Data Communications Networking Devices - 4th Ed.pdf

3.1 OVERVIEW ___________________________________________________________________ 271communications support to an area ranging in size from a town or city to a state,country, or even a good portion of the entire world. Here, the major factor governingtransmission is the availability of communications facilities at differentgeographic areas that can be interconnected to route data from one location toanother.Data transmission and error ratesTwo additional areas that differentiate LANs from WANs and explain the physicallimitation of the LAN geographic area of coverage are the data transmission rateand the error rate for each type of network. LANs normally operate at a megabitper-secondrate, typically ranging from 4 Mbps to 16 Mbps, with several LANsoperating at 100 Mbps and the recently introduced Gigabit Ethernet networkoperating at 1 Gbps. In comparison, the communications facilities used to constructa major portion of most WANs provide a data transmission rate at or under the T1and E1 data rates of 1.544 Mbps and 2.048 Mbps.Since LAN cabling is primarily within a building or over a small geographicalarea, it is relatively safe from natural phenomena, such as thunderstorms andlightning. This safety enables transmission at a relatively high data rate, resulting ina relatively low error rate. In comparison, since wide area networks are based on theuse of communications facilities that are much farther apart and always exposed tothe elements, they have a much higher probability of being disturbed by changes inthe weather, electronic emissions generated by equipment, or such unforeseenproblems as construction workers accidentally causing damage to a communicationscable. Because of these factors, the error rate on WANs is considerably higherthan the rate experienced on LANs. On most WANs you can expect to experiencean error rate between 1 in a million 10 6 ) and 1 in 10 million 10 7 ) bits. In comparison,the error rate on a typical LAN may exceed that range by one or moreorders of magnitude, resulting in an error rate from 1 in 10 million 10 7 ) to 1 in 100million 10 8 ) bits.OwnershipThe construction of a wide area network requires the leasing of transmissionfacilities from one or more communications carriers. Although your organizationcan elect to purchase or lease communications equipment, the transmission facilitiesused to connect diverse geographical locations are owned by the communicationscarrier. In comparison, an organization that installs a local area networknormally owns all of the components used to form the network, including thecabling used to form the transmission path between devices.RegulationSince wide area networks require transmission facilities that may cross local, state,and national boundaries, they may be subject to a number of governmentalregulations at the local, state, and national levels. In comparison, regulations