Computer Networks - LAN / WAN / MAN

Networking Basics

A network is a series of points or nodes interconnected by communication paths. The points or nodes may be devices dedicated to a single function, such as a PC used for client applications, or a router used to interconnect networks. The whole purpose of any network is to enable two endpoints, be they networks, servers, routers, and so on, to communicate with each other and pass data. Networks are typically differentiated by the amount of geographical coverage that they provide, as greater coverage and distance requires different technology than smaller coverage and distance networks.

 

There are three primary types of networks, the LAN, the metropolitan area network (MAN), and the wide area network (WAN).The line between each type is blurring, and is generally used in the context of planning and design for control purposes.

 

The distinguishing feature of these networks is the spatial distance covered. LANs are typically contained in a single structure or small geographic region such as a campus or building. MANs connect points or nodes in a large geographic region, such as a city-sized grouping of networks sharing a common medium such as a fiber-optic backbone connecting several city blocks worth of networks. Some of the same LAN technologies may be employed in a MAN, such as a Gigabit Ethernet.

 

WANs are geographically dispersed networks and typically use technologies different from LANs or MANs.WANs are typically comprised of high-speed circuits leased from a telecommunications provider to facilitate connectivity between networks separated by great distances. WANs use certain communications technologies such as point-to-point circuits, Frame Relay, Integrated Services Digital Network (ISDN), X.25, Asynchronous Transfer Mode (ATM), Digital Subscriber Line (DSL) and so on.

 

LAN technologies such as Ethernet, Fast Ethernet, and Gigabit Ethernet are prevalent, with some Token Ring and FDDI. This chapter focuses on LANs and Chapter 2 covers WAN technology.

 

Computer networks come in many different shapes and sizes. Over the years, the networking industry has coined terms like "LAN" and "WAN" attempting to define sensible categories for the major types of network designs. The precise meaning of this terminology remains lost on the average person, however.

 

Area Networks

For historical reasons, the industry refers to nearly every type of network as an "area network." The most commonly-discussed categories of computer networks include the following -

 

  • Local Area Network (LAN)
  • Wide Area Network (WAN)
  • Metropolitan Area Network (MAN)
  • Storage Area Network (SAN)
  • System Area Network (SAN)
  • Server Area Network (SAN)
  • Small Area Network (SAN)
  • Personal Area Network (PAN)
  • Desk Area Network (DAN)
  • Controller Area Network (CAN)
  • Cluster Area Network (CAN)

 

 

LANs and WANs were the original flavors of network design. The concept of "area" made good sense at this time, because a key distinction between a LAN and a WAN involves the physical distance that the network spans. A third category, the MAN, also fit into this scheme as it too is centered on a distance-based concept.

 

As technology improved, new types of networks appeared on the scene. These, too, became known as various types of "area networks" for consistency's sake, although distance no longer proved a useful differentiator.

 

LAN

A Local Area Network connects network devices over a relatively short distance. A networked office building, school, or home usually contains a single LAN, though sometimes one building will contain a few small LANs, and occasionally a LAN will span a group of nearby buildings. In IP networking, one can conceive of a LAN as a single IP subnet (through this is not necessarily true in practice).

Besides operating in a limited space, LANs include several other distinctive features. LANs are typically owned, controlled, and managed by a single person or organization. They also use certain specific connectivity technologies, primarily Ethernet and Token Ring.

 

WAN

As the term implies, a Wide Area Network spans a large physical distance. A WAN like the Internet spans most of the world!

A WAN is a geographically-dispered collection of LANs. A network device called a router connects LANs to a WAN. In IP networking, the router maintains both a LAN address and a WAN address.
 

WANs differ from LANs in several important ways. Like the Internet, most WANs are not owned by any one organization but rather exist under collective or distributed ownership and management. WANs use technology like Dedicated and Dial-Up Access, Integrated Services Digital Network (ISDN), Asynchronous Digital Subscriber Line (ADSL), Cable Access, Wireless Access, Frame Relay and X.25 for connectivity.

 

MAN

A Metropolitan Area Network connects an area larger than a LAN but smaller than a WAN, such as a city, with dedicated or high-performance hardware.
 

Metropolitan Area Networks (MANs) channel traffic within the metro-domain (i.e., inter-business, inter-office, metropolitan connectivity) to and from large long-haul POPS (points of presence). With the successful deployment of many long-haul fiber networks, the focus has shifted towards MANs. The goal is to bring the cost benefits and networks efficiencies of the optical networking to end-users wanting to link campuses with multi-gigabit LANs.

 

SAN

A Storage Area Network connects servers to data storage devices through a technology like Fibre Channel.

 

A SAN's architecture works in a way that makes all storage devices available to all servers on a LAN or WAN. As more storage devices are added to a SAN, they too will be accessible from any server in the larger network. In this case, the server merely acts as a pathway between the end user and the stored data.

 

Because stored data does not reside directly on any of a network's servers, server power is utilized for business applications, and network capacity is released to the end user.

 

 

LANs and WANs at Home

Home Networkers with cable modem or ADSL service already have encountered LANs and WANs in practice, though they may not have noticed. A cable/ADSL router join the home LAN to the WAN link maintained by one's ISP. The ISP provides a WAN IP address used by the router, and all of the computers on the Home Network use private LAN addresses. On a Home Network, like many LANs, all computers can communicate directly with each other, but they must go through a central gateway location to reach devices outside of their Local Area.