Timer-initiated fallback

1. A method performed by a User Equipment (UE), the method comprising:

identifying a policy indicating a first dedicated bearer associated with a first guaranteed Quality of Service (QoS) level is network-initiated, the first dedicated bearer being used to establish voice services through a core network and an Internet Protocol (IP) Media Subsystem (IMS) network;

initiating a call by transmitting a first Session Initiation Protocol (SIP) message to the core network, the first SIP message requesting the voice services from the core network and the IMS network;

receiving a second SIP message from the core network;

in response to the second SIP message being received as a dedicated bearer establishment request message including a request to establish the dedicated bearer, triggering a timer associated with a wait time to start;

determining, as an expired timer, the timer at expiration of the wait time, without a confirmation of establishment of the dedicated bearer associated with delivery of the voice services through the core network and the IMS network having been received; and

in response to the expired timer being associated with a start time at which the dedicated bearer establishment request message has been received, and an expiration time at which establishment of the first dedicated bearer has not been confirmed, initiating a fallback option for the call,

wherein initiating the fallback option comprises transmitting, to the core network, a request for a second dedicated bearer associated with a second guaranteed QoS level, the second guaranteed QoS level being lower than the first guaranteed QoS level; receiving a confirmation of the second dedicated bearer from the core network; and receiving the voice services from the core network via the second dedicated bearer.

2. The method of claim 1 , wherein the core network is associated with a 5G network technology, and

wherein initiating the fallback option comprises:

transmitting, to the core network the request for the second dedicated bearer being associated with delivery of the voice services via a second core network,

the second core network being associated with a 4th Generation (4G) network technology or a Circuit-Switched (CS) network technology;

receiving the confirmation of the second dedicated bearer from the second core network; and

receiving the voice services from the second core network via the second dedicated bearer.

3. The method of claim 1 , wherein the request to establish the dedicated bearer indicates a QoS level associated with the voice services.

4. The method of claim 1 , wherein the wait time is associated with a time interval by which the UE waits before causing a connection associated with the core network to be reset.

5. A method performed by a User Equipment (UE) implementing a network-initiated policy, the method comprising:

receiving, from a core network, a message including a request to establish Quality of Service (QoS)-sensitive services;

in response to the message, initiating a timer associated with a wait time;

determining, as an expired timer, the timer at expiration of the wait time, without having received a confirmation that a first 5th Generation (5G) QoS Indicator (5QI) data flow associated with a first guaranteed QoS level has been established in the core network; and

in response to the expired timer being associated with a start time at which establishment of the first 5G 5QI data flow has been requested, and an end time at which establishment of the first 5QI data flow has not been confirmed, initiating a fallback process,

wherein initiating the fallback process comprises transmitting, to the core network, a request for a second 5QI data flow associated with a second guaranteed QoS level, the second guaranteed QoS level being lower than the first guaranteed QoS level; receiving, from the core network, a confirmation that the second 5QI data flow has been established through the core network; and receiving, from the core network, the QoS-sensitive services via the second 5QI data flow.

6. The method of claim 5 , further comprising:

transmitting, to the core network, a Session Initiation Protocol (SIP) INVITE message requesting the QoS-sensitive services,

wherein the message including the request to establish the QoS-sensitive services is a SIP 100 Trying response.

7. The method of claim 5 , wherein the message indicates a QoS level of the first 5QI data flow that is assigned by the core network.

8. The method of claim 7 , wherein the QoS level comprises at least one of a priority of the QoS-sensitive services, a maximum packet delay budget of the QoS-sensitive services, or a maximum packet error loss rate of the QoS-sensitive services.

9. The method of claim 5 , wherein the core network is a first core network associated with a first network technology, and

wherein initiating the fallback process comprises:

transmitting, to a second core network associated with a second network technology, a request to establish second QoS-sensitive services;

receiving, from the second core network, a confirmation that a dedicated bearer has been established through the second core network; and

receiving, from the second core network, the QoS-sensitive services via the dedicated bearer.

10. The method of claim 9 , wherein the first network technology is a 5G network technology and the second network technology is a 4th Generation (4G) network technology or a Circuit-Switched (CS) network technology.

11. The method of claim 5 , wherein:

the message is a SIP 100 Trying response; and

the timer is triggered to start at the start time at which the SIP 100 Trying response is received.

12. The method of claim 5 , wherein the wait time is associated with a time interval by which the UE waits before causing a connection associated with the core network to be reset.

13. A device implementing a network-initiated policy, the device comprising:

at least one processor; and

memory storing instructions that, when executed by the at least one processor, cause the at least one processor to perform operations comprising:

receiving, from a core network, a message including a request to establish Quality of Service (QoS)-sensitive services;

in response to the message, initiating a timer associated with a wait time;

determining, as an expired timer, the timer at expiration of the wait time, without having received a confirmation that a first 5th Generation (5G) QoS Indicator (5QI) data flow associated with a first guaranteed QoS level the QoS-sensitive services has been established in the core network; and

in response to the expired timer associated with a start time at which establishment of the first 5G 5QI data flow has been requested, and an end time at which establishment of the first 5QI data flow has not been confirmed, initiating a fallback process,

wherein initiating the fallback process comprises transmitting, to the core network, a request for a second 5QI data flow associated with a second guaranteed QoS level, the second guaranteed QoS level being lower than the first guaranteed QoS level; receiving, from the core network, a confirmation that the second 5QI data flow has been established through the core network; and receiving, from the core network, the QoS-sensitive services via the second 5QI data flow.

14. The device of claim 13 , wherein the operations further comprise:

transmitting, to the core network, a Session Initiation Protocol (SIP) INVITE message requesting the QoS-sensitive services, and

wherein the message including the request to establish with the QoS-sensitive services is a SIP 100 Trying response.

15. The device of claim 13 , wherein the message indicates a QoS level of the first 5QI data flow that is assigned by the core network.

16. The device of claim 15 , wherein the QoS level comprises at least one of a priority of the QoS-sensitive services, a maximum packet delay budget of the QoS-sensitive services, or a maximum packet error loss rate of the QoS-sensitive services.

17. The device of claim 13 , wherein the timer expires 5 seconds to 30 seconds after initiating the timer.

18. The device of claim 13 , wherein the QoS-sensitive services are first QoS-sensitive services, and the core network is a first core network associated with a first network technology, and

wherein initiating the fallback process comprises:

transmitting, to a second core network associated with a second network technology, a request to establish second QoS-sensitive services;

receiving, from the second core network, a confirmation that a dedicated bearer has been established through the second core network; and

receiving, from the second core network, the second QoS-sensitive services via the dedicated bearer.

19. The device of claim 13 , wherein the second guaranteed QoS level comprises at least one of a lower priority of the QoS-sensitive services than a priority associated with the first guaranteed QoS level, a larger maximum packet delay budget of the QoS-sensitive services than a maximum packet delay budget associated with the first guaranteed QoS level, or a larger maximum packet error loss rate of the QoS-sensitive services than a maximum packet error loss rate associated with the first guaranteed QoS level.

20. The device of claim 13 , wherein the wait time is associated with a time interval by which the device waits before causing a connection associated with the core network to be reset.