Layer 4 switching is an illusion. You can't do switching without addressing, and there is no addressing at Layer 4. Layer 4 is an end-point function; Layer 3 does the addressing. But application awareness at Layer 4 and up - across your network or in front of your server farms - can solve real business problems.
Layer 4 switching technologies use application information to provide preferential treatment in the switch. This application awareness is very important in achieving two key objectives for users: preferential treatment for certain applications and end users, and server load balancing and improved server application resiliency.
In an ideal world, applications would indicate their requirements using Differentiated Services, Integrated Services or IEEE 802.1p protocols. But most current applications can't do this. Therefore, application awareness is built into intelligent Layer 2 switches at the workgroup level, routing switches at the campus level, and routers and enterprise network switches at the WAN-edge level.
Server load balancing is less an end-to-end network function than an end-point optimisation function, which again requires application awareness. To this end, a specialised class of products referred to as server switches, or server load balancers, has emerged. These products provide three levels of functionality, all geared toward choosing the best available server to handle client requests.
The simplest form of functionality provides balancing and redundancy on a local basis. The next level adds content awareness, allowing a customer query to be handled differently from a customer order. The third level extends the functions of the previous two levels across geographically dispersed servers and redirects traffic based on server proximity. Server switches require a high degree of customisability at layers 4 to 7 because the possibilities are unlimited.
This is just the tip of the iceberg. Under Nortel Networks Unified Networks vision, we see the convergence of data and telephony enabling a whole new range of applications. Delivering preferential treatment through application-aware networking across the enterprise not only meets the needs of data applications, but also enables new unified applications, such as packet telephony and interactive multimedia. The future for server switches is even more exciting, as they become an element of Internet-enabled call centres (or telephony-enabled Web centres) that blend all kinds of traffic of a company's choosing to enhance customer care, broaden markets and grow business.
So next time a vendor tries to sell you a Layer 4 switch, ignore the hype and challenge him. You have real business problems to solve.
Rybczynski is director of strategic marketing and technologies at Nortel in Ottawa. He can be reached at tonyryb@ nortelnetworks.com.