Trunk Capacity Guidelines - 3Com corebuilder 3500 Implementation Manual

148 C 8: T
HAPTER RUNKING
Trunk Capacity
Guidelines
3Com recommends that you use trunks to increase network
availability in the following scenarios:
Switch-to-switch connections in the data center and campus
interconnect areas
Switch-to-server connections in the data center and campus
interconnect areas
Downlinks from the data center to the campus interconnect
The trunking feature in 3Com switches is currently a proprietary
implementation. No de facto standards currently exist.
The device-to-device burst-transmission rate across a trunk is limited
to the speed of just one of the port-to-port links within the trunk. For
example, the maximum burst rate over a 400 Mbps pipeline with four
trunked Fast Ethernet links is 100 Mbps. This limitation preserves
frame ordering between devices, usually by moving all traffic between
two specific MAC addresses across only one port-to-port link.
Therefore, trunking provides no direct benefit for some one-way
applications, such as server-to-server backups. This limit exists for most
vendor implementations.
The total throughput of a trunk is typically less than the bandwidth
obtained by adding the theoretical capacity of its individual links. For
example, four 1000 Mbps links do not yield a 4000 Mbps trunk. This is
true with all vendor implementations.