Sequence Errors; Crc - Sun Microsystems storagetek sl500 Reference Manual

FC-2 Features
For sequences which do not transfer Sequence Initiative:
Consecutive FCP_DATA Sequences for the same exchange follow the FC-PH
■
rules for streamed sequences which include:
The first FCP_DATA Sequence after transfer of sequence initiative is not a
■
streamed sequence. It can use any eligible SEQ_ID, and the SEQ_CNT can be
either zero or a continuously increasing number.
The second and subsequent sequences within the same exchange are treated
■
as streamed.
Because frame delivery is not confirmed, the sequence initiator cannot reuse a
■
SEQ_CNT within a given sequence.
For sequences beginning with a SEQ_CNT of zero, the SEQ_CNT cannot wrap
when reaching a hexadecimal count of "FFFF".
For sequences beginning with a SEQ_CNT of 'n' (where n is not zero), the
SEQ_CNT can wrap when reaching a hexidecimal count of "FFFF" and continue
from zero up to a value of n-1.

Sequence Errors

Sequence errors are managed as defined in FC–Tape with the following additions:
1. If a frame with an SOFi3 delimiter is received and the SEQ_CNT is not equal to
zero or +1 from the SEQ_CNT of the last frame of the previous Sequence of that
Exchange.
2. If the SEQ_CNT of a received frame with an SOFn3 delimiter is not +1 greater
than the previous frame received for that Sequence (such as a frame was lost).
This also detects the case where a frame with an SOFn3 delimiter is received for
a SEQ_ID that is not currently open since the SEQ_CNT of the previous frame
for that sequence is undefined.
3. If a frame with an SOFi3 delimiter is received and the previous sequence of that
exchange is still open.
4. If the relative offset in the parameter field of a received frame with an SOFn3
delimiter is not equal to the (relative offset + the payload size) of the previous
frame received for that Sequence.
5. If the next frame of a sequence is not received within E_D_TOV.
6. If, during the same sequence initiative, a sequence is received which has the
same SEQ_ID as the previous sequence of that exchange.
When a sequence error is detected by the library, it discards that sequence, and all
remaining sequences for the exchange containing the sequence in error. The library
attempts to take the appropriate action as defined in FCP–2.

CRC

Fibre Channel adds another level of protection over the content of each frame
called a cyclic redundancy check (CRC). Each frame is protected by a 4-byte CRC
which provides a separate and independent error detection mechanism.
64 SL500: Interface Reference Manual • July 2008 Revision: F • 96122