Routing electronic signals is a bit like running a railway network: there are lots of points and sidings to manage and if the 9.05 express ends up heading towards the 9.10 commuter train on the same track, woe betide you. Optical networking is no better, because signals must still be converted into electrons for decoding and switching.
The first alternative approaches are now appearing though, with one of the most interesting being an optical switch developed by a Texan start-up company called Chiaro Networks. Signals still need to be decoded into electronic form for processing but the routing itself involves beams of light.
"Optical beams can cross-over in air, which electrons can't - photons are good neighbours," says Carey Parker, Chiaro's product management and marketing VP at Chiaro (pronounced "Key-ah-roh").
Chiaro's Optical Phased Array (OPA) uses a Gallium-Arsenide material which has the curious property that if you apply an electric field to it, its index of refraction changes, as does the speed of the photons travelling through it. By stacking 128 slivers of this material side by side as optical waveguides, each of a different length, the electric field causes the light beam to bend.
"We have a stateless optical fabric. We bring the fabric up and down, configuring it in software. In the middle there's a five inch air gap with photons flying across it," says Parker. "There are 64 sets of waveguides, so we can switch 64 optical signals and aim each one at a different output fibre."
The way it works is that packets come in as an optical signal, this is converted to electronic for processing then back to optical for switching on a 400ns cycle. During that 400ns, a global scheduler goes through 12 to 14 iterations, looking for the best set of optical paths for switching, then configures the OPA accordingly. The OPA can switch in 1ns, or 25ns if you include the electronics.
"What's unique is we have one scheduler which has complete visibility of the system - it gives the most efficient and optimised use of the fabric," Parker adds. "The speed limit at the moment is the digital-to-analogue converter steering the OPA."
At the moment, OPA-based routers are mainly aimed at carriers and at users who need massive networks for grid or cluster computing. Chiaro has units deployed in the Optiputer project, for example, linking grid computers at CERN and at academic sites in California.
But by far the biggest opportunity the company sees is in network consolidation, and in particular among network operators who are now consolidating multiple legacy networks onto single converged IP/MPLS (multi protocol label switching) cores.
It has therefore recruited people from a wide range of disciplines, including networking, telecoms, photonics and supercomputing, to develop Enstara, a highly reliable 6.3 Tbps multi-chassis router with 320 Gigabit Ethernet ports and room for growth.
"I haven't seen a new ATM build for two years, we see a lot of maintenance but most people now believe MPLS has the capabilities to supplant ATM," says Parker. "They're saying MPLS is not the perfect technology, but it's good enough for convergence. It made some of ATM's merits possible in IP, now more and more features have been put on MPLS and the flip happened about two years ago."
He adds that the hardest thing for IP switch and router companies to grasp here is the need for absolute reliability. Most networking kit aims for three nines reliability, or 99.9 percent uptime, and when asked for the five nines (99.999 percent) that carriers need, they will suggest using dual redundant routers, but Parker claims this will not deliver the goods.
"Why do we have so much redundancy? It has become standard practice, but it's not a small network anymore so you are using more and more ports for interconnects," he says.
"From a hardware perspective two routers gives five nines, but not from the software perspective, as if one fails, it takes time to fail-over to the other. Whenever you have a failure there is a time when packets are sent and lost because the other routers don't know about the failure yet - it's called route flap. So a single five-nines router is actually more reliable," even though it costs more.
Looking forward, Parker claims that OPA and Enstara still have room for growth. "The architecture is designed for 640 ports, not just the 320 on offer today," he says. "In the future, we might run multiple light colours, for instance. Scale is not the thing that keeps us awake at night."
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