Telecom Glossary
Essential telecom terms explained in plain English
A
AMF
Access and Mobility Management Function
5G Core function responsible for registration, connection, reachability, and mobility management of UE devices.
APN
Access Point Name
Gateway identifier between mobile network and external packet data networks (internet, IMS, MMS).
D
Diameter
RFC 6733
AAA protocol replacing RADIUS. Used for authentication (S6a), policy control (Gx), and online charging (Gy) in LTE networks. Runs over TCP/SCTP port 3868.
E
EPC
Evolved Packet Core
LTE core network architecture comprising MME, SGW, PGW, HSS, and PCRF. Handles packet switching for 4G networks.
G
GTP
GPRS Tunneling Protocol
Tunneling protocol for carrying user data (GTP-U) and control signaling (GTP-C) in mobile networks. Runs over UDP ports 2123 (C) and 2152 (U).
H
HSS
Home Subscriber Server
Central database storing subscriber profiles, authentication data, and service information. Connects to MME via Diameter S6a.
M
MME
Mobility Management Entity
Key EPC control node handling NAS signaling, authentication, and handover decisions for LTE devices.
N
NAS
Non-Access Stratum
Signaling protocol between UE and core network, carried over S1-AP (4G) or NG-AP (5G). Handles attach, auth, and session management.
NRF
Network Repository Function
5G Core service discovery function. Maintains profiles of available NFs and enables NF registration and discovery.
O
OCS
Online Charging System
Real-time credit control system. Grants quotas to PGW/UGW for data usage. Connects via Diameter Gy interface.
P
PFCP
Packet Forwarding Control Protocol
5G protocol between SMF and UPF. Manages forwarding rules, QoS enforcement, and usage reporting. Runs over UDP 8805.
PCRF
Policy and Charging Rules Function
Makes policy and charging decisions. Connects to PGW via Diameter Gx. In 5G, replaced by PCF.
S
SBA
Service-Based Architecture
5G Core architecture where NFs communicate via HTTP/2 REST APIs over a service bus, replacing point-to-point interfaces.
SGW
Serving Gateway
EPC node that routes and forwards user data packets. Handles inter-eNodeB handover and mobility anchoring.
SMF
Session Management Function
5G Core function for PDU session establishment, modification, and release. Interacts with UPF via PFCP.
U
UDM
Unified Data Management
5G Core function storing subscriber data and service profiles. Replaces HSS in 5G architecture.
UPF
User Plane Function
5G Core function that forwards user traffic, applies QoS rules, and performs deep packet inspection.