LTE Architecture

LTE Architecture and Its Components

The LTE (Long Term Evolution) network architecture is divided into three primary parts:

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1. User Equipment (UE)

• Function: Acts as the end-user device (e.g., smartphone, tablet).

• Role:

  • Connects to the network via the LTE-Uu interface.

  • Contains a SIM card for authentication and mobility tracking.

  • Sends/receives voice and data services.

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2. Evolved UMTS Terrestrial Radio Access Network (E-UTRAN)

• Responsible for wireless communication with UE.

• Main Component: eNodeB (eNB)

  • Replaces traditional base stations.

  • Functions:

    • Radio Resource Management (power control, scheduling).

    • Mobility Management (handover decisions).

    • Interfaces:

      • S1-MME: Signaling with the MME.

      • S1-U: User data transfer with the SGW.

      • X2: For inter-eNodeB handover and coordination.

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3. Evolved Packet Core (EPC)

The EPC handles all data and control functions in the core network.

i. MME (Mobility Management Entity)

• Manages signaling related to mobility and security.

• Key functions:

  • UE authentication via the HSS (using the S6a interface).

  • Mobility management and session tracking.

  • S10 interface: Used for handovers between MMEs.

ii. SGW (Serving Gateway)

• Forwards user data packets.

• Maintains data paths during UE movement across eNodeBs.

• Connects:

  • To eNB via S1-U

  • To PGW via S5

iii. PGW (Packet Data Network Gateway)

• Provides access to external IP networks like the internet.

• Allocates IP addresses and enforces QoS.

• Communicates with:

  • PCRF (via Gx) for policy enforcement.

  • External networks via SGi interface.

iv. HSS (Home Subscriber Server)

• Centralized database.

• Stores subscriber identity, service information, and security credentials.

• Communicates with MME using S6a.

v. PCRF (Policy and Charging Rules Function)

• Controls bandwidth, QoS, and charging rules.

• Ensures efficient use of resources and enforces policies via the Gx interface.

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Interfaces in the Diagram

Interface	Description
LTE-Uu	Between UE and eNB (radio link).
S1-MME	eNB to MME (signaling).
S1-U	eNB to SGW (user data).
X2	Between eNBs for handover.
S6a	MME to HSS (authentication).
S11	MME to SGW (session setup).
S5/S8	SGW to PGW (data path).
SGi	PGW to external PDNs (Internet).
Gx	PGW to PCRF (policy control).

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This structure provides the foundation for LTE’s high-speed data transmission, low latency, seamless mobility, and efficient use of network resources.