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Forward error correction has long been widely deployed at the physical-link layer in conjunction with advanced line-coding schemes. These techniques check and correct bit errors on WAN links to ensure that upper-layer protocols receive error-free datagrams. But even when a network's physical link is free from bit errors, packets may still get dropped in transit on WAN links because of queue overflows in oversubscribed networks.
By applying FEC at the packet level, enterprises can minimize the effects of packet loss. This avoids service disruption, which is essential for ensuring optimum application performance across the WAN.
Packet-level FEC works by adding another error-recovery packet for every "N" packets that are sent. This FEC packet contains information that can be used to reconstruct any single packet within the group of N. If one of these N packets happens to be lost during transfer across the WAN, the FEC packet is used on the far end of the WAN link to reconstitute the lost packet. This eliminates the need to retransmit the lost packet across the WAN, which dramatically reduces application response time and improves WAN efficiency.
When implemented properly, packet-level FEC provides a significant increase in application performance under a wide range of network conditions. For example, in an average sampling across live enterprise networks,
it takes approximately 85 seconds to download a very large file across a 10M bit/sec WAN link with 3% packet loss and no FEC. When adaptive FEC is enabled on the same type of link (keeping all other parameters the same), the identical file is transferred in approximately 5 seconds. In this scenario, FEC provides a 17x improvement in application-response time.
To learn more about how best to implement FEC in your enterprise network, download the whitepaper, "Taking FEC to the Packet Level."
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