Expand Configuration and Management Manual (G06.24+)

Subsystem Description
Expand Configuration and Management Manual—523347-008
18-20
Example of End-to-End Protocol Packet Exchanges
Node \B receives the ENQ, responds by resending ACK sequence number 3 to
acknowledge the three LRQs, and then sends an LCMP in response to each LRQ.
Node \A acknowledges node \B’s LCMPs with ACK sequence number 3.
If node \B did not acknowledge node \A’s ENQ, node A would continue to send ENQs
until it reached its Level 4 retry limit or until node \B acknowledged the ENQ.
Data Exchange With Buffer Pool Failure
Figure 18-6 illustrates a data exchange in which the destination node is unable to
allocate sufficient buffer space to accept the sending node’s request. This problem is
usually caused by insufficient buffer pool space and is indicated by pool failures in the
SCF STATS display.
Node \A sends LRQ sequence number 0 to node \B. Because node \B is unable to
allocate buffer space for the message, it replies with NAK sequence number 0 with its
wait bit set. The wait bit indicates to node \A that a resource limitation has occurred
and that node \A should not resend its LRQ until the wait condition has cleared.
Figure 18-6. Buffer Pool Failure
Note. The OOS buffer and the buffer pool are described in Message Handling and Buffer
Allocation on page 18-38 and Message Buffering on page 18-46.
036CDT .CDD
LRQ (0)
ACK (1), WAIT BIT RESET
NODE \A NODE \B
ACK (4)
LCMP (0)
LCMP (1)
LCMP (2)
ACK (3)
NAK (0), WAIT
LCMP(0)
(no buffer)
(to prior request
from NODE \B)
(buffer deallocated)
LRQ (1)
LRQ (2)
LRQ (3)