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Part 1
Definition of Local Area Network
Local area network is a data communication network, typically a packet communication network, limited in geographic scope. A local network generally provides high bandwidth communication over inexpensive transmission media.
Components of a Local Area Network
A Local Area Network is composed of three basic hardware elements:
  • a transmission medium (twisted pair, coaxial cable or fiber optics)
  • a mechanism for control of transmission over the medium
  • an interface to the network for the host computers or other devices - the nodes of the network - that are connected to the network.

In addition, local area networks have a fourth software component: a set of software protocols, implemented in host computers or other devices connected to the networks, which control the transmission of information from one host or device to another via the hardware elements of the network.

Relationship of Local Area Networks to Long-Haul Networks
  1. The Evolution of Networking: Local area networks share a kinship with both long-haul packet communication networks and with I/O bus structures of digital systems; their structure and protocols are rooted in packet communication, while their hardware technology derives from both networks and computer buses.
  2. Geographic Scope; Economic and Technical Considerations: Long-haul packet networks typically span distances ranging from meters to tens of thousands of kilometers; bus structures used in computer systems range from those of microprocessor systems, which can be as short as 1-10cm, to those used in large-scale multiprocessor systems, which can be as much as 100 m in length.  For long haul networks, the cost of communication is high. Wide-band common carrier circuits, satellite circuits, and private microwave links are expensive.
  3. New opportunities: The economic and technical characteristics of local area networks engender new applications of networking techniques and provide some unique opportunities to simplify traditional networking problems. The high-bandwidth and low-delay attributes of local area networks make possible distributed multiprocessor systems utilizing the sort of information sharing between processors commonly   associated with multiprocessor systems sharing primary memory. Local area networks can also be used to provide a central file system for a group of small computers which do not have their own secondary storage.  The high bandwidth of local area networks can be exploited to simplify the control structure of communication protocols by removing any motivation to minimize the length of control or overhead information in a packet. Fields of packet headers in local area networks can be arranged to simplify the processing involved in creating or interpreting the packet header, using as many bits as are necessary.
Interconnection with Other Networks
While some local area networks now in use are "stand-alone" networks, not connected to other networks, the trend is toward interconnection of local are networks with long-haul networks. There are several motivations for this:
  1. A computer based mail system
  2. Access to specialized computing resources not available locally
  3. Communication between local area networks maintained by a Compton at each of its major locations.

The interconnection of a local area network to a long-haul network presents problems,as well as benefits. At some point, the protocols used within the local area network must be made compatible with those of the long-haul networks.