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

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

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

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

UMTS Radio Network Controller Iu 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

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

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

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

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

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