ISDN user part
Part of SS7 protocol for telephone call setup.
In UMTS, part of this is being used for CS call.

IAM: Initial Address Message
ACM: Address Complete Message
ANM: Answer Message
REL: Release message
RLC: Release complete Message

1. MAC (Medium access control)
2. RLC (Radio link control)
3. PDCP (Packet data convergence protocol)
4. BMC (Broadcast and multicast control)

SN = Sequence Number
P = Poll bit

The physical layer combines the transport blocks together, interleaves them and then transmits them via two radio frames.
Thus, RLC PDUs in the receiver cannot be recovered until all of the data from that 20 ms TTI has been received.

SN=12, Poll bit is set.
At receiving side, it took 20ms for processing. Then send STATUS PDUs.
After 20ms, the missing SN=6, 8 will be retransmitted.

1. AM data (AMD) PDUs: user data
2. AM control PDUs

AM control PDUs are further classified into:

1. STATUS PDU
2. Piggybacked STATUS PDU
3. RESET and RESET ACK PDU

1. transparent

2. unacknowledged

3. acknowledged mode

Each mode provides a different set of services to the higher layers.

Some of them are

1. segmentation and reassembly

2. concatenation

3. reliable transfering data

4. flow control

5. in-sequence delivery

6. Error correction by ARQ(automatic repeat request)

(there are some few exceptions such as speech and signaling where multiple RLC entities per service.)

The configuration or the RLC depend on the specific QoS for the service.

1. MAC protocol

2. RLC protocol

3. PDCP (packet data convergence protocol)

4. BMC (broadcast and multicast control) protocol

MAC layer transfer service is done in unacknowledged mode. That is, no guaranteed delivery service.

RLC layer has mechanisms to detect errors and retransmit.

Note that RB vs. SRB

At the UTRAN side, RLC and above protocols are located at RNC.

MAC protocols: some functionalities are at Node B, others are at RNC.