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    Understanding PTSP-SAE Interactions

    This topic describes the sequences of Diameter messages exchanged between PTSP and the SAE as they interact to perform the following tasks for subscriber access:

    • Subscriber login

      When a packet-triggered subscriber logs in, PTSP sends a Diameter AA-Request message to request service provisioning from the SAE that includes the Session-Id attribute for the new subscriber. If the AA-Request fails, then the subscriber is not considered logged in and the subscriber session is not managed by the SAE. Only the static PTSP rules apply to the subscriber.

      The SAE returns a Diameter AA-Answer message with the Result-Code. The AA-Answer message can include the Juniper-Policy-Install AVP (AVP code 2020), which is used to specify a service to attach to the subscriber’s IP address.

      PTSP can send an AA-Request message to the SAE to confirm activation. The SAE returns a AA-Answer message in acknowledgment. If the AA-Request message fails or the SAE does not respond with an AA-Answer message, the subscriber session is managed by the SAE.

    • Service activation and deactivation

      The SAE policies provision subscriber services. After a packet-triggered subscriber is logged in, the SAE can send a PPR message to PTSP to activate or deactivate services. A given PPR can include the Juniper-Policy-Install AVP (AVP code 2020) to activate a service or the Juniper-Policy-Remove AVP (AVP code 2027) to deactivate a service.

      PTSP sends a PPA message to the SAE when it has completed the tasks requested in the PPR. The PPA indicates the success or failure of the actions requested in the PPR.

    • Resynchronization

      Either PTSP or the SAE initiates the resynchronization.

      The SAE initiates resynchronization at startup or when a backup SAE takes over session control due to resource limits or conditions on the primary SAE. The SAE clears its database of all entries in preparation for the synchronization.

      PTSP initiates resynchronization at startup, such as when AAA starts or restarts. PTSP uses the Juniper-Last-Origin-Host AVP (AVP code 2055) to keep track of the active SAE host in a multi-SAE environment. When an SAE in a multi-SAE environment becomes active, it must send an SRQ to PTSP as its first message. PTSP initiates a synchronization when it receives any other message type from an SAE that is different from the SAE indicated in the Juniper-Last-Origin-Host AVP.

      Both entities initiate a resynchronization by sending an SRQ message. The recipient responds with an SRR message.

    • Statistics collection and reporting per service rule

      Statistics information can be sent from the router to the SAE or from the SAE to the router. Both the Diameter Accounting-Request and Accounting-Answer messages include the Juniper-Acct-Record AVP (AVP code 2053) which identifies the policy for which accounting information is requested.

    • Subscriber logout

      PTSP can determine when there is a logout request for a packet-triggered subscriber in two ways:

      • The SAE terminates a subscriber session by sending an ASR message to PTSP.
      • PTSP monitors a subscriber session and starts the logout process after 30 minutes of inactivity.

      The subscriber logout triggers the final statistics aggregation for all policies and the removal of any policies installed by the SAE. PTSP sends an STR message that indicates the logout event to the SAE.

    Modified: 2012-03-28