The document provides an overview of GPRS (General Packet Radio Service) technology. It discusses: - The need for GPRS to provide faster speeds, immediacy, new applications, and user-friendly billing. - The history and development of GPRS from HSCSD as an upgrade path for GSM networks. - Key GPRS network elements like the SGSN, GGSN, and their roles in routing packets and connecting to external networks. - GPRS architecture and how it works in parallel with existing GSM networks. - Logical channels used for control, signaling, and transport of user data packets.

1. GPRS
Presented by
Hrudya

2. Need for GPRS
 Speed
 Immediacy
 New
and better applications
 User friendly billing

3. History

In 1994, a Special Mobile Group started to think
about a High Speed Data upgrade for GSM.

The first step was HSCSD (High Speed Circuit
Switched Data).


HSCSD is a circuit-switched extension to GSM.
The next step was GPRS.

GPRS is a packet-switched extension to GSM.

4. What is HSCSD?

HSCSD (High Speed Circuit Switched Data).



The simplest high speed data upgrade for GSM.
Provides GSM users with a bandwidth up to 57.6 Kbps.
Does not require a hardware upgrade within BSS or core
network (NSS), but different MS are needed.

5. What is GPRS?



GPRS is a packet oriented data service for IP and
X.25 over GSM networks.
GPRS is a step towards 3G and is often referred to
as 2.5G.
The GPRS network acts in parallel with the GSM
network, providing packet switched connections to
the external networks.

6. Functions

Traditional mobile communication network +
Traditional packet switched computer network.






Capability to separate circuit switched and packet
switched traffic from mobile station (MS)
Interfaces to Internet, intranets, Public Data Networks
(PDN)
Routing of packets to appropriate destination
Allocation of static or dynamic address for packets
originating from MS
Protection of the GPRS network from security threats
Translation between logical names and IP addresses
using Domain Name System (DNS)

7. The GPRS network and it’s new
elements.

8. GPRS Architecture

9. From GSM to GPRS....


10. 
Figure shows the architecture of a GPRS network. The GPRS system
brings some new network elements to an existing GSM network. These
elements are:










Packet Control Unit (PCU)
Serving GPRS Support Node (SGSN): the MSC of the GPRS
network
Gateway GPRS Support Node (GGSN): gateway to external
networks
Border Gateway (BG): a gateway to other PLMN (Public Land
Mobile Network)
Intra-PLMN backbone: an IP based network inter-connecting all
the
GPRS elements
Charging Gateway (CG)
Legal Interception Gateway (LIG)
Domain Name System (DNS)
Firewalls: used wherever a connection to an external network is
required.
Not all of the network elements are compulsory for every GPRS network.

11. SGSN (Service GPRS Support Node )




The SGSN is the most important element of the GPRS
network.
The SGSN of the GPRS network is equivalent to the MSC of
the GSM network. There must at least one SGSN in a GPRS
network.
There is a coverage area associated with a SGSN. As the
network expands and the number of subscribers increases,
there may be more than one SGSN in a network.
Handles:
 PDP contexts for Mobile Stations.
 Determines Quality of Service assigned to user.
 Routes packets to Mobile Stations.
 “Pages” Mobile Stations when data is to be sent.
 Handover/cell Change

12. 
Stores:



Security:



Subscriber data for all Mobile Stations in the location area.
Store not-acknowledged packets in case of a cell change during
an ongoing packet data transfer
Authentication, by means of identity or equipment check.
Data compression is used to minimise the size of transmitted data
units
Charging

The SGSN collects CDR's (Call Data Records) for the use of the
own network resources.

13. GGSN (Gateway GPRS Support Node)





The GGSN is the gateway to external networks.
Every connection to a fixed external data network
has to go through a GGSN.
The GGSN acts as the anchor point in a GPRS data
connection even when the subscriber moves to
another SGSN during roaming.
There are usually two or more GGSNs in a network
for redundancy purposes, and they back up each
other up in case of failure.
The functions of a GGSN are given below:

14. 
Handles:





Stores:


Interconnects a PLMN to the external world (Internet).
Routes IP packets to the appropriate SGSN.
Routing packets originating from a mobile to the correct external
network
Activation and Deactivation of PDP-Contexts / Session
Management.
Subscriber data for active Mobile Stations.
Security:

Interfaces to external IP networks and deals with security issues



Firewall.
Screening.
Charging


The GGSN will, in addition to the SGSN, collect CDRs and forward
them to the charging gateway (CG).
GGSN will collect call data records based on the usage of external
network resources .

15. Charging Gateway

GPRS users have to be charged for the use of the
network.




In a GSM network, charging is based on the destination,
duration, and time of call.
However, GPRS offers connectionless service to users, so it
not possible to charge subscribers on the connection
duration.
Charging has to be based on the volume, destination, QoS,
and other parameters of a connectionless data transfer.
These GPRS charging data are generated by all the SGSNs
and GGSNs in the network. This data is referred to as
Charging Data Records or CDRs.

16. 




One data session may generate a number of CDRs, so
these need to collected and processed.
The Charging Gateway (CG) collects all of these
records, sorts them, processes it, and passes it on to
the Billing System.
The GPRS subscriber is billed for the data transaction.
All CDRs contain unique subscriber and connection
identifiers to distinguish it.
A protocol called GTP„ (pronounced GTP prime) is
used for the transfer of data records between GSNs
and the Charging Gateway.

17. Border Gateway




The Border Gateway (BG) is a router that can provide a
direct GPRS tunnel between different operators' GPRS
networks. This is referred to as an inter- PLMN data
network.
It is more secure to transfer data between two operators„
PLMN networks through a direct connection rather than
via the public Internet.
The Border Gateway will commence operation once the
GPRS roaming agreements between various operators
have been signed.
It will essentially allow a roaming subscriber to connect to
company intranet through the Home GGSN via the
visiting PLMN network.

18. Domain Name Servers

These devices convert IP names into IP addresses
for example, server.nokia.com to 133.44.15.5.

19. Lawful Intercept Gateway


This is for monitoring traffic for law-enforcement
agencies that require court order.
When data packets traverse the GPRS network , it
may be intercepted and forwarded to the agencies.

20. Packet Control Unit




GPRS cell phone will trasmit data in Packet switched
mode and voice in circuit switched mode .
So there needs to be a network to differenciate the
different kinds of calls and send them to respective core
networks – voice call to MSC and data calls to SGSN.
PCU does this . PCU is placed at the Base station
subsystem (BSS) .
The functions of PCU are




Packet segmentation and reassembly
Access control
Scheduling for all active transmissions including radio channel
management
Controlling transmission for checking, buffering and
retransmission

21. Classes Of GPRS Equipments


As GPRS users need to handle both voice and data
services, the following classifications are made in the
perspective of GPRS equipment.
Class A.


Class B.


Equipments that handle voice calls and transfer data at
the same time
Equipments that can handle voice or data traffic
separately, and can put a packet transfer on hold to
receive a phone call
Class C.

Equipments that handle voice calls and transfer data , but
has to be disconnected from one mode explicitly inorder
to enable the other

22. GPRS Interfaces

23. 
Gb:




Gr:




Between a SGSN and a BSS.
The Gb interface carries the GPRS traffic and signalling
between the GSM radio network (BSS) and the GPRS network.
Frame Relay based network services is used for this interface.
Between an SGSN and the HLR.
The Gr gives the SGSN access to subscriber information in the
HLR.
The HLR can be located in a different PLMN than the SGSN
(MAP).
Gs:


Between a SGSN and a MSC.
The SGSN can send location data to the MSC or receive
paging requests from the MSC via this optional interface.

24. 


Gf:
 Between an SGSN and the EIR.
 The Gf gives the SGSN access to GPRS user equipment
information.
 The EIR maintains three different lists of mobile equipment:
black list for stolen mobiles, grey list for mobiles under
observation and white list for other mobiles .
Gc
 Between the GGSN and the HLR.
 The GGSN may request the location of an MS via this optional
interface.
 The interface can be used if the GGSN needs to forward
packets to an MS that is not active.
Gn

Between two GSNs (GPRS support node) within the same
PLMN. (GP interface is used if they are in different PLMN)

25. It consist of a protocol stack that includes IP and GPRS
Tunnelling Protocol (GTP)
 GTP has two parts , the GTP-U which is used to carry user
data and GTP-C to carry control data.
Gd:
 Interface connects the SGSN to an SMS gateway , thus
enabling the SGSN to support SMS services.
Gi:
 Is a references rather than an interface.
 It refers to the connection between the GGSN and some
external network
 IPV4, IPV6, and PPP are supported by GGSN
Um:
 Modified air interface between mobile device and the GPRS
network.





26. GPRS Logical channel

Logical channels in the GPRS network , are divided
into two categories




Traffic channels
Signalling/Control Channels
Logical channels are defined to perform multiple
functions like broadcast , paging , signalling and
payload transport.
They are listed in table

27. Group
Channel
Function
Direction
Packet Broadcast Control Channel
PBCCH
Broadcast
Control
BSS  MS
Packet Data Traffic Channel
PDTCH
Data traffic
flow
MS BSS
Packet Dedicated Control Channel
PACCH
Associated
Control
MS BSS
PTCCH
Timing Cntrl
PRACH
Random
Access
MS BSS
PAGCH
Access
Grant
MS BSS
PPCH
Paging
MS BSS
PNCH
Notification
MS BSS
Packet Common Control Channel
MS BSS

28. 
PDTCH:




PBCCH:



Packet Data Traffic Channel
Is employed for the transfer of user data, assigned to one
mobile station (MS) during data transfer.
Each MS can use several PDTCHs simultaneously
Packet Broadcast Control Channel.
Is a uni-directional point to multi point signalling channel
from base station sub system (BSS) to mobile stations.
PTCCH:


Packet Timing Advance Control Channel .
used for adaptive frame synchronisation.

29. 
PCCCH:




Packet Common Control Channel.
bi-directional point to multi point channel
Transport signalling information for network access
management
It consist of for sub channels as shown in table

30. GPRS Service Types

A PLMN provider is responsible for the data transfer
between the GPRS Service Access Points
Two kinds of services are presents

PTP (Point to Point):






Used for single packet transfer between two subscribers.
Operated in connection oriented (CONS) and connection
less mode (CLNS)
CONS for X.25
CLNS for IP
PTM (Point to Multipoint):

Supports transmission of data packets between a service
user and a specified group inside a certain geographical
region.

31. 
It is again divided into






PTM- Multicast (PTM-M).
PTM- Group (PTM-G)
In PTM-M Data packets are broadcast over a certain
geographical area.
A group identifier indicates whether the packets are intended
for all users or a group of users
PTM- Group (PTM-G) is meant for only certain group of users
The messages are addressed explicitly to a specified group
and are sent to all geographical region where the group
members are located .

32. GPRS States
Idle
GPRS Attach
GPRS Detach
Ready
Ready Timer
expired
Data transfer or
reception
Standby

33. 
Idle Mode. (MS off or not attached yet.).


Ready Mode. (MS is able to send and receive data).




If the MS is on, and is a Class B or Class C MS, the MS will
listen to the network, but not make any updating of where
the MS is. It is not possible to page an MS.
Cell updating is necessary.
If no activity within the timer (44s) the MS will fall back to a
stand-by state.
NOTE: an MS can be forced back to standby mode due to
lack of recourses.
Standby Mode. (MS is listening to the Network).

It is possible to page the MS.