UniPro protocol stack: Difference between revisions

Revision as of 19:37, 13 June 2011

Revision as of 11:19, 17 May 2012

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High speed communication at low power levels can lead to occasional errors in the received data. The Data Link layer contains a protocol to automatically acknowledge correctly received data frames (using AFC control frames) and to actively signal errors that can be detected at L2 (using NAC control frames). The most likely cause of an error at L2 is that a data frame was corrupted at the electrical level (noise, EMI). This results in an incorrect data or control frame checksum at the receiver side and will lead to its automatic retransmission. Note that data frames are acknowledged (AFC) or negatively acknowledged (NAC). Corrupt control frames are detected by timers that monitor expected or required responses.

A bandwidth of 1 Gbit/s and a bit-error rate of 10⁻¹² at a speed of 1 gigabit/s would imply an error every 1000 seconds or once veryevery 10001000th transmitted Gbit. Layer 2 thus automatically corrects these errors at the cost of marginal loss of bandwidth and at the cost of buffer space needed in L2 to store copies of transmitted data frames for possible retransmission or "replay".

===L2 flow control===