UniPro protocol stack: Difference between revisions

Revision as of 06:23, 9 October 2009

Revision as of 06:36, 9 October 2009

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===L2 retransmission===

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 any error visible at L2 (using NAC control frames). The lattermost islikely usuallycause becauseof an error at L2 is that a data frame withwas corrupted at the electrical level (noise, EMI). This results in an incorrect checksum wasat receivedthe receiver side and will lead to its automatic retransmission.

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 ofor once very 1000 transmitted useGbit. Layer 2 thus, automatically corrects these infrequent eventserrors at the cost of marginal loss of bandwidth and at the cost of buffer space needed in L2 to "replay"store copies of sent data packetsframes for possible retransmission or "replay" in case of errors.

===L2 flow control===