SDSL, ADSL and Wireless LAN links can be very susceptible to packet loss. Although the rate of packet loss may be negligible for many applications, real-time applications such as Voice-Over-IP (VoIP) telephone systems can be rendered virtually unusable by as little as 2% packet loss.

A FireRack customer was trying to operate a VoIP telephone system over an SDSL (EPS9) connection, which was proving to be very unreliable. Although the line quality was within the specification for EPS9, it was still dropping up to 2.5% of packets when multiple voice calls were in progress.

FireRack developers were already working on a "small frame multiplexer" which was intended to encapsulate multiple Ethernet frames into one. In response to this customer's needs, the FireRack developers delivered a beta test version of their packet multiplexer, which had been enahnced specifically to compensate for packet loss on Ethernet networks. As a result the effective rate of packet loss on the network was reduced from 2.50% down to 0.05%.

The technique used is simple and very effective. The FireRack appliance acts as a network bridge between the SDSL modem and the LAN. For each Ethernet frame passed to the FireRack for bridging, the FireRack transmits two or more copies of the frame to its remote peer at the other side of the link. The receiving FireRack then de-duplicates these Ethernet frames and bridges just one copy onto the remote network segment. Only one copy needs to make it across the link for delivery to be successful. In the example given above, just 2 copies of each packet were sent, resulting in 98% reduction in effective packet loss. The number of duplicates sent is user definable.

This multiplexer is now a standard feature of FireRack and will be made available to existing customers by the end of June 2004.