Multilevel Precedence and Preemption (MLPP) for Assured Services - Session Initiation Protocol (AS-SIP)

Multilevel Precedence and Preemption (MLPP) enables you to configure a precedence level for outgoing calls. Polycom implements MLPP in accordance with the standards set by Assured Services for Session Initiation Protocol (AS-SIP).

Higher precedence calls preempt—end—active calls with a lower precedence level. When an active call is preempted, the phone plays a preemption tone and displays a preemption screen. The preemption screen display time can be configured in the config file. The default time for the preempted screen is 0 seconds for callee and 3 seconds for caller. If the default time for the preempted screen is 0 seconds, then preemption screen is displayed until you press the OK button. The preemption screen shows that the current call was preempted, and an OK button to acknowledge the preemption. The user can then answer the incoming higher-precedence call or reject the call. If the callee doesn’t acknowledge the incoming call, the notification disappears and the current call ends.

If a lower-precedence call is on hold, and you receive a higher-precedence call, the preemption screen doesn’t display, and the preemption tone doesn’t play.

MLPP treats incoming calls with the same precedence level as the active call depending on the call state, as shown in the following table.

Table 1. MLPP Behavior
Current Call State New call—same precedence: one active call

One call per line

New call—same precedence: multiple active calls

Multiple calls per line

Active Call Rejected

If you accept the new call, it’s placed in the first slot. The active call is placed on hold and moved to the second slot.

If all lines and call appearances are at capacity, new incoming call with the same precedence will get rejected.

Ringing State Rejected The new call displays in the top center corner and the current call is in the main screen.
Call on Hold Rejected If the user acknowledges the new call, the current call is moved to the second slot. The new call is placed in the first slot.
The caller’s phone displays the precedence of the outgoing call. Callee phones display call precedence on each phone line: 1 indicates the lowest precedence and 5 indicates the highest precedence. Phone models vary in how they display precedence:
    • VVX 101, VVX 201, VVX 3xx business media phones: P-1, P-2, P-3, P-4, P-5
    • VVX 4xx, VVX 5xx, VVX 6xx, VVX 15xx business media phones: Priority-1, Priority-2, Priority-3, Priority-4, Priority-5
    • VVX 150 business IP phone: P-1, P-2, P-3, P-4, P-5
    • VVX 250, 350, 450 business IP phones: Priority-1, Priority-2, Priority-3, Priority-4, Priority-5