5G NR - Radio Link Control (RLC) Protocol - RAN Layer 2

Explore the transparent mode entity in the 5G NR RLC protocol, which forwards SD without segmentation or headers, and can act as transmitting or receiving without waiting for peer responses.

Explore the semantics of the RLC PDU, detailing the bitstream as octets read left to right, and the roles of MSB and LSB, plus the rule that non-multiples of eight bits are discarded.

Describe how the rlc pdu comprises one or more octets read from msb to lsb, with a header and a complete rlc sd payload.

Describe um 12-bit sn pdu format, where sn spans two octets and is decoded by concatenating bits from first and second octet, increasing header length from one to two octets.

Explore the tm pdu in rlc, a simple transparent mode format with only a data field; the entity passes data from input to output without processing, across multiple octets.

examine the am pdu without so field, compare 12-bit and 18-bit sequence numbers, and outline the new dbi and pipit rules affecting mprda field placement and ndu carry.

In 5G NR RLC, the ACK_SN field indicates the sequence number of the next not received PDU, and the receiver reports 0-N-1 as received, awaiting N onwards.

Explain NACK SN field for reporting lost packets in the RLC layer, using 12 or 18 bit sequence numbers, and how EXT bits enable combining losses into a status PDA.

The SO_Start and SO_End fields report a range of lost RLC PDUs from the receiver to the transmitter, enabling selective retransmission of only the missing segments.

Use the NACK_SN range field to specify the number of lost RLC starting from and including the value, allowing the receiver to report lost RLC range back to the transmitter.

Explore how a fixed window of sequence numbers regulates data flow between transmitter and receiver, advancing as status is reported and packets are acknowledged, with zero-based sequencing in RLC.

Explain how RLC protocol constants set window sizes via 2^SN_bits divided by two, yielding 2048 for 12-bit and 32 for 6-bit as the window slides with acks.

Explore the Paul Retransmit timer in the RLC protocol, used by the transmitting side as a backoff before polling and by the receiver to time a single status PDU retransmission.