General Packet Radio

Service (GPRS)
 Topics
GPRS and packet data network
 Capacity and Other End-user Aspects
 Quality of Service (QoS)
 Integral Part of the Future 3G Systems
GPRS network architecture
 GPRS Network Enhancements
 Channel Coding
 Transmission Plane Protocol Architecture
 Security
GPRS network operation
 Attachment and Detachment Procedure
 Mobility Management
 Routing
 Communicating with the IP Networks
 Topics
Data services in GPRS
 GPRS Handsets
 Device Types
 Bearers in GPRS
Applications of GPRS
 Generic Applications
 GPRS-Specific Applications
LIMITATIONS OF GPRS
Billing and charging in GPRS
 Tarifing
 Billing
 Introduction
The popularity of GSM, Internet, and digital
communication forced GSM to look For wireless
data with higher band-width. General Packet Radio
Service (GPRS) is a step to efficiently transport
high-speed data over the current GSM and TDMA-
based wireless network infrastructures.
 GPRS and Packet Data Network
Capacity and Other End-user Aspects

 data speeds of 14.4 KBps to 171.2 KBps.

 It also allows short `bursty' traffic, such as e-
mail and web browsing, as well as large
volumes of data.
 For GPRS, no dial-up modem connection is
necessary
 Capacity and Other End-user Aspects
 It offers fast connection set-up mechanism to
offer a perception of being `always on'.
 Immediacy is one of the advantages of GPRS
compared to Circuit Switched Data.

By allowing information to be transmitted more

quickly, immediately and efficiently across the
mobile network, GPRS may well be a relatively
less costly mobile data service compared to
SMS and Circuit Switched Data.
 Quality of Service (QoS)
GPRS allows definition of QoS profiles using the
parameters :
• Service precedence
is the priority of a service in relation to another service.
• Reliability
indicates the transmission characteristics required by an
application. Three reliability classes are defined, which guarantee
certain maximum values for the probability of loss, duplication, mis
sequencing and corruption (an undetected error) of packets.

• Delay
define maximum values for the mean delay and the 95-percentile
delay.
• Throughput
specifies the maximum/peak bit rate and the mean bit rate.
Integral Part of the Future 3G Systems
The different approaches to third generation (3G) wireless
systems (IMT-2000, UMTS, CDMA, WCDMA, 3GPP,
3GPP2 etc.) were intended to address the challenge of
voice-to-data crossover and integration.
The complexities of new and exciting wireless technologies
have slowed down progress in their development and
widespread deployment. To lessen the impact of the delay
in implementing 3G wireless systems, GPRS is introduced
as an intermediate step to efficiently transport high-speed
data over the current GSM and TDMA-based wireless
network infrastructures.
GPRS is therefore called the 2.5G (two and
half G or two and half generation) in the evolution process
of wireless cellular networks.
 GPRS NETWORK ARCHITECTURE
GPRS uses the GSM architecture for voice.
In order to offer packet data services through GPRS, a new
class of network nodes need to be introduced as an
upgrade to existing GSM network.
These network nodes are called GPRS support nodes (GSN).
GPRS support nodes are responsible for the delivery and
routing of data packets between the mobile stations and the
external packet data networks (PDN).
There are two types of support nodes, viz.,
SGSN (Serving GSN) and
GGSN (Gateway GSN).
 GPRS NETWORK ARCHITECTURE
Serving GPRS Support Node (SGSN):
A serving GPRS support node (SGSN) is at the same hierarchical level
as the MSC. Whatever MSC does for voice, SGSN does the same
functions for packet data.
SGSN's tasks include packet switching, routing and transfer, mobility
management (attach/detach and location management), logical link
management, and authentication and charging functions.
SGSN processes registration of new mobile subscribers and keeps a
record of their location inside a given service area.
The location register of the SGSN stores location information (e.g.,
current cell, current VLR) and user profiles of all GPRS users registered
with this SGSN.
SGSN sends queries to Home Location Register (HLR) to obtain profile
data of GPRS subscribers. The SGSN is connected to the base station
system with Frame Relay.
GPRS NETWORK ARCHITECTURE
 GPRS NETWORK ARCHITECTURE
Gateway GPRS Support Node (GGSN):
A gateway GPRS support node (GGSN) acts as an interface between
the GPRS backbone network and the external packet data networks.

GGSN maintains routing information that is necessary to tunnel the

Protocol Data Units (PDUs) to the SGSNs that service particular mobile
stations. It converts the GPRS packets coming from the SGSN into the
appropriate packet data protocol (PDP) format for the data networks like
Internet or X.25.

PDP sends these packets out on the corresponding packet data

network. In the other direction, PDP receives incoming data packets
from data networks and converts them to the GSM address of the
destination user. The re addressed packets are sent to the responsible
SGSN. For this purpose, the GGSN stores the current SGSN address of
the user and his or her profile in its location register.

The GGSN also performs authentication and charging functions related

to data transfer.
 GPRS Network Enhancements
Base Station System (BSS)
BSS system needs enhancement to recognize and send packet data.
This includes BTS upgrade to allow transportation of user data to the
SGSN. Also, the BTS needs to be upgraded to support packet data
transportation between the BTS and the MS (Mobile Station) over the
radio.
Home Location Register (HLR)
HLR needs enhancement to register GPRS user profiles and respond
to queries originating from GSNs regarding these profiles.
Mobile Station (MS)
The mobile station or the mobile phone for GPRS is different from that
of GSM.
SMS nodes
SMS-GMSCs and SMS-IWMSCs are upgraded to support SMS
transmission via the SGSN. Optionally, the MSC/VLR can be enhanced
for more efficient co-ordination of GPRS and non-GPRS services and
functionality.
 Channel Coding
Channel coding is used to protect the transmitted data packets
against errors.
The channel coding technique in GPRS is quite similar to the
one employed in conventional GSM.
Under very bad channel conditions, reliable coding scheme is
used.
In reliable coding scheme many redundant bits are added to
recover from burst errors. In this scheme a data rate of 9.05
Kbps is achieved per time slot.
Under good channel conditions, no encoding scheme is used
resulting in a higher data rate of 21.4 Kbps per time slot.
With eight time slots, a maximum data rate of 171.2 Kbps
can be achieved.
 Transmission Plane Protocol Architecture
Signaling Plane
The protocol architecture of the signaling plane comprises protocols for
control and support of the functions of the transmission plane.
This includes GPRS attach and detach, PDP context activation, control
of routing paths, and allocation of network resources.
The signaling architecture between SGSN and the registers like HLR,
VLR, and EIR uses the same protocols as GSM. However, they are
extended to support GPRS-specific functionality.
Between SGSN and HLR as well as between SGSN and EIR, an
enhanced MAP (Mobile Application Part) is employed.
MAP is a mobile network-specific extension of the Signaling System
SS#7 used in GSM.
It transports the signaling information related to location updates,
routing information, user profiles, and handovers
 Transmission Plane Protocol Architecture
The exchange of MAP messages is accomplished over the transaction
capabilities application part (TCAP) and the signaling connection
control part (SCCP).

The base station system application part (BSSAP+) is an enhancement

of GSM's BSSAP. It is used to transfer signaling information
between the SGSN and the VLR.

GPRS Backbone
GPRS backbone includes the transmission plane between SGSN and
GGSN.

User data packets and related signaling information within the GPRS
network are encapsulated using the GPRS Tunneling Protocol
(GTP).

The GTP protocol is used in both intra-PLMN (between SGSN and

GGSN within one PLMN) and inter-PLMN (between SGSN and
GGSN of different PLMNs).
 GPRS Backbone
In the transmission plane, GTP protocol tunnels the user data packets
through the GPRS backbone by adding GPRS specific routing
information. GTP packets carry the user's data packets from both IP
and X.25 data networks.

Below GTP, the standard protocols TCP or UDP are used to transport
the GTP packets within the backbone network.

X.25 expects a reliable data link; therefore TCP is used for tunneling
X.25 data.

For IP based user data, UDP is used as it does not expect reliability in
the network layer or below. Ethernet, ISDN, or ATM-based
protocols may be used in the physical layer in the IP backbone.

In essence, in the GPRS backbone we have an IP/X.25-over-GTP-over-

UDP/TCP-over-IP transport architecture.
GPRS Backbone
 BSS-SGSN Interface
The BSS and SGSN interface is divided into the following
layer:
o Sub-Network Dependent Convergence Protocol (SNDCP)
o Logical Link Control (LLC)
o Base Station System GPRS Protocol (BSSGP)
o Network Service

SNDCP
The SNDCP is used to transfer data packets between SGSN and MS.
Its functionality includes:

• Multiplexing of several connections of the network layer onto

one virtual logical connection of the underlying LLC layer.
• Segmentation, compression, and decompression of user
data.
 BSS-SGSN Interface

Logical Link Control (LLC)

a data link layer protocol for GPRS which functions similar to Link
Access Procedure-D (LAPD). This layer assures the reliable
transfer of user data across a wireless network.

Base Station System GPRS Protocol (BSSGP)

The BSSGP delivers routing and QoS-related information between BSS
and SGSN.

Network Service
This layer manages the convergence sublayer that operates between
BSSGP and the Frame Relay Q922 Core by mapping BSSGP's
service requests to the appropriate Frame Relay services.
 Air Interface
The air interface of GPRS comprises the physical and data link layer.
Data Link Layer
The data link layer between the MS and the BSS is divided into three
sub layers:
the logical link control (LLC) layer,
the radio link control (RLC) layer
the medium access control (MAC) layer.
Logical Link Control (LLC)
This layer provides a reliable logical link between an MS and its
assigned SGSN.
Its functionality is based on HDLC (High-level Data Link Control)
protocol and includes sequence control, in-order delivery, flow
control, detection of transmission errors, and retransmission
(automatic repeat request, ARQ)
 Air Interface
Variable frame lengths are possible.
Both acknowledged and unacknowledged data transmission modes are
supported. This protocol is an improved version of the LAPDm
protocol used in GSM.

Radio Link Control (RLC)

The main purpose of the radio link control (RLC) layer is to establish a
reliable link between the MS and the BSS.

This includes the segmentation and reassembly of LLC frames into

RLC data blocks and ARQ of uncorrectable data.
 Air Interface

Medium Access Control (MAC)

The medium access control (M.AC) layer controls the access attempts
of an MS on the radio channel shared by several :VISs. It employs
algorithms for contention resolution, multiuser multiplexing on a
packet data traffic channel (PDTCH), and scheduling and prioritizing
based on the negotiated QoS.
 Air Interface
Physical Layer
Physical Link Layer (PLL)

This layer provides services for information transfer over a physical channel
between the MS and the network.

These functions include data unit framing, data coding, and the detection
and correction of physical medium transmission errors.

The Physical Link layer uses the services of the Physical RF layer.

Physical RF Layer (RFL):

This layer performs the modulation of the physical waveforms based on the
sequence of bits received from the Physical Link layer above.
The Physical RF layer also demodulates received wave forms into a
sequence of bits that are transferred to the Physical Link layer for
interpretation.
 Multiple Access Radio Resource
Management
As in GSM, GPRS uses two frequency bands at 45
MHz apart; viz.,
890-915 MHz for uplink (MS to BTS),
935-960 MHz for downlink (BTS to MS).
Each of these bands of 25 MHz width is divided into
124 single carrier channels of 200 kHz width.
Each of these 200 kHz frequency channels is divided
into eight time slots.
Each time slot of a TDMA frame lasts for a duration of
156.25 bit times and contains a data burst.
 Multiple Access Radio Resource
Management
As with GSM channels can be divided
into two categories: traffic channels and signaling channels.
Traffic channel allocation in GPRS is different from that of GSM.

in GPRS traffic, channels are only allocated when data packets are
sent or received. They are released after the transmission of data.

GPRS allows a single mobile station to use multiple time slots of the
same TDMA frame for data transmission. This is known as
multislot operation and uses a very flexible channel allocation.

One to eight time slots per TDMA frame can be allocated for one
mobile station.

Uplink and downlink are allocated separately, which efficiently

supports asymmetric data traffic.
 Multiple Access Radio Resource
Management
In GPRS, physical channels to transport user data packet is
called data traffic channel (PDTCH). The PDTCHs are taken
from a common pool of all channels available in a
cell. Thus, the radio resources of a cell are shared by all
GPRS and non-GPRS mobile stations located within the
cell. The mapping of physical channels to either packet
switched data (in GPRS mode) or circuit switched data (in
GSM mode) services are performed dynamically depending
on demand.
SECURITY
SGSN performs the authentication
 GPRS Network Operations
Attachment and Detachment Procedure
The network checks if the MS is authorized to use the services; if so, it
copies the user profile from the HLR to the SGSN, and assigns a
packet temporary mobile subscriber identity (P-TMSI) to the MS.
In order to exchange data packets with external PDNs after
a successful GPRS attach, a mobile station must apply for an
address. If the PDN is an IP network, it will request for an IP
address; for a X.25 network it will ask for a X.25 DTE (Data Terminal
Equipment) address. This address is called PDP (Packet Data
Protocol) address.
For each session, a PDP context is created. It contains
the PDP type (e.g., IPv4)
the PDP address assigned to the mobile station (e.g., 129.187.222.10)
 GPRS Network Operations
the requested QoS, The address of the GGSN that will
function as the access point to the PDN.
This context is stored in the MS, the SGSN and the GGSN.
With an active PDP context, the MS is `visible' to the
external PDN.
The allocation of the PDP address can be static or
dynamic.
Static PDP address is permanently assigned by the
network operator.
Dynamic PDP address
GGSN is responsible for the allocation and the
activation/deactivation of the PDP addresses.
GPRS Network Operations
 GPRS Network Operations
Mobility Management
SGSNs communicate with each other to update the MS's
location in the relevant registers.
The mobile station's profiles are preserved in the VLRs that
are accessible to SGSNs via the local MSC.
A logical link is established and maintained between the
mobile station and the SGSN at each PLMN.
At the end of transmission or when a mobile station moves
out of the area of a specific SGSN, the logical link is released
and the resources associated with it can be reallocated.
GPRS Network Operations
 GPRS Network Operations
Routing
The network components are
Intra-PLMN backbone
Inter-PLMN backbone (border gateways)

Let us assume the home-PLMN of the mobile station is PLMN2. An IP

address has been assigned to the mobile by the GGSN of PLMN2. Thus,
the MS's IP address has the same network prefix as the IP address of the
GGSN in PLMN2.
The HLR stores the user profile, the current SGSN address, and the PDP
addresses for every GPRS user in the PLMN. For example, the SGSN
informs the HLR about the current location of the MS. When the MS
registers with a new SGSN, the HLR will send the user profile to the new
SGSN. The signaling path between GGSN and HLR may be used by the
GGSN to query a user's location and profile in order to update its location
register.
Communicating with the IP Networks
 Communicating with the IP Networks
Each registered user who wants to exchange data packets with the IP
network gets an IP address.

The IP address is taken from the address space of the GPRS operator
maintained by a DHCP server (Dynamic Host Configuration Protocol).

The address resolution between IP address and GSM address is performed

by the GGSN, using the appropriate PDP context.

a domain name server (DNS) managed by the GPRS operator or the

external IP network operator is used to resolve host names.

To protect the PLMN from unauthorized access, a firewall is installed

between the private GPRS network and the external IP network.

With this configuration, GPRS can be seen as a wireless extension of the

Internet all the way to a mobile station or mobile computer. The mobile user
has direct connection to the Internet.
 DATA SERVICES IN GPRS
A wide range of corporate and consumer applications are enabled by GPRS
services. A user is likely to use either of the two modes of the GPRS
network.
Application mode
Tunneling mode.
Application mode:
In this mode the user will be using the GPRS mobile phone to access the
applications running on the phone itself. Some GPRS devices support mobile
execution environment (MExE classmark 3). These devices support development of
client application that can run on the device. The device operating execution
environments supported are Symbian and J2ME. Applications can be developed in
C/C++ or Java.
Tunneling mode:
This mode is for mobile computing where the user will use the GPRS interface as an
access to the network. The end user device will be a large footprint device like
laptop computer or small footprint device like PDAs. The mobile phone will be
connected to the device and used as a modem to access the wireless data network.
 DATA SERVICES IN GPRS
GPRS Handsets
A GPRS terminal can be one of three classes A, B or C.

A Class A terminal supports GPRS data and other GSM services such as
SMS and voice simultaneously.
This includes simultaneous attach, activation, monitor, and traffic.
Class A terminal can make or receive calls on two services simultaneously.
SMS is supported in Class A terminal. Like GSM, SMS can be received while
a voice or data call is in progress.

A Class B terminal can monitor GSM and GPRS channels simultaneously, but
can support only one of these services at any time. Class B terminal can
support simultaneous attach, activation, and monitor but not simultaneous
traffic. users can make or receive calls on either a packet or a switched call
type sequentially but not simultaneously.
 DATA SERVICES IN GPRS
A Class C terminal supports only non simultaneous attach. The user must
select which service to connect to. Therefore, a Class C terminal can make or
receive calls from only the manually selected network service. The service
that is not selected is not reachable. The GPRS specifications state that
support of SMS is optional for Class C terminals.

Device Types

In addition to the three types of terminals, each handset will have a unique
form factor. Terminals will be available in the standard form factor with a
numeric keypad and a relatively small display. Other types of phones with
different form factors, color displays, with cameras are common. Smart
phones with built-in voice, non voice and Web-browsing capabilities are
common too. Smart phones have various form factors, which may include a
keyboard or an icon drive screen.
 DATA SERVICES IN GPRS
Bearers in GPRS
The bearer services of GPRS offer end-to-end packet switched data transfer.
GPRS is planned to support two different kinds of data transport services.

the point-to-point (PTP) service

the point-to-multipoint (PTM) service.

GPRS will support the following types of data services:

SMS
WAP
MMS
 APPLICATIONS FOR GPRS
Generic Applications
Generic applications are applications like information services, Internet
access, email, Web Browsing,
There are generic mass market applications offering contents like sports
scores, weather, flight information, news headlines, prayer reminders, lottery results,
jokes, horoscopes, traffic information and so on.

GPRS Specific Applications

Chat
Multimedia Service
Virtual Private Network
Personal Information Management
Job Sheet Dispatch
Unified Messaging
Location-based Services and Telematics
 LIMITATIONS OF GPRS

Limited Cell Capacity for All Users:

Lower Speed in Reality

 BILLING AND CHARGING IN GPRS
For voice networks tariffs are generally based on distance and time.

This in other words means that user pays more for long distance calls. They
also pay more if they keep the circuit busy by talking for a longer period of
time.

Data services have evolved from research and education without any
concept of charging. In packet network keeping the circuit busy does not
have any meaning. Also, charging a customer by the distance traversed by
a packet does

Tariffing
Charging different packets at different rates can make things complicated
for the user, whilst flat rates favor heavy users more than occasional ones.

It is believed that the optimal GPRS pricing model will be based on two
variables, time and packet
 BILLING AND CHARGING IN GPRS
Network operators will levy a nominal per packet charge during peak times
plus a flat rate. There will be no per packet charge during non-peak times.

Time and packet-related charging will encourage applications such as

remote monitoring, meter reading and chat to use GPRS at night when
spare network capacity is available.

a nominal per packet charge during the day will help to allocate scarce
radio resources, and charge radio heavy applications such as file and
image transfer more than applications with lower data intensity. It has the
advantage of automatically adjusting customer charging according to their
application usage.
 BILLING AND CHARGING IN GPRS
GPRS is essentially a packet switching overlay on a circuit switching
network. The GPRS specifications stipulate that the minimum charging
information that must be collected are:
• Destination and source addresses
• Usage of radio interface
• Usage of external Packet Data Networks
• Usage of the packet data protocol addresses
• Usage of general GPRS resources and location of the Mobile Station.

The billing of the services can be based

on the transmitted data volume,

the type of service,
the chosen QoS profile.