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

Tuning
Expand Configuration and Management Manual — 529522-013
19 - 32
Example 2: Reducing Passthrough Traffic
through to other nodes. Passthrough traffic is shown in the SENT-FWD and RCVD-
FWD counters. Total passthrough traffic is shown in the TOTAL FORWARD column.
Notice that the source and destination of passthrough traffic cannot be identified from
Measure data.
By comparing the total DIRECT frames to the total FORWARD frames, you can
determine that \JUICE is used primarily as a switch in the network among \TOPPER,
\TONY, and \TRGGR. Ninety-seven percent of the data (1,184,392 frames, as shown
in the TOTAL FORWARD column) sent to \JUICE from \TOPPER was passed on to
other nodes.
Similar measurements made on \TOPPER and \TONY would show that all the frames
forwarded through \JUICE to and from \TONY went to \TOPPER. About 300,000 bytes
were received from \TONY and sent to \TOPPER, and about 300,000 bytes were
received from \TOPPER and sent to \TONY. As a result, \JUICE is spending more time
processing passthrough traffic between \TOPPER and \TONY than it is sending direct
traffic.
Making a direct connection between \TONY and \TOPPER would eliminate 600,000
frames of passthrough traffic on \JUICE and would cause a 40 percent reduction in
unnecessary switched traffic. Additional benefits would include a reduction in the
number of processors, communications devices, and communications links used on
\JUICE and in the network.
Measuring Passthrough Traffic in an Entire Network
Example 19-8 on page 19-33 shows another step in the complete analysis of
passthrough traffic in an Expand network. In this example, dat
a taken from SCF is
used to compute the total network overhead of passthrough traffic for each source and
destination at one node. This single-node analysis could be extended to all nodes in a
network.
Example 19-7. Passthrough Traffic From Measure SYSTEM Counters on \JUICE
<========Expand FRAMES============> TOTAL TOTAL
SYSTEM LINKS SENT RECEIVED SENT-FWD RCVD-FWD DIRECT FORWARD
===================================================================
\TOPPER 9816 21605 20549 604067 580325 42154 1184392
\TONY 98328 292025 386625 294042 310158 678650 604200
\TRIGGR 46 177 140 123022 85795 317 208817
\SCOUT 24779 51396 55189 102819 2160 106585 104979
\FURY 10529 21725 23774 50291 50734 45499 101025
Note. The table in Example 19-8 on page 19-33 was prepared by combining information from
Expand subsystem SCF PATH STATS and PROBE commands and
then manipulating the data
with a spreadsheet. The STATS command showed the traffic, while the PROBE command
showed the number of hops. Example
19-8 on page 19-33 is an illustration of one simple
technique for deriving a thorough understanding of ne
twork performance from standard, readily
available instrumentation.