ISO 9542:1988 情報処理システム—システム間の電気通信および情報交換—接続レスモードネットワークサービスを提供するためのプロトコル（ISO 8473）と組み合わせて使用​​するためのエンドシステムから中間システムへのルーティング交換プロトコル | ページ 2

Foreword

ISO (the International Organization for Standardization) is a worldwide federation of national standards bodies (ISO member bodies). The work of preparing International Standards is normally carried out through ISO technical committees. Each member body interested in a subject for which a technical committee has been established has the right to be represented on that committee. International organizations, governmental and non-governmental, in liaison with ISO, also take part in the work. ISO collaborates closely with the International Electrotechnical Commission (IEC) on all matters of electrotechnical standardization.

Draft International Standards adopted by the technical committees are circulated to the member bodies for approval before their acceptance as International Standards by the ISO Council. They are approved in accordance with ISO procedures requiring at least 75 % approval by the member bodies voting.

International Standard ISO 9542 was prepared by Technical Committee ISO/TC 97, Information processing systems.

Users should note that all International Standards undergo revision from time to time and that any reference made herein to any other International Standard implies its latest edition, unless otherwise stated.

Annex A forms an integral part of this International Standard. Annexes B and C are for information only.

0 Introduction

This International Standard is one of a set of International Standards produced to facilitate the interconnection of open systems. The set of standards covers the services and protocols required to achieve such interconnection.

This International Standard is positioned with respect to other related standards by the layers defined in ISO 7498 and by the structure defined in ISO 8648. In particular, it is a protocol of the Network Layer. This International Standard permits End Systems and Intermediate Systems to exchange configuration and routeing information to facilitate the operation of the routeing and relaying functions of the Network Layer.

The aspects of Network Layer routeing that are concerned with communication between End Systems and Intermediate Systems on the same subnetwork are to a great extent separable from the aspects that are concerned with communication among the Intermediate Systems that connect multiple subnetworks. This protocol addresses only the former aspects. It will be significantly enhanced by the cooperative operation of an additional protocol that provides for the exchange of routeing information among Intermediate Systems, but is useful whether or not such an additional protocol is available.

This International Standard is designed to operate in close conjunction with ISO 8473 and its addenda.

This International Standard provides solutions for the following practical problems.

• a) How do End Systems discover the existence and reachability of Intermediate Systems that can route NPDUs to destinations on subnetworks other than the one(s) to which the End System is directly connected?
• b) How do End Systems discover the existence and reachability of other End Systems on the same subnetwork (when direct examination of the destination NSAP address does not provide information about the destination subnetwork address)?
• c) How do Intermediate Systems discover the existence and reachability of End Systems on each of the subnetworks to which they are directly connected?
• d) How do End Systems decide which Intermediate System to use to forward NPDUs to a particular destination when more than one Intermediate System is accessible?

The protocol assumes that:

• a) routeing to a specified subnetwork point of attachment address (SNPA) on the same subnetwork is carried out satisfactorily by the subnetwork itself, but
• b) the subnetwork is not, however, capable of routeing on a global basis using the NSAP address alone to achieve communication with a requested destination. ¹⁾

In addition, certain protocol functions assume that:

• c) the subnetwork supports broadcast, multicast, or other forms of multi-destination addressing for nway transmission.

The protocol is connectionless, and is designed to:

• • minimize the amount of a priori state information needed by End Systems before they can begin to communicate with other End Systems;
• • minimize the amount of memory needed to store routeing information in end systems; and
• • minimize the computational complexity of End System routeing algorithms.

1 Scope and Field of Application

This International Standard specifies a protocol which is used by Network Layer entities operating ISO 8473 in End Systems and Intermediate Systems (referred to herein as ES and IS respectively) to maintain routeing information. The Protocol herein described relies upon the provision of a connectionless-mode underlying service. ¹⁾

This International Standard specifies:

• a) procedures for the transmission of configuration and routeing information between Network entities residing in End Systems and Network entities residing 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 functional requirements for implementations claiming conformance to this International Standard.

The procedures are defined in terms of:

• a) the interactions between End System and Intermediate System Network entities through the exchange of protocol data units; and
• b) the interactions between a Network entity and an underlying service provider through the exchange of subnetwork service primitives.

This International Standard does not specify any protocol elements or algorithms for facilitating routeing and relaying among Intermediate Systems. Such functions are intentionally beyond the scope of this International Standard.

2 References