Voice in IP networks

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Currently there is an increased interest in the implementation of triple play communications (voice, video and data) in corporate computer networks. This is because the technologies that support these solutions show their economic viability in a time when traditional telephone services reached their highest point. The introduction of IP telephony technology in the information infrastructure of the organization results in a real reduction in the cost of telephone calls. In addition, the move to IP-telephony provides a unified approach to network administration and security issues of corporate information. No need to purchase additional protection for video and voice for security since they both use the same tools as those used for the protection of the common data circulating in the corporate network.

The term “IP-telephony” means much more than just voice transmission over the IP protocol. In fact, this term denotes a wide range of multiservice networking technologies for integrated data, voice and video into existing corporate data networks. The support of voice in IP networks in the long term will replace the services of voice and video delivered through the traditional telephone network.

The main reasons for the transition to multiservice network technologies are improving the quality of customer service, cost reduction and innovation that increases the competitiveness of companies. Multiservice applications and services offered by leading manufacturers of network equipment, include:

• unified messaging
• call centers
• personal telephony
• data sharing (using tools such as NetMeeting)
• interactive and recorded video


Integrated voice, data and video is important for the development of both ISPs and corporate networks. Providers are attracted by the low-cost of packet transmission, which is between 20 to 50% of the cost of transmission over traditional voice channels. Similarly, designers of corporate networks are interested in reducing costs associated with payment of traffic and transit switching. There are also the so-called implicit savings associated with the cheapening of service and more effective control and management.

The main technological bases for triple-play services are the protocols for voice over ATM “(VoATM),” Voice over Frame Relay “(VoFR),” Voice over IP “(VoIP), and their supporting products.

Voice in the ATM network (Voice over ATM, VoATM) is using a standard emulation of the speech channel with pulse-code modulation (AAL1) or transfer to the ATM cell with a variable bit rate (AAL2). The main advantage of voice transport in ATM networks is guaranteed quality of service (QoS). Nevertheless, VoATM inherently has excessive complexity, high cost (due to the use of optical communication channels), and lack of support from manufacturers. VoATM was commonly used as a connecting highway or transit exchange between remote PBXs.

Voice over Frame Relay (Voice over FR, VoFR) is favorably compared to Voice over ATM cost and ease of use (administration). Nevertheless, the absence of Quality of Service in Frame Relay networks with the traffic saturation that is usually found in such networks, voice traffic may experience delays and hence reduction in voice quality.

Voice over IP networks (Voice over IP, VoIP) differs from the above technologies in that the transport happen at the network level and therefore voice packets can be carried out both in WAN (including networks of ATM and Frame Relay), and in local area networks (Fast Ethernet, Gigabit Ethernet).

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