ABSTRACT
Local Area Networks (LANs) have the following characteristics:
Limited area: Most LANs cover distances from a few feet to at most a few miles. The most common LAN technology today, twisted pair Ethernet, is typically limited to 100 meters of wire between networked device and LAN hub.
High speed: Most LANs support data rates of 1M to 100M bits per second. Typical is 10M bits per second burst capacity (which does not equate to 10M bits per second sustained transmission, see below).
Private operation: LANs are normally owned and operated by the user, and reside entirely on the user’s premises.
Data mode: Today most LANs are used only for data transmission. This is beginning to change as multimedia systems push real-time voice and video applications onto the LAN.
Broadcast mode: The fundamental mode of operation is that when one station sends a data frame, all other stations receive it. Each station is responsible to listen to all the data frames and select those addressed to that particular station. This implies a need for a control mechanism to ensure that only one station sends at a time. The particular control mechanism is part of the LAN standard (see IEEE Standards below). It also facilitates multicast (sending to a group address, see Section 64.3).
Baseband or broadband: Baseband LANs transmit digital signals directly; broadband LANs modulate a carrier, typical frequency in the range 5 to 400 MHz, which permits transmission using cable TV technology.
Physical address: Each station in a LAN must have a unique address. The general solution to this is that every LAN adapter is built with a different address, 6 bytes long. Address assignment is coordinated between the manufacturer and Xerox Corporation, the creator of Ethernet. Each data frame carries the address of the destination station. Exchange of addresses at LAN startup is a responsibility of the network software in the stations.
