The Response Handler module manages the outstanding queues. These queues hold the information about all packets sent to the remote host but have not yet been acknowledged or responded to. In addition, this module triggers a re-transmission if the remote host sends a Negative Acknowledgment (NAK). If this module does not receive a response from the remote host within a specified time (timeout value), it triggers a timeout related retransmission.
Retransmission is triggered either due to an incoming NACK or an internal timeout. When a retransmission is triggered, ERNIC IP takes care of the following:
1. Identifies the PSN and MSN values to be retransmitted.
2. Rolls back the PSN and MSN values for that queue pair.
3. Rolls back the current SQ pointer to the WQE that needs to be retransmitted.
4. ERNIC IP supports partial WQE retransmission, it retransmits from the PSN for the incoming NACK.