelli
46、ng aggregation. In this case,“IP user“ directly accesses the “IP service provider“. Several transport systems can be cascadedwithout IP and PPP processing in the access network.Case 1) Layer 2 multiplexing in IP access network (e.g. direct IP access)This is a case that only Layer 2 multiplexing tran
47、sport function such as ATM or FR are supported inIP access network. This functional model is shown in Figure 4.T1317510-00PHY PHY PHYPHYIP Access Function IP Service ProviderIPIPPPPPPPIP UserATM,FR etc.ATM, FRetc.Figure 4/Y.1231 Functional model of Layer 2 multiplexingCase 2) PPP tunnelling (e.g. L2
48、TP 22)This is a case that L2TP function is used in IP access network. This functional model is shown inFigure 5.T1317520-00PHYPHYL2TPPHYL2TPPHYIP Access FunctionIPIPPPPPPPIP User IP Service ProviderIP(Note)ATM, FRetc.ATM, FRetc.IP(Note)NOTE This IP layer provides a transport function between IP acce
49、ss function and IP service provider.Figure 5/Y.1231 Functional model of PPP tunnelling8 ITU-T Y.1231 (11/2000)5.1.2 PPP terminated aggregationThis clause gives some examples of protocol stacks for the PPP terminated aggregation. In this case,PPP is terminated in IP access network.Case 1) IP tunnelling (e.g. IPSEC)This is a case that IP tunnelling is used in IP access network. This functional model is shown inFigure 6.T1317530-00PHYIPSECPHYIP Access FunctionIPIPIP User IP Service Pr
