Multilevel Precedence and Preemption (MLPP)


Multilevel Precedence and Preemption (MLPP) is typically utilized in military communications that incorporate a priority scheme.

This can help when it comes to assigning one of several precedence levels to specific calls or messages so that the system handles them in a predetermined order and time frame; for gaining controlled access to network resources in which calls and messages can be preempted only by higher priority calls and messages; calls and messages recognized only within a predefined switch partition; where the precedence level of a call outside the predefined switch partition is usually not recognized.

These precedence levels, in descending order, are as follows:

  • Flash Override Override: cannot be preempted; not enabled on all DoD networks.
  • Flash Override: cannot be preempted in the DSN.
  • Flash: reserved generally for telephone calls pertaining to command and control.
  • Immediate: reserved generally for telephone calls pertaining to situations that gravely affect national security.
  • Priority: reserved generally for telephone calls requiring expeditious action by called parties and/or furnishing essential information for the conduct of government operations.
  • Routine: designation applied to those official government communications that require rapid transmission but do not require preferential handling.

MLPP rules state that more important calls override less important calls when congestion occurs within a network. Station-based preemption is used when a more important call needs to be placed to either party in an existing call. Trunk-based preemption is used when trunk bandwidth needs to be reallocated to facilitate a higher precedence call over a given path in the network. In both station- and trunk-based preemption scenarios, preempted parties are positively notified, via preemption tone, that their call can no longer be supported. The same preemption tone is always used.



  • Use Existing JITC-Certified Switches. This allows for minimal MLPP implementation to all current and future WITS customers.
  • Utilize Existing MLPP Test Plans. The unique requirements are associated with the current WITS network.
  • WITS Switch Solution. This allows T1.619a compliant JITC-certified PBX’s full MLPP capability with WITS switches and their connectivity to the DSN.
  • Scalable Per Switch Licensing. This allows for location-based MLPP needs for DSN MLPP operation.



MLPP Features – The following MLPP features can be implemented as part of the switch feature upgrades for the WITS DoD serving trunks:

    • Abbreviated dialing for DSN
    • Direct station select for DSN
    • Precedence Network In-Dialing (PNID)
    • Main-satellite DSN/AUTOVON compatibility
    • DSN autovon console
    • Business Residential Custom Services (BRCS) adaptation for DSN
    • Precedence and preemption
    • MLPP on SS7 – Stage 1
    • MLPP on SS7 – Stage 2
    • MLPP on PRI
    • Connection arrangements are supported for the following:
      • Analog line to PRI
      • BRI to PRI
      • PRI to PRI
      • PRI to DP/MF trunk
      • An MLPP call can be routed over a PRI B-channel or over a DP/MF trunk depending on how the route indices are provisioned.
    • The following DSN features are supported using these features:
      • Precedence access threshold limits the number of calls at each precedence level that can be offered to the DSN.
      • Polygrid routing is a robust, redundant trunking scheme, where in the limiting case, all DSN switches are interconnected with each other.
    • DSN/autovon ISDN attendant console
    • Precedence and preemption ISDN attendant displays
    • Attendant queuing by precedence levels
    • Attendant originating and terminating calls