Broadband Packet Switching Technologies: A Practical Guide to ATM Switches and IP Routers

CHAPTER 2

BASICS OF PACKET SWITCHING

This chapter discusses the basic concepts in designing an ATM switch. An ATM switch has multiple input/output ports, each connecting to another port of an ATM switch or an ATM terminal. An ATM terminal can be a personal computer, a workstation, or any other equipment that has an ATM network interface card (NIC). The physical layer of interconnecting ATM switches or ATM terminals can be SONET (such as OC-3c, OC-12c, OC-48, or OC-192) or others (such as T1 or T3). Physical layer signals are first terminated and cells are extracted for further processing, such as table lookup, buffering, and switching. Cells from different places arrive at the input ports of the ATM switch. They are delivered to different output ports according to their labels, merged with other cell streams, and put into physical transmission frames. Due to the contention of multiple cells from different input ports destined for the same output port simultaneously, some cells must be buffered while the other cells are transmitted to the output ports. Thus, routing cells to the proper output ports and buffering them when they lose contention are the two major functions of an ATM switch.

Traditional telephone networks use circuit switching techniques to establish connections. In the ...