[rescue] 802.11 + VoIP

Kevin Loch kloch at gurunet.net
Fri Oct 17 00:28:48 CDT 2003

----- Original Message -----
From: "Geoffrey S. Mendelson" <gsm at mendelson.com>
Date: Thursday, October 16, 2003 9:37 pm
Subject: Re: [rescue] 802.11 + VoIP

> Eric Webb wrote:
> > I see a lot of opinions that 802.11 and VoIP are a bad 
> combination, but I need 
> > more proof and stats if anyone has anything.  (I'm kind of anti-
> wireless 
> > anyway when it comes to wanting performance, which voice seems to 
> demand.)
> Performance is not an issue with VoIP, latency is. To get a decent 
> VoIP 
> connection you need to sustain 64k BITS per second of DATA, which 
> meansabout 96k-128k of IP throughput. Just about any WiFi network 
> can do that,
> but if the delay is too long in getting a packet out there, then there
> will be echo and other problems.
> > Also, do they even make 802.11-based VoIP handsets?  Can someone 
> point me in 
> > the direction of a few models?
> I was just searching and haven't seen any. The closest you can come is
> either a USB phone for your WiFI equiped laptop, or an ethernet phone
> and a WiFi router. 
> Or for the real gearheads, a Cisco or Packet8 ATA (analog telephone 
> adaptor),a WiFi router, and a "real" (POTS aka analog) phone.
> This is not as far fetched as you might think. Sambo will be here 
> in a week,
> bringing WiFi access points and a Packet 8 ATA. I've got a Cisco 
> 186 comming
> around the same time with service on a competing network. We can do 
> some"real" testing in our spare time. :-)
> I've spent several hours this week getting QOS (quality of service) 
> routingto work on my Linux based router/firewall machine. Tonight's 
> installmentwas to put traffic limiting on the LAN side, so my son 
> does not swamp
> the connection to the outside world with his downloads. 

FreeBSD dummynet does traffic limiting very well.  Just plumb a pipe,
assign it a bandwidth limit, then assign ipfw rules to match traffic
you want put through that pipe.

Here's an example:

Add these to your kernel config:

options         IPFIREWALL
options         IPFIREWALL_VERBOSE
options         IPDIVERT
options         DUMMYNET

And something like this to your firewall script:
(assuming your local lan is and
you are blocking from coming in from 
the outside)

 ipfw pipe 1 config bw xxKbit/s # xxx is outbound bandwidth for your son
 ipfw pipe 2 config bw yyyKbit/s # yyy is inbound bandwidth for your son
 ipfw add pass all from xx.xx.xx.xx to
 ipfw add pass all from to xx.xx.xx.xx
 ipfw add pipe 1 all from xx.xx.xx.xx to any
 ipfw add pipe 2 all from any to xx.xx.xx.xx

Or, you could put a rule to pass the traffic for the voip device and
then send all other traffic through the limiting pipes.


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