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In the case of virtual circuit a specific route is

established for the entire transmission, which all

packets belonging to the same transmission will

use. In contrast to circuit switched networks,

described above, no specific resources are dedi-

cated to this transmission. This means that the

packets sent would be received in the same order

that they were sent, but the inter-arrival times

could differ. The traffic load on the route chosen

could vary during the transmission and hence

also the inter-arrival times of the packets.

Convergence

In general the connection-oriented networks are

thought of as voice networks, while connection-

less networks are thought of as data networks.

The growth in voice and data transmissions on

the networks has had different outcome. A

generic diagram of their respective growth is

depicted in Figure 1.

The idea of converging both voice and data into

the same network is not a new one, however the

prerequisite for doing it has not yet been fully

present on a more global basis. For many rea-

sons, data networks (i.e. packet switched net-

works) are generally more efficient than the

voice networks (i.e. circuit switched networks).

Further, the growth in data traffic is far greater

than that of voice traffic. It should however be

pointed out that voice connections are still

greater in number than data connections. If we

look at the convergence of the two networks, it

makes much more sense to enhance the capabili-

ties of the packet switched network to also cater

for the voice traffic than vice versa. If this is the

solution something has to be done to the voice

traffic coding and transmission in order to make

it suitable for a packet switched environment.

VoIP Applications

The real power of data and telephony integration

is its potential to spawn new applications. Inte-

gral to this opportunity is the use of industry

standard architectures upon which independent

third parties can build applications. Such appli-

cations have the power to spark radical shifts in

collective business behaviour. While the poten-

tial impact of this convergence is enormous, the

size of the separate installed bases of data and

voice make integration a formidable task. Solu-

tions available have generally been limited to

point to products with relatively narrow scope

and with no answer to the installed base dilemma.

Some examples of voice over IP (VoIP) applica-

tions that are possible and also likely to happen

are;

• Internet-aware telephones – “ordinary” tele-
  phones that are enhanced to also cater for
  Internet access. An example could be to look
  up a telephone number in a directory over the
  Internet and directly dial the received number.


• Voice calls from a mobile PC via the Internet
  
  
  • to use the PC in the hotel room or at a meet-
    ing connected to the Internet to call the office
    for some information. This could also be used
    to send and receive voice mail.
  
  
  
  


• Voice calls from Internet cafés – not only to
  play some games and look at the ordinary
  email, the Internet café could also be a place
  for making calls to friends all over the world
  or receive voice mails.


• Public telephone gateways – this could enable
  interconnections between the Internet and the
  public telephone network. Features of this
  configuration is for example that a voice
  application on a PC could connect to the pub-
  lic telephone network gateway closest to the
  destination and from this point the connection
  goes through the public telephone network.
  In this way long distance charges are avoided
  even though the receiver of the call is only
  connected through the public telephone net-
  work.


• Information centre access – through different
  types of call centres people call to get infor-
  mation. If this voice call is made through the
  VoIP concept via the Internet the same con-
  nection could also contain data transfer. The
  requested information (long number series,
  instructions, account statements, pictures,
  manuals, ...) could be received in parallel.
  This further enables a continued discussion
  where both parts have the same document
  (information) in front of them, which will cer-
  tainly decrease the possibilities of misunder-
  standings.

Speech Quality and

Characteristics

Speech quality and characteristics is a very

important, however subjective matter. The same

quality as for ordinary telephony is viewed as a

basic requirement, although some experts argue

that a cost function versus quality trade-off

should be applied.

Figure 1 The generic growth
of data and voice transmis-
sions in the networks versus
time

Traffic

Data

Voice

Time