Why VoIP?

IP clearly has a number of advantages over circuit-switching. The most
notable of these is the fact that it can leverage today’s advanced voice coding
techniques, such as the Adaptive MultiRate (AMR) coder used in
Enhanced Data Rates for Global Evolution (EDGE) and UMTS networks.
Thus, voice can be transported with far less bandwidth than the 64 Kbps
used in traditional circuit-switched networks.
If we consider, for example, the network architecture of GSM, we find
that speech from the MS must be transcoded to 64 Kbps before it enters the
MSC. Thereafter, it is carried to the destination at 64 Kbps. If the voice were
to be carried most of the way with a packet transport such as IP, then the
transcoding up to 64 Kbps might not be needed at all, or might be needed
only very close to the destination. The bandwidth savings enabled by such
technology can be significant. Of course, IP is not the only technology that
can enable such bandwidth savings. ATM, for example, can also transport
voice at rates less than 64 Kbps. IP, however, has other advantages.

Perhaps the biggest advantage of IP over technologies such as ATM is
the fact that IP is practically everywhere. Not only is it supported by every
PC on the market today, it is also supported by handheld computers and
personal organizers.ATM just does not have the same ubiquitous presence.
Moreover, the availability of IP knowledge and experience is widespread,
with numerous companies devoted to the development of IP-based applications.
If IP resides in the handset and IP is used to carry both voice and
data, then real voice-data convergence opportunities arise, offering the possibility
of exciting new services.