The Architecture and Design of the Network

Part 1 Architectural Principles

Geoff Huston, July 1994

Architectural Principles

      - Assumption:
            Implementation of Public Infrastructure on a national scope
            Design issues will vary for commercial and/or corporate networks

There are of course a number of assumptions made within this presentation to bring the content down to finite size, but the principle assumption made here is that the subject area is that of the architecture and design of public network infrastructure which is national in scope.

Explicitly this presentation does not consider the issues in the architecture and design of corporate network service structures, or other non-public services which may be confined to a particular set of objectives.

It should also be noted that this presentation is not a comprehensive one, in so far as it is intended to cover aspects of architecture, design, operation and public policy areas, without explicitly covering related issues such as Internet infrastructure administration, Internet service structures, service offerings and access technology options, to name but a few of such additional areas of consideration. Within the scope of the ISOC Workshop for developing countries these topics were covered by other presenters within the National Network Management track, and by presenters in the other three workshop tracks.

Architectural Principles

      - Simplicity
      - Functional Adequacy
      - Affordability
      - Implementable today
      - Designed to meet actual end client requirements
      - Uses (and develops) local expertise
      - Where feasible uses locally available components

When considering the architectural aspects of a public national network infrastructure the major considerations are the following:

In terms of network architecture the most critical aspect is that of simplicity of structure. Simplicity is a key principle in so far as it effectively imposes the minimum of constraints, and allows each client of the service to readily interface their infrastructure and service environment into a national environment, and allows the national network the capability to adapt to changing technologies and changing service requirements that may be imposed by the client base in the future.
The second critical architectural principle is that of functional adequacy. This implies that the architecture should meet the basic client service objectives without imposing additional qualifications or constraints.
Affordability is perhaps implied within any such architecture, but it is explicitly stated here simply to note that any network architecture which is not affordable within available resources will never be implemented.
Technical feasibility is also a principle which is effectively implied within any architecture, but again it perhaps worth explicitly noting within the set of architectural principles that if a network architecture relies on technologies which cannot be purchased and deployed today, then the architecture cannot be used as the basis of subsequent implementation engineering, and accordingly such an architecture specification is functionally irrelevant for any other purpose than a vision statement of potential future service objectives.
Networks are service structures, and the architecture of a network should accordingly be designed to meet actual end client needs, rather than impose additional constraints and conditions on the client base. This implies that a network should provide service to the end user application services and protocols which are being deployed by the user base, rather than implement a service environment which forces clients to deploy new services and protocols.
Critically within the area of public national network infrastructure provision, it is also highly desirable that any such program uses, and fosters the further development of national expertise and skills within the adopted service technology domain. A "black box" approach to this area results in a service operation which has significant negative impact on issues of quality, integrity and future viability of the service.
To assist in this development of local capability and expertise the network should be able to use locally available components and services wherever feasible.

Architectural Principles

      - Simplicity is the key attribute of any network architecture
      - Diverse, complex and uncoordinated architectures result in very
            high implementation and operational costs, and are resistant
            to subsequent incremental engineering.

The principle of simplicity is perhaps the key attribute of any such national service architecture. The issue here is that by its very nature a national public infrastructure will be cast in the role of providing services to a diverse and distributed client base. Architectures which are effectively developed in an environment of ad hoc engineering, and architectures which are in themselves diverse and complex present the implementation engineer and the operational service group with a set of complex problems which are typically very expensive to address. In addition such complex architectures often exhibit meta-stability, such that subsequent incremental engineering efforts intended to enhance the service may prove either highly expensive, or at times impossible, to undertake.

Simple uniform architectures for a national service may prove cumbersome in terms of obtaining the initial political consensus that enables the project to proceed, in so far as in specifying a uniform simple service structure the sum of the client requirements may have to be "factored" in some fashion in order to arrive at a common denominator of requirements. However this initial effort will result in a network which is far more robust, scalable, useful, and efficient to operate.

Introduction

1. Architectural Principles

2. The Design of the Network

3. Engineering the Network - The Client Interface

4. Engineering the Network - External Peering

5. Engineering the Network - Infrastructure

6. Implementing the Network

7. The Operational Environment

8. The Policy Environment

GH, July 1994