Calls can be made and received with indication that the caller ID should be withheld. In SIP terminology, these are 'anonymous' calls.

For outgoing calls, the call can be set as anonymous using the following methods:

• W Short Code Character

  Adding a W as a suffix to the Telephone Number setting of a short code indicates withhold the caller ID. For SIP calls, this is supported if the line URI being used is set to Auto.

• User/Group Anonymous Setting

  Each system user and hunt group has a set of SIP settings (User > SIP, Group > SIP, System > Voicemail > SIP ). If selected, the Anonymous setting indicates that the user or group should treated as anonymous when making/receiving SIP calls. The voicemail service also has SIP settings that include the option to be anonymous. For SIP calls, this is supported if the line URI used is set to Use Internal Data.

• Withhold Number Option

  Avaya feature phones can be configured to withhold the caller ID (Features > Call Settings > Withhold Number). That matches the W short code operation above.

How Does Setting a Call as Anonymous Affect the Call Headers?

Setting anonymous/caller ID withheld has the following effect on the information added to SIP URIs sent by the system:

• The system adds a Privacy header to the call information.

• If Send From In Clear is not enabled (the default):

  • The SIP URI in the From header is anonymized:

    • The display name part is set to "Anonymous".

    • The content and host parts are set to dummy values (anonymous@anonymous.invalid).

  • The Privacy header is set to user, otherwise it is set to id.

  • A PPI or PAI header is used to contain the caller's number. This is done using the line's Use PAI for Privacy setting (off and so PPI is used by default). PAI headers should only be used in a trusted network.

• If Send From In Clear is enabled:

  • The From header is not anonymized,

• When used in SIP URI and SIP Line Appearances, the P Preferred ID or P Asserted ID entries should be configured to be the same or only one of them should be configured.