[mmmBacon]

Modern optical systems require strong FEC and it’s not uncommon for systems to have pre-FEC BER 1e-3. The FEC gain is high enough to guarantee 1e-12 to 1e-15 post-FEC. Due to FEC it’s not necessary or desirable to have pre-FEC BERs of 1e-12.

[jpmattia]

> and it’s not uncommon for systems to have pre-FEC BER 1e-3.

Old guy here: I'm wondering when that changed. Early OC-768 requirements were 10^-12 BER preFEC (e: at least in short-haul), which was down from 10^-9 for OC-192.

[londons_explore]

People realised that you maximize the throughput of the raw medium if you push it hard enough it has a high error rate, and then correct those errors.

Error correction tech has reached information theory perfection (if you ignore latency), so it always makes sense to use as much of it as possible. In the future I wouldn't be surprised to see bit error rates pretty close to 1:1, and massive amounts of FEC.

[jpmattia]

> People realised that you maximize the throughput of the raw medium if you push it hard enough it has a high error rate

When?

FEC has been used in optical systems for decades. The undersea fiber guys have been using it in production at least since the 90s, for example. So I'm a little amazed that decades went by before someone noticed that you can throw BER out the window for the components and drivers to improve the overall system BER.

[londons_explore]

From systems pre-error-correction... Think RS-232 serial for example... No error correction there, so people typically don't push hardware too close to the limits of bit rates because every bit error will cause some breakage. Even today, a lot of modern devices talk with RS232-like protocols, and none of them have even parity bits - it's just assumed error rates are so low as to be zero across the useful life of the product.

[wmf]

It probably used to be cheaper to use high-quality optical components until Moore's Law brought down the cost of FEC enough.