Application Function (AF) is responsible for interacting with external applications and services to provide 5G network capabilities. It plays a key role in traffic management and QoS assignments through interaction with the policy elements. It is powerful but undervalued. It exposes the Application Layer for interaction with 5G NFs and network resources [1].

Key Functions

• Accessing the NEF for retrieving resources.
• Interacting with the Policy Control Function (PCF), enabling policy control.
• Traffic routing for applications
• Provides application services to subscribers.

Here's a detailed explanation of the AF's responsibilities:

1. Application Interface: The AF provides an interface for external applications and services to interact with the 5G network.
2. API Management: The AF manages APIs for external applications and services, enabling them to access 5G network capabilities.
3. Service Discovery: The AF enables external applications and services to discover available 5G network services an capabilities.
4. QoS Management: It manages Quality of Service (QoS) policies for external applications and services, ensuring that they receive the required QoS.
5. Security Management: It manages security policies for external applications and services. Ensuring that they access the 5G network securely.

AF Deployment Scenarios:

1. Cloud-Based AF
2. Edge-Based AF
3. On-Premises AF

Example Scenario for Better Understanding

A video streaming service Netflix wants to provide high-quality video streaming to its users over a 5G Network. To do this, Netflix needs to interact with the 5G network to request the necessary resources and Quality of Service (QoS) policies.

In this scenario, the AF acts as an interface between Netflix and the 5G network. The AF receives requests from Netflix to establish a connection and request resources, and then forwards these requests to the relevant network functions, such as the Session Management Function (SMF) and the Policy Control Function (PCF).

AF Procedures:

1. Application Registration: Netflix registers with the AF, providing its application ID and other relevant information.
2. Resource Request: Netflix sends a request to the AF to establish a connection and request resources, such as bandwidth and latency.
3. QoS Request: Netflix also sends a request to the AF to apply specific QoS policies to its traffic, such as prioritizing its video streaming traffic over other types of traffic.
4. AF-SMF Interaction: The AF forwards the resource request to the SMF, which establishes a session for Netflix and allocates the necessary resources.
5. AF-PCF Interaction: The AF also forwards the QoS request to the PCF, which applies the requested QoS policies to Netflix's traffic.
6. Resource Allocation: The SMF and PCF work together to allocate the necessary resources and apply the requested QoS policies.
7. Connection Establishment: The AF notifies Netflix that the connection has been established and the requested resources have been allocated.

Bibliography:

1. https://emblasoft.com/blog/exploring-the-3gpp-af-application-function
2. https://www.ericsson.com/en/core-network/5g-core
3. https://medium.com/@googler_ram/open-source-5g-core-application-function-af-and-application-server-as-97b04ba7c81d#:~:text=Application%20function%20is%20one%20of,framework%20for%20policy%20control%2C%20MS