TABLE OF CONTENTS Multi-board architectures are needed since a single-processor/single-board system cannot scale to handle a large number of ports or increasing port speeds. While hardware acceleration could be used to address the port speed problem, there is a limit to the amount of board real estate available for high port densities.
Modularity is another reason for multi-board architectures. The customer needs to be able to add or remove ports from the system as his/her requirements change. In this scenario, an enterprise or service provider can purchase a low-end multi-board system with only a few I/O slots populated. Based on his need, the customer can add more cards to the system to expand the system s capacity and capability without having to throw out the original investment. This is the pay as you go philosophy which many equipment vendors use. There are several variations of the multi-board architecture. This chapter focuses on the functional organization and interconnects using a Layer 3 switch/router, also termed the IP Switch (IPS) to illustrate the concepts.
The most common types of cards in a multi-board communications system are the control cards, switch fabric cards and transport cards (often called line cards). Control cards have the following functions:
Running control (e.g., routing protocols such as OSPF and BGP) and management protocols. The messages generated by these protocols are sent out on line card ports.
Building tables using information from control and management protocols for...
