AASTRA 6700i series, 9143, 9480i, 9480i CT SIP Administrator Guide EN - Manual (Page 257)

4-94 41-001343-01 Rev 03, Release 3.2.2
Out-of-Band DTMF
The IP phones support out-of-band Dual-Tone Multifrequency (DTMF) mode according to
RFC2833. In the Aastra Web UI, you can enable or disable this feature as required. The
"out-of-band DTMF" is enabled by default.
In out-of-band mode, the DTMF audio is automatically clamped (muted) and DTMF digits are
not sent in the RTP packets.
You can configure out-of-band DTMF on a global-basis using the configuration files or the
Aastra Web UI.
DTMF Method
A feature on the IP phone allows you to select the DTMF method that the phone uses to send
DTMF digits from the IP phone via INFO messages. You can set the DTMF method as
Real-Time Transport Protocol (RTP), SIP info, or both.
You can configure the DTMF method on a global or per-line basis using the configuration files
or the Aastra Web UI.
RTP Encryption
The IP Phones include support for Secure Real-time Transfer Protocol (SRTP), using Session
Description Protocol Security (SDES) key negotiation, for encryption and authentication of
RTP/RTCP messages sent and received by the Aastra IP phones on your network.
As administrator, you specify the global SRTP setting for all lines on the IP phone. You can
choose among three levels of SRTP encryption, as follows:
• SRTP Disabled (default): IP phone generates and receives nonsecured RTP calls. If the IP
phone gets called from SRTP enabled phone, it ignores SRTP tries to answer the call using
RTP. If the receiving phone has SRTP only enabled, the call fails; however, if it has SRTP
preferred enabled, it will accept RTP call.
• SRTP Preferred: IP phone generates RTP secured calls, and accepts both secured and
non-secured RTP calls. If the receiving phone is not SRTP enabled, it sends non-secured
RTP calls instead.
• SRTP Only: IP phone generates and accepts RTP secured calls only; all other calls are
rejected (fail).
You can override the global setting as necessary, configuring SRTP support on a per-line basis.
This allows IP phone users to have both secured and unsecured lines operating on the same
phone.