Transparent Bridges

The first 802 Bridges is transparent Bridges or spanning tree Bridges. Support the design of the people first concern is completely transparent. According to their point of view, equipped with the DuoGe LAN unit in buy back the IEEE standard after Bridges, only to the connection plug into the Bridges, everything is all right. Do not need to change hardware and software, without setting address switch, do not need to load the routing table or parameters. In short what also not stem, simply insert cable is finished, the operation of the existing LAN is completely free of the Bridges any impact. This is just incredible, they finally succeeded.

Way to work

Transparent Bridges to mode of hybrid, it accepts the work and connect all the LAN transmission each frame. When a frame arrived, the bridge must be decided to discard or forwarding. If you want to, then must decide to send to which LAN. This need through a large spread in Bridges inquires's the list of the destination address and make a decision. The table can list every possible destination, and it belongs to which a output lines (LAN). The insert Bridges at the beginning of, all the hash table are empty. Because Bridges don't know any destination, and the position of dispersion algorithm (done) : the flooding every coming, and the destination of the frame to the output even unknown in the Bridges in all the LAN (except to send the frame of LAN). With the passage of time, the bridge will understand each destination location. Once you know the destination location, to send to the place only on the appropriate frame LAN, and no longer send out.

Work algorithm

The algorithm is transparent Bridges reverse learning method (backward days). According to the working way hybrid Bridges, so it can see the connected on the transfer of any one of the LAN frame. View source address can know in which LAN access on which machine, so in the hash table added a.

When the computer and Bridges, electric power, or transfer, the topology of the network will change accordingly. In order to deal with dynamic topology problem, whenever increase list item, are scattered in the noted in the frame arrival time. Whenever the destination has set up a file in the table of frame arrived, will with the current time to update the. So, from the table every time can know the final frame of the arrival time machine. There is a process of Bridges regularly scanning the hash table, clear the time early in the current time several minutes of all the table. So, if from LAN taken a computer, and elsewhere to connect to the LAN words, so in a few minutes, and it can start work without manual intervention. This algorithm also means that if the machine in a few minutes without action, then sent to its frame will have to send out, until its own sends a frame so far.

To frame routing process depends on the source LAN LAN (send) and a destination in the LAN (purpose), LAN shown below:

1, if the source LAN and purpose LAN different, then the discard the frame.

2, if the source LAN and purpose LAN is different, forwarding this frame.

3, if the goal is unknown, LAN diffusion.

In order to improve the reliability, someone in a parallel between LAN set up two or DuoGe Bridges, but this configuration caused some other problems, because in topology structure produced loop and could cause infinite circulation.

Transparent Bridges and the advantages and disadvantages of the:

The advantages of transparent Bridges are easy to install, only need to insert cable is to have done it. Usually in a bus in the net. Defect is not the best use of network bandwidth.