LTE_Stacks

Physical Layer (Layer 1)

Physical Layer carries all information from the MAC transport channels over the air interface. Takes care of the link adaptation (AMC), power control, cell search.

Medium Access Layer (MAC)

MAC layer is responsible for Mapping between logical channels and transport channels, Multiplexing of MAC SDUs from one or different logical channels onto transport blocks (TB) to be delivered to the physical layer on transport channels, de multiplexing of MAC SDUs from one or different logical channels from transport blocks (TB) delivered from the physical layer on transport channels, Scheduling information reporting,Priority handling between logical channels of one UE, Logical Channel prioritization.

Radio Link Control (RLC)

RLC operates in 3 modes of operation: Transparent Mode (TM), Unacknowledged Mode (UM), and Acknowledged Mode (AM).

RLC Layer is responsible for transfer of upper layer PDUs, Concatenation, segmentation and reassembly of RLC SDUs (Only for UM and AM data transfer).

RLC is also responsible for re-segmentation of RLC data PDUs.reordering of RLC data PDUs, duplicate detection,RLC re-establishment, and protocol error detection. 

A RLC TM/UM entity is with can be transmitter or receiver. That means when acting as a transmitter the transparent mode RLC entity receives SDUs from upper layer and transmit those to it’s peer RLC TM/UM entity via lower layer.

The difference between TM and UM entity is

When RLC TM entity acts as a transmitter

• It should not segment or concatenate the RLC SDUs
• No header will be included in TMD PDUs

Radio Resource Control (RRC)

 The main services and functions of the RRC sublayer include broadcast of System Information,Paging, establishment, maintenance and release of an RRC connection between the UE and E-UTRAN.

Packet Data Convergence Control (PDCP)

PDCP Layer is responsible for Header compression and decompression of IP data, Transfer of data (user plane or control plane), Maintenance of PDCP Sequence Numbers (SNs),Ciphering and deciphering of user plane data and control plane data, Integrity protection and integrity verification of control plane data.

Logical Channels : Define whattype of information is transmitted over the air, e.g. traffic channels, control channels, system broadcast, etc. Data and signalling messages are carried on logical channels between the RLC and MAC protocols. 

Logical channels can be divided into control channels and traffic channels. Control Channel can be either common channel or dedicated channel. A common channel means common to all users in a cell (Point to multipoint) while dedicated channels means channels can be used only by one user (Point to Point).

Channel Name	Acronym	Control channel	Traffic channel
Broadcast Control Channel	BCCH	X
Paging Control Channel	PCCH	X
Common Control Channel	CCCH	X
Dedicated Control Channel	DCCH	X
Multicast Control Channel	MCCH	X
Dedicated Traffic Channel	DTCH		X
Multicast Traffic Channel	MTCH		X

Transport Channels : Define howis something transmitted over the air, e.g. what are encoding, interleaving options used to transmit data. Data and signalling messages are carried on transport channels between the MAC and the physical layer. 

Channel Name	Acronym	Downlink	Uplink
Broadcast Channel	BCH	X
Downlink Shared Channel	DL-SCH	X
Paging Channel	PCH	X
Multicast Channel	MCH	X
Uplink Shared Channel	UL-SCH		X
Random Access Channel	RACH		X

Physical Channels : Define whereis something transmitted over the air, e.g. first N symbols in the DL frame. Data and signalling messages are carried on physical channels between the different levels of the physical layer.

Data and signalling messages are carried on physical channels between the different levels of the physical layer and accordingly they are divided into two parts:

• Physical Data Channels
• Physical Control Channels