Hi everyone,
802.11b has a really great limit because it works as a very old hub, with a speed of 11Mb/s for all the customers attached to a single AP.
So, without any bandwidth limit, if you have 10 customers all goes ok, if your customers become 25-30 all speeds go down because of collisions become very frequent and every customer has to manage their CSMA alghoritm and so on.
If you use Nstreme on the AP, all your customers have to use it so the solution is less flexible.
I tried to define a Virtual AP with a different SSID, but the channel is always the same, and I didn't get any improvement.
My question is:
without limit the bandwidth, without using Nstreme, does exist a way to go over this limit of 802.11b with Mikrotik equipments?
Regards,
Alessio
Re: 802.11b limit - CSMA
Probably, consider to switch to 802.11a/g devices.
Re: 802.11b limit - CSMA
The only way to avoid collisions on standard 802.11b is csma, but as you mentioned, the more clients, the more trouble. (Hidden station problem comes to mind...) Nstreme with polling and csma disabled is one way to avoid the problem of loosing bandwith for negotiating who is allowed to send and who isn't at the time. For me Nstreme works well, with new 411 RB as client you have more than enough power to use it and get good speed for your clients. But with as many as 25 or more clients I would recommend using 802.11G with Nstreme (more bandwith to share among clients). You need a stronger Signal to get 54 MBit/s rates, but weak signal of only one link (client - AP) will kill bandwith for all attached to this AP, so you have to make sure all clients are at least in the lower -70s, giving at least 18 - 20 db snr (of course more is always better).
Perhaps other vendors have some other function to avoid collisions, but tjat would be as proprietary as Nstreme is. You have not much choices, use Mikrotik with Nstreme for all your clients, use some other vendors proprietary enhancements for all your clients or you will have to live with standard 802.11B/G shortcomings.
EDIT:
Actually, one more possibility would be to use up to 3 (real Hardware) AP'S on different channels and split customers on them, but only good for small scale networks, because only three non-overlapping channels on 802.11B/G, so interference will occur if you use more than one point with 3 AP's in your network, as they will probably "hear" each other and disturb themselves.
Sincerly
Schnulch
Perhaps other vendors have some other function to avoid collisions, but tjat would be as proprietary as Nstreme is. You have not much choices, use Mikrotik with Nstreme for all your clients, use some other vendors proprietary enhancements for all your clients or you will have to live with standard 802.11B/G shortcomings.
EDIT:
Actually, one more possibility would be to use up to 3 (real Hardware) AP'S on different channels and split customers on them, but only good for small scale networks, because only three non-overlapping channels on 802.11B/G, so interference will occur if you use more than one point with 3 AP's in your network, as they will probably "hear" each other and disturb themselves.
Sincerly
Schnulch
Re: 802.11b limit - CSMA
Hello,
Sergejs, Schnulch, first of all thanks for your time and your suggests.
I already tried to switch the R52H to 802.11b/g, instead of 802.11b and probably, as Sergejs said, in this way I get 54Mb/s of speed shared.
Making so, I lost some customer because of the signal was not so good anymore, and there wasn't any improvement for the other ones. I tried to minimize its calculation time putting the Rx/Rate of all customers at 1Mb/s. But probably the miniPCI is not able to manage 20-25 customers without a speed limitation.
I cannot use Nstreme for everyone because of not all the CPEs are Mikrotik.
In my opinion I have two possibilities:
1. change the R52H with a more performing miniPCI;
2. build another sector with another antenna, another miniPCI and so on, using a different channel, taking care about the channel distance to minimize the interferences.
Of course if you have anyother suggests I really would appreciate them.
Regards,
Alessio
Sergejs, Schnulch, first of all thanks for your time and your suggests.
I already tried to switch the R52H to 802.11b/g, instead of 802.11b and probably, as Sergejs said, in this way I get 54Mb/s of speed shared.
Making so, I lost some customer because of the signal was not so good anymore, and there wasn't any improvement for the other ones. I tried to minimize its calculation time putting the Rx/Rate of all customers at 1Mb/s. But probably the miniPCI is not able to manage 20-25 customers without a speed limitation.
I cannot use Nstreme for everyone because of not all the CPEs are Mikrotik.
In my opinion I have two possibilities:
1. change the R52H with a more performing miniPCI;
2. build another sector with another antenna, another miniPCI and so on, using a different channel, taking care about the channel distance to minimize the interferences.
Of course if you have anyother suggests I really would appreciate them.
Regards,
Alessio
Re: 802.11b limit - CSMA
Hi Alessio,
I don't think the minipci-card is your problem, there's no need for a "stronger" one. I have AP's with up to 40 Customers on one mini-pci. With that many clients you don't want (need) a limitation for clients, as they will limitate themselves - sort of.
If you can't use Nstreme as mentioned above, you have to use sector antenna (3 pieces of 120° each for 802.11b/g) and use a separate mini-pci card for every antenna. Use channel 1, 6, 11 or 1, 7, 13 depending on where you live so you have clients separated.
As you say, signal wasn't good enough for some clients when using 802.11g, I suggest using good antenna for your clients which are far away. If you have only one or two clients that have bad signal, the AP will have to switch down to 1 MBit every time one of those "weak" clients send data, slowing down your whole AP-client network, and with many clients on that one AP you will suffer packet loss very often.
If you want to expand your wireless network in the future, switch to 5 GHz and use only mikrotik CPE and AP for new clients. And step by step replace the old 2,4 GHz hardware at your clients with 5 GHz CPE too. At some point 2,4GHz is very hard to use for larger networks with lots of clients, remember that.
If your network won't grow anymore, go with 2,4 and sector antenna.
Sincerly
Schnulch
I don't think the minipci-card is your problem, there's no need for a "stronger" one. I have AP's with up to 40 Customers on one mini-pci. With that many clients you don't want (need) a limitation for clients, as they will limitate themselves - sort of.
If you can't use Nstreme as mentioned above, you have to use sector antenna (3 pieces of 120° each for 802.11b/g) and use a separate mini-pci card for every antenna. Use channel 1, 6, 11 or 1, 7, 13 depending on where you live so you have clients separated.
As you say, signal wasn't good enough for some clients when using 802.11g, I suggest using good antenna for your clients which are far away. If you have only one or two clients that have bad signal, the AP will have to switch down to 1 MBit every time one of those "weak" clients send data, slowing down your whole AP-client network, and with many clients on that one AP you will suffer packet loss very often.
If you want to expand your wireless network in the future, switch to 5 GHz and use only mikrotik CPE and AP for new clients. And step by step replace the old 2,4 GHz hardware at your clients with 5 GHz CPE too. At some point 2,4GHz is very hard to use for larger networks with lots of clients, remember that.
If your network won't grow anymore, go with 2,4 and sector antenna.
Sincerly
Schnulch
Re: 802.11b limit - CSMA
Hi Schnulch,
thanks for your suggest, we are trying to split all users on 2 sector antennas on different channels.
In any case, having a lot of requests we are thinking to swap our future customers on 5Ghz, even if the cost of CPEs working at 5Ghz is higher.
You are right about the problem in activating customers with a poor signal, and I really interested in knowing what do you think about the signal level of all customers on just one board: in your opinion is there a need to define a design rule about the differences of signal level between all customers on one miniPCI?
For example all customers between -65dBm and -75dBm?
Doing so, how many customers do you think could I have on 1 miniPCI like R52H without bandwidth limitation?
Regards,
Alessio
thanks for your suggest, we are trying to split all users on 2 sector antennas on different channels.
In any case, having a lot of requests we are thinking to swap our future customers on 5Ghz, even if the cost of CPEs working at 5Ghz is higher.
You are right about the problem in activating customers with a poor signal, and I really interested in knowing what do you think about the signal level of all customers on just one board: in your opinion is there a need to define a design rule about the differences of signal level between all customers on one miniPCI?
For example all customers between -65dBm and -75dBm?
Doing so, how many customers do you think could I have on 1 miniPCI like R52H without bandwidth limitation?
Regards,
Alessio
Re: 802.11b limit - CSMA
Personally I only connect clients that have a signal of at least -70 db at the day of installation with a SNR of at least 20 db. The Equipement gets not really better when it's older, so you need some margin that you have a "real - life - performance" of at least -75 db even at bad weather conditions, with some more noise in the area etc...
If I can't get a signal like that I check if there are more customers in the area around that said customer, if so, I build a new AP near to them to get good signal. If it's the only customer in that range, I'd rather tell him to wait, look for some neighbors interested too, or choose another (W)ISP than connect him to my AP's with a weak signal.
with SNR of 20db + and signal of -70db + all your clients will stay at least at 36 to 54 MBit rate (most of the time it's 54MBit).
The weaker the signal or SNR gets, the lower the rate you get, with one or two bad linked clients your AP will switch down to 6 MBit or less very often, so you don't have much traffic going over that AP (mind you, 6 MBit is the "name" of that rate, 3 to 4 MBit is more like what you get at all. Then having 20 clients who have to split that 4 MBit with overhead for csma etc, you will have about 20 unsatisfied customers, because of one or two weak links.)
With good links for ALL clients, you could have 20 very satisfied customers on the very same Hardware. There's no absolut max. possible users on one AP, but the viewer, the better for everyone. With standard 802.11b/g I guess 20 clients would be the upper limit for good service quality, because not all of them will be transferring lots of data at the same time.
With Nstreme and polling, csma disabled, you could go up to 30 to 40 clients on one AP, because the overhead for csma is gone.
All these figures are "rule of thumb", you have to test the performance of your setup from time to time and listen to your customers complaints (if there are any).
I would also make sure none of your clients has a signal higher than -50 db, because that could also cause you some trouble, too. Reduce their transmit power (and / or antenna gain) until the signal fit's your need.
If you are going to switch to 5 GHz I would suggest you go all the way with mikrotik (AP and client side). The client CPE will cost you with 17 to 19 dbi antenna, poe, RB411, R52 about 100-130 Euro. It's a bit more expensive, but if you calculate with 24 months of using it, well, 5 Euro a month is not that expensive at all. And your service quality will improve a lot. You can manage your network up to every client cpe with one interface, you could use RB433 at some clients where you need another AP in the area, just put in 2 R52, one for Backhaul, one for AP, one ether NAT to wlan-bridge, and the client will be served well, and you have yourself a nice new AP for little money.
Sincerly
Schnulch
If I can't get a signal like that I check if there are more customers in the area around that said customer, if so, I build a new AP near to them to get good signal. If it's the only customer in that range, I'd rather tell him to wait, look for some neighbors interested too, or choose another (W)ISP than connect him to my AP's with a weak signal.
with SNR of 20db + and signal of -70db + all your clients will stay at least at 36 to 54 MBit rate (most of the time it's 54MBit).
The weaker the signal or SNR gets, the lower the rate you get, with one or two bad linked clients your AP will switch down to 6 MBit or less very often, so you don't have much traffic going over that AP (mind you, 6 MBit is the "name" of that rate, 3 to 4 MBit is more like what you get at all. Then having 20 clients who have to split that 4 MBit with overhead for csma etc, you will have about 20 unsatisfied customers, because of one or two weak links.)
With good links for ALL clients, you could have 20 very satisfied customers on the very same Hardware. There's no absolut max. possible users on one AP, but the viewer, the better for everyone. With standard 802.11b/g I guess 20 clients would be the upper limit for good service quality, because not all of them will be transferring lots of data at the same time.
With Nstreme and polling, csma disabled, you could go up to 30 to 40 clients on one AP, because the overhead for csma is gone.
All these figures are "rule of thumb", you have to test the performance of your setup from time to time and listen to your customers complaints (if there are any).
I would also make sure none of your clients has a signal higher than -50 db, because that could also cause you some trouble, too. Reduce their transmit power (and / or antenna gain) until the signal fit's your need.
If you are going to switch to 5 GHz I would suggest you go all the way with mikrotik (AP and client side). The client CPE will cost you with 17 to 19 dbi antenna, poe, RB411, R52 about 100-130 Euro. It's a bit more expensive, but if you calculate with 24 months of using it, well, 5 Euro a month is not that expensive at all. And your service quality will improve a lot. You can manage your network up to every client cpe with one interface, you could use RB433 at some clients where you need another AP in the area, just put in 2 R52, one for Backhaul, one for AP, one ether NAT to wlan-bridge, and the client will be served well, and you have yourself a nice new AP for little money.
Sincerly
Schnulch
Re: 802.11b limit - CSMA
Dear Schnulch,
your suggests are really useful for me.
To get not more than -70dBm at the moment results quite difficult for us, our site is on mountain, the direct distance from our site to our customers is between 2 and 3 Km., of course in LOS conditions, and normally I get a signal between -70dBm and -80dBm.
If our signals are all in this range, I think that all the calculation of the miniPCI should be always the same, because of I don't have any strong differences between our customers.
My situation is the following, and probably there is something that is not correct:
1. from mountain side I have 25dBm set on miniPCI and a sector antenna of 14dBi;
2. on the CPE I get always SNR > 30, so I don't have any weak signal problem;
3. from CPE side I have 26dBm (nominally), HPBW/ Horizontal=20 HPBW/ Vertical=20 on an antenna of 14dBi, but on mountain I get SNR between 10 and 20 and a signal between -70 and -80 and I don't understand why.
Does it sound strange even to you?
Regards,
Alessio
your suggests are really useful for me.
To get not more than -70dBm at the moment results quite difficult for us, our site is on mountain, the direct distance from our site to our customers is between 2 and 3 Km., of course in LOS conditions, and normally I get a signal between -70dBm and -80dBm.
If our signals are all in this range, I think that all the calculation of the miniPCI should be always the same, because of I don't have any strong differences between our customers.
My situation is the following, and probably there is something that is not correct:
1. from mountain side I have 25dBm set on miniPCI and a sector antenna of 14dBi;
2. on the CPE I get always SNR > 30, so I don't have any weak signal problem;
3. from CPE side I have 26dBm (nominally), HPBW/ Horizontal=20 HPBW/ Vertical=20 on an antenna of 14dBi, but on mountain I get SNR between 10 and 20 and a signal between -70 and -80 and I don't understand why.
Does it sound strange even to you?
Regards,
Alessio
Re: 802.11b limit - CSMA
Hi Alessio,
the signal strength at your CPE side is a bit low for that distance with your power settings. The free-space loss is about 110 db for 3 Km, given your 25 db tx-power and 14 dbi antenna on AP side, and a 14 db antenna on cpe side you should be at 110 -25 -14 -14 = -57 db (without cable loss, that depends on your antenna cable type and length. Short cables of good quality about 1 or 2 db at each side, signal should be in the low -60's, -70 to -80 is a bit too weak, I think. Are you sure the polarity of your client antenna and of your sectors at AP are the same (horizontal / vertical)? Alignment of antenna (both sides) is as good as possible? How long are your cables to antenna at client and AP? What quality of cable do you use? Are all antenna cable connectors protected against moisture (water)?
At your AP side there seems to be a lot of noise, with signal of -70 to -80 and snr of 10 to 20 I think noise is about -90db, right? That's quite high, is there any other RF-source (TV, Radio, other WLAN-Equipment, Amateur radio, etc.) on that hill?
Is (are) your AP('s) in well grounded metal housings?
The noise could of cause come from the side where the clients are, too. Is there something of the above?
I would make a scan of all possible frequencies and look out for the one with the least noise (the higher the noise numbers, the better, -98 to -102 (or more) would be nice).
If everything of the above is checked and no solution is found, you could try to exchange the mini-pci card. It is remotely possible that it's receiver-side has a problem, the sending side seems to be all right, as the clients get a tolerable signal.
Sincerly
Schnulch
the signal strength at your CPE side is a bit low for that distance with your power settings. The free-space loss is about 110 db for 3 Km, given your 25 db tx-power and 14 dbi antenna on AP side, and a 14 db antenna on cpe side you should be at 110 -25 -14 -14 = -57 db (without cable loss, that depends on your antenna cable type and length. Short cables of good quality about 1 or 2 db at each side, signal should be in the low -60's, -70 to -80 is a bit too weak, I think. Are you sure the polarity of your client antenna and of your sectors at AP are the same (horizontal / vertical)? Alignment of antenna (both sides) is as good as possible? How long are your cables to antenna at client and AP? What quality of cable do you use? Are all antenna cable connectors protected against moisture (water)?
At your AP side there seems to be a lot of noise, with signal of -70 to -80 and snr of 10 to 20 I think noise is about -90db, right? That's quite high, is there any other RF-source (TV, Radio, other WLAN-Equipment, Amateur radio, etc.) on that hill?
Is (are) your AP('s) in well grounded metal housings?
The noise could of cause come from the side where the clients are, too. Is there something of the above?
I would make a scan of all possible frequencies and look out for the one with the least noise (the higher the noise numbers, the better, -98 to -102 (or more) would be nice).
If everything of the above is checked and no solution is found, you could try to exchange the mini-pci card. It is remotely possible that it's receiver-side has a problem, the sending side seems to be all right, as the clients get a tolerable signal.
Sincerly
Schnulch