UMTS Terrestrial Radio Access Network (UTRAN)Control plane. User plane. Cellular Communication...

UMTS Terrestrial Radio Access Network (UTRAN)

• UMTS Terrestrial Radio Access (UTRA) • UTRAN Architecture

Focus on FDD only

Cellular Communication Systems 2Andreas Mitschele-Thiel, Jens Mueckenheim Nov-18

UMTS Terrestrial Radio Access (UTRA)Radio Interface Protocols

• Air interface protocol architecture• Layer 1, 2 and 3 protocols• Mapping between logical, transport and

physical channels


Radio Protocols – Overview

RLC

RRC

L1

GMM /SM / SMS

RRC

MAC

ATM

RANAP

AAL5

Relay

ATM

AAL5

3G SGSNRNSMSIu-PsUu

RLC SCCP

SignallingBearer

MAC

L1

SignallingBearer

RANAP

SCCP

GMM /SM / SMS

L1

RLC

PDCP

MAC

E.g., IP,PPP

Application

L1

RLC

PDCP

MAC

ATM

UDP/IP

GTP-U

AAL5

Relay

L1

UDP/IP

L2

GTP-U

E.g., IP,PPP

3G-SGSNUTRANMSIu-PSUu Gn Gi

3G-GGSN

ATM

UDP/IP

GTP-U

AAL5

L1

UDP/IP

GTP-U

L2

Relay

Layer 3– IP (user plane)– RRC (control plane)

Layer 2– PDCP (user plane)– BMC (user plane)– RLC – MAC

Layer 1– PHY

See 3GPP 25.301 andUMTS Networks book, ch. 9

Control plane

User plane


Source: 3GPP 25.301

Radio Protocol ArchitectureRadio Access BearersAS control plane SAPs

L3

cont

rol

cont

rol

cont

rol

cont

rol

Logical Channels

Transport Channels

C-plane signalling U-plane information

PHY

L2/MAC

L1

RLC

DC Nt GC

L2/RLC

MAC

RLC RLC

RLC RLC

RLC RLC

RLC

BMC L2/BMC

control

PDCP PDCP L2/PDCP

Radio Bearers

RRC


L3

cont

rol

cont

rol

cont

rol

cont

rol

Logical Channel

Transport Channels


PHY

L2/MAC

L1

RLC

DC Nt GC

L2/RLC

MAC

RLC RLC

RLC RLC

RLC RLC

RLC

Duplication avoidance

UuS boundary

BMC L2/BMC

control

PDCP PDCP L2/PDCP

DC Nt GC

Radio Bearers

RRC

Radio Access BearersAS control plane SAPsPhysical Layer – Services

Transport channels do not define whatis transported (which is defined by logical channels)Example: DCH offers the same type of service for control and user data

Physical layer offers information transfer services (transport channels) to MAC and higher layers

Physical layer transport services define–how and –with what characteristics data are transferred over the radio interface


Radio Access BearersAS control plane SAPs

L3

cont

rol

cont

rol

cont

rol

cont

rol

Logical Channel

Transport Channels


PHY

L2/MAC

L1

RLC

DC Nt GC

L2/RLC

MAC

RLC RLC

RLC RLC

RLC RLC

RLC


UuS boundary

BMC L2/BMC

control

PDCP PDCP L2/PDCP

DC Nt GC

Radio Bearers

RRC

Physical Layer – Channel Types (R99)• Common transport channels: with inband identification of the UEs

– BCH for broadcast information (DL)– PCH for paging information (DL)– RACH for contention-based access by UEs (UL)– FACH for data to individual UEs (DL)

• Dedicated transport channels where UEs are identified by the code – DCH for individual UE (UL &DL)


Common Transport Channels - Details

Random Access Channel (RACH)• Contention-based UL channel used for transmission of relatively small

amounts of data, e.g. for initial access or non-real-time dedicated control or traffic data

Forward Access Channel (FACH)• Common DL channel for relatively small amount of data• no closed-loop power control

High-Speed Downlink Shared Channel (HS-DSCH)• High-speed DL channel shared by several UEs

Broadcast Channel (BCH)• DL channel used for broadcast of system information into an entire cell

Paging Channel (PCH)• DL channel used for broadcast of control information into an entire cell

allowing efficient UE sleep mode procedures • Information types are paging and notification


Dedicated Transport Channels & Transport Formats

Dedicated Channel (DCH)Channel dedicated to one UE used in UL or DL

Enhanced Dedicated Channel (E-DCH)• Channel dedicated to one UE used in UL only• Subject to Node-B controlled scheduling and HARQ

Transport Formats and Transport Format Sets• A Transport Format or a Transport Format Set is associated with each

transport channel• A Transport Format defines the format offered by L1 to MAC (encodings,

interleaving, bit rate and mapping onto physical channels)• A Transport Format Set is a set of Transport Formats• Example: a variable rate DCH has a Transport Format Set (one Transport

Format for each rate), whereas a fixed rate DCH has a single Transport Format

See 3GPP 25.302, ch. 7 and Walke, ch 5.10, for details on Transport Formats and Transport Format Sets


Physical Layer – Functions

• Macrodiversity distribution/combining and soft handover execution• Error detection on transport channels and indication to higher layers (CRC)• FEC encoding/decoding and interleaving/deinterleaving of transport channels• Multiplexing of transport channels and demultiplexing of coded composite

transport channels• Rate matching (fit bits into physical channel)• Mapping of coded composite transport channel on multiple physical channels• Power weighting and combining of physical channels• Modulation and spreading/demodulation and despreading of physical channels• Frequency and time (chip, bit, slot, frame) synchronisation• Measurements and indication to higher layers (e.g. frame error rate, signal-to-

interference ratio, interference power, transmit power, etc.)• Closed-loop power control• RF processing


L3

cont

rol

cont

rol

cont

rol

cont

rol

Logical Channel

Transport Channels


PHY

L2/MAC

L1

RLC

DC Nt GC

L2/RLC

MAC

RLC RLC

RLC RLC

RLC RLC

RLC


UuS boundary

BMC L2/BMC

control

PDCP PDCP L2/PDCP

DC Nt GC

Radio Bearers

RRC

Radio Access BearersAS control plane SAPsMedium Access Control (MAC) – Services

Data transfer (logical channels SAPs)– Unacknowledged transfer of MAC SDUs between peer MAC entities– No data segmentation (performed by higher layers) in R.99

Reallocation of radio resources and MAC parameters– Radio resource reallocation and change of MAC parameters by

request of RRC, i.e. change of transport format (combination) sets, change of transport channel type

Reporting of measurements– Local measurements such as

traffic volume and quality indication (reported to RRC)


MAC – Logical Channels

• Control Channels (transfer of control plane information)

– Broadcast Control Channel (BCCH) – DL– Paging Control Channel (PCCH) – DL– Common Control Channel (CCCH) – DL/UL– Dedicated Control Channel (DCCH) – DL/UL

• Traffic Channels (transfer of user plane information)

– Dedicated Traffic Channel (DTCH) – DL/UL– Common Traffic Channel (CTCH) – DL/UL

Logical channels define what information is transported(transport channels (PHY SAP) define how data are transported)

o


MAC – Functions (1)

PHY PHY

ATM

DschFP

IubUE NodeB CRNCUu Iur SRNC

AAL2

ATM

DschFP

MAC-c/sh

ATM ATM

MAC-d

DCCH DTCH

AAL2

MAC-c/sh

MAC-d

DTCH DCCH

AAL2

DschFP

AAL2

DschFP

• Mapping between logical channels and transport channels• Selection of appropriate Transport Format for each Transport Channel

depending on instantaneous source rate• Priority handling (multiplexing) between data flows of one UE (MAC-d)• Priority handling (scheduling) between different UEs (MAC-c/sh)• Identification of UEs on common transport channels

Example: DTCH/DCCH mapped on DSCH (TDD only)


MAC – Functions (2)

PHY PHY

ATM

DschFP

IubUE NodeB CRNCUu Iur SRNC

AAL2

ATM

DschFP

MAC-c/sh

ATM ATM

MAC-d

DCCH DTCH

AAL2

MAC-c/sh

MAC-d

DTCH DCCH

AAL2

DschFP

AAL2

DschFP

• Multiplexing/demultiplexing of upper layer PDUs on common transport channels

• Multiplexing/demultiplexing of upper layer PDUs on dedicated transport channels

• Traffic volume measurement• Transport channel type switching (controlled by RRC)• Ciphering for transparent RLC mode

Example: DTCH/DCCH mapped on DSCH (TDD only)


Mapping between Logical, Transport & PhysicalChannels

BCCH

PCCH

CCCH

DCCH

DTCH

CTCH

BCH

DCH

RACH

FACH

PCH

P-CCPCH

S-CCPCH

P-CPICH

PRACH

DPDCH

DPCCH

PICH

P-SCH

S-SCH

AICH

S-CPICH

Logical Channels(MAC SAP)

Transport Channels(PHY SAP)

Physical Channels

DPCHKey: Uplink

DownlinkBidirectionalData TransferAssociation

Control ChTraffic Ch

Common Ch (no FPC)Common Ch (FPC)Dedicated Ch (FPC) Info Channels

Assoc Channels

Fixed Channels

Notes:• Figure describes a subset of possible mappings only! See 25.301, sc. 5.6

for complete list of possible mappings.• FPC denotes Fast Power Control


L3

cont

rol

cont

rol

cont

rol

cont

rol

Logical Channel

Transport Channels


PHY

L2/MAC

L1

RLC

DC Nt GC

L2/RLC

MAC

RLC RLC

RLC RLC

RLC RLC

RLC


UuS boundary

BMC L2/BMC

control

PDCP PDCP L2/PDCP

DC Nt GC

Radio Bearers

RRC

• Transparent data transfer (TM)• Unacknowledged data transfer (UM)• Acknowledged data transfer (AM)

Radio Link Control (RLC)


RLC – Services (1)Transparent data transfer (TM)• Transmission of upper layer PDUs without adding any protocol information (no

RLC header)• Possibly including segmentation/reassembly functionalityUnacknowledged data transfer (UM)• Transmission of upper layer PDUs without guaranteeing delivery to the peer

entity– Error detection: The RLC sublayer shall deliver only those SDUs to the

receiving upper layer that are free of transmission errors by using the sequence-number check function

– Immediate delivery: The receiving RLC sublayer entity shall deliver a SDU to the upper layer receiving entity as soon as it arrives at the receiver

Acknowledged data transfer (AM)• Transmission of upper layer PDUs and guaranteed delivery to the peer entity• Notification of RLC user at transmitting side in case RLC is unable to deliver the

data correctly• in-sequence and out-of-sequence delivery• error-free delivery (by means of retransmission)• duplication detection


RLC – Services (2)Maintenance of QoS as defined by upper layers• retransmission protocol configurable by layer 3 to provide different

levels of QoSNotification of unrecoverable errors• RLC notifies the upper layer of errors that cannot be resolved by RLC

itself by normal exception handling procedures

There is a single RLC connection per Radio Bearer


RLC – Functions • Transfer of user data (AM, UM, TM)• Segmentation and reassembly (RLC PDU size adapted to transport

format)• Concatenation• Padding• Error correction (selective-repeat ARQ) • Sequence number check (UM mode)• Duplicate RLC PDUs detection• In-sequence delivery of upper layer PDUs• Flow control between RLC peers• SDU discard• Protocol error detection and recovery• Exchange of status information between peer RLC entities• Ciphering (non-transparent mode)• Suspend/resume and stop/continue of data transfer• Re-establishment of AM/UM RLC entity

Convert variable-size higherlayer PDUs into fixed-size

RLC PDUs (TBs)

Convert radio link errors into packet

loss and delay

Avoid Tx and Rxbuffer overflows or

protocol stalling


RLC Modes during CS Voice Call R

LC

Call signalling: RLC Entities / Channels / Radio Bearers (RB) Relationships

Abbr. Mode RLC EntitiesTr. Transparent mode 2 (one tx. and one rx.)UM Unacknowleged Mode 2 (one tx. and one rx.)AM Acknowleged Mode 1 (bi-directional for ARQ)

SRB1 SRB2 SRB3/4

Notes:This is for a single user. SRB0 is not shown as this is for the CCCH - i.e. not used for a dedicated call, only for establishment.

RLC Entity RLC EntityUM RLC EntityAM

MAC

DCCH DCCH DCCH DCCH

LAYER 1CCTrCH

RLC

RLC

RLC

RLC

RLC

RLC

Cla

ss A

(81b

its)

Cla

ss B

(103

bits

)

Cla

ss C

(60b

its)

AMR

VO

ICE

CO

DEC

DL

Cla

ss A

(81b

its)

Cla

ss B

(103

bits

)

Cla

ss C

(60b

its)

AMR

VO

ICE

CO

DEC

UL

Tr

RB RB

RB RB

RB

RB

DTCH DTCH

Control Plane

Use

r Pla

ne

DCH DCH

DPDCHPhysicalChannels

RLC EntityAM

DCH DCH

CCTrCH

DPDCH


L3

cont

rol

cont

rol

cont

rol

cont

rol

Logical Channel

Transport Channels


PHY

L2/MAC

L1

RLC

DC Nt GC

L2/RLC

MAC

RLC RLC

RLC RLC

RLC RLC

RLC


UuS boundary

BMC L2/BMC

control

PDCP PDCP L2/PDCP

DC Nt GC

Radio Bearers

RRC

Radio Access BearersAS control plane SAPsPacket Data Convergence Protocol (PDCP)

Service: PDCP SDU delivery PDCP is defined for PS domain only!


PDCP – Functions

Header compression and decompression• Header compression and decompression of IP data streams (e.g.

TCP/IP and RTP/UDP/IP headers)Header compression method is specific to the upper layer protocol combinations, e.g. TCP/IP or RTP/UDP/IP (RFC 2507 & RFC 3095)

Transfer of user data• PDCP receives PDCP SDU from the NAS and forwards it to the RLC layer

and vice versa

Support for lossless SRNS relocation• Maintenance of PDCP sequence numbers for radio bearers that are

configured to support lossless SRNS relocation


L3

cont

rol

cont

rol

cont

rol

cont

rol

Logical Channel

Transport Channels


PHY

L2/MAC

L1

RLC

DC Nt GC

L2/RLC

MAC

RLC RLC

RLC RLC

RLC RLC

RLC


UuS boundary

BMC L2/BMC

control

PDCP PDCP L2/PDCP

DC Nt GC

Radio Bearers

RRC

Radio Resource Control (RRC)

Services Provided to Upper LayersGeneral Control (GC) – information broadcast serviceNotification (Nt) – paging and notification broadcast servicesDedicated Control (DC) – connection management and message transfer


RRC – Interaction with Lower Layers

R R C R R C

R L C R L C

Radio Resource Assignment [Code, Frequency, TS, TF Set, Mapping, etc.]

Measurement Report

RLC retransmission control

L 1 L 1

U T R A N U E

Con

trol

Mea

sure

men

ts

Con

trol

Mea

sure

men

ts

Con

trol

Mea

sure

men

ts

Con

trol

Mea

sure

men

ts

M A C M A C

Con

trol

Con

trol


RRC – Functions RRC handles control plane signaling between the UEs and UTRAN:

- Broadcast of information provided by non-access stratum (Core Network) and access stratum (UTRAN)

- Establishment, re-establishment, maintenance and release of RRC connections- Establishment, reconfiguration and release of Radio Bearers (L2 SAPs)- Assignment, reconfiguration and release of radio resources for the RRC

connection- RRC connection mobility functions- Paging/notification- QoS control- UE measurement reporting- Outer loop power control- Arbitration of radio resources on uplink DCH- Initial cell selection and re-selection in idle mode- Control of ciphering- Integrity protection (message authentication for sensitive data)- Control of Cell Broadcast Service (CBS)


RRC State Machine

• RRC state machine exists as two peer entities (MS and UTRAN)• The two peer entities are synchronized (apart from transient situations

and error cases)

Idle mode

CellConnected

RRCconnectionestablishment

URAConnected

RRCconnectionrelease

Enter URAconnected state

Enter cellconnected state

Connected mode


UTRAN Registration Area (URA)

LA RA

RA

RA RA

RA

RA RA

RA

RA

URA

URAURA

URA URA

URA

URAURA

URA URA

URA

URAURA

URA URA

URA

URAURA

URA URA

URA

URAURA

URA URA

URA

URAURA

URA URA

URA

URAURA

URA URA

URA

URAURA

URA URA

URA

URAURA

URA URA

• URA is used to optimizetradeoff betweenpaging traffic andlocation update traffic

• URA is known to theUTRAN only

• URA is established in RRC connected mode

• URAs may overlap• URA usually in the

order of 10 cells

URA

URAURA UR

A

URA

URA

URA

URA

URA

URA

URA


RRC State Machine

RRC Connected mode:– two main states

• Cell Connected: MS position is known at the cell level; RRC connection mobility is handled by handover and cell update procedures

• URA Connected: MS position is known at the URA level; URA updating procedures provide the mobility functionality; no dedicated radio resources are used in the state.

– there is one RNC that is acting as serving RNC, and an RRC connection is established between the MS and this SRNC

An UE has either zero or one RRC connection

Idle mode

CellConnected


URAConnected




Connected mode


RRC State Machine

Idle mode

CellConnected


URAConnected




Connected mode

RRC Idle mode:– no connection established between the MS and UTRAN– no signalling between UTRAN and the MS except for system

information sent from UTRAN on a broadcast channel to the MS– MS can only receive paging messages from a CN identity on the PCH – no information of the MS is

stored in UTRAN


UMTS RRC State Optimization (PS mode)Goal: Minimization of Radio Resource

Consumption during Idle Times

Tradeoff for idle periods• retaining in state => continuous state cost or• move to cheaper state => transition cost

Limited resources• radio resources (transmit power)• channelization codes• processing resources (signaling)• power consumption• transport resources (Iu, Iub, …)

Find optimal timeout settings depending on • traffic model (distribution of idle times)• cost per state and scarcity of allocated resources• cost per transition • user mobility• …

cell_DCH

URA_PCH

cell_PCH

idle

T1

T2

T3


UTRAN Architecture

• UTRAN Components and Interfaces• Macro diversity: Serving and Drift RNC• UTRAN architecture details and protocols• AS and NAS services• RRC connection and signaling connection


UTRAN Components and Interfaces

RNS

RNC

RNS

RNC

Core Network

Node B Node B Node B Node B

Iu Iu

Iur

Iub Iub Iub Iub

UTRAN

Source: 3GPP 25.401

A Radio Network Subsystem (RNS) consists of a RNC and a number of Node B‘s


UTRAN Architecture Principles – User Plane

Source: 3GPP 25.401

Non-Access Stratum (NAS): • Protocols between UE and CN that are not

terminated in the UTRANAccess Stratum (AS): • Provides UE-CN transport service to NAS services• AS protocols are closely linked to radio technology

UTRAN UE CN

Access Stratum

Non-Access Stratum

Radio (Uu)

Iu

Radio protocols (1)


Iu protocols (2)

Iu protocols (2)

radio access bearer SAPs (user plane)


UTRAN Architecture Principles – Control Plane

UTRAN UE CN

Access Stratum

Non-Access Stratum

Radio (Uu)

Iu



Iu protocols (2)

Iu protocols (2)

CM,MM,GMM,SM (3)

CM,MM,GMM,SM (3)

Source: 3GPP 25.401

Non-Access Stratum control plane functions:CM: Connection ManagementMM: Mobility ManagementGMM: GPRS MMSM: Session Management

signaling connection


Macro Diversity: Serving and Drift RNS

Serving RNS (SRNS)

Core Network

Iu

Drift RNS (DRNS) Iur

UE

Cells

Source: 3GPP 25.401

Each RNS is responsible for the resources of its set of cellsFor each connection between User Equipment (UE) and the UTRAN, one RNS is the Serving RNS (SRNS)Drift RNSs (DRNS) support the Serving RNS by providing radio resourcesMacro-diversity and handover is jointly supported by Node B(s) and RNC(s)


Serving, Drift and Controlling RNC

RNS

RNC

RNS

RNC

Core Network


Iu Iu

Iur

Iub Iub Iub Iub

UTRAN

UE

SRNCDRNC

Softer handover: maximum ratio combiningin Node B

Soft handover: radio frame selection (layer 1) in SRNC (and DRNC)


Roles of RNSs/RNCsServing RNS (SRNS)• A role an RNS can take with respect to a specific UE• There is one Serving RNS for each UE connected to the UTRAN• The Serving RNS is in charge of the RRC connection of the UE• The Serving RNS terminates the Iu for this UE

Drift RNS (DRNS)• A role an RNS can take with respect to a specific UE• An RNS supports the Serving RNS with radio resources when the UE uses cells

controlled by this RNS

Controlling RNC (CRNC)• A role an RNC can take with respect to a specific set of UTRAN access points,

i.e. the cells with its resources• Exactly one CRNC serves an UTRAN cell• CRNC has the overall control of the logical resources of its cells

Source: 3GPP 21.905


Distribution of RRM Functions between RNCs

• CRNC owns the radio resources of a cell

• SRNC handles the connection (RRC) to one UE, and may borrow radio resources from other CRNC

• SRNC performs dynamical control of power for dedicated channels, within limits admitted by CRNC

• Node B implements inner loop power control of its radio links

• SRNC has overall responsibility for outer loop power control

• SRNC schedules data on dedicated channels• CRNC schedules data on common channels (no macro diversity)

Source: 3GPP 25.401, Ch 6.3


Serving, Drift and Controlling RNC

RNS

RNC

RNS

RNC

Core Network


Iu Iu

Iur

Iub Iub Iub Iub

UTRAN

UE 1

SRNCDRNC

UE 2

Dedicated channel with single link

SRNC

Dedicated channel in macro-diversity mode with multiple links


UTRAN Architecture: Functional Split

Control plane

Bearer plane

Core Network

Node-B

Paging

Com./ SharedChannel

Processing

Cell Control

DedicatedChannel

Processing

Mobile Control (RRC state)

Broadcast

CRNC/DRNC SRNC


Serving and Controlling RNCExample: DCH (Dedicated Channel – UL&DL macro diversity)

PHY PHY

ATM

DchFP

ATM

MAC-d

Iub UE NodeB CRNC Uu SRNC

ATM ATM

Iur

MAC-d

DCCH DTCH

DchFP PHY-upper PHY

AAL2 AAL2

DTCH DCCH

AAL2 AAL2

DchFP DchFP PHY

Source: 3GPP 25.401, sc 11.2.4 (see also 25.301, sc 5.6.1)

Combining/splitting of

phy. channels

Combining/splitting is supported for DCH only(no layer 2 processing in Node B and DRNC)

Combine links served by the same node B

Combine links served by the same

CRNC (optional)

Combine links served by different RNCs


Access Stratum Services Revisited

DC Nt GC

UTRAN UE Core Network

Access Stratum (AS)

Non-Access Stratum (NAS)

Radio (Uu) Iu

DC Nt GC

DC Nt GC DC Nt GC DC Nt GC DC Nt GC

end AS entity end AS entity

Relay/RNC functions

Uu Stratum (UuS)

Iu Stratum

L2/L1

RRC

L2/L1

RRC

Source: 3GPP 25.301 (see also 3GPP 23.110)

• General Control (GC) – general network-specific broadcasts• Notification (Nt) – UE-specific infos, e.g. paging• Dedicated Control (DC) – connected mode• User data transfer (RAB) – connected mode


MSC/VLRor SGSN

SRNCUE

RRC Connection and Signaling Connection

RRC Connection RANAP Connection

RRC RANAPRRC RANAP

Signaling Connection(provides DC SAP for SM, CM, MM)

Radio Access Bearer

Signaling Radio Bearer Iu Signaling Bearer

Higher layer control

Higher layer control


Radio Link, RRC Connection & Signaling Connection

RNS

RNC

RNS

RNC

Core Network


Iu Iu

Iur

Iub Iub Iub Iub

UTRAN

UEradio link

RRC connection -> connected mode


SRNC

RRC connections and signaling connections are logical links


Radio Link, RRC Connection & Signaling Connection

RNS

RNC

RNS

RNC

Core Network


Iu Iu

Iur

Iub Iub Iub Iub

UTRAN

UEradio link

SRNCDRNC

RRC connection



Signaling Connection

• No signaling connection exist (idle state)– UE has no relation to UTRAN, only to CN– no data transfer– paging identification by IMSI, TMSI, P-TMSI

• Signaling connection exist (connected state)UE position can be known on different levels:

- URA level (UTRAN registration area): URA is a specified set of cellsidentified on the BCCH

- Cell level: Different channel types can be used for data transfer:- Common transport channels (RACH, FACH)- Dedicated transport channels (DCH)

Source: 3GPP 25.301, ch 6.2


Recap on Important VocabularyRRC connection• point-to-point bi-directional connection between RRC peer entities on the UE and

the UTRAN sides• UE has either zero or one RRC connectionSignaling connection• an acknowledged-mode link between the UE and the CN to transfer higher layer

information between the entities in the non-access stratum (via RRC and RANAP)Radio link• a logical association between a single UE and a single UTRAN access point (cell)• its physical realization comprises one or more radio bearer transmissions

Radio bearer (compare signaling radio bearer)• service provided by the RLC layer for transfer of user data between UE and SRNCRadio interface• interface between UE and a UTRAN access point• radio interface encompasses all the functionality required to maintain the

interface

Source: 3GPP TR 21.905


UTRAN ProceduresElementary procedures

– Paging– RRC connection setup– Transaction reasoning– Authentication and security control– Transaction setup with RAB allocation– Transaction clearing and RAB release– RRC connection release

RRM procedures– Radio link addition and deletion– Intersystem handover from UMTS to GSM (CS/PS)– UE state transitions/ bearer reconfiguration

MM and CM procedures -> see separate slides


Basic Model of UMTS Network TransactionsPaging

RRC Connection Establishment

Transaction Reasoning(Signaling conn. establishment)

Authentication andSecurity

Transaction Setup andRAB Allocation

Transaction(user or control plane)

Transaction Release andRAB Release

RRC Connection Release

UE indicates the CN the requested service

A transaction comprises all the elementary procedures required to enable

– the transport of user data (PS or CS mode) or

– the exchange of higher-layer signaling messages (e.g. MM or CM)

Allocation of bearers to support required UMTS bearer service

Transfer of data

Release of all bearers to support UMTS bearer service


Paging

Paging type 1:• UE idle mode (no RRC connection) or• RRC connected modes (cell_PCH or URA_PCH)

Example: paging for a UE in idle modeUE Node B

1.1Node B

2.1RNC

1RNC

2CN

RANAPRANAP 1. Paging

2. PCCH : Paging Type 1

RANAP RANAP1. Paging

3. PCCH : Paging Type 1

(Requesting CN domain, IMSI, ...)

Paging








Paging type 2 (not shown here):• UE is in RRC connected mode (cell_DCH or cell_FACH)• Paging request from another CN domain


Initial Random Access on RACH

UE addressing• CCCH: UE ID embedded in the RRC message• DTCH/DCCH: UE ID included in MAC header

UE Node B Controlling RNC

Preamble

Preamble

Preamble

Acquisition Indication (AICH)

PRACH Message

Resourcing Node B Hardware

RACHFP

RACH Message [RRC Connection Request]

CRC Check

RACHFP

Persistency check before


RRC Connection Setup

Establishment of a RRC connection in cell_DCH mode

Paging








UE Node B RNC CN

UE_Idle

CELL_DCH

Initial Random Access

CCCH (TM)/ RACH: RRC Connection Request

RL Setup Request

RL Setup Response

ALCAP Iub Transport bearer Setup

UL/DL Synchronisation

CCCH (UM)/ FACH: RRC Connection Setup

DCCH (AM)/ DCH: RRC Connection Setup Complete • Addr.: by DCH • DCCH established • UE capabilities

known

• Addr.: Initial UE ID • Request for DCCH • Incl. Establishment

cause

Establishment of UTRAN DCH resources incl. CAC

Addr.: Initial UE ID


RRC Connection SetupReasons for RRC connection setup:• Call setup (mobile-originated and mobile-terminated calls)

– Conversational call– Streaming call– Interactive call– Background call– Emergency call– Call re-establishment

• Exchange of signaling messages (low/high priority)

RRC connection request message contains, e.g.• IMSI, TMSI, IMEI• Location area, routing area identity, etc.• Other information: e.g. UE capabilities


NAS Signaling Connection Establishment(Transaction Reasoning)

UE ServingRNC

CN

1. RRC Connection Establishment

RRCRRC2. DCCH : Initial Direct Transfer

RANAP RANAP3. Initial UE Message

Payload contains system network message: Information about the transaction initiated by the UE (IMSI, TMSI, location area, kind of requested transaction)

Paging









Authentication and Security Control

Authentication request/response: mutual authentication of UE and networkSecurity mode command/complete: CN domain indicates to UTRAN and UE the encryption

details (method/algorithms and encryption keys)

Paging









Transition Setup and RAB Establishment (CS Mode)

Paging









Transition Setup and RAB Establishment (PS Mode)

Paging








⇒ see next slide for details


Transaction Release and RAB Release (PS Mode)

Note: signaling connection and RRC connection remain

Paging









RRC Connection ReleasePaging









Soft Handover – Radio Link Addition UE SRNC Target

Node B DRNC

ALCAP Iur bearer Setup

Active Set Update (Radio Link Addition)

ALCAP Iub Data Transport bearer Setup

RNC Decides to add a new Radio Link

Target Node B is ready

UE starts Rx on new radio link

E.g. new neighbour cell list

Radio Link Restore Indication Radio Link Restore Indication

Active Set Update Complete

Measurement Control

start Rx

start Tx

When RL Setup

Radio Link Add/ Setup Request

Radio Link Add/ Setup Response

Radio Link Add/ Setup Request

Radio Link Add/ Setup Response

Unsynchronized addition


Soft Handover – Radio Link Deletion

Unsynchronized deletion


SRNS Relocation (CS)


UE RRC Connected States – Traffic Perspective

• Cell_DCH– Dedicated Traffic and Control carried over DCH

• Cell_FACH– Dedicated Traffic and Control carried over RACH/FACH

• URA_PCH– No air interface resources required, “dormant” RB– UE receives paging on UTRAN Routing Area (URA) basis rather than

standard routing area (RA)

Cell FACH

Cell DCHURA PCHNo data

No data

Data activity

Data activity

Low traffic

High trafficor CS call

Dynamic RBreconfigure

Cell FACH

Cell DCHURA PCHNo data

No data

Data activity

Data activity

Low traffic

High trafficor CS call

Dynamic RBreconfigure

optional


ReferencesBooks:• Kaaranen, Ahtiainen, Laitinen, Naghian, Niemi: UMTS Networks –

Architecture, Mobility and Services. 2nd edition, Wiley, 2005• Cornelia Kappler: UMTS Networks and Beyond, Wiley, 2009• Holma, Toskala: WCDMA for UMTS. 4th edition, Wiley, 2007

Central 3GPP Documents on UTRAN:• 25.401: UTRAN overview• 25.301: Radio link protocols (UTRA)• 25.931: UTRAN procedures

UMTS Terrestrial Radio Access Network (UTRAN)Control plane. User plane. Cellular Communication...

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