Gprs 2 Architecture w

1 GPRS/EDGE INTRODUCTION

GPRS Architecture: GPRS Architecture: Interfaces and ProtocolsInterfaces and Protocols


Module objectivesAfter this module, the participant will be able to:• Name the GPRS specific network elements and their

most important functions• Name the most important open interfaces in the GPRS

network• Explain the principles of the GPRS Tunnelling Protocol


Network elements• GPRS provides mobile users worldwide access to

• Value-added WAP services and • Different external packet networks (e.g. Internet or

intranets)• GSM-BSS provides the radio interface

BSSGPRS

Core Network

ExternalPacket

Networks

Value-AddedServices

(WAP)


Requirements of GPRS network

• Use existing GSM infrastructure with little modifications to it

• GPRS should support one or more packet switched connections • referred to as PDP context activations

• Support different Quality of Service (QoS) user subscriptions

• Compatible with 3G and 4G systems

• Support both point-to-point and point-to-multipoint data connections

• It should provide secure access to external networks


GPRS network: Logical network elements

BTS BSC

SGSN

GGSN Intranet

GGSN Internet

CG

BillingCentre

Router Server

LAN

Corporate

BG

Inter-PLMNNetwork

LIG

SGSN = Serving GPRS Support NodeGGSN = Gateway GPRS Support NodeNMS = Network Management SystemBG = Border GatewayCG = Charging GatewayFW = FirewallLIG = Lawful Interception Gateway

FW

NMS

DNS

GPRS Backbone

FWOperatorServices

LAN

GGSN

What are the functions of SGSN?• The SGSN is the MSC of the GPRS network• At least one SGSN per GPRS network• SGSN has the following functions:

• Protocol conversion between IP backbone and BSS protocols

• Authentication of GPRS users • Mobility management of GPRS enabled MS• Routing of data to the relevant GGSN• Interaction with the NSS (MSC/VLR, HLR, EIR) via SS7

network• Collection of charging data records pertaining to GPRS

calls• Collection of traffic statistics

What are the functions of GGSN?• GGSN acts as a router to the external network• GGSN has the following functions:

• Routes mobile-destined packets coming from external networks to the relevant SGSN

• Routes packets originating from a mobile to the correct external network

• Interfaces to external IP networks• Collects charging data and traffic statistics• Allocates dynamic or static IP addresses to mobiles either

by • itself or • with the help of a DHCP (Dynamic Host Configuration Protocol ) or a

RADIUS (Remote Authentication Dial In User Service ) server


How is GPRS seen by an external network?

Host155.222.33.55

Corporate subnetwork131.44.15.xxx

GPRS subnetwork155.222.33.xxx

Host131.44.15.3

RouterRouter

LAN

Internet

• External point of view, GGSN is a router to an IP network• When the GGSN receives data addressed to a user in the

mobile network, it first checks if the address is active • If it is, GGSN forwards the data to the SGSN serving the

mobile • If the address is inactive, the data is discarded

DNS• DNS: Domain Name System • Converts IP names into IP addresses

• for example, server.telefonica.com to 133.44.15.5

• Every GPRS network must have one• Why?

Firewall• Protects the IP network against external attack (for

example, hackers from the mobile users or from the Internet)

• Firewall might be configured to reject all packets that are not part of a GPRS subscriber initiated connection• Advantage of dynamic addressing

Border Gateway (BG)• Necessary to interconnect operators' GPRS backbone

networks to support roaming• Provides a direct tunnel between different operators'

GPRS networks (rather than transferring via the public Internet)

Charging Gateway (CG) • GPRS charging data records (CDR) are generated by

SGSNs and GGSNs in the network • SGSN and GGSN transfer CDR using GTP’ (GTP Prime)• The Charging Gateway

• collects all this data together• processes it • passes it on to the Billing System

Lawful Interception Gateway (LIG)• Lawful interception is an action based on the law, which

is performed by the GPRS network • It provides information for a Law Enforcement Agency

(LEA) about some pre-defined target subscriber• Information could include

• data sent and received by the interception target• location information• subscriber information• etc.


GPRS interfacesHLR

Air (Um)

Gb

GsGr Gf

Gn

GnInter-PLMN

GPRSbackbone

Gp

Externalpacket network

Gi

SGSN

EIR

BSC

MSC/VLR

SMS-GMSC

Gd

GGSN

BG

Signalling and data

Signalling

GaGa

CG


Container

User packetUser

packetUser packet User packet

SGSN GGSN

The stream of containers forming a tunnel.

User

packet


Tunnelling

User packetTunnel ID:

IMSI…

THE GTP PACKETIP (+TCP/UDP)

Who is the user?

To which GSN?

GSN IP-address

E.g. a TCP/IP packetcarrying e-mail


Tunnelling

GGSN

GTP

IP IP

IP backbone data using private IP addresses

SGSNMS

IP

GTPTunnel

user data using 'public' IP addresses


BTS BSC

SGSN

GGSN Internet

GPRS Backbone IP Network

FWL1L2IP

GTP

USERPAYLOAD TCP/UDP

L1L2IP

APP

UDP

Gn G iBackbone Internet

Gn Gi

BTS BSCSGSN

GPRS Tunnelling Protocol (GTP)GTP tunnel between SGSN and GGSN• Carrying signalling and user traffic• Hiding backbone from Internet and the MSs• Mobility management• Tunnel Identifier TID= IMSI + NSAPI


GPRS transmission plane protocols


Gb Interface: Frame Relay


Gb interface using point-to-point FR

Gprs 2 Architecture w

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