How it Works
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 |
|
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:
-
SMF/CP is not upgraded
-
Priority values are sent based on N-1 support
-
WPS prioritization is enabled on UPF
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. |