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Repeaters:
With many networking terms, the name is indeed the recipe, and that's very true of a repeater. A repeater's job is to repeat an electrical signal, the form that our data has taken to be sent across a cable. Remember, "it's all ones and zeros!"
The repeater takes an incoming signal and then generates a new, clean copy of that exact signal. This prevented maximum cable lengths from stopping transmissions, and also helped to wanrd off attenuation - the gradual weakeing of an electric signal as it travels.
Hub:
A hub is basically the same as a repeater, but the hub will have more ports. That's the only difference between the two. (Some hubs have greater capabilities than others, but a "basic" hub is simply a multiport repeater.)
Neither hubs nore repeaters have anything to do with the Data Link Layer of the OSI model, nor do they perform any switching at all. Hubs and repeaters are strictly Physical layer devices, and that's where the trouble comes in. For our next example, we'll consider a hub with four PCs connected to it.
To prevent this, a host on a shared Ethernet segment will use CSMA/CD (Carrie Sense Multiple Access with Collision Detection). To review, here's the CSMA/CD process:
- A host that wants to send data will first "listen to the wire", meaning that it checks the shared media to see if it's in use.
- If the media is in use, the host backs off for a few milliseconds before chcking again.
- If the media is not in use, the host sends the data.
If two PCs happen tos end data at the exact same time, the voltage on the wire will actually change, indicating to the hosts that there has been a data collision.
The two PCs that sent the data will generate a "jan signal", which indicates to the other hosts on the shared media that they should not send data due to a collision.
Those two PCs both invoke a backoff timer, also in milliseconds. When each host's random timer expires, they will each begin the entire process again by listening to the wire. Since the backoff timer value is totally random, it's unlikely the two hosts will have the same problem again.
The above topology is never suggested as it eats up a lot of bandwidth. As each time each system broadcasts some message its highly unlikely that each system needs it, but they all get it.
Bridges:
The bridges were introduced to the networks so that we can make smaller collision domains that results in fewer collisions. Typically a bridge is placed between multiple repeaters and hubs More collision domains does not means that we will have more collisions but as we segment one single network into two there will be fewer collisions The network segments are like logical divisions in physical network.
Bridges do NOT help to lower the number of broadcasts. So we still have one big broadcast domain.
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Repeaters:
With many networking terms, the name is indeed the recipe, and that's very true of a repeater. A repeater's job is to repeat an electrical signal, the form that our data has taken to be sent across a cable. Remember, "it's all ones and zeros!"
The repeater takes an incoming signal and then generates a new, clean copy of that exact signal. This prevented maximum cable lengths from stopping transmissions, and also helped to wanrd off attenuation - the gradual weakeing of an electric signal as it travels.
Hub:
A hub is basically the same as a repeater, but the hub will have more ports. That's the only difference between the two. (Some hubs have greater capabilities than others, but a "basic" hub is simply a multiport repeater.)
Neither hubs nore repeaters have anything to do with the Data Link Layer of the OSI model, nor do they perform any switching at all. Hubs and repeaters are strictly Physical layer devices, and that's where the trouble comes in. For our next example, we'll consider a hub with four PCs connected to it.
To prevent this, a host on a shared Ethernet segment will use CSMA/CD (Carrie Sense Multiple Access with Collision Detection). To review, here's the CSMA/CD process:
- A host that wants to send data will first "listen to the wire", meaning that it checks the shared media to see if it's in use.
- If the media is in use, the host backs off for a few milliseconds before chcking again.
- If the media is not in use, the host sends the data.
If two PCs happen tos end data at the exact same time, the voltage on the wire will actually change, indicating to the hosts that there has been a data collision.
The two PCs that sent the data will generate a "jan signal", which indicates to the other hosts on the shared media that they should not send data due to a collision.
Those two PCs both invoke a backoff timer, also in milliseconds. When each host's random timer expires, they will each begin the entire process again by listening to the wire. Since the backoff timer value is totally random, it's unlikely the two hosts will have the same problem again.
The above topology is never suggested as it eats up a lot of bandwidth. As each time each system broadcasts some message its highly unlikely that each system needs it, but they all get it.
Bridges:
The bridges were introduced to the networks so that we can make smaller collision domains that results in fewer collisions. Typically a bridge is placed between multiple repeaters and hubs More collision domains does not means that we will have more collisions but as we segment one single network into two there will be fewer collisions The network segments are like logical divisions in physical network.
Bridges do NOT help to lower the number of broadcasts. So we still have one big broadcast domain.
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