Multilevel precedence and preemption
Multilevel precedence and preemption, or MLPP, is used to assign priorities to some calls, for example emergency calls.
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).
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.
| 4 possible MLPP outgoing modes | |
| Mode | Explanation |
|---|---|
| No MLPP insertion | No MLPP field is inserted in the outgoing leg. |
| Relay MLPP information | MLPP fields are inserted in the outgoing leg only if they present in the incoming leg. The missing MLPP parameters from the incoming leg will be completed by the values of this profile. |
| Always insert MLPP information | MLPP fields are inserted in the outgoing leg. MLPP fields from the incoming leg will be used if available. The missing MLPP parameters from the incoming leg will be completed by the values of this profile. |
| Forced MLPP information | MLPP fields are always inserted in the outgoing leg by using the values of this profile. The incoming MLPP fields will NOT be used. |
MLPP can be inserted or removed from the call flows. Depending on the networks involved, these are the results of the calls for different scenarios:
| 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 MLPP | SS7: incoming MLPP |
| SS7 without MLPP | SS7: MLPP info from profile |
| SS7 with MLPP | SIP: Resource-Priority=q735.[incoming precedence level] |
| SS7 without MLPP | SIP: Resource-Priority=q735.[precedence level from profile] |
| SIP with Resource-Priority=q735.x | SS7: Precedence Level = x and profile MLPP info (LFB + Network ID + Service Domain) |
| SIP without resource priority | SS7: MLPP info from profile |
| SIP with Resource-Priority=q735.x | SIP: Resource-Priority=q735.x |
| SIP Resource-Priority | SIP: Resource-Priority=q735.[precedence level from profile] |
| Forced 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.
See
MLPP Precedence values
