8 FC-4 Link Service definitions

8.1FC-4 Link Services for the Fibre Channel Protocol

FC-4 Link Service functionality is specified in FC-LS. For FCP FC-4 Link Services, the FCP frame header fields (see 5.2) shall be set as follows:

a)R_CTL bits 31-28 (Word 0) shall be set to 0011b (i.e., an FC-4 Link_Data frame);

b)the TYPE field shall be set to 08h (i.e., FCP FC-4 Link Service frame); and

c)the R_CTL Information Category bits 27-24 shall be set to 0010b (i.e., unsolicited control) for request Se-

quences and 0011b (i.e., solicited control) for response Sequences.

The FCP FC-4 Link Service Requests and Responses defined in this standard are shown in table 10.

Table 10 - FCP FC-4 Link Service Requests and Responses

8.2Sequence Retransmission Request (SRR)

The SRR FCP FC-4 Link Service request Sequence is transmitted by an initiator FCP_Port to request that a target FCP_Port retransmit information or request retransmission of information for the specified Exchange.

If task retry identification (see 4.7) is active for the Originator and the Responder, the PARAMETER field of the request Sequence shall contain the task retry identifier for the task specified by the OX_ID and RX_ID field values.

If the target FCP_Port determines that the ORIGINATOR S_ID, OX_ID, or RX_ID field values, or task retry identifier are inconsistent, then it shall respond with an FCP_RJT (see 8.3) Sequence with a reason code of “Unable to perform the command request” and a reason code explanation of “Invalid OX_ID-RX_ID combination”.

If the target FCP_Port is unable to retransmit the Sequence or data at the requested Relative Offset, the target FCP_Port shall respond with an FCP_RJT Sequence with a reason code of “Unable to perform the command request” and a reason code explanation of “Unable to supply requested data”.

If the initiator FCP_Port receives an FCP_RJT response, the initiator FCP_Port shall terminate the Exchange referenced by the SRR using recovery abort (see 12.3.2).

The SRR shall be sent in a new Exchange. The Exchange shall be ended by the response to the SRR.

Sequence Initiative for the Exchange referenced by the SRR shall be transferred to the target FCP_Port to resend the requested Sequence.

For unacknowledged classes, the Sequence Count for a retransmitted FCP_DATA IU shall start at zero, even if continuously increasing sequence count is being used. For acknowledged classes, the Sequence Count for a retransmitted FCP_DATA IU shall start at one higher than the last Sequence Count used in the Exchange to prevent it from being within the range of the Recovery_Qualifier.

Addressing:

The S_ID field designates the initiator FCP_Port requesting the information retransmission. The D_ID field designates the target FCP_Port that is to receive the request. In the event that the target FCP_Port responds to the SRR with an FCP_RJT, the target FCP_Port shall return CHECK CONDITION status with the sense key

set to HARDWARE ERROR and the additional sense code set to INITIATOR DETECTED ERROR MESSAGE RECEIVED. A target FCP_Port that has agreed during Process Login to support retransmission should not reject requests for retransmission of the requested frames unless unusual conditions make the retransmission impossible. SRR requests for exchanges involving logical units that do not support retransmission on a target FCP_Port that supports retransmission for other logical units shall be rejected with an FCP_RJT containing a reason code of “Unable to support command request” and a reason code explanation of “Unable to supply requested data”.

Payload for SRR FCP FC-4 Link Service request:

The format of the Payload is shown in table 11.

Table 11 - SRR Payload

The R_CTL FOR IU field encoding is as described in FC-FS-2 (i.e., Data Descriptor (FCP_XFER_RDY IU), Command Status (FCP_RSP IU), Solicited Data (FCP_DATA IU)).

The RELATIVE OFFSET parameter is only valid if the R_CTL FOR IU field is set to 01h for Solicited Data or to 05h for Data Descriptor. The RELATIVE OFFSET field contains the Relative Offset of the lowest byte the initiator FCP_Port has identified as requiring retransmission. The two low-order bits of the RELATIVE OFFSET field shall be zero, such that the data to be retransmitted begins on a four-byte boundary.

The amount of data to transfer is implicitly the remainder of that for the Exchange.

Possible responses to SRR FCP FC-4 Link Service request:

FCP_RJT

Signifies rejection of the SRR request.

SRR Accept

Signifies that the Payload is accepted.

SRR Accept Payload:

The payload for the SRR Accept is shown in table 12.

Table 12 - SRR Accept Payload

Word

8.3FCP FC-4 Link Service Reject (FCP_RJT)

FCP_RJT notifies the originator of an FCP FC-4 Link Service request that the FCP FC-4 Link Service request Sequence has been rejected. A four-byte reason code shall be contained in the Data_Field (see table 13).

An FCP_RJT may be a response Sequence to any FCP FC-4 Link Service request.

Addressing:

The D_ID field designates the source of the FCP FC-4 Link Service request being rejected. The S_ID field designates the destination of the request FCP FC-4 Link Service frame Sequence being rejected.

Payload for FCP_RJT:

The first word of the Payload shall contain the FCP_RJT code (01000000h). The next four bytes of this field shall contain a reason code and reason code explanation for rejecting the request. The format of the FCP_RJT Payload is shown in table 13.

Table 13 - FCP_RJT Payload

The reason codes for FCP_RJT are specified in table 14.

Table 14 - FCP_RJT reason codes

The first error condition encountered shall be the error reported.

FCP_RJT reason code explanations

Table 15 lists the reason code explanations for FCP FC-4 Link Service commands.

Table 15 - FCP_RJT reason code explanations