UMTS CORE

NETWORK and its

EVOLUTION

By: Naveen Jakhar, ITS

3G Vision Multimedia (voice, data & video)

Increased data rates

384 kbps while moving

2 Mbps when stationary at specific locations

Increased capacity (more spectrally efficient)

IP architecture

22-Sep-

162

Core Network

The Core Network is divided in circuit switched and packet switched

domains.

Some of the circuit switched elements are Mobile services Switching

Centre(MSC), Visitor location register (VLR) and Gateway MSC. Packet

switched elements are Serving GPRS Support Node (SGSN) and Gateway

GPRS Support Node (GGSN).

Some network elements, like EIR, HLR, VLR and AUC are shared by both

domains

3GPP Release 99

• Figure shows the UMTS architecture as specified in 3GPP Release

99.

• The system architecture is based on the enhanced GSM Phase 2+

core network with GPRS and a new radio network called UMTS

terrestrial radio access network (UTRAN). UTRAN is connected

with the core network by the Iu interface.

• UTRAN consists of several radio network subsystems (RNSs).

An RNS is supported by the core network.

• Each RNS consists of base stations, termed as Node B in UMTS, and

a radio network controller (RNC). The RNC is a BSC equivalent and

controls several Node Bs.

• The 3G terminals (UE) interface with UTRAN using the Uu

interface, which is a WCDMA-based radio link

The core network consists of network elements to support

subscriber control and circuit and packet switching.

The core network also supports interfaces to the external network.

The RNCs are connected to a 3G MSC by the Iu-CS interface, which

supports circuit-switched services. Iu-CS is equivalent to the A

interface in GSM.

The RNCs are also connected to a 3G SGSN by the Iu-PS interface,

which supports packet-switched data services. Iu-PS is equivalent to

the Gb interface in GPRS. All the new interfaces, i.e., Iub, Iur, Iu-

CS, and Iu-PS, are based on ATM.

In UMTS, the user equipment (UE) or mobile station (MS)

comprises mobile equipment (ME) and a UMTS subscriber identity

module (USIM)

3GPP Release 4

Architecture

The MSC server uses ITU-T H.248 to control the media gateway. The ITU-T BICC (bearer-independent call control) protocol is used between the MSC and the GMSC server The core network supports coexistence of both UTRAN and GSM/GPRS radio access network (GERAN).

Figure illustrates the Release 4 architecture. As can be noticed,

the core network is evolved further and introduces changes in the CS

domain. The 3G MSC functions are divided into two parts, i.e., MSC

server and media gateways.

The MSC server contains call control and mobility management logic.

The MSC server also contains a VLR to hold mobile subscriber service

data.

The media gateway contains the switching function and is controlled

by the MSC server. MGW terminates the bearer channels from the

circuit-switched network. The same applies to the GMSC server,

which is split into GMSC server and media gateway.

Separating the call control and physical interfaces has distinct

advantages.

It offers scalability and lower cost. Moreover, the information

transfer between MS server, media gateways and other

components are IP based. Therefore, many components in the

core network, including SGSN, GGSN, and MSC server, can be

hooked up on the intra PLMN IP backbone, taking advantage of

shared and cheaper IP transport.

The basic principle is that the MSC is split into an MSC server and a

(Circuit - Switched) Media Gateway (CS-MGW), the external

interfaces remaining the same as much as possible as for a

monolithic MSC. The MSC server provides the call

control and mobility management functions, and the CS-MGW

provides the stream manipulating functions, i.e. bearer control

and transmission resource functions.

The Fig. explains the Bearer Independent

Call Control Architecture

The MSC Server comprises all the call control and mobility control parts of an MSC. As such, it is responsible for the control of mobile originated and mobile terminated CS domain calls .

It terminates the network signaling and translates it into the relevant network to network signaling. It also contains the VLR. The MSC Server controls the parts of the call state that pertain to connection control for media channels in a CS-MGW.

A GMSC Server is to a GMSC as an MSC Server is to an MSC CS-MGW.A GMSC Server is to a GMSC as an MSC Server is to an MSC.

Circuit Switched -Media Gateway (CS- MGW) The CS-MGW interfaces thetransport part of the UTRAN/BSC with the one of the core network, over Iu or the A interface.

It interacts with the (G) MSC server for resource control. A CS-MGW may also terminate bearer channels from a circuit switched network and media streams from a packet network (e.g., RTP streams in an IP network).

As the entity interfacing the access and the core network, the CS-MGW operates the requested media conversion (it contains e.g. the TRAU), the bearer control and the payload processing (e.g. codec, echo canceller, conference bridge). It supports the different Iu options for CS services (AAL2/ATM based as well as RTP/UDP/IP based).

The CS-MGW bearer control and payload processing capabilities also need to support mobile specific functions such as SRNS relocation/handover and anchoring. Current H.248 standard mechanisms are applied to enable this.

Further tailoring (i.e packages) of the H.248 may be required to support additional codecs and framing protocols, etc

3GPP Release 5 Architecture

The salient point for this architecture is that it is all IP based. The voice is over IP, and hence there is no need of circuit switching within PLMN. At the gateway, appropriate conversion is required tointerconnect to legacy systems.

The SGSN and the GGSN are enhanced to supportcircuit-switched services such as voice. The new roaming signaling gateway (RSGW) and transport signaling gateway (T-SGW) are needed to provide interworking with the external system over legacy SS7 and SS7-over-IP.

The call state control function (CSCF) provides call control functions for multimedia sessions. The media gateway control function (MGCF) controls media gateways, which are IP multimedia subsystems. The media resource function (MRF) supports features such as multiparty conferencing and "meet me."

The objective of release 5 Architecture was to support applications involvingmultiple media components per session in such a way that the network is able todissociate different flows with potentially different QoS characteristics associatedto the multimedia session. These applications are called IP Multimediaapplications (or "services").

Examples of such applications are multimedia sessionoffering the possibility to add and drop component(s) such as video, audio, endusers, or tools as shared online whiteboards. The impact on the network is thecreation of a set of new entities dedicated to the handling of the signalling anduser traffic flows related to these applications. This set is called the "IPMultimedia CN subsystem" (IMS).

All IMS entities are located in the CoreNetwork. The fixed Internet multimedia call control "Session Initiated Protocol"(SIP) defined by IETF is chosen as IMS main protocol for its flexible syntax and asto facilitate development and interconnectivity between 3GPP networks and fixedIP networks.

IMS architecture

RNC

P-CSCFI-CSCF

MRFIMS

S-CSCF

MSC(Server)SGSN

GGSN

CN

MGW

BSC

GSM/GPRS/WCDMA/HSDPA

WLAN

Corporate

SIP Application

ServersSIP Application

Servers

HSS

CDMA 2000Fixed

IMS – a cornerstone for Convergence

HLR

IMS paved an evolutionary path towards an all-IP core and is the core controller of choice for long term evolution (LTE) networks offering VoLTE and multimedia services. IP Multimedia Subsystem (IMS) offers a standardized, futureproofnetwork architecture with open interfaces, guaranteeing interoperability in multivendor environments with maximum reuse of existing network gear.

IMS Key Elements:

Proxy-Call State Control Function (P-CSCF):this is the

“first contact point” of IMS. It is located in the same

network as the GGSN (visited or home network,

shown as being in the visited network in the figure above).

Interrogating-CSCF (I-CSCF): this is the “main entrance”

of the home network. it

selects (with the help of HSS) the appropriate S-CSCF

Serving-CSCF (S-CSCF): it performs the actual Session

Control:

R6 Architecture

22-Sep-

1619

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3G Network Components

Circuit Core ( Voice Services)

MSC Server

Media Gateway

Home Location Register (HLR)

Packet Core ( Data Services)

GGSN

SGSN

Radio ( Coverage &

connectivity)

RNC

Node B

– Transmission▪ IP/ MPLS▪ SDH▪ E1

– Value Added Services▪ SMSC ( Short Message Service

Centre )▪ VMS ( Voice Mail Service )▪ Streaming etc……

– Subscriber Equipment▪ Handset▪ USIM

Core Network

Elements

Circuit Switched

Mobile Switching Centre-Server (MSC-S)

Media Gateway (MGW)

GMSC-S and GMGW

Home Subscriber Server (HSS)

Equipment Identity Register (EIR)

Packet Switched

Gateway GPRS Support Node (GGSN)

Serving GPRS Support Node (SGSN)

Border Gateway Router (BGR)

GPRS Roaming Exchange (GRX)

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1621

Interfaces and Protocols

C/ D interface: It is the interface between MSC – HLR/FNR and protocol used is MAP.

F interface: It is the interface between MSC – EIR and protocol used is MAP.

MSC

server

HSSHLR AuC FNR

HSSHLR AuC FNRHLR EIR FNR

C/D/F

NTIPRIT

Interfaces and Protocols

MSC

server

MediaGateway

Mc

WCDMARadioNetwork Iu- RANAP

GSMRadioNetwork

A -BSSAP

HSSHLR AuC FNR

HSSHLR AuC FNRHLR EIR FNR

C/D/F

IN

L-INAP/CAP

NTIPRIT

Interfaces and Protocols

L interface: It is the interface between MSC – INnodes and protocol used is INAP/ CAP.

Iu interface: It is the interface between MSC –RNC and protocol used is RANAP.

A interface: It is the interface between MSC –BSC and protocol used is BSSAP.

NTIPRIT

PSTNISDN

InternetIntranet

Packet Backbone Network

MGwMgw

SGSN

CSCF

GMSCServer

MSCServer

MSCServer

HSSHLR AuC FNR

MAP

MAP

BICCH.248

RANAP

MGCFSIP

RNC

BSC

BICC

Gn

BSSAP

RANAP

Q.AAL2

GGSN

PSTNISDN

InternetIntranet

Packet Backbone Network

MGwMGwMGW

SGSNSGSN

CSCF

GMSCServerGMSCServer

MSCServerMSC

ServerMSC

ServerMSC

Server

HSSHLR AuC FNR

HSSHLR AuC FNR

MAP

MAP

BICC

RANAP

MGCFSIP

RNCRNC

BSC

BICC

GnBSSGP

RANAP

Q.AAL2

Core Network Protocols

NTIPRIT

Circuit Switched Domain Protocols

Just as the horizontally integrated networkmodel demands the splitting of nodes intoServers and Media Gateways, there is alsoneed for separation of control protocols intocall control and bearer control

Control Protocols

Call Control Protocols

Bearer Control Protocols

NTIPRIT

At the control layer, there are two main requirements:

•The control servers (MGC) must beable to control remote MGWs

• Control servers must be able tocommunicate call requirements to eachother so that calls may be set up end-toend.

Circuit Switched Domain Protocols

NTIPRIT

MSC GMSC

HLR

MGW

MGW

MGW

MGW

Control Layer

Connectivity Layer

H.248

H.248

H.248

BICC

Call Control

MAP MAP

Q.2630 Bearer Control

AAL2 bearer/connectivity network

Protocols used in Mobile core Network

NTIPRIT

Access Control Protocol

Circuit Switched Domain Protocols

The control servers in the core network are responsiblefor various aspects of communication with UE, Radionetwork controllers and external networks.

BSSAP, RANAP, DTAP and ISUP are used.

NTIPRIT

Access Control Protocol

Circuit Switched Domain Protocols

•For GSM radio access the Core Network re-uses Base Station System Application Part (BSSAP) to allow the MSC servers to control BSCs.

•For WCDMA, the Core Network uses Radio Access Network Application Part (RANAP) to allow the MSC servers to control RNCs.

NTIPRIT

Access Control Protocol

Circuit Switched Domain Protocols

MSC GMSC

HLR

MGW

MGW

MGW

MGW

Control Layer

Connectivity Layer

H.248

H.248

H.248

BICC

Call Control

MAP MAP

AAL2 bearer/connectivity network

BSC

BSSAP

RNC

RANAP

ISUP

ISDN/PSTN

NTIPRIT