Getting more bang from your routers

A new way to string routers together across the Internet, or an enterprise network, could save companies money and reduce traffic congestion.

The approach used by these Galois networks differs from the practice of employing expensive high-end routers linked together over ever-lengthening paths. Instead, Galois networks comprise router arrays, or so-called metarouters, which are clusters of inexpensive, off-the-shelf routers connected together. These metarouters work in much the same way that a RAID system connects storage devices.

Just as computers can be hooked together to act as a single supercomputer, metarouters let users harness their routing power without upgrading equipment every few months. And because Galois nets are based on a nonproprietary architecture of physical connections, users can implement the technology without waiting for vendors to include it in software.

The routers in a metarouter are linked using group theory mathematics. Developed in the 19th century by Evariste Galois, group theory states that a finite set of numbers creates a pattern that repeats itself predictably. Applied to clusters of routers, this means that a defined set of routers hooked together in a minimal amount of rows and columns will guarantee fault tolerance and redundancy - two critical elements in a large network.

To determine how the ports should be connected, a computer program, included in the Galois patent or supplied by a vendor, generates a wiring diagram based on the number of external ports a user needs and the number of ports in the routers they will be using. The program uses a formula derived from group theory to calculate which port in which row to connect to a port in a subsequent row.

In today's nets, overloaded routers drop packets, causing massive congestion. Traffic that traverses a Galois network is spread across the metarouter array so if one router becomes congested, the packets can be rerouted instantly to avoid packet loss and bottlenecks.

Galois networks can handle voice and video traffic. Neither data type can tolerate the jitter and delay caused by the retransmission of packets. Also, traditional nets suffer from port blocking, where collisions can cause a domino effect with other traffic. Because traffic in a Galois network is spread across the minimum number of routers, the chances of packet collisions are reduced.

Galois networks are also highly scalable. In a traditional net, when routers are added, the time it takes packets to reach their destination is increased because they have to make more hops. But in a metarouter array, routers can be added to rows without increasing the hops.

Also, to increase fault tolerance, users can add a row of routers without having to reconfigure the other routers in the array. Because metarouters know how to shift traffic without losing bits, if a router fails, or one needs to be added, it can be swapped in without having to take the net down.

Metarouters can include a combination of products from a variety of vendors.The Galois technology has been offered to several firms for adoption in router gear, but none has accepted. The approach runs counter to the marketing pitch vendors use to sell bigger and faster equipment. However, users can implement Galois using the instructions in the patent (See DocFinder 3633).

Also, the Advanced Research Project Agency at the U.S. Department of Defense is studying the technology as part of its Next-Generation Internet project.

Huang, a former Bell Labs researcher, holds the patent for the Galois network and its metarouter technology. He is also the founder of Terabit Corp. in Menlo Park, Calif. He can be reached at alan@isl.stanford.edu. Gittlen is managing editor of Network World Fusion and can be reached at sgittlen@nww.com.