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Wireless data speeds?

RWBRWB Icrontian
edited August 2011 in Science & Tech
On a wireless B or G access point how does the bandwidth of that AP get shared? For example the 11Mbps for wireless B... if I have 11 people on this AP and each user is trying to download a file at the same time does this 11Mbps get split up or does each user get 11Mbps?

This is not referring to the network connection going into the AP though, which at 100Mbps couldn't support 11 people at 11Mbps obviously.

I'm having a hard time getting a straight answer for such an easy question. This is for a Cisco 1200 series AP.

Comments

  • KwitkoKwitko Sheriff of Banning (Retired) By the thing near the stuff Icrontian
    edited August 2011
    It's the total bandwidth available for all connections.
  • RWBRWB Icrontian
    edited August 2011
    Kwitko wrote:
    It's the total bandwidth available for all connections.

    Damn, that would explain everything and pretty much what I figured, though I was hoping the opposite.... just wish these AP's would give at least be able to support more users at higher data rates. They claim to support something like 30 people but if that's the case those 30 people simply trying to use the internet would have god awful connections. Not only that but from my reading there is a large overhead for wireless and it effectively runs at half duplex which when you have 10 or more people connecting to the same AP creates a huge problem.
  • GrayFoxGrayFox /dev/urandom Member
    edited August 2011
    For 802.11B
    in long preamble mode ~4.5megabits in short preamble mode ~ 5.8megabit's

    For 802.11G in short preamble you should see about 24 megabits of TCP throughput.


    For 802.11N in 20mhz operation with 2x2 spatial multiplexing. ~50-65 megabit's of aggregate TCP throughput.


    About 20-25 people is the peak you can fit on an AP before you will run out of bandwidth assuming you guys have a traffic shaping system in place as well, Also with just 1 or 2 with weak signal's you can run into the hidden node effect. Where CSMA on one client will not hear another client further away. When this happens you can tell because you will have high ping (From CSMA), packet loss (due to collisions because clients are waiting to transmit).


    Also with how non-tdma OFDM system's work's your only as quick as your slowest client. The guy with the -92DB signal @ a 6megabit rate will drop your other client's down to his speed and he will consume large amounts of radio time on retransmits.

    Setting a policy on the AP where you will only allow users with signals stronger then -76DB will keep you to the upper half of the rates this will also solve CSMA hidden node issues.


    Another issue wireless is vulnerable to is interference and CSMA backoff. (When there's too many wireless routers in use and CSMA just keep's waiting for the other routers to stop transmitting on the carrier).
  • RWBRWB Icrontian
    edited August 2011
    Thanks for the reply and PM, I have no say in what is used. We generally install "Ruckus" systems, which we get no complaints from but some places we only do support for and those already have systems installed. I do hotel internet support, and the hotel we get lots of speed complaints from supposedly has a super awesome install. But we always get complaints of weak wireless signals and damned slow speeds. It's a triangular hotel and the AP's are on each corner of each floor, and between the AP's there is virtually no signal.

    There's no traffic shaping, of course, don't know the reason why but I have yet come across a hotel that does.

    You've given me plenty to read up on, hopefully what I don't figure out on my own my CCNA course I am signing up for will.
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