VLR even if some cooperation exists
network management capable of handling the GPRS-specific elements
a new air interface for packet traffic
new security features for the GPRS backbone and a new ciphering algorithm
new MAP and GPRS-specific signalling
Nokia White Paper Wed Mar 16 00:26:40 CST 2011

GSM w/o GPRS	end-to-end transmission
GSM with GPRS	link-by-link transmission

Serving GPRS Support Nodes SGSN
Gateway GPRS Support Nodes GGSN
GPRS backbone
Point-to-multipoint Service Centre PTM SC

Untitled Document

GPRS Logical Architecture

Wed Mar 16 00:26:41 CST 2011 Untitled Document

GPRS Architecture

Wed Mar 16 00:26:41 CST 2011 Untitled Document

GPRS Network Elements

SGSN	Serving GPRS Support Node
GGSN	Gateway GPRS Support Node
NMS	Network Management System
BG	Border Gateway
CG	Charging Gateway
FW	Firewall
LIG	Lawful Interception Gateway

Additional Facilities

GPRS-specific mobility management: the location of the MS is handled separately by the SGSN and by the MSC/VLR even if some cooperation exists
network management capable of handling the GPRS-specific elements
a new air interface for packet traffic
new security features for the GPRS backbone and a new ciphering algorithm
new MAP and GPRS-specific signalling

Wed Mar 16 00:26:42 CST 2011 Untitled Document

SGSN and GGSN Functionalities

SGSN	GGSN
Authentication GTP tunneling to GGSN Ciphering & compression Mobility management Interaction with HLR, MSC/VLR Charging & statistics NMS interfaces	GTP tunneling to SGSN Interfaces to external IP networks Charging & statistics NMS interfaces

Wed Mar 16 00:26:43 CST 2011 Untitled Document

GPRS Data Transfer

Wed Mar 16 00:26:44 CST 2011 Untitled Document

GPRS Addressing

Core Network and the GPRSsubscribers use different IP address spaces
Core invisible to subscribers and vice versa
Core carries subscriber traffic in GPRS Tunnel

Wed Mar 16 00:26:45 CST 2011 Untitled Document

GPRS GPRS Multislot Capabilities

Wed Mar 16 00:26:45 CST 2011 Untitled Document

GPRS Core Network

Connect core elements together

SGSN	GGSN	Border Gateway
DNS	NMS	Charging Gateway

Private IP network which is isolated and invisible to external networks or GPRSsubscribers

Carries subscriber IPtraffic in GPRSspecific tunnels (GTP)

Carries GPRS specific signaling between GSNs

Carries charging data from GSNs to Charging Gateway

Carries GPRS core management information (SNMP, Web)

Interconnectd GPRS Core network comprise a large private network

Wed Mar 16 00:26:45 CST 2011 Untitled Document

GPRS Protocol Layer

Wed Mar 16 00:26:46 CST 2011 Untitled Document

Protocol Stack for Tunneling

Wed Mar 16 00:26:47 CST 2011 Untitled Document

GPRS Authentication

Wed Mar 16 00:26:47 CST 2011 Untitled Document

MS State Model

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MS Attach

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MS Dettach

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Signal Flow

Wed Mar 16 00:26:49 CST 2011 Untitled Document

PDP Activation

Subscriber data transfer is possible only when the PDP Context is activated

MS, SGSN, GGSN

PDP Context is activated per PDP address

PDP context contains mapping and routing information in MS, SGSN & GGSN

Enables data transfer between MS and GGSN

PDP Context Activation initiated by the MS

Request from application/TE via PPP protocol or AT command

GPRS Attach procedure may be performed if not yet GPRS attached

PDP	Packet Data Protocol (e.g. IP)
MS	Mobile Station
TE	Terminal Equipment
PPP	Point-to-Point Protocol

Wed Mar 16 00:26:50 CST 2011 Untitled Document

PDP Context Activation - 1

(1) MS sends "Activate PDP Context Request" to SGSN

Access Point Name

PDP Type (IP)

PDP Address (empty == dynamic)

QoS & other options

(2) SGSN checks against HLR

Access Point Name

Dynamic / static IP address

Wed Mar 16 00:26:51 CST 2011 Untitled Document

PDP Context Activation - 2

Finding the GGSN

(1) SGSN gets the GGSN IP address from DNS

APN maps to the GGSN IP address

(2) SGSN sends "Create PDP Context Request" to GGSN

PDP Type (IP)

PDP Address (if empty=> dynamic address)

Access Point Name

QoS & other options

Wed Mar 16 00:26:51 CST 2011 Untitled Document

PDP Context Activation - 3

Access Point Selection

Access Point Name refers to the external network the subscriber wants to use

Physical/logical interface in GGSN

Access Point configuration in GGSN defines where to connect the user

If dynamic address, can be allocated by GGSN or external RADIUS or DHCP server

DHCP	Dynamic Host Configuration Protocol
RADIUS	Remote Authentication Dial In User Service

Wed Mar 16 00:26:52 CST 2011 Untitled Document

PDP Context Activation - 4

Context Activated

User authenticated OK (non-transparent case)

User dynamic IP address allocated by

RADIUS server, or

DHCP server, or

GGSN internal pool

(1) GGSN sends "Create PDP Context Response" back to SGSN

(2) SGSN sends "Activate PDP Context Accept" to the MS

SGSN now ready to route user traffic between MS and GGSN

Wed Mar 16 00:26:52 CST 2011 Untitled Document

Location Management

Intra SGSN Routing Area Update

MS sends Routing Area Update Request to SGSN
The SGSN validates the MS's presence in the new RA. If OK SGSN updates MM context for the MS
Routing Area Accept message returned to MS

Inter SGSN Routing Area Update

MS sends Routing Area Update Request to new SGSN
New SGSN sends context request to old SGSN
Old SGSN sends response and starts tunnelling data to new SGSN
The new SGSN sends "Update PDP Context Request" to GGSN
The new SGSN informs HLR of the SGSN change by sending "Update Location" to HLR
HLR sends "Cancel Location" to old SGSN

Wed Mar 16 00:26:53 CST 2011 Untitled Document

GPRS Mobility Management

Wed Mar 16 00:26:54 CST 2011 Untitled Document

Roaming

Roaming Between Two Interconnected Operators

Wed Mar 16 00:26:54 CST 2011 Untitled Document

Roaming in GPRS

While attached to the visited network the subscriber can use Access Point provided by

Home network, or

Visited network

HLR subscriber information includes flag if

User is allowed to use visited network Access Point

User can select home or visited Access Point, or

User needs to use the Access Points in home network

Access Point Name syntax:

Wed Mar 16 00:26:55 CST 2011 Untitled Document

Using Access Point in Home PLMN

1. Visiting user selects to use Home APN
2. MS sends "Activate PDP Context"
3. SGSN asks for GGSN IP address (using APN as the key) from Visited DNS
4. Visited DNS asks Root DNS "who knows the IP address for this name ?"
5. Root DNS replies the Home DNS address to Visited DNS
6. Visited DNS asks Home DNS for GGSN address
7. Home DNS replies the GGSN IP address
8. Visited DNS replies SGSN
9. SGSN creates PDP Context with Home GGSN

APN: my.isp.com.myoperator.fi.gprs

Wed Mar 16 00:26:56 CST 2011 Untitled Document

Roaming Arrangements between Operators

Routing between operator's networks

Border Gateways (routers)

Border Gateway Protocol (BGP-4)

Domain Name System

Each backbone needs its own DNS

SGSN to find GGSN (Access Point Name) for Context Activation

SGSNs to find each other during RA Update

Root DNS required to manage name resolving between PLMNs

Who will establish and maintain root DNS ?

MoU ? Some operator ? Service Provider ?

Billing clearing between operators

Not defined by ETSI standards, operators need to agree mutually

Wed Mar 16 00:26:56 CST 2011 Untitled Document

External Network Connections:

Basic Access types

Transparent access to the Internet

GGSN has no active role in user authentication

Subscriber IP address static or allocated by GGSN from operator's address space

Operator acting as ISP providing Internet access and possibly own Value Added Services (email, web etc)

Non-Transparent access to Intranets, ISPs

GGSN provides user authentication towards RADIUS server

Subscriber IP address allocated from intranet address space

This is a typical intranet access case

The same GGSN can provide both Transparent and Non-Transparent Access Points

Wed Mar 16 00:26:57 CST 2011 Untitled Document

Transparent access to the Internet

Subscriber IP address from operator addres space

Static (by subscription) or dynamic address

Operator acting as ISP

"Transparent access"

Wed Mar 16 00:26:58 CST 2011 Untitled Document

Internet Access - Large Subscriber Base

NAT	Network Address Translation

Wed Mar 16 00:26:58 CST 2011 Untitled Document

IP Address Translation

Mapping several private, unregistered IP addresses used in GPRS mobiles to a single public IP address + port number.

10.1.1.1	123.45.40.1:61001
10.1.1.2	123.45.40.1:61002
10.1.1.3	123.45.40.1:61003
10.1.1.4	123.45.40.1:61004
10.1.1.5	123.45.40.1:61005
…	…
10.1.1.254	123.45.40.1:61254

Pros and Cons

+ Less public IP addresses needed
+ Security: private addresspace invisible to the Internet
- IP Multicast does not work
- IPsec does not work

Wed Mar 16 00:26:59 CST 2011 Untitled Document

Access to Intranets

Non-transparent Access

Subscriber IP address allocated from intranet address space

Address allocation from GGSN pool or intranet RADIUS server

The subscriber can be authenticated by the intranet RADIUS server

"Non-transparent access"

RADIUS	One widely used protocol/method for dynamic IP address allocation and user authentication

Wed Mar 16 00:26:59 CST 2011 Untitled Document

Access to Intranets: VPN

For a small and remote corporation, instead of a dedicated link, a VPN between GGSN and the intranet may be the reasonable solution.

Wed Mar 16 00:27:00 CST 2011 Untitled Document

GPRS Management Functions

Wed Mar 16 00:27:01 CST 2011 Untitled Document

GPRS OA&M Architecture

Wed Mar 16 00:27:01 CST 2011 Untitled Document

GPRS Core Network Management

Performance management

Configuration management

Alarms

Security management

Real-time clock management

Software download

Wed Mar 16 00:27:02 CST 2011 Untitled Document

MS Class

Wed Mar 16 00:27:02 CST 2011 Untitled Document

GPRS Charging

Charging data is collected from SGSN and GGSN

Collected charging information:

Mobility management data
Duration of PDP context
Data volume uplink/downlink
Usage of external networks (= Access Point)
SGSN & GGSN address

Specific GTP' protocol used to carry CDRs from SGSN/GGSN to Charging Gateway

Wed Mar 16 00:27:03 CST 2011 Untitled Document

Security Consideration

Source of Attack

GPRS mobile users
External networks
Operator's personnel
Other mobile networks
Malfunctioning equipment

Damage Zone

Crash of network
Access to management, charging etc. information
Misconfigure the network
Denial of service. lower QoS
Information confidentiality
Integrity and authenticity
etc.

Security Mechanisms

Physical security against network element access
Host authentication
Ciphered links
Personnel security with authorization

Wed Mar 16 00:27:03 CST 2011 Untitled Document

Using Access Point in Home PLMN

Wed Mar 16 00:27:04 CST 2011