1. Policy and Charging Application
  2. Policy DRA Overview
  3. Suspect Binding Removal

Suspect Binding Removal

The Policy DRA function provides the capability to bind and correlate between policy service subscribers and policy servers (PCRFs) specified by the subscriber identifiers such as IMSIs, MSISDNs or IP addresses. All service requests on behalf of a subscriber from all relevant Diameter applications (for example, Diameter interfaces such as Gx or Rx ) will be routed to the bound PCRF so that policy decisions can be made with the knowledge of all the policies being applicable for that particular subscriber. Routing failures occur if a bound PCRF fails to operate or loses connection to the PCA after the binding is established.

P-DRA contains a set of configurable rules that invoke a series of suspect binding cleanup steps if the suspect binding removal rules are matched by Diameter Answer messages with error response.

These rules monitor the error responses received from PCRF or from the DSR routing layer on behalf of the PCRF, comparing the error responses (such as types and the number of error responses) with the configured rules. Bindings are labelled as suspect if some rules are matched, cleaning up the suspect binding records in the SBR and invoking sending RAR procedure to the policy clients.

The rules also include the configuration of the timing when an action needs to be taken to start a suspect binding cleanup if it is detected, be it immediately or after a provisioned threshold number of detections is reached.

P-DRA initiates the suspect binding removal procedure if a matched suspect binding removal rule for a given subscriber is configured as Yes to Remove Suspect Binding Immediately in the PCA configuration, or the Suspect Binding Removal Event Threshold value is exceeded by the number of matched rules. The suspect binding removal procedure involves several components/actions:
  • coordination among the P-DRA MP, Binding and Session SBRs via back-end communications (stack event messages) between them
  • clean up the binding SBR databases for the suspect binding records
  • sending Diameter RAR messages to the policy clients (PCEF) to trigger the policy clients to initiate the removal of the sessions related to those suspect bindings

Specifically, the initiation of the suspect binding removal procedure can be triggered by either P-DRA MP, if the matched suspect binding removal rule is configured as Yes to Remove Suspect Binding Immediately in the PCA configuration, or by the binding SBR, if the Suspect Binding Removal Event Threshold value is exceeded by the number of Suspect Binding Removal Events. In either case, the session SBR that receives the request to clean up the sessions related to the suspect bindings invokes the Session Integrity Service (SIS) functionality.

The SIS is used by session SBRs to verify session integrity and to trigger policy clients to remove the problematic sessions. This functionality allows external servers such as a binding SBR or DA-MP to invoke the SIS service on the session SBR . SIS on the session SBRs can be used to provide two types of session integrity handling:
  1. requesting DA-MP to send Query type RAR messages to policy clients for verifying session integrity of some session records stored on the Session SBR. Based on the RAA responses, the sessions in question will either be re-authorized or torn down in a later time by the policy clients
  2. requesting DA-MP to send Release type RAR messages to policy clients for tearing down the sessions that the Session SBR has records. A Release RAR will request the policy clients to tear down the session in question by sending CCR-T messages to the bound PCRF.

After receiving a session release RAR, PCEF may initiate a CCR-T request to remove the binding capable (Gx or Gxx) session and the corresponding IP-CAN session that in turn triggers the involved UE to re-initiate the IP-CAN session. This may result in a new binding capable session that are bound to a working PCRF this time by P-DRA. If the subscriber has multiple binding capable sessions (Gx or Gxx) associated with the same PCRF, P-DRA initiates session release RAR requests for each of these sessions.

If a subscriber has multiple Bound Sessions associated with a failed PCRF, it is possible that one Bound Session is torn down and is being re-established before cleaning up other remaining binding capable sessions. The suspect binding removal procedure marks the Bound Sessions to this failed PCRF in the binding SBR as pending delete such that no newly created bindings could use the failed PCRF anymore until it returns functional. The execution of the suspect binding removal procedure leads to removing the Bound Sessions associated with the suspect bindings for a given subscriber and a PCRF. Therefore, the Bound Sessions of the same subscriber associated with different PCRFs, if they exist, are not impacted.

For information on how to configure Suspect Binding Removal Rules, refer to Suspect Binding Removal Rules.