What is the interface between SGW and PGW in 4G network?
Today, I’m going to explain the interface between the Serving Gateway (SGW) and the Packet Data Network Gateway (PGW) in a 4G LTE network. If you’ve read our earlier discussions on LTE core network architecture, you already know that both SGW and PGW are vital components of the Evolved Packet Core (EPC). Now, let’s dive deeper into how these two nodes communicate with each other and what role their interface plays.
The interface that connects the SGW and PGW is known as the S5/S8 interface. This interface is used to transfer user data packets and to manage bearer paths for user sessions. Although both S5 and S8 serve the same function, the naming depends on the deployment model:
- S5 Interface: Used when the SGW and PGW are within the same Public Land Mobile Network (PLMN), i.e., the same operator’s network.
- S8 Interface: Used when the SGW and PGW are in different PLMNs, typically when roaming is involved.
You can think of the S5/S8 interface as the communication bridge that allows your data traffic—from activities like web browsing or video streaming—to flow smoothly between the core elements of the LTE system and the external internet.
Let me walk you through how this works with a simple flow. When your UE (User Equipment) initiates a data session, the data packets first reach the eNodeB, which then forwards them to the SGW. The SGW is responsible for routing and forwarding these packets. From there, they travel across the S5/S8 interface to reach the PGW, which connects you to external data networks such as the internet or private corporate networks.
The interface is based on the GTP (GPRS Tunneling Protocol) and supports both GTP-C (control plane) and GTP-U (user plane). Here’s a quick breakdown of what they do:
- GTP-C: Used for control signaling—like establishing and modifying bearers (the logical paths for user data).
- GTP-U: Handles the actual user data traffic that flows between your device and the internet.
This S5/S8 interface also plays a big part in mobility management. If you’re moving between LTE cells or from LTE to another technology like 3G during an active session, the interface allows the session to be maintained without interruption. This ensures you experience seamless connectivity even while on the move.
In earlier articles, we’ve explored how LTE supports high-speed, low-latency connections. The S5/S8 interface is a big part of achieving that, because it’s optimized for efficient data delivery, QoS enforcement, and mobility anchoring. Without it, the entire data session management framework in LTE wouldn’t function smoothly.
So, in short, the S5/S8 interface is what links SGW to PGW in LTE networks. Whether you’re browsing on your home network or roaming abroad, this interface ensures your data sessions are routed correctly, managed securely, and delivered without interruption.