PERSONAL AREA NETWORK
A personal area network (PAN) is a computer network used for communication among computer devices (including telephones and personal digital assistants) close to one person. The devices may or may not belong to the person in question. The reach of a PAN is typically a few meters. PANs can be used for communication among the personal devices themselves (intrapersonal communication), or for connecting to a higher level network and the Internet (an uplink).
Personal area networks may be wired with computer buses such as USB and FireWire. A wireless personal area network (WPAN) can also be made possible with network technologies such as IrDA and Bluetooth.
A Bluetooth PAN is also called a piconet, and is composed of up to 8 active devices in a master-slave relationship (up to 255 devices can be connected in "parked" mode). The first Bluetooth device in the piconet is the master, and all other devices are slaves that communicate with the master. A piconet typically has a range of 10 meters, although ranges of up to 100 meters can be reached under ideal circumstances.
Recent innovations in Bluetooth antennas have allowed these devices to far exceed the range for which they were originally designed. At DEF CON 12, with the right equipment a group of hackers known as "Flexilis" was able to achieve connectivity to bluetooth devices more than half a mile away. The type of antenna used was homemade and Yagi-based. They named the antenna "The BlueSniper". This is a rifle stock with a scope and Yagi antenna attached. A cable attaches the antenna to the Bluetooth card, which can be in a PDA or laptop computer. The laptop can be carried in a backpack with the cables connecting into the backpack, giving it the Ghostbusters look.
Another PAN technology, Skinplex, transmits via the capacitive near field of human skin. Skinplex can detect and communicate up to one meter from a human body. It is already used for access control (door locks) and jamming protection (so people are not caught in convertible roofs) in cars.
LOCAL AREA NETWORK
A local area network (LAN) is a computer network covering a small local area, like a home, office, or small group of buildings such as a home, office, or college. Current LANs are most likely to be based on switched Ethernet or Wi-Fi technology running at 10, 100 or 1,000 Mbit/s.
LAN redirects here, for other uses see LAN (disambiguation).
The defining characteristics of LANs in contrast to WANs (wide area networks) are: their much higher data rates; smaller geographic range; and that they do not require leased telecommunication lines.
Although switched Ethernet is now most common at the physical layer, and TCP/IP as a protocol, historically many different options have been used (see below) and some continue to be popular in niche areas. Larger LANs will have redundant links, and routers or switches capable of using spanning tree protocol and similar techniques to recover from failed links. LANs will have connections to other LANs via routers and leased lines to create a WAN. Most will also have connections to the large public network known as the Internet, and links to other LANs can be 'tunnelled' across this using VPN technologies.
HomePNA (also known as Home PNA, HPNA, Home Phoneline Networking Alliance, Home Phoneline Networking and Homepna) is an incorporated non-profit association of more than 150 companies, including the founding companies Epigram, Inc., 3Com, AMD, AT&T, Compaq,HP, IBM, Intel, Lucent, Rockwell and Tut Systems. The Home Phoneline Networking Alliance seeks to establish standards among telecom, computer and network products such that they are compatible for HomePNA. Home Phoneline Networking Alliance does not enforce standards; it provides advice to the International Telecommunication Union (ITU) which is a standards body.
POWER LINE COMMUNICATION
Power line communication (PLC), also called Mains Communication, Power Line Telecoms (PLT), Powerband or Power Line Networking (PLN), is a term describing several different systems for using power distribution wires for simultaneous distribution of data. The carrier can communicate voice and data by superimposing an analog signal over the standard 50 or 60 Hz alternating current (AC). It includes Broadband over Power Lines (BPL) with data rates sometimes above 1 Mbit/s and Narrowband over Power Lines with much lower data rates. Traditionally electrical utilities used low-speed power-line carrier circuits for control of substations, voice communication, and protection of high-voltage transmission lines. High-speed data transmission has been developed using the lower voltage transmission lines used for power distribution. A short-range form of power-line carrier is used for home automation and intercoms.
METROPOLITAN AREA NETWORK
Metropolitan Area Networks or MANs are large computer networks usually spanning a campus or a city. They typically use wireless infrastructure or optical fiber connections to link their sites.
For instance a university or college may have a MAN that joins together many of their local area networks (LANs) situated around site of a fraction of a square kilometer. Then from their MAN they could have several wide area network (WAN) links to other universities or the Internet. Specifically, this type of MAN is known as a campus area network.
Some technologies used for this purpose are ATM, FDDI and SMDS. These older technologies are in the process of being displaced by Ethernet-based MANs (e.g. Metro Ethernet) in most areas. MAN links between LANs have been built without cables using either microwave, radio, or infra-red free-space optical communication links.
DQDB, Distributed Queue Dual Bus, is the Metropolitan Area Network standard for data communication. It is specified in the IEEE 802.6 standard. Using DQDB, networks can be up to 30 miles long and operate at speeds of 34 to 155 Mbit/s.
Several notable networks started as MANs, such as the Internet peering points MAE-West and MAE-East and the Sohonet media network
WIDE AREA NETWORK
A wide area network or WAN is a computer network covering a wide geographical area, involving a vast array of computers. This is different from personal area networks (PANs), metropolitan area networks (MANs) or local area networks (LANs, first invented by the United States military during the Cold War, the network was known as ARPAnet) that are usually limited to a room, building or campus. The most well-known example of a WAN is the Internet.
WANs are used to connect local area networks (LANs) together, so that users and computers in one location can communicate with users and computers in other locations. Many WANs are built for one particular organization and are private. Others, built by Internet service providers, provide connections from an organization's LAN to the Internet. WANs are most often built using leased lines. At each end of the leased line, a router connects to the LAN on one side and a hub within the WAN on the other. Leased lines can be very expensive. Instead of using leased lines, WANs can also be built using less costly circuit switching or packet switching methods. Network protocols including TCP/IP deliver transport and addressing functions. Protocols including Packet over SONET/SDH, MPLS, ATM and Frame relay are often used by service providers to deliver the links that are used in WANs. X.25 was an important early WAN protocol, and is often considered to be the "grandfather" of Frame Relay as many of the underlying protocols and functions of X.25 are still in use today (with upgrades) by Frame Relay.
Academic research into wide area networks can be broken down into three areas: Mathematical models, network emulation and network simulation.
Such a network generally requires the crossing of public right-of-ways, and rely at least in part on circuits provided by a common carrier, Typically, a WAN consists of a number of interconnected switching nodes. A transmission from any one device is routed through these internal nodes to the specified destination device. These nodes (including the boundary nodes) are not concerned with the contents of data; rather their purpose is to provide a switching facility that will move the data from node to node until they reach their destination. Performance improvements are sometimes delivered via WAFS or WAN Optimization.
Traditionally, WANs have been implemented using one of the two technologies: circuit switching & packet switching. Transmission rate usually range from 1200 bits/second to 2 Mbps. Typical communication links used in WANs are telephone lines, microwave links & satellite channels.
Active networking is a communication paradigm that allows packets flowing through a communication telecommunications network to dynamically modify the operation of the network. The active network architecture is comprised of execution environments (similar to a unix shell that can execute active packets), a node operating system capable of supporting one or more execution environments, and active hardware, capable of routing or switching as well as executing code within active packets. This differs from the traditional network architecture which seeks robustness and stability by attempting to remove complexity and the ability to change its fundamental operation from underlying network components. Network processors are one means of implementing active networking concepts. Active networks have also been implemented as overlay networks.
Active networking allows the possibility of highly tailored and rapid "real-time" changes to the underlying network operation enabling such ideas as sending code along with packets of information allowing the data to change its form (code) to match the channel characteristics. The smallest program that can generate a sequence of data can be found in the definition of Kolmogorov Complexity. The use of real-time genetic algorithms within the network to compose network services is also enabled by active networking.
Client-server is a network architecture which separates the client (often a graphical user interface) from the server. Each instance of the client software can send requests to a server or application server. There are many different types of servers; some examples include: a file server, terminal server, or mail server. While their purpose varies somewhat, the basic architecture remains the same.
Although this idea is applied in a variety of ways, on many different kinds of applications, the easiest example to visualize is the current use of web pages on the internet. For example, if you are reading this article on Wikipedia, your computer and web browser would be considered a client, and the computers, databases, and applications that make up Wikipedia would be considered the server. When your web browser requests a particular article from Wikipedia, the Wikipedia server finds all of the information required to display the article in the Wikipedia database, assembles it into a web page, and sends it back to your web browser for you to look at.
A peer-to-peer (or P2P) computer network is a network that relies primarily on the computing power and bandwidth of the participants in the network rather than concentrating it in a relatively low number of servers. P2P networks are typically used for connecting nodes via largely ad hoc connections. Such networks are useful for many purposes. Sharing content files (see file sharing) containing audio, video, data or anything in digital format is very common, and realtime data, such as telephony traffic, is also passed using P2P technology..
A pure peer-to-peer network does not have the notion of clients or servers, but only equal peer nodes that simultaneously function as both "clients" and "servers" to the other nodes on the network. This model of network arrangement differs from the client-server model where communication is usually to and from a central server. A typical example for a non peer-to-peer file transfer is an FTP server where the client and server programs are quite distinct, and the clients initiate the download/uploads and the servers react to and satisfy these requests.
Some networks and channels, such as Napster, OpenNAP, or IRC @find, use a client-server structure for some tasks (e.g., searching) and a peer-to-peer structure for others. Networks such as Gnutella or Freenet use a peer-to-peer structure for all purposes, and are sometimes referred to as true peer-to-peer networks, although Gnutella is greatly facilitated by directory servers that inform peers of the network addresses of other peers.
Peer-to-peer architecture embodies one of the key technical concepts of the internet, described in the first internet Request for Comments, "RFC 1, Host Software"  dated 7 April 1969. More recently, the concept has achieved recognition in the general public in the context of the absence of central indexing servers in architectures used for exchanging multimedia files.