This section describes how WPS prioritization works in UPF.
Priority Handling
The session-priority-profile maps the session-priority values from 0 to 15 to precedence values from 1 to 4. It is used internally
in modules like RCM and data-queue distribution.
SR and ICSR
When the feature is not enabled, any session with a valid session-priority received over N4/SX will be prioritized for SR/ICSR
as per earlier design.
When the feature enabled, there is a change such that only the Emergency and WPS sessions will be prioritized for SR/ICSR.
During UPF downgrade, the priority values are recovered with an offset of +1.
Data Queue
The following table describes the traffic distribution over data queues based on session precedence:
Queue #
|
Details
|
3 (Highest priority)
|
Reserved for Sx
|
2
|
Used for Precedence 1,2 sessions
|
1
|
Used for Precedence 3,4 sessions
|
0 (Lowest priority)
|
Used for Data/Non-prioritized sessions
|
The default precedence values will be used when:
-
Only session-type is configured and precedence is not defined for session-priority
-
No priority value is configured in the session-priority profile
-
WPS feature is enabled with the default session-priority profile
Note
|
-
If the feature is disabled, UPF uses N-1 support prioritization.
-
For session recovery of combo calls, the highest priority value received on Sxa or N4 will be used for both sessions.
|
Mapping to Session Type
UPF maps the session priority values (WPS, Emergency, and IMS) received over N4 to the session types using the "associate
session-priority-profile" CLI configuration.
For VoLTE non-active sessions, mapping is not available. For VoLTE active sessions, the priority value 'ims' will be used,
while the next priority value (+1) is implicitly used for VoLTE non-active sessions. Hence, "ims+1" priority should not be
configured in the session-priority profile.
Version Compatibility
-
For the latest version (X) of RCM and a prior version (X-1) of UPF:
-
RCM will support the previous UPF version (X-N), as the priority set is extended without affecting the previously supported
set of priorities (1, 2, 3).
-
During switchover, the flush sequence will be completely based on the priority received from the UPF, which was not the case
in earlier versions.
-
For the prior version (X-1) of RCM and latest version (X) of UPF:
-
RCM will not support the extended set of priorities, and the checkpoints received for priority 4 will be dropped.
-
During switchover, calls for priority 1, 2, and 3 can be restored.
Control-Plane Compatibility
To enable WPS prioritization, upgrade the UPF to the new configuration. Prioritization will not be guaranteed in the following
scenarios when:
Based on the priority values received from the Control Plane, the following combinations will work:
S. No.
|
SMF / cnSGW / PGW-C / SGW-C Version
|
UPF Version
|
WPS prioritization enabled on UPF
|
UPF Behavior
|
1
|
N-1
Or
N without config
|
N-1
|
N/A
|
No WPS prioritization - same as previous behavior.
|
2
|
N-1
Or
N without config
|
N
|
No
|
No WPS prioritization - same as previous behavior.
|
3
|
N-1
Or
N without config
|
N
|
Yes
|
Session prioritization will not be guaranteed.
|
4
|
N (Config present)
|
N-1
|
N/A
|
This is not recommended as session prioritization will not be guaranteed. RCM checkpoints will be dropped for priority>3.
|
5
|
N (Config present)
|
N
|
Yes
|
WPS prioritization works.
|
6
|
N (Config present)
|
N
|
No
|
This is not recommended as session prioritization will not be guaranteed.
|