air at 1, 4, and 16Mbit/s. LAYER LAYER Table 56.1 shows the characteristics of some popular LANs. MEDIUM Table 56.1 Characteristics of some popular LANs Figure 56.15 OSI model of a repeater Signallin Access method Transmis Network 802.3 802.4 topology Repeaters can extend the physical range of a LAN by collecting technique medium the stream of electrical impulses on one LAN and repeating that signal on to another identical LAN. Repeaters, however are limited in their ability to extend LANs. This is because LAN architectures Broadban incorporate certain assumptions regarding propagation delays, and Bus/Tree as repeaters are added to networks, propagation delays eventually increase beyond tolerable thresholds. In addition, use of repeaters often requires careful and detailed network design and planning. Baseband (See Figure 56.16.) Twisted Since they operate at the Physical Layer, repeaters perform inde- pendently of the higher-level processing required in more complex Multi- networks. Therefore, they can effectively operate at the same speeds as the extended network. This, however, also means that repeaters are only capable of interconnecting LANs with similar protocol Bus/Star formats. Fibre Bus/Star A further advantage to the deployment of repeaters in extending a Optic LAN is that they can effectively isolate cable faults to a single segment of the extended LAN. On the other hand, indiscriminate use of repeaters can create problems with network performance and Twisted station-to-station accessibility. 56.5.2 Bridges Twisted As more and more devices become attached to the LAN, the utili- sation increases. As the amount of traffic on the network approaches Fibre the prescribed operating limits of the LAN, network efficiency begins to decrease. For example, on a non-contention LAN, such as an IEEE 802.5 Token Passing Ring, the station must wait a finite time before the token makes its way around the ring to it, thereby enabling it to Internetworking devices transmit. This minimum time to transmission increases wit