UE

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RADIO PROTOCOLS BETWEEN UE & RNC COMMUNICATIONS


Let's look first at the radio protocols. Radio protocols are used to exchange signaling and traffic data between the UE and the UTRAN, mainly the RNC. 
Here is common representation of protocols called a protocol stack. In a protocol stack, the higher layer of protocols close to the service is represented at the top. Below this layer, other protocols are applied to the data in order to pass through the network as well and as quickly as possible.
Each protocol has specific function. We are going to describe each one briefly. Let's begin with the user plane in the layer of the access stratum of the UE. No protocols are usually used at this level in order to transmit a voice call. 
Regarding the transfer of data, two different protocols can be applied.
The PDCP allow to compress the header of IP packets. The broadcast/Multicast control protocol allows to broadcast message such as sms to all user of a cell for Ex. Then, the radio link control protocol controls the link. For Ex, the RLC protocol can apply a retransmission algorithm to insure the reception of a frame, or perform segmentation of big packets. 
The output of the RLC protocol down to the MAC layer is called a logical channel. The medium access control layer has a very important role regarding the resource management. Indeed, the MAX layer multiplexes logical channel between each other in order to optimize the size of the radio frame send over the air interface.
The result is called a transport channel. Once in the physical layer, those channels are multiplied by the codes, modulated, multiplied by the carrier frequency, ete to be sent over the air interface and received by the Node B.
At the Node B, the physical layer filters around the carrier frequency, demodulates and re-multiplies by the codes to rebuild the transport channel which are then, mapped on to protocol such as the Iub frame protocol, for the transport up to the RNC.
A new physical layer allows to map those transport frame onto the medium which can be an optical fiber for ex. 
Up to the RNC, transport channels are rebuilt again, then the MAC layer demultiplexes them to rebuild the logical channels.
Eventually, the RLC layer will concatenate or ask for a retransmission.
And finally, the voice can be decoded or in case of data transfer, the PDCP protocol will be used to decompress the IP header of IP packets. 
Now if we look at the transmission of a signaling message. First, the radio resource control protocol will be used.
Indeed, the RRC protocol provides information transfer upper to the upper to the Non-Access stratum and controls the configuration of the radio interface through lower layers.
Otherwise, nothing changes for the transmission of RRC message. RRC message go down the different layer RRC, MAC, Physical layer, over the air interface, mapped on ATM cells in the Node B and then up to the RrC protocol of the RNC to be treated.

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