IMS/AS 560 stops sending SIP OPTIONS messages when the call is answered or cancelled. As shown on FIG. 5b, when IMS/AS 560 receives a SIP answer message, such as 200 OK [INVITE], from UE 540, it stops sending SIP OPTIONS message. As will be understood, when the call is cancelled, for example, if IMS/AS 530 receives a SIP CANCEL message from the originating UE, or if it decides to cancel the call due to expiration of a ringing timer, e.g. a NoReply timer, it will also stop sending SIP OPTIONS message to UE 540.
As will be appreciated, IMS/AS 530, 560 illustrated on FIGS. 5a and 5b may be one and the same IMS/AS, or they may be different IMS/ASs.
FIG. 6 illustrates a block diagram of an apparatus 600 according to an embodiment of the present invention. The apparatus 600 is for establishing a VoLTE call in a communication network. Preferably, the apparatus 600 may be implemented in an application server in IMS.
The apparatus 600 may comprise a communication interface 610, an identification module 620, and a control module 630, which are operatively coupled together.
The communication interface 610 may be adapted to receive a request for establishing a VoLTE call. The communication interface 610 is configured to receive a request from any of wireless or wired networks, such as LTE network, 3G/2G network, IP network or PSTN network.
