Functionality of NR-PDCP, NR-RLC & NR-MAC in 5G-NR

The functionalities of NR-PDCP, NR-RLC & NR-MAC in 5G-NR are similar to LTE but there are few updates.

Functions of NR-PDCP:

1. Transfer of control plane & User plane data

2. Maintenance of PDCP Sequence number

3. Header compression & Decompression using ROHC protocol.

4. Ciphering & Deciphering of packets. [Applicable for both Control plane & User Plane data]

5. Integrity protection & integrity verification of packets. [Applicable for Control plane & optional for User Plane data]

6. Discarding of SDUs based on timer

7. For Split bearers & DAPS bearer 

    a. Routing of the packets

    b. Duplication of the packets & Duplicate discarding of the packets.

    c. Re-ordering & in-order delivery of the packets

    d. Out-of-delivery of the packets

NR PDCP - v16.6.0

Functions of NR-RLC:

RLC works in three different modes : AM, UM & TM. We will discuss the functionalities based on different modes used by RLC.

Common functions in All modes:

1. Transfer of Upper layer PDUs

2. RLC re-establishment

Transparent Mode (TM):

(No extra functions in TM mode apart from common functions)

NR RLC TM

Unacknowledged Mode (UM) :

1. Segmentation and Reassembly of RLC SDUs

2. RLC SDU discard 

NR RLC UM

Acknowledged Mode (AM) :

1. Error correction through ARQ 

2. Segmentation and Reassembly of RLC SDUs 

3. Duplicate detection

4. RLC SDU discard

5. Protocol error detection 

NR RLC AM

Functions of NR-MAC:

1. Mapping between logical channels and transport channels
2. Multiplexing and Demultiplexing of MAC SDUs from one or different logical channels onto transport blocks (TB) to be delivered to the physical layer on transport channels and vice-versa.

3. Logical channel prioritization

4. Scheduling information reporting

5. Error correction through HARQ (Hybrid ARQ)

References : 3GPP release 16 version 16.6.0 for NR-PDCP, v6.1.0 for NR-RLC & v16.8.0 for NR-MAC from 38 series.