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1. Evidence of such latencies can be seen in data collected by the National Laboratory for Applied Network Research, which are available at <>.

2. ISPs typically have POPs in major urban areas; a large provider might have 30 or more POPs in the United States.

3. The 30 Tbps figure was calculated by multiplying the number of strands per fiber (30) by the number of wavelengths that can be transmitted over each fiber (100) and the capacity of each fiber at each wavelength (10 Gbps). A terabit is 1012 (one thousand billion) bits per second.

4. SONET is a standard developed by telephone companies for transmitting digitized voice and data on optical fibers.

5. See <>.

6. The 10 Gbps figure results from multiplying 10 Mbps by 1,000 applications (10 Mbps × 1,000 = 10 Gbps).

7. For example, even if available bandwidth were 10 times greater than the average required, the load on certain links over short time periods could be large enough to impose large delays over those links.

8. IP is a connectionless, packet-switching protocol that serves as the internetwork layer for the TCP/IP protocol suite. It provides packet routing, fragmentation of messages, and reassembly.

9. Because of its reliance on RSVP, the int-serv model sometimes is referred to as the RSVP model.

10. With RSVP, the load on the router can be expected to increase at least linearly as the number of end points increases. Growth may even be quadratic—related to the square of the number of end points (Birman, 1999).

11. An example of a scaling issue for today's ISPs is the size of routing tables, which currently hold about 60,000 routes (address prefixes) each. Entries in the routing table consume memory, and the processing power needed to update tables increases with their size. It is important that such tables grow much more slowly than do the numbers of users or individual applications, making it infeasible to store RSVP information if it grows in direct proportion to the number of application flows.

12. The charter of the Integrated Services Over Specific Link Layers working group of the IETF is available online at <>.

13. The Department of Defense has a long-standing interest in using multicast technology to support distributed simulations. See CSTB (1997b).

14. One of the more notorious cases occurred when the "414" group broke into a machine at the National Cancer Institute in 1982, although no damage from the intrusion was detected. See Marbach (1983).

15. Unix's Network File System (NFS) protocol, commonly used to access file systems across an Internet connection, has weaknesses that enable a "mount point" to be passed to unauthorized systems. Surreptitious programs called Trojan horses can be exploited to perform actions that are neither desired by nor known to the user.break

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