WCDMA RAN Interface Specifications

RNC3005-2.0 Nokia WCDMA RNC, RN2.0 v.2, Product Documentation

WCDMA RAN Interface Specifications

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The information in this document is subject to change without notice and describes only the product defined in the introduction of this documentation. This document is intended for the use of Nokia's customers only for the purposes of the agreement under which the document is submitted, and no part of it may be reproduced or transmitted in any form or means without the prior written permission of Nokia. The document has been prepared to be used by professional and properly trained personnel, and the customer assumes full responsibility when using it. Nokia welcomes customer comments as part of the process of continuous development and improvement of the documentation. The information or statements given in this document concerning the suitability, capacity, or performance of the mentioned hardware or software products cannot be considered binding but shall be defined in the agreement made between Nokia and the customer. However, Nokia has made all reasonable efforts to ensure that the instructions contained in the document are adequate and free of material errors and omissions. Nokia will, if necessary, explain issues which may not be covered by the document. Nokia's liability for any errors in the document is limited to the documentary correction of errors. NOKIA WILL NOT BE RESPONSIBLE IN ANY EVENT FOR ERRORS IN THIS DOCUMENT OR FOR ANY DAMAGES, INCIDENTAL OR CONSEQUENTIAL (INCLUDING MONETARY LOSSES), that might arise from the use of this document or the information in it. This document and the product it describes are considered protected by copyright according to the applicable laws. NOKIA logo is a registered trademark of Nokia Corporation. Other product names mentioned in this document may be trademarks of their respective companies, and they are mentioned for identification purposes only. Copyright © Nokia Corporation 2005. All rights reserved.

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Contents

Contents Contents 3 1

Iub interface specification 5

2

Iur interface specification 11

3

Iu interface specification 17

4

Iu-BC interface specification 23 Related Topics 27



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Iub interface specification

1

Iub interface specification The Iub interface is the logical interface between a BTS and an RNC in the radio access network. The RNC is connected to one or many BTSs. The BTS is always connected to one RNC, which is the controlling RNC. The Iub interface allows the RNC and BTS to negotiate about radio resources and to transport uplink and downlink transport frames. The Iub interface telecommunication part between the RNC and BTS is mainly implemented according to the 3GPP functions and features. The common NBAP signalling part of the Iub interface contains the basic functionality of 3GPP interface, and additionally some functions and features not included in the 3GPP specifications.

Note Iub is partly a proprietary interface.

The Iub interface protocol architecture consists of two functional layers:


1.

The radio network layer defines procedures related to the operation of a BTS. The radio network layer consists of a radio network control plane and a radio network user plane.

2.

The transport network layer defines procedures for establishing logical connections by dynamic allocation of fixed physical connections between a BTS and an RNC.


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Radio Network Layer

User Plane

Radio Network Control Plane NBAP

Transport Network Layer

Transport Network Control Plane Q.2630.1 Q.2150.2 SSCF-UNI

SSCF-UNI

SSCOP

SSCOP

AAL5 CP

AAL5 CP

AAL2

ATM Physical Layer

Figure 1.

Iub interface protocol architecture

The main functions of the Iub interface are:

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.

managing Iub transport resources

.

handling logical O&M of BTS

.

transporting O&M data

.

managing system information

.

managing traffic of common channels

.

managing traffic of dedicated channels

.

managing timing and synchronisation




Transport network layer

In the Iub interface, transport is based on ATM. The ATM layer as such is a very simple bit transport media and in theory suitable for transmission purposes. In practise, the ATM layer must be adapted to the higher protocol layers and the lower physical layer. The transport network layer must use different adaptation layers because the services using the transport network layer set different QoS requirements (real time and non-real time) for the connection. Two ATM adaptation layers are located on top of the ATM layer: AAL2 and AAL5. In the transport network layer, additional convergence protocols are needed to support NBAP signalling in the radio network control plane. For this plane SSCF-UNI and SSCOP are required in the transport network layer. They are parts of SSCS of AAL5. In the transport network control plane Q.2630.1 signalling is used for the dynamic management of the AAL2 connections used in the user plane. The signalling transport converter relevant to Iub is Q.2150.2 and its main task is to re-establish a connection if the underlying SSCOP has released the connection for some reason. The AAL5 common part contains CPCS and SAR. O&M data is transported using the protocol stack consisting of PHY/ATM/ AAL5/IPv4. Refer to Administrative interfaces specification. Control plane

The control plane carries signalling maintaining the functions of the service stratum. A signalling protocol called NBAP maintains the control plane. NBAP is a layer 3 protocol in the Iub interface. NBAP functions are divided into two groups: .

common NBAP (C-NBAP) defines the signalling procedures across the common signalling link.

.

dedicated NBAP (D-NBAP) defines the signalling procedures across the dedicated signalling link.

The NBAP signalling connections can all have their own radio network control plane transport bearer.



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Common NBAP

Common NBAP procedures are used for signalling that is not related to a specific user equipment context that already exists in the BTS (except initialising radio link specific measurements). Common NBAP procedures are used for creating new BTS communication contexts, manage logical O&M and control BCCH broadcast information. Common NBAP defines all the procedures for the logical O&M of a BTS, such as configuration and fault management. There is always one signalling connection for common NBAP procedures on the Iub. The main functions of common NBAP: .

setting up the first radio link of a user equipment and selecting the traffic termination point

.

configuring cells

.

handling RACH, FACH and PCH channels

.

initialising radio link specific measurements

.

initialising and reporting cell or BTS specific measurements

.

managing faults

Dedicated NBAP

When the RNC requests the first radio link for a user equipment through a CNBAP radio link setup procedure, the BTS assigns a traffic termination point for handling this user equipment context. From then on every subsequent signalling related to this mobile station is exchanged with dedicated NBAP (D-NBAP) procedures across the dedicated control port of the given traffic termination point. There can be many signalling connections for dedicated NBAP procedures on the Iub. The main functions of dedicated NBAP are:

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.

adding, releasing, and reconfiguring radio links

.

handling dedicated channels

.

reporting radio link specific measurements

.

handling softer combining

.

managing radio link faults




User plane

User plane signalling takes place between the application of a mobile station and the destination over the physical connection established over the transport layer using control plane. The user plane Iub frame protocols (FP) define the structure of the frames and the basic inband control procedures for every type of transport channel. The frame protocols are dedicated protocols that maintain the user information of the common and dedicated radio channels. In other words, they handle the information carried through the DCH data ports. In the Iub interface, every set of coordinated transport channels related to a MS context communicated over a set of cells, that are macro diversity combined within a BTS, are carried on one transport bearer. This means that there are as many transport bearers as sets of coordinated transport channels and Iub user ports for that communication. Common transport channel frame protocol services

Common transport channels are RACH, FACH and PCH. Common transport channel frame protocol provides the following services: .

transporting transport block sets between a BTS and controlling RNC for common transport channels

.

supporting transport channel synchronisation mechanisms

In-sequence delivery of frame protocol PDUs is required from the transport layer. Dedicated transport channel frame protocol services

The dedicated transport channel is DCH. Dedicated transport channel frame protocol provides the following services: .

transporting transport block sets across Iub interface

.

transporting outer loop power control information between serving RNC and BTS

.

supporting transport channel synchronisation mechanisms

In-sequence delivery of frame protocol PDUs is required from the transport layer.



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Iur interface specification

2

Iur interface specification The Iur interface is the logical connection between any two RNCs within a radio access network. The interface allows more independent radio resource management compared to GSM, for example in different handover control cases. The Iur interface supports increased mobility of terminals within the radio access network. Simultaneous mobile station connections between two RNCs are managed by soft handovers. All necessary data from the serving RNC is transferred to the drifting RNC via the Iur interface. The Iur interface is an open and standard interface. Iur is a point-to-point interface between two RNCs. Iur interface allows connections between RNCs supplied by different manufacturers. It also allows continuation of services between radio access networks through the Iu interface. The Iur interface protocol architecture consists of two functional layers:


.

radio network layer

.

transport network layer


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Radio Network Layer


Control Plane

User Plane

RNSAP

DCH Frame Protocol

Transport Network User Plane

Transport Network Control Plane


Q.2630.1 SCCP

Q.2150.1

MTP3b

MTP3b

SSCF-NNI

SSCF-NNI

SSCOP

SSCOP

AAL5

AAL5

AAL2

ATM Physical Layer

Figure 2.

Iur interface protocol architecture

Signalling is used to support mobility of terminals within the radio access network. The user plane data is also carried over Iur when BTSs controlled by the serving RNC and BTSs controlled by the drifting RNC are used simultaneously for the same MS-RAN connection. The main functions of the Iur interface are:

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.

managing transport network

.

managing traffic of dedicated transport channels

.

reporting measurements for dedicated measurement objects





In the Iur interface, the transport is based on ATM. Two ATM adaptation layers are located on top of the ATM layer and they are AAL2 and AAL5. The transport plane must use different adaptation layers because the services using the transport plane set different QoS requirements (real time and non-real time) for the connection. Control plane

Control plane carries signalling that maintains the functions of the service stratum. A signalling protocol called radio network subsystem application protocol (RNSAP) maintains the control plane. To make it suitable for ATM, additional convergence protocols are needed. The main functions of RNSAP are: .

Radio link management allows the SRNC to manage radio links using dedicated resources in a DRNS. Hard handover procedure is not supported.

.

Physical channel reconfiguration allows the DRNC to reallocate the physical channel resources for a radio link.

.

Radio link supervision allows the DRNC to report failures and restorations of a radio link.

.

Compressed mode control (FDD) allows the SRNC to control the usage of compressed mode within a DRNS. Power setting procedure is not supported.

.

Measurement of dedicated resources allows the SRNC to initiate measurements on dedicated resources in the DRNS. This function also allows the DRNC to report the result of the measurements.

RNSAP is divided into modules. Modules follow the main functions of the interface and are the building blocks of the Iur interface. In general, it is possible to use only part of the functions of the modules. The modules are:


.

support for basic inter-RNC mobility

.

support for dedicated transport channel traffic

.

support for global procedures


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Support for basic inter-RNC mobility

This module provides the functions needed for the mobility of the user between two RNCs, but it does not support the exchange of any user data traffic. Because of that, the user plane and transport network control plane protocols are not needed. The support functions of basic inter-RNC mobility module are: .

supporting serving RNC relocation

.

supporting CCCH signalling transfer

Support for dedicated transport channel traffic

This module requires the Dedicated Channel module of RNSAP signalling and allows the dedicated channel traffic between two RNCs. Even if the initial need for this module is to support the inter-RNC soft handover, it also allows the anchoring of the serving RNC for all the time the user is utilising dedicated channels, for as long as the user has an active connection to the circuit-switched domain. This module also requires the user plane frame protocol for the dedicated channel and the transport network control plane protocol Q.2630.1 used for the setup of the transport connections (AAL2). Each dedicated channel is conveyed over one transport connection, except the coordinated DCHs used to obtain unequal error protection in the air interface that are conveyed over the same transport connection. The support functions of the dedicated channel traffic module are:

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.

establishing, modifying and releasing a dedicated channel in a drifting RNC due to hard and soft handover in the dedicated channel state

.

setting up and releasing dedicated transport connections across the Iur interface

.

transferring DCH transport blocks between a serving RNC and a drifting RNC

.

managing radio links in a drifting RNC, via dedicated measurement report procedures and power setting procedures




Support for global procedures

This module contains procedures that are not related to a specific user equipment. The procedures are in contrast to the other modules involving two peer controlling RNCs. Its function is to indicate errors in incoming messages, if there are no other means to report errors. User plane

Frame protocols are dedicated protocols maintaining the user information of the dedicated radio channels. In other words, they handle the information carried through the DCH data ports. The frame protocol for dedicated channels (DCH FP) defines the structure of data frames carrying the user data and the control frames used to exchange measurements and control information. For this reason, the frame protocol specifies also simple messages and procedures. The user data frames are normally routed transparently through a drifting RNC, therefore the Iur frame protocol is used also in the Iub interface. The complete configuration of the transport channel is selected by a serving RNC and signalled to a BTS via the Iub and Iur control planes. Transport channels are multiplexed in the downlink direction by the BTS on radio physical channels and they are demultiplexed in the uplink direction from radio physical channels to transport channels. In the Iur interface, every set of (coordinated) transport channels of one user equipment context communicated over a set of cells, that are macrodiversity combined within the BTS, are carried on one transport bearer. Transport bearer is a service provided by the transport layer and used by frame protocol for the delivery of FP PDU. This means that there are as many transport bearers as there are sets of coordinated transport channels and Iur user ports for that communication. Bi-directional transport bearers are used. The dedicated transport channel frame protocol (DCH FP) services are: .

transporting transport block sets across the Iub and Iur interface

.

transporting outer loop power control information between a serving RNC and a BTS

.

supporting transport channel synchronisation mechanism

In-sequence delivery of frame protocol PDUs is required from the data transport layer.



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Iu interface specification

3

Iu interface specification The Iu interface is a logical interface connecting the radio access network to the core network. Iu is an open interface that divides the system into the radio access network and core network. The core network handles switching, routing and service control. The interface is implemented in accordance with the 3GPP interface specifications. Iu has separate user and control planes. As the Iu interface is physically based on ATM, the user plane uses AAL2 over ATM (CS) or IP over AAL5 over ATM (PS) technology, while the signalling plane is SS7 based and uses broadband SS7 to carry the signalling over ATM. Iu has three different instances: .

Iu-CS between the radio access network and the circuit switched domain in the core network

.

Iu-PS between the radio access network and the packet switched domain in the core network

.

Iu-BC between the radio access network and the cell broadcast domain in the core network

A fully optimised user plane transport for circuit and packet switched traffic is achieved by using different transport technologies that are AAL2 (CS) or GTP/ UDP/IP over AAL5 (PS). Consequently, the transport network control plane is different in both instances. The main functions of the Iu interface are:


.

establishing, maintaining, and releasing radio access bearers

.

performing intra-system and inter-system handovers as well as serving RNC relocations

.

general procedures, not related to specific user equipment, such as reporting general errors


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.

separating each user equipment on the protocol level for user specific signalling management

.

transferring non-access stratum signalling messages between user equipment and core network (direct transfer)

.

Location services - the Iu interface transfers requests from the core network to RAN, and location information from RAN to the core network. Location information is based on service areas and geographical coordinates.

.

simultaneous access to CS and PS core network domains for single user equipment

.

paging the user, this function provides the core network with the capability to page user equipment

.

controlling the security by sending the security keys to RAN and by setting the operation mode for security functions

.

reporting data volume

.

controlling the tracing of the user equipment activity

Iu-CS interface

The Iu-CS interface connects the radio access network to the circuit switched core network. The interface carries the communication between an RNC and an MSC. It also carries the direct communication between user equipment and the MSC, which is transparent to the RNC.

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Radio Network Layer

User Plane

Control Plane

Iu UP

RANAP





Q.2630.1 SCCP

Q.2150.1

MTP3b

MTP3b

SSCF-NNI

SSCF-NNI

SSCOP

SSCOP

AAL5

AAL5

AAL2

ATM Physical Layer

Figure 3.

Iu-CS interface protocol architecture

Iu-PS interface

The Iu-PS interface connects the radio access network to the packet switched core network. The interface carries the communication between an RNC and an SGSN. It also carries the direct communication between user equipment and the SGSN, which is transparent to the RNC.



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Radio Network Layer

User Plane

Control Plane

Iu UP

RANAP





SCCP MTP3b

GTP

SSCF-NNI

UDP

SSCOP

IP

AAL5

AAL5

ATM

ATM

Physical Layer

Physical Layer

Figure 4.

Iu-PS interface protocol architecture


Transport in the Iu interface is based on asynchronous transfer mode (ATM) technology. The Iu user plane protocol has been defined to be independent of the transport technology in the core network. The control and user plane ATM virtual circuits do not need to use the same ATM interface. The ATM layer is adapted to higher protocol and lower physical layers. Services set different QoS requirements (real time and non-real time) for the connection and therefore two adaptation layers, AAL2 and AAL5, are used. AAL is divided to two sublayers:

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.

Convergence sublayer adapts AAL to upper protocol layers.

.

Segmentation and reassemly sublayer segments transmitted data into suitable payload pieces and reassembles them into original data flow at the receiving end.

The transport network control plane protocol stack in Iu-CS consists of the signalling protocol for setting up AAL2 connections (Q.2630.1 and adaptation layer Q.2150.1) on top of broadband SS7 protocols. There is no transport network control plane for Iu-PS. A signalling stack is used to carry RANAP over ATM permanent virtual circuits. The signalling stack consists of the SCCP, MTP3b and SAAL-NNI. The SCCP protocol offers direct signalling connections (Layer 3 session and mobility management) for each active MS. The SCCP connections are used for differentiating the signalling transactions between different subscribers. The MTP3b protocol is used for transporting the SCCP packets over several parallel signalling links. If one of the signalling links fails, MTP3b layer directs the traffic to the remaining links. SAAL-NNI is further divided into SSCF, SSCOP and AAL5 layers. SSCF and SSCOP layers are specifically designed for signalling transport in ATM networks, and handle such functions as signalling connections management. AAL5 segments the data to ATM cells. SSCOP is used for reliable transport over the ATM permanent virtual circuit to monitor the operation of one signalling link. SSCF maps general signalling transport services provided by the SSCOP to more simple services used by the MTP3b layer. The broadband SS7 signalling will not be connected to a public SS7 network but is used in a point-to-point manner. The broadband SS7 has built-in protection features. Control plane

The control plane's protocol stack consists of RANAP located on top of the broadband SS7 protocols. RANAP supports the functions of the Iu interface by different signalling procedures. RANAP handles the signalling between an RNC and a core network on the Iu-CS and Iu-PS. RANAP manages the user connections and the use of the resources on the Iu interface. RANAP also facilitates the transmission of signalling messages between user equipment and the core network - this direct transfer service uses the following protocols:



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.

RRC between the user equipment and the RNC

.

RANAP between the RNC and the SGSN or the MSC

A control plane in the Iu-CS can be terminated in an MSC server and a user plane in the Iu-CS can be terminated in an MGW. In such a case, separate Iu-CS interfaces can be configured from the RNC to the MSC server and to the MGW. Setting up GPRS tunnelling protocol (GTP) tunnel requires identifiers for the tunnel end points in the RNC and SGSN, and the IP addresses of both network elements. These are included in the RANAP RAB assignment messages. The main functions of RANAP are explained in The main functions of the Iu interface. User plane in Iu-CS

A dedicated AAL2 connection is reserved for each individual circuit switched service. The user plane protocol, Iu UP, transfers user data related to radio access bearers over the Iu interface. Two operating modes are defined for Iu UP: Transparent mode This provides only transparent user data transfer, and no other Iu protocol services. All Iu-CS traffic has predefined SDU size, no separate agreements on the SDU size is needed for the Iu UP in transparent mode. Support mode

This supports predefined SDU size that changes during the connection. It is intended to transfer, for example, speech data for the adaptive multirate (AMR) speech codec.

User plane in Iu-PS

In the Iu-PS user plane, only Iu UP transparent mode is used. Multiple packet data flows are multiplexed on one or several AAL5 permanent virtual circuits in the Iu-PS user plane. The GTP-U (user plane part of the GPRS tunnelling protocol) is the multiplexing layer that provides identities for individual packet data flows. Each flow uses UDP connectionless transport and IP addressing. The user plane implementation is based on IP over ATM connections. IP datagrams are encapsulated on ATM according to multiprotocol encapsulation (LLC / SNAP) over the ATM adaptation layer type 5 (AAL5). Inverse ATM address resolution protocol (optional) is used to allocate IP addresses for the O&M (also manually) in the Iu-PS.

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Iu-BC interface specification

4

Iu-BC interface specification The Iu-BC interface is a logical interface between an RNC in the radio access network and a cell broadcast centre (CBC) in the core network, in its broadcast domain. Iu-BC is one instance of the Iu interface and is used for the cell broadcast services. There can be several Iu-BC interfaces from the RNC towards the broadcast domain. One CBC can be connected to the RNC through one Iu-BC interface. The RNC can be connected in maximum to four (4) CBCs due to Nokia MultiOperator RAN feature. With this feature there could be four different operators' core networks in the network and each operator would have one CBC. Iu-BC supports the procedures related to the cell broadcast service. Iu-BC interface is implemented according to 3GPP release 4 specifications and it is in accordance with TS25.419: UTRAN Iu-BC Interface: Service Area Broadcast Protocol (SABP) for release 4; v.4.6.0, 2002-09. Iu-BC interface protocol architecture consists of two functional layers:


.

Radio network layer contains the user plane protocol service area broadcast protocol (SABP).

.

Transport network layer contains protocols related to transporting the user data.


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Radio Network Layer

SA Broadcast Plane SABP Protocol Layer



TCP IP AAL5

ATM Physical Layer

Figure 5.

Iu-BC interface protocol architecture


In transport network user plane the path protocol used is TCP/IP, which is used as the bearer for the radio network layer protocol over the Iu-BC, IPv4 is supported. The TCP connection is normally established by the core network using standard TCP procedures. A new TCP connection is established by the RNC only when there is information that needs to be sent from the RNC to the core network, and there is no existing TCP connection. This happens only in failure or recovery situations. The RNC establishes the connection using standard TCP procedures. The network element that established the connection also releases the TCP connection. AAL5 is used to transport the IP packets across the interface towards the packet switched domain. Iu-BC is a direct interface between the RNC and CBC, but IuBC can also be routed to the CBC via a serving GPRS support node (SGSN).

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Iu-BC interface specification

Multiple virtual channels (VC) may be used over the interface. An association is made between a VC and the IP addresses that are related to this VC during creating Iu-BC when the connections between the RNC and CBC are configured. Classical IP over ATM protocols are used to carry the IP packets over the ATM transport network. Radio network layer

SABP is used between the RNC and CBC for both data transfer and signalling. There is no clear separation of control and user planes. The protocol has the following functions:


.

It handles messages from the CBC and distributes the messages to the correct BMCs that are responsible for service areas. Messages contain service area lists indicating where the messages are to be sent. Reply messages from the BMCs are collected and forwarded to the CBC.

.

It sends the broadcast status of the messages in service areas to the CBC when requested to do so by the CBC.

.

It sends the load status of the service areas to the CBC when requested to do so by the CBC. It is used to obtain the current permissible bandwidth available for broadcast within particular service area(s).

.

It kills messages by permitting the CBC to stop broadcasting a specific message.

.

It handles resets by permitting the CBC to end broadcasting in one or more service areas.

.

It reports general service area errors, such as service area failures or protocol errors, to the CBC.


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Related Topics

Related Topics Iu interface specification Reference Iu-BC interface specification



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WCDMA RAN Interface Specifications

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