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SRTP (Secure Real-time Transport Protocol) is the secure variant of the RTP protocol using AES encryption.
It shares the same features and uses an even port above 1024 like the RTP protocol.

SRTP works in conjunction with the SRTCP (Secure Real-time Control Protocol), which uses an odd port above 1024.
While SRTP provides the audio or video stream the SRTCP protocol provides stream control and status feedback.


In FRITZ!OS SRTP is used for VoIP and is performed by voipd using librtpstream.so.

For every Fritzbox with configured Telephony the 40 ports Port-7078-7109-udp are open to the Internet.
This is required for a maximum of 20 SIP accounts, 20 even ports for RTP / SRTP and 20 odd ports for RTCP / SRTCP.

SRTP and SRTCP support was prerpared since long time, the variable CONFIG_SRTP exists since fw 4.38.
However, it was never enabled. This happened in fw 7.19, when this variable turned to y the first time.

libsrtp.so by Cisco is present in FRITZ!OS since fw 4.80 and is optionally loaded by librtpstream.so used by voipd.

The Webinterface maintains the SRTP / SRTCP settings per SIP account in the sip ui-module, which is maintained by libfon.so.

Keys added in fw 7.19:


$N is the SIP account number (0-19). In fw 7.39 further keys were added:


The settings are stored in the ua* sections of voip.cfg which is maintained by libar7cfg.so.


Information is currently being retrieved from the backend.


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