MME vs PGW vs SGW in LTE: Roles, Functions, and Differences

The LTE (Long Term Evolution) network architecture relies on key components to deliver high-speed mobile connectivity. The MME (Mobility Management Entity), PGW (Packet Gateway), and SGW (Serving Gateway) are critical elements of the LTE core network. Each plays a unique role in managing user mobility, routing data, and ensuring seamless communication.

In this page, we will explore the functions of MME, PGW, and SGW, highlight their differences, and understand their significance in the LTE ecosystem. The figure below depicts the LTE EPS architecture.

In the diagram, UE refers to User Equipment. It is the mobile phone device used to access the LTE network. It can also be a tablet or USB dongle that is LTE compliant to access 4G LTE internet. The eNodeB or eNB is the formal name, which refers to the LTE base station or cell tower. eNB provides radio access to the UEs using the Uu air interface. Multiple eNBs talk to each other using the X2 interface when a UE moves through the LTE network. The tunneling of data happens between the UE and the IP network using the S1-U interface. Tunneling of control information from the UE toward the network happens using the S1-MME interface.

LTE MME: Mobility Management Entity

Following are the functions of the MME (Mobility Management Entity):

• It keeps track of UEs that are registered on the LTE network.
• It takes care of user requests for network access.
• It helps in setting up and tearing down data sessions.
• It authenticates and authorizes users on the network.
• It selects the S-GW and P-GW to be used for a given session.
• A user can be registered or located with only one MME at a time.
• HSS acts as a database of subscriber information which can be queried by MMEs to determine permitted services. Moreover, it holds primary security key information for all SIM cards in a mobile network.

LTE SGW: Serving Gateway

Following are the functions of SGW (Serving Gateway):

• One or more SGWs will serve a given group of eNBs for user plane data.
• A single UE is served by one S-GW at any time.
• It receives instructions from MME to set up and tear down sessions for a particular UE.
• It acts as an interface module for signaling between PGW and MME.
• It takes care of user IP packets between P-GW and eNB.
• SGW functions as an IP router with GTP support and charging functionality.

LTE PGW: Packet Data Network (PDN) Gateway

Following are the functions of PGW (Packet Data Network Gateway):

• It provides access to external PDNs (Packet Data Networks).
• If a UE has multiple data sessions to multiple PDNs, the UE can be connected with multiple PGWs, but it will still be served by only one SGW.
• It is also known by the name PCEF, as it is responsible for dictating QoS and BW parameters for the subscriber’s session.
• PGW acts as an IP router with support for mobile-specific tunneling and signaling protocols.

Conclusion

MME, PGW, and SGW are integral to the LTE network, working together to provide seamless mobility management, efficient data routing, and high-speed connectivity. Understanding their roles and differences is crucial for grasping how LTE networks handle complex communication tasks.