The LCR Frame is a Link Control Frame termed a Link Control Command. Link Control Commands initiate a low-level action at the destination N_Port specified by the D_ID, such as reset. LCR is currently the only defined Link Command Frame, although others may be defined in the future.

The LCR Frame is used to recover from hang or deadlock situations that arise due to a loss of credit, where a source N_Port mistakenly stops sending Data Frames to a destination N_Port because it perceives that there is no more credit. This can occur as a secondary effect due to the loss of either Data Frames or Link Control Frames on a link, over a period of time.

The LCR Frame commands the destination N_Port to reset and clear any buffers containing Data Frames from the source N_Port. This allows the source N_Port to reset its end-to-end Credit to the value determined at Login.

Since it is a low-level reset function for the end-to-end Credit, the LCR Frame is sent outside of any existing Exchanges or Sequences and isn t itself controlled by any end-to-end flow control mechanisms. All fields other then R_CTL, D_ID, and S_ID are reserved and ignored by the Recipient except for CRC calculation, and the SOFn2 and EOFn delimiters are used. Dedicated Connections are not affected by the LCR Frame and should be removed prior to LCR transmission, if possible.

Following transmission of the LCR Frame, all active Sequences with the...