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188 posts

Master Geek


Topic # 30627 16-Feb-2009 04:21
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Very silly question but if there are 10 users on a 54 Mbps router - does it get split by ten so each user will get 5.4 Mbps ?

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  Reply # 195979 16-Feb-2009 07:09
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Hi, all depends on the traffic loading characterisitic, but yes if you have 10 folk pulling files across the network simultaneously it would. Things to think about, WiFi is a half duplex system, so real throughput on continuous throughput is only half ie 26Mb/s, if all the traffic is coming from the internet to each of those PCs and the broadband connection is only say 6Mb/s then this would limit the rate of traffic within the network before you take the WiFi limitation into account.

If you compare this to a wired situation, each connection to the a switch is independant, if you had PC1 pulling a file from PC2 and PC3 from PC4 and PC5 taking traffic off the net then each of those connections will run at full 100Mb/s (full duplex) as they would not share any common connection although the net is naturally limited, however if PC3 was also pulling the file from PC2 as is PC1 then the capacity of the link from the switch to PC2 would be shared, but due to the higher rate and duplex and less retry situations to WiFi it will be much better.

However from my experience in a small office with several users largely just web browsing and not transfering files between themselves all the time, a 54Mb/s WiFi link is reasonable for up to around 10Mb/s, beyond that or if there are lots of file transfers then cable it even if only a couple of users.

Cyril

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  Reply # 195993 16-Feb-2009 08:59
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portege: Very silly question but if there are 10 users on a 54 Mbps router - does it get split by ten so each user will get 5.4 Mbps ?

Good comprehensive answer from Cyril above.

Heres a smaller answer, with less comprehensiveness :)

If your question is really about internet speeds, then if you are on say, an average ADSL2 connection, you might be getting say, 10Mbps throughput from the net. In this case, your 54Mbps pipe is not going to make your 10Mbps connection any faster.

Chances are your network and router are just basic stuff, and one user getting a fast download can easily slow the other PCs to a crawl. So you may not find a 10Mbps divided by 10 user scenario, but perhaps one user getting 8Mbps, and 9 users sharing the remaining 2Mbps of capacity.

To get a better answer, we need the following info:

What is your internet connection (ADSL?) and what throughput can a single PC get on a speedtest.
Are you referring to LAN traffic, or Internet (WAN) traffic?
What network switches and routers do you have (makes/models)?
What is the network topology like?









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  Reply # 195994 16-Feb-2009 09:05
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Thanks Cyril and Tony!

We were just discussing in our flat and were really just curious, it's just funny that none of us knew the answer - my flatmate is an analyst with IDC and I used to be an analyst with Telecom

Not really that worried about our internet speed as I'm fairly hapy with our internet connection - our BT line seems to be working fairly well...

Thanks again!

T

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  Reply # 196096 16-Feb-2009 17:22
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It is actually FAR more complicated than either answer suggests.

802.11 traffic is time sliced, rather than bandwidth sliced.  If 10 users are connected, they all transmit and recieve at maximum speed, but only one is able to do it at once.  This is what creates so many problems with VoWLAN on cheap equipment.  You are not getting a nice even 5.4Mbps, if everything is fair, you transmit at 54Mbps for 10% of the time, and 0Mbps for 90% of the time while you wait for the other 9 clients.

The other thing to bear in mind, is that 802.11 bandwidth does NOT equate to IP data throughput.  Each individual packet has a small overhead, but the big killer is the ACK's.  Every 802.11 packet MUST be acknowledged, so sending one frame of IP data, requires two packets at L2 802.11 - DATA, ACK.  54Mbps aggregate throughput is closer to 25Mbps of IP traffic. 

To really kick you in the nuts, if your AP is configured in b/g mode, then everytime a b client is heard by the AP regardless of whether it connects to your AP or not, protection mode is invoked.  This turns your 1 packet of IP data into a four frame process.  RTS, CTS, DATA, ACK.  And in case the burning sensation between your legs wasn't bad enough, all management frames travel at the lowest supported rate (1Mbps).  This means that your 54Mbps connection, is actually 14.25Mbps when averaged out with 3 management frames.

And while I'm really killing your fun, 54Mbps is the perfect 802.11 bandwidth.  This is based on the modulation types used, which is in turn based on signal strength.  The further away from the AP you get, the weaker the signal, this causes the AP to negotiate different modulations, which support lower bandwidth.  Your average speed is affected by the speeds of all other clients, since you have to wait while they use the medium.  If they want to send 10Kb, and are only connected at 2Mbps, that is 26 x longer you have to wait.

All of this adds up to some very good reasons to use quality wireless equipment, and some good incentives to make sure it is set up and configured properly.


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