1-17
Cisco IE 3000 Switch Software Configuration Guide
OL-13018-03
Chapter 1 Overview
Network Configuration Examples
Topology Options
Topology design starts with considering how devices are connected to the network. The cell network also
requires physical topologies that meet the physical constraints of the production floor. This section
provides guidelines for topology designs and describes the trunk-drop, ring, and redundant-star
topologies.
•
Physical layout—The layout of the production environment drives the topology design. For
example, a trunk-drop or ring topology is a good choice for a long conveyor-belt system, but a
redundant-star configuration is not a good choice.
•
Real-time communications—Latency and jitter are primarily caused by the amount of traffic and
number of hops a packet must make to reach its destination. The amount of traffic in a Layer 2
network is driven by various factors, but the number of devices is important. Follow these guidelines
for real-time communications:
–
The amount of latency introduced per Layer 2 hop should be considered. For instance, there is
a higher latency with 100 Mb interfaces than there is with 1 Gigabit interfaces.
–
Bandwidth should not consistently exceed 50 percent of the interface capacity on any switch.
–
The CPU should not consistently exceed 50 to 70 percent utilization. Above this level, the
switch might not properly process control packets and might behave abnormally.
These are the key connectivity considerations:
•
Devices are connected to a switch through a single network connection or an IP-enabled I/O block
or linking device if they do not support Ethernet. Most devices have no or limited failover
capabilities and therefore cannot effectively use redundant network connections.
•
Redundant connections can be used in certain industries and applications, such as process-related
industries that are applied to critical infrastructure.
Cell Network—Trunk-Drop Topology
Switches are connected to each other to form a chain of switches in a
trunk-drop
topology (also known
as a
cascaded
topology). See
Figure 1-2
.
•
The connection between the Layer 3 switch and the first Layer 2 switch is very susceptible to
oversubscription, which can degrade network performance.
•
There is no redundancy to the loss of a connection.
