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 From:  Jim Thompson <jim at netgate dot com>
 To:  Jim Wang <jim dot wang at troposnetworks dot com>
 Cc:  m0n0wall at lists dot m0n0 dot ch
 Subject:  Re: [m0n0wall] Max number of reported users on a m0n0.
 Date:  Mon, 16 May 2005 19:06:51 -1000
On May 16, 2005, at 4:48 PM, Jim Wang wrote:

>  Jim Thompson wrote:
>
>  On May 16, 2005, at 4:32 PM, Jim Wang wrote:
>
>>> What's the highest reported number of simultaneous users on a  
>>> m0n0wall?
>>

>> are your "simultaneous users" doing, which hardware are you running  
>> on, etc?


> be installed on a 1U Dell Rack Mount Server, but what are your  


You'll need to specify what the clients are doing.

Lets assume that you've got two thousand APs all talking back to a  
single gateway over a wired network, and that these APs all have a  
single associated client, and that they're all in lead-lined rooms, so  
none of the clients or APs co-interfere.

For reasons I won't got into here, you can get about 446 TCP segments  
per second through an 802.11b link. Assuming that each TCP segment has  
1460 bytes of payload. Thus, 1460 x 8 x 446 yields a throughput of  
approximately 5.21 Mbit/s for the 802.11b wireless LAN component of the  
network path.

This is a reasonable 802.11b upper bound throughput limit of TCP  
end-to-end performance with the long 802.11b preamble. Using a short  
96-bit preamble we get an even better throughput of approximately 6.28  
Mbit/s.

Using 802.11a, or 802.11g with no "11b protection", you can get about  
2000 TCP segments per second through the link. Thus, 1460 x 8 x 2000  
yields a throughput of approximately 23.36 Mbit/s for the 802.11a or  
802.11g part of the path..

So, assuming that you've got users who transfer big files (P2P anyone?)  
while sitting in small rooms,
and your 1U dell (wouldn't you rather have something with no moving  
parts (disk drives?) if so, see me off list) has a couple Gigabit  
Ethernet interfaces, and that m0n0wall's performance will be  
approximated by FreeBSD's performance on the same hardware (its the  
same kernel, after all)

http://lists.freebsd.org/pipermail/freebsd-questions/2004-November/ 
064401.html

(Wherein we can fill a 100Mbps path with any recent version of FreeBSD  
using a Celron)

On all but very recent mobos, the PCI slots are 32 bit, 33MHz. This  
means they can in theory transfer at speeds of 133MB/s. Since the bus  
is shared between many parts of the computer, and due to timing  
constraints, it's realistically limited to around 80MB/s in the best  
case (and constant load).

Gigabit network cards (*) provide 1000Mb/s, or 125MB/s, in theory.   
However, if the PCI bus is only capable of 80MB/s this is a limiting  
factor for gigabit network cards. Assuming the 80MBps, or 640Mb/s,
you can do the math above.

However,  your traffic mix probably isn't steady-state maximum-sized  
packets.  Nor are your 802.11 installations free of interference (even  
if you do work for Tropos :-).   As the packet size goes down, the  
throughput on the 802.11 links will drop (faster than the throughput on  
an equivalent Ethernet link would drop).   Assuming you've got the CPU  
and Ethernet cards to deal, you will probably find that the freeBSD  
router is not the source of your throughput choke point.

Jim

(*) Note that GigE cards that deal in Jumbo frames aren't going to help  
you here.

>

>



:-)

>


> of what they do.
>
> Airpath is the preferred OSS and Roaming hosted solutions provider for  
> wireless ISPs, service providers, network providers and systems  
> integrators focused on wireless broadband services delivery for  

> to cafes and campgrounds. Airpath-enabled carriers are able to quickly  
> negotiate, activate and settle roaming agreements with other carriers.  
> Airpath is making the fragmented nature of wireless broadband  
> availability a thing of the past.

Feh.

I was the CTO @ Wayport from founding until 2001.   Airpath has no  
carrier relationships, and no relationship with anyone other than ...  
other companies like them (iPass, FatPort, etc).   Complete  
non-starter.

You want roaming?  Get a big 802.1x cloud with RADIUS servers that can  
locate "provider X" going.

jim