[Freeswitch-users] In-call artifacts with PCMA/PCMU

Michael Jerris mike at jerris.com
Fri Oct 17 18:56:35 MSD 2014

The bad udp checksum can happen with cards that offload udp checksumming, which is common.  If you are not transcoding, we are not doing any digital modification of the codec payload, and its unlikely that the issue is related to anything freeswitch is doing.  You can confirm this by examining the audio stream of the incoming and outgoing rtp stream in wireshark.


> On Oct 17, 2014, at 8:49 AM, Iskren Hadzhinedev <iskren.hadzhinedev at ikiji.com> wrote:
> Hello,
> Apologies for the late reply.
> I don’t think there’s any transcoding, as the endpoint negotiation is set to “generous” and examining the SDPs shows that both endpoints negotiate on PCMA/PCMU. I got a pcap of the RTP streams with tcpdump and I see that from the 126500 packets, 62964 are marked with “bad udp cksum”. All packets with bad udp checksum are originating from the FreeSWITCH box. Is this information helpful at all and what else can I do to figure out the reason behind these issues? Thank you!
> Kind regards,
> -- 
> Iskren Hadzhinedev
> On Tuesday 14 October 2014 10:03:32 Michael Jerris wrote:
> is there even any transcoding involved in your scenario?  Are the artifacts present in the inbound stream as well.  I would get a tcpdump and analyze the inbound and outbound streams to see a bit more detail of what is going on.
> Mike
> On Oct 14, 2014, at 5:12 AM, Iskren Hadzhinedev <iskren.hadzhinedev at ikiji.com <mailto:iskren.hadzhinedev at ikiji.com>> wrote:
> Hi everyone,
> Some of the calls using PCMA/PCMU have artifacts (distorted sound, “robotic” voice, stutter) on what looks like a random basis. The other codecs I have tried don’t have issues (tried GSM, iLBC,G722, G729, SILK). Apart from FreeSWITCH, the only other thing running on the machine is a static webpage served by nginx and the load is almost always at 0. Any help or advise on how to chase down this issue is highly appreciated!
> System specs:
> Machine: Xen VM
> RAM: 1GB
> CPU: Dualcore 2.4 Ghz 64bit
> OS: CentOS 6.5
> FreeSWITCH Version: 1.5.13b+git~20140621T003222Z~47891d5caa~64bit
> Max # simultaneous calls: 12
> Calls per second: at most 3
> Endpoints used for testing:
> Hardware phones: Yealink T42G, Yealink T48G, Gigaset DE900, Cisco 7975 (with SIP firmware)
> Softphones: CounterPath Bria for Android, CsipSimple (android), Linphone, Jitsi
> Mobile provider and a landline via gateway.

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