two AP's with same SSID for coverage

Having seen several threads about this type of WiFi coverage issue, I was wondering about having 2 AP's at ends of the house to provide better coverage....

If we have 2 AP's with the same SSID, both connected to the same IP segment, and the DHCP coming from one router, then what are the issues involved ??

Not really a roaming issue, but it can be...

SO - we have one AP upstairs in the middle of the upstairs bedroom area, and another down in the family room area. Will you "associate" with the strongest signal ? Is that always true ? In the middle, can you ping-pong between them ?

For the most part - you are either upstairs or downstairs. What happens if you are downstairs, and then walk up to your room to do homework - will you re-associate with the closer & stronger AP ?

Just wondering how this could/would/should work with multiple AP's all on the same channel & SSID ?

Reply to
ps56k
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The multiple APs should be set to DIFFERENT channels and the same SSID. This is the standard configuration for multiple APs and wireless roaming. It generally works well, though is best with identical APs and the same protocol (e.g. both 11g). Yes, you will re-associate with stronger signal AP. You will not generally "ping pong" between them is signal strengths are similar. It's generally no problem to move from one coverage area to the other though if you have an active download (for example) going on it could be interrupted by the momentary delay in the changeover.

Reply to
GTS

~ Having seen several threads about this type of WiFi coverage issue, ~ I was wondering about having 2 AP's at ends of the house ~ to provide better coverage.... ~ ~ If we have 2 AP's with the same SSID, ~ both connected to the same IP segment, ~ and the DHCP coming from one router, ~ then what are the issues involved ??

Should work. This is the best way to provide WiFi coverage to a house that can't be covered by one AP.

~ Not really a roaming issue, but it can be... ~ ~ SO - we have one AP upstairs in the middle of the upstairs bedroom area, ~ and another down in the family room area. ~ Will you "associate" with the strongest signal ?

Hopefully.

~ Is that always true ? In the middle, can you ping-pong between them ?

Could happen. Wireless clients have gotten smarter about roaming over the last few years.

~ ~ For the most part - you are either upstairs or downstairs. ~ What happens if you are downstairs, and then walk up to your room ~ to do homework - will you re-associate with the closer & stronger AP ?

You probably will. Some clients may remain associated with first AP till they absolutely can't communicate any longer, and only then will scan for a new AP.

~ Just wondering how this could/would/should work with multiple AP's ~ all on the same channel & SSID ?

In the general case, this can be quite complicated, but in your case I wouldn't worry about it too much. However, I will note that our APs should probably NOT be on the SAME channel, but on different non-overlapping channels. I.e., if using 2.4GHz in the US, you would likely want to use two of {1, 6, 11}. Otherwise the two APs will interfere with each other and you will get reduced performance.

Aaron

Reply to
Aaron Leonard

why the same? To eliminate the prob I have different SSID's (don't roam, just associate with whichever gets the best signal, PPinUSA and PPinUSB)... As to your q, depends on your client software, no standards if it hangs on to the last one, or trys to reassociate with a stronger one).... Actually have a 3rd now (PPinUSN, mimo/pre-n, so devices that can do it's n can see that too)

Reply to
Peter Pan

Meru Networks have been doing this as an enterprise solution for a while.

Reply to
LR

just looked at the setup screen thing for my linksys pre-n, and you CAN't set a channel! manual at

formatting link
(guess there are no more channels, but you can change the ssid)

Reply to
Peter Pan

If you want lots of speed, the spatial diversity flavor of 802.11n needs two 40MHz wide channels crammed into 83.5MHz of available spectrum. The two channels are always the same. In effect, this mode uses the entire legally allowed bandwidth. Therefore, you have no choice.

If you set the access point for 20Mhz channel mode, which is the same channel bandwidth used by ordinary 802.11g, you can select from the usual assortment of 11 channels.

Incidentally, even if you decide to use two 40MHz channels (wideband mode), all it takes is one local 802.11g radio, and the system switches to CTS (flow control) mode to prevent collisions and interference. The only way it works fast is if everything is using

802.11n. There are some comments on this and other issues at:
Reply to
Jeff Liebermann

If your setting for "Radio Band" is set to "Standard-20MHz Channel" then you can set the Channel No. in the "Standard Channel" box.

Reply to
LR

Could you clarify the "use 2 40MHz channels" as I was under the impression that 802.11n could use 2 20MHz channels to produce one 40MHz channel and that they haven't as yet tried to bond 2 40MHz "channels".

Reply to
LR

my understanding is that instead of using numbers (and IMO there aren't 11 since some overlap, so you could really only use 3 anyway), now they use the terms primary and secondary, each being twice as wide but not bonded... think 3 1 inch hoses (labeled #1 #6 #11) versus 2 2 inch hoses (labeled primary and secondary), which would you rather use on a fire? and when bonding happens, one 4 inch hose

Reply to
Peter Pan

"Channel Bonding The most straightforward way to increase the capacity of a network is to increase the operating bandwidth. However, conventional wireless technologies are limited to transmitting over one of several 20-MHz channels. 802.11n networks employ a technique called channel bonding to combine two adjacent 20-MHz channels into a single 40-MHz channel. The technique more than doubles the channel bandwidth. Channel bonding is most effective in the 5-GHz frequency given the far greater number of available channels. The 2.4-GHz frequency has only 3 non-overlapping

20-MHz channels. Therefore, bonding two 20-MHz channels uses two thirds of the total frequency capacity. Therefore, the IEEE has defined rules on when a device can operate in 40MHz channels in the 2.4GHz space to ensure optimal performance. Cisco expects that the greatest benefits of channel bonding will be realized in the 5-GHz frequency."

"The major changes this time around involved the implementation of the

40-MHz channel, which was tweaked to accommodate older 2.4-GHz band devices that could be confused by the wider channel bandwidth.

Version 2.0 of the spec also calls for the use of two 20-MHz bands that will allow the system to scan a given environment for legacy devices that might not understand the wider bandwidth. If such a device is found, the 802.11n device will defer and send data over only a single

20-GHz band. " I assume this is a misprint and should read 20MHz
Reply to
LR

Sorry. You're right. It should be "use two 20MHz channels" which are bonded to produce one 40MHz channel.

Reply to
Jeff Liebermann

or plan B.... (using different ssid's one for normal and one for High Speed) i use PPinUS for normal b/g pda/tablet/tivo's and PPinUSN for the two laptops that can do n, and the router part connected to the powerline (injectors? 1/2 a pair? what do you call one of two?) and use that (and an ethernet cable) for even higher speed connection/stuff when i want to xfer huge stuff.... at work i have two (different ssid's DH-Public and DH-Private), now i have to admit it is nice having the same ssid at airports/coffee shops/hotels/etc, but it's sort of neat to have different ones for different purposes.... Wonder why people beat their heads against the wall trying to get them the same, rather than celebrate diversity and exploit the cool extra things you can do?

Reply to
Peter Pan

Won't work. As soon as the 802.11n router hears *ANY* 802.11g signal, regardless of SSID, it will switch on flow control to prevent collisions. In the 40Mhz mode, it can't decode the preamble or beacons from an 802.11b/g AP or client. So, it has to treat everything as a potential co-channel user and give them some airtime.

Also, there are some AP's (i.e. DD-WRT) that can do multiple SSID's. However, the only options offered for these multiple SSID's are encryption and authentication methods. The modulation and 802.11 modes are apparently identical for all SSID's. It is therefore not currently possible to set one SSID for 802.11g and the other to

802.11n. I don't see any reason why an AP cannot do this, it's just that I haven't seen any that have bothered.

Huh? Is this one router or two, each with it's own SSID? I can see how it would work with two routers, but not one.

Well, 3 of a kind beats two pairs.... I dunno.

Gigabit ethernet rules. I've been slowly upgrading the office boxes to gigabit. It's sure noticable when cloning or backing up a machine over the network.

I kinda prefer to have some control over which access point I'm connecting to. Some wireless client managers will show multiple SSID's differentiated by unique MAC addresses. Most don't.

Easy. I once fired up WZC from the parking lot facing a big office building complex in Los Gatos CA. I didn't count the number of SSID's but it was well over 100. WZC was constantly refreshing and updating as it scanned and picked up new SSID's. The problem with a good thing is that too much of it is considered pollution.

Reply to
Jeff Liebermann

actually 3, but i assume you only care about the first b/g and the third n only... Tivo's and one of the PDA's and tablets will only do G, and one pda and smartphone b only, so I tend to leave old working stuff working, and just add new as I aquire it

oddly enuf, i've been getting them donated/collecting old ones (if nothing else, now I have 7 I can play with/brick, and many spare/backup walwarts, i'm retired, so now time to putter and fix instead of destroying :) , and just change the starting ip address for both wired and wireless, so they don't conflict, leaving the dhcp servers on etc, and plugging the router parts/port to each other to daisy chain em

Reply to
Peter Pan

I thought there were perf probs when letting a B signal exist within the same range as a G - and therefore probably N ?

Reply to
ps56k

There are mutual interference problems only if there is traffic moving on BOTH access points. If either access point is idle, a few broadcasts and beacons aren't going to create much interence. Of course B and G can coexist if on different non-overlapping (1,6,11) channels.

My rule-de-thumb is that if the receiving access point can decode the packet, then the normal flow control mechanisms will only result in a general slow down. This is not the case with 40MHz 802.11n, where the

802.11b/g access point treat the modulation as if were noise or garbage.

The problem between B and G was mostly historical. When G first appeared, it included an 802.11b compatibility mode. If the G receiver heard even one B packet, it would leave a big chunk of the timing open to listen exclusively for slow B packets. This was a huge performance hit as initially implimented. See:

802.11g only could get 24.4Mbits/sec thruput. The same radio with 802.11b compatibility mode enabled would only get 14.4Mbits/sec or a bit more than half. (Remind me to update the chart one of these daze).

However, the situation did not remain. More intelligent algorithms were invented to reduce the compatibility performance hit. At this time, the mere presence of an 802.11b access point, that's only belching beacons and broadcasts, has almost no effect on 802.11g thruput. I've tried it with various access points and it works. However, when 802.11b traffic is moving, even to a different system with a differeent SSID, the 802.11g compatibility mode kicks in, and things really slow down.

Reply to
Jeff Liebermann

beats me, I use wired connections for big stuff (like tivo recordings, usually over 2 gig)... As for n, oddball things (and I have no clue why), you know those silly wifi finders and some laptop clients that show what wireless networks are around? the one set for n only, doesn't show up on either! (microwave oven does on the wifi finder thing when I nuke my pizza rolls, course my dog comes running and howls too, so I assume it (wifi finder) looks for some sort of transmission on that frequency, but dang if I know why the nuker shows but the n ap doesn't, nor why the dog comes running ((unless he likes snacks/junk food)))

Reply to
Peter Pan

Specifically to allow roaming.

That works, but it ensures that clients will see a disconnect when jumping from one to another, as well as requires additional configuration upfront. Maybe that's a problem, maybe not.

Reply to
DevilsPGD

So move to 5.8GHz. There are so few 802.11a networks out there that

802.11n 5.8GHz is, at least for now, the holy grail of wireless performance.
Reply to
DevilsPGD

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