Circuit switching works well for voice calls, for which it is designed. All voice is basically the
same rate - 64 kb/s without compression, i.e., 8,000 samples/s and 8 bits/sample. TDM can easily
handle bandwidth reservations of the same amount. Also, voice calls require minimal delay between
the two parties because excessive delays interfere with interactivity. Circuit switching imposes only
propagation delay through the network which is dependent only on the distance. Delay is considered
one of the important quality of service (QoS) metrics. There is also minimal information loss, another
QoS metric, because the reserved bandwidth avoids interference from other calls.
A number of drawbacks to circuit switching are typically cited for data. The first drawback is
inefficiency when data is bursty (meaning intermittent data messages separated by variable periods of
inactivity). The reserved bandwidth is wasted during the periods of inactivity. The inefficiency
increases with the burstiness of traffic. The alternative is to disconnect the call during periods of
inactivity. However, this approach is also inefficient because releasing and re-establishing a connection
will involve many signaling messages, which are viewed as an overhead cost.
Another drawback cited for circuit switching is its inflexibility to accommodate data flows of
different rates. Whereas voice flows share the same (uncompressed) rate of 64 kb/s, data applications
have a broad range of different rates. TDM is designed for a single data rate and can not easily handle
multiple data rates.