Expand Configuration and Management Manual (G06.24+)

Subsystem Description

Expand Configuration and Management Manual—523347-008

18-71

Congestion Control Feature

Congestion in a network occurs when performance on a connection degrades due to

the saturation of a resource that is needed to deliver data from the source to the

destination. Congestion control mechanisms regulate system resources in order to

avoid network bottleneck and resource contention situations.

This subsection describes the following topics:

•

Congestion Control Configuration on page 18-73

•

Congestion Control Considerations on page 18-73

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

in order to support it.

In Figure 18-22, 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.