IP Telephony, Advent and Future



With the ever increasing availability of the internet to big public corporations, medium businesses and individual private home networks, the use of the internet to make phone calls which is broadly refers to as IP Telephony has experience tremendously increased in recent years.

This thesis aims to look at the benefits of incorporating IP Telephony on the exiting internet infrastructures to make for a more efficient use of exiting broadband and to take a critical look at the techniques of it deployments by simulating different models.

A comparison of IP Telephony and the older convectional PSTN telephone system is made with a view to analyse their reliability, quality of service, security and availability. The technology to transfer data, video and voice simultaneously over the internet is faced with issues of competent packet switching and security; the study will therefore aim to illustrate advancement in different firewalls and encryption techniques that have been designed to greatly reduce these security concerns.

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The study concludes by discussing the viability of investing on the IP Telephony and predicting the future of Telephony based on current trends within the industry.

AIMS: The aim of this project is to look at the technologies and trend of making voice calls over the internet with the important roles of various protocols and it security implications.


2.1 What is IP Telephony

IP Telephony is the generic name for the transmission technologies for delivery of voice communication over IP networks such as the Internet or other similar packet switched networks, traditional PSTN telephone voice channel normally provides a fixed 64Kb connection, using PCM-encoded voice, and routes the call over a single path [1 William Stallings (1997) Data and computer communications. Prentice

Hall, ISBN 0-13-571274-2.].

A more conclusive definition is given by the SearchUnifiedCommunications.com as a general term for the technologies that use the Internet Protocol's packet-switched connections to exchange voice, fax, and other forms of information that have traditionally been carried over the dedicated circuit-switched connections of the public switched telephone network (PSTN) [2SearchUnifiedCommunications.com].

In this thesis the term IP Telephony which broadly refers to voice, video and data communication will be used interchangeably with VOIP which is an acronym for Voice over IP.

I will very briefly like to highlight some of the major benefits and disadvantages of deploying IP Telephony when compared to the traditional PSTN Telephone system.

  1. IP Telephony is low cost and very cheap.
  2. In Wireless connections, IP Telephony is portable.
  3. IP Telephony is location independent as long as there is access to the internet calls can be made in any part of the world.


  1. Electricity is mostly needed to make calls
  2. Emergency calls can be unreliable.
  3. Interference, echo and Data loss are some of the problems that do affect the quality of service obtainable with IP Telephony.

Broadly speaking, IP Telephony can be deployed in any of the following ways:

    • Computer to Computer: This is the most commonly used and easiest type of IP Telephony which has been popularised by Skype, the cost of this type is actually free of charges, all the users need is an internet connection to their computers and the software which is mostly free of charge installed on their computers.
    • Computer to Phone: This type has the further ability to communicate with phones on the PSTN network and a charge is applied which usually is less than what would have been charged by providers of PSTN services. The IP Telephony software has to be installed only on the computer end of the connection.
    • IP Phones: This type of deployment is free of any call charges if both users have compactable software such as Skype installed on their phones and they are connected to the internet instead of PSTN (http://threestore.three.co.uk/skype.aspx). In the case of land lines RJ-45 connector is used instead of RJ-11 and these phones looks exactly like normal phones there may be call charges if both do not have the supporting software or internet connectivity.
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IP Telephony utilises packet technology which fragments the voice traffic which is part of conversations into IP packets, traversing the network not necessarily making use of the same paths and then these regrouping at the destination.

IP telephony transmits voice communications over the network using open-standards-based Internet Protocol. [3 http://www.cisco.com/en/US/products/ps6788/Products_Sub_Category_Home.html]

One major difference between data and voice traffic is that with voice traffic, it is often importance that all the packets sent arrives at the same time at the destination even if a small fraction is lost or damaged whereas for data traffic we can afford a few delays as long as all the packets sent arrives at the destination.

One major difference between data and voice traffic is that with voice traffic, it is often importance that all the packets sent arrives at the same time at the destination even if a small fraction is lost or damaged whereas for data traffic we can afford a few delays as long as all the packets sent arrives at the destination.

IP Telephony allows for the use of any of various compression/decompression techniques which increase or decrease the quality of the conversation versus the available bandwidth, unlike the fixed voice encoding used in the convectional PSTN system.

The use of different compression/decompression techniques with voice activity detection makes IP Telephony more efficient than convectional telephony in terms of bandwidth utilisation.

One very good aspect of IP Telephony is that if a user want to make a call that need better quality and there is available bandwidth for doing so, the has the possibility of selecting an appropriate compression/decompression technique and forward error correction scheme which in conjunction with other factors can guarantee the desired call quality.

Usually the compression/decompression techniques of both devices are known before a call is initiated or it can be dynamically negotiated at call setup if the device the compression negotiations.

IP Telephony systems make use of session control protocols to regulate the set-up and termination of calls that encode speech transmission over the network as digital audio stream. The range of compression/decompression used varies between the different implementations of IP Telephony; there are some implementations that rely on high fidelity stereo while others are the compressed and narrowband speech compression methods. High fidelity which is more commonly known as hi-fi is a terminology for the high-quality reproduction of sound or images.

IP Telephony which falls in between the two fields of datacommunications and telecommunications, it struggles with which protocols would best be used as it new standard. Various protocols have been developed over the years to aid the deployment of IP Telephony which include those for signalling, supporting and media protocols [http://iptel.org/sip/siptutorial.pdf]

Two of the most common signalling protocols are SIP and H.323; they are basically used to coordinate the communication establishment and to manage the session.

The support protocols which include the Telephony Routing over IP (TRIP) and the Resource Reservation Setup Protocols (RSVP) takes care of address translation and Quality of Service (QoS) issues. The Media protocols included the transportation protocols such as Transport Control Protocol (TCP), Real-Time Protocol (RTP) and the User-Datagram Protocol (UDP) is more concern with the standards of transporting audio and video packet.