Function of Network Element

As per the LTE Architecture from my previous post, the function of each network element is defined below:

  • Interfaces with UE. The interface is known as Uu interface.
  • Connects to MME with interface S1-MME or S1-C
  • Connects to S-GW with interface S1-U
  • Admission Control
  • Scheduling
  • Radio Resource Management
  • Enforcement of negotiated UL QoS
  • Cell Information Broadcast
  • Ciphering/deciphering of user and Control Plane data
  • Compression and decompression of DL/UL user plane packet headers
 It is the main control node in the LTE access network.
  • Connects to SGSN with interface S3 (provides Control plane function for Mobility between LTE and 2G/3G)
  • Connects to another MME with interface S10
  • Connects to HSS with interface S6a
  • Responsible for IDLE mode UE tracking and PAGING procedure including re-transmissions.
  • Authentication of user. This is achieved by interacting with HSS.
  • NAS signaling terminates at the MME
  • Generation and allocation of temporary ID's to UE
  • Enforces UE roaming restrictions and also checks the authorization of UE to camp on the service provider's PLMN 
  • Handles the security key management and is the termination point in the access network for ciphering and integrity protection for NAS signaling.
  • Involves in bearer Activation/Deactivation
  • Responsible for choosing S-GW for a UE during the Initial Attach and also during the Intra LTE Handover which also involves the core network node relocation

  • Connects to P-GW with interface S5/S8
  • Connects to SGSN with interface S3
  • Acts as Mobility anchor for the User plane during Inter eNB handover
  • Anchor for mobility between LTE and other 3GPP technologies
  • For Idle state UE's, the S-GW terminates the DL data path and triggers paging when DL data arrives for the UE.
  • Manages and stores UE context (parameters of the IP bearer service, network's internal routing information)
  • Performs replication of the user traffic in case of lawful interception

  • Acts as the entry and exit point of Traffic for the UE
  • Provides connectivity to the UE to external packet data networks
  • UE can have more than one PDN-GW for accessing multiple PDN's
  • Connects to PCRF with S7 interface
  • Connects to IMS with Gx interface
  • Performs policy enforcement
  • Packet filtering with each user
  • Charging support
  • Packet screening and lawful interception
  • Anchor for mobility between 3GPP and non 3GPP technologies(WiMax) and 3GPP2 (CDMA 1x and EVDO)
The next post will explain the RACH procedure.


  1. gr8 keep posting...

  2. * S-GW Connects to SGSN with interface S3 - its s4 interface