Expand Networks speeds voice through slow links

Expand Networks Inc. is trying to improve the performance of voice over IP on small data links so that users can stave off upgrades to faster and more expensive WAN connections.

The company is adding software that fragments packets that are larger than a pre-set size. That way, delay-sensitive voice packets don't get stuck behind them, which would break up the stream of voice traffic and degrade the quality of phone calls.

Expand is adding this feature to its Accelerator appliance, which can already compress and organize traffic in priority queues. The compression feature alone was enough to improve performance on a 256K bit/sec line between Frederick, Md., and New Delhi, India, says Ashish Deshpande, network engineer for Bechtel in Frederick. "My 256K line is acting almost like a 512K line," he says. And that was sufficient improvement to clear up congestion problems on the link.

Accelerators are placed between LANs and WAN routers, where they analyze traffic, cache selected parts of packets so these parts don't have to be sent repetitively over the link, and compress traffic before they enter the WAN. The devices are deployed in pairs, one at each end of a link, and decompress incoming packets.

However, the company plans to run VoIP on 64K bit/sec connections, and will invoke the fragmentation feature for them. "This will allow us to maximize bandwidth without increasing line costs," says Deshpande.

Expand recommends the fragmentation option for 128K bit/sec lines and smaller. Users set the maximum size of packets that are acceptable without being fragmented based on the size of the connection and the amount of latency that is tolerable before it degrades voice quality too much.

The new option comes standard as part of new purchases and is a free upgrade to current customers with service contracts.

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