Voice over packet: But which packet?

Despite the hoopla surrounding voice over IP and its purported savings potential, the companies currently running packetized voice tend to be using frame relay instead. The reasons are that the still questionable reliability of IP quality of service and the additional overhead associated with using IP over a packet-based Layer 2 network are giving customers pause.

While the actual percentage of installed public frame relay ports used for voice is small, voice over frame relay usage is definitely on the map. This is because frame relay is so widely deployed that even a small percentage adds up to a significant number. It is estimated that there are about 14,000 ports used for voice in the U.S. and about 18,000 in the rest of the world. While those numbers equal less than 5% of U.S. frame relay ports and less than 10% of international ports, usage is growing. Some research analysts expect the number of voice frame relay ports to quadruple over the next few years.

Customers are still shying away from running voice over IP VPNs or the Internet because of shaky service level agreements (SLA) for these types of services compared with frame relay. Most of the major frame relay service providers publicly publish their standard SLAs for frame relay, and because of frame relay's virtual circuit underpinnings and committed information rate basis (compared with IP's connectionless orientation), it is much easier to deliver appropriate levels of service for frame-based voice.

Reliability-wise, voice over IP running on a frame relay transport is equally as reliable as voice directly over frame relay, but you do add significant overhead with IP because you are encapsulating the voice in both a frame relay frame and an IP packet. Once "native IP" networks emerge and the various lower network layers are converged, the double-overhead disadvantage should disappear.

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Steven Taylor, consultant and broadband packet evangelist, and Joanie Wexler, an independent networking technology editor and writer, team up to bring you this analysis and commentary. Taylor specializes in education and market analysis, and Wexler adds incisive reporting and research. For more detailed information on most of the topics discussed in this newsletter, connect to www.webtorials.com, the first Web site dedicated exclusively to market studies and technology tutorials in the Broadband Packet areas of Frame Relay, ATM, and IP. Feedback and additional topic ideas are welcome. Please contact taylor@webtorials.com or joanie_wexler@mindspring.com>

White paper: Voice Technologies for IP and Frame Relay Networks. Motorola Information Systems Group

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