LTE (4G) Network Architecture

LTE network nodes

LTE refers to 'Long Term Evolution', and the architecture of the LTE network is as following,

LTE Network Architecture
LTE Network Architecture

eNodeB

The eNodeB is the 4G site that the UE connects to. It provides the radio interface to the UE.

MME

MME refers to 'Mobility Management Entity'. The MME is responsible for authenticating the UE. In addition, it tracks the location of the UE. Also, it selects the suitable SGW and PGW that should serve this UE.

SGW

SGW refers to 'Serving Gateway'. In order to eliminate any effect on user data while the UE moves between different eNodeBs, the SGW works as an anchor point for user data of the UE, while the UE is moving between different eNodeBs. In addition, the SGW forwards user data between the eNodeB and the PGW.

PGW

PGW refers to 'PDN Gateway'. The PGW is the node that connects between the LTE network, and the PDN.

HSS

HSS refers to 'Home Subscriber Server'. The HSS is the Database that stores the subscription information of the users in the network, like which PDN they should be able to access, and the QoS they should have, .. etc.

PDN

PDN refers to Public Data Network , and it is the network that the UE would like to connect to.

LTE Control Plane vs. User Plane

In order to well understand the architecture of LTE network, we need to know what is the difference between the control plane, and the user plane.

The nodes use the control plane, in order to exchange signaling messages between each other. The signaling messages controls the data session of the UE. using the signaling messages, the nodes can initiate, modify, or terminate the data session of the UE.

While the nodes are using the user plane, in order to exchange the user data sent and received between the UE and the PDN.

The following graph shows the path of the control plane, and the user plane,

Control Plane vs. User Plane
Control Plane vs. User Plane

Th path of the control plane if from the UE to the eNodeB, then to the MME, then to the HSS and the SGW, then from the SGW to the PGW.

While the path of the user plane is from the UE to the eNodeB, then from the eNodeB directly to the SGW, then from the SGW to the PGW, and from the PGW to the PDN.

LTE interfaces

The link between every two nodes is having a unique interfaces name. This interface name represents the protocols that the nodes are using in the communication between each other.

Below graph shows the interface names between different nodes, in addition to the protocols that the nodes are using to communicate between each other,

LTE Network Interfaces and Protocols
LTE Network Interfaces and Protocols