[Kamailio-Users] NAThelper and multipart SDP

[Andreas Granig]

Hi,

> Someone does need to do a study to see if kernel vs. userspace 
> forwarding really makes that much of a difference, though.  I suspect 
> that although it does make a difference, it is not nearly as much of a 
> difference as is commonly thought.

We did a benchmark (only cpu usage for now) comparing the standard 
rtpproxy with mediaproxy-ng, a proprietary implementation of Sipwise 
(implemented as iptables module based on the mediaproxy dispatcher 
protocol). The results should be pretty equal for mediaproxy2 and 
iptrtpproxy as well, although I don't know anything about their design.

http://pub.sipwise.com/OpenSER.rtpproxy.benchmark.2009.06.24.pdf

The machine is a Dual-CPU Intel(R) Xeon(TM) CPU 2.80GHz with 2GB of RAM. 
Test-Setup is done with sipp (rtp is sent via pre-recorded pcap and 
echoed via "-rtp-echo" option on UAS).

Some observations we found:

- rtpproxy seems to not take advantage of SMP
- jitter is reduced in mediaproxy-ng compared to rtpproxy because socket 
polling is eliminated in kernel
- delay is reduced in kernel-space due to elimination of context switching
- the peaks in mediaproxy-ng are a result of the mediaproxy-ng design 
(relaying is done in user-space until all ip/port information is 
available by receiving rtp packets from both sides, besides some other 
processing like packet inspection etc. [although cpu usage can be 
lowered even more by further optimizing the userspace part])

Andreas