Distributed processing is on top

The need for flexible hardware solutions to process higher-layer applications within IP packets is spurring the use of network processors. As deployments proceed and backplanes push above the 50-Gbit/second range, designers will discover that distributed processing is the preferred method for cost-effective, highly scalable designs in an IP world.

A short history of the technology can be instructive. In the late 1980s, two-port bridges appeared as a means of connecting shared LAN subnets. The bridges used dual network interface functionality with a high-performance CPU engine performing the Layer 2 packetprocessing functions. The CPU performance was adequate and the flexibility of software programming was ideal. But by the early 1990s, multiport bridges called switches were needed to connect the growing number of LAN subnets. Additionally, Ethernet became the dominant Layer 2 LAN protocol, thus solidifying the switching requirements and enabling clever designers to look to ASICs to provide more bandwidth for increasing port counts. The CPU became RISC-based andwas still involved in most data path transactions, providing protocol demultiplexing, higher layer processing and supervisory and control functions.

By the mid-1990s, itwas clear that IP over Ethernet would become the dominant LAN protocol. The race to design switch/routers was on.

Companies began introducing IP switches using ASICs to provide pseudo Layer 3 processing for IP packets on the fast data path. Exception processing for all other packet types used a RISC engine or engines on a much slower data path. Then Internet growth exploded and Fast Ethernet LANs began to overwhelm the corporate backbone. A new Gigabit Ethernet standard was quickly deployed, pushing ATM out of the LAN space. So LAN switch companies had to redesign their L2-L3 boxes for gigabits of bandwidth while ATM switch vendors were redeploying their architectures for IP traffic in the lucrative Internet service provider (ISP) market.

As the end of the decade approached, the higher bandwidth requirements of Gigabit Ethernet in the LAN and OC3/12/48 in the WAN accelerated the move to distributed ASIC-based switching solutions. Unfortunately, these solutions must continually change to support quality of service in the converging world, but they lack the flexibility of the software solutions of the late 1980s.

Market trends

An inter-switch view of switching fundamentals highlights the market trends driving megaswitches. This is where...