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I am a student doing my honours dissertation and I am trying to set up a secure voip connection  using secure RTP, I have attached the configuration file and basic network  diagram.

I am using IP phones using Cisco  Call Manager express. When setup with SRTP, the packets over the link were then  sniffed using Wireshark, however the only traffic was RTP  packets. I am wondering if perhaps there is a command  necessary that I am missing? The router in use has been configured as a  CTL client and in one of the lab manuals I am using it states that a  the CTL file is stored as a .tlv file, however this file does not exist  so the IP phones are continually looping, trying  to find this file. It also states that the TFTP server will provide a  signed certificate file for each phone, again this .sgn file does not  exist within flash. Again, not sure if the use of a CTL client is the  right method for this.

When one phone is set up with no security, it connects easily, so obviously the problem is something to do with the encryption.

The model of IP phone in use is the Cisco  Unified IP phone 7940G, and we have downloaded the appropriate SCCP  firmware for this phone.

Any help would be greatly appreciated.

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