Suppressing Refer Implicit Subscription
The recipient of the REFER method [1] creates an implicit subscription to the 'refer' event. This subscription causes the REFER recipient to send NOTIFY messages to the sender informing him of the progress of the REFER. This memo provides for the requirements and one potential mechanism to suppress the creation of this implicit subscription, via an option tag - 'norefersub'. This gives the agent sending the REFER control over the creation of the subscription, while being backwards compatible with [1].