VoIP Playback options for RTP and SIP

Unsniff Network Analyzer has the ability to perform VoIP analysis of H.323, SIP, IAX2 signalling and the RTP and IAX2 transport protocols. For the IAX2 (protocol used by the Asterisk PBX system), you can also use the add-on script “Asterisk Call Analyzer” to draw charts for Jitter, Delay, Bandwidth, etc.

Unsniff supports one-click playback of captured VoIP traffic for most common codecs such as G.711 uLaw, G.711 aLaw, iLBC, GSM, and Linear.

Playback call legs

By default Unsniff extracts all VoIP calls into two legs – the forward and reverse legs. To hear the voice you must

  • Switch to the “User Objects” sheet
  • Right click on the desired leg and select “Play”

How to listen to call legs :



Stereo playback for RTP transport

If you want to hear both talkers you can use some of the cool mixing features built into Unsniff.  When enabled, you will now have three entries in the “User Objects” sheet for each call.

  1. the forward leg
  2. the reverse leg
  3. both legs mixed so you can hear the complete VoIP conversation


headphone.jpgThe mixing supported for the RTP protocol is very unique compared to other tools, you can even mix the legs to output one leg on the right speaker and the other on the left.



  1. Mix in stereo mode (with caller on left and callee on right speakers). We found this useful while dealing with a noisy direction. You can just turn the speaker balance down to focus on a particular channel.
  2. Mix interleaved caller + callee legs
  3. Merges both call legs into a single mono channel

To use these features

First ensure RTP conversations is enabled (the default). Go to “Plugins->Conversations” and confirm that the Mix Two-Way conversations is not “Disabled“. Select one of the three mixing options.


Thats it really ! Now you can capture RTP packets using H.323 or SIP protocols and three entries will now appear in the “User Objects Sheet“. Click on the call named “Conversation_XXX” and select Play or Save to WAV file.



Feedbacks and comments welcome.


[tags] VoIP, VoIP Analysis, RTP Playback, Asterisk, IAX2, SIP, H.323 [/tags]

Author: Vivek Rajagopalan

Vivek Rajagopalan is the a lead developer for Trisul Network Analytics. Prior products were Unsniff Network Analyzer and Unbrowse SNMP. Loves working with packets , very high speed networks, and helping track down the bad guys on the internet.

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