Workshop

Tree Trunks
Previous Table of Contents Next
As I mentioned in Hour 9, “Ethernet Basics,” full duplex communication between a switch and a node
such as a server is possible. This is true of both Token-Ring and Ethernet switches. This makes the
effective bandwidth double what it might ordinarily be between the server and the switch: 32Mbps for
Token-Ring and 200Mbps for Fast Ethernet.
Full duplex is really cool for connecting servers or high-utilization users to switches, but switch-toswitch
communications might need even more bandwidth than this provides, because a switch is
responsible for many more users than just one. Accordingly, some switches are starting to have the
capability to use multiple lines to communicate in between two switches. This is known as trunking. This
allows you to add as much bandwidth as might be necessary to connect two switches. You can think of
this as adding lanes to a highway.
Because the switches in Figure 14.6 have six 100Mbps segments apiece, the aggregate throughput (or
combined amount of stuff going through these switches) could be 600Mbps. To make sure that there’s
not a choke point between the two switches, you might connect three full-duplex trunks between the
switches, giving you a 600Mbps superhighway between the switches.
Figure 14.6 Full duplex and trunking can be a great solution if you need to connect high-capacity
switches.
Because trunking is relatively new on the scene—and full duplex is not terribly long in the tooth
either—you should definitely suspect compatibility issues if you implement either one or both and your
network starts acting screwy.
Summary
You can think of routers and switches as being cousins. Routers switch packets at the network protocol
(TCP/IP or IPX/SPX) level, whereas switches route packets at the data link (Ethernet or Token-Ring)
level. Switches are usually wire-speed devices, whereas routers can handle delay (as is the case over a
wide-area connection). Switches are typically used for one geographically separate area; routers are used