Download - 1 WCDMA RAN Protocols and Procedures Chapter 8 Iu Interface - RANAP Protocol.

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WCDMA RAN Protocols and Procedures

Chapter 8

Iu Interface - RANAP Protocol

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Objectives of Chapter 8, Iu Interface - RANAP Protocol

After this chapter the participants will be able to:

1. Explain the Iu interface and the Radio Access Network Application Protocol (RANAP) protocol structure.

2. Explain the main functions and procedures of RANAP.

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RADIO ACCESS NETWORK

APPLICATION PART (RANAP)

PROTOCOL---INTRODUCTION---

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• The Iu interface connects WCDMA RAN to the Core Network.

• The Radio Access Network Application Part (RANAP) protocol is used over

the Iu interface

• RANAP carries Non-Access Stratum (NAS) messages, which are relayed

between the CN nodes and the Ues.

• The Iu interface is divided into two instances:

* the Iu Circuit Switched (CS) to connect WCDMA RAN to the MSC server

* the Iu Packet Switched (PS) to connect to the SGSN

• The Iu interface is divided into:

* a control plane

* a user plane.

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Iu-CS Interface (figure 8-1)

Physical Layer

RANAP Iu UP protocol layer

RNL

TNL TN User Plane TN Control Plane TN User Plane

Control Plane User Plane

ATM

SCCPMTP3b

Q.2630.1

Q.2150.1MTP3b

AAL2

NNI-SAAL NNI-SAAL

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Iu-PS Interface (figure 8-2)

ATM

Physical LayerPhysical Layer

RANAP Iu UP protocol layer

RNL

TNL TN User Plane TN Control Plane TN User Plane

Control Plane User Plane

ATM

SCCPMTP3b GTP-U

UDPIP

AAL5

NNI -SAAL

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RANAP signaling over the lu interface(figure 8-3)

Node B(RBS 3000)

Uu RNCIub

SGSN

MGW

MSC/VLR

Iu UP

Iu UP

NAS-messages

NAS-messages

RANAP

RANAP

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RADIO ACCESS NETWORK

APPLICATION PART (RANAP)

PROTOCOL---RANAP PROTOCOL STACK---

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1. RANAP uses the SS7 over ATM protocol stack for signaling transport.

2. Signaling Connection Control Part (SCCP) are used to transmit RANAP

PDUs over the broadband MTP architecture:

(1) connection-orientedconnection-oriented

• For Dedicated control services: maintenance of an associated Iu signaling

connection for a specific UE (such as NAS messages ).

(2) connectionless servicesconnectionless services

• For General control services : relate to the entire Iu interface instance

between an RNC and the CN (such as block and reset ).

• For Notification services : relate to a single UE or all UE's in a specified

area (such as paging)

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SRNC MSCIub

SCCP SAP SCCP SAP

SCCP

MTP-3B

NNI-SAAL

AAL5

ATM

PHY

SCCP

MTP-3B

NNI-SAAL

AAL5

ATM

PHY

RANAP RANAP

Lower layer signaling

RANAP Signaling

Uu

IuCS

RANAP Protocol stack (figure 8-4) IuPS SGSN

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IU USER PLANE (UP)

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1. The Iu User Plane protocol is part of the Radio Network Layer.

2. The purpose of the User Plane protocolThe purpose of the User Plane protocol : to carry user data related to RABs

over the Iu interface.

3. The protocol supports two modes:

(1) Transparent Mode (TrM)

• protocol does not perform any framing or control. For instance, the transfer

of GTP-U PDUs (packet data) could utilize the transparent mode of the Iu UP

protocol.

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(2) Support Mode for Predefined SDU sizes (SMpSDU)

• performs framing of the user data into segments of predefined size.

correspond to AMR speech frames, or derived from the data rate of a

CS data call.

• control procedures for initialization and rate control are defined

• functionality is specified for indicating the quality of the frame based, for

example, on CRC from the radio interface .

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Iu UP protocol layer in transparent occurrence over Iu interface(figure 8-5)

Iu UP layer intransparent mode

TNL-SAP

RNL-SAP

Iu Interface

TNL-SAP

Iu UP layer intransparent mode

CNUTRAN

Rad

io I

nte

rfac

eP

roto

cols

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Iu UP protocol layer in support mode occurrence over Iu interface(figure 8-6)

Iu UP layer insupport mode

TNL-SAP

RNL-SAP

Iu Interface

TNL-SAP

Support ModeFunctions

Iu UP layer insupport mode

CNUTRAN

Rad

io In

terf

ace

Pro

toco

ls

Transfer of IuUP protocol

frames

Support ModeFunctions

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SRNC MGWIub

Uu

Q.2150.1

MTP-3B

NNI-SAAL

AAL5

ATM

PHY

Q.2150.1

MTP-3B

NNI-SAAL

AAL5

ATM

PHY

Q.2630.1 Q.2630.1


Q.2630.1 Signaling

IuCS

Transport Network Control Plane for Iu CS(figure 8-7)

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SRNC MGWIub

Uu

Iu UP

AAL2

ATM

PHY

Iu UP

AAL2

ATM

PHY

IuCS

Transport Network User Plane for Iu CS(figure 8-8)

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SRNC SGSNIub

Uu

GTP-U

UDP

IP

AAL5

ATM

PHY

GTP-U

UDP

IP

AAL5

ATM

PHY


Signaling

IuPS

Transport Network User Plane for Iu PS(figure 8-9)

• a GTP-U tunnel is set up by RANAP.

• It only needs an identifier for the tunnel and the IP addresses for the RNC and SGSN.

• Further on a GTP-U tunnel is set up between the SGSN and the GGSN.

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User Plane/GTP-U

Iu Connections between RNC and the Core Network

(figure 8-10)

User Plane/AAL2

RANAP

Q.AAL2

RANAP

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FUNCTIONS OF RANAP

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1. RANAP supports functionalities that are implemented by various RANAP

Elementary Procedures (EPs). Each function may require the execution of one

or more EPs.

2. Three kinds of EPs are used:

–Class 1: EPs with response (success and/or failure)

–Class 2: EPs without response

–Class 3: EPs with possibility of multiple responses

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3. RANAP has the following functions:

• Paging

This function provides the CN for capability to page the UE.

• Common ID management

IMSI of the UE is sent from the CN to WCDMA RAN .

• Transport of NAS information between UE and CN.

provides transparent transfer of UE-CN signaling messages that are not

interpreted by WCDMA RAN.

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• Security mode control

used to send the security keys and the algorithms (ciphering and integrity

protection) to the WCDMA RAN, and setting the operation mode for security

functions.

• Radio Access Bearer (RAB) Management

responsible for setting up, modifying and releasing RABs.

• Iu Release

Releases all resources (control and user plane) from a given instance of Iu

related to the specified UE.

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• Relocating Serving RNC (SRNC)

* handles both SRNS relocation (not implemented) and hard handover.

* In SRNC relocation the serving Radio Network Subsystems (RNS)

functionality is relocated from one RNS to another without changing the

radio resources and without interrupting the user data flow. Only when all

Radio Links are already in the same DRNC that is target for the relocation.

• Management of overload

Controls the overload of the Iu interface.

• Reset

used to reset the Iu interface in error situations.

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• Location reporting

allows the CN to receive information on the location of the given UE.

• Data volume reporting

responsible for reporting unsuccessfully transmitted data

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RANAP PROCEDURES

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Paging

Paging is used by the CN to page a UE– This procedure uses connectionless signaling

The PAGING message includes: – Permanent NAS UE Identity (i.e. IMSI) for calculation of paging group and also

for WCDMA RAN paging co-ordination.

* paging coordination means that if a Radio Resource Control (RRC) connection already exists for this UE, the radio-interface paging-message will be sent via this RRC connection instead of via the broadcast paging channel.

– The DRX Cycle Length Coefficient (if available) may be included in the Paging message, which used for calculating the paging occasions for the UE.

– Temporary UE ID (that is, the TMSI). Used over the paging channel. If TMSI is not included the RNC shall use the Permanent NAS UE Identity instead,

– Paging Cause shall indicate the reason for sending the paging message.

– Non Searching Indication. If set to non-searching, the RNC does not need to do WCDMA RAN paging

co-ordination.– Paging Area.

Can be the LAI, RAI and (if omitted) the whole RNC area.

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Initial UE Message

The Initial UE Message procedure is used to establish an Iu signaling connection between a CN domain and the RNC.

– This procedure uses connection oriented signaling.

The SRNC sends a SSCP Connect Request (CR) message to the CN. The SCCP Connection Request message carries the RANAP Initial UE message.

The Initial UE Message carries the NAS messages with the establishment cause, the UE identity and the current location, on cell level of the UE.

The SRNC receives confirmation that the signaling connection has been setup by a SCCP Connection Confirm (CC) message. The SCCP CC message may include a RANAP message, for example “Common Id”

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Common ID

The Common ID procedure informs the RNC about the permanent NAS UE Identity (i.e. IMSI).


The permanent NAS UE Identity is tied to the RRC connection and is used at Paging to check if an RRC connection already exists for this UE;

– That is WCDMA RAN paging co-ordination.

The WCDMA RAN also needs the permanent NAS UE Identity from this message in order to be able to calculate the paging group in case of WCDMA RAN initiated paging.

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Direct Transfer

The Direct Transfer procedure is used to transfer NAS information between the CN and the RNC or vice versa.


Besides NAS-PDU for the NAS information, this message also includes

– SAPI for indicating the priority of the message. SAPI 0 for high priority and SAPI 3 for low priority (SMS). Only used downlink.

– LAI + RAC. Needed in connection with Routing Area Update. Only used towards the PS domain.

In this specific case Direct Transfer is used for Authentication and Ciphering Request and Response.

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Security Mode Control

The Security Mode Control procedure is used by the CN to pass cipher and integrity protection information to the WCDMA RAN. – This procedure uses connection oriented signaling.

Messages– If WCDMA RAN can support the requested ciphering and integrity

protection, the message SECURITY MODE COMPLETE is returned.

– Otherwise the message SECURITY MODE REJECT with an appropriate cause value is returned.

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Security Mode Control continued

In case a UE has RABs towards both the PS and CS CNs (not supported), the following is valid:

– User data for RABs towards CS are ciphered with the ciphering key received from the CS domain.

– User data for RABs towards PS are ciphered with the ciphering key received from the PS domain.

– Signaling data is ciphered and integrity protected with the latest received keys.

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RAB Assignment

The RAB Assignment procedure is used to establish one or more new RABs for a given UE and/or to modify or release already existing RABs.


The RAB Establishment consists of two parts:

– Iu bearer setup between the CN and the SRNC.

– Radio Bearer Setup between the UE and the SRNC.

The RAB ASSIGNMENT REQUEST message contains:

– list of RABs to establish with their bearer characteristics

– list of RABs to modify with their bearer characteristics

– list of RABs to release

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RAB Assignment continued

Upon reception of RAB ASSIGNMENT REQUEST, the WCDMA RAN executes the requested configuration. The result is reported to CN in one or more RAB(s)

ASSIGNMENT RESPONSE messages. The first of these messages contains:

– successfully established RABs

– successfully modified RABs

– released RABs

– RABs failed to establish, modify or release

– queued RABs

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RAB Assignment continued

The subsequent messages are used for reporting the outcome of the queued RABs. (The procedure is not completed until all RABs have been reported.)

The following outcomes are possible:

– successfully established or modified

– failed to establish or modify

– failed to establish due to timer expiry

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Iu Release(figure 8-12)

The Iu Release procedure is used to release an Iu connection and all WCDMA RAN resources related to that Iu connection.


Any RABs still existing for the UE will also be released.

CNCN

”Iu Release Command”

RNCRNC

”Iu Release Complete ”

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Iu Release Request

This procedure is used by WCDMA RAN to ask the CN to initiate the release of an Iu connection.

– This procedure uses connection oriented signalling.

The CN can follow the request and initiate the Iu Release procedure. It can, however, also choose to take some other action, including ignoring the request.

CNCN

”Iu Release Request”

RNCRNC