BS 7221:1989

National foreword
Committees responsible
Specification
0 Introduction
1 Scope and field of application
2 References
3 Definitions
4 Abbreviations
5 Network Layer concepts and terminology
6 Organization of the Network Layer
7 Application of the Network Layer Internal
    organization
8 Interconnection scenarios
Tables
1 Correspondence between real world objects and
    abstract elements
2 Summary of interconnection scenarios
Figures
1 "Direct" communication between end systems (without
    an intermediate system)
2 End systems communicating through an intermediate
    system
3 Interconnection of real subnetworks that include
    integral interworking unit functionality
4 Interconnection of real subnetworks by a separate
    interworking unit
5 Relationship between subnetwork service and data
    transmission service
6 Network Layer protocol rules
7 Provision of CO-NS or CL-NS over a single data-link
8 Provision of CO-NS or CL-NS over a single subnetwork
9 Interconnection of subnetworks utilizing a single NL
    protocol to provide the CO-NS or CL-NS over two CO-
    or CL- subnetworks
10 Provision of the CO-NS over two CO- subnetworks
    using hop-by-hop harmonization
11 Provision of the CO-NS over two CL- subnetworks
    using an internetworking protocol approach
12 Provision of the CL-NS over two CL- subnetworks
    using hop-by-hop harmonization
13 Provision of the CL-NS over two CL- subnetworks
    using an internetworking protocol approach
14 Provision of the CL-NS over two CO- subnetworks
    using hop-by-hop harmonization
15 Provision of the CL-NS over two CO- subnetworks
    using an internetworking protocol approach
16 Provision of the CO-NS over two CL- subnetworks
    using hop-by-hop harmonization
17 Provision of the CO-NS over two CL- subnetworks
    using an internetworking protocol approach
18 Provision of the CL-NS over a CL- subnetwork and a
    CO- subnetwork using hop-by-hop harmonization
19 Provision of the CL-NS over a CL- subnetwork and a
    CO- subnetwork using an internetworking protocol
    approach
20 Provision of the CO-NS over a CL- subnetwork and a
    CO- subnetwork using hop-by-hop harmonization
21 Provision of the CO-NS over a CL- subnetwork and a
    CO- subnetwork using an internetworking protocol
    approach

Describes an architectural model of the OSI Network Layer as a framework for OSI Network Layer standardization, allowing incorporation of existing networks within the OSI architecture. Encourages the design of real subnetworks that fully support the OSI Network Service whilst accommodating the participation, of other subnetworks that do not fully support the OSI Network Service. Intended for both design and application of Network Layer protocols, operating between network-entities either in end systems providing the OSI Network Service, or in intermediate systems providing the routing and relay functions.

This International Standard provides an architectural model of the OSI Network Layer as a framework for OSI Network Layer standardization, allowing incorporation of existing networks within the OSI architecture.

This framework encourages the design of real subnetworks that fully support the OSI Network Service whilst accommodating the participation, in the OSI environment, of other subnetworks that do not fully support the OSI Network Service.

This International Standard is intended for use both in the design and application of Network Layer protocols, operating between network-entities either in end systems providing the OSI Network Service, or in intermediate systems providing the routeing and relay functions.

It shall be used to

1. provide a common set of concepts and terminology for use in Network Layer standards (such standards shall reference this International Standard);
2. analyse Network Layer functionality and classify Network Layer protocols;
3. specify how “real networks” should be used in supporting or providing the OSI Network Service, in particular, in circumstances where multiple “real networks” are to be interconnected and used.

The organization defined herein does not address Network Layer management; in particular it is not concerned with the relationships among Network Layer entities which may be required for Network Layer management purposes. In addition, this International Standard does not specify the operational requirements for relay functions in intermediate systems, nor address how specific combinations of permitted functions might be practically and efficiently utilized.