Expand Configuration and Management Manual (H06.21+, J06.10+)

Subsystem Description
Expand Configuration and Management Manual — 529522-013
17 - 69
Considerations for Paths Using the Variable Packet
Size Feature and the Multipacket Frame Feature
Considerations for Paths Using the Variable Packet Size Feature
and the Multipacket Frame Feature
The main difference between the variable packet size feature and the multipacket
frame feature is that the multipacket frame feature benefits users who send many small
concurrent requests, while the variable packet size feature benefits users who send
large blocks of data (bulk transfers). Packet size and multipacket frame size can be
configured and negotiated separately on each path.
With variable packet size, the Expand line-handler process should be able to send a
full variable packet inside a multipacket frame. For this reason, the value of the
PATHBLOCKBYTES modifier must be equal to or greater than the value of the
PATHPACKETBYTES modifier.
Congestion Control Feature
Congestion in a network occurs when performance on a connection degrades
because of the saturation of a resource that is needed to deliver data from the source
to the destination. Congestion control mechanisms regulate system resources to
avoid network bottleneck and resource contention situations.
This subsection describes these topics:
•
Congestion Control Configuration on page 17-71
•
Congestion Control Considerations on page 17-71
Congestion control provides improved throughput over LANs and other types of
networks that are subject to varying delays. It also improves the response time for
message transfers and provides a more efficient error-recovery mechanism. For these
reasons, HP recommends that the congestion control feature be enabled for all types
of connections.
The congestion control feature can be enabled in one direction only for each
connection. If the congestion control feature is enabled on both ends of a connection,
then it is executed for traffic in both directions. Traffic in a given direction is subject to
congestion control if the sender has congestion control enabled and the receiver
supports it. The receiver does not have to have the congestion control feature enabled
to support it.
In Figure
17-22 on page 17-70, congestion control is enabled on nodes \A and \C.
Congestion control is supported, but not enabled, on node \B. Traffic from node \A to
node \B and from node \C to node \B is subject to congestion control. Traffic from node
\B to either node \A or \C is not subject to congestion control.
Note. The congestion control feature is supported on NonStop K-series servers with D30 and
later versions of the operating system installed, or with the D20 operating system and
T9057ABS installed.