26
SETTINGS
G711 Alaw G.711 is an ITU-T standard codec that uses audio companding.
Companding algorithms reduce the dynamic range of an audio
signal. In analogue systems, this can increase the signal-to-noise
ratio achieved during transmission and, in the digital domain,
can reduce the quantization error.
Two main compression algorithms are dened in the standard,
the µ-law algorithm (used in North America and Japan) and
A-law algorithm (used in Europe and the rest of the world).
G711 Ulaw See G711 µ-law above.
G729 G.729 is an ITU-T standard codec that operates at 8 kbit/s. It
is mostly used in VoIP applications with low bandwidth require-
ment.
On phone: MENU > SETTINGS > ADVANCED > (PIN) > MEDIA > CODEC (6,2,4,1).
Security
The media in VoIP calls is usually sent using the RTP protocol (Real-time Transport
Protocol). RTP is a standardized packet format for delivering audio and video over the
Internet.
SRTP (Secure Real-time Transport Protocol) is an extension of RTP to provide encryp-
tion, message authentication and integrity for the audio and video streams.
All devices must support SRTP to establish a connection. It is therefore possible to set
SRTP as disabled, optional or mandatory.
SRTP If set to disabled, the media is sent using RTP. Note that despite
this setting, the OmniTouch 4135 IP will still use a secure chan-
nel if the opposite device demands it.
If set to optional or mandatory, a padlock will be shown in the
bottom right-hand corner of the screen. If the other devices
support SRTP, the padlock will be locked. Otherwise, an open
padlock will be displayed.
If set to mandatory, the call will not be connected if the other
devices do not support SRTP.
Secure signalling The SIP messages (signalling) and the SRTP cipher key are sent
on a different channel than the media and are not affected by
the RTP/SRTP setting. To ensure a secure connection, the signal-
ling must be secured using TLS or SIPS, see page 20. Note that
the SIP transport setting must be set accordingly.
On phone: MENU > SETTINGS > ADVANCED > (PIN) > MEDIA > SECURITY (6,2,4,4).
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