64b/66b encoding

In data networking and transmission, 64b/66b is a <a href="/facts/Line_code/x9IuaYNL">line code</a> that transforms 64-<a href="/facts/Bit/RwfjaYSv">bit</a> data to 66-bit <a href="/facts/Line_code/x9IuaYNL">line code</a> to provide enough state changes to allow reasonable <a href="/facts/Clock_recovery/hrTr6rlS">clock recovery</a> and alignment of the data stream at the receiver. It was defined by the <a href="/facts/Institute_of_Electrical_and_Electronics_Engineers/UddC4pUW">IEEE</a> <a href="/facts/IEEE_802.3/Q9jxNSNT">802.3 working group</a> as part of the IEEE 802.3ae-2002 amendment which introduced 10 Gbit/s Ethernet. At the time 64b/66b was deployed, it allowed 10 Gb Ethernet to be transmitted with the same lasers used by <a href="/facts/SONET/G3LgtGS6">SONET</a> <a href="/facts/OC-192/GVABpoYY">OC-192</a>, rather than requiring the 12.5 Gbit/s lasers that were not expected[when?] to be available for several years.
The <a href="/facts/Protocol_overhead/e2jgPrHr">protocol overhead</a> of a coding scheme is the ratio of the number of raw payload bits to the number of raw payload bits plus the number of added coding bits. The overhead of 64b/66b encoding is 2 coding bits for every 64 payload bits or 3.125%. This is a considerable improvement on the 25% overhead of the previously-used <a href="/facts/8b%2f10b_encoding/bxnMBwaC">8b/10b encoding</a> scheme, which added 2 coding bits to every 8 payload bits.
The overhead can be reduced further by doubling the payload size to produce the 128b/130b encoding used by <a href="/facts/PCIe/ADhsLCUK">PCIe</a> 3.0.

64b/66b encoding open-in-new

64b/66b encoding