Nortel 2033 Installation And Operation Manual page 472

Page 472 of 600
SRTP media encryption
553-3001-368 Standard 20.00
Features overview
Enhanced UNIStim Firmware download feature requires a Signaling Server
to be present on the node. Without a Signaling Server, the only firmware files
available for downloading are the three available in CS Release 4.0 for the
Phase 0/1/2 IP Phone 2001, IP Phone 2002, and IP Phone 2004.
For further information on Enhanced UNIStim Firmware download, refer to
IP Line: Description, Installation, and Operation (553-3001-365).
Secure Real-time Transport Protocol (SRTP) RFC 3711 is a standards based
way to encrypt a Real-time Transport Protocol (RTP) media stream. The
SRTP media encryption feature provides a mechanism to exchange session
keys which are used to create an SRTP session over an existing RTP stream.
The session keys are dynamically created each time an RTP stream is created
and are used to generate an SRTP Master key. The session key is protected
by a preshared secret embedded in the IP Phone to generate and exchange
encryption parameters.
When SRTP media encryption feature is enabled and a traditional RTP call is
set up, the new feature reuses part of the RTP packets to determine if the
SRTP media encryption feature is supported at the far end. If the SRTP media
encryption feature is supported, the encryption parameters are encrypted
using a secret, preshared key and are sent in an RTP packet to the far end.
Each side then switches to SRTP/SRTCP mode and all media and control
streams are encrypted. A small icon appears on the display to indicate the call
is encrypted. If the SRTP media encryption feature is not supported at the far
end, the call continues using an unencrypted RTP/RTCP stream.
The SRTP media encryption feature is supported on the following IP Phones:
• IP Phone 2001
• IP Phone 2002
• IP Phone 2004
• IP Phone 2007
• IP Phone 1120E
December 2006