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[Linphone-developers] Blackberry version CMR byte sending and reception

From: Luigi Sambucini
Subject: [Linphone-developers] Blackberry version CMR byte sending and reception
Date: Thu, 19 May 2011 15:04:33 +0200

I am trying to investigate the problem about the 523 error and the playerListener.ERROR state that often occurs after 30 seconds of call on the BlackBerry version.
I can't understand the mechanism implemented around the CMR byte. In [] the OutputStream.write() method creates an RtpPacket as follows:

RtpPacket packet=JOrtpFactory.instance().createRtpPacket(mFrameSize+1);
System.arraycopy(buffer, lOffset, packet.getBytes(), packet.getDataOffset()+1, mFrameSize);
//set cmr byte

it adds the CMR byte to the packet payload, and sets it to a fixed value (15) which means that no mode request is present.
In [] the method reads the RtpPacket skipping the CMR byte just added:

//+1 because we need to skip the CMR bytes
int datalen=packet.getRealLength()-packet.getDataOffset()-1;
System.arraycopy(packet.getBytes(),packet.getDataOffset()+1, b, offset, datalen );

Why is there a need to add a CMR byte if the audio from the microphone is in AMR format (and therefore should contain it)?
Why is this byte removed on packet reception?
Do the RtpPackets still contain a valid AMR format? I captured the AMR stream of a call between two blackberry devices via wireshark, dumped it in a file and added the AMR header, but it does not resemble the original audio conversation (it seems a random noise).

Thanks in advance,

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