What is TM,AM and UM Modes in LTE?

Question

Is any restriction on number of bearer of AM/UM rlc mode per UE?

Answer 1

All three are used in LTE for data transmission mode. These are known as Transparent Mode, Acknowledgement Mode and Unacknowledgement mode data transmission. Every data transmission mode is used for different purpose. Radio Link Control i.e. RLC layer is responsible to implement these different types of data transmission mode.
- For TM mode of data, there is no addition or removal of header to/from input data.
- For AM mode, header addition or removal, segmentation and re-assembling, re-transmission of buffer, all things are applicable.
- For UM mode, header addition or removal, segmentation and re-assembling are applicable.

Answer 2

RLC TM and AM mode are used for signalling purpose. for example SIB, paging and CCCH signalling messages are broadcast in TM mode and dedicated signalling(DCCH) messaged are transmitted in AM mode.

RLC AM and UM mode are used in data transmission.

Answer 3

A TM RLC entity can be configured to deliver/receive RLC PDUs through the following logical channels: BCCH, DL/UL CCCH and PCCH.
A TM RLC entity delivers/receives the following RLC data PDU: TMD PDU

An UM RLC entity can be configured to deliver/receive RLC PDUs through the following logical channels: DL/UL DTCH, MCCH or MTCH.
An UM RLC entity delivers/receives the following RLC data PDU: UMD PDU.
NOTE: HARQ reordering is not applicable for MCCH or MTCH reception

An AM RLC entity can be configured to deliver/receive RLC PDUs through the following logical channels: DL/UL DCCH or DL/UL DTCH.
An AM RLC entity delivers/receives the following RLC data PDUs:
- AMD PDU;
- AMD PDU segment.

An AM RLC entity delivers/receives the following RLC control PDU:
- STATUS PDU