Voice over Data Transports

We’ve covered the building blocks for voice/data integration. Now, let’s take a look at the different transports customers can consider. The most widely used is Voice over IP. Voice over Frame Relay and Voice over ATM are also important so we’ll cover these as well.

Standards— VoIP, VoFR, and VoATM


   – International Telecommunications Union (ITU) —International standards body for telephony
   – ITU-T H.323—International Telecommunications Union recommendation for multimedia (including       voice) networking over IP
   – International Multimedia Teleconferencing Consortium (IMTC) —International standards body       providing recommendations for multimedia networking over IP, including VoIP
   – Internet Engineering Task Force (IETF) —Internet standards body 


   – FRF.11—Implementation agreement, ratified in May 1997 by the Frame Relay Forum, that defines the       transport of voice over Frame Relay
   – FRF.12—Provides an industry-standard approach to implement small frame sizes (Frame Relay       fragmentation) to help reduce delay and delay variation
   – Other related FRF standards —FRF.6 – Customer Network Management, FRF.7 – Multicast, FRF.8 –       FR/ATM Service Interworking, FRF.9 – Data Compression, FRF.10 – Frame Relay Network to Network


   – ATM Forum:
     – Traffic Management Specification Version 4.0—af-tm-0056.000
     – Circuit Emulation Service 2.0—af-vtoa-0078.000
     – ATM UNI Signaling, Version 4.0—af-sig-0061.0000
     – PNNI V1.0—af-pnni-0055.000

Voice over Data Transports

All types of packetized voice implementations lend themselves well to both corporate and service provider use. 

The Voice over IP (VoIP) approach provide Internet service providers (ISPs) with a competitive weapon against telecommunications companies, while telecommunications companies prefer a virtual circuit environment using Voice over Frame Relay (VoFR) or Voice over ATM (VoATM).

VoIP, VoFR, and VoATM Quality

In terms of quality, voice over Frame Relay (VoFR), voice over ATM (VoATM), and voice over IP (VoIP differ). However, they also differ in terms of cost and in terms of general usability.

Frame Relay’s variance does have an impact on voice quality, but Frame Relay can maintain a business-quality level of communication at lower cost. Therefore, VoFR is slightly lower cost than VoATM, but VoFR provides some usually undetectable variations in quality. 

VoIP can go anywhere from utility quality, if used over the Internet to toll quality, if used over an intranet with QoS mechanisms enabled. Yet it will generally provide the lowest cost for connectivity. Thus, VoIP in intranets is highly viable for the business user today and provides the most attractive cost option of the three.

VoATM, meaning voice over real-time variable bit rate (RT-VBR) or constant bit rate (RT-CBR), is fully deterministic in terms of QoS. Voice quality never varies. However, VoATM is generally more costly to implement than is, say, VoFR.

All three options offer significantly lower costs than the costs of building a private or using a PSTN, and usually require a fraction of the bandwidth.

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