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IP communicator observation


i was doing a packet capture using wireshark and noticed that calls i made from the ip communcator to my cell or another IP communicator packets coming from the subscriber.  meaning the packet capture shows RTP source is my PC ip add and the destination is subscriber IP.  vise versa for imcoming packets.  this is kind of weird since i was under the impression that it would be end to end. 

but when I made a call from ip comm to a cisco phone which shows hte source and destination are my pc ip and phone IP.           

any clues why?


3 Replies 3


This is usual behaviour when an MTP has been allocated to the call. MTP's are usually added to the call to resolve negotiation issues like DTMF.

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William Bell


It sounds like you have a Media Termination Point (MTP) involved in the call path. You would need to look at the various components involved in the affected call path. Based on the fact you have a valid scenario where no MTP is involved (your CIPC to a physical phone) then your device is not initiating the request for a MTP.

For devices involved in the call, check the device config to see if a MTP is being forced. Also look to see if you are forcing a Trusted Relay Point (TRP), which is basically a MTP anyway.


HTH -Bill (b) (t) @ucguerrilla

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ya , it is using MTP but the reason is that the called party had the "optimize for low bandwitdh" in the ip communicator checked. this will force the call to use iLBC codec instead of known g729/g711.  thus require MTP.

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