Umts Call Flows

Module 01 UE-UTRAN Signalling Protocols

Version 0.0.1 0.0.1 (07/02/2005) Author: Alexander Seifarth (a.seifarth@techco ([email protected]) m.de)

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CONFIDENT CONFI DENTIAL IAL - DRAFT

Alexander Seifarth

1. Network Architecture

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1. Network Architecture 1.1. Top Level Network Architecture

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1.1. Top Level Network Architecture

UTRAN UTRAN Uu

Iu

(UMTS (UMTSTerrestrial Terrestrial Radio RadioAccess Access Network) Network)

CCNN

(Core (CoreNetwork) Network)

UE

Non Acces Access s Pro Pro t ocols Acce ss Pr o t o co l s

Ac ce ss Pr o t o c o l s

intra-CN protocols

intra-UTRAN protocols

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1.1. Top Level Network Architecture UMTS inherits its top level network architecture from second generation mobile communication networks. Any UMTS network can be divided into three major network subsystems: • UE ( User hard- and software to to gain User Equip Equip m ent ) : The UE is built from Mobile Equipm ent (M E) providing all required hardaccess to the network and a UMTS UMTS Subscri ubscri ber I denti t y Module (USI USI M ). In other words the UE is a 3G enabled cell phone. • UTRA UTRAN N ( UMTS UMTS Terr Terr est est ri al Radio Access Access Net Net w ork ) : The major change of UMTS compared to second generation systems like GSM is the radio access technology. Instead of the classical GSM BSS (Base Station Subsystem) using TDMA/FDMA radio access there is now UTRAN utilizing CDMA (Code Division Multiple Access). UTRAN currently comes in three different flavours – FDD mode, TDD mode and low low chip rate TDD mode. (This script focuses focuses on FDD mode). • CN (Core (Core Netw ork) : The core network is the same for GSM and UMTS. It is responsible to provide telecommunication services like mobility handling, handling, circuit switched call services, packet switched data data services and messaging service. The CN can be split into into domains – the CS domain domain and the packet switched domain. Several signalling protocols provide the communication facilities between these subsystems. To establish the basic communication links (access links) between UE-UTRAN and UTRAN-CN there are acces access s signalli ng pr ot ocols between these subsystems. On the other hand for telecom services there are protocols between UE and CN for mobility management, CS call management, PDP context management, SMS, etc. These protocols belong to the so called nonprotocols are exchanged between UE and CN directly. directly. UTRAN must acces access s signalli ng pr ot ocols. These non-access protocols transparently pass signalling messages from non-access signalling protocols from UE to CN and vice versa. Obviously there are also protocols inside UTRAN and inside CN. These are labelled intra-UTRAN or intra-CN protocols respectively.

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1. Network Architecture 1.2. Netw Network ork Eleme Elements nts and Inte Interface rfacess

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1.2.. Netw 1.2 Network ork Ele Elemen ments ts and Int Interf erface acess Nod e B

RNC RN C

I ub

MSC MSC/ VLR Server# erver# 1

Iu-CS

CS MGW MGW # 1 I ub Uu

...

Nod e B MSC MSC/ VLR Server# erver# N

I ur

RNS RN S

UE Nod e B

I ub

CS MGW MGW # K

RNC RN C

CS-CN

BTS

BSC

...

A Iu-PS

BSS 7

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SGSN # 1

Iu-PS

RNS RN S

Gb


SGSN # L

PS-CN Alexander Seifarth

1.2.. Netw 1.2 Network ork Ele Elemen ments ts and Int Interf erface acess UTRAN is composed of two different network elements: • RNC ( Radio Netw ork Cont roller) : The RNC is responsible responsible for all radio management management tasks inside inside of UTRAN. This includes channel allocation/modification/removal, handover procedures, security functions, etc. • Node B: The Node B serves one or more cells. The tasks of the Node B is to terminated the physical layer (WCDMA FDD) and convert it to the transport protocol on the Iub interface towards RNC. In other words the Node B is a relay point. Anything above the the radio physical layer layer must pass transparently transparently through the the Node B. Between RNC and Node B there is the Iub interface. Its task is to transfer data (user data, signalling) between UE and RNC. Furthermore there is an optional interface Iur between two RNC. The Iur interface is related to soft handover procedures. This interface is similar to the Iub interface used for transparent transfer of data between UE and the so called serving RNC. For the connection between between UTRAN and CN there there is the Iu interface defined. It comes in two different different versions – Iu-CS for the connectivity between RNC and MSC (MSC server, CS Media Gateway MGW) and Iu-PS for RNC-SGSN communication. The Iu interfaces shall transfer user data (CS speech calls, CS data calls, PDP context data), non-access signalling to and from the UE and access signalling between RNC and MSC/SGSN. Iu, Iub and Iur interfaces are currently based on ATM as transport layer technology, but also IP may be used. The IP based UTRAN is already specified. In parallel to UTRAN the classical GSM BSS may still be used together with UTRAN. Thus the core network still provides connectivity for A and Gb interface. Note that in future releases also the GSM BSS may be based on Iu interfaces rather than the old second generation protocols.

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1.2.. Netw 1.2 Network ork Ele Elemen ments ts and Int Interf erface acess CS-MGW

M SC Server

SGSN Iu-PS

Iu-CS

Serving RNC

Serving RNC RN C

• radio radio manage managemen mentt (handover decision, channel channel de/allo de/allocat cation ion • NAS messag message e relay relay • Iu man manag agem emen entt • backwa backward rd error error correction • splitti splitting/ ng/com combin binatio ation n function • loca locall and and glo globa ball admission control

Drift RNC RN C I ur

I ub Nod e B

I ub

I ub

Nod e B

Nod e B

Drift RNC

• relay relay betw between een Iur and Iub • splitti splitting/ ng/com combin bining ing functio function n [optio [optional] nal] • loca locall admiss admissio ion n control

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1.2.. Netw 1.2 Network ork Ele Elemen ments ts and Int Interf erface acess A UE can be in one of two states: • I DLE words there is no signalling relation with an RNC and of DLE: A UE in IDLE mode has no connectivity to UTRAN, in other words course no radio resources are allocated for the UE. • CONNECTED : A CONNECTED mode UE has a signalling relation with an RNC which performs all radio management tasks for this UE. This special RNC is called the servi ng RNC ( S-RNC) -RNC) for the UE. A single UE has in CONNECTED mode exactly one serving RNC, in IDLE mode there is no serving RNC for the UE. During soft handover procedures it can happen, that a UE is connected with a cell that does not belong to the serving RNC’s area. The RNC managing this cell is called a dr if t RNC RNC ( D-RNC) D-RNC) . A D-RNC must have an Iur interface to the serving RNC of the UE. The drift RNC must not perform radio management procedures for the UE, this is task of the serving RNC. The drift RNC provides functionality to relay data between serving serving RNC and UE. In other words the drift RNC is a Iub/Iur relay. In some RNC equipment also functionality to combine and split data streams to/from a UE during soft handover can be provided.

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1. Network Architecture 1.3. UTRAN/UE Main Functional Protocols Overview

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1.3. UTRAN/UE Main Functional Protocols Nod e B

WCDMA WCDMA UE

Iu-CS

NBAP NBAP ALCAP ALCAP

Uu

Uu

RANAP RANAP

MSC MSC/ VLR Server

I ub

RRC RRC

RNC RN C

ALCAP ALCAP

CS-MGW Iu-CS

I ub

I ur

ALCAP ALCAP RNSAP RNSAP RNC RN C

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RANAP RANAP

SGSN Iu-PS

Alexander Seifarth

1.3. UTRAN/UE Main Functional Protocols There are some main functional protocols within UTRAN that implement the UMTS specific operations. These protocols are: • RRC RRC ( Radio Resour Resour ce Cont Cont r ol) : The RRC protocol is exchanged between UE and serving RNC. It provides functions for radio channel management, handover, security functions, measurements, etc. • RANAP RANAP ( Radio Radio Acces Access s Ne Nett w ork Applicat ion Part ) : RANAP is the main protocol on the Iu interfaces. MSC server and SGSN use RANAP signalling messages to allocated radio access bearers and to handle relocation of the serving RNC. • NBAP NBAP ( Node B Applicat ion Part ) : NBAP is the control protocol on the Iub interface. It allows the RNC to command the Node B to allocate or delete channels on the air interface, to transport Node B measurements to the RNC. Although there is a detailed specification of NBAP, most of all available UTRAN equipment implements a propriety version of NBAP. • RNS RNSAP ( Radio Radio Acces Access s Net Net w ork Applicat ion Part ) : RNSAP is used on Iur interface, thus it is an open protocol. The RNSAP protocol extends the NBAP protocol, so that a serving RNC can allocate radio resources on cells owned by a drift RNC. Some other functions of RNSAP concern the relocation relocation of the serving RNC function and packet data data forwarding from old to new RNC over Iur. The mentioned protocols RRC, NBAP, RANAP, RNSAP are UTRAN specific protocols. On Iub, Iur and Iu-CS interfaces realtime data streams will be transported. Thus before such a real-time data stream can be transferred, an appropriate transmission bearer must be allocated on the transport network, this requires another protocol: • ALC transport network ALCAP ( Acces Access s Link Cont rol Applicat ion Part ) : The term ALCAP is a generic “placeholder” for a transport specific control protocol to allocate transport bearers for delay sensitive data. In case of ATM-AAL2 transport network the ACLAP is the ITU-T protocol protocol Q.2630 (AAL type 2 signalling signalling protocol). protocol). If IP/UDP is used instead, the ALCAP ALCAP is not defined, because in IP/UDP there is no resource allocation defined.

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1.3. UTRAN/UE Main Functional Protocols NAS Sig nal li ng Relay

M MM M

CCCC

SS SS

MSC MSC/ VLR VLR Server

SMS SMS

RNC RN C

UE

CS-MGW

CCSSdat dataa

RNS RN S

GMM GMM

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SM SM


SMS SMS

PPSSdat dataa

SGSN

Alexander Seifarth

1.3. UTRAN/UE Main Functional Protocols The non-access signalling protocols between UE and MSC server/SGSN are the direct transfer application part (DTAP) protocols known from GSM/GPRS. For the CS services there are: • MM (Mobilit y Management) Management) : This protocols provides location area update, authentication, IMSI detach procedures and some others (e.g. identity request, MM information). • CC ( Call Cont ro l) : Here we find mobile originated and mobile terminated call setup, local and remote call release, as well as call related supplementary services, mid-call modification and DTMF interaction. • SS (Supplem (Supplem ent ary Servi ces) ces) : This protocol allows to trigger non-call related supplementary services like USSD, management of call forwarding and call barring, etc. For PS core network the following protocols are used: • GMM ( GPRS Mobil it y Management ) : This protocol defines GPRS attach, GPRS detach, routing area update, authentication, service request and some other procedures (e.g. identity request, GMM information). • SM ( Session ession Managem ent ) : The SM protocol provides the functionality for PDP context activation, PDP context deactivation and PDP context modification. For PS and CS core network domain the the short messaging service is possible. The protocols protocols for SMS are identical for both domains: • SMS (Short Message Message Serv Serv ice) : The SMS protocol suite consists of SM-CP (Short Message Control Protocol), SM-RP (Short Message Relay Protocol), SM-TL (Short Message Transfer Layer) and SM-AL (Short Message Application Layer).

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1. Network Architecture 1.4.. UTRA 1.4 UTRAN N Prot Protoco ocoll Stac Stacks ks on Iux Int Interf erface acess

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Umts Call Flows

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