Switch/Router Architectures

5Architectures with Bus-Based Switch Fabrics: Case Study—Decnis 500/600 Multiprotocol Bridge/Router

5.1 Introduction

The DEC Network Integration Server 500 and 600 (DECNIS 500/600), developed by Digital Equipment Corporation (also known as DEC or Digital), are examples of the earlier first-generation switch/routers that integrated (multiprotocol) Layer 3 forwarding (routing), Layer 2 forwarding (bridging), and network gateway functions on a single platform [BRYAN93, COBBGR93]. These devices offered multilayer switching over a number of LAN and WAN interface types available at that time.

The DECNIS 500/600 was developed in the early 1990s during the era of multiprotocol networking (IP, IPX, AppleTalk, FDDI, X.25, etc.) and when switches and routers were mostly implemented in software. The DECNIS 500/600 was designed to be flexible enough to support a wide range of Layer 2 and 3 functionalities while offering high forwarding performance. This chapter describes the architecture and implementation of the DECNIS 500/600 switch/route along with the main ideas that influenced the design of this family of switch/routers.

To achieve high packet forwarding performance, the DECNIS 500/600 employed a centralized forwarding engine assisted by distributed forwarding algorithms and buffer management mechanisms implemented on the line cards. This method of centralized forwarding, where only packet headers are sent to the centralized forwarding engine, and actual packet forwarding performed ...