220.127.116.11 CPS Transfer of the Parkee to the Parker Fails
When a transfer of the parkee to the parker (auto-ringback) fails because the parkee disconnects the call during the attempted transfer, the event MUST be handled as described in section 18.104.22.168. Otherwise, the following processing applies.
The CPS MUST increment the ringback attempt count. If the count has not yet reached the maximum, the auto-ringback timer MUST be restarted and additional processing of this event MUST NOT be done. Otherwise the following processing applies. The maximum number of auto-ringback attempts is not defined in the ms-call-park protocol; an implementation is free to choose any maximum, or to make the maximum user-configurable.
If the maximum ringback count has been reached and there is a configured fallback URI, the CPS MUST initiate a transfer of the parkee to that fallback URI. This MUST be done by sending a SIP REFER to the parkee. The Refer-To target of the transfer MUST be the configured fallback URI.
If the maximum ringback count has been reached and there is no configured fallback URI, the CPS MUST terminate the call with the parkee by sending a SIP BYE. If the control dialog with the parker is still active, the CPS MUST send an unpark-notification with a reason code of "drop". This notification MUST NOT contain a target element. After sending this notification, the CPS MUST then send a BYE on the parker-CPS dialog. This BYE SHOULD include an ms-diagnostics code of 35014 as defined in [MS-OCER]. The CPS MUST return the orbit to the pool and release any resources associated with the parked call.