This problems relates to unattended REFER transfers in an IMS network.
 
Background: 3GPP IMS does not mandate a NOTIFY to be sent for the implicit
Subscription created by the REFER. But the UAC, sending the REFER, will
create a Subscription before sending the REFER out. The subscription
created by REFER will end under the following situations.
- a response to the REFER is not received
- A NOTIFY is received with the "Subscriptionn-State" header set to "terminated"
- A NOTIFY contains a Expires timer, which will trigger the expiration of the
  subscription in the UAC.
 
Problem: Since IMS implementations do not send a NOTIFY, the subscription 
created by the REFER request will hang around indefinately.
 
Are there any known solutions to deal with the non-receipt of NOTIFY messsages
to end the subscription in the UAC that sent the REFER.
 
Thanks,
Nagesh Shekar
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