1. UMTS Terrestrial Radio Access Network Architecture
Raul Bruzzone
December 18
V2.0

2. UMTS Architecture A UMTS System comprises three main parts:
Core Network (CN)
UMTS Terrestrial Radio Access Network (UTRAN)
The User Equipment (UE) CN Iu
UTRAN Uu UE
UTRAN
UMTS Terrestrial Radio Access Network CN
Core Network UE
User
Equipment
December 18
Raul Bruzzone

3. System Domains December 18 ETSI Home Network Domain [ Zu] Cu Uu Iu [
Yu]
Serving
Transit
Network
Network
Domain
Domain
USIM
Mobile
Access
Core
Domain
Equipment
Network
Network
Domain
Domain
Domain
User Equipment
Infrastructure
Domain
Domain
December 18
ETSI

4. Structure of the UTRA Network
Core Network Iu Iu
RNS
RNS
Iur
The fixed part of the radio access network is composed by cells, grouped in sets called Radio Network Systems (RNS).
RNS are under the control of a switching and control unit, which manages nearby Base Stations. This unit is called Radio Network Controller (RNC) and fulfils similar functions as Base Station Controllers (BSC) used in GSM.
Cells
December 18
Source: ETSI

5. UMTS Radio Network ControllerIu
RNS
RNC
Iur
Iur
Iub
Iub
Node B
Node B
This chart shows the position of the RNC.
An important function of this module is Macro Diversity, that is to say, the capability to simultaneously communicate with one mobile station through more than one channel.
Macro-diversity is possible through the use of different spreading codes for a fixed network/mobile station link.
Cells
December 18
Source: ETSI

6. Serving and Drift Radio Access Networks
Core Network Iu Iu
DRNS
SRNS
Iur
RNS can communicate their respective RNCs without passing through the Core Network. See figure.
This capability, not present in GSM, allows fast UE handover between nearby BS that are not in the same subsystem.
It must be stressed another difference between GSM and UMTS. While in GSM the Handover function is implemented in the Core Network, UMTS implements Handover in the UTRAN with participation of the CN only in some special cases (see next slide).
Cells UE
December 18
Source: ETSI

7. Streamlining of the UTRAN - Core Network Connection
SRNS Iu
DRNS
Iur UE
Before
SRNS Relocation
Core Network
RNS Iu
SRNS UE
After
SRNS Relocation
Core Network
The RNS-RNS direct connection capability makes possible that Handover of a MS may be implemented in two phases.
Consider the situation in the left figure. The UE was formerly communicating with a Cell of the right RNS (caller “Serving” RNS). Due to displacement of the UE, a new cell in the left hand RNS must be selected (this second RNS is called “Drift” RNS).
At the beginning, the connection between DRNS and SRNS is made through the Iur interface. The old Core Network access is used. In a second stage (see right figure) an access to the CN through the new DRNS is established, and the old RNS (SRNS) is disconnected from this UE.
December 18
Source: ETSI

8. Evolution of the GSM Network towards the UMTS Network: Starting Point (2002)
G-MSC
IWU
1Gb 1A I u A G b
GSM BSS
UTRAN
N-ISDN
GGSN
IP networks
MAP
ISUP IP
X.25
MSC
HLR
SGSN
CSE
CAP
UMTS
Segment
December 18
ETSI

9. Evolution of the GSM Network towards the UMTS Network: Introduction of a UMTS Core Network (2005 ?)
CSE
HLR
CAP
MAP
ISUP A
ISUP
MSC
G-MSC
N-ISDN
GSM BSS G IP IP b
SGSN
GGSN
IP networks
UMTS
Segment
X.25
IWU 1A
IWU
1Gb
X.25
UTRAN
UMTS CN I u
December 18
ETSI

10. Terrestrial Radio Access Network Architecture Summary
UMTS is composed of Core Network, Radio Access Network and User Equipment.
The Radio Access Network (UTRAN) handles radio link connections, enabling Base Station handover.
Handover management is done at the UTRAN Controller.
The UMTS Fixed Network will evolve from the GSM Network model, following several phases.
December 18
Raul Bruzzone