For
example, each client on a 100BaseT segment can transmit at 100 Mbps, but only one
segment at a time. The same principle can be applied to switched or bridged Ethernet
segments. A segment connecting a set of other segments to a server may have less
TDM: Circuit Bonding 277
bandwidth available than the sum of the segments connected to each workstation. This
oversubscription is a useful tool for a network designer to control network costs while
offering adequate performance.
Broadly defined, oversubscription is a state that allows more traffic to be switched
or routed over a given transmission link than that link is normally capable of transmitting.
In other words, the sum of the possible input to a given link is greater than
the link itself. In general, all networks have some form of oversubscription. Although
it is often associated with packet networks, even circuit networks are oversubscribed.
In fact, you could argue that the whole purpose of switching and routing is to oversubscribe
links purposely. For example, in a voice network, the entire capacity of voice circuits
subtending from the switch is, in practice, always larger than the capacity of the
Inter-Machine Trunks (IMTs) connecting the switch to other switches.
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