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

CHAPTER 9

THE TANDEM-CROSSPOINT SWITCH

The HOL blocking problem in input-buffered switches can be eliminated by using the parallel-switch technique, where one switch fabric consists of multiple switch planes. The switch fabric operates at the line rate, and thus the arbitration timing is relaxed compared with the internal speedup switch architecture.

However, the parallel-switch architecture suffers from a cell-out-of-sequence problem at output ports. A resequencing circuit needs to be implemented at the output ports to ensure that cells are delivered in order. For example, timestamps can be carried in the cell headers and stored at output buffers.

A tandem-crosspoint (TDXP) switch [11, 12] developed by NTT has logically multiple crossbar switch planes. These switch planes are connected in tandem at every crosspoint. The TDXP switch achieves a high throughput without increasing the internal speed of switch fabric. It also preserves the cell-sequence order.

The remainder of this chapter is as follows. Section 9.1 briefly reviews basic input and output buffered switch architectures. Section 9.2 presents the TDXP switch architecture. Section 9.3 shows its performance. Throughout this chapter, we assume that the switch size is N × N (N input ports and N output ports). Input and output ...