View metadata, citation and similar papers at core.ac.uk brought to you by CORE provided by International Institute for Science, Technology and Education (IISTE): E-Journals Journal of Information Engineering and Applications www.iiste.org ISSN 2224-5782 (print) ISSN 2225-0506 (online) Vol.3, No.4, 2013 Voice over Internet Protocol (VOIP): Overview, Direction And Challenges 1 U. R. ALO and 2 NWEKE HENRY FIRDAY Department of Computer Science Ebonyi State University Abakaliki, Nigeria 1Email:- [email protected] 2Email: [email protected] ABSTRACT Voice will remain a fundamental communication media that cuts across people of all walks of life. It is therefore important to make it cheap and affordable. To be reliable and affordable over the common Public Switched Telephone Network, change is therefore inevitable to keep abreast with the global technological change. It is on this basis that this paper tends to critically review this new technology VoIP, x-raying the different types. It further more discusses in detail the VoIP system, VoIP protocols, and a comparison of different VoIP protocols. The compression algorithm used to save network bandwidth in VoIP, advantages of VoIP and problems associated with VoIP implementation were also critically examined. It equally discussed the trend in VoIP security and Quality of Service challenges. It concludes by reiterating the need for a cheap, reliable and affordable means of communication that would not only maximize cost but keep abreast with the global technological change. Keywords: Voice over Internet Protocol (VoIP), Public Switched Telephone Network (PSTN), Session Initiation Protocol (SIP), multipoint control unit 1. Introduction Voice over Internet Protocol (VoIP) is a technology that makes it possible for users to make telephone calls over the internet or intranet networks. The technology does not use the traditional Public Switched Telephone Network (PSTN); instead calls are made over an internet protocol data network. VoIP has great benefits of increased saving, high quality voice and video streaming and several other added value services. Examples of VoIP software are: Skype, Google talks and windows live messenger (Di Wu, 2002). 2. Overview of VoIP VoIP stand for Voice over Internet Protocol. VoIP enables us to compress and convert voice signal to digital signal and transmit it through Internet Protocol (IP)-enabled network like Internet, Ethernet and Wireless LAN. VoIP uses Internet protocol to manage voice packet over Internet protocol (IP) network. Types of VoIP Service There are different types of VoIP based on the infrastructures employed by the owner of the network. Listed are some popular services used in VoIP. Computer to Computer Computer to Computer service provides Internet telephony free using the same softphone software such as Skype, Instant Messaging, AOL etc. It is a software-based VoIP service and both the caller and the receiver must be using their computer in order to place calls. The following requirement must be met to use computer to computer VoIP service: softphone software, a sound card and good Internet service. With computer to computer VoIP service, the user may not be able to call either landline or mobile phones, and also the recipient must be online in order to call him/her. Computer to phone and vice versa This is a software-based and hardware-based service. Softphone software is used to route the call to an Internet protocol and hands off to a conventional telephone network . To use the service, one needs to subscribe and be charged at a low rate. Examples include Skype, MSN and Google Talk that provides the service to enable their customers to call landline from their computer. Computer to phone requirements are Internet-enabled phone and computer, VoIP service subscription, modem and Analog Terminal Adapter to convert the call signal to digital signal and also back to analog signal. Computer to phone does not allow emergency call users and needs to have a computer connected to the internet. Phone to Phone 18 Journal of Information Engineering and Applications www.iiste.org ISSN 2224-5782 (print) ISSN 2225-0506 (online) Vol.3, No.4, 2013 This is a hardware-based service that allows the caller and receiver to call each other using the Internet. Many telephone companies use this to handle long distance calls. VoIP convert the audio sound into data packets and transfer these packets over the Internet. It allows emergence calls and does not need PSTN for initiation and termination of calls. 2.1 VoIP system Voice over Internet Protocol (VoIP) system is made up of End User Equipments, Network component, call processor, Gateway and Server. The End User Equipment is the part mainly used to access the VoIP system and communicates with other End point (Greg Tucker , 2004). End User equipments initiate and maintain the signals needed to establish calls over the IP network. It also helps to convert voice to data packet, voice and video communication, monitoring and network surveillance capability. They are connected to the network with cable and maybe wireless devices. Examples of end user equipment are IP-enabled phones, multimedia computers and VoIP enabled workstations installed with softphone . The Network Component includes routers, switches, cables, firewalls and wireless access point. There are many existing institution’s Internet Protocol networks that will enable the installation of our VoIP system. The network must be strong enough to support the VoIP system because the impact of IP network is higher than the data network. Gateway is an optional component of VoIP network that helps to route calls, handle call connection, and manage terminal and Multipoint control unit (MCU) (Mona & Nirmala, 2002). It is responsible for providing address translation, bandwidth control, and access control and helps to improve the quality of service and security of VoIP network. Gateway serves as an interface between public switched telephone networks (PSTN) and VoIP network. Gateway is made up of Signalling Gateway (GS), Media Gateway (MG), Media Controller and multipoint control unit (MCU). Signalling Gateway helps to manage signal traffic while the media gateway manages media signal. The media gateway controller manages traffic between signalling gateway and media gateway while multipoint control unit is the part that establishes conference calls between three or more people for converged voice, video and data conference. It provides audio or combination of audio, video and data conference depending on the strength of participating endpoint (Greg, 2004). Call processor is software running on end user equipment operating system that helps in call set up, call monitoring, user authorisation, signal coordination and bandwidth control. It translates a phone number to IP address. Figure 1 shows the components of VoIP system. Figure 1 Typical topology of VoIP network 19 Journal of Information Engineering and Applications www.iiste.org ISSN 2224-5782 (print) ISSN 2225-0506 (online) Vol.3, No.4, 2013 The server enables the establishment of call and support for other features in the system. The Session initiation server allows the user to forward calls to different location in the VoIP network. 2.2 VoIP Protocols and Standard There are many protocols and standards for VoIP network (H.323, SIP, MGCP, RTSP, RSVP, SDP etc) but only the most commonly used ones are discussed. H.323 protocol H.323 protocol was developed by International Telecommunication Union and Telephony (ITU-T) in 1997 based on Real-time Transport Control protocol (RTCP) for sending voice, video and data over IP-based network (Rakesh, 2000). H.323 provides multimedia conferencing on Local Area Network (LAN) and brings together point to point communication and multipoint conferences. It was widely adopted because it is reliable and easy to maintain. The components include terminals, Gateway, Gatekeeper and Multipoint control unit (MCU). Terminal is the end point that provides real-time communication for the VoIP network. Gateway is the interface between IP network and the PSTN to another H.323 gateway. It provides Internet translation between the different terminals. Gatekeeper is the most vital component of the H.323 protocol. It acts as the central point for all calls and provides services for end point registrations. The functions of Gatekeeper are: • Translate alias address to transport address • Deny or grant access based on call authorisation, source and destination address. • Call signalling with end point terminals • Control the number of terminals permitted at a time in H.323 protocol (bandwidth management) • Maintain the list of ongoing call H.323 calls to determine the busy terminals for bandwidth management. • Rejection of call from terminal due to authorisation failure in the use of H.225 signalling (Call authorisation). Another important component of H.323 protocol is the multipoint control unit (MCU). It acts as a bridge that enables two or more terminals and Gateway to participate in a multipoint conferencing. MCU is made up of Multipoint controller (MC) and Multipoint processor. Multipoint controller determines the capabilities of the network terminal using H.245 protocol stack but does not perform multiplexing of audio, video and data. Multipoint processor is responsible for multiplexing of media stream . H.323 consists of a number of protocol suites. The protocol suites and functions are listed: • H.245 provides capabilities for channel usage, advertisement, establishment and