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Howard2k · 12-21-04, 10:04 AM

The adverse effect is that all devices on the same channel are using the same frequency. Just like in a room if you have two people talking at the same time things get messed up. The voices overlap. Not good.

The repeater is listening for data on channel 6 (for example, and I'm talking about wifi repeaters that re-broadcast on the same channel, as the vast majority do) and re-broadcasting it. So let's pretend that the range of the AP and the Router are the same, both 5 metres at 11Mb/s.

You want to position the repeater towards the edge of the 11Mb/s area. So you put the router 5 metres away.

Router -- 5m -- Repeater -- xm -- client. Pretend that you client is 5m away too.

Router -- 5m -- Repeater -- 5m -- client. This is ok. Kind of. What's happening is that in the space between the router and the repeater, the signal comes from the router, to the repeater, the repeater repeats it and it goes to the client. Of course it goes back to the router too. It's ignored by the router but the router cannot transmit at the same time as the repeater since they are sharing the same air. Conversely I believe that the repeater will also have problems if the router and client both transmit together. Even though the client will not see the router signal the repeater will see both.

Make sense?

So extrapolate that further and you'll see that if the client is in between the router and the repeater. Then if the transmission is sent from the router the client will hear it. That's good. But the repeater will hear it and retransmit it. So neither the client nor the router can transmit while the repeater is bouncing the signal.

There is a similar effect with multiple wireless clients of course. If you have two wireless clients and no repeater, just the router/ap then when the router is transmitting, neither client can transmit. While client A is transmitting, neither client B nor the router can transmit.

These are of course examples. The actual positioning depends on where you need coverage etc. Hope it illustrates the point though.

There are also protocols within the wireless spec such as CSMA/CA (carrier sense multiple access with collision avoidence) that play a part in making this process easier and controlling it. So it's not quite as random as it sounds above. So if Client A transmits and realises that there is Client B transmitting at the same time, they both wait a random interval and retransmit. The idea being that becaues the interval is random it will also be different on both clients. The repeater should also be running the CSMA/CA algorithm so it too should be doing this "intelligently".

Lastly. It's a vicious circle. As your clients are transmitting more data, there is a higher chance of collisions. More collisions means more re-transmissions. More re-transmissions means more traffic and more collisions.

I should say that I'm no wireless guru. I could be wrong, but this is my understanding of it.

12-21-04, 10:04 AM	#11 (permalink)
Howard2k Aximsite Legend Addicted Member Join Date: Jun 2003 Location: Toronto, Canada Posts: 13,721 Thanked 4 Times in 4 Posts Awards Showcase Total Awards: 3	The adverse effect is that all devices on the same channel are using the same frequency. Just like in a room if you have two people talking at the same time things get messed up. The voices overlap. Not good. The repeater is listening for data on channel 6 (for example, and I'm talking about wifi repeaters that re-broadcast on the same channel, as the vast majority do) and re-broadcasting it. So let's pretend that the range of the AP and the Router are the same, both 5 metres at 11Mb/s. You want to position the repeater towards the edge of the 11Mb/s area. So you put the router 5 metres away. Router -- 5m -- Repeater -- xm -- client. Pretend that you client is 5m away too. Router -- 5m -- Repeater -- 5m -- client. This is ok. Kind of. What's happening is that in the space between the router and the repeater, the signal comes from the router, to the repeater, the repeater repeats it and it goes to the client. Of course it goes back to the router too. It's ignored by the router but the router cannot transmit at the same time as the repeater since they are sharing the same air. Conversely I believe that the repeater will also have problems if the router and client both transmit together. Even though the client will not see the router signal the repeater will see both. Make sense? So extrapolate that further and you'll see that if the client is in between the router and the repeater. Then if the transmission is sent from the router the client will hear it. That's good. But the repeater will hear it and retransmit it. So neither the client nor the router can transmit while the repeater is bouncing the signal. There is a similar effect with multiple wireless clients of course. If you have two wireless clients and no repeater, just the router/ap then when the router is transmitting, neither client can transmit. While client A is transmitting, neither client B nor the router can transmit. These are of course examples. The actual positioning depends on where you need coverage etc. Hope it illustrates the point though. There are also protocols within the wireless spec such as CSMA/CA (carrier sense multiple access with collision avoidence) that play a part in making this process easier and controlling it. So it's not quite as random as it sounds above. So if Client A transmits and realises that there is Client B transmitting at the same time, they both wait a random interval and retransmit. The idea being that becaues the interval is random it will also be different on both clients. The repeater should also be running the CSMA/CA algorithm so it too should be doing this "intelligently". Lastly. It's a vicious circle. As your clients are transmitting more data, there is a higher chance of collisions. More collisions means more re-transmissions. More re-transmissions means more traffic and more collisions. I should say that I'm no wireless guru. I could be wrong, but this is my understanding of it. __________________ Always read stuff that will make you look good if you die in the middle of it.