Expand Configuration and Management Manual (G06.24+)

Tuning
Expand Configuration and Management Manual—523347-008
20-29
Tuning Examples
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 of the data shown was
captured by Measure or SCF and then extracted manually and entered in spreadsheet
programs.
Example 1: Changing Packet Size
The following 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 20-6 is an example of
an SCF PATH STATS display.
The key statistics in Example 20-6 are the Level 4/Level 3 Sent and Rcvd packets and
links. Each link reflects a network request. Each request requires at least one packet to
be sent, plus one to be received. Both packets are seen in the history.
In this example, the frame size (FRAMESIZE modifier) was 132 words and the variable
packet size (PATHPACKETBYTES modifier) was not available. The extended packet
format was enabled (L4EXTPACKETS_ON modifier), which means that 75 percent of
each packet was Expand subsystem overhead. Assuming 192 bytes of user data per
packet, the average message sizes are easily calculated using the following formula:
The following average message sizes are derived from the data shown:
Example 20-6. SCF PATH STATS Display
-------------------- LEVEL 4 MESSAGE HISTOGRAM ---------------------------
<= 64 .. 71027 <= 128 .. 25609 <= 256.. 4211
<= 512 .. 1676 <= 1024 .. 1466 <= 2048.. 370
<= 4096 .. 179 > 4096 .. 2288
-------------------- LEVEL 4 / LEVEL 3------------Average--------Average---
Packets Forwards Links Packets/Block Bytes/Block
Sent 230144 0 24888 1.0 238
Rcvd 94921 0 28559 1.0 178
L4 Packets Discarded......... 0
average_message_size = (packets / links) * 192
Average message size sent: (230144/24888) * 192 = 9.25 * 192 = 1776
Average message size received: (94921/28559) * 192 = 3.32 * 192 = 638
Average overall message size: (325065/53477) * 192 = 6.08 * 192 = 1167