 serdes modules that serialize data for transfer over the backplane and deserialize it for the line cards. Many backplane products are currently encoding the high-speed serial links using a coding scheme originally developed by IBM, which is known as 8b/10b coding. The 8b/10b coding technique is very robust for error resilience and link reliability. As a result, it is also used in the basis of the Fibre Channel used in storage area networks (SANs) and other media such as the ubiquitous switched Ethernet. However, it suffers from a significant degree of transmission inefficiency since only 80 percent of the available bandwidth is utilized for actual data transfer. The rest is eaten up by the redundancy of the code. This weakness has pushed many backplane manufacturers to design their own proprietary coding methods to improve the use of their backplane's bandwidth. The design of high-speed backplanes remains a tricky engagement and consequently manufac- turers usually go to extreme lengths to acquire, compile, and present to their customers simulation runs that can confirm and prove signal integrity and actual data delivery results. They also provide ample application engineering help in order to help their customers with the development of high- performance products, which are necessarily dependent on precise PCB trace lengths, correct place- ment and routing, and SO on. THE SCALABILITY OF SWITCH FABRICS The concept of scalability in switch fabrics can affect multiple aspects of the design. The problem of scaling is usually three dimensional based on the following: Varying the number of ports. Varying the speed of ports. Varying the type of ports (such as protocols). Note that the different types of traffic impose different buffering and scheduling constraints on the data traffic produced by line cards for the switch fabric. More specifically, the following is expected in a multiservice switch/MSR: ATM traffic requires deep buffering and extensive scheduling capabilities from the switch fabric. TDM traffic needs t