CP6100 I/O Process Programming Manual

Using CP6100: Managing Lines
LINE MONITORING AND LOAD BALANCING
When you first establish a NonStop System or EXPAND network
configuration, you take into account the traffic patterns of your
network and its applications, as well as the quality you expect
of the communication lines. As the network and its applications
grow and change, and as communication carriers change their
offerings and standards, you may find you have to tune your
configuration for performance, reliability, and
cost-effectiveness.
A thorough discussion of how to tune a network, a system, or even
a CP6100 line for quality and performance is outside the scope of
this document. Such a discussion would have to include ways to
monitor line quality and throughput, to analyze the consumption
of resources, to decide on specific configuration adjustments and
analyze the impact of those adjustments on other parts of the
system. The next few pages abbreviate that effort by presenting
some general tuning guidelines and describing the tools Tandem
provides for line monitoring and load-balancing.
Monitoring Line Quality
The quality of a communication line--its ability to convey data
accurately from one place to another--affects the throughput,
reliability, and cost of applications. In the worst case, line
problems can thwart communication altogether. In other cases,
they impede performance by requiring frequent retries of the same
transmission.
It is often hard to tell whether a problem is caused by the line,
a modem, the sending or receiving station. Each has a chance to
garble information that passes through it; each can lose
synchronization. Sometimes an apparent problem signifies a real
malfunction or incompatibility; sometimes it means the equipment
can't sustain the traffic or data rate imposed on it. A line of
a given grade, with a given level of conditioning, works well for
a range of data rates; if you try to run the line at a higher
rate, it will not work as reliably. Modems, multiplexers, and
other hardware are subject to the same kinds of limitations.
Similarly, a large number of timeouts or overruns on a line need
not mean anything is broken; rather, a device in its current
configuration cannot handle all the work it is given. By
changing the configuration or balancing the load, you can often
solve what looked like a quality problem.
October 1985
3-18