Connects the P-GW to external IP networks (Internet/IMS). 3. Detailed 4G LTE Attach Call Flow

The interfaces between EPC elements use specific protocol stacks to manage signaling and traffic safely:

Together with the (Evolved Universal Terrestrial Radio Access Network, or eNodeB), the EPC forms the Evolved Packet System (EPS) . Key EPC Features

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The attach procedure registers the UE with the EPC, establishes a default EPS bearer, and provides IP connectivity.

: The MME sends an Initial Context Setup Request to the eNodeB to establish the data tunnels ( S1-U ).

4G LTE Evolved Packet Core (EPC): Concepts and Call Flows The 4G Long Term Evolution (LTE) network represents a major shift in mobile technology, moving away from hybrid circuit-switched and packet-switched architectures toward a purely IP-based, packet-switched system. The core of this revolution is the .

MME requests the SGW and PGW to create a default bearer.

To protect user privacy, the network avoids sending the permanent identity (IMSI) over the airwaves whenever possible. Instead, the MME generates a temporary ID called the . The UE uses the GUTI for subsequent connections to avoid being tracked by third parties.

Anchors the data path during inter-eNodeB handovers.

The UE sends a TAU Request without a location change to refresh its registration state before a timer expires.

📡 Deep Dive: 4G LTE Evolved Packet Core (EPC) – Concepts & Call Flows

The UE sends an attach request to the eNodeB, establishing a signaling link.

: The eNodeB configures the radio link with the UE and sends an Attach Complete acknowledgment back to the MME. 2. Service Request Procedure (UE-Triggered)

Illustration of a city skyline with towers, phones, and data streams labeled as "Netflix packet," "WhatsApp message," "Instagram video."

Protocols driving these interfaces include (bearer control), GTP-U (user data encapsulation), SCTP (reliable control plane transport), and S1-AP (eNodeB-MME signaling). The NAS protocol operates between UE and MME, managing attach requests, authentication, and TAU signaling.

A central database containing subscriber-related information, used for authentication and access authorization. Policy and Charging Rules Function (PCRF):