system toolbox » voip

http://www.howtoforge.com/voip_qos_traffic_shaping_iproute2_asterisk

The quality of my VoIP phone calls suffered whenever I was downloading or uploading anything. This was irritating, especially for those calling me (I heard them better than they heard me). So I poked at Iproute2 and other howtos, especially with regard to VoIP traffic, but I couldn't find anything that worked well. After some playing around, I've found settings that were right for me: consistant VoIP quality, regardless of any activities on the wire.

A note regarding my VoIP system: I'm using Asterisk on a spare laptop (IBM T20), and my VoIP provider is the excellent Unlimitel, in Canada. Since I host my own Asterisk box, I can pretty much configure it to do whatever I want. I also bought an IAX hardphone which resides on my intranet.

Setup

I assume you already have in place your Linux firewall. VoIP packets transverse your firewall and your NAT is already set and working. We won't even touch your firewall with this setup. All you need to do is to create the right qdisc, classes and filters to prioritize your VoIP packets. Iproute2's tc command is here for that.

Let's pretend your network is as such:

Internet <------> Cable modem <-------> Linux Firewall <-----> Intranet <-----> VoIP phone

Since I'm using Asterisk with IAX, the port of interest is port 4569. If you're using SIP, adapt the port in the following lines.

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