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Testing mobile apps which make phone calls using wifi connection, encountered a problem with audio quality and excessive delay on certain phones. Captured traffic between mobile phone and wifi router using AirPcap, but can not find a way to Decode As SIP/RTP. All packets shown as 802.11 protocol naturally.

Is there a way to decode the wifi packets into the SIP and RTP used for the VoIP call?

asked 30 Aug '13, 09:35

BobD8487's gravatar image

accept rate: 0%

Is there a way to decode the wifi packets into the SIP and RTP used for the VoIP call?

Yes, but if they were captured on a "protected" network, using WEP or WPA/WPA2 encryption, you will have to decrypt them.

It's also possible configure AirPcap adapters to do the decryption for you when capturing; see the "Adding Keys: Wireless Toolbar" of the page I linked to. That won't handle an existing capture, however, it will only handle captures you make after you add the passwords.

Also, pay attention to the "Gotchas" section.

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answered 30 Aug '13, 13:15

Guy%20Harris's gravatar image

Guy Harris ♦♦
accept rate: 19%

Thanks, Guy. But you are such a tease. :-) You tell me "Yes" then do not tell me how it would be done. The AirPcap only does WEP so I would have to handle the WPA2 decryption within Wireshark except that I temporarily disabled my encryption to take the trace, so there is nothing to decrypt...except the 802.11 packets. I need to see SIP, and most importantly, RTP. If you can embelish on your "Yes" answer to tell me how this is done, I would very much appreciate it.

btw - I would have expected to be able to use the Wireshark Analyze>Decode As option, however this option is grayed out.

(30 Aug '13, 16:38) BobD8487

I need to see SIP, and most importantly, RTP.

If you're not seeing IP and TCP/UDP headers for the traffic you believe to be SIP and/or RTP, then your traffic is probably encrypted at the 802.11 layer, whether you believe you disabled that decryption or not (i.e., you didn't).

If you're seeing IP and TCP/UDP headers, you should be able to use Decode As to decode the packets as SIP and/or RTP.

(30 Aug '13, 21:00) Guy Harris ♦♦

Thanks, Guy. That must be it. I turned off the WPA2 encryption, but there must be something else turned on which is encrypting the data. I'll have a look through my router settings and see if there is something I missed. I will also go through the decryption section of this wiki to see if it mentions another layer I may have missed. Worst case I turn it back on, then decrypt in Wireshark (which is what I was trying to avoid thinking it was simpler...which was obviously not the case).

(04 Sep '13, 15:29) BobD8487
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question asked: 30 Aug '13, 09:35

question was seen: 2,199 times

last updated: 04 Sep '13, 15:29

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