Differences between bridges & Switches / Method of Switching

Differences between bridges & Switches:

The basic functionality of the bridges & Switches is same, they forward the frames based on the MAC address, by which they solved the collision problems. The main difference between them is: switches have some enhanced capabilities as compared to bridges.

Bridges:

1. The maximum number of ports is 16.
2. Bridges operate in half duplex.
3. They switch the frames by using software.
4. The frame switching rate of bridges is 10,000 to 50,000 per second (frame processing speed).
5. Each port of a bridge is a separate collision domain.
6. Only one instance of STP (Spanning Tree Protocol (which removes the layer2 loops)) for all the VLANs.
7. The method of switching is: Store & Forward.

Switches:

1. Now a day’s switch can have hundreds of ports. A typical 2960 switch is having 48 ports.
2. Switches can operate in full-duplex & half-duplex modes.
3. Switches switch frames by using hardware such as specialized processors called ASICs (Application Specific Integrated Circuits).
4. The frame switching rate of switches is in millions, a typical 2960 switch can process 2.7 million frames per second. And a high end switch such as a 6500 can process up to 400 million frames per second.
5. Each port of a switch is a separate collision domain.
6. One instance of STP for each VLAN. Per VLAN STP.
7. The method of switching is: Store & Forward.

 Method of Switching:

            I’ll discuss about the only method switches are using now a days. Actually there are three methods of switching frames.

1. Store and Forward
2. Cut-Through
3. Fragment free

Out of the above three switching methods, the most commonly used and reliable method is “Store and Forward”

Store and Forward:

            In this method when a switch receives a frame, it stores the frame in its buffer and performs the CRC (Cyclic Redundancy Check) to see whether the frame is corrupted or not.

            If the frame is corrupted then the switch won’t forward that frame to the destination device, the switch just discards the frame.

            If the frame is not corrupted then the switch will forward the frame to the destination device on basis of CAM table, if an entry for the destination mac is not found then it will flood the frame.

Representation of Hub, Bridge and Switch in network diagrams:

Hub:

Bridge:

           

Switch:

In the next post we will discuss briefly about Ethernet.