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A packet (also called a network packet) is

the sequence of binary digits transmitted and switched as a composite whole.[1]
a stand-alone piece of data, like an individual piece of postal mail, and contains source, destination, and reassembly information.
[a] piece of a message, usually containing the destination address, transmitted over a network by communications software.[2]
[a] specially formatted group of bits containing data, IP address, and control information that is transmitted over a network as a collective unit.[3]


Packets are effectively anonymous; they are simply chunks of data, routed highly efficiently — though to all appearances indiscriminately — around a computer network, such as the Internet. The information is then reassembled at the end point, by means of applications installed on end user machines. It is these applications, not the network, that are concerned about the identity of the source of the information.

"Messages are usually broken down into a sequence of several transmitted packets that are reconstructed for completeness at their destination. Different systems use packets of varying sizes, and abnormal or spikes in packet length, especially in light of the protocol being used, could be indicia of malicious activity."[4]

Unlike traditional circuit-switched telephone networks, packet-switched networks do not require a dedicated line to be allocated exclusively for the duration of each communication. Instead, individual data packets comprising a larger piece of information, such as an e-mail message, may be dispersed and sent across multiple paths before reaching their destination and then being reassembled.[5] This process is analogous to the way that the individual, numbered pages of a book might be separated from each other, addressed to the same location, forwarded through different post offices, and yet all still reach the same specified destination, where they could be reassembled into their original form.[6]


  1. Cybersecurity A Primer for State Utility Regulators, App. B.
  2. Practices for Securing Critical Information Assets, Glossary, at 56.
  3. Privacy Impact Assessment EINSTEIN Program: Collecting, Analyzing, and Sharing Computer Security Information Across the Federal Civilian Government, at 7.
  4. Id.
  5. See generally Jonathan E. Uechterlein & Philip J. Weiser, Digital Crossroads: American Telecommunications Policy in the Internet Age 39-45 (paperback ed. 2007) (comparing circuit-switched and packet-switched networks).
  6. See id. at 42.

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