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LANs, WANs, MANs, GANs, and PANs

A LAN is a Local Area Network. A LAN is a comparatively small network, typically confined to a building or an area within one. A MAN is a Metropolitan Area Network, which is typically confined to a city, a zip code, a campus, or office park. A WAN is a Wide Area Network, typically covering cities, states, or countries. A GAN is a Global Area Network, a global collection of WANs.

The Global Information Grid (GIG) is the US Department of Defense (DoD) global network, one of the largest private networks in the world.

At the other end of the spectrum, the smallest of these networks are PANs: Personal Area Networks, with a range of 100 meters or much less. Low-power wireless technologies such as Bluetooth use PANs.

Exam Warning
The exam is simpler and more clear-cut than the real world. There are real-world exceptions to statements like “A LAN is typically confined to a building or area within one.” The exam will be more clear-cut, as will this book. If you read examples given in this book, and think “that’s usually true, but a bit simplistic,” then you are correct. That simplicity is by design, to help you pass the exam.

Internet, Intranet, and Extranet

The Internet is a global collection of peered networks running TCP/IP, providing best effort service. An Intranet is a privately owned network running TCP/IP, such as a company network. An Extranet is a connection between private Intranets, such as connections to business partner Intranets.

Circuit-Switched and Packet-Switched Networks

The original voice networks were circuit-switched: a dedicated circuit or channel (portion of a circuit) was dedicated between two nodes. Circuit-switched networks can provide dedicated bandwidth to point-to-point connections, such as a T1 connecting two offices.

One drawback of circuit-switched networks: once a channel or circuit is connected, it is dedicated to that purpose, even while no data is being transferred. Packet-switched networks were designed to address this issue, as well as handle network failures more robustly.

The original research on packet-switched networks was conducted in the early 1960s on behalf of the Defense Advanced Research Projects Agency (DARPA). That research led to the creation of the ARPAnet, the predecessor of the Internet. For more information, see the Internet Society’s “A Brief History of the Internet,” at https://www.isoc.org/internet/history-internet/brief-history-internet/.

Early packet-switched network research by the RAND Corporation described a “nuclear” scenario, but reports that the ARPAnet was designed to survive a nuclear war are not true. The Internet Society’s History of the Internet reports "... work on Internetting did emphasize robustness and survivability, including the capability to withstand losses of large portions of the underlying networks" [1].

Instead of using dedicated circuits, data is broken into packets, each sent individually. If multiple routes are available between two points on a network, packet switching can choose the best route, and fall back to secondary routes in case of failure. Packets may take any path (and different paths) across a network and are then reassembled by the receiving node. Missing packets can be retransmitted, and out-of-order packets can be re-sequenced.

Unlike circuit-switched networks, packet-switched networks make unused bandwidth available for other connections. This can give packet-switched networks a cost advantage over circuit-switched.