Destination selection for an offline charging system to avoid reversion

1. A system comprising:

a distributor unit configured to connect to a plurality of Charging Data Functions (CDFs) of an Offline Charging System (OFCS) through an interface, and to receive information from the CDFs for registering queues associated with the CDFs;

the distributor unit comprising a processor configured to receive an initial accounting request from a Charging Trigger Function (CTF) for a session through the interface, to generate a prioritized list of the queues for the session based on a distribution algorithm, to select a destination queue from the prioritized list for the session, and to transmit the initial accounting request to the destination queue through the interface;

the processor is configured to receive a subsequent accounting request from the CTF for the session through the interface, to extract a first identifier from a parameter of the subsequent accounting request indicating the destination queue previously selected for the session, and to determine a status of the destination queue;

when the status of the destination queue indicates that the destination queue is not accepting new sessions or ongoing sessions, the processor is configured to:

identify the prioritized list for the session;

identify a position of the destination queue in the prioritized list;

search the prioritized list for a first alternate queue having a lower priority than the destination queue, and having a status indicating that the first alternate queue is accepting new sessions;

select the first alternate queue as an alternate destination queue for the session; and

transmit the subsequent accounting request to the alternate destination queue through the interface.

2. The system of claim 1 wherein:

the subsequent accounting request comprises a Diameter Accounting Request (ACR); and

the processor is configured to extract the first identifier from a Destination-Host Attribute Value Pair (AVP) of the ACR indicating the destination queue.

3. The system of claim 1 wherein:

the processor is configured to receive an accounting answer for the subsequent accounting request from a CDF associated with the alternate destination queue through the interface, to add a second identifier for the alternate destination queue in a parameter of the accounting answer, and to transmit the accounting answer toward the CTF through the interface.

4. The system of claim 3 wherein:

the accounting answer comprises a Diameter Accounting Answer (ACA); and

the processor is configured to add the second identifier for the alternate destination queue to an Origin-Host Attribute Value Pair (AVP) of the ACA.

5. The system of claim 1 wherein:

when the processor fails to find the first alternate queue in the prioritized list having a lower priority than the destination queue, and having a status indicating that the first alternate queue is accepting new sessions, the processor is configured to search from a top of the prioritized list for a second alternate queue having a status indicating that the second alternate queue is accepting new sessions.

6. The system of claim 5 wherein:

when the processor fails to find the second alternate queue in the prioritized list having a status indicating that the second alternate queue is accepting new sessions, the processor is configured to determine that the OFCS is in an overload state.

7. The system of claim 1 wherein:

the distribution algorithm comprises a consistent hashing algorithm that generates the prioritized list of the queues based on a session identifier for the session, and names for the queues.

8. The system of claim 1 wherein:

the processor is configured to monitor the status of each of the queues; and

the status of each of the queues indicates one of the following: accepting new sessions and ongoing sessions, accepting ongoing sessions only, or not accepting new sessions or ongoing sessions.

9. The system of claim 1 wherein:

in response to the initial accounting request, the processor is configured to search the prioritized list for a candidate queue having a status indicating that the candidate queue is accepting new sessions, and to select the candidate queue as the destination queue for the session.

10. A method of distributing accounting requests for a session from a distributor unit to a plurality of Charging Data Functions (CDFs) of an Offline Charging System (OFCS), the method comprising:

receiving information in the distributor unit from the CDFs for registering queues associated with the CDFs;

receiving an initial accounting request in the distributor unit from a Charging Trigger Function (CTF) for a session;

generating, at the distributor unit, a prioritized list of the queues for the session based on a distribution algorithm;

selecting, at the distributor unit, a destination queue from the prioritized list for the session;

transmitting the initial accounting request from the distributor unit to the destination queue;

receiving a subsequent accounting request in the distributor unit from the CTF for the session;

extracting, at the distributor unit, a first identifier from a parameter of the subsequent accounting request indicating the destination queue previously selected for the session;

determining, at the distributor unit, a status of the destination queue;

when the status of the destination queue indicates that the destination queue is not accepting new sessions or ongoing sessions, the method includes:

identifying the prioritized list for the session;

identifying a position of the destination queue in the prioritized list;

searching the prioritized list for a first alternate queue having a lower priority than the destination queue, and having a status indicating that the first alternate queue is accepting new sessions;

selecting the first alternate queue as an alternate destination queue for the session; and

transmitting the subsequent accounting request from the distributor unit to the alternate destination queue.

11. The method of claim 10 wherein:

the subsequent accounting request comprises a Diameter Accounting Request (ACR); and

extracting the first identifier from the parameter of the subsequent accounting request comprises extracting the first identifier from a Destination-Host Attribute Value Pair (AVP) of the ACR indicating the destination queue.

12. The method of claim 10 further comprising:

receiving an accounting answer for the subsequent accounting request in the distributor unit from a CDF associated with the alternate destination queue;

adding, at the distributor unit, a second identifier for the alternate destination queue in a parameter of the accounting answer; and

transmitting the accounting answer from the distributor unit toward the CTF.

13. The method of claim 12 wherein:

the accounting answer comprises a Diameter Accounting Answer (ACA); and

adding the second identifier for the alternate destination queue in the parameter of the accounting answer comprises adding the second identifier for the alternate destination queue to an Origin-Host Attribute Value Pair (AVP) of the ACA.

14. The method of claim 10 wherein:

when the search fails to find the first alternate queue in the prioritized list having a lower priority than the destination queue, and having a status indicating that the first alternate queue is accepting new sessions, the method comprises:

searching from a top of the prioritized list for a second alternate queue having a status indicating that the second alternate queue is accepting new sessions.

15. The method of claim 14 wherein:

when the search fails to find the second alternate queue in the prioritized list having a status indicating that the second alternate queue is accepting new sessions, the method comprises:

determining, at the distributor unit, that the OFCS is in an overload state.

16. The method of claim 10 further comprising:

monitoring the status of each of the queues;

wherein the status of each of the queues indicates one of the following: accepting new sessions and ongoing sessions, accepting ongoing sessions only, or not accepting new sessions or ongoing sessions.

17. The method of claim 10 further comprising:

in response to the initial accounting request, the method comprises:

searching the prioritized list for a candidate queue having a status indicating that the candidate queue is accepting new sessions; and

selecting the candidate queue as the destination queue for the session.

18. A non-transitory computer readable medium embodying programmed instructions executed by a processor of a distributor unit that connects to a plurality of Charging Data Functions (CDFs) of an Offline Charging System (OFCS), wherein the instructions direct the processor to:

receive information from the CDFs for registering queues associated with the CDFs through an interface;

receive an initial accounting request from a Charging Trigger Function (CTF) for a session through the interface;

generate a prioritized list of the queues for the session based on a distribution algorithm;

select a destination queue from the prioritized list for the session;

transmit the initial accounting request to the destination queue through the interface;

receive a subsequent accounting request from the CTF for the session through the interface;

extract a first identifier from a parameter of the subsequent accounting request indicating the destination queue previously selected for the session;

determine a status of the destination queue;

when the status of the destination queue indicates that the destination queue is not accepting new sessions or ongoing sessions:

identify the prioritized list for the session;

identify a position of the destination queue in the prioritized list;

search the prioritized list for a first alternate queue having a lower priority than the destination queue, and having a status indicating that the first alternate queue is accepting new sessions;

select the first alternate queue as an alternate destination queue for the session; and

transmit the subsequent accounting request to the alternate destination queue through the interface.

19. The computer readable medium of claim 18 wherein:

when the search fails to find the first alternate queue in the prioritized list having a lower priority than the destination queue, and having a status indicating that the first alternate queue is accepting new sessions, the instructions direct the processor to:

search from a top of the prioritized list for a second alternate queue having a status indicating that the second alternate queue is accepting new sessions.

20. The computer readable medium of claim 19 wherein:

when the search fails to find the second alternate queue in the prioritized list having a status indicating that the second alternate queue is accepting new sessions, the instructions direct the processor to:

determine that the OFCS is in an overload state.