|
Techniques for transmitting voice and fax
over the internet. There are two ways of making telephone calls across the
internet. The first, which relies on the use of a pc, has the
attraction of being essentially free, regardless of distance. The same as
any other dial-up internet connection used for browsing the web or sending
e-mail. A combination of hardware and software compress and convert the
sound of a voice (or a fax machine) into a binary file, which is then broken
up into packets just as any other message would be. The pc at the
recipient's end of the call then converts the packets back into an audible
voice signal.
The technology behind this sort of communication has
advanced significantly and a version of it is now included in the most
popular instant messaging programs can talk to each other freely
without the need to buy expensive bespoke hardware or software. But there
are problems with this sort of communication. In particular, the quality of
service (qos) is far from perfect because of the inherent
difficulties in managing time lags across the internet and reassembling
packets in the right order.
The second way of using the internet to make phone calls is to use
a normal telephone, but instead of the call being routed all the way on
public telephone networks, it is converted into Ip packets and then
routed via the internet. At the other end, the digitised voice is converted
back again by a local server. Although this kind of call suffers from the
same packet reassembly problems, it gets over the compatibility issue:
sender and receiver need only standard telephone equipment. It has many
benefits for business, which can use the same network to transmit voice and
data rather than rely on two separate sets of cables. Concerns about quality
of service remain, however, and many important requirements of a hybrid
service such as accounting billing and roaming support for mobile devices
have yet to be fully worked out. |
