Researchers in Hong Kong are helping to build the technology needed to take the Internet to the next generation. Demands of the information highway are expected to increase dramatically over the next few years, especially with users turning more and more to multimedia communications.
Broadband networks may seem fast, says Prof Victor O K Li, Chair of Information Engineering at The University of Hong Kong (HKU), but restrictions are inherent in their optical-electronic infrastructure.
Prof Li and other researchers in Hong Kong are backing the adoption of all-optical networks to overcome today’s Internet bottlenecks caused when optical signals are converted to electrical signals for processing.
All-optical networks will require new devices and a new means of processing where data is sent.
While processing electronically is easy, “it’s difficult in the optical domain because optical processing technology is not very mature,” said Prof Li. To succeed, processing needs to be as simple as possible.
Processing takes place in routers where the “header” of an information “packet” is read and the “payload” is directed to its destination (see illustration below).

	Above: address for Tokyo encodes all paths from other cities to Tokyo. Below: Prof Li and presentation of his scheme

Prof Li and his team devised a self-routing address scheme which dramatically simplifies the packet processing. The scheme, which is awaiting US patent approval, was motivated by an established algorithm which allows self-routing in a network with a regular structure. “By regular structure, we mean something like the road system in Manhattan US where streets are set out like a grid,” said Prof Li.
“But a typical fibre optical network may not have a regular structure,” he added. “The question is, how do you implement self-routing when there is no fixed structure?”
The research team invented a novel algorithm that can be used with an irregular or arbitrary topology. In the example of a Hong Kong-Tokyo transmission (above), the address would read as 010-0010-010-000-001.
Processing is simplified since routers in each city only need to read their own portion of the address.
The Hong Kong router would read 0010, directing the transmission on Link 3 (the third bit is a “1”) bound for Beijing. Upon receipt, the Beijing router reads 010 and forwards the transmission on Link 2 for Tokyo. When the Tokyo router reads 000 it realises the transmission is at its destination.
In conventional electronic switching, the header of information packets carries only the end address, and not the specific path to the destination. Today’s electronic routers therefore need to use look-up tables stored in memory to work out the best routes to take. “A lot of processing is needed at each intermediate node,” said Prof Li.
With Prof Li’s photonic switching scheme, paths are predetermined so the packet header may specify any intermediate routers. “It’s a much simpler process,” said Prof Li.
An important feature of the innovation, added Prof Li, is that the same address can be used for packets originating anywhere around the world and destined for the same place.
Note: The length of the header (in bits) is equal to the number of links in the whole network. In the example, there are 16 links in the network, and the header has 16 bits. Since each packet typically has a payload of tens of thousands of bits, the header is a very small percentage.

Principal Investigator
Prof Victor O K Li : vli@eee.hku.hk