Expand Configuration and Management Manual (G06.24+)

Expand Modifiers
Expand Configuration and Management Manual—523347-008
17-15
L4SENDWINDOW n
request before reporting an error. You should read the description of Layer 4 retries in
Section 18, Subsystem Description, before using this modifier.
L4SENDWINDOW n
Default: 254
Units: Packets
Range: 187 through 254
This path modifier is applicable to all Expand line types. This modifier specifies the
size, in packets, of the Layer 4 send window. This window determines how many
packets are sent before an acknowledgment is required. The default value allows up to
254 unacknowledged packets in any single end-to-end (Layer 4) connection.
The L4SENDWINDOW modifier value should be reduced from the default of 254 for
paths that consist of multiple lines of greatly varying speeds. Using the default value in
this type of configuration can result in the retransmission of many packets during error-
recovery and can increase out-of-sequence (OOS) packet processing.
For example, if a path has two lines, one at a speed of 224 Kbps and the other at a
speed of 19.2 Kbps, setting the L4SENDWINDOW modifier to its lower limit of 187 will
help ensure that packets traveling on the faster line are not discarded because they
are too far ahead of packets traveling on the slower line.
L4TIMEOUT n
Default: 2000 (20.00 seconds)
Units: 0.01 seconds
Range: 50 through 32767 (0.5 seconds through 5:27.67 minutes)
This path modifier is applicable to all Expand line types. This modifier specifies the
time interval, in one-hundredth of a second increments, that the Expand line-handler
process will wait for a response to an end-to-end (Layer 4) request before retrying. You
should read the description of the Layer 4 timeout in Section 18, Subsystem
Description, before using this modifier.
The Layer 4 timeout should not expire until all Layer 2 activity related to a specific
message transmission has ceased. Therefore, the L4TIMEOUT modifier value should
be large enough to span the worst case (the sum of the intermediate Layer 2 timers for
the longest end-to-end route).
The following algorithm can be used to determine the L4TIMEOUT value:
L4TIMEOUT = (((l2retries * l2timeout * 3) + 10) * q)
l2retries is the number of times that the Expand line-handler process will try a
request at Layer 2 before reporting an error. (You can modify this value using the
L2RETRIES modifier as described in L2RETRIES n on page 17-12.)
Note. The L4RETRIES modifier value should be set to the same value for every Expand line-
handler process on every node in the network.