Routers

A wireless bridge is a hardware component used to connect two or more network segments which are physically separated. Consumers have been presented with wireless bridges operating in different frequencies and licensing models. One of the most prominent is the license free use of the frequency 2.4GHz reflected in the 802.11 standard.Other important frequencies used for wireless bridging are the frequencies around 5.8GHz and mm-Wave 60GHz. Both frequency bands can be used in most of the countries license free.Wireless bridges usually work only in pairs or more, and can be used in two types of implementations. They are the point-to-point link, or the point to multipoint link.In point to point link, there are a pair of bridges which are used to connect two network segments, typically in two separate buildings. In a point to multipoint scenario, one bridge is installed as the “root bridge”, and multiple non-root bridges connect to this root bridge. With this arrangement, if one non-root network segment wants to pass data to the other non-root segment, it passes it through the root bridge.During bridge setup, all the bridges must be set to the same service set identifier (SSID) and radio channel.

To translate between two segments types, a bridge reads a frame’s destination MAC address and decides to either forward or filter. If the bridge determines that the destination node is on another segment on the network, it forwards it (retransmits)the packet to that segment. If the destination address belongs to the same segment as the source address, the bridge filters (discards) the frame. As nodes transmit data through the bridge, the bridge establishes a filtering database (also known as a forwarding table) of known MAC addresses and their locations on the network. The bridge uses its filtering database to determine whether a packet should be forwarded or filtered.

* Does not limit the scope of broadcasts
* Does not scale to extremely large networks
* Buffering introduces store and forward delays - on average traffic destined for bridge will be related to the number of stations on the rest of the LAN
* Bridging of different MAC protocols introduces errors
* Because bridges do more than repeaters by viewing MAC addresses, the extra processing makes them slower than repeaters
* Bridges are more expensive than repeaters

* Self configuring
* Primitive bridges are often inexpensive
* Reduce size of collision domain by microsegmentation in non switched networks
* Transparent to protocols above the MAC layer
* Allows the introduction of management - performance information and access control
* LANs interconnected are separate and physical constraints such as number of stations, repeaters and segment length don’t apply

With source route bridging two frame types are used in order to find the route to the destination network segment. Single-Route (SR) frames comprise most of the network traffic and have set destinations, while All-Route(AR) frames are used to find routes. Bridges send AR frames by broadcasting on all network branches; each step of the followed route is registered by the bridge performing it. Each frame has a maximum hop count, which is determined to be greater than the diameter of the network graph, and is decremented by each bridge. Frames are dropped when this hop count reaches zero, to avoid indefinite looping of AR frames. The first AR frame which reaches its destination is considered to have followed the best route, and the route can be used for subsequent SR frames; the other AR frames are discarded. This method of locating a destination network can allow for indirect load balancing among multiple bridges connecting two networks. The more a bridge is loaded, the less likely it is to take part in the route finding process for a new destination as it will be slow to forward packets. A new AR packet will find a different route over a less busy path if one exists. This method is very different from transparent bridge usage, where redundant bridges will be inactivated; however, more overhead is introduced to find routes, and space is wasted to store them in frames. A switch with a faster backplane can be just as good for performance, if not for fault tolerance.