Up to this point we have focused on communication between two stations (with the exception of multiplexing) and have not considered the larger picture of connecting many stations. This chapter deals with local area networks which we normally refer to simply as LANs. Local area networks or LANs are used to interconnect distributed communities of computer-based DTEs located within a single building or localized groups of buildings. For example, we may use a LAN to interconnect workstations distributed around offices within a single building or a group of buildings such as a university campus, to interconnect computer-based equipment distributed around a factory or hospital complex. However, since all the equipment is located within a single establishment, LANs are normally installed and maintained by the organization. Hence they are also referred to as private data networks.
The development of LANs was motivated bY the need to share resources and information among workstations in the department or workgroup. In this chapter we discuss some aspects of LAN standards. Most LA_N standards have been developed by the IEEE 802 committee of the Institute of Electrical and Electronic Engineers (IEEE), which has been accredited in the area of LAN by the -American National Standards Institute (ANSI).
In recent years, two significant trends have altered the role of the personal computer and therefore the requirements on the LAN
The speed and computing power of personal computers has been continuously on the rise. Today's more powerful platforms support graphics-intensive applications and even more elaborate graphical user interfaces to the operating system.
Management Information Systems (MIIS) organizations have recognized the LAN as a viable and indeed essential computing platform. resulting in he focus on networking computing. This trend began with client/'server computing, which has become a dominant architecture in the business environment and the more recent intranetwork trend. Both of these approaches involve the frequent transfer of potentially large volume of data in a transaction-oriented environment.
These trends have effected the handing of large volume of data over LAN's and because applications are more interactive they have reduced the acceptable delay on data transfers. The earlier generation of 10 Mbps Ethernet and 16-Mbps token rings are simply not up to the job of supporting these requirements.
The following are the examples of requirements that call for higher-speed LANs:
Centralized server farms: In many applications, there is a need for user, or client, systems to be able to draw a huge amount of data from multiple centralized servers called server farms. An example is a colour publishing operation, in which servers typically contain tens of gigabytes of image data that must be downloaded to imaging work stations. As the performance of the servers themselves has increased, the bottleneck has shifted to the network. Switched Ethernet alone would not solve this problem because of the limit of 10 Mbps on a single link to the client.
Power workgroups: These groups typically consist of a small number of cooperating users who need to draw massive data files across the network. Some examples are a software development group that runs tests on a new software version or a computeraided design (CAD). Company that regularly runs simulations of new designs. In such cases, large amounts of data are distributed to several workstations, processed, and updated at very high speed for multiple iterations.
High-speed local backbone: As the processing demand grows, LAN's proliferate at a site, and high-speed interconnections is necessary.
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