(IP) specifications, the basic transmission protocol for the Internet.1 All IP packets include IP addresses for the sender and the receiver of the packet. Packets travel through a series of routers as they progress from sender to receiver in IP networks. The destination IP address in each packet is used by the routers to determine what path each packet should take on its way toward the receiver. Because the forwarding decision is made separately for each packet, the individual packets that make up a single data transmission may travel different paths through the network. For this reason, someone monitoring the Internet at an arbitrary point, even a point located between a sender and receiver, might not be able to collect all of the packets that make up a complete message. As monitoring takes place closer to the end user's computer or the source of the transmission, the probability of collecting all of the packets of a given message increases. Thus, monitoring the Internet to steal content or to see what content is being transferred for rights enforcement purposes can be difficult.
There is no equivalent to the telephone system's admissions control process deployed in the current Internet (i.e., there is no busy signal). If the computers attached to the Internet try to send more traffic than the network can deal with, some of the packets are lost at the network congestion points.2 Transmission Control Protocol (TCP), which is used to carry most of the Internet's data and rides on top of IP, uses lost packets as a feedback mechanism to help determine the ideal rate at which individual data streams can be carried over a network. TCP slows down whenever a packet in a data stream is lost; it then speeds up again until packets start being lost again. If there is too much traffic, all the data transmissions through the congested parts of the network slow down. In the case of voice or video traffic, this produces lower-quality transmissions. Thus, network congestion causes all applications using the path to degrade roughly evenly.3
Another difference between the Internet and the telephone networks is in the way one service provider exchanges traffic with another. In the case of the telephone networks, the individual long distance providers do not connect to each other. All long distance telephone networks must connect to each local telephone office in which they want to do business. Interconnections between providers are far more complex in the Internet,
1Individual computers are identified on Internet Protocol (IP) networks using addresses that are 32 bits long. In the Internet these addresses, known as IP addresses, must be globally unique and can theoretically identify over four billion separate computers. (The actual limit is far less than 4 billion because of the inefficiencies inherent in the processes used to ensure that the assigned addresses are unique.)
2These packets are not lost forever but are retransmitted until they are received successfully.
3For further discussion of TCP, see Stevens (1996).