17.6 LAN BRIDGE

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A bridge is used to interconnect two LANs. If both LANs use the same set of protocols, the bridge need not do any protocol conversion. However, if the two LANs run different protocols, the bridge needs to do the necessary protocol conversion. Figure 17.7 shows the protocol conversion required. One LAN is based on IEEE 802.3 standard running CSMA/CD protocol. The other LAN is based on IEEE 802.4 standard running Token Ring protocol. The bridge has to run both the stacks as shown in the figure. It takes a packet from the 802.3 LAN and obtains the LLC frame. The LLC frame is then given to the 802.4 MAC protocol for transfer over the physical medium.

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Figure 17.7: LAN bridge.

A bridge interconnects two LANs. If the protocols used by the two LANs are different, the bridge will carry out the necessary protocol conversion.

All the LANs mentioned in this section use guided media (twisted pair, coaxial cable, or optical fiber) as the transmission medium. Another set of IEEE standards is available for wireless LANs (WLANs). WLANs have become extremely popular in recent years. These WLAN standards are discussed in the next section.

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