In LTE, depending upon User plane or Control Plane, the protocol stack has been divided into 2 different types.
1. LTE User Plane Protocol Stack
2. LTE Control Plane Protocol Stack
In this chapter we shall see the LTE User Plane Protocol Stack.
Below is the detailed image for LTE User Plane Protocol Stack:
From the above image we can see that:
The communication between UE and eNB is done by using LTE-Uu interface.
The layers include:
PDCP: Packet Data Convergence Protocol
RLC: Radio Link Control Protocol
MAC: Medium Access Control Protocol
Again the communication between eNB, S-GW, P-GW is done by using S1-U/S5/X2 interface respectively.
The layer include:
GTP-U
A high level User Plane stack is as below:
Below image is high level image for both user and control plane protocol stack along with Layers and brief of each layer functionality:
According to the image above:
Layer 3 has NAS and RRC Protocol
Layer 2 has PDCP, RLC, MAC
Layer 1 has Physical layer
Now we shall see the functions of each layer in brief:
1. PDCP : Packet Data Convergence Protocol
2. RLC : Radio Link Control
3. MAC : Medium Access Control
4. GTP-U : General Packet Radio System (GPRS) Tunneling Protocol User Plane
1. PDCP : Packet Data Convergence Protocol
Below are few of the functions of PDCP User plane layer:
1. Header Compression and decompression: RHOC
2. Transfer of user data.
3. Access Stratum (AS) Ciphering and deciphering.
4. Retransmission of PDCP SDUs at handover for RLC AM;
5. Packet re-ordering
6. It will use LTE-Uu interface.
Protocol specification
3GPP TS 36.323 – Evolved Universal Terrestrial Radio Access (E-UTRA); Packet Data Convergence Protocol (PDCP) specification
2. RLC : Radio Link Control
1. Transfer of upper layer PDUs.
2. Error correction using ARQ
3. Concatenation, segmentation and reassembly of RLC SDUs (only for UM and AM data transfer);
4. RLC re-establishment.
5. Protocol error detection and recovery;
6. It will use LTE-Uu interface.
Protocol specification
3GPP TS 36.322 – Evolved Universal Terrestrial Radio Access (E-UTRA); Radio Link Control (RLC) protocol specification
3. MAC : Medium Access Control
1. Mapping between logical channels and transport channels;
2. Multiplexing/demultiplexing of MAC SDUs
3. Error correction through HARQ;
4. Transport format selection;
5. logical channel priority
6. It will use LTE-Uu interface.
Protocol specification
3GPP TS 36.321 – Evolved Universal Terrestrial Radio Access (E-UTRA); Medium Access Control (MAC) protocol specification
4. GTP-U : General Packet Radio System (GPRS) Tunneling Protocol User Plane
1. GTP-U protocol is used over S1-U/S5/X2 interface interface of Evolved Packet System (EPS).
2. GTP-U tunnels are used to carry encapsulated T-DPU and signaling messages
3. It follows the protocol specification : 3GPP TS 29.281
Mapping of SAE Bearers, Radio Bearers, Logical and Transport channel mapping
