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

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Transcript of 1 WCDMA RAN Protocols and Procedures Chapter 8 Iu Interface - RANAP Protocol

Telecom WorldChapter 8
Iu Interface - RANAP Protocol
After this chapter the participants will be able to:
Explain the Iu interface and the Radio Access Network Application Protocol (RANAP) protocol structure.
Explain the main functions and procedures of RANAP.
The Iu interface connects WCDMA RAN to the Core Network.
The Radio Access Network Application Part (RANAP) protocol is used over
the Iu interface
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.
(figure 8-3)
Node B
(RBS 3000)
1. RANAP uses the SS7 over ATM protocol stack for signaling transport.
Signaling Connection Control Part (SCCP) are used to transmit RANAP
PDUs over the broadband MTP architecture:
(1) connection-oriented
For Dedicated control services: maintenance of an associated Iu signaling
connection for a specific UE (such as NAS messages ).
(2) connectionless 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)
1. The Iu User Plane protocol is part of the Radio Network Layer.
2. The purpose of the User Plane protocol : to carry user data related to RABs
over the Iu interface.
(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
(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 .
Iu UP protocol layer in transparent occurrence over Iu interface
(figure 8-5)
Iu UP protocol layer in support mode occurrence over Iu interface
(figure 8-6)
(figure 8-7)
(figure 8-8)
(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.
(figure 8-10)
User Plane/GTP-U
User Plane/AAL2
1. RANAP supports functionalities that are implemented by various RANAP
Elementary Procedures (EPs). Each function may require the execution of one
or more EPs.
Class 1: EPs with response (success and/or failure)
Class 2: EPs without response
Class 3: EPs with possibility of multiple responses
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.
• 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
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.
* 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
• Reset
• Location reporting
allows the CN to receive information on the location of the given UE.
Data volume reporting
(figure 8-2)
Elementary Procedure
Initial message
(figure 8-3)
Elementary procedure
Initial message
Response message
RAB Assignment
RNC from CN
Signaling Connection Establishment
When the paging is received by the UE, a RRC Connection Establishment is performed
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.
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.
Common ID
The Common ID procedure informs the RNC about the permanent NAS UE Identity (i.e. IMSI).
This procedure uses connection oriented signaling.
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.
Direct Transfer
The Direct Transfer procedure is used to transfer NAS information between the CN and the RNC or vice versa.
This procedure uses connection oriented signaling.
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.
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.
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.
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.
This procedure uses connection oriented signaling.
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
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
queued RABs
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 due to timer expiry
For RABs to be setup or modified:
IE name
RAB parameters
Gives attributes for the RAB like: Bit rate, SDU size, Transfer Delay, Priority, Traffic Class.
Data Volume Reporting Indication
Indicates if unsuccessfully transmitted data shall be recorded and reported to CN.
User Plane Mode
UP Mode Versions
Transport Layer Address
Iu Transport Association
These four IEs are used for preserving PDU sequence numbers at handover between GPRS and UMTS. The first two are also used to allow the CN to preserve the sequence numbers at re-establishment of an Iu-connection.
DL N-PDU Seq. No.
UL N-PDU Seq. No.
For RABs to be released:
IE name
For RABs to be setup or modified:
For RABs failed to setup or modified:
IE name
Transport Layer Address
Iu Transport Association
IE name
For RABs released:
IE name
The identity of the RAB.
Unsuccessfully Transmitted DL Data Volume
Data received from CN but not successfully sent to the UE.
Data Volume Reference
To be preserved by the CN in case the Iu connection is re-established.
For RABs queued:
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.
This procedure uses connection oriented signaling.
Any RABs still existing for the UE will also be released.
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.