Domain ID of the destination domain.

This field contains the domain ID of the destination domain of the request. Domain ID is a unique identifier assigned to every virtual domain handled by SERi [1] in multi-domain mode. Domain ID is not necessarily same as the host part of the URIi [2] in Request-URIi [3] or To header field.

For outbound requests (those that are targeted to a domain that resolves to another SIP server) this field will be either empty or missing, because outbound requests have no virtual domain assigned on the server.