For SIP-based calls, the map contains the list of SIP headers that are unknown to the SDK. SIP header name is used as the map key, and the header content is used as to the value of the map entry. During the lifetime of a call session, the extra properties of the call may be updated based on the information received from the network. The extra properties field tracks cumulative list of properties added to the call. For instance, an unknown SIP header of the form "header1: content1" is received, it is added to the map (key = "header1", value = "content1")

A subsequent SIP message carrying two unknown headers "header1: contentA" and "header2: content2" will result in the update of the existing property as well as addition of a new map entry, as follows: (key = "header1", value = "contentA”") (key = "header2", value = "content2")

If there are multiple occurrences of an unknown SIP header, a unique map entry is created for each occurrence by appending a unique integer to the header name. For instance, if a SIP message contains two occurrences of an unknown SIP header, "unknownHeader:content1" and "unknownHeader:content2", then two separate map entries are created: (key="unknownHeader", value ="content1") (key="unknownHeader2", value ="content2") The application will be notified of this change using the event.

Av-Phone-Global-Session-ID Header will be available in computer and shared control modes. In case of computer mode, there will be an entry in the map as follows:
(key = "Av-Phone-Global-Session-ID", value = "Global Session ID of the incoming call received from far end.") In the case of shared control, there will be an entry in the map as follows:
(key = "Av-Phone-Global-Session-ID", value = "Global Session ID of the incoming call received from controllable endpoint.")

Reference