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Communications of the ACM

Communications of the ACM

Technical Opinion: Does Data Traffic Exceed Voice Traffic?

Mergers and acquisitions of enormous financial proportions have been redefining the media and telecommunication industries since the Internet began to emerge as a form of mass communication and commerce. The view that the Internet represents the future on a grand scale appears to motivate many of these megadeals. More and more good money from established telecommunication corporations is chasing Internet dreams, some of them based on claims that Internet traffic exceeds telephone traffic.

But claims of data and Internet superiority over voice in terms of network traffic are exaggerated and seem to be based mostly in folklore. I offer some simple estimates to argue that voice traffic (measured in bits) far exceeds data traffic and most likely will continue to do so for the foreseeable future (see the accompanying sidebar). The gap between data and voice traffic should not be surprising. A single-spaced typed sheet of paper contains about 30,000b of ASCII, which is equivalent in bits to only about 0.5 seconds of a telephone speech channel. Thus, a five-minute telephone conversation generates as much traffic—in bits—as 640 typed sheets of paper. Speech, though natural, is an inefficient means of communication in terms of bits.

The greatly exaggerated claims by some analysts that data will exceed voice are wishful thinking, stimulated by the media and stock market frenzy surrounding the Internet. When billions of dollars chase a limited number of high-technology investment opportunities, the investment climate stimulates exaggeration and hyperbole—and increasingly risky investment strategies.

The notion that data traffic exceeds voice traffic goes back to 1961 when Frederick R. Kappel, then president of AT&T, forecast that "...within 15 years or so, the volume of information communicated between machines may be even greater than the amount of communication between people" [2]. To refute this claim, R. Hough, while at Stanford Research Institute in 1970, showed through careful analysis that telephone traffic would exceed data traffic for the foreseeable future [2]. I confirmed the conclusion that telephone traffic would continue to exceed data for the foreseeable future again two decades later [3].

Claims continue to be made by telecom analysts and executives betting billions on Internet business strategies that Internet data traffic either already exceeds voice traffic or will do so very soon—even this year. Some telecom analysts go so far as to predict the decay—and even the death of—plain old telephone service [1, 6]. Other telecom analysts claim data traffic will predominate under any Internet growth scenario [7]. But, as far as I am concerned, no real data or analysis has yet been presented to support these claims.

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The Video Factor

Is there any way Internet traffic could exceed voice telephone traffic. The only way this could occur would be for video to be carried over the Internet. Video involves long holding times, typically measured in hours of television viewing. Video requires a bit stream of about 4Mb/sec when compressed. But from an engineering perspective, a packet-switched network, like the Internet, is no way to transmit television to consumers, due to the disjointed nature and address overhead inherent in packet switching. A broadcast network architecture using either radio waves or coaxial cable is much more efficient and far less costly. The failure by telephone companies to provide switched video in the supposed convergence of television and telephony shows how visions of the future go sour. I doubt consumers will be watching television over the Internet anytime soon.

The historically "free" Internet makes it difficult to determine true costs and corresponding prices to consumers. I estimate that a reasonable price for the Internet-backbone, packet-switched network would be 1 micro-¢/b (10−6¢/b) [5]. At this price, downloading a 2MB video file would cost 16¢. This cost is not prohibitive for a typical consumer downloading a movie one time, but done routinely every day would be costly. Video compressed at 4Mb/sec would be extremely costly at 4¢/sec, or $2.40/min, although discounts would certainly be available for transmitting such large volumes of data. From a financial perspective, it would be far too costly to use the Internet to download large files, particularly video. Buying a compact disc or even renting a tape from a store and watching it through a VCR would be much less costly.

Local access for Internet traffic is the real issue for phone companies. The local telephone switch is designed to handle voice traffic with relatively short holding times and continuous transmission. Data, however, has long holding times and bursty transmission. Converted into bits, local-loop data traffic would far exceed voice telephone traffic, due to the long holding times for data. But because much of the traffic being switched is zeros, the challenge for phone companies is how to separate data from voice traffic as early as possible at the local level. One high-bandwidth solution is an asymmetric digital subscriber line (ADSL).

From a technology perspective, the requirements for voice, data, and television are quite different [4]. The need for multiple transmission modes, rates, media, and financial incentives implies different network architectures for their delivery—contrary to the claims that telephone calls will soon all be carried over the Internet.

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1. Gilder, G. The death of telephony. Gilder Tech. Rep. 2, 9 (Sept. 1997), 2.

2. Hough, R. Future data traffic volume. Comput. 3, 5 (Sept./Oct. 1970), 6–12.

3. Noll, M. Voice vs. data: An estimate of future broadband traffic. IEEE Commun. 29, 6 (June 1991).

4. Noll, M. CyberNetwork technology: Issues and uncertainties. Commun. ACM 39, 12 (Dec. 1996), 27–31.

5. Noll, M. Internet pricing vs. reality. Commun. ACM 40, 8 (Aug. 1997), 118–121.

6. Rockstrom, A., and Zdebel, B. A network strategy for survival. IEEE Commun. 36, 1 (Jan. 1998), 36–40.

7. Wohlstetter, J. Packet policies: Petabits, photons, phonemes, and the feds. New Telecom Quart. 6, 1 (First Quarter 1998), 3–13.

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A. Michael Noll is a professor at the Annenberg School for Communication at the University of Southern California in Los Angeles. His home page is at

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T1-1Table 1. Summary of Traffic Estimates

T1-2Table 2. Details of Estimates

©1999 ACM  0002-0782/99/0600  $5.00

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