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Old 09-14-03, 08:22 PM   #1
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Wireless repeater channel question

I've got the D-Link DI-614+ wireless router and the DWL-800+ repeater for my home wireless network.

Should the two units (the router and the repeater) be on the same channel? It seems to me that they would interfere with each other's signals. I didn't see anything about this in the setup, but I may have missed it.

TIA.
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Old 09-14-03, 08:45 PM   #2
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Good question. I think you can do either actually. The better way is to put them on alternate channels (1,6,11 are the non-overlapping channels) but if you do put them on the same channel it will work with with side effects (liek vastly reduced throughput).. I did read something about that, let me do some digging.
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Old 09-14-03, 08:53 PM   #3
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Looks like they typically repeat on the SAME channel... So this means that within an area of overlap I guess you'd be seeing a potentially reduced throughput. But hey, that's wireless. Another option to consider if you have not already purchased one is to use two APs and connect them via Ethernet. You can then use the same SSID on both, put them on different channels and work that way.. Less seamless but an alternative.

The IEEE is working on an 802.11(insert letter here, can't remember which) that will support PROPER roaming between APs. It's not a high priority though.
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Old 09-20-03, 09:21 PM   #4
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I've got the exact same hardware setup (DI 614+ and DWL-800) that I just set up this past week.

Both are on the same channel (8), and I have noticed no adverse effects, but...... sometimes when I check the connection speed by hovering over the network icon in the system tray, I see that the speed may drop down from 11mbps to 2 or 6mbps. Moving the laptop around will bring it back to 11mbps.

Yes I would be interested too in hearing about any adverse effects of having both devices on same channel. I may go ahead and change the channel on the repeater to see what happens too.
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Old 09-20-03, 10:24 PM   #5
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11Mb/s 2Mb/s etc. are the "line rates" through the air. The clocking.

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 8 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.

If your repeater will listen on channel 8 and rebroadcast on another channel you're good. Just remember that there is overlap between the channels. So 1 overlaps with 2,3. 2 overlaps with 1,3,4 etc. The non-overlapping channels are 1,6 and 11. So if you are using 8 right now you should not be using 6,7,9 or 10. To do this your repeater needs to have two radios. So I'm not sure how common that is.

I should say that I'm no wireless guru. I could be wrong, but this is my understanding of it.
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Old 09-21-03, 04:12 PM   #6
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Thanks for the in-depth explanation. One problem though, when set to "repeater" mode, the DWL-800 does not allow the selection of the channel. If you configure it as an access point, it does.

I did, however, change my router channel to 11 (one of those not shared). When I did this, the DWL-800 immediately showed the change to channel 11, as did my two laptops.

Not sure if that will make any difference or not, but performance does not really seem to be an issue--- I am more concerned with adequate signal strength in the lower level of my home/deck that maintains good performance and I think I have accomplished that.
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Old 09-21-03, 04:57 PM   #7
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Yeah I had a feeling that would be the case. That's because it only has one radio. So to listen and transmit on another channel they'd have to build a second radio.

Glad thing are working out. The performance issues will increase in proportion to load. So with one or two clients who are not running flat out it should not be too much of a problem.

The "better" way to do it is to use a second Router/AP on an alternate non-overlapping channel with the same SSID. Of course this requires running a cat5 cable between the two router/APs which is not always possible.

Anyway, glad you have it working. :)
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