What are the key network functions in 5GC?

AMF (Access and Mobility Management Function): handles registration, connection, mobility, and security. Replaces LTE MME's mobility functions. SMF (Session Management Function): manages PDU sessions, IP allocation, QoS policy enforcement, and UPF selection. Replaces LTE MME's session functions + PGW-C. UPF (User Plane Function): forwards user data packets, applies QoS, performs traffic measurement. Replaces LTE SGW-U + PGW-U. Can be deployed at the edge for low latency. AUSF (Authentication Server Function): handles UE authentication. UDM (Unified Data Management): stores subscriber data. NRF (Network Repository Function): service discovery. NSSF (Network Slice Selection Function): selects the appropriate network slice.

How does 5GC differ from LTE EPC?

Architecture: EPC uses point-to-point interfaces (S1, S5, S11) between monolithic nodes (MME, SGW, PGW). 5GC uses service-based architecture where all control plane functions communicate via HTTP/2 APIs. This enables cloud-native deployment (containers, Kubernetes). CUPS: EPC's control and user planes are tightly coupled in SGW/PGW. 5GC separates them (SMF + UPF), allowing UPF deployment at the network edge for low latency while centralizing control. Statelessness: 5GC network functions are designed stateless, storing state in external databases (UDSF). This enables horizontal scaling and fault tolerance. Registration: 5GC supports concurrent access to multiple network slices per UE, which EPC cannot do.

mmWave & 5G

5G Core (5GC)

Q: What is network slicing?

Network slicing creates multiple virtual end-to-end networks on shared physical infrastructure, each optimized for a different service type. An eMBB slice might prioritize throughput with best-effort latency. A URLLC slice guarantees <1 ms latency with dedicated UPF at the edge. An mMTC slice handles millions of IoT devices with relaxed throughput but optimized signaling. Each slice has its own SMF, UPF, and QoS configuration. The UE requests a specific slice via S-NSSAI (Single Network Slice Selection Assistance Information) during registration. The AMF and NSSF route the UE to the correct slice's network functions.

The cloud-native, service-based core network architecture defined in 3GPP Release 15 that replaces the monolithic LTE EPC. 5GC disaggregates the core into independent network functions (AMF, SMF, UPF, AUSF, UDM, etc.) communicating via HTTP/2 APIs. This enables network slicing (multiple virtual networks on shared infrastructure), control/user plane separation (CUPS) for edge deployment, and cloud-native scaling via containers and Kubernetes.

Category: mmWave & 5G

Architecture: Service-Based (SBA)

3GPP Release: Release 15+

Understanding the 5G Core

The LTE EPC was designed as interconnected monolithic nodes (MME, SGW, PGW) with fixed interfaces. Scaling required adding entire nodes, and edge deployment was impractical because control and user planes were coupled. 5GC was designed from the ground up as a cloud-native, microservices-based architecture where each function runs independently and communicates via standard REST APIs.

The most transformative feature is network slicing: the ability to create isolated virtual networks, each with its own SMF, UPF, and QoS policies, running on shared physical infrastructure. An operator can simultaneously serve an eMBB smartphone slice (high throughput), a URLLC factory automation slice (1 ms latency), and an mMTC IoT slice (millions of devices) from the same 5GC deployment.

5GC Network Functions

Control Plane:
AMF: Registration, mobility, security (replaces MME)
SMF: Session management, QoS, UPF selection
AUSF: Authentication
UDM: Subscriber data (replaces HSS)
NRF: Service discovery
NSSF: Network slice selection
PCF: Policy control (replaces PCRF)

User Plane:
UPF: Packet forwarding, QoS, usage reporting
Can be deployed at edge, regional, or central

Interfaces:
All CP ↔ CP: HTTP/2 APIs (SBI)
AMF ↔ gNB: N2 (NGAP over SCTP)
UPF ↔ gNB: N3 (GTP-U over UDP)

5GC vs. LTE EPC Comparison

Feature	LTE EPC	5G Core
Architecture	Point-to-point interfaces	Service-based (HTTP/2)
Deployment	Monolithic VMs	Cloud-native containers
CUPS	Coupled (SGW/PGW)	Separated (SMF + UPF)
Network slicing	Not supported	Native (S-NSSAI)
Edge computing	Limited	UPF at edge (MEC)
State management	Stateful nodes	Stateless + external DB

Common Questions

Frequently Asked Questions

Key network functions?

AMF (mobility, security), SMF (sessions, QoS), UPF (data forwarding), AUSF (auth), UDM (subscriber data), NRF (discovery), NSSF (slice selection), PCF (policy). All CP functions use HTTP/2 APIs.

What is network slicing?

Virtual end-to-end networks on shared infrastructure: eMBB (throughput), URLLC (<1 ms), mMTC (millions of IoT). Each slice has own SMF, UPF, QoS. UE requests via S-NSSAI during registration.

5GC vs. LTE EPC?

SBA vs. point-to-point, containers vs. VMs, native CUPS vs. coupled, network slicing vs. none, stateless vs. stateful. 5GC enables edge UPF, horizontal scaling, and multi-slice per UE.

Related Terms

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