UMTS Protocols 2

UMTS Protocols 2

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OutlinesRadio Interface Protocol Architecture. Logical Channels & Transport Channels.MAC Protocol. 1) MAC Services. 2) MAC Functions. 3) MAC Entities.RLC Protocol. 1) RLC Functions. 2) RLC Modes.

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Radio Interface Protocol Architecture.

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Radio Interface Protocol Architecture.The Radio Interface Layers :-1- The Physical Layer (L1).2- The Data Link Layer (L2). 2-1 MAC : Medium Access Control. 2-2 RLC : Radio Link Control. 2-3 PDCP : Packet Data Convergence Protocol. 2-4 BMC : Broadcast / Multicast Control .3- The Network Layer (L3). RRC : Radio Resource Control .

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Logical Channels & Transport Channels

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Transport Channels

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Transport Channel(1)Random Access Channel (RACH)Used to carry control information from the terminals in the cell area. This

is used, for example, when a terminal requests to set up a connection to the network.

The RACH is always received from the entire cell and thus in practice the data rates need to be rather low .

Forward Access Channel (FACH)Used to carry downlink control information to a terminal known to be

located in the cell area. The FACH is used, for example, after a random access message has been

received by the BTS and control information needs to be sent to the terminal.

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Transport Channel(2)Paging Channel (PCH)Carries paging procedure related data, which is used when the network

needs to initiate communication with a specific terminal, for example when a speech call is coming to the terminal.

The paging message can be transmitted in a single cell or in up to a few hundred cells, depending on the system configuration and location area size.

The PCH is always transmitted over the entire cell and all terminals in the cell area must be able to receive the paging information.

Broadcast Channel (BCH) Downlink channel used for broadcast of system information into cell. Ex: Random access codes, cell access slots, and cell-type transmit diversity

methods.

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Transport Channel(3)Downlink Shared Channel (DSCH) – TDD only Downlink channel shared by several UEs carrying dedicated control or

traffic data.Uplink Shared Channel (USCH) – TDD only Uplink channel shared by several UEs carrying dedicated control or traffic

data.Dedicated Channel (DCH) Channel dedicated to one UE used in uplink or downlink. EX : speech frames, measurement reports and control commands from UE.Enhanced Dedicated Channel (E-DCH) Channel dedicated to one UE used in uplink only. Provides data speeds of up to 5.8 Mbps in the uplink direction.

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Logical Channels ”Relate to the content and what kind of data are

transmitted through the radio interface”

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Logical Channel

Traffic Channel Control Channel

DTCH(UL/DL)

CTCH(DL)

BCCH(DL)

PCCH(DL)

DCCH(UL/DL)

CCCH(UL/DL)

Logical Control Channel

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Logical Traffic Channel

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Medium Access Control

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RLC

MAC

Physical

Transport Channels

Logical Channels

MAC ProtocolMAC is a Layer 2 protocol and it resides between Physical

Layer (L1) and RLC Layer (L2).The internal configuration of MAC is done by the RRC

layer (L3). The interface between PHY and MAC are the transport

channels .The interface between RLC and MAC are the logical

channels. MAC protocol is not symmetrical protocol as it is

different in UL and DL .15

MAC ServicesData Transfer : This service provides unacknowledged transfer of MAC

SDUs between peer MAC entities without data segmentation & peer-to-peer transportation of LRC PDUs.

Reallocation of radio resources and MAC parameters : This service performs, on request of RRC,execution of RR

reallocation and change of MAC parameters .Reporting of Measurements: Traffic Volume Measurements are reported to RRC.

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MAC Functions (1)Mapping between logical channels and transport

channels.Selection of appropriate Transport Format for each

Transport Channel depending on instantaneous source rate.

Priority handling between data flows of one UE.Priority handling between UEs by means of dynamic

scheduling.Identification of UEs on common transport channels.

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MAC Functions (2)Multiplexing/ Demultiplexing of upper layer PDUs

into/from transport block sets delivered to/from the physical layer on dedicated transport channels.

Traffic volume measurement.Transport Channel type switching.Ciphering for transparent mode RLC.Access Service Class selection for RACH and CPCH

transmission.

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Mapping (1)Mapping between logical channels and transport channels

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Transport FormatTransport format : Format offered by the physical layer to

the MAC for the delivery of a Transport Block set during TTI on a Transport Channel.

Transport format : is a format applied to a transport block set on a given transport channel for a given TTI.

This parameter controls how much data is transferred on the transport channel in that particular transmission time interval and how the data is coded etc. by the physical layer.

Given the Transport Format Combination Set assigned by RRC, MAC selects the appropriate transport format for each active transport channel depending on source rate.

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Transport Format

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Transport Format PartsThe transport format constitutes of two parts:The semi-static part : includes parameters are fixed for all transport block sets of the corresponding transport

channel until the RRC parameters are reconfigured.The dynamic part : includes parameters whose value can change from one transport block set to another.Both are configured by RRC.It is the MAC layer’s responsibility to choose an appropriate

set of parameters from the allowed values for the transmission.

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Transport format set

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Transport format setTTI [Transmission Time Interval ] :defines the time

interval between two subsequent transport block set transfers between MAC and PHY.

Rate matching : indicate how the transmission process is carried out so that the block size matches the radio frames. Rate matching will either repeat bits to increase the rate or puncture bits to decrease the rate.

Transport Format Indicator (TFI) : The representation of a specific transport format within a TFS.

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Example on TFTwo transport channels mapped onto a single physical channel

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Example on TF

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Inband IdentificationAt RACH : when several Random Access packets are

received at Node-B , The Physical layer detects them and deliver them to the MAC layer .

MAC distinguishes the valid random access packets by different identifications.

So inband identification is needed as the MAC handles access to, multiplex onto , the transport channels .

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Multiplexing / DemultiplexingMAC should support service multiplexing for common

transport channels, since the physical layer does not support multiplexing of these channels.

Multiplexing/ demultiplexing data between Logical channels [ CCCH – DCCH – DTCH ] and Transport channels [ FACH – RACH ] in consideration of “The Appropriate Prioritization “ using LID.

LID : Logical Channel Identifier .

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FACH / RACH

LIDMAC PDU

10000-11111

00100

00010

DTCH

DCCH

CCCH

Traffic Volume MeasurementsTraffic volume information is measured at the MAC layer

and the results are reported to RRC.RRC takes the decisions and performs Transport channel

switching . Switching : Execution of the switching between common

& dedicated channels based on switching decision by RRC.

Ciphering : prevents unauthorized acquisition of data performed in MAC only for [ Transparent RLC Mode ].

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Access Service ClassRACH & CPCH resources may be divided between Access

Service Classes in order to provide different priorities of RACH & CPCH classes .

Each ASC will have a set of parameters associated with it RACH resources in TDD [ Time slot ] and in FDD [ Access

slot ].CPCH resources only in FDD [ Access slot ] .ASC is classified between [ ASC0 to ASC7 ] .ASC0 : Highest Priority.ASC7 : Lowest Priority .

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MAC PDU

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MAC PDUTCTF : Target Channel Type Field : Provides identification of the logical

channel in case of RACH and FACHC/T : provides identification of logical channel when multiple logical

channels are carried on the same transport channel.UE-ID Type : Provides identification of UE on Common Transport

Channel . 1- U-RNTI :For DCCH at DL. 2- C-RNTI : for DTCH at UL & DL.UE-ID Type Field : to decode UE-ID in MAC header.

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MAC Logical Architecture

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MAC EntitiesMAC-b : represents the control entity for BCH. - There is one MAC-b entity in UE . - There is one MAC-b entity in UTRAN .MAC-c/sh : handles PCH,FACH,RACH (FDD) handles DSCH,USCH (TDD) - There is one MAC-b entity in UE . - There is one MAC-b entity in UTRAN .MAC –d : handles DCH - There is one MAC-b entity in UE . - There is one MAC-b entity in UTRAN .

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MAC Entities

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Distribution of MAC Functions (DSCH –TDD only)

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MAC c/sh

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MAC c/shTCTF MUX : represents the handling of TCTF field in the MAC

header .Add/read UE ID : the UE ID is added for CPCH and RACH

transmissions.UL : TF Selection: The possibility of TF selection existsASC Selection : MAC indicates ASC associated with PDU to the

physical layer ,to ensure that RACH & CPCH messages with given ASC are send to appropriate time slot(s).

Scheduling / Priority handling : used to transmit the information received from MAC-d on RACH & CPCH based on Logical Channel Priorities .

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MAC-d

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MAC-dTransport Channel Type Switching: - Performed by MAC based on decision taken by RRC. - If requested by RRC , MAC shall switch the mapping of

one logical channel between common & dedicated Transport channels.

C/T MUX : is used when multiplexing of several dedicated logical channels onto one transport channel is used .

Ciphering / Deciphering : For Transparent RLC mode .Flow Control : To limit buffering between MAC-d and

MAC-c/ sh entities . 40

MAC-d UTRAN side

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Radio Link Control

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RRC – PDCP – BMC

RLC

MAC

TR-SAP AM - SAP UM - SAP

Logical Channels

RLC FunctionsData Transfer .Segmentation & Reassembly .Error Detection & Correction .Flow Control .Ciphering .In-sequence delivery of upper layer PDUs.Sequence number check.Padding.Concatenation.

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RLC ModesProvides segmentation/reassembly (payload units, PU)

and retransmission service for both user and control dataTransparent mode (TM): no overhead is added to higher

layer data.Unacknowledged mode (UM): no retransmission

protocol is used and data delivery is not guaranteed.Acknowledged mode (AM): Automatic Repeat request

(ARQ) mechanism is used for error correction.

Packet Construction PDUs from Upper Layers are “ Too Large “ - Segmented into smaller units of equal sizePDUs from Upper Layers are “Too Small “ 1- Concatenated with first segment of the next

incoming PDU from the upper layer. 2- Extended by adding padding bits.Header is added to each segment and the resulting

packet is passed to the MAC Layer.

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Packet Construction AM&UM

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Packet Construction TM

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RLC Logical ArchitectureThere is one transmitting and one receiving

entity for TM and UM .There is one combined transmitting and receiving

entity for AM .The mode to be used is determined by the SAP

into which the higher layer deliver their PDUs.The mode chosen indicates which services and

functions are to be applied .

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RLC Logical Architecture

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RLC Logical Architecture

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RLC PDU types1. Data PDUs : used to transfer user data . 1- TMD PDU. 2- AMD PDU. 3- UMD PDU.2. Control PDUs : carry control information . 1- RESET. 2- STATUS. 3- RESET ACK. Note : Control PDUs used only in AM.

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Data PDUs Transparent PDU : used to carry any length of user data

without adding any RLC Header.Unacknowledged PDU : transfers user data sequentially

using the sequence number in the header but does not provide any ACK to the sender.

Acknowledged PDU : transfers user data sequentially using the sequence number in the header and also provide ACK to the sender by means of Control PDUs like STATUS.

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Control PDUsSTATUS PDU : used to inform the transmitter which

PDUs are received correctly and which PDUs are missing .

RESET PDU : command the other end to reset its protocol state variables & timers so that the two ends maybe synchronized with each other .

RESET ACK PDU : to ACK the RESET command .

Transparent Mode ( TM )Transparent Mode Functions : 1. Segmentation and reassembly .2.Transfer of user data .3.SDU discard .

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TM Trans. & Receive.

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1-Receiving TM-RLC Entity

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The receiving TM-RLC entity receives TMD PDUs through the configured logical channels from the lower layer.

If segmentation is configured by upper Layers?

If segmentation is not configured by upper layers?

The receiving TM RLC entity delivers RLC SDUs to upper layers through the TM-SAP.

2-Transmitting TM-RLC Entity The transmitting TM-RLC

entity receives RLC SDUs from upper layers through

the TM-SAP.If segmentation has been

configured by upper layers ?If segmentation has not been

configured by upper layers ?When the processing of a RLC

SDU is complete, the resulting one or more TMD PDU(s) are/is submitted to the lower layer through logical channel.

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Unacknowledged Mode (UM)Unacknowledged Mode Functions : 1. Segmentation and reassembly.2.Concatenation.3.Padding.4.Transfer of user data.5.Flow Control.6.Sequence number check.7.Ciphering.8.SDU discard.

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Sequence number checkAfter receiving a packet , RLC examines the sequence

number :1.Erroneous : The packet is discarded .2.Non-erroneous : It is delivered to higher layers .In this mode : the responsibility of the high layers to

recover the missing packets using an appropriate error receiving mechanism.

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UM Trans. & Receive.

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1-Receiving UM-RLC EntityThe receiving UM-RLC entity

receives UMD PDUs through the configured logical

channels from the lower layer.The receiving UM RLC entity

deciphers the received UMD PDUs (except for the UMD PDU header).

It removes RLC headers from received UMD PDUs, and reassembles RLC SDUs

RLC SDUs are delivered by the receiving UM RLC entity to the upper layers through the UM-SAP.

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2-Transmitting UM-RLC Entity The transmitting UM-RLC entity receives RLC

SDUs from upper layers through the UM-SAP. The transmitting UM RLC entity segments the

RLC SDU into UMD PDUs of appropriate size, if the RLC SDU is larger than the length of available space in the UMD PDU.

The UMD PDU may contain segmented and/or concatenated RLC SDUs and Length Indicators are used to define boundaries between RLC SDUs within UMD PDUs.

If ciphering is configured and started, an UMD PDU is ciphered (except for the UMD PDU header) before it is submitted to the lower layer.

The transmitting UM RLC entity submits UMD PDUs to the lower layer through logical channel.

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Acknowledged Mode (AM)Acknowledged Mode Functions : 1. Segmentation and reassembly.2. Concatenation.3. Padding.4. Transfer of user data.5. Error correction.6. In-sequence delivery of upper layer PDUs.7. Duplicate detection.8. Flow Control.9. Protocol error detection and recovery.10. Ciphering.11.SDU discard.

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Error Detection & Correction

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Guaranteed, Error-Free DeliveryRLC checks the sequence number of the packet that

come from MAC layer .Correct : receive & reassembly and send to higher layers.Incorrect : the receiver discards the packet and attempts

to recover that error by :- 1- ARQ : Automatic Repeat Request . 2- Receiving End . 3- Desired Packets .

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TM Trans. & Receive.

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1-Receiving AM-RLC Entity

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1-Receiving AM-RLC Entity The receiving side of the AM-RLC entity receives AMD and Control PDUs

through the configured logical channels from the lower layer. AMD PDUs are routed to the Deciphering Unit and then delivered to the

Reception buffer. The AMD PDUs are placed in the Reception buffer until a complete RLC SDU has

been received. The Receiver acknowledges successful reception or requests retransmission of

the missing AMD PDUs by sending one or more STATUS PDUs to the AM RLC peer entity, through its transmitting side.

The associated AMD PDUs are reassembled by the Reassembly Unit and delivered to upper layers through the AM-SAP.

RESET and RESET ACK PDUs are delivered to the RLC Control Unit for processing. If a response to the peer AM RLC entity is needed by the RLC Control Unit to the transmitting side of the AM RLC entity.

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2-Transmitting AM-RLC Entity

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2-Transmitting AM-RLC Entity The transmitting side of the AM-RLC entity receives RLC SDUs from upper layers

through the AM-SAP. RLC SDUs are segmented and/or concatenated into AMD PDUs of a fixed length. After the segmentation and/or concatenation are performed, the AMD PDUs are

placed in the Retransmission buffer at the MUX. The MUX multiplexes AMD PDUs from the Retransmission buffer that need to be retransmitted, and the newly generated AMD PDUs delivered from the

Segmentation/Concatenation function. The PDUs are delivered to the function that completes the AMD PDU header and

potentially replaces padding with piggybacked status information. A Piggybacked STATUS PDUs can be of variable size in order to match the amount of free space in

the AMD PDU. The ciphering (if configured) is then applied to the AMD PDUs. AMD PDUs are submitted through logical channels to the lower layers .

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MAC Modes

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Documents

UMTS Protocols 2