1、INTERNATIONAL STANDARD INTERNATIONAL ORGANIZATION FOR STANDARDIZATION ORGANISATION INTERNATIONALE DE NORMALISATION MEX/JYHAPOAHAR OPrAHM3AUMR Il0 CTAHAAPTMSAUMM Information processing systems - Telecommunications and information exchange between systems - End system to Intermediate system routeing e
2、xchange protocol for use in conjunction with the Protocol for providing the connectionless-mode network service (IS0 8473) Systhes de traitement de Iinformation - Tdldinformatique - Protocole de routage dun systhe dextr6mitd B un syst o minimize the amount of memory needed to store routeing informat
3、ion in end systems; and o minimize the computational complexity of End Sys- tem routeing algorithms. 1 Scope and Field of Application This International Standard specifies a protocol which is med by Network Layer entities operating IS08473 in End Systems and Intermediate Systems (referred to herein
4、as ES and IS respectively) to maintain route- ing information. The Protocol herein described relies upon the provision of a connectionless-mode underlying service.) This International Standard specifies: a) procedures for the transmission of configuration and ronteing information between Network ent
5、ities residing in End Systems and Network entities re- siding in Intermediate Systems; b) the encoding of the protocol data units used for the transmission of the configuration and routeing information; c) procedures for the correct interpretation of protocol control information; and d) the function
6、al requirements for implementations claiming conformance to this International Stan- dard. The procedures are defined in terms of: a) the interactions between End System and Inter- mediate System Network entities through the ex- change of protocol data units; and b) the interactions between a Networ
7、k entity and an underlying service provider through the exchange of subnetwork service primitives. This International Standard does not specify any pro- tocol elements or algorithms for facilitating routeing and relaying among Intermediate Systems. Such functions are intentionally beyond the scope o
8、f this International Standard. 2 References ISO7498, Information processing systems - Open systems interconnection - Basic reference model. IS0 74D8lAdd.1, Informa.tion processing systems - Open systems interconnection - Ba.sic reference model. ADDENDUM 1: Connectionless-mode tra.nsmission. IS0 7498
9、lAdd.4, Information processing systems - Open systems interconnection - Basic reference model. ADDENDUM 4: OSI Management Framework. IS0 8208, Information processing systems - Da.ta. communica.tions - X.25 Packet Level Protocol for Dada. Terminal Equipment. IS0 8348, Information processing systems -
10、 Da.ta. communications - Network Service Definition. IS0 83481Add.1, Information processing systems - Data communica.tions - Network Service Definilion ADDENDUM 1: Connectionless-mode Tra.nsmission. IS0 8348lAdd.2, Informa.tion processing systems - Data communications - Network Service Definition. A
11、DDENDUM 2: Network La.yer Addressing. IS0 8473, Informa.tion processing systems - Da.t.a. communications - Protocol for providing th.e connec- tionless-mode Network Service. IS0 8648, Information processing systems - Open- Systems Interconnection - Interna.1 orga.niza.tion. of Ch.e Network layer. IS
12、0 8802, Information processing systems - Da.ta. communications - Local Area Networks. CCITT X.25, Interface Between Data. Termina.1 Equ.ip- ment (DTE and Data Circuit Termina.ting Equ.ipment (DCE for Terminals Operating in the Pa.cket Mode a.nd Connected to Public Data Networks by Dedicated Cir- cui
13、t, 1985. 1) See Clause 8 of IS0 8473 for the mechanisms necessary to re- olize this service on subnetworks based on IS0 8208 and IS0 8802. 2 * Section one: .General 3 Definitions 3.1 Reference Model Definitions IS0 9542 makes me of the following terms defined in IS0 i498. a) Network layer b) Network
14、 service access point c) Network service access point address d) Network entity e) routeing f) Net.work protocol g) Network relay h) Network protocol data unit 3.2 Network Layer Architecture Defini- tions IS0 9542 makes use of the following terms defined in IS0 8G48. a) Subnetwork b) End System c) I
15、ntermediate System d) Subnetwork Service e) Subnetwork Dependent Convergence Function 3.3 Network Layer Addressing Defini- tions IS0 9542 makes use of the following terms defined in IS0 8348/Add.2. a) Subnetwork address b) Subnetwork point of attachment c) Network Protocol Address Information d) Net
16、work Entity Title 3.4 Local Area Network Definitions IS0 9542 makes use of the following terms defined in IS0 8802. a) multicast address b) broadcast medium 3.5 Additional Definitions For the purposes of this International Standard, the fol- lowing definition applies. 3.6.1 Configuration: The collec
17、tion of End and In- termediate Systems attached to a single subnetwork, defined in terms of the system types, NSAP addresses present, Network Entities present, and the correspon- dence between systems and SNPA addresses. 4 Symbols and Abbreviations 4.1 Data Units PDU Protocol Data Unit SNSDU Subnetw
18、ork Service Data Unit NPDU Network Protocol Data Unit SNPDU Subnetwork Protocol Data Unit 4.2 Protocol Data Units ESH PDU End System Hello Protocol Data Unit. ISH PDU Intermediate System Hello Protocol Data RD PDU Redirect Protocol Dah Unit. Unit 4.3 Protocol Data Unit Fields NPlD Network Layer Prot
19、ocol Identifier LI Length Indicator VIP Version/Protocol Identifier Extension TP Type CS Checksum N ETL Network Entity Title Length Indicator N ET Network Entity Title DA L Destination Address Length Indicator DA Destination Address SAL Source Address Length Indicator SA Source Address BSNPAL SN Add
20、ress Length Indicator of bet.t.er BSNPA SN Address of better route to destinat.ion HT Holding Time route to destination 4.4 Parameters CT Configuration Timer RT Redirect Timer ESCT Suggested End System Configuration Ti- mer 4.5 Addresses NSAP Network Service Access Point SNPA Subnetwork Point of Att
21、achment N PAI Network Protocol Address Inform a t Ion 3 IS0 9542 : 1988 (E) 4,6 Miscellaneous ES End system . IS Intermediate system LAN Local area. network PICS Protocol Implementation Conformance QoS Quality of service SN Subnetwork Statement 5 Overview of the Protocol 5,l Information Provided by
22、the Proto- col This International Standard provides two types of infor- mation to Network entities which support its operation: o Configuration information, and o Route redirection information Configuration information permits End Systems to discover the existence and reachability of Intermedi- ate
23、Systems and permits Intermediate Systems to dis- cover the existence and reachability of End Systems. This information allows ESs and ISS attached to the same subnetwork to dynamically discover each others existence and availability, thus eliminating the need for manual intervention at ESs and ISS t
24、o establish the identity of Network entities that can be used to route NPDUs. Configuration information also permits End Systems to obtain information about each other in the absence of an available Intermediate System. NOTE - The term “configuration information” is not intended in the broad sense o
25、f configura- tion as used in the context of OS1 system man- agement. Rather, only the functions specifically defined herein are intended, Route redirection information allows Intermedi- ate Systems to inform End Systems of (potentially) bet- ter paths to use when forwarding NPDUs to a particular des
26、tination. A better path could either be another IS on the same subnetwork as the ES, or the destination ES itself, if it is on the same subnetwork as the source ES. Allowing the ISS to inform the ESs of routes minimizes the compIexitp of routeing decisions in End Systems and improves performance bec
27、ause .the ESs may make use of the better IS or local subnetwork access for subsequent transmissions. 4 5.2 Addressing The Source Address and Destination Address pa- rameters referred to in this International Standard are OS1 Network Service Access Point Addresses. The syn- tax and semantics of an OS
28、1 Network Service Access Point Address are described in IS0 8348jAdd.2. 5.3 Underlying Service Assumed by the Protocol The underlying service required to support this Inter- national Standard is defined by the primitives in table 1. NOTE - These service primitives are used to de- scribe the abstract
29、 interface which exists between the protocol machine and an underlying real snb- network or a subnetwork Dependent Convergence Function which operates over a real subnetwork or real data link to provide the required underlying service. 1) 6.3.1 Subnetwork Addresses The source and destination address
30、es specify the points of attachment to a public or private subnettvork(s) in- volved in the transmission (known as Subnetwork Points of Attachment, or SNPAs). Subnetwork addresses are defined in the service definition of each individual sub- network. This International Standard is designed to take a
31、d- vantage of subnetworks which support broa.dcasf., m.u.ll.i- CQ., or other forms of multi-destination addressing for n-way transmission. It is assumed that the.SN-Destina- tion-Address parameter may take on one of the following multi-destination addresses in addition to a normal sin- gle destinati
32、on address: o All End System Network entities o All Intermediate System Network entities Where a real subnetwork does not inherently sup- port broadcast or other forms of transmission to multi- destination addresses, a convergence function may be used to provide n-way transmission to these multi- de
33、stination addresses. When the SN-Destination-Address on the SN-UNIT- DATA-Request is a multi-destination address, the SN-Destination-Address parameter in the corresponding SN-UNITDATA.lndication shall be the same multi-des- tination address. Usee Clause 8 of IS08473 for the mechanisms necessary to re- alize this service on subnetworks based on IS0 8208 and IS0 8802.
