What is LAN, WAN, MAN?

What is a LAN, or a MAN, or even a WAN?

Let’s start with a LAN connection.

A LAN (Local Area Network) is a group of computers and the network devices connected together usually within the same building. By definition, the connections must be high-speed and relatively inexpensive (e.g. token ring or Ethernet). A “LAN Connection”   is a high-speed connection to a LAN. See “What is a LAN (local area network)?” below.

A MAN (Metropolitan Area Network) is a larger network that usually spans several buildings in the same city or town.

A WAN (Wide Area Network) is, in comparison, not restricted to a geographical location, although it might be confined within the bounds of a state or a country. A WAN connects several LANs, and may be limited to an enterprise (a corporation or an organization) or accessible to the public. The technology is high-speed, and is relatively expensive. The Internet is an example of a worldwide public WAN.

What is a LAN (local area network)?

Local area networks (LAN) are computer networks ranging in size from a few machines in a single office to hundreds or even thousands of devices spread across several buildings. They function to link computers together and provide shared access to printers, file servers, and other services. LANs, in turn may be plugged into larger networks such as larger LANs or wide area networks (WANs), connecting many computers within an organization or to the Internet.

Because the technologies used to build LANs are extremely diverse, it is impossible to describe them all except in the most general way. Universal components consist of the physical medium that connects devices, interfaces on the individual devices that connect to the medium, protocols that transmit data across the network, and software that negotiates, interprets and administers the network and its services. Many LANs also include signal repeaters, and bridges or routers, especially if they are large or connect to other networks.

The level of management required to run a LAN depends on the type, configuration, and number of devices involved, but in some cases it can be considerable. Forums for LAN discussion include news groups in the comp.dcom.lans.* hierarchy.

What is Asynchronous Transfer Mode (ATM)?

Asynchronous Transfer Mode (ATM) is a transfer protocol with the following characteristics:

• It is scalable and flexible. It can support megabit to gigabit transfer speeds and is not tied to a specific physical medium.
• It efficiently transmits video, audio, and data through the implementation of several adaptation layers.
• Bandwidth can be allocated as it is needed, lessening the impact on and by high-bandwidth users.
• It transmits data in fixed-length packets, called cells, each of which is 53 bytes long, containing 48 bytes of payload and 5 bytes of header.
• It is asynchronous in the sense that although cells are relayed synchronously, particular users need not send data at regular intervals.
• It is connection-oriented, using a virtual circuit to transmit cells that share the same source and destination over the same route.

For more information, visit the Web page of the ATM Forum.

What is Ethernet?

Ethernet (the name commonly used for IEEE 802.3 CSMA/CD) is the dominant cabling and low level data delivery technology used in local area networks (LAN). First developed in the 1970s, it was published as an open standard by DEC, Intel, and Xerox (or DIX) and later described as a formal standard by the IEEE. Following are some Ethernet features:

• Ethernet transmits data at up to ten million bits per second (10 Mbps). Fast Ethernet supports up to 100 Mbps and Gigabit Ethernet supports up to 1000 Mbps.
• Ethernet supports networks built with twisted-pair (10BaseT), thin and thick coaxial (10Base2 and 10Base5, respectively), and fiber-optic (10BaseF) cabling. Fast Ethernets can be built with twisted-pair (100BaseT) and fiber-optic (100BaseF) cabling. Currently, 10BaseT Ethernets are the most common.
• Data is transmitted over the network in discrete packets (frames) which are between 64 and 1518 bytes in length (46 to 1500 bytes of data, plus a mandatory 18 bytes of header and CRC information).
• Each device on an Ethernet operates independently and equally, precluding the need for a central controlling device.
• Ethernet supports a wide array of data types, including TCP/IP, AppleTalk, IPX, etc.
• To prevent the loss of data, when two or more devices attempt to send packets at the same time, Ethernet detects collisions. All devices immediately stop transmitting and wait a randomly determined period of time before they attempt to transmit again.

For more information Ethernet, including quick reference guides, specification overviews, and history, visit Charles Spurgeon’s Ethernet Web site at:

Also read the news groups comp.dcom.lans.ethernet and comp.dcom.cabling.

In networking, what is bandwidth and latency?

Bandwidth and latency are the two main factors governing the performance of a network. Bandwidth, typically measured in bits per second, is the rate at which data flows over the network. Latency is the time that elapses between a request for information and its arrival. Bandwidth is a measure of capacity rather than speed, but just as more water flows through a wide river than a small creek, high bandwidths generally result in faster networks. Unfortunately, a high latency can tremendously degrade the performance of even the largest capacity network. Because the speed of light is finite, there will always be some latency present, but slow servers, inefficient data packing, and excessive network hopping can add up to a lot of transmission delay. Also, while most vendors advertise the theoretical bandwidths of their products, due to bottlenecks, hardware problems, and high loads, the effective bandwidth will usually be substantially less.

Follow this link for a scorecard of the bandwidths and other characteristics of a number of networking technologies.

While the above document doesn’t address latencies, modems typically have values of around 100 milliseconds, vastly higher than any of the technologies reviewed on the scorecard. For a good overview of latency and its effects, read Stuart Cheshire’s It’s the Latency, Stupid!