Elementary Procedure Iu Release Request Relocation Complete Relocation Detect IU RELEASE REQUEST RELOCATION COMPLETE Paging PAGING
Initial UE Message INITIAL UE MESSAGE Direct Transfer DIRECT TRANSFER
RELOCATION DETECT Message
Class 2 Elementary Procedures Examples
Class 3 Elementary Procedures Examples
Elementary Procedure Intiating Message Response Message RAB Release Request RAB RELEASE REQUEST
RAB Assignment RAB ASSIGNMENT
7.14
GSM and UMTS Core Network
RAB (Radio Access Bearers)
RABs represent the service provided to higher layers in the user plane to transfer traffic data between the CN domain and the required UE.
RANAP sets up the RAB path between the CN and the UTRAN. RRC sets up the RAB path between the UTRAN and the UE. Each UMTS bearer service is supported by a RAB. The RABs in turn are described by the QoS parameters. There may be one or several RAB candidates for supporting a UMTS bearer service.
Set-up
by RRC by RANAPSet-up
UTRAN
Radio
Protocols TerrestrialProtocols
RAB x RAB y RAB x RAB y
UE
CN
UMTSCircuit-Switched Functionality
The RAB Assignment Procedure
RANAP uses the RAB Assignment Request message to establish a RAB. This message specifies the requirements of a RAB that the MSC is requesting to be assigned to a UE based on the UMTS bearer service. The message is routed to the RNC by SCCP/MTP3-b across an ATM AAL5 connection.
The message contains the following IE:
The RAB ID provides the association between a UE that the RAB is supporting and its RAB context in the RNC/MSC. This value is the same as the Stream Identifier (SI). If the UE supports multicall, it shall include the SI information element in the Set-up message. For the first call, i.e. when there are no other ongoing calls, the SI value shall be 1.
RAB parameters specify the characteristics of the bearers required to support the QoS requested in the Set-up message sent by the UE or the MSC.
The user plane mode indicates whether the Iu protocol is operating in TrM (Transparent Mode) or SMpSDU (Support Mode for predefined SDU size).
UP mode versions: the first phase of UMTS supports version 1 of the Iu protocol.
The transport layer address constitutes the AAL2 Path Id and the Channel Id allocated to this RAB. The Iu transport association is the Binding Id and associates the RAB with the AAL2 transport bearer.
RNC MSC Server
CS-MGW
Mc
RAB Assignment Request
IE Comment Presence
Message Type (Elementary Procedure) RAB ASSIGNMENT REQUEST M M M M M M M RABs to be set up >RAB ID RAB Parameters
User Plane Information
User Plane Mode UP Mode Versions Transport Layer Address Iu Transport Association
Stream Identifier (SI) QoS Profile TrM or SMpSDU Version1 AAL2 Path Id and Channel Id or IP Address Binding Id
7.16
GSM and UMTS Core Network
The lu UP Protocol
The Iu UP protocol is located in the User Plane of the Radio Network Layer over the Iu interface. The Iu UP protocol is used to convey user data associated to RABs.
One Iu UP protocol instance is associated with one RAB. If several RABs are established towards one UE, then these RABs make use of several Iu UP protocol instances. These Iu UP protocol instances are established and released together with the associated RAB.
One objective of the Iu UP protocol is to remain independent of the CN domain (CS or PS) and to have limited or no dependency upon the Transport Network Layer. Meeting this objective provides the flexibility to evolve services regardless of the CN domain and to migrate services across CN domains.
The Iu UP protocol is therefore defined with modes of operation that can be activated on a RAB basis rather than on a CN domain basis or teleservice basis. The Iu UP mode of operation determines if features shall be provided to meet the RAB QoS requirements and, if so, which set.
RNC MSC Server CS-MGW Mc Iu Radio
Protocol PlaneUser Data Bearers Iu UP User Plane Data Bearers Iu UP Radio Protocol
Circuit-Switched Functionality
Iu UP Protocol Modes of Operation
The Iu UP protocol operates in one of two modes, TrM or SMpSDU.
Determination of the Iu UP protocol instance mode of operation is a CN decision taken at RAB establishment based on the RAB characteristics. It is signalled in the Radio Network Layer Control Plane at RAB assignment for each RAB.
It is internally indicated to the Iu UP protocol layer at User Plane establishment. The choice of a mode is bound to the nature of the associated RAB and cannot be changed unless the RAB is changed.
Version 1 of the Iu protocol is currently supported.
TrM is intended for RABs that do not require any feature from the Iu UP protocol other than transfer of user data. In this mode, no Iu frame structure exists.
RNC CS-MGW User Data Radio Interface Protocols Iu UP layer in TrM No additional frames generated Iu UP layer in TrM No additional frames generated
7.18
GSM and UMTS Core Network
SMpSDU (Support Mode for predefined SDU size)
The support modes are intended for RABs that require features from the Iu UP protocol in addition to transfer of user data. When operating in a support mode, Iu UP frames are exchanged, whereas in transparent mode no Iu UP frames are generated.
When requesting Iu UP protocol support, some RABs constrain the Iu UP protocol and possibly the radio interface protocols in specific ways. For instance, certain RABs can have variable predefined rates, e.g. AMR speech. The Iu UP support mode is prepared to support these variations.
RNC CS-MGW User Data Radio Interface Protocols Iu UP layer in SMpSDU Initialization of Iu UP Protocol Transfer of Iu UP Protocol frames Iu UP layer in SMpSDU
Circuit-Switched Functionality
Functions of SMpSDU
The Iu UP protocol layer in Support mode is made up of three sets of functions.
The Frame Handler function is responsible for framing and deframing the different parts of an Iu UP protocol frame. This function is also responsible for the CRC check of the Iu protocol frame header. The Procedure Control functions offer the control of a number of procedures handled at the Iu UP protocol level. The procedures defined are initialization, rate control, time alignment an handling of error events.
Initialization controls the exchange of initialization information. It can contain the RAB sub-flow Combination Indicator (RFCI), set to be used until termination of connection or until next period initialization. Rate control manages the set of permitted rates that can be controlled, represented by RFCI indicators. Time alignment controls the timing of downlink data to RNC over Iu-CS interface, and error event handling controls the information exchanged following the detection of fault situations.
The NAS Data Streams consist of functions related to consistency checking of the frame number, CRC checking, Frame Quality Classification handling, and padding and depadding of Iu payloads as required. Iu SMpSDU frames are classified with a Frame Quality Classifier. This is based upon radio frame classification to see if delivery of erroneous SDUs shall be delivered or not. The delivery of erroneous SDUs is also indicated during RAB assignment (in the RAB attributes information element).