AF (Application Function)

In telecommunications, the AF is a 5G entity that interacts with the core (typically through the NEF for untrusted AFs, or directly for trusted AFs) to influence traffic routing, request specific QoS, or expose services. AFs include IMS components, MEC applications, and third-party services consuming GSMA Open Gateway APIs.

Categories: Core NetworkProtocols and StandardsInternet and Routing

AF in context

The mobile core carries subscriber sessions, mobility and policy. In 4G it is the EPC (MME, HSS, S/PGW); in 5G it is the Service-Based Architecture with AMF, SMF, UPF, AUSF, UDM and the NRF.

Telecom security is written into standards from 3GPP, GSMA, ETSI, IETF and ITU-T. Understanding which body owns which specification, and how they interlock, is essential for both design and audit work.

To place AF in the wider telecom-security picture, review URSP, 3G, 3GPP, AES, A5/1 and A5/3 — each entry cross-references back to this page so you can walk the topic in either direction.

Related terms

More from the TelcoSec Glossary

Browse the full TelcoSec Glossary, the Ultimate Guide to Mobile Network Security, or the P1 Arsenal of telecom-security tools.