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Tuesday, September 10, 2013

What are the differences between bridges and repeaters?

Bridges and repeaters are both important devices in the field of telecommunications and computer networking. In this article we discuss about these two and differences between them. 
- The repeaters are deployed at the physical layer whereas one can find bridges at the MAC layer. 
- Thus, we called repeaters as the physical layer device. 
- Similarly, bridge is known as the MAC layer device. 
- Bridge is responsible for storing as well forwarding the data packets in an Ethernet.
- Firstly, it examines the header of the data frame, selects few of them and then forwards them to the destination address mentioned in the frame. 
- Bridge uses the CSMA/CD for accessing a segment whenever the data frame has to be forwarded to it.
- Another characteristic of a bridge is that its operation is transparent. 
- This means that the hosts in the network do not know that the bridge is also present in the network. 
- Bridges learn themselves; they do not have to be configured again and again. 
They can be simply plugged in to the network. 
- Installing a bridge causes formation of LAN segments by breaking a LAN. 
Packets are filtered with the help of bridges. 
- The frames that belong to one LAN segment are not sent to the other segments. 
- This implies separate collision domains are formed. 
The bridge maintains a bridge table consisting of the following entries:
  1. LAN address of the node
  2. Bridge interface
  3. Time stamp
  4. Stale table entries

- Bridges themselves learn that which interface can be used for reaching which host. 
- After receiving a frame, it looks for the location of the sending node and records it.
- It keeps the collision domains isolated from one another thus, giving the maximum throughput. 
- It is capable of connecting a number of nodes and offer limitless geographical coverage. 
- Even different types of Ethernet can be connected through it. 
- Even the repeaters are plug and play devices but they do not provide any traffic isolation. 
- Repeaters are used for the purpose of regenerating the incoming signals as they get attenuated with time and distance. 
- If physical media such as the wifi, Ethernet etc. is being used, the signals can travel only for a limited distance and after that their quality starts degrading. 
The work of the repeaters is to increase the extent of the distance over which the signals can travel till they reach their destination. 
- Repeaters also provide strength to the signals so that their integrity can be maintained. 
- Active hubs are an example of the repeaters and they are often known as the multi-port repeaters. 
- Passive hubs do not serve as repeaters. 
- Another example of the repeaters are the access points in a wifi network. 
- But it is only in repeater mode that they function as repeaters. 
- Regenerating signals using repeaters is a way of overcoming the attenuation which occurs because of the cable loss or the electromagnetic field divergence. 
For long distances, a series of repeaters is often used. 
- Also, the unwanted noise that gets added up with the signal is removed by the repeaters. 
- The repeaters can only perceive and restore the digital signals.
- This is not possible with the analog signals. 
- Signal can be amplified with the help of amplifiers but they have a disadvantage which is that on using the amplifiers, the noise is amplified as well. 
- Digital signals are more prone to dissipation when compared to analog signals since they are completely dependent up on the presence of the voltages. 
- This is why they have to be repeated again and again using repeaters. 

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