[OpenSIPS-Users] Max TCP connections

Muhammad Shahzad shaheryarkh at googlemail.com
Sat Sep 29 16:59:02 CEST 2012

Every thing is a file in UNIX / Linux, so every TCP connection is a file
too. Also persistent connects are sometime memory intensive too. So make
sure adjust following things carefully.

1. Number of Open Files Limit, use either ulimit -n <number> in opensips
startup script or set open_files_limit in global section on opensips dial
plan. I usually use second options and set open_files_limit to 1024000.
2. Increase TCP children, tcp_children, default is i think 8, increase it
to 16 or even 32 if you have very large deployment, this will speed up
connection processing significantly, however consume much more memory. Also
make sure to set all other TCP related opensips variables to reasonable
values, such as tcp_connect_timeout, tcp_connection_lifetime etc. etc. Look
here for details,


3. If you have a dedicated SIP server, running only OpenSIPs then reduce
stack size as well. I found setting it to 1024KB or even less gives good

Now some practical results. On Dell server R510 with 8GB RAM and 2.4GHz
quad core Intel processor I was able to test 104,981 concurrent SIP
registrations with load average between 1.0 to 1.5.

Two important things to remember.

1. What is estimated / expected number of requests per second?
2. What is SIP re-register time?

For me, i tested up to 350 requests per second with re-register time as 300
seconds this gives theoretically possible concurrent SIP connections to 350
x 300 = 105,000. Which means you can't have more then this number of
concurrent connections. So i can safely say per my testing that opensips
can practically handle up to ~100K SIP concurrent connections.

Thank you.

On Fri, Sep 28, 2012 at 7:21 PM, Ali Pey <alipey at gmail.com> wrote:

> I am also interested in this. Any responds/updates?
> Regards,
> Ali Pey
> On Wed, Sep 12, 2012 at 9:34 AM, John Quick <john.quick at smartvox.co.uk>wrote:
>> Does anyone know what the practical limit is for the maximum number of TCP
>> connections to OpenSIPS?
>> It is a question that often comes up with clients who are developing
>> SIP-based apps for smart phones. Persistent TCP seems to be strongly
>> favoured over UDP for connections with mobile devices such as iPhone,
>> iPad,
>> etc. However, I cannot even get OpenSIPS to start if I set
>> tcp_max_connections to a number greater than about 55000. Have tried it
>> with
>> v1.7 and 1.8. Is there a way to overcome this ceiling? Has anyone tested
>> it
>> with 10's of thousands of TCP connections?
>> John Quick
>> Smartvox Limited
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Muhammad Shahzad
CISCO Rich Media Communication Specialist (CRMCS)
CISCO Certified Network Associate (CCNA)
Cell: +92 334 422 40 88
MSN: shari_786pk at hotmail.com
Email: shaheryarkh at googlemail.com
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