Any selection of a VoIP application has to be based on the existing
Internet connection a user has been provided with. If, for example, the G.711
codec is to be used with a 56K connection, there will be a sort of communication
that is not to be performed. For such a connection the G.723.1 and G.729 codecs
are considered to be the ideal ones.
Jitter. Assuming that a codec is capable of providing voice packets every 30ms,
the person’s to be called telephone appliance or application will have
to receive these packets every 30ms. Unfortunately, the delays due to the Internet,
with the intervention of dozens of networks and routers, seem to be the cause
to the problem. Yet, it looks that buffers in both VoIP applications and appliances
are a partial solution to the problem.
Delay. Any delays while coded packets are being created by codecs are added
to the one caused by the Internet, adding thus to the appearance of problems.
instance, Internet delay while a VoIP communication is being performed must
range between 150 and 450ms and the codec delay to follow must not exceed 40ms
voice packets are being created.
Lost packets. While a data transfer in the Internet is carried out, loss of
some packets is expected up to a point and can be dealt with, with the help
techniques. In voice transmission though, the margins to the loss of packets
are not many, since the problems arising are to be immediately “heard” by
both parties involved. The selection of an ISP with a high quality network
and an efficient bandwidth may be the most effective measure of precaution
NAT/Firewall. Fear for crackers along with hackers has resulted in the addition
of firewalls to each PC as well as network, be them either big or small ones.
However, both firewalls and NATs are cause for trouble in VoIP connections.
All applications provide different ways to override these obstacles.
Echo. The really disturbing echo case [listening to our voice while the voice
of the person being called is being heard at the same time], is a common
occurrence with VoIP communication and sometimes with mobile telephony
calls. The echo
is a direct outcome of the delay in communication between the two parties.
techniques to handle the problem are being provided by all VoIP applications
and appliances as well, not to mention communication codecs themselves.
MORE INFORMATION ON VoIP
Voice over Internet Protocol is not just a single, unique protocol. It involves
a group of technologies-protocols, devices and applications, which allow
voice call compression, coding, transport and routing to IP networks, like,
for example, the LAN, theWLAN, theWAN, and naturally the Internet, by means
of overriding fixed public telephone networks. Of course, an internet voice
call may be commenced or end up to a fixed public service, while VoIP technologies
are likely to be set to operational status in some sections of a conventional
voice communication. In short, the cases setting VoIP to action are as follows:
1st VoIP case
VoIP technologies are being utilized by providers in the
telecommunications sector in this case, either in setting up their internal
network or in the so-called “last mile.” To facilitate their internal
substructure, numerous telecommunications services in the private sector have
selected to equip
themselves with cheaper TCP/IP-VoIP networks rather than developing a rather
extravagant transmission line network.
2nd VoIP case
New and profitable services offered by emergent telecommunications
VoIP providers are what this case comprises from. They are related to the relatively
cheap communication developed between VoIP subscribers throughout the world and
fixed as well as mobile networks via the Internet, overriding this way any fixed
public telephony services.
3rd VoIP case
VoIP user-VoIP user
It has to do with the birth of the Internet telephony, the two VoIP users
achieving peer- to- peer communication, through the Internet of course,
charged. Such a communication can be achieved through a computer, the
use of headphones and a microphone or any USB/DECT telephone appliance