Introduction |
| 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 |
|
- 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.
- 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.
- 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:
- A computer based mail system
- Access to specialized computing resources not available
locally
- 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.
|