Policy control function fallback

1. A system, comprising:

one or more processors;

a memory storing components executable by the one or more processors to perform operations comprising:

receiving, from a session management function (SMF), a first SIP request that requests a policy associated with a voice session;

transmitting, to a first policy control function (PCF), the first SIP request;

receiving, from the first PCF, a first SIP response that comprises a first policy identifier corresponding to the policy of the voice session;

forwarding, to the SMF, the first SIP response;

transmitting, to a second PCF, the first SIP request;

receiving, from the second PCF, a second SIP response that comprises a second identifier corresponding to the policy of the voice session;

receiving, from the SMF, a second SIP request that comprises the first policy identifier;

determining that a communication link with the first PCF is interrupted;

generating a modified second SIP request by replacing the first policy identifier with the second policy identifier in the second SIP request; and

transmitting, to the second PCF, the modified second SIP request.

2. The system of claim 1 , wherein the one or more processors and the memory are comprised in at least one of a service communication proxy (SCP), a building support function (BSF), or an interworking function (IWF).

3. The system of claim 1 , wherein the second SIP request comprises at least one of an Rx message originating from an Internet Protocol (IP) Multimedia Subsystem (IMS) network, a policy control update message, or a policy control delete message.

4. A system, comprising:

one or more processors;

a memory storing components executable by the one or more processors to perform operations comprising:

receiving, from a session management function (SMF), a request for a policy corresponding to a session, the request comprising a first policy identifier corresponding to a first policy control function (PCF);

determining that the first PCF is unavailable;

generating a modified request by replacing the first policy identifier with a second policy identifier in the request, the second policy identifier corresponding to a second PCF;

transmitting, to the second PCF, the modified request;

receiving, from the second PCF, a response based on the modified request, the response comprising the second policy identifier;

generating a modified response by replacing the second policy identifier with the first policy identifier in the response; and

transmitting, to the SMF, the modified response.

5. The system of claim 4 , wherein the one or more processors and the memory are comprised in at least one of a service communication proxy (SCP), a building support function (BSF), or an interworking function (IWF).

6. The system of claim 4 , wherein the modified request comprises at least one of an Rx message originating from an Internet Protocol (IP) Multimedia Subsystem (IMS) network, a policy control update message, or a policy control delete message.

7. The system of claim 4 , wherein the memory comprises a datastore that comprises:

an entry comprising the first policy identifier, the second policy identifier, and an identifier of the session,

wherein generating the modified request comprises:

identifying the entry based on the first policy identifier; and

identifying the second policy identifier based on the entry.

8. The system of claim 7 , wherein the entry further comprises a subscription permanent identifier (SUPI) and a data network name (DNN) of the session.

9. The system of claim 4 , wherein the session comprises a voice over new radio (VONR) session.

10. The system of claim 4 , the request being a first request, the response being a first response, the operations further comprising:

receiving, from the SMF, a second request that requests the policy associated with the session;

transmitting, to the first PCF, the second request;

receiving, from the first PCF, a second response that comprises the first policy identifier;

forwarding, to the SMF, the second response;

transmitting, to the second PCF, the second request; and

receiving, from the second PCF, a third response that comprises the second policy identifier.

11. The system of claim 4 , the request being a first request, the response being a first response, the operations further comprising:

receiving, from the SMF, a second request that requests a change to the policy associated with the session, the second request comprising the first policy identifier;

transmitting, to the first PCF, the second request;

receiving, from the first PCF, a second response that comprises the first policy identifier;

transmitting, to the SMF, the second response;

generating a revised second request by replacing the first policy identifier with the second policy identifier in the second request;

transmitting, to the second PCF, the revised second request; and

receiving, from the second PCF, a third response that comprises the second policy identifier.

12. A method, comprising:

receiving, from a session management function (SMF), a request for a policy corresponding to a session, the request comprising a first policy identifier corresponding to a first policy control function (PCF);

determining that the first PCF is unavailable;

generating a modified request by replacing the first policy identifier with a second policy identifier in the request, the second policy identifier corresponding to a second PCF, and the generating includes:

identifying, in a datastore, an entry comprising the first policy identifier, the second policy identifier, and an identifier of the session; and

identifying the second policy identifier based on the entry; and

transmitting, to the second PCF, the modified request.

13. The method of claim 12 , wherein the method is performed by at least one of a service communication proxy (SCP), a building support function (BSF), or an interworking function (IWF).

14. The method of claim 12 , wherein the entry further comprises a subscription permanent identifier (SUPI) and a data network name (DNN) of the session.

15. The method of claim 12 , wherein the session comprises a voice over new radio (VONR) session.

16. The method of claim 12 , further comprising:

receiving, from the second PCF, a response based on the modified request, the response comprising the second policy identifier;

generating a modified response by replacing the second policy identifier with the first policy identifier in the response; and

transmitting, to the SMF, the modified response.

17. The method of claim 12 , the request being a first request the method further comprising:

receiving, from the SMF, a second request that requests the policy associated with the session;

transmitting, to the first PCF, the second request;

receiving, from the first PCF, a second response that comprises the first policy identifier;

forwarding, to the SMF, the second response;

transmitting, to the second PCF, the second request; and

receiving, from the second PCF, a third response that comprises the second policy identifier.

18. The method of claim 12 , the request being a first request, the method further comprising:

receiving, from the SMF, a second request that requests a change to the policy associated with the session, the second request comprising the first policy identifier;

transmitting, to the first PCF, the second request;

receiving, from the first PCF, a second response that comprises the first policy identifier;

transmitting, to the SMF, the second response;

generating a revised second request by replacing the first policy identifier with the second policy identifier in the second request;

transmitting, to the second PCF, the revised second request; and

receiving, from the second PCF, a third response that comprises the second policy identifier.