VeEX VePAL TX300M, Руководство пользователя

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Protocol Stack
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Physical Layer
The following Line bit rates are defined from the standard:
Line Coding:
8B/10B line coding shall be used for serial transmission according to IEEE 802.3-2005, clause 36. (Same encoding as
used for Gigabit Ethernet and Fibre Channel)
Bit Error Correction/Detection:
The physical layer is designed in such a way that a very low bit error ratio can be achieved without expensive forward
error correction schemes. Therefore, no general bit error correction is applied at Layer 1.
The RE and the REC shall support detection of 8b/10b code violations. Link failures shall be detected by means of
8b/10b code violations.
8B/10B Encoding - What is it and Why is it Used?
8b/10b is the line code used for Gigabit Ethernet and Fibre Channel.
It maps 8 bits of data into a 10 bits symbol, each 8 bits can map into 2 possible 10 bit
symbols. The symbols are chosen so that there is a limit of 5 consecutive equal bits and the
difference of the count of 0s and 1s is no more than 2.
The goal is to achieve DC balance by having a running disparity of 1s and 0s and to provide
enough state changes to allow clock recovery.
Clock recovery is particularly important because in the CPRI implementation, the RE must
recover timing from the 8B/10Bencoded line rate and regenerate the original reference
frequency to the required UMTS accuracy.
In addition the 8b/10b has several error detection mechanisms: Validation of correct codes
(only 268 of the possible 1024 10-bit codes are used)
Validation of correct running disparity
Validation that running number of 1s or 0s does not exceed 5
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TX300S_e-manual_D07-00-064P_RevA00