Installation guide

Global SIP Settings
41-001561-00 REV00 – 10.2014 4-73
You can specify a customized codec preference list on a global-basis using the configuration files or the Mitel Web UI.
Out-of-Band DTMF and DTMF Method
The IP phones support out-of-band Dual-Tone Multifrequency (DTMF) mode as referenced in RFC2833. In the Mitel 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 Mitel Web UI.
An additional 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 Mitel Web UI.
The matrix below details DTMF behavior when the out-of-band DTMF and DTMF method settings are configured in vari-
ous scenarios:
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 Mitel 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 non-secured 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.
When an active call is using SRTP (i.e. when an SRTP enabled IP phone initiates a call and the receiving phone is also SRTP
enabled) and the transport protocol is set to TLS, the IP Phone UI displays a “lock” icon, indicating that the call is secure. If
one of the phones does not support SRTP and/or TLS is not enabled, the IP Phone UIs do not display the lock icon, indicat-
ing that the call may not be secure.
You can configure SRTP on a global or per-line basis using the configuration files or the Mitel Web UI.
Web UI Setting/Configuration Parameter Setting DTMF Behavior
DTMF Method/
sip dtmf method
Force RFC2833 Out-of-Band DTMF/
sip out-of-band dtmf
SIP INFO In-Band DTMF
Out-of-Band DTMF
(RFC2833)
RTP (0) Disabled (0) No Yes No
RTP (0)Enabled (1)NoNoYes
SIP INFO (1) Disabled (0) Yes No No
SIP INFO (1) Enabled (1) Yes No Yes
RTP and SIP INFO (2) Disabled (0) Yes Yes No
RTP and SIP INFO (2) Enabled (1) Yes No Yes
Note:
If you enable SRTP, then you should also enable Transport Layer Security (TLS). This prevents capture of the key used for
SRTP encryption. To enable TLS, set the Transport Protocol parameter (located on the Global SIP Settings menu) to
TLS.