Expand Configuration and Management Manual (G06.24+)

Tuning
Expand Configuration and Management Manual—523347-008
20-21
Network Topology
pair-count shortfall. This is continued until there are no excess pairs or all possible
moves increase the load-factor spread.
Network Topology
Network topology is the pattern of interconnection of nodes in the network. Network
topology, particularly the location of passthrough nodes, can affect response time.
Passthrough traffic is shown in Figure 20-5.
As shown in Figure 20-5, node \B handles passthrough traffic between node \A and
node \C, so it must have two Expand line-handler processes: one for node \A and one
for node \C. As a result, passthrough traffic uses at least twice as much processor time
as does direct traffic.
Passthrough data has a 4-to-1 priority over locally originated data. This ratio is tuned
fairly well for small passthrough packets. If all nodes in a route are configured for a
large variable packet size (PATHPACKETBYTES modifier) such as 4095 bytes, the
intermediate nodes can send up to 16 Kbytes of passthrough traffic between packets of
a locally originated message.
Configuring a large variable packet size might have undesirable consequences at
nodes in Expand networks that support network applications and provide connectivity
between other network nodes. Using the default value for PATHPACKETBYTES (1024
bytes) allows a maximum of 4 Kbytes of passthrough data between locally originated
packets; however, each local request can now be up to 1 Kbytes.
Figure 20-5. Passthrough Traffic
Note. The advantages and disadvantages of different network topologies are discussed in
Section 3, Planning a Network Design.
Node \A Node \B
Node \C
$LINEB $LINEA $LINEC $LINEB
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