Exam 300-610 topic 1 question 30 discussion

B is correct

, 2, 4, and 8 Gb Fibre Channel all use 8b/10b encoding. Meaning, 8 bits of data gets encoded into 10 bits of transmitted information – the two bits are used for data integrity. Well, if the link is 8Gb, how much do we actually get to use for data – given that 2 out of every 10 bits aren’t “user” data? FC link speeds are somewhat of an anomaly, given that they’re actually faster than the stated link speed would suggest. Original 1Gb FC is actually 1.0625Gb/s, and each generation has kept this standard and multiplied it. 8Gb FC would be 8×1.0625, or actual bandwidth of 8.5Gb/s. 8.5*.80 = 6.8. 6.8Gb of usable bandwidth on an 8Gb FC link. 10GE (and 10G FC, for that matter) uses 64b/66b encoding. For every 64 bits of data, only 2 bits are used for integrity checks. While theoretically this lowers the overall protection of the data, and increases the amount of data discarded in case of failure, that actual number of data units that are discarded due to failing serialization/deserialization is minuscule. For a 10Gb link using 64b/66b encoding, that leaves 96.96% of the bandwidth for user data, or 9.7Gb/s.