[asterisk-biz] About zitter and delta control

[Gerrit Jacobsen]

Hello Rifat,

what is the performance improvement of doing this in the kernel ? 2 times, 3 times ?


Kind regards, / Ar cieņu, / Mit freundlichen Grüßen


Gerrit Jacobsen
Managing Director
www.x164.com




On 9 Mar 2013, at 14:02, Rifat Rahman wrote:

> Hello there,
> 
> I have built a kernel module that is responsible for sip and rtp
> encryption/decryption, padding/depadding, ptime decrease (splitting a
> large rtp packet to splitting into smaller packets of ptime 20) for
> incoming packets and ptime increase (merging small rtp packets into a
> big rtp packet of desired ptime) for outgoing packets. This is meant
> to be a faster process and indeed it is. The whole purpose is to
> taking the load from the sip server and to manage this things in
> kernel space.
> 
> Now my problem is that, when packets are splitted in kernel space, no
> harm is done. But when packets are merged, i see somehow large zitter
> and delta that makes the voice robotic. I am quite new to this line.
> So from my experience I can say nothing on which side it is the
> problem. I carefully observed RTP sequencing and timestamping, and
> yes, it is handled perfectly. To have a work around, I suspect the
> following things:
> 
> 1. The zitter control might be the problem. But on which side I should
> concentrate? Should I look the client's zitter buffer handling or
> server side zitter buffer handling?
> 
> 2. If asterisk is run from a RT (real time) kernel, should it make any
> problem? Or, is it necessary to run asterisk from an RT kernel to
> mitigate my issue?
> 
> 3. If both RT kernel and zitter control mechanism is taken to the
> asterisk server, can I hope to solve this problem?
> 
> I am in doubt whether the process gets somehow expensive while ptime
> increase. Because I have to drop a few packets, making lists of
> packets referring to a communication, and etc. etc. I am running out
> of ideas. Because debugging in kernel space is not easy.
> 
> -- 
> Rifat Rahman
> 
> --
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