[Asterisk-Dev] High performance on Network interface -

[Steven Smith]

Is there any one working on the network performance features of linux
running asterisk ? Has anyone had voice quality problem with
linux/asterisk over WAN connections ?

This may help.

Tuning a Linux 2.4 system
Enabling and disabling some of the advanced features of TCP:
(Usually it is a good idea for these to be enabled)

	/proc/sys/net/ipv4/tcp_timestamps
	/proc/sys/net/ipv4/tcp_window_scaling
	/proc/sys/net/ipv4/tcp_sack 

To enable all these features, for example, do the following as root:


	echo 1 > /proc/sys/net/ipv4/tcp_timestamps
	echo 1 > /proc/sys/net/ipv4/tcp_window_scaling
        echo 1 > /proc/sys/net/ipv4/tcp_sack 

Path MTU discovery can be enabled and disabled using the following
boolean sysctl variable:

	/proc/sys/net/ipv4/ip_no_pmtu_disc

But be on the lookout for blackholes if this is enabled, as indicated at
the beginning of the document. Please see the following URL for
additional documentation on sysctl variables:

http://www.linuxhq.com/kernel/v2.4/doc/networking/ip-sysctl.txt.html
    

Tuning the default and maximum window sizes:

	/proc/sys/net/core/rmem_default   - default receive window
	/proc/sys/net/core/rmem_max       - maximum receive window
	/proc/sys/net/core/wmem_default   - default send window 
	/proc/sys/net/core/wmem_max       - maximum send window

	/proc/sys/net/ipv4/tcp_rmem       - memory reserved for TCP rcv buffers
	/proc/sys/net/ipv4/tcp_wmem       - memory reserved for TCP snd buffers

The following values would be reasonable for path with a large BDP:


       	echo 8388608 > /proc/sys/net/core/wmem_max 
       	echo 8388608 > /proc/sys/net/core/rmem_max 
       	echo "4096 87380 4194304" > /proc/sys/net/ipv4/tcp_rmem
       	echo "4096 65536 4194304" > /proc/sys/net/ipv4/tcp_wmem

You will find a short description in
LINUX-SOURCE_DIR/Documentation/networking/ip-sysctl.txt

If you would like these changes to be preserved across reboots, it may
be a good idea to add these commands to your /etc/rc.d/rc.local file.

Linux users may want to look into the Web100 project. In addition to
providing complete instrumentation of the TCP stack, it has features for
doing auto tuning of send and receive buffers.

For paths with a very large BDP, it also has some features that will
allow you to get better transfers.

User testimonial: With the tuned TCP stacks it was possible to get a
maximum throughput between 1.5 - 1.8 Mbit/s via a 2Mbit/s satellite
link, measured with netperf.


Reference: http://www.psc.edu/networking/perf_tune.html