Expand Configuration and Management Manual (G06.24+)

Tuning
Expand Configuration and Management Manual—523347-008
20-11
Layer 2 Window Size
For more information about configuring the congestion control feature, refer to
Congestion Control Feature on page 18-71.
Layer 2 Window Size
At the OSI Data Link Layer (Layer 2), the mechanisms for flow control and windowing
are provided by the particular Layer 2 protocol used (for example, HDLC or, if a
network access method (NAM) is used, SNAX/APN, X25AM, ServerNet, or FOX).
Small Layer 2 windows (as specified with the TXWINDOW modifier) tend to use
communications lines inefficiently. Large Layer 2 windows can be used effectively
when propagation delay is long or line quality is very high.
For Expand-over-IP connections, the TXWINDOW modifier specifies the number of
packets the Expand-over-IP line-handler process can send to the NonStop TCP/IP
process (with which it is associated) before waiting for a reply from the NonStop
TCP/IP process; it does not control the transfer of data across the link.
Processor Type
The processing power of the NonStop S-series servers (through which a message is
transmitted) determines throughput if there are no bottlenecks in the other components
of the network. The relative processor power factors are a good starting point for
estimating Expand line-handler process performance limits.
Process location and load balancing within a system can also have a major impact on
network performance. The same type of analysis used for any other NonStop™
process can also be applied to Expand line-handler processes.
NAM Process Configuration
Configuring an Expand-over-NAM line-handler process and a NAM process in the
same processor is more processor-efficient than configuring these processes in
separate processors.
However, when an Expand line-handler process and the NAM process it uses are in
the same processor, total throughput is limited. Because you can configure an Expand
line-handler process and its associated NAM process in separate processors, you can
achieve a combined processor usage of greater than 100 percent for this type of
Expand connection.
Note. A small Layer 2 window size can be used to cope with poor quality lines when line
efficiency is not important.
Note. In general, the newer processor types are faster than the older processor types. Contact
your HP representative for detailed performance information regarding a specific type of HP
processor.