There is a single MAC instance within the UE.
In the network, usually a single MAC instance for each UE exists.
However, multiple MAC instances for a single UE may happen (e.g., one in a CRNC and one in an SRNC)
Layer 2 protocols consists fo 4 protocol entities:
1. MAC (Medium access control)
2. RLC (Radio link control)
3. PDCP (Packet data convergence protocol)
4. BMC (Broadcast and multicast control)
The MAC is responsible for dynamic resource allocation under the control of RRC layer.
Using relative priorities betweeservices, MAC does
1. mapping between logical and the transport channels
2. transport format selection
3. priority handling of data flow
4. UE identification management to facilitate transactions such as random access and the use of downlink common channels
5. data ciphering when RLC [...]
Layer 2 comprises of 4 protocol entities.
1. MAC protocol
2. RLC protocol
3. PDCP (packet data convergence protocol)
4. BMC (broadcast and multicast control) protocol
No!
MAC layer transfer service is done in unacknowledged mode. That is, no guaranteed delivery service.
RLC layer has mechanisms to detect errors and retransmit.
Radio interface protocol structure:
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.
