This topic provides a general overview of MLPP call processing behavior.
An MLPP outgoing trunk call is defined as trunk call from a subscriber on the local system to a subscriber at the remote system.
If an MLPP outgoing trunk call is above the Routine precedence level and there are no trunks available in the selected MLPP trunk route, the system will attempt to find a busy trunk circuit that has a lower precedence. If it finds a busy trunk circuit, the system will attempt to preempt the call and use the circuit for a new call. Only T1 ISDN PRI circuits that are programmed to support T1-619a signalling can be preempted.
An incoming trunk call is defined as a trunk call from a subscriber on the remote switch to a subscriber at a local switch.
If an incoming trunk call is above the Routine precedence level, the remote switch will follow its own routing and hunt algorithms to find a trunk for the call. The remote switch knows the precedence level and Service Domain of the incoming call and can determine whether preemption should be applied. If there are no trunks available, the two switches use the following process to seize an MLPP-capable (T1 ISDN PRI) circuit:
The remote switch sends a preemption request.
The local switch preempts a call for a local subscriber and replies to the remote switch with a preemption release indication. The trunk is now in Releasing state.
The remote switch replies to the preemption release indication, which causes the local switch to put the trunk in reserved state.
The remote switch uses normal PRI call setup procedures to initiate a new call on the trunk . The new call is then sent to the destination. The precedence level that is transmitted by the remote switch is assigned to the call for its duration.
An internal call is defined as a call in which both the originator of the call and the call destination are on the same switch.
If an internal call is above the Routine precedence level, it can preempt a call of lower precedence that is in the same Service Domain. This functionality interworks with call completion and call diversion features. For example, if the call cannot be preempted because the circuit is not pre-emptable or the called party's precedence level is too high, the system will forward the call or route the call to a programmed intercept (either MLPP Blocked Precedence or MLPP Cannot Preempt). The Call Diversion Timer (see below) runs until the call is answered or routed to a programmed intercept.
If it has been enabled, the Call Diversion Timer is started for all calls at a precedence level above ROUTINE (both internal and MLPP-capable trunk calls). This "global" timer runs until the call is answered or routed to a programmed intercept. It carries on through ringing, call forwarding, and call rerouting. If the timer expires, the call is routed to the Call Diversion Directory Number (usually an Attendant console or group of consoles). The system cancels the Call Diversion Timer when the user answers the call or when the call is queued to the Call Diversion Directory Number.
The Call Diversion Timer is disabled if the Call Diversion Directory Number is not programmed.
The following table describes call handling when the system is in Night Service and when the MLPP Call Diversion Answer Point is out of service or in Do Not Disturb
|
State of System or Call Diversion Answer Point |
Call Processing Behavior |
|
System in Night Service |
Calls follow the programming in the Intercept Handling form for the first instance (Intercept Number 1) of the two Attendant in Night Service fields. |
|
Call Diversion Answer Point is Out of Service |
The system will attempt to follow the First Alternative No Answer programming of the Answer Point. If no First Alternate rerouting is programmed, the system will continue to ring the originally called number. |
|
Call Diversion Answer Point is Do Not Disturb |
If the Answer Point is a non-console device, normal MLPP handling is invoked: the call will override DND and ring the answer point. If the Answer Point is a SUPERCONSOLE 1000 and the attendant is "Absent", the system will attempt to follow the Answer Point's First Alternate No Answer programming. If no First Alternate rerouting is programmed, the system will continue to ring the originally called number. |
Note: MLPP Call Diversion will not follow Second Alternative rerouting so the Answer Point should not have a second alternate programmed.
If a call at a precedence level above Routine is not answered and the Call Diversion Timer expires, the system routes the call to the Call Diversion Directory Number. If the Call Diversion Directory Number has not been programmed, then the call will continue to ring. A call above Routine precedence is never forwarded to voice mail.
