h the number of attached devices. Similarly, on a contention LAN, such Although local area networks have been in existence in one form or as an IEEE 802.3 CSMA/CD, as the number of devices contending another for many years, the unprecedented growth of LANs during for control of the medium increases, the number of collisions on the the latter half of the 1980s made network users increasingly aware network also rises, thereby reducing its overall performance. of the limitations of their installed networks, and refocused attention Analysis of the nature of traffic on the LAN, in most cases, led to on ways to overcome them. the conclusion that effectively segmenting the network into two or The first problems realised were those concerned with the physi- more separate LANs could increase overall network performance. cal distance of the network. A typical 10 Base 5 coaxial Ethernet, This would certainly be the case when the network could be for example, has a maximum segment length of 500 metres and may segmented into heavy users, (e.g. CAD/CAM users, computer only accommodate up to 100 'taps' per segment. rooms), and light users, (e.g. word processing). (See Figure 56.17.) The requirement to extend the length of the network led to the A further advantage of such segmentation is that failures on a development of what is commonly acknowledged as the first inter- particular segment of the LAN can be contained within that seg- network device, the repeater. ment. 56/12 Local and Wide Area Networking Departmental Backbone = REPEATER Figure 56.16 Repeater application within a building The solution to the congestion problem led to the development of Upon receipt of a data packet, bridges examine the source and the bridge, or to be more precise, the local bridge. destination address of the data packet. If the destination device is on Since a local bridge could be used to create two networks out of a a network other than that of the source device, then the bridge will single network, it followed that it could also be employed t