3 ms·
This is known as "forward error correction". If the nature of the corruption is known and predictable, then you can design a reasonably efficient scheme to miti
by sgtnoodle 4y ago
This is known as "forward error correction". If the nature of the corruption is known and predictable, then you can design a reasonably efficient scheme to mitigate it. Otherwise, I suspect some amount of acknowledgement and retransmission at the MAC layer or above is a good idea. It really depends on the latency of the link, though, and the probability of corruption. If a round-trip delay is larger than a reasonable window size, and corruption is frequent, then FEC would help a lot. It's the only option for one-way comms such as digital broadcast television.
- jpmattia 4y ago> This is known as "forward error correction". Fun factoid: Reed and Solomon were working at MIT Lincoln Laboratory (ie where the OP result is from) when they invented RS codes. ISTR they were also working on satellite comm, in which Lincoln has a long history. [Source: I spent a decade there myself and drank the kool aid.]
- thehappypm 4y agoThat’s super cool. Error correcting codes are truly amazing technology.
- sizzle 4y agoAwesome, what are you up to nowadays? Anything interesting brewing you can share?
- jpmattia 4y agoThese days, most of my time is spent on video encoding and distribution for fun and profit: https://www.centaurdelivery.com https://www.centaurdelivery.com
- MayeulC 4y agoWhich is exactly what Wi-Fi does, adjusting the amount of parity data depending on link loss, to keep retransmissions to a minimal.
- sgtnoodle 4y agoIndeed. It's fun to look at the MCS table for something like 802.11ac. a lot of different rates are actually the same underlying modulation, but with varying amounts of overhead from forward error correction. 802.11 data frames also have an acknowledgement at the MAC layer. The radios dynamically ramp up the MCS rate until packets start dropping, then ramp the rate back down.
- wongarsu 4y agoAnd still, wifi links are among the top sources of packet loss. Without sophisticated forward error correction it would probably be much worse, but it shows that this is not an either-or question. The correct answer is: do both.
- cycomanic 4y agoI think communications theorists would argue that retransmitting is essentially an FEC, and likely a suboptimal one for these links. That said, real-world constrains don't always match up with theory, while modern optical communication makes extensive use of FEC (however RS codes are not used much anymore, in long-haul it's LDPC codes) AFAIK FECs for these type of "intermittent" links are very underdeveloped. Moreover, if the probabilities of long outages is too high, one would need a lot of memory for the FEC which becomes difficult to do in real-time processing (remember we need to process at >100Gb/s).