2.ran interface & protocols

1 NOKIA 2001 RAN Interfaces & Protocols.ppt / 051001 / RNC PCT

RAN Interfaces & Protocols

At the end of this module you will be able to:

List and describe briefly the different interfaces in the RAN

Describe briefly how ATM is used in the RAN

List the different protocols involved in the RAN interfaces


UTRAN Elements and Interfaces

UTRAN

Iu

Uu

User Equipment(UE)

IurIub

RNC

WCDMA BTS

WCDMA BTS

WCDMA BTS

WCDMA BTS

RNC

Core Network (CN)

The UTRAN is a conceptual term identifying the part of the network that consists of RNCs and WBTSes (Node B) and that is located between Iu interface and air interface (Uu). The main purpose of the UTRAN is to separate from the Core Network the radio interface technology (WCDMA) and procedures (e.g. handovers, channel coding, radio resource handling, error detection).

Iub interfaceConnecting the WBTS to the RNC, it should be a fully open interface (Nokia proprietary at the moment). It contains both packet and circuit switched traffic as well as control signalling for the WBTS and user equipment (UE). Control information includes power control, handover commands, radio access parameters, etc.

Uu interface This is the traditional 'air' interface of GSM, however very few similarities exist since, instead of TDMA to access the interface using a variety of frequencies and timeslots, we now use CDMA which allocates different codes to individual users.

Iur interfaceIt lies between RNCs and supplies functionality such as: basic inter-RNC mobility, sharing of dedicated traffic channels between two RNCs, support of common channel traffic between RNCs. It's an open interface.

Iu interfaceIt is an ATM based interface between CN and RNC and it is divided into two separate functional parts to support Circuit Switched (Iu-CS) and Packet Switched (Iu-PS) services.

A detailed explanation of the protocols and the procedures for each interface is provided in the following pages.


Air Interface Protocols

RRCRRC

ControlPlane

UE WBTS

RLC

SRNC

MAC

FPFPWCDMA L1

RLC

WCDMA L1

MAC

FP

DRNC

Transport and transmission layer


Transport and transmission layers

UserPlane

PDCP

NRT & RTRT

UE WBTS

RLC

SRNC

MAC

FPFPWCDMA L1

RLC

WCDMA L1

MAC

FP

DRNC



Transport and transmission layers

PDCP

NRT & RTRT

Packet Data Convergence Protocol (PDCP) Header compression and decompression of IP data streams (e.g., TCP/IP and RTP/UDP/IP headers)

at the transmitting and receiving entity, respectively. The header compression method is specific to the particular network layer, transport layer or upper layer protocol combinations e.g. TCP/IP and RTP/UDP/IP. PDCP layer shall be able to support several header compression algorithms and it shall always be possible to extend the list of supported algorithms in the future.

Transfer of user data. Transmission of user data means that PDCP receives PDCP-SDU from the NAS and forwards it to the RLC layer and vice versa.

Provide the PDCP SDU Sequence Numbering to guarantee lossless SRNS relocation. Multiplexing of different RBs onto the same RLC entity. Multiplexing is not part of release `99

but will be included in release 2000.

Radio Link Control (RLC) functions Segmentation/reassembly of higher layer PDUs into/from smaller RLC payload units. Concatenation. Padding (when concatenation is not possible). Transfer of user data (acknowledged, unacknowledged and transparent data transfer). Error correction (retransmission in acknowledged mode). In-sequence delivery of higher layer PDUs. Duplicate detection. Flow Control. Ciphering (for acknowledged and unacknowledged modes).

Medium Access Control (MAC) functions Mapping of logical channels onto appropriate transport channels. Selection of the appropriate Transport Format (from TFCS) for each transport channel, depending

on the instantaneous source rate. Priority handling between data flows of one UE. Priority handling between UEs by means of dynamic scheduling. Identification of UE on common transport channels (RNTI). Multiplexing/demultiplexing of higher layer PDUs into/from transport blocks delivered to/from

the physical layer on common and dedicated transport channels. Traffic volume monitoring. Dynamic Transport Channel type switching. Ciphering (for transparent RLC mode only). Access Service class selection for RACH transmission.

Frame Protocol (FP) layer Iub/Iur user plane protocol on top of AAL2 which is used to transfer user data, plus the necessary

control information, between the SRNC and WBTS/DRNC Payload contains the data (transport blocks) Header/trailer contains control information used, for example, for synchronisation, power

control, CRC check, Quality Estimates, etc.


Logical and Transport Channels

Logical Channels

Transport Channels

Uplink Downlink

CCCH DTCH/DCCH BCCH PCCH CCCH CTCH DTCH/DCCH

RACH CPCH DCH BCH PCH FACH DSCH DCH

Logical Channels: they are provided for data transfer services above MAC. Each logical channel is defined by what type of information is transferred.

Control Channels are used for transfer of control information only Broadcast Control Channel (BCCH): DL channels for broadcasting system information. Paging Control Channel (PCCH): DL channel that transfer paging information. Common Control Channel (CCCH): bi-directional channel for transmitting control

information between network and Ues (commonly used by Ues with no RRC connection and by Ues using common transport channels when accessing a new cell after cell reselection).

Dedicated Control Channel (DCCH): a point to point bi-directional channel that transmits dedicated control information between a UE and the network (established at RRC connection setup procedure)

Traffic Channels are used for transfer of user plane information only. Dedicated Traffic Channel (DTCH): point to point channel, dedicated to one UE, for the

transfer of user information. Common Traffic Channel (CTCH): point to multipoint unidirectional channel for transfer of

dedicated user information for all or a group of specified UEs.

Transport Channels: the data transport services are provided to the higher layers as transport channels (TrCH's). They carry user data or higher layer maintenance data between the higher layer entities. The transport channel data is handled in transport blocks (TB's). TB's are delivered to L1 periodically and this period is known as the transmission time interval (TTI). It may be 1, 2, 4, or 8 times the frame duration, i.e. 10, 20, 40, or 80 ms. Several transport blocks can be transferred over a single transport channel during one TTI. These blocks are multiplexed by the physical layer for transmission but are handled separately for error detection during the transmission. This kind of multiplexing is usual in data communications applications where the transport block size (higher layer packet size) is fraction of the transport channel capacity.

BCH is used to broadcast the system information over each cell. From that information the UE can obtain all required network dependent parameters it needs to setup and maintain a radio link. Also the identity of the network and information that make it possible to find other cells belonging to the same network are broadcast on this channel in form of system information blocks [TS 25.331].

CPCH is used to transfer instantaneously possibly large amounts of data in up-link (from the user equipment (UE) to the network. This kind of situation occurs mainly in connectionless packet communication, e.g. when transmitting a multimedia message, a multimedia service equivalent of a short message service (SMS) extending the SMS to transfer of still images and short audio and video clips.

DCH is the main means of communicating the user data between the UE and the network. A dedicated channel is allocated e.g. for the duration of speech call or a connected packet data link. The QoS of the transport over DCH will be guaranteed (if possible at all) so that the time delays are acceptable and needed transport capacity is available to the UE during the DCH connection.

DSCH is a shared channel used to carry dedicated control or user data from the network to the UE. DSCH is always associated with a DCH link and is mainly used to balance the peak transport needs in downlink between several users. Sharing of DSCH is done in frame-by-frame basis and transport of DSCH data directed to a particular user is indicated in the dedicated physical control channel (see below).

FACH is used to transfer relatively small amounts of data to the UE. Such data is e.g. reply to random access communication over RACH when establishing a radio link or when transferring small user or control messages to the UE.

PCH is used to send periodically to the UE's paging and notification data. It is suggested that PCH could be used to notify e.g. about changes in network data broadcast over BCH, so that the UE does not need to monitor the BCH continuously. This kind of procedure allows for the UE to stay in sleep for a larger part of the time thus conserving power and extending the stand-by time.

RACH is used by the UE to hail the network when it needs to setup a communication link. It may also be used to send small amounts of control data or non time critical user data, such as traditional short messages.

More on the use of the transport channels can be found in e.g. MAC specification [TS 25.321].


Transport vs. Physical Channels

Dedicated channels

Dedicated channels

Common channels

Common channelsCPICH

P-CCPCHPSCHSSCH

S-CCPCH

AP- AICH

AICH

PICH

CD/CA-ICH

CSICH

PDSCH

DPCCH DPDCH

DPDCHDPCCH

PRACH

PCPCH

BCH

PCH, FACH

DCH

DCH

RACH

CPCH

DSCH

AICH is used by the WBTS to indicate that it has heard the RACH access preamble, a code used by the UE to hail the network. After positive acknowledge of the access preamble the UE will transport the data over the RACH.

AP-AICH is used by the WBTS to indicate that it has heard the CPCH access preamble. The indication may be positive, in which case the UE can initiate further preparations for using the CPCH, or negative in which case the UE aborts the transmission procedure.

CD/CA-ICH is used by the network to indicate CPCH resource assignment to the UE after acknowledging the initial access by the UE.

CPICH is used to by each WBTS to broadcast a pilot signal that can be used for exact chip synchronization and sounding of the radio channel. Based on the common pilot sequence timing and correlation properties it is possible to adjust the UE receiver so that best possible reception can be achieved.

CSICH is used by the WBTS to broadcast the status information concerning the CPCH. DPCCH is used to carry dedicated control information concerning a dedicated physical channel (DPCH)

which consists of DPCCH paired with DPDCH. The control information includes pilot symbols that can be used to optimize reception of DPCH, indication of the transport formats used in the DCH multiplexing and DSCH, and fast power and antenna diversity control information.

DPDCH is the channel most commonly used to carry the user data, especially when a higher QoS is needed. E.g. speech call always uses DPCH's that are mapped to a DPDCH.

PCCPCH carries the BCH. PCPCH is used by the UE for the CPCH related negotiations and data transmission. PDSCH is used to carry the DSCH and its operation is indicated to the UE by transport format

information in DPCCH. PICH carries periodically the paging indicators. When the UE detects these indicators it knows to listen

to the SCCPCH that is used to broadcast paging information. Since the paging is periodical with known period and paging indicators last only a short time the UE can spend a large amount of idle time in sleep and does not need to keep the receiver on during that time.

PRACH is used by the UE for the RACH preamble and data transmissions. SCCPCH is used by the network to transmit paging on PCH and small amount of dedicated user

oriented control or service data on FACH. SCH is time multiplexed with PCCPCH and carries synchronization signals that can be used by the UE to

acquire slot and frame synchronization and assist in finding the primary scrambling code used by the WBTS. The SCH transmission carries both primary search code (PSC) used to detect the existence of the BS and its chip and slot timing, and the secondary search code (SCH) used to detect the frame timing and the scrambling code class the primary scrambling code belongs to.

The physical channels are described in detail in [TS 25.211]. For details of the random access procedures on RACH and CPCH see [TS 25.214].


General Protocol Modelfor UTRAN Terrestrial Interfaces

TransportNetworkLayer

RadioNetworkLayer

ALCAP(s)

Signalling Bearer(s)

User PlaneControl Plane

TransportNetwork

Control Plane

Physical Transmission layer

Data Stream(s)

Data Bearer(s)

Application Protocol

Signalling Bearer(s)

TransportNetwork

User Plane

TransportNetwork

User Plane

The protocol structures of UTRAN terrestrial interfaces (Iu, Iur, Iub) are designed according to the same general protocol model. The structure is based on the principle that layers and planes are logically independent of each other and, if needed, parts of the protocol structure may be changed in the future while other parts remain intact.

Horizontal LayersThe protocol structure consists of two main layers, the Radio Network Layer and the Transport Network Layer. All UTRAN related issues are visible only in the Radio Network Layer. The Transport Network Layer represents standard transport technology that is selected to be used for UTRAN but without any UTRAN specific changes.

Vertical Planes Control Plane

The Control Plane is used for all UMTS specific control signalling. It includes the Application Protocol (i.e. RANAP in Iu, RNSAP in Iur, NBAP in Iub) and the Signalling Bearer needed to transfer the Application Protocol messages.The Application Protocol is used, among other things, for setting up bearers to the UE. The Signalling Bearer for the Application Protocol is always setup by O&M actions.

User PlaneAll information sent and received by the user, such as coded voice in a voice call or the packets in an internet connection, are transported via User Plane. Non-Access Stratum signalling (e.g. Connection Management, Session Management, Mobility Management) is also sent via User Plane, because it is included in RRC messages.The User Plane includes the Data Stream(s), and the Data Bearer(s) for the Data Stream(s). Each Data Stream is characterised by one or more Frame Protocols specified for the interface.

Transport Network Control PlaneThe Transport Network Control Plane is used for all control signalling within the Transport Network Layer. It includes the ALCAP protocol (that is needed to setup the Data Bearers for the User Plane) and the Signalling Bearer needed for the ALCAP.ALCAP (Access Link Control Application Part) protocol is the generic name for the transport signalling protocols used to setup and tear-down transport bearers.The introduction of the Transport Network Control Plane makes it possible for the Application Protocol in the Control Plane to be completely independent of the technology selected for the Data Bearer in the User Plane.When the Transport Network Control Plane is used, the transport bearers in the User Plane are setup in the following fashion:

First there is a signalling transaction by the Application Protocol in the Control Plane.

This transaction triggers the setup of the Data Bearer by the ALCAP protocol that is specific for the User Plane technology.

The independence of the Control Plane and the User Plane assumes that an ALCAP signalling transaction takes place. It should be noted that ALCAP may not be used for all types of Data Bearers. If there is no ALCAP signalling transaction, the Transport Network Control Plane is not needed at all. This is the case when pre-configured Data Bearers are used.The Signalling Bearer for ALCAP is always setup by O&M actions.

Transport Network User PlaneThe Data Bearer(s) in the User Plane and the Signalling Bearer(s) for the Application Protocol belong also to the Transport Network User Plane. As described in the previous section, the Data Bearers in the Transport Network User Plane are directly controlled by the Transport Network Control Plane, but the control actions required for setting up the Signalling Bearer(s) for the Application Protocol are considered O&M actions.


UserPlane

ATM

PDH / SDH

Microwave, fiber, copper

Physical Media layer

Transport layer


ATM

PDH / SDH

Microwave, fiber, copper

WBTS RNC

AAL5

AAL2

Interfaces E1, STM-1, Flexbus

Microwave

Fiber

Copper

ControlPlane

ControlPlane

UserPlane

Iub Transport Network Layer


48 bytes

5 bytes

HEADER PAYLOAD

ATM cell (53 bytes)

Transmission path

Virtual Path (VP)

Virtual Channel (VC)ATM Cell

ATM Layer

ATM in Brief

HEADER

PAYLOAD

ATM (Asynchronous Transfer Mode) is a cell-switched data communications method. It uses packets with a fixed length of 53 bytes (called cells) to transmit both user and signalling information. This means that it is distinctly different from packet-switched systems such as X.25 or Frame Relay, which make use of data packets of varying lengths. The cells are time-related and thus form a continuous data stream. Being fixed length also allows the information to be transported in a predictable manner. This predictability accommodates different traffic types on the same network.

Compared with synchronous procedures that have a fixed assignment of timeslots, the ATM cells used by a particular terminal equipment do not have a fixed position in the cell stream. The bandwidth requirements of the source are met by using a corresponding number of cells per unit time.

The cell is broken into two main sections, the header and the payload. The Header (5 bytes) is the addressing mechanism. The payload (48 bytes) is the portion that carries the actual information (either voice, data, or video).

ATM has a layered architecture. Three lower level layers have been defined: Physical layer, ATM layer and Adaptation layer.

The Physical layer defines the electrical characteristics and network interfaces. This layer "puts the bits on the wire. ATM is not tied to a specific type of physical transport.

The ATM layer takes the data to be sent and adds the 5 byte header information that assures the cell is sent on the right connection.

The ATM adaptation layer, as its name suggests, adapts the data of higher layers to the format of the information field of the ATM cell. This takes place as determined by the services being used. The AAL also reconstructs the original data stream from the information fields and equalizes out variations in cell delay. Matching of protocols for the superior layers also takes place in this layer.To be able to meet the various requirements that data communications demands, four service classes were created. In turn, these classes are assigned to various service types.Four service types exist, namely: AAL1, AAL2, AAL3/4 and AAL5.The AAL is divided into two sublayers, the convergence sublayer (CS) and the segmentation and reassembly sublayer (SAR). The CS takes care of such functions as identifying messages and regenerating timing or clock information; these functions will vary depending on the service selected. The SAR sub-layer divides or segments the data from higher layers to fit into the information field of the cells, and reassembles the data on the receive side to form the original data.


String of AAL2 Packet Data Units String of AAL2 Packet Data Units

31 2 3 1 2

AAL2 header

ATM cell payloadATM cell

3ATM CELLHEADERATM CELLHEADER1 2 3 1 1 2

OFFSET FIELD, 1-byte (indicates where the next AAL2 PDU starts)

AAL2 PACKET, 3-byte fixed header, variable length payload (packet size up to 48 bytes or fixed 67 bytes)

ATM CELL, 5-byte header + 48-byte payload

PADDING

AAL2e.g., 3 different users

AAL2 provides for the bandwidth-efficient transmission of low rate, short and variable packets in delay sensitive applications. It enables support for both Variable-Bit-Rate (VBR) and Constant-Bit-Rate (CBR) applications within an ATM network. VBR services enable statistical multiplexing for the higher layer requirements demanded by voice applications, such as compression, silence detection/suppression and idle channel removal. AAL2s VBR and CBR capabilities mean that network administrators can take traffic variations into account when designing an ATM network and optimise the network to match traffic conditions.

In addition, AAL2 enables multiple user channels on a single ATM virtual circuit and varying traffic conditions for each individual user, or channel. The structure of AAL2 also provides for the packing of short length packets into one (or more) ATM cells, and the mechanisms to recover from transmission errors. In contrast to AAL1, which has a fixed payload, AAL2 offers a variable payload within cells and across cells.

The ITU specification that describes this is ITU-T I.363.2.


PADDING FIELD, variable length to fill the 48-byte ATM cell

AAL5 PACKET, 5-byte fixed header, variable length payload, 8-byte trailer

ATM CELL, 5-byte header + 48-byte payload

USER DATA = Variable length 1-65535 bytes USER DATA = Variable length 1-65535 bytes

AAL5 Packet Data Unit AAL5 Packet Data Unit

ATM cell 1 ATM cell 2 ATM cell n

AAL5AAL5 trailer

AAL5, also known as Simple and Efficient Adaptation Layer (SEAL), has been adopted as a method of connecting data oriented systems. AAL5 has support for large datagrams of up to 64K octets. It also has 10% less overhead and better error detection than AAL3/4.


ATM over E1

Header Payload

ATM cell

0 1 2 16 1817 3115

TS0TS1-15

TS16TS17-31

. . . . . . 0 1 2 16 1817 3115

TS0TS1-15

TS16TS17-31

. . . . . .

E1 frameE1 frame

When transmitting ATM cells over a digital interface like E1, we map the cells into the physical layer frame. ITU-T Recommendation G.804 and ATM Forum specification af-phy-0064.000 define this ATM direct mapping (ADM) process. ADM uses the header error check (HEC) field in the cell header to identify the first bit of a cell in an E1 frame. A receiving E1 IMA interface examines the incoming bit stream and checks if a set of eight bits comprises a valid CRC for the preceding 32 bits.

The alternative to ADM is the physical layer convergence protocol (PLCP). PLCP uses special overhead bytes to delineate the start and end of the ATM cells inside the E1 frame and thus reduces the effective payload rate. Since PLCP adds overhead, ADM replaces PLCP.


ATM over SDH

STM-1 (155,52 Mbps) can fit 44.15 cells per frame -> 353 207 cells per second.

VC-4

VP1

VP2

VP3

Section

Overhead ...

260 bytes

9 bytesP

O

H

9 bytes

1 byte

VC-4


Protocol Structure for Iub


RadioNetworkLayer

Q.2630.1

NBAP

AAL2

Transport NetworkUser Plane

ATM

Transport NetworkControl Plane


AAL5

SSCF-UNISSCOP

AAL5

Q.2150.2SSCF-UNI

SSCOP

DCH FP

RACH FP

FACH FP

PCH FP

DSCH FP*



Note that DSCH is not implemented in RAN 1.5; it is a feature candidate for RAN 2.1.

In this case the ALCAP protocol consists of Q.2630.1 and Q.2150.2 protocols. AAL2 signalling capability set 1 (Q.2630.1) protocol provides services for establishing, maintaining and

releasing AAL type 2 point to point data connections between two AAL type 2 end users. The connections can be created across a network that consists of both ATM and AAL type 2 switches. Q.2150.2 is a signalling transport converter. It is needed to adapt the AAL2 signalling protocol to lower layers.

ATM adaptation layer type 2 (AAL type 2) is designed exclusively to serve the needs of wireless applications such as mobile telephony. AAL type 2 allows low bit rate and delay-sensitive applications to share a single ATM connection to maximise the network utilisation. At the same time the protocol also guarantees the delay requirements. Since AAL type 2 enables multiplexing of voice packets from many users on a single ATM connection, it increases the number of mobile telephony users who can be accommodated in a certain fixed bandwidth.

Signalling ATM Adaptation Layer (SAAL)Signalling across ATM networks to establish SVCs is broadly divided into two functional parts:

- signalling between the user equipment and the network at the access- signalling between network elements within a network

The former is called the User Network Interface (UNI) while the latter is called Network Node Interface or Network-Network Interface (NNI).SAAL consists of SSCF, SSCOP and AAL5 protocols.

Service Specific Coordination Function (SSCF): this layer sits above the SSCOP layer. It provides a mapping between the SSCOP capabilities and the needs of the signalling protocol module (in this case NBAP). There is an SSCF defined for UNI and an SSCF defined for NNI, since the needs of the signalling protocol module are different at the two interfaces.SSCF at UNI: this is a very simple SSCF since it provides a restricted subset of SSCOP functions to the UNI signalling layer 3. It is defined in ITU-T Recommendation Q.2130. In addition to being used at the UNI, it is also specified to be used at the P-NNI interface, as P-NNI uses an extension of UNI signalling.

Service Specific Connection Oriented Protocol (SSCOP): SSCOP - Defined in ITU Q.2110, "B-ISDN SAAL Service-Specific Connection-Oriented Protocol" the Service Specific Connection Oriented Protocol is responsible for providing mechanisms for the establishment, release and monitoring of signaling information exchanged between peer signaling entities. SSCOP provides many of the same services for Q.2931 signalling that TCP provides for IP. Some of these services are:

Flow control. A switch or end system can control the rate at which it receives signallingmessages

Error handling and sequencing. Since each SSCOP PDU contains a sequence number, SSCOP can determine if one has been lost and request retransmission. SSCOP can also ensure sequential integrity by using these sequence numbers.

Connection establishment and resynchronization. Involves negotiation of buffer sizes and other transfer characteristics and renegotiation of these parameters should a connection fail.

Polling and status exchange. The health of a connection is monitored via exchange of status messages and connections are maintained through use of keep alive messages.


Iub: Common NBAP procedures

Radio Link Setup WBTS Logical Resource Management

Information Broadcasting WBTS configuration WBTS capability query Operational state query

Channel handling Common channel power control RACH Setup, Release and Reconfiguration FACH/PCH Setup, Release and Reconfiguration DSCH Control Channel Setup (feature candidate for RAN 2.1)

Fault Management RNC Restarted Indication Traffic termination point failure notification Error Indication

Common NBAP (C-NBAP) procedures are used for signalling that is not related to one specific UE context already existing in the WBTS. In particular, the C-NBAP defines all the procedures for the logical O&M of the WBTS, such as configuration and fault management.

Radio Link setupWhen controlling RNC makes the decision to add a cell to the active set of a specific RRC connection, the Radio Link Setup Request message is sent to the WBTS. One Radio Link setup Request message can be used to setup simultaneously several radio links.After receiving Radio Link Setup Complete message from the WBTS, the RNC informs the UE about radio link parameters with a RRC message.

WBTS logical resource management Information Broadcasting: RNC tells the WBTS to start or stop the BCCH transmission. This is

considered to be a mean to administratively control the cell state (more in RAN Functionality).

WBTS configuration: used by RNC to update WBTS configuration when radio network parameters are changed or the configuration is requested by the WBTS.Here are listed some of the parameters: NBAP version number; radio resource indication control parameters; load measurement control parameters; number of cells; cell configuration parameters (cell radius, primary scrambling code); power control parameters (e.g. common channels transmission power); load threshold parameters; radio link measurement parameters.

WBTS capability query: used by RNC to query WBTS capability (NBAP, CCH FP, DCH FP version numbers; WBTS feature set version number; WBTS HW capabilities; number of cells).

Operational state query: used by RNC to ask the WBTS to send updated information on the current operational status information of each cell.

Channel handling Common channel power control: used by RNC to change the size of a cell. Allocation and management of WBTS resources for RACH, FACH, PCH, (DSCH; feature

candidate RAN 2.1) transport channels. Fault management

RNC Restarted Indication: it is used to inform the WBTS that RNC has lost the AAL2 connection, radio link or cell information of the WBTS.

Traffic termination point failure notification: it is used either by WBTS or RNC to inform the peer about a failure in a traffic termination point.

Error Indication: it is initiated by a node (RNC or WBTS) to report detected errors in an incoming message, provided they cannot be reported by an appropriate failure message.


Iub: Dedicated NBAP procedures

Radio link addition, reconfiguration and deletion Power Balancing (feature candidate for RAN 2.1) Compressed Mode Control Error Indication

When RNC requests the first radio link for one UE using the C-NBAP RADIO LINK SETUP procedure, the WBTS assigns a traffic termination point for the handling of this UE context. Every subsequent signalling related to this mobile is exchanged with dedicated NBAP (D-NBAP) procedures across the dedicated control port of the given traffic termination point.

Radio link addition, reconfiguration and deletion Radio link addition: used for adding radio links for an UE, which already has a radio link. Radio link reconfiguration: a RB setup, renegotiation, release or NRT RB scheduling may

require modification of the L1 parameters of an existing radio link. Radio link deletion: used by the RNC to release one or several radio links.

Power Balancing (feature candidate for RAN 2.1) It is used to control that base stations have the same and minimised transmission power

when one UE communicates with them simultaneously. With this procedure the RNC updates the DL power reference level of the radio link, level that

is initially set in the radio link setup phase. Compressed Mode Control

The compressed mode is needed when making measurements on another frequency in a CDMA system without a full dual receiver terminal.

Transmission and reception are halted for a short time in order to perform the measurements.


Protocol Structure for Iur


RadioNetworkLayer

Q.2630.1

RNSAP

ATM



AAL5

SCCPMTP3b

SSCF-NNISSCOP

AAL5

Q.2150.1MTP3b

SSCF-NNISSCOP




AAL2

DCH FP

RACH FP

FACH FP

PCH FP

DSCH FP*

Note that DSCH is not implemented in RAN 1.5; it is a feature candidate for RAN 2.1.

Q.2150.1 is used to adapt AAL2 signalling protocol to the MTP3b protocol. SCCP: the Signalling Connection Control Part provides other applications two different services,

connection-oriented and connectionless services. The SCCP itself uses the MTP as a service. The connection-oriented service is used for virtual connections between network elements, and it provides the procedures for establishment and release of those virtual connections. The connectionless service enables non-call-related communication between network elements which have to exchange information only for short periods.

MTP3b (Message Transfer Part Level 3 broadband) can be divided into two parts: message handling, which includes message routing and distribution to the respective user part and network management, which provides all necessary procedures for using the signalling network in an optimal way.

SAAL NNI Signalling ATM Adaptation Layer, Network Node Interface (NNI) consists of protocol stacks SSCF-NNI (service specific coordination function NNI), SSCOP (service specific connection oriented protocol) and AAL5 (ATM adaptation layer 5).SSCF at NNI: this SSCF performs a coordination function between the service required by the SAAL user at the NNI (MTP3b) and the service provided by SSCOP. It provides additional services such as link error monitoring and SDU retrieval when a link fails so these can be retransmitted over another link. This SSCF allows an ATM link to be seamlessly incorporated into an existing SS7 stack employing MTP3b as its network layer.


Iur: RNSAP procedures Basic Mobility Management procedures

UL/DL signalling transfer Relocation execution Paging

DCH procedures Radio link management Physical channel reconfiguration Measurements on dedicated resources Compressed mode control Power Balancing (feature candidate for RAN 2.1)

Common Transport Channel procedures Common transport channel initialisation/release

Global Procedures Error indication

Basic Mobility Management proceduresThe first brick for the construction of Iur interface provides by itself the functionality needed for mobility of user between two RNCs, but does not support the exchange of any user data. If this module is not implemented, the Iur interface as such does not exist, and the only way for a user connected to UTRAN via RNC1 to utilise a cell controlled by the RNC2 is to release the RRC connection and set up a new one.

DCH proceduresThis functionality allows the dedicated channel traffic between two RNCs.

Establishment, modification and release of radio links in DRNC due to hard and soft handover in CELL_DCH state.

Setup and release of dedicated transport connections across the Iur interface. Management of radio links in the DRNC cells, via dedicated measurement report procedures and

power setting procedures. Common Transport Channel procedures

This functionality allows handling of common and shared channel data streams across Iur interface. If it is not implemented, every inter-RNC cell update triggers a SRNC relocation, i.e. the SRNC is always the RNC controlling the cell used for common or shared channel transport.

Global proceduresThese procedures are not related to a specific UE.

Error indication allows reporting of general error situations, for which function specific error messages have not been defined.


Protocol Structure for Iu-CS


RadioNetworkLayer

Q.2630.1

RANAP Iu User Plane Protocol

AAL2

ATM

Control Plane


User Plane


AAL5

SCCPMTP3b

SSCF-NNISSCOP

AAL5

Q.2150.1MTP3b

SSCF-NNISSCOP



Iu User Plane ProtocolWhen UMTS Radio Access Network is used with a 2G-MSC (UMTS Release '99) the Iu-interface is terminated in Multimedia Gateway. Multimedia Gateway provides the necessary interworking functions between the RNC and the MSC.In UMTS Release '99 standards, the Circuit Switched Iu interface (Iu-CS) is based on Asynchronous Transfer Mode (ATM) technology. However, the Iu UP protocol has been defined to be independent of the Core Network domain transport technology.Two operating modes are defined for Iu UP, that is transparent mode and support mode for predefined SDU size (TrM and SMpSDU, respectively). The transparent mode provides only transparent user data transfer, and no other Iu protocol services. The support mode is intended to transfer for example speech data for the Adaptive Multi-Rate (AMR) speech codec. It also provides, in addition to the user data transfer, several protocol procedures:

Initialisation Rate control Time alignment Error event handling

The time alignment procedure is left for further study, and therefore has not been implemented.Several versions of the Iu UP protocol may co-exist and support for protocol version negotiation procedures are implemented for support mode.


Protocol Structure for Iu-PS


RadioNetworkLayer RANAP

Iu User Plane Protocol

(transparent mode)

ATM



AAL5

SCCPMTP3b

SSCF-NNISSCOP

AAL5

GTP-UUDPIP




LLC/SNAP

The Transport Network Control Plane is not applied to Iu-PS. Setting up of GTP tunnel requires only an identifier for the tunnel and the IP addresses for both directions, and these are already included in the RANAP message RAB Assignment Request.Iu-PS interface provides the UEs packet switched (PS) data service from the public data networks (PDN). One RNC is connected via Iu-PS interface to only one SGSN (at least in R99) but on the other hand one SGSN can have several RNCs under it's control. Generally speaking, the most central issues in RNC packet data handling are:

On the radio interface side (UE RNC) the segmentation/reassembly (RLC) of the user data packets with possible compression/decompression (PDCP) of their headers.

On the core network side (RNC SGSN) the specific tunnelling protocol carrying the user data packets (GTP over UDP/IP).

GTP tunnelling enables multiplexing of user data traffic into a single IP address over the Iu-PS. Tunnelling enables also transparent transferring of multiprotocol user data across the Iu-PS, so that Iu-PS does not have to support several network layer protocols. IP is enough at the Iu-PS and still the users may utilise various network layer protocols (IPv4, IPv6, PPP, OSP etc).For example, in packet data delivery from Public Data Network to UE (downlink) the RNC:

Maps the incoming GTP-packet to the right radio bearer. Strips away the Iu-PS level IP/UDP/GTP layer headers. Performs buffering and header compression (PDCP) to the remaining user data packet (T-PDU). Sends the user data packet (having now compressed header) through RLC, MAC etc layers

towards the radio interface and UE.


Iu: RANAP procedures Radio Access Bearer handling

Iu Release

Serving RNC relocation

Paging

Common ID

Trace Invocation

Security Mode Control

Location Reporting

Data Volume Reporting

Initial UE message

Direct Transfer

CN Information Broadcast

Overload

Reset

Error Indication

Support for Volume Based Charging

Radio Access Bearer (UE-CN bearer) handling: RAB setup (including queuing), RAB modification and RAB release (including RAN initiated case).

Iu release: releases all Iu resources (signalling link and user plane) related to the specified UE. Includes RAN initiated case.

Serving RNC relocation: handling of both SRNC relocation (UE already in target RNC; data transfer via Iur) and Hard Handover (simultaneous switch of Radio and Iu). Includes lossless relocation and Inter-System Handover.

Paging: CN to page an UE for a terminating call/connection. Common ID: UE NAS identity (e.g. IMSI) sent to RNC for paging coordination. Trace invocation: CN may request UTRAN to start/stop tracing a specific UE. Security Mode Control: controls ciphering and integrity checking (see RAN Functionality). Location Reporting: CN can request the RNC to report the location of a specific UE. Data Volume Reporting: CN can request RNC to report unsuccessfully transmitted DL data. Initial UE message: carries the first radio interface L3 message to the CN and sets p the Iu signalling

connection. Direct Transfer: carries CN and UE signalling information over Iu (content not interpreted by UTRAN). CN information broadcast: allows CN to set CN system information (NAS) to be broadcast to all users. Overload: used for flow control (to reduce flow) over the iu interface e.g. due to processor overload at

CN or UTRAN. Reset: it is used to reset the CN or the UTRAN side of Iu interface in error situations (includes resetting

the signalling connection). Error Indication: used for protocol errors where no other error applies.

Support for Volume Based Charging: Packet switched data can be charged according to the amount of data bytes sent by the 3G-SGSN towards RNC. However, it is possible that data is lost on the way to UE and the subscriber is overcharged. Possible causes for data loss include repetitious unsuccessful retransmissions of data over the air interface and processing overload at the RNC. In both cases, data packets sent to RNC by 3G-SGSN are discarded from the downlink transmission buffer at RNC, thus resulting in overcharging.Volume based charging adds a new feature by which RNC is able to inform 3G-SGSN about non-delivered downlink data. Upon RAB release, the RNC indicates the unsuccessfully transmitted DL data volume per Radio Access Bearer to the 3G-SGSN so that it can correct its data volume counters.


Protocol Structure for Iu-BC


RadioNetworkLayer SABP

ATM

AAL5

TCPIP

Control Plane


LLC/SNAP


Service Area Broadcast: The WCDMA Service Area Broadcast (SAB) known also as Cell Broadcast Service (CBS) is a teleservice, which enables information provider to submit short messages for broadcasting to a specified area within the PLMN. These messages could be used for informing of, for example, PLMN news, emergencies, traffic reports, road accidents, delayed trains, weather reports, theatre programmes, telephone numbers or tariffs.CBS messages will be broadcasted to all receivers within a particular region. Defined geographical areas are known as Service Areas. Radio Network Controller can be interfaced to one or more, max.4, Cell Broadcast Center.The basic network structure in the RAN contains the RNC and BTS. The Cell Broadcast Center (CBC) is part of the core network and connected via luBC reference point to the RNC. Service Area Broadcast Protocol (SABP) is used between the CBC and RNC for CBS message transferring. Broadcast/Multicast Control protocol (BMC) is used between the RNC and MS for the message broadcasting on the radio interface.Service Area Broadcast is offered towards the broadcast domain that is logically separate from the IuPS. A new protocol called "Service Area Broadcast Protocol (SABP)" is used to carry control information and broadcast data over the Iu. SABP uses TCP/IP/AAL5/ATM transport.The SAB data uses the CTCH logical channel. At the MAC layer the CTCH is mapped to the FACH transport channel which is broadcast to the whole cell. Information about the scheduling of the SAB data is sent to the UEs in the System Information broadcast in the BCH transport channel.


CS side protocol stack (user plane)

AAL2

PHY

ATM

PHY

ATM

AAL2

FP

PHY

AAL2

PHY

ATM

Link

Layer

PHY

AAL2

PHY

ATM

WCDMAL1

FP

E.g.,

Vocoder

PHY

PSTN/

N-ISDN

MGW

RNC

WBTS

UE

Iu-CS UP

E.g.,

Vocoder

Link

Layer

A/m- law,PCM,etc.

MSC

RLC - U

Iu-CS UP

A/m- law,PCM,etc.

UTRAN Transport Network LayerSDH / PDH

UTRAN Radio Interface Protocols

Transcoding function

MAC

RLC - U

MAC

WCDMA L1

Uu IuIub A E


PS side protocol stack (user plane)

IP

AAL5

PHY

GTP-U

ATM

PHY

ATM

AAL2

FP

PDCP

UDP

IP

Link

Layer

PHY

GTP

UDP

IP

Link

Layer

PHY

GTP

AAL2

PHY

ATM

WCDMAL1

FP

PDCP

E.g.,IPv4, IPv6

PHY

Uu

GGSN

3G-SGSNRNC

WBTS

UE

RLC-U

MAC

RLC-U

MAC

AAL5

PHY

GTP-U

ATM

LLC/SNAP

UDP

E.g., IPv4, IPv6

IP

LLC/SNAP

TF scheduling and Logical Channel

multiplexing

Segmentation and reassembly (UM/AM)

Header compression(no payload compression)

UDP

Header for packet directing(UP only, RANAP otherwise)

Application

WCDMAL1

TCP

Iub Iu Gn Gi

Length of the GTP header is normally 8 or 12 octets (12 used here) and let the backbone MTU be 1500 octets (GTP tunneled user data + GTP header + UDP header + IPv4 header).Overhead caused by e.g. SDH framing (10/270) below the ATM is not considered. Thus:

Maximum size AAL5 PDU is 1508 octets + trailer 8 octets + padding 20 octets i.e. 1536 octets which will be transferred in 32 ATM cells i.e. 1696 octets altogether.

Maximum size user application PDU is 1500-20-8-12-40-20 octets i.e. 1400 octets. Max user application payload ratio is then 1400/1696 = 83 %.

Medium size 500 octets tunneled user data packet means that application PDU is 440 octets and AAL5 PDU is then 500+12+8+20+8+8+20 (padding) octets i.e. 576 octets which will be transferred in 12 ATM cells i.e. 636 octets altogether. User application payload ratio is then in this case 440/636 = 69 %.

Minimum size Iu-packet carrying application PDU of 1-28 octets is 3 ATM cells i.e. 144+(3x5) = 159 octets altogether.

If user data header compression in PDCP is used, it would decrease the T-PDU size, but only beyond/below the PDCP, not on the Iu-PS.

LLC/SNAP-H8 octets

IPv4-H20 octets

UDP-H8 octets

GTP-H8-12 octets

IPv6-H40 octets

TCP-H20 octets

ApplicationE.g. TELNET

Padding + AAL5-trailerAAL5 SDU

GTP Tunneled User Data

ATM H ATM cell payload ATM H ATM cell payload ATM H ATM cell payload

RAN Interfaces & ProtocolsUTRAN Elements and InterfacesAir Interface ProtocolsLogical and Transport ChannelsTransport vs. Physical ChannelsGeneral Protocol Modelfor UTRAN Terrestrial InterfacesIub Transport Network LayerATM in BriefAAL2AAL5ATM over E1ATM over SDHProtocol Structure for IubIub: Common NBAP proceduresIub: Dedicated NBAP proceduresProtocol Structure for IurIur: RNSAP proceduresProtocol Structure for Iu-CSProtocol Structure for Iu-PSIu: RANAP proceduresProtocol Structure for Iu-BCCS side protocol stack (user plane)PS side protocol stack (user plane)

2.ran interface & protocols

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