Ericsson This specification define a new type of Globally Routable User Agent URI (GRUU) [RFC5627], called emergency GRUU (eGRUU). When a User Agent (UA) provides makes an emergency call, it can provide the eGRUU to a PSAP, which can then use it to make a PSAP callback call. The specification also defines a new URI parameter, "psapcb", which can be used to indicate that a URI can be used for PSAP callback calls. A registrar will provide the URI parameter as part of the generated eGRUU value. Later, when a PSAP makes a PSAP callback call the URI, including the "psapcb" URI parameter, can be used by SIP entities to identity callback calls.