WPS Prioritization
Feature Description
How it Works
- Limitations
Configuring WPS Prioritization
- Enabling WPS Prioritization
- Mapping the Session Priority Profile
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WPS Prioritization

Table 1. Feature History
Feature Name	Release Information	Description
WPS Prioritization on UPF	2023.04	The Wireless Priority Services (WPS) feature provides finer control for priority handling over multiple interfaces. UPF supports WPS services based on the message priority indicated by SMF. The configured priority value set on SMF will be sent to UPF over N4 as part of the PFCP header.

Feature Description

The Wireless Priority Services (WPS) feature provides finer control for priority handling over multiple interfaces. UPF supports WPS based on the message priority indicated by SMF.

The priority value set on SMF will be sent to UPF over N4 as part of the PFCP header. The message priority values from SMF/CUPS-CP are currently supported for Emergency, VoLTE, and non-VoLTE IMS sessions.

Note

WPS supports only N4 (SMF) and Sxa (cnSGW) terminations on UPF. WPS does not support Sxb (PGW-C) and Sxa (SGW-C) terminations in this release.

For information on WPS prioritization support on RCM, see the UCC 5G RCM Configuration and Administration Guide.

For information on WPS prioritization support on SMF, see the UCC 5G SMF Configuration and Administration Guide.

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

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:
1. 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).
2. 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:
1. RCM will not support the extended set of priorities, and the checkpoints received for priority 4 will be dropped.
2. 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.

Limitations

The WPS Prioritization feature has the following limitations:

In a multi-Sx/N4 scenario, all Control Plane nodes must use the same process to send MP values. This applies to SMF/cnSGW and PGW-C/SGW-C working with the same UPF.
The sessions recovered during the UPF software upgrade will retain their prioritization values. As a result, after the UPF upgrade between N-1 and N, the prioritization for existing sessions will not work as expected, and the show CLI output will be undetermined.
In the case of a configuration change at the SMF that changes existing priority values or a configuration change at the UPF that changes the session type, the session type and priority are not re-evaluated. As a result of such a configuration change, incorrect statistics updates may occur.
Due to any mid-session priority changes, some of the statistics may be inconsistent.

Configuring WPS Prioritization

This section describes how to configure the WPS Prioritization feature.

Enabling WPS Prioritization

Use the following configuration to enable or disable WPS prioritization support and associate a session-priority-profile with the user-plane-service:

config 
   context context_name 
      user-plane-service up_service_name 
         [ no ] associate session-priority-profile { name | default } [ name_string ] 
         end

NOTES:

associate session-priority-profile { name | default } [ name_string ] : Enables WPS prioritization support.
- name : Specify the name of the session priority profile to be associated with the User Plane service.
- default : Specify the default precedence value associated with the session priority.
- name_string : Specify the name string associated with the session priority.
no associate session-priority-profile : Disables WPS prioritization support.
On a given UPF, you can configure a total number of 16 session-priority profiles. Only one session-priority profile can be associated with a user-plane service.
When a session does not receive any message-priority within the N4/Sx messages, it is classified as a 'Normal' session with a 'precedence' value set to 0.
If a priority is not specified in the session-priority-profile configuration, the session-type will be shown as 'Unclassified' and uses the default1 precedence value.
When there is no session-priority-profile association in the user-plane-service, UPF utilizes the existing (N-1) behavior with fixed priority values, including Emergency, IMS-VoLTE, and IMS-nonVoLTE.

Mapping the Session Priority Profile

Use the following configuration to configure the session priority value with a session type and precedence value.

config 
   session-priority-profile spp_name 
      priority priority_value type { wps | emergency | ims } precedence precedence_value 
      end

NOTES:

session-priority-profile : Specify the session priority profile name.
priority : Specify the priority value as an integer in the range of 0 to 15.
type { wps | emergency | ims } : Specify the session type.
precedence : Specify the precedence value as an integer in the range of 1 to 4.
The session-priority profile must not be configured with the priority value next to the one assigned for ims .

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