A Bridge is a device that interconnects two separate LANs. It is designed to store and forward frames, it is protocol independent and transparent to end station.

A bridge must contain addressing and routing capability. Two routing algorithms have been proposed for a bridged LAN environment. The first, produced as an extension of IEEE 802.1 and applicable to all IEEE 802 LANs, is known as transparent bridge and the other, developed for the IEEE 802.5 token rings, is based on source routing approach. It applies to many types of LAN including token ring, token bus and CSMA/CD bus.

Use of bridges offer many advantages, such as higher reliability, performance, security, convenience and larger geographic coverage. But, it is desirable that the quality of service (QoS) offered by a bridge should match that of a single LAN. The parameters that define the QoS include availability, frame mishaps, transit delay, frame lifetime, undetected bit errors, frame size and priority.

 Key features of a bridge are mentioned below:

  • A bridge operates both in physical and data-link layer.
  • A bridge uses a table for filtering/routing.
  • A bridge does not change the physical (MAC) addresses in a frame.
  • Types of bridges:
  • Transparent Bridges
  • Source routing bridges

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