Halving of speed of repeater... router or ISP max speed?

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2bam
DD-WRT Novice


Joined: 22 Sep 2015
Posts: 6

PostPosted: Tue Sep 22, 2015 17:33    Post subject: Halving of speed of repeater... router or ISP max speed? Reply with quote
(Note: This is a general question out of curiosity, not for a specific router model. I don't expect advice on configuration, just want to understand better because I don't have the knowledge Smile )

In various posts I've seen they just type this mantra, "It's slow because it has to double the transfers", which makes logical sense.

But I imagine it has to do with the router's throughput (e.g. 27Mbps for a 54Mbps/Wireless-G router) and not the internet provider's (E.g. 10Mbps router speed for 20Mbps ISP cap).

Because I'm getting like 7Mbps download for a 54Mbps repeater (router <-> dd-wrt <-> notebook), which is 35% of the ISP cap of 20Mbps and 13% of the Wireless-G max.

Maybe I'm missing something.
Could you clear this confusion for me?

Thanks a lot!
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Murrkf
DD-WRT Guru


Joined: 22 Sep 2008
Posts: 12675

PostPosted: Tue Sep 22, 2015 18:21    Post subject: Reply with quote
When a router acts as a bridge, it can't talk and hear at the same time. So it has to SPLIT the AVAILABLE bandwidth it has on the channel that it is using so that it can do both. Having a repeater is exactly the same as having two laptops connected to the router. It has to split the bandwidth between the clients. With equal demands from both, each will get half "speed".

So the idea of "halving" is not precise. It is splitting its communication in order to "talk" (send and receive) to two different devices. In the case of a repeater it is the primary router and the client computer that it splits its TIME between.

So the right way to see this is to see that the router cannot do two things at once, and has to talk to one device, and then the other. If the speed of each connection is equal, they will each get half of what they would otherwise have.

If there are TWO clients making EQUAL demands on the bridged router, the available bandwidth would be 1/4 of what they would get if they were the sole client hooked to the primary router, as the bridge has to spend half its time with the primary, and split the other half with the client computers.

WAN speed is normally irrelevant when looking at a bridge, as even half bandwidth on LAN can be more than available WAN. However, if two CLIENT computers want WAN at the same time, they will also have to split that speed.

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2bam
DD-WRT Novice


Joined: 22 Sep 2015
Posts: 6

PostPosted: Tue Sep 22, 2015 23:51    Post subject: Reply with quote
Just what I needed.

Thanks for the detailed info and your time.
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