Repeater - Do Routers Regenerate

marioc

A repeater regenerates the signal which in effect extends the cable maximum cable distance. This is performed by switches and active hubs.

Do routers also act as repeaters?

Devilsbane

Yes they do.

astorrs

Yes and No (mostly No).

Yes in that they extend the signal distance, but No in that packets they "route" are changed as a result of that process (unlike layer 2 switches/hubs).

marioc

Thank you. Can you clarify your "no" statement please?

Devilsbane

marioc wrote: »

Thank you. Can you clarify your "no" statement please?

I believe he is saying that yes, they regenerate the signal (thus increasing the distance) but no, because a repeater just sends out the same signal while a router sends out a slightly different signal.

Forsaken_GA

No, a router does not function as a repeater, it operates at a higher level. A repeater connects two segments of the same network, routers move packets between networks. That is a *significant* difference.

Forsaken_GA

To clarify -

A repeater is a layer 1 device. Purely. The only thing it does is receive a signal on one interface and send it out the other. A hub is, essentially, a multi-port repeater.

A router does not just receive packets on one interface and then shunt them out the other. There is a decision making process involved.

Generally when you're talking repeater, you're talking LAN. And when you're talking LAN, you're generally talking Ethernet, and that means MAC addresses. That means when a router moves a frame from one interface to another, it makes changes to the frame. It is no longer sending the same signal.

A router is essentially terminating the signal, and then generating a new one on a different interface, it is not regenerating the same signal that it received, and is not acting in the capacity of a repeater. Extending transmission distance is *not* the sole attribute of a repeater.

astorrs

marioc wrote: »

Thank you. Can you clarify your "no" statement please?

Sure, but I see I need to clarify for everyone’s benefit.

By "Yes", I meant that in a way it extends how far the source/destination devices can be apart, but "No" in that it makes changes to the packet and doesn’t just repeat what its seen; they have very different functions and are not comparable. Probably the easiest thing to do is discuss some of the differences between these devices.

We tend to talk about modern computer networks as operating over 7 layers (the OSI model) with each layer being wrapped around a higher layer (layer 2 encapsulates layer 3, etc) something akin to Russian Matryoshka dolls, where each doll fits inside the next largest doll.



A network hub operates at layer 1 (as does a repeater) and performs essentially the same function, it “repeats” (without making any changes to other layers – we’re ignoring media conversion here for simplicity ) every packet received out every other port.

A network switch is a little smatter and can look into each packet a little deeper (to layer 2) in there it will find the MAC address of the destination and rather than broadcasting it out every port (like a hub) can consult its internal table (that it’s built by listening to the traffic crossing through it) and direct the packet out a single port where that MAC address can be found.

A network router operates at an even higher layer (layer 3) and can see inside the packet another layer (remember it’s like peeling an onion) and find the IP address of the destination device, it then looks in its routing table and determines the best path to send that packet on its way to the destination which is in a different network segment (aka subnet or broadcast domain). It does this by wrapping a new layer-2 header around the packet that specifies the MAC address of the next device along that path (which could be tens/hundreds of hops away – think the Internet - with each router in between the source/destination networks repeating this "where do I send this next" process).

Very different use cases and you’d do best in not trying to group them together as each device has a specific function.

Does that make any sense?

Note: this is a very high-level overview and there are many more differences between the devices and the layers they operate at, but I wanted to keep things simple.