Multilevel precedence and preemption
Multilevel precedence and preemption, or MLPP, is used to assign priorities to some calls, for example emergency calls.<br\> The MLPP is an SS7 ISUP Information element. The IE is identified by 4 parameters:
- Look ahead for busy (LFB): Allowed, Path reserved or not allowed
- Network identity: Information to identify the Network. A value from 0 to 999.
- Service domain: Defines the specific MLPP domain. A value from 0 to 16777215 (24 bits).
- Precedence Level: Flash override (Highest, 0), Flash (1), Immediate (2), Priority (3), Routine (lowest, 4)
In SIP, it is a header parameter called Resource-Priority. The parameter will be q735.x, "x" being the priority (same value as precedence level for SS7 ISUP).<br\>The priorities are defined as emergency (0), urgent (1), normal (2), non-urgent (3) and other-priority (4)
TelcoBridges and MLPP
It is possible to configure the MLPP options in the profiles. Profiles can be assigned to any network. There are 3 outgoing modes possible:
- No MLPP insertion
- Relay MLPP information
- Always insert MLPP information
MLPP can be inserted or removed from the call flows. Depending on the networks involved, these are the results of the calls:
| No MLPP Insertion | |
| Incoming | Outgoing |
|---|---|
| SS7 with or without MLPP | SS7: no MLPP |
| SS7 with or without MLPP | SIP: no Resource-Priority header |
| SIP with or without Resource-Priority | SS7: no MLPP |
| SIP with or without Resource-Priority | SIP: no Resource-Priority header |
| Relay MLPP information | |
| Incoming | Outgoing |
|---|---|
| SS7 with MLPP | SS7: incoming MLPP |
| SS7 without MLPP | SS7: no MLPP |
| SS7 with MLPP | SIP: Resource-Priority=q735.[incoming precedence level] |
| SS7 without MLPP | SIP: no Resource-Priority header |
| SIP with Resource-Priority=q735.x | SS7: Precedence Level = x and profile MLPP info (LFB + Network ID + Service Domain) |
| SIP without resource priority | SS7: no MLPP |
| SIP with Resource-Priority=q735.x | SIP: Resource-Priority=q735.x |
| SIP without Resource-Priority | SIP: no Resource-Priority header |
| Always insert MLPP information | |
| Incoming | Outgoing |
|---|---|
| SS7 with or without MLPP | SS7: MLPP info from profile |
| SS7 with or without MLPP | SIP: Resource-Priority=q735.[precedence level from profile] |
| SIP with or without resource priority | SS7: MLPP info from profile |
| SIP with or without resource priority | SIP: Resource-Priority=q735.[precedence level from profile] |
In addition to this profile configuration, MLPP values can be set in the routing scripts.<br\> See
MLPP Precedence values