The Mobility Based Policy Control for Overlay Deployments function provides direct communication between the SAPC and the SGSN-MME by using the Smp interface. The SAPC works in Smp only mode and only serves the Smp traffic and other PCRFs in the network serve Gx, Rx, and Sy traffic.

This function enables the SGSN-MME to get the following policy decisions from the SAPC:

• The preferred list of GWs, and

• The SPID to be selected for a specific user based on subscription type, device type, APN, or location, for better network resource efficiency.

The function enables new innovative use cases, for example:

• Dynamically allocation of the best radio resources on a per-user, per-terminal basis.

• Preferred access for subscribers.

• Dynamic selection of the GW based on, for example, the subscriber profile.

The following figure shows an overview of Network Elements providing Mobility Based Policy Control for Overlay Deployments function:

An Smp session is based on the PDN connection and established between the SGSN-MME and the SAPC.

The life cycle of an Smp session includes its establishment and termination. The SAPC does not support currently session modification nor reauthorization.

The SGSN-MME establishes an Smp session when:

• UE Attach or PDN connectivity.

• The UE moves to a new SGSN-MME through Inter SGSN-MME Tracking Area Update (TAU) or handover.

The SGSN-MME terminates an Smp session when:

• The associated PDN is deleted owing to UE Detach or PDN disconnection.

• The UE moves to a new MME owing to TAU, handover, or it moves to a new Radio Access Type (RAT).

• An abnormal situation occurs on the Smp interface.

Smp session Access Control is used to allow or reject Smp session establishment. Even if Smp session is rejected, SGSN-MME can continue with the IP-CAN session establishment towards the PGW.

Smp session Access Control policies are evaluated according to the following precedence allocation and applying permit overrides algorithm among them (that is, if any policy evaluates to true, the Smp session is authorized):

• Subject policy locator.

• Subject group policy locator. All the active subscriber groups are considered.

  Therefore, it is recommended to configure Dynamic Group Selection policies to evaluate only the desired subscriber group policies.

• Global policy locator.

In case there are conflicts among the rules within a policy, the result for the policy depends on the Rule combining algorithm configured. See Solving Policies Conflicts section in Subscription and Policy Management.

In case there are no Smp Session Access Control policies configured, the Smp session is authorized.

With the PDN-GW selection function, the SAPC can select the IP address (IPv4 and/or IPv6) and/or FQDN of a list of PDN-GWs for a UE when the UE attaches to the network.

The SAPC allows to select the list of PDN-GWs based on the following information:

• Subscriber profile, for example, subscriber with content filtering or Deep Packet Inspection (DPI) can be statically associated with a certain PDN-GW,

• User location, for example, users located in a concert hall, stadium, or festival,

• International Mobile Subscriber Identity (IMSI),

• International Mobile Station Equipment Identity (IMEI),

• Device type,

• APN,

• Other data received through the Smp interface

The SAPC selects the list of PDN-GWs applying the mechanism for controls using both Policies and Qualification Data explained in Selection of Data to apply to the Subscriber section in Subscription and Policy Management.

The PDN-GW selection is performed only in the Smp session establishment procedure in the UE Attach or PDN connectivity scenario. During the Smp session lifetime, the selected list of PDN-GWs cannot be changed.

The following figure shows how to perform the PDN-GW selection:

• 1–2: When a UE attaches to the network, the SGSN-MME establishes the connection to the SAPC depending on the APN.

• 3–4: The SAPC makes a policy decision to select a list of PDN-GWs, for example the PDN-GWs connected with Content Filtering function for the underage subscriber, and informs the SGSN-MME of the list.

• 5: The SGSN-MME selects one PDN-GW from the list provided by the SAPC for the subscriber.

The SPID selection function enables the SAPC to control the camp priorities in Idle mode and inter-RAT/inter-frequency handover in Active mode for subscribers. This index is mapped by the eNodeB (E-UTRAN), RNC (UTRAN), or BSC (GERAN) to locally defined configuration. For more information, see 1 and 2. This increases the flexibility and service awareness for radio optimizations.

The SAPC allows to select the SPID based on the following information:

• Subscriber profile, for example, subscriber with content filtering or Deep Packet Inspection (DPI) can be statically associated with a certain PDN-GW,

• User location, for example, users located in a concert hall, stadium, or festival,

• International Mobile Subscriber Identity (IMSI),

• International Mobile Station Equipment Identity (IMEI),

• Device type,

• APN,

• Other data received through the Smp interface

The SAPC selects the SPID applying the mechanism for controls using both Policies and Qualification Data explained in Selection of Data to apply to the Subscriber section in Subscription and Policy Management.

The following figure shows how to perform the SPID selection based on user information provided during the Smp session establishment:

• 1–2: During the UE attach or PDN connectivity, or during the inter-SGSN-MME TAU or handover procedures, the SGSN-MME receives the location information and reports the ULI to the SAPC, only during the Smp session establishment.

• 3–4: The SAPC makes a policy decision to select an SPID, and informs the SGSN-MME of the selected SPID.

• 5: The SGSN-MME forwards the selected SPID to the eNodeB, and finally to the UE.

The subscriber and subscriber group data can be stored in the SAPC internal or external database.

The SAPC uses the International Mobile Subscriber Identity (IMSI) to obtain the subscriber ID. This subscriber ID is used to access to the subscriber profile.

The subscriber can be associated with subscriber groups, having the possibility to specify the date and time, and the subscriber group priority.

Also, the SAPC supports dynamic selection of the subscribed groups by using Dynamic Group Selection policies.

The autoprovisioning and subscriber unknown functions are also applicable to Smp session procedures.

When any subscriber data is updated, the SAPC does not perform Smp reauthorization to check whether any data need to be added or removed, so updated subscriber data will be applied at next Smp session establishment.

When a subscriber is removed, the SAPC does not indicate the SGSN-MME to terminate the associated Smp sessions.

For more information, refer to Subscription and Policy Management.