 At the time 64b/66b was deployed, it allowed 10 Gb Ethernet to be transmitted with the same lasers used by SONET OC-192, rather than requiring the 12.5 Gbit/s lasers that were not expected to be available for several years.The protocol overhead 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%.