Compression Mode: Default = Automatic Selection
This defines the type of compression which is to be used for calls on this line.

VOIP Silence Suppression: Default = Off
When selected, this option will detect periods of silence on any call over the line and will not send any data during those silent periods.

Call Initiation Timeout: Default = 4 seconds.
Sets how long to wait for successful connection before treating the line as busy.

RE-Invite Supported: Default = Off.
When enabled, Re-Invite can be used during a session to change the characteristics of the session, for example when the target of an incoming call or a transfer does not support the codec originally negotiated on the trunk. Requires the ITSP to also support Re-Invite.

DTMF Support: Default = RFC2833
This setting is used to select the method by which DTMF key presses are signaled to the remote end. The supported options are In Band, RFC2833 or Info.

Use Offerer's Codec: Default = Off.
Normally for SIP calls, the answerer's codec preference is used. This option can be used to override that behavior and use the codec preferences offered by the caller.

Registration Expiry: Default = 60 minutes.
This setting defines how often registration with the SIP ITSP is renewed following any previous registration.

! WARNING - Reboot Required
Changing this setting requires the system to be rebooted for the change to take effect. Rebooting the system will end all calls currently in progress.

PRACK/100rel Supported: Default = Off. Software level = 8.0
This option sets whether Provisional Reliable Acknowledgement (PRACK) and 100rel are enabled. 100rel allows SDP negotiation to be completed while the call is in ringing state and allows further media changes for announcements or progress tones before a call is actually answered. PRACK, as defined in RFC 3262, provides a mechanism to ensure the delivery of provisional responses such as announcement messages. Provisional responses provide information on the status of the call request that is still in progress.

Example: When a call to a mobile or cell phone is in the process of being connected, there may be a delay while the cell phone is located. Provisional information allow features such as an announcement "please wait while we attempt to reach the subscriber" to be played while the call setup is still in progress.

Fax Transport Support: Default = Off. Software level = 8.0+
This option is only available if Re-Invite Supported is selected. When enabled, the system performs fax tone detection on calls routed via the line and, if fax tone is detected, renegotiates the call codec as configured below. The SIP line provider must support the selected fax method and Re-Invite.

Select this option if fax is not supported by the line provider.

G711 is used for the sending and receiving of faxes.

T38 is used for the sending and receiving of faxes.

T38 Fallback  
T38 is used for the sending and receiving of faxes. On outgoing fax calls, if the called destination does not support T38, a re-invite it sent for fax transport using G711.

Caller ID from From Header: Default = Off. Software Level = 8.1.
Incoming calls can include caller ID information in both the From field and in the PAI fields. When this option is selected, the caller ID information in the From field is used rather than that in the PAI fields.

Send From In Clear: Default = Off. Software Level = 8.1.
When selected, the user ID of the caller is included on the From field. This applies even if the caller has selected to be or is configured to be anonymous, though their anonymous state is honored in other fields used to display the caller identity.

User-Agent and Server Headers: Default = Blank (Use system type and software level). Software Level = 8.1.
The value set in this field is used as the User-Agent and Server value included in SIP request headers made by this line. Setting a unique value can be useful in call diagnostics when the system has multiple SIP trunks.