Sip refer extensions

A method, comprising:

• receiving a refer message configured to transfer a first endpoint of a call session, the call session being between at least the first endpoint at a first communications device and a second endpoint at a second communications device, the refer message indicating to transfer the first endpoint from the first communications device to a third communications device;
• subscribing the first communications device to notification messages associated with the referral of the transferred call session, the subscription to the referral extending beyond the call transfer until termination of the call;
• receiving a subscribe message from the first communications device configured to refresh the subscription;
• determining whether the subscription has expired, and if so whether the subscription has expired within a predetermined amount of time
• if the subscription has not expired or if the subscription has expired within the predetermined amount of time, refreshing the subscription;
• otherwise, rejecting the refresh of the subscription;
• and
• sending, if the subscription has not expired or is refreshed, through the subscription to the first communications device, a notification message indicating termination of the transferred call.

A non-transitory computer-readable medium storing a software program, the software program being executable to provide operations comprising:

• receiving a refer message configured to transfer a first endpoint of a call session, the call session being between at least the first endpoint at a first communications device and a second endpoint at a second communications device, the refer message indicating to transfer the first endpoint from the first communications device to a third communications device;
• subscribing the first communications device to notification messages associated with the referral of the transferred call session, the subscription to the referral extending beyond the call transfer until termination of the call;
• receiving a subscribe message from the first communications device configured to refresh the subscription;
• determining whether the subscription has expired, and if so whether the subscription has expired within a predetermined amount of time
• if the subscription has not expired or if the subscription has expired within the predetermined amount of time, refreshing the subscription;
• otherwise, rejecting the refresh of the subscription;
• and
• sending, if the subscription has not expired or is refreshed through the subscription to the first communications device, a notification message indicating termination of the transferred call.