TABLE OF CONTENTS Earlier chapters specified that communications software modules use several tables for their operation. One of the functions of control plane software is building tables for data plane operations. This chapter details some of the tables and other data structures typically used in communications systems and discusses the related design aspects. While the term table implies a data structure involving contiguous memory, this chapter uses the term to also signify data structures with multiple entries, each of the same base type.
Tables are used for storing information referenced by the communications system. In a router, a forwarding table is used by the forwarding software/hardware to forward packets. In a frame relay switch, a connection table can provide the switch map from one Permanent Virtual Circuit (PVC) to another. Global configuration and port-related configuration for a device can be stored in tables. The key issues with tables are:
Tables are referenced for both reading and writing. So, both storage and access methods should be optimized for frequent references.
Tables can be stored in different parts of memory depending upon their application. For example, forwarding tables can be located in fast SRAM (Static Random Access Memory), while other tables such as configuration and statistics are stored in slower DRAM (Dynamic Random Access Memory).
Tables can also be organized according to the access method. For example, an IP forwarding table can be organized in the form of a PATRICIA tree. This structure is commonly used to optimize the access of the entries...
