User`s guide

Vigor2820 Series User’s Guide
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Secure Phone ZRTP is a cryptographic key-agreement protocol to encrypt
VoIP phone calls to ensure the phone security. It allows users to
encrypt any Session Initiation Protocol (SIP) VoIP voice stream,
as long as the peer side on the call is also using such protocol.
None - If the incoming or outgoing call matches the phone
book entry with secure phone option set to "None", it means the
call should be unprotected.
ZRTP+SRTP – If the incoming or outgoing call matches the
phone book entry with secure phone option set to
"ZRTP+SRTP", it means the call would be protected. A
warning message will be played out if the call ends
up unprotected.
Note: If the incoming or outgoing calls do not match any entry on the phonebook, the router
will try to make the call "being protected". But, if the call ends up "unprotected"(e.g. peer
side does not support ZRTP+SRTP), the router will not play out a warning message.