Aastra Telecom 9480i Series User Manual

41-001160-03, Rev 00, Releaes 2.4

4-97

Configuring Network and Session Initiation Protocol (SIP) Features

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.

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. 

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