UMTS(Universal Mobile Telecommucation System) Overview
FeaturesHigh quality Speech ( Wideband speech) – A new wideband AMR (Adaptive Multi-Rate) codec to
increase the quality of speech over UMTS.
High Speed Packet Access – With HSDPA (high speed downlink packet access) and HSUPA (high
speed uplink packet access) a peak data rate of 10.2Mbit/sec in the download direction. Further
improvements to the radio network and user devices will be able to offer user peak rates in the
download direction of 3.6Mbit/sec.
Handover to GSM/GPRS – Voice calls and data traffic can be transferred between GSM and UMTS
Multimedia Messaging Service (MMS) – It allows the transfer of multimedia messages between
users without the requirement for the multimedia messages to be transferred in real-time.
Multimedia Telephony for IMS – This uses IMS to offer telephony services such as
video, text, picture sharing, video clip sharing etc.
IP-based multimedia core network subsystem (IMS) – This provides support for IP multimedia
sessions in a flexible manner to allow new multimedia products and services to be offered. The IMS
can use both the GPRS and UMTS radio access technologies.
Operation in other frequency bands - In addition to the 2GHz band, UMTS can also operate in the
810MHz; 900MHz; 1700MHz and 2.6GHz bands.
End to end Quality of Service – Quality of Service management for the Packet Switched (PS)
domain including the IMS and the radio interface.
MBMS (Multimedia Broadcast Multicast Service) – This allows information such as streamed audio
and video to be sent over one radio channel to many customers simultaneously.
Wireless LAN inter-working – This allows connection to the core network using WLAN as well as
the usual GSM/UMTS radio access.
Network Selection– Network operators/users can select best network for their needs while roaming.
Major UMTS Components
The UMTS Release 99 architecture is composed of three components-
User Equipment (UE) :
UMTS mobile station can operate simultaneously in both Packet
Switched (PS)/Circuit Switched (CS) mode or only any one of them.
It is composed of Universal Subscriber Identity Module-card (USIMcard), the radio equipment (receiver-transceiver), the Man-Machine
Interface (MMI) (support for multimedia, WAP, and other services) and
UMTS Terrestrial Radio Access Network (UTRAN) :
UMTS radio access infrastructure is called UTRAN. It uses Wideband
Code Division Multiple Access (WCDMA ) radio technology for air
interface to communicate with UE.
Core Network (CN) :
It provide switching, routing and transit for user traffic. It also contains
the databases and network management functions.
Core Network is split into the following domains:
CS (Circuit Switch) domain It uses 64 kbps Time Division Multiplexed (TDM)
channels. This domain provides a similar set of
services as those provided by GSM.
It uses Iu-CS interface as A interface in GSM.
PS (packet switch) domain The PS domain is based on GPRS, with substitution of
the Iu-PS interface for the Gb interface.
It is composed of one or more RNS connected to core
network through IuCS/IuPS interface.
UMTS Core Network
A Node B is responsible for radio transmission/reception in one or more
cells to/from the user equipment. It can support Frequency Division
Duplex (FDD) mode, Time Division Duplex (TDD) mode or dual-mode
operation. It provides the following interfaces • Iub interface towards the UMTS RNC
• Uu interface towards the UE
The RNC is the central element in the UTRAN. It’s main function is to
control and manage the RAN(Radio Access Network) and the radio
channels. For each connection between a UE and the UTRAN, there is
one serving RNS. A drift RNS supports the serving RNS by providing
The UTRAN provides the following functions:
• Transfer of user data
Provides user data transfer capability across the UTRAN between the Iu and
Uu reference points.
• Radio channel ciphering and deciphering
Provides Ciphering and deciphering services for radio channel sessiondependent key, derived through signaling and/or session dependent
• Services related to Broadcast and Multicast traffic
Provides Broadcast and Multicast Information distribution and flow control
• CBS status reporting
RNC collects status data per cell (No-of-Broadcast-Completed-List, RadioResource-Loading-List) and provides to CBC if requested.
• Data volume reporting - reports the volume of unacknowledged data to
the CN for accounting purpose.
• Functions related to overall system access control
The purpose of the admission control is to admit or deny new users, new
radio access bearers or new radio links.
The task of congestion control is to monitor, detect and handle situations
when the system is reaching a near overload or an overload situation
with the already connected users.
System information broadcasting
This function provides the mobile station with the Access Stratum and
Non-Access Stratum information. The basic control and synchronization
of this function is done in UTRAN.
• Functions related to mobility
This function is based on radio measurements. It manages the mobility
of the radio interface and maintains the Quality of Service(QOS)
negotiated between the UE and the CN.
The SRNS relocation function coordinates the activities when the SRNS
role is to be taken over by another RNS.
This function provides the Core Network with the ability to contact the
UE when it is in the PLMN_IDLE state
This function provides the capability to determine the geographic
position of a UE.
• Functions related to radio resource management and control
Radio resource management is concerned with the allocation and
maintenance of radio communication resources.
Radio resource configuration and operation
It configures the radio network resources (cells ,transport channels)
Radio environment survey
It performs measurements on radio channels.
It controls the combining/splitting of information streams through cells
connection set-up and release
It is responsible for the control of connection element set-up and release.
Allocation and deallocation of radio bearers
It translates the connection element set-up or release requests into
physical radio channel allocation or deallocation.
RF power control
This group of functions controls the level of the transmitted power to
minimize interference and keep the quality of the connections.
Radio channel coding
It provides functions for detection or correction of signal errors
introduced by the transmission medium.
Radio channel decoding
It provides channel coding function to detect or correct possible errors in
the received data flow.
Initial (random) access detection and handling
It provides functions that has the ability to detect an initial access
attempt from a mobile station and respond appropriately.
It provides functions that has the ability to detect an initial access
attempt from a mobile station and respond appropriately.
The UMTS Core Network is split into a circuit-switched (CS) domain
and a packet-switched (PS) domain
The circuit-switched domain of the UMTS PLMN is called the Circuit
Core Network (CCN). The CCN performs the main circuit switching
functions and manages the following:
• communication among UMTS UE
• communication between UMTS UE and users in other networks
Major circuit-switched components
• Transcoder and Rate Adaptation Unit (TRAU)
• Mobile Switching Center (MSC)
• Home Location Register (HLR)
The TRAU is a device that takes UMTS speech packets as input and it
converts them into standard ISDN 64 kbps speech flow.
The MSC is responsible for circuit domain call processing and circuitswitched data. It coordinates the setup of calls to and from all UMTS
subscribers operating in its area. It controls the paging function
(incoming calls) and performs ticketing on calls for all subscribers based
in its area. The MSC transfers encryption parameters from Visitor
Location Registers (VLR) to the UTRAN to enable ciphering on the
It is a network database used for permanent management of mobile
subscribers within a PLMN. It is accessible from the 3G-SGSN and the
The packet-switched domain contains the following major components:
• 3G-Serving GPRS Support Node (3G-SGSN)
• Gateway GPRS Support Node (GGSN)
The 3G-SGSN requests location information from the HLR through the
Gr interface. It performs setup and routing of data sessions.
provides the point of interconnection with external Packet Data
Networks (PDN) for Public Land Mobile Networks (PLMN) supporting
UMTS. This interconnection utilizes the Gi interface. The GGSN stores
routing information for attached UMTS users. The routing information is
used to tunnel Protocol Data Units (PDU) to the current 3G-SGSN
serving the MS(UE).
Other Core Network elements
VLR (Visitor Location Register)
The VLR contains all subscriber data required for call handling for the mobile subscribers currently located in the area
controlled by it.
AuC (Authentication Center)
It is a database that contains secret subscriber keys and security algorithms. It generates security information for
authentication and ciphering.
EIR (Equipment Identity Register)
It is a database that stores IMEIs used within a GSM or UMTS network. Additionally, the register may store the status
of said IMEI (classified as "white listed", "gray listed" or "black listed").
SMS Gateway MSC
It acts as an interface between a Short Message Service Center and the PLMN. Short messages can so be delivered to
mobile stations from the Service Center (SC).
SMS Interworking MSC
It acts as an interface between a Short Message Service Center and the PLMN.
IWF (Interworking Function)
It provides the functionality necessary for interworking between a PLMN and the fixed networks (ISDN, PSTN and
DNS (Domain Name Service) Server
It translates between Fully Qualified Domain Names and IP address. It translates the Access Point Names requested by
the subscribers to the IP address of the access point.
DHCP (Dynamic Host Configuration Protocol ) Server
It assigns IP addresses as required.
Uu – Air interface between a nodeB and UE.
Iub -Interface between an RNC and its nodeBs.
Iur - Interface between two RNCs support specific functions such as handover.
Iupc - Interface between an RNC and a SAS (Stand-alone A-GPS SMLC) within the UTRAN.
Iu-CS - Circuit switched variant of the Iu interface.
Iu PS - Packet switched variant of the Iu interface.
B - Interface between the GSM/UMTS MSC and the VLR.
C - Interface between the GSM/UMTS MSC and the HLR.
D - Interface between the HLR and VLR.
E - Interface between the GSM/UMTS MSC and the VLR.
F - Interface between the Nortel GSM/UMTS MSC and the EIR.
G - Interface between VLRs using MAP/TCAP signaling over CCS7 SCCP and MTP.
Ga - interface between 3G-SGSN and the Charging Gateway Function (CGF) for billing.
Ge - Interface between SGSN and the SCP for CAMEL Phase III.
Gf - Interface between SGSN and EIR.
Gi - Interface between GGSN and the external network.
Gn - Interface between 3G-SGSN and GGSN, between different 3G-SGSNs in same PLMN.
Gp - Interface between 3G-SGSN and SGSN in different PLMNs. It is used for inter-PLMN.
Gr - Interface between the 3G-SGSN and the HLR.
X1 - A set of three interfaces (X1-1 – Administration, X1-2 Intercept Related Information, X1-3 Communication
Content) between a network and a Lawful Intercept Delivery Domain.
UMTS traffic classes
The UMTS network services have different QoS classes for four types of traffic:
• conversational class
The conversational class is the typical class for speech telephony. The conversational call
is the most demanding class for transfer delays (the maximum affordable value is given
by human perception).
• streaming class
The streaming class has the same real-time constraints as the conversational class.
However, since it is a one-way class of service (the user is just listening or viewing) the
streaming class is less transfer-delay sensitive than the conversational class.
• interactive class
The interactive class is not as real-time constraining as the conversational and streaming
classes. However, the interactive class requires a very low bit-error rate.
• background class
The background class is equivalent to the interactive class. The difference between the
two classes is that the background class is less delivery-time sensitive and has a lower
UMTS Base Stations (NodeB)
Femto Cell – It is a small, low-power cellular base station designed for use
in a home or small business. It connects to the service provider’s network
via broadband (such as DSL or cable).
Pico Cell - It is capable of providing services to UE within a building.it is
used to extend coverage to indoor areas where outdoor signals do not reach
well or to add network capacity in areas with very dense phone usage.
Micro Cell - It is served by a low power cellular base station (tower),
covering a limited area such as a mall, a hotel, or a transportation hub. A
microcell uses power control to limit the radius of its coverage area.
Macro Cell – It is served by a high power cellular base station (tower)
covering larger than microcell. The antennae for macrocells are mounted on
ground-based masts, rooftops and other existing structures. It is capable of
providing services to UE within a city.
UMTS PLMN (Public Land Mobile Networks) use unique numbers to identify and route calls to
UE. The numbers used in UMTS are described as below IMEI - The International Mobile Equipment Identity (IMEI) uniquely identifies the mobile
MSISDN - The Mobile Subscriber Integrated Services Digital Network (MSISDN) number is the
unique phone number that consists of Country Code + National Destination Code + Subscriber
Number. MSISDNs are allocated according to the CCITT E.164 numbering plan.
IMSI - The International Mobile Subscriber Identity (IMSI) is a unique identification of the
subscriber. It is stored in the SIM (see below) and Home Location Register (HLR). IMSIs are
allocated according to CCITT E.212.
TMSI - The Temporary Mobile Subscriber Identity (TMSI) is a unique identity temporarily
allocated to visiting UE. The TMSI identifies the UE within a specific VLR as part of the
confidentiality service. The TMSI is used in the Circuit Switched (CS) domain.
P-TMSI - The P-TMSI (Packet-Temporary Mobile Subscriber Identity) is equivalent to the
TMSI, for the Packet Switched (PS) domain.
MSRN - The Mobile Subscriber Roaming Number (MSRN) is temporarily assigned to the UE
while roaming and is used to terminate calls to the UE.