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

Tuning
Expand Configuration and Management Manual — 529522-013
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Measuring Passthrough Traffic
Measuring Passthrough Traffic
Although passthrough traffic is reported in the SYSTEM entity (SENT-FWD and RCVD-
FWD counters), Measure does not directly account for the source and destination of
passthrough traffic when examining a path. An Expand line-handler process only sees
the node to which it is connected. The only way to map the passthrough traffic
accurately is to know the topology of your network and to measure each Expand line-
handler process on each node. This is usually not feasible or necessary for most
tuning efforts.
Setting Measurement Intervals
It is important to set appropriate measurement intervals when using Measure to
characterize Expand network performance. For example, if you want to define the peak
traffic of a path at a critical hour during the day, you should take a sample at short
intervals of perhaps 1-minute during the sample period. To gather information for a
daily traffic profile, you should take a sample every 30 minutes during a 24-hour period.
Regardless of your objectives, you should make sure that you take samples often
enough so that you do not allow Measure’s counters to overflow.
You can simultaneously measure the same Expand entities with more than one interval
using two separate measurement files. An effective management strategy is to sample
network performance at long intervals (possibly every hour on a regular basis) while
simultaneously taking short-interval snapshots during critical periods for a particular
study.
Tuning Examples
The figures shown in this subsection are based on actual Expand networks. These
figures demonstrate simple methods for capturing and analyzing data, estimating
results, and adjusting tunable Expand network components. All the data shown was
captured by Measure or SCF and then extracted manually and entered in spreadsheet
programs.
Example 1: Changing Packet Size
This example illustrates one simple method to determine if altering a path’s packet size
can reduce processor overhead and improve bandwidth utilization on communications
lines. Data for this type of analysis is available using Expand subsystem SCF PATH
STATS command or the Measure NETLINE utility. Measure is preferred for long-term
studies, while data shown by SCF PATH STATS is resettable and can be used to log
statistics for any range of time. Example 19-6 on page 19-29 is an example of an SCF
PATH STATS display.
Note. Measuring adds no burden to the measured entity; the counters maintained by the
system are sampled by Measure without affecting the measured process.