Expand Configuration and Management Manual (G06.24+)

Subsystem Description
Expand Configuration and Management Manual—523347-008
18-19
Example of End-to-End Protocol Packet Exchanges
If node \B did not acknowledge node \A’s ENQ, node \A would continue sending ENQs
until it reached its Level 4 retry limit or until node \B acknowledged the ENQ, whichever
came first.
Data Exchange With Lost Acknowledgment
Figure 18-5 shows a data exchange in which messages are received successfully but
the recipient’s acknowledgment is not received by the sender. This problem is usually
caused by network congestion, or by an Expand Level 4 timeout period that is too
short, and is indicated by a large number of ENQs on the SCF STATS display.
Node \A sends three LRQs to node \B. Node \B sends ACK sequence number 3 to
acknowledge all three LRQs. Node \A does not receive an acknowledgment within the
Expand Level 4 timeout period, so it sends an ENQ sequence number 3 to node \B.
The ENQ sequence number 3 indicates to node \B that node \A has sent LRQ
sequence numbers 0 through 2.
Note. The default OOS timeout is 300 (3 seconds). The OOS timeout can be controlled with
the Expand SCF ALTER PATH command or the WAN subsystem SCF ALTER DEVICE
command. You can control the Expand subsystem’s retry limit by setting the L4RETRIES
modifier. This modifier is explained in Section 17, Expand Modifiers
.
Figure 18-5. Lost Acknowledgment
035CDT .CDD
LRQ (0)
LRQ (1)
LRQ (2)
NODE \A NODE \B
Lost packet
ACK (3)
LCMP (0)
LCMP (1)
LCMP (2)
ACK (3)
ENQ (3)
ACK (3)
(L4TIMEOUT)