1 GPRS/EDGE INTRODUCTION
GPRS Architecture: GPRS Architecture: Interfaces and ProtocolsInterfaces and Protocols
2 GPRS/EDGE INTRODUCTION
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
3 GPRS/EDGE INTRODUCTION
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)
4 GPRS/EDGE INTRODUCTION
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
5 GPRS/EDGE INTRODUCTION
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
8 GPRS/EDGE INTRODUCTION
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.
14 GPRS/EDGE INTRODUCTION
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
15 GPRS/EDGE INTRODUCTION
Container
User packetUser
packetUser packet User packet
SGSN GGSN
The stream of containers forming a tunnel.
User
packet
16 GPRS/EDGE INTRODUCTION
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
17 GPRS/EDGE INTRODUCTION
Tunnelling
GGSN
GTP
IP IP
IP backbone data using private IP addresses
SGSNMS
IP
GTPTunnel
user data using 'public' IP addresses
18 GPRS/EDGE INTRODUCTION
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
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