S-GW (Serving gateway)

The Serving Gateway (S-GW) is a key component in the Evolved Packet Core (EPC) architecture of Long Term Evolution (LTE) and 5G networks. It serves as an anchor point for user traffic and plays a crucial role in the data forwarding and routing functions within the network.

The primary functions of the S-GW include:

1. Mobility anchoring: The S-GW acts as the anchor point for user equipment (UE) mobility. It tracks the UE's location and manages the mobility-related procedures such as handovers between base stations (eNodeBs in LTE) and mobility across different network nodes.
2. Packet forwarding: The S-GW is responsible for forwarding user data packets between the UE and the Packet Data Network Gateway (P-GW) in the EPC architecture. It serves as a central point of connectivity for the UE, ensuring efficient and reliable data transfer.
3. IP address allocation: The S-GW assigns and manages IP addresses for the UEs connecting to the network. It performs dynamic IP address allocation, allowing UEs to have unique network identities for proper routing and communication.
4. Quality of Service (QoS) management: The S-GW enforces QoS policies and manages the traffic flow between the UE and the network. It ensures that different types of traffic, such as voice, video, or data, receive the appropriate level of priority and bandwidth allocation, optimizing the overall network performance.
5. Charging and accounting: The S-GW collects information related to the UE's data usage, session duration, and other relevant statistics for billing and accounting purposes. This data is crucial for service providers to accurately charge customers based on their network usage.
6. Lawful interception: The S-GW supports lawful interception requirements, allowing authorized entities to monitor and intercept network traffic as mandated by legal regulations. It provides the necessary interfaces for lawful interception systems to capture and analyze data.

From a network architecture perspective, the S-GW is typically located at the edge of the LTE or 5G network, serving as an interface between the radio access network (RAN) and the core network. It establishes and maintains bearer tunnels for data transmission between the UE and the core network elements. These tunnels ensure secure and efficient transport of user data while facilitating seamless mobility across different network nodes.

In summary, the Serving Gateway (S-GW) is a critical component in LTE and 5G networks, providing mobility management, data forwarding, IP address allocation, QoS management, charging, accounting, and lawful interception functionalities. It acts as a central point for user traffic and plays a crucial role in ensuring efficient and reliable connectivity for mobile subscribers.