FIBRE CHANNEL - T11

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FC-Tape Fibre Channel Tape Rev 1.07 August 7, 1998 1) The first FCP_DATA Sequence after transfer of Sequence Initiative is not a streamed Sequence. It may use any eligible SEQ_ID and the SEQ_CNT may be either zero or continuously increasing (incremented by one from the last Frame of the previous Sequence of that Exchange); NOTE – Some existing devices require the SEQ_CNT for the first FCP_DATA Frame following the transfer of Sequence Initiative to be zero. 2) The second, and subsequent, Sequences of a group of consecutive Sequences within the same Exchange shall be treated as streamed. The following rules apply (where X in the following discussion is the number of Open Sequences per Exchange from PLOGI (see table 9)): NOTES: i) X+1 different SEQ_IDs shall be used; ii) The X+1 different SEQ_IDs may be assigned by the Sequence Initiator in any order (they are not required to be monotonically increasing); iii) A SEQ_ID may be reused after X different intervening SEQ_IDs have been used, provided that R_A_TOV SEQ_QUAL (as defined in 7.5) has expired for all Frames associated with the prior use of that SEQ_ID; iv) The Sequence Count (SEQ_CNT) across streamed Sequences shall be continuously increasing. That is, the SEQ_CNT of the first Frame of the streamed Sequence shall be incremented by one from the SEQ_CNT of the last Frame of the previous Sequence; 1 FC-PH-3 adds a bit to PLOGI that indicates that a port uses continuously increasing SEQ_CNT on all Sequences within an Exchange with the first Sequence of the Exchange beginning at SEQ_CNT zero. Ports that set this bit during login are obligated to follow this behavior since the Sequence Recipient may use the expected behavior to perform Sequence checking. 2 Some existing devices are not capable of generating continuously increasing SEQ_CNT across consecutive Sequences. In this case, the following rules apply: A minimum of two different SEQ_IDs shall be used by the Sequence Initiator and the SEQ_CNT across consecutive Sequences may restart at x‘0000’. b) The Target may use one or more Sequences to transfer the data requested by a SCSI readtype command. The Target may break the associated transfer up into as many arbitrary sized Sequences as the Target chooses (subject to the Sequence boundary requirements specified elsewhere in this document). This means that: 1) When there is additional read data still to transfer and all of the data Frames associated with a given Sequence have been sent, or all permissible SEQ_CNT values used, the Target may begin a new Sequence in order to continue sending the read data; 2) The Target may send less than the maximum permissable number of data Frames per FCP_DATA Sequence, even if there is additional data to send (for example, if the maximum Sequence size is 1000 Frames (as defined by the maximum burst size field of the SCSI disconnect/reconnect mode page), the Target may terminate the current Sequence after 600 Frames and subsequently start a new Sequence to send any remaining Frames). c) During a read type command with at least one FCP_DATA Sequence, the FCP_RSP Sequence may optionally be considered a streamed Sequence and observe the rules for streamed Sequences listed previously. 26
TR-xx-1998 Fibre Channel Tape Rev 1.07 August 7, 1998 d) A SCSI Target may reuse a SEQ_ID previously used for a Read FCP_DATA Sequence immediately following transmission of the FCP_RSP of that Exchange. Examples of SEQ_ID and SEQ_CNT usage during streamed Sequences may be found in Annex B. 5.13.4 Sequence errors The following conditions shall constitute a Sequence error when detected by the Sequence Recipient: a) 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; b) if the SEQ_CNT of a received Frame with an SOFn3 delimiter is not +1 greater than the previous Frame received for that Sequence (i.e., a Frame was lost); c) if a Frame with an SOFn3 delimiter is received for a SEQ_ID that is not currently open; d) if a Frame with an SOFi3 delimiter is received and the previous Sequence of that Exchange is still open (see 5.13.3.1 for a definition of when a Sequence is open); e) if the relative offset bit in the F_CTL field is set to ‘1’b and the value contained 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; f) the next Frame of a Sequence is not received within E_D_TOV; g) if, during the same Sequence Initiative, a Sequence is received that has the same SEQ_ID as the immediately prior Sequence of that Exchange. Refer to the FC-PH document(s) for a description of Sequence errors pertaining to class 2 operation. When a Sequence error is detected by the Sequence Recipient, it shall take the appropriate action as described in clause 9. 27
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FIBRE CHANNEL - T11

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