Control of quality-of-service preconditions in an IP multimedia subsystem

An IP Multimedia Subsystem (IMS) network entity that comprises a Quality of Service (QoS) Precondition Inter-Working Function (IWF) operable for establishing a session between a client accessing the IMS network and a client accessing another IMS network, the IMS network entity comprising:

• at least one processor:
• and
• a non-transitory computer-readable storage medium including computer-readable instructions, when executed by the at least one processor, are configured to:
• receive, at the IWF, an IMS session initiation request originated by an originating client, the request indicating a terminating client for the session,
• determine, based on the IMS session initiation request, that the IMS session initiation request requires the use of QoS preconditions, that the originating client is not using QoS reconditions and that the terminating client, or IMS network with which the terminating client is registered, requires the use of QoS preconditions,
• forwarding, by the IWF, a set of QoS preconditions along with a session description protocol (SDP) offer on behalf of the originating client that is not using QoS preconditions, to the IMS network with which the terminating client is registered, and
• completing, by the IWF the session establishment only after QoS resources complying with the set of QoS preconditions have been established by the terminating client.