Aastra-telecom 53I User Manual download pdf (Page 40)

Security Features

34 RN-001029-00, Rev 03, Release 2.1

IP Phone Release Notes 2.1

Secure Real-Time Transfer Protocol (SRTP) Support with SDES Key

Exchange

Release 2.1 includes 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).

An Administrator 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.

If an SRTP enabled IP phone initiates a call, and the receiving phone is also SRTP

enabled, the IP Phone UI displays a “lock” icon, indicating that the call is secure.

If the receiving phone does not support SRTP, the IP phone will send unsecured

RTP messages instead of SRTP encrypted messages. However in this case, the IP

Phone UI does not display the lock icon - indicating a non-secure call.

An Administrator can configure SRTP on a global or per-line basis using the

configuration files and the Aastra Web UI.

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 TLC, set the Transport Protocol parameter

(located on the Global SIP Settings menu) to TLS.

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Aastra-telecom 53I User Manual Page 40