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Multi-processor PC with Windows 2003 jitter solution

Art King

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We've been testing pbxnsip v2.0.2.1676 (Win32) installation on a Dell Server with Xeon 3.0 GHZ dual-processor and 2GB of RAM, running Windows 2003 Server R2.


We kept seeing jitter. For example, if the web interface Call Status screen was up (http://pbx/dom_calls.htm), each time it would refresh we would get a short burst of jitter on the phones. We saw similar jitter episodes on a conference call each time someone would join or leave the conference.


We were monitoring Windows Task Manager and we noticed that the per-processor CPU Usage History graph did a lot of jumping around concurrent with the jitter. Under Task manager Processes, we selected pbxctrl.exe, right-clicked and chose "Set Affinity". By default the PBXnSIP process was set to use both of the processors. We changed it to only use one processor and the jitter problem vanished!


We found a Windows utility that allows us to set the Affinity to one processor for a specific process, so we don't have to remember to set this each time we reboot.


Looks to us like PBXNSIP needs to do more testing on multi-processing machines.

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Whow! That finding is very cool!!! That could explain why we sometime see (even on very powerful machines) jitter coming up as a problem.


We will add a setting for 2.1 so that this can be set up as a setting.


Seems that Linux also supports this, and it is probably not a bad idea to include it there as well.

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To permanently set an EXE's processor affinity we used the tool "imagecfg.exe" apparently from the Server 2000 Resource Kit. See here: http://www.robpol86.com/Pages/imagecfg.php or do a google search on "imagecfg."


To use task manager to change pbxnsip.exe's affinity you may need to run taskmgr as "LOCAL SYSTEM." The trick to do that is run "at 1:35pm /interactive taskmgr.exe" where the time specified is a couple of minutes in the future.

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I can confirm the same - similar confg: dual Xeon 3 GHz dual-core processors (8 total processors seen by system), 4GB RAM. dual 1GB NICs with Windowns 2003 Server R2 running pbxctrl - jitter occurs whenever there is a process interupt that crosses cpu threads. Set affinity to a single processor and the jitter is gone. The issues where magnified in Grandstream GXW-4108 gateway and GXP-2000 and 2020 series phones - especially using BLF lit buttons.

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