Voice over IP

VoIP Stands for (Voice over Internet Protocol) which is a category of hardware and software was originally developed to make voice communication between computers in different locations achievable. VoIP works by sending voice data in packets using IP rather than by traditional circuit transmissions of the PSTN, it converts the voice signal from the telephone into a digital signal using codec then once the voice digitise it is compressed into smaller package and then converted into datagram format, the voice datagram is then encapsulated with the appropriate UDP and IP headers and sent over the internet or private network. However it is essential in VoIP to compress voice since traffic usually travels over low-speed links.

Voice compression
Since traffic usually travels over low speed network, voice compression is essential in VoIP however ITU G.723.1 algorithm is used to maintain high quality voice.

Echo Cancellation
G.165 and G.168 are some of the specs recommended to deal with echoes, which can occur in VoIP networks. Echoes which take place as a result of any differences in the impedance in the circuit switched. [1]

Advantages of VoIP
One of the advantages of VoIP is that the telephone calls over the Internet are free; therefore the data network can be used for both voice and data, which could eliminate the expense of having a separate voice system.

Disadvantages of VoIP
VoIP does not offer any method to ensure that data packets are delivered in sequential order. Furthermore Quality of Service is not guarantee.
VoIP implementations may face problems dealing with latency, and jitter that causes non-smooth voice streams, however jitter can be controlled by a jitter buffer that avoids delay. [2]

References

1. Voice over IP now, http://www.voipnow.org/2005/09/carrying_voice__1.html
2. Fatima Ahmed, Developer.com, http://www.developer.com/voice/article.php/3112781