If you have read this far in the article, you should have a good basic understanding of the current state of the Internet---we hope that most of the questions you have had about the how the Internet works have been answered. Starting here we will move from FAQs and ``facts'' towards conjectures, FEOs (firmly expressed opinions), and PBIs (partially baked ideas). We first discuss congestion problems.
Nearly all usage of the Internet backbones is unpriced at the margin. Organizations pay a fixed fee in exchange for unlimited access up to the maximum throughput of their particular connection. This is a classic problem of the commons. The externality exists because a packet-switched network is a shared-media technology: each extra packet that Sue User sends imposes a cost on all other users because the resources Sue is using are not available to them. This cost can come in form of delay or lost (dropped) packets.
Without an incentive to economize on usage, congestion can become quite serious. Indeed, the problem is more serious for data networks than for many other congestible resources because of the tremendously wide range of usage rates. On a highway, for example, at a given moment a single user is more or less limited to putting either one or zero cars on the road. In a data network, however, single user at a modern workstation can send a few bytes of e-mail or put a load of hundreds of Mbps on the network. Today any undergraduate with a new Macintosh is able to plug in a digital video camera and transmit live videos to another campus or home to mom, demanding as much as 1 Mbps. Since the maximum throughput on current backbones is only 45 Mbps, it is clear that even a few users with relatively inexpensive equipment could bring the network to its knees.
Congestion problems are not just hypothetical. For example, congestion was quite severe in 1987 when the NSFNET backbone was running at much slower transmission speeds (56 Kbps) [Bohn et al. 1993]. Users running interactive remote terminal sessions were experiencing unacceptable delays. As a temporary fix, the NSFNET programmed the routers to give terminal sessions (using the telnet program) higher priority than file transfers (using the ftp program).
More recently, many services on the Internet have experienced severe congestion problems. Large ftp archives, Web servers at the National Center for Supercomputer Applications, the original Archie site at McGill University and many services have had serious problems with overuse. See [Markoff1993] for more detailed descriptions.
Congestion on the trans-Atlantic link, which has been only 6Mbps, has been quite severe, causing researchers requiring substantial bandwidth to schedule their work during the wee hours. Since the advent of WWW and CU-SeeMe video-conferencing, there has also been seriously disruptive congestion in Europe on the E-Bone.
If everyone just stuck to ASCII email congestion would not likely become a problem for many years, if ever. However, the demand for multi-media services is growing dramatically. Although the supply of bandwidth is increasing dramatically, so is the demand. If congestion remains unpriced it is likely that there will be increasingly damaging episodes when the demand for bandwidth exceeds the supply in the foreseeable future.