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The radio interface (Uu) is layered into three protocol layers:

the physical layer (L1)

the data link layer (L2)

the network layer (L3).

The layer 1 supports all functions required for the transmission of bit streams on thephysical medium. It is also in charge of measurements function consisting in indicating to

higher layers, for example, Frame Error Rate (FER), Signal to Interference Ratio

(SIR), interference power, transmit power, It is basically composed of a layer 1

management entity, a transport channel entity, and a physical channel entity.is used to transmit information under the form of electrical signals corresponding to bits,

between the network and the mobile user. This information can be voice, circuit orpacket data, and network signaling.

The UMTS layer 1 offers data transport services to higher layers. The access to these

services is through the use of transport channels via the MAC sublayer.

L3

contr

ol

contr

ol

contr

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LogicalChannels

TransportChannels

C-planesignalling

U-planeinformation

PHY

L2/MAC

L1

RLC

DC

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GC

L2/RLC

MAC

RLC

RLCRL

CRLC

RLCRL

CRLC

Duplicationavoidance

UuS

boundary

BMC

L2/BMC

control

PDCP

PDCP

L2/PDCP

DC

Nt

GC

RadioBearers

RRC

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These services are provided by radio links which are established by signaling

procedures. These links are managed by the layer 1 management entity. One radio link

is made of one or several transport channels, and one physical channel.

The UMTS layer 1 is divided into two sublayers:

the transport and the physical sublayers.

All the processing (channel coding, interleaving, etc.) is done by the transport

sublayer in order to provide different services and their associated QoS.

The physical sublayer is responsible for the modulation, which corresponds to the

association of bits (coming from the transport sublayer) to electrical signals that can

be carried over the air interface. The spreading operation is also done by the physical

sublayer. These sublayers are well described in chapters 6 and 7.These two parts of layer 1 are controlled by the layer 1 management (L1M) entity. It is

made of several units located in each equipment, which exchange information through

the use of control channels.

The layer 2 protocol is responsible for providing functions such as mapping,ciphering, retransmission and segmentation. It is made of four sublayers:

MAC (Medium Access Control),

RLC (Radio Link Control),

PDCP (Packet Data Convergence Protocol)

and BMC (Broadcast/Multicast Control).

The RLC s main function is the transfer of data from either the user or the control planeover the Radio interface. Two different transfer modes are used: transparent and non-

transparent. In non-transparent mode, 2 sub-modes are used: acknowledged or

unacknowledged.RLC provides services to upper layers:

data transfer (transparent, acknowledged and unacknowledged modes),

QoS setting: the retransmission protocol (for AM only) shall be configurable by

layer 3 to provide different QoS,

notification of unrecoverable errors: RLC notifies the upper layers of errors

that cannot be resolved by RLC.The RLC functions are:

mappingbetween higher layer PDUs and logical channels,

ciphering: prevents unauthorized acquisition of data; performed in RLC layer for

non-transparent RLC mode,

segmentation/reassembly: this function performs segmentation/reassembly of

variable-length higher layer PDUs into/from smaller RLC Payload Units. The

RLC size is adjustable to the actual set of transport formats (decided when service

is established). Concatenation and padding may also be used,

error correction: done by retransmission (acknowledged data transfer mode

only),

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flow control: allows the RLC receiver to control the rate at which the peer RLC

transmitting entity may send information.

MAC services include:

Data transfer: service providing unacknowledged transfer of MAC SDUs

between peer MAC entities.Reallocation of radio resources and MAC parameters: reconfiguration of

MAC functions such as change of identity of UE. Requested by the RRC layer.

Reporting of measurements: local measurements such as traffic volume andquality indication are reported to the RRC layer.

The functions accomplished by the MAC sublayer are listed above. Heres a

quick explanation for some of them:

Priority handling between the data flows of one UE:since UMTS ismultimedia, a user may activate several services at the same time, having possibly

different profiles (priority, QoS parameters...). Priority handlingconsists in

setting the right transport format for a high bit rate service and for a low bit rate

service.Priority handling between UEs:use for efficient spectrum resourcesutilization

for bursty transfers on common and shared channels.

Ciphering: to prevent unauthorized acquisition of data. Performed in the MAC

layer for transparent RLC mode.

Access Service Class (ACS) selection for RACH transmission: the RACHresources are divided between different ACSs in order to provide different

priorities on a random access procedure.

PDCP

UMTS supports several network layer protocols providing protocol transparency for the

users of the service.

Using these protocols (and new ones) shall be possible without any changes to UTRANprotocols. In order to perform this requirement, the PDCP layer has been introduced.

Then, functions related to transfer of packets from higher layers shall be carried out

in a transparent way by the UTRAN network entities.

PDCP shall also be responsible for implementing different kinds of optimization

methods. The currently known methods are standardized IETF (Internet Engineering

Task Force) header compression algorithms.

Algorithm types and their parameters are negotiated by RRC and indicated to PDCP.Header compression and decompression are specific for each network layer protocol

type.

In order to know which compression method is used, an identifier (PID: Packet Identifier)is inserted. Compression algorithms exist for TCP/IP, RTP/UDP/IP,

Another function of PDCP is to provide numbering of PDUs. This is done if lossless

SRNS relocation is required.To accomplish this function, each PDCP-SDUs (UL and DL) is buffered and numbered.

Numbering is done after header compression. SDUs are kept until information of

successful transmission of PDCP-PDU has been received from RLC. PDCP sequence

number ranges from 0 to 65,535.

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BMC (broadcast/multicast control protocol)

The main function of BMC protocol are:

Storage of cell broadcast message. the BMC in RNC stores the cell broadcast

message received over the CBC-RNC interface for scheduled transmission.

Traffic volume monitoring and radio resource request for CBS. On theUTRAN side, the BMC calculates the required transmission rate for the cell

broadcast service based on the messages received over the CBC-RNC interface,

and requests appropriate .CTCH/FACH resources from from RRC

Scheduling of BMC message. The BMC receives scheduling information

together with each cell broadcast message over the CBC-RNC interface. Based on

this scheduling information, on the UTRAN side the BMC generates schedule

message and schedules BMC message sequences accordingly. On the UE side ,theBMC evaluates the schedule messages and indicates scheduling parameters to

RRC, which are used by RRC to configure the lower layers for CBS

discontinuous reception.

Transmission of BMC message to UE. The function transmits the BMCmessages according to the schedule

Delivery of cell broadcast messages to the upper layer. This UE functiondelivers the received non-corrupted cell broadcast messages to the upper layer

The layer 3 is split into 2 parts: the access stratum and the non access stratum.The access stratum part is made of RRC (Radio Resource Control) entity

and duplication avoidance entity.

The non access stratum part is made of CC, MM parts.

Note shown on the figure are connections between RRC and all the other protocol layers

(RLC, MAC, PDCP, BMC and L1), which provide local inter-layer control services.

The protocol layers are located in the UE and the peer entities are in the node B or theRNC.`

The radio interface (Uu) is spitted into 2 plane, left is control plane ,right is user

plane ,control plane transfer control massage such as signalling, measurement

control. User plane transfer user data such as speech ,packet data etc.

Many functions are managed by the RRC layer . Here is the list of the most

important:

Establishment, re-establishment, maintenance and release of an RRC

connection between the UE and UTRAN: it includes an optional cell re-

selection, an admission control, and a layer 2 signaling link establishment. Whena RNC is in charge of a specific connection towards a UE, it acts as the Serving

RNC.

Establishment, reconfiguration and release of Radio Bearers: a number ofRadio Bearers can be established for a UE at the same time. These bearers are

configured depending on the requested QoS. The RNC is also in charge of

ensuring that the requested QoS can be met.

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Assignment, reconfiguration and release of radio resources for the RRC

connection: it handles the assignment of radio resources (e.g. codes, shared

channels). RRC communicates with the UE to indicate new resources allocationwhen handovers are managed.

Paging/Notification: it broadcasts paging information from network to UEs.

Broadcasting of information provided by the non-access stratum (CoreNetwork) or access Stratum. This corresponds to system information regularly

repeated.The radio interface (Uu) is layered into three protocol layers:

UE measurement reporting and control of the reporting: RRC indicates whatto measure, when and how to report.

Outer loop power control: controls setting of the target values.

Control of ciphering: provides procedures for setting of ciphering.

The RRC layer is defined in the 25.331 specification from 3GPP.