Oracle Communications Diameter Signaling Router (DSR)
 

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In this Document

Symptoms

Cause

Solution

References

Created from <SR 3-12181059051>

Applies to:

Symptoms

P-DRA is sending Credit Control Answer (CCA) Message with AVP: Result-Code (268) - DIAMETER_UNABLE_TO_DELIVER (3002) and Error Message (281): AVP: PDRA-ERR-3002521: Policy SBR Error. Maximum number of sessions per binding is exceeded that fails the binding creation for given subscriber's key.

At the same time below event ID got generated on P-DRA:

Cause

The Event (22719) and Error (PDRA-Err-3002521) indicate that session binding for a subscriber (IMSI) could not be created because this subscriber already has the Maximum supported session binding created on P-DRA.

Hence P-DRA could not process Credit Control Request Message (CCR) message and sent a CCA with Result Code: Diameter-Unable-To-Deliver.

In the DSR GUI following message can be seen:

In pcap trace:

Here is a simple flow explaining how Binding and Session is created on P-DRA.

1. Policy & Charging Enforcement Function (PCEF) sends Credit Control Request (CCR) with CC-Request-Type - Initial Request (CCR-I) message to P-DRA.
2. P-DRA hashes the International Mobile Subscriber Identity (IMSI) in the CCR-I message and looks for any existing Binding or creates a new Binding in Binding Data Base (DB).
3. According to the Binding, P-DRA sends CCR-I message to Policy & Charging Rules Function (PCRF).
4. PCRF responds with Credit Control Answer Message with CC-Request Type - Initial Request (CCA-I).
5. P-DRA routes the CCA-I to the PCEF.
6. At this point P-DRA creates a Session record to maintain the local state indicating that this Diameter Session is bound to this PCRF.
   
7. PCEF sends a CCR with CC-Request-Type - Termination Request (CCR-T) message to the P-DRA to end the session.
8. P-DRA routes the CCR-T to PCRF selected according to the session.
9. PCRF responds with CCA-T.
10. P-DRA routes the CCA-T to PCEF.
11. At this point P-DRA removes the session from the Policy Session Binding Repository (pSBR) DB.
12. And because it is the only session remaining the Binding is also removed.

Now, For this specific case as observed from wireshark captures:

1. PCEF is not sending CCR-T to terminate the session.
2. So the session created with CCR-I message is maintained at the P-DRA.
3. In case other updates (CCR-U, CCR-T) are received then PDRA will use the same session to route the message to PCRF.
4. PCEF continues to send new CCR-I message with same IMSI to P-DRA without terminating the old session.
5. Since a new CCR-I message is received, so a new session is created on P-DRA with same Binding (As the PCRF will be same for the IMSI).
6. As per the current Design, P-DRA can create max 10 Binding capable session for a subscriber.
7. So after 10 sessions P-DRA is generating the Event 22719 indicating that maximum sessions are created for this binding and sending PDRA-ERR-3002521.

Binding Key Query Report can be executed from Network OAM (NOAM) GUI to verify how many binding capable session exist for a specific IMSI.

No new binding capable session for a subscriber can be created if maximum 10 binding capable session for subscriber already exist,

At this point if it is required to create a new binding capable session on P-DRA then existing sessions for the subscriber must be terminated.

Solution

There are 2 ways in which a session can be terminated:

1. (Preferred Method) Work with PCEF node and have them send the CCR-T message to terminate the existing session.
2. (Optional method) If the existing sessions are not used any more then they will be considered as Stale Session.
   A session is considered stale only if no RAR / RAA messages are received in longer than the configured time.
   The stale session will terminate automatically after Stale Session Timer expires on P-DRA.
   Stale Session Timeout (Hrs): The time value (in hours) after which a session is considered to be stale.
   A session is considered stale only if no RAR/RAA messages are received in longer than the configured time.
   This value is used for sessions associated with this Access Point Name. For sessions that are not associated with any configured Access Point Names, the Default Stale Session Timeout value configured on the NOAM Policy DRA > Configuration > Network-Wide Options page is used.
   If a session's age exceeds this value, that session is eligible to be audited out of the database.
   Range: 1-2400 (1 hour to 100 days), Default: 168 hours (7days)

There may be a 3rd method also (Optional method) in which pSBR database cleanup may be required on P-DRA which may be tedious and complex procedure.

Refer Document 2161294.1- Policy Diameter Routing Agent (P-DRA) - Does Not Clears Stale Sessions [Event -22719 - Maximum Number of Sessions Per Binding Exceeded]Delete Reference

 FD007968 and FD007479 are used as reference

References

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