Uac Session Refresh Settings; Configurable Srtp Rollover Counter (Roc) Reset Behavior - Mitel 6800 Series Administrator's Manual

Mitel 6800 Series SIP Phone Release 4.2.0 SP2 Administrator Guide
The value "n" above corresponds to the session timer value (either defined in the "sip session
timer" parameter or provided by the server). The parameter is disabled by default.
Notes:
1. The "sip session timer" configuration parameter must be configured to enable UAC
Session Refresh feature functionality.
2. When the "sip force uac session refresh" parameter is enabled:
• If a phone processes an incoming initial INVITE with a Session-Expires header
set but without the refresher parameter, the refresher=uac parameter is added
in the 200 OK response instead of the default refresher=uas. This ensures the
call initiator performs the refresh.
• If a phone processes an incoming initial INVITE with a Session-Expires header
set and the refresher parameter set to "uas" (i.e. refresher=uas), the phone will
follow the directive received in the INVITE.
• If a phone initiates an outbound call, the outgoing INVITE will only include the
Session-Expires header.
Enabling UAC Session Refresh Support
Use the following procedure to enable UAC session refresh support:
CONFIGURATION FILES
For the specific parameters you can set in the configuration files, see Appendix A, the section,

"UAC Session Refresh Settings"

CONFIGURABLE SRTP ROLLOVER COUNTER (ROC) RESET
BEHAVIOR
In a Secure Real-time Transport Protocol (SRTP) environment, when a re-INVITE is sent but
there is no change to the media Synchronization Source (SSRC) identifier, as per RFC3711
the phone must not reset its Rollover Counter (ROC) to zero. Certain call managers do not
adhere to RFC3711 and with these call managers one-way audio may be observed after a
re-INVITE is sent (e.g. in a call hold/unhold scenario).
To allow interoperability with these call managers that do not adhere to RFC3711 ROC
processing, the "srtp loose roc" parameter has been introduced. By default (i.e. when the
parameter is not defined or if the parameter is defined as "0") the phone strictly adheres to
RFC3711 and does not reset the ROC to zero after a re-INVITE. Enabling this parameter (i.e.
by defining the parameter as "1") the phone loosely adheres to RFC3711 and resets the ROC
to zero after a re-INVITE.
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