The IMS is a service management architecture which was introduced by the 3GPP. Designed to operate using SIP signalling, the IMS is IP-CAN agnostic. That is, regardless of the IP-CAN that the subscriber is connected to, that subscriber should still be able to access their services using SIP signalling directed towards the IMS. The IMS does not provide services itself, rather, it manages requests for services between the subscriber and the AS that provides the service. Core network entities associated with the IMS include the CSCF and HSS.