2.2.20.1 Id Element

The id element defines a unique identifier generated by the authoring device, either the protocol client or the server, of the call context data to differentiate one set of call context data from another across all call context generated by a given author. The id element MUST be unique among all call context data created by a given author and appear only once in the call context data.

<xs:element name="id" type="xs:token"  minOccurs="1" maxOccurs="1"/>