• GSM is by far the biggest 2G system, with more than 400
million subscribers (by the end of 2000) and adding 10 million
more each month.
• As with other 2G systems, GSM handles voice efficiently, but
the support for data and Internet applications is limited.
• A data connection is established in just the same way as a
regular voice call: The user dials in and a circuit-switched
connection continues during the entire session. If the user
disconnects and wants to reconnect, the dial-in sequence has
to be repeated. This issue, coupled with the limitation that
users are billed for the time that they are connected, creates
a need for packet data for GSM.
For Data Communication:--
2G GSM std BW of 9.6 kbps is not sufficient
Web browsing, file download and e-mail with attachments
etc were not possible.
So data transmission capabilities of GSM were enhanced using
a. Connection oriented traffic channels (HSCSD)
b. Packet oriented traffic channels (GPRS)
Connection oriented traffic channels (HSCSD):
Higher data rates are achieved by bundling several
• With High-Speed, Circuit -Switched Data (HSCSD), the same
circuit-switched technology is used as regular GSM, but
multiple timeslots can be used for one connection. In other
words, one user can achieve up to 57.6Kbps of data speed.
• The first HSCSD systems appeared in 2000.
• This format enables users who are already frequently
checking their mail and using the Internet/intranet on the go
to achieve higher speeds.
Comparison of GSM & GPRS
Circuit – Switched
14.4 to 115.2
Three key features of GPRS
• Always online.
– Removes the dial-up process, making applications only one click away.
• An upgrade to existing networks (GSM and TDMA).
– Operators do not have to replace their equipment; rather, GPRS is
added on top of the existing infrastructure.
• An integral part of EDGE and WCDMA.
– GPRS is the packet data core network for these 3G systems.
The Need for Packet Data
• A circuit -switched connection to some site works just like a
regular telephone call. You dial in to your Internet Service Provider
(ISP) and have your 9.6Kbps as long as you are connected
What is GPRS ?
General Packet Radio Service (GPRS) is a new
bearer service for GSM that greatly improves and
simplifies wireless access to packet data networks
GPRS applies packet radio principal to transfer
user data packets in an efficient way between MS &
external packet data network
GPRS is a step towards 3G and is often referred to
GPRS is a step towards 3G and is often referred to
Here are some key benefits of GPRS
GPRS is packet switched.
Higher connection speeds are attainable at around 14–115 kbps, a
vast improvement on circuit switched networks of 9.6 kbps.
By combining standard GSM time slots theoretical speeds of 171.2
kbps are attainable.
Always on connectivity:
GPRS is an always-on service.
There is no need to dial up like you have to on a home PC for
instance. This feature is not unique to GPRS but is an important
standard that will no doubt be a key feature for migration to 3G.
It makes services instantaneously available to a device.
Reserves radio resources only when there is data to send
New and Better applications
Due to its high-speed connection and always-on connectivity GPRS
enables full Internet applications and services such as video
conferencing straight to your desktop or mobile device.
Users are able to explore the Internet or their own corporate
networks more efficiently than they could when using GSM. There is
often no need to redevelop existing applications.
GSM operator Costs
GSM network providers do not have to start from scratch to deploy
GPRS. GPRS is an upgrade to the existing network that sits along side
the GSM network.
This makes it easier to deploy, there is little or no downtime of the
existing GSM network whilst implementation takes place, most updates
are software so they can be administered remotely and it allows GSM
providers to add value to their business at relatively small costs.
Features of GPRS:
Important step on the path to 3G
Standardized by ETSI (European Telecommunications Standard Institute)
GPRS is an overlay network over the GSM
Provides Data Packet delivery service
Support for leading internet communication protocols
Billing based on volume of data transferred
Utilizes existing GSM authentication and privacy procedures
High Data Rate
• GPRS uses radio channel i.e. 200 kHz wide
• Radio channel carries digital data stream of
• This rate is divided into 8 time slots each
carrying 34 kbps per time slot
• Data rate approx.~14 kbps per time slot
achieved after corrections
• GPRS can combine up to 8 time slots giving
data rate of approx. ~114 kbps
1. GPRS is a 2.5G technology.
2. It uses existing cellular n/w infrastructure
3. S/w upgrade at base stations and the addition of a
GPRS Gateway that connects the GPRS network to
the Internet is required.
4. FDMA based multiple access techniques.
5. A user is assigned to one pair of up-link and downlink frequency channels. This is combined with
time domain i.e. packet mode communication.
6. The packets have constant length, corresponding
to a GSM time slot.
Duplex separation: 45 MHz
RF carrier spacing: 200 kHz
Total number of RF Duplex channels: 124
Number of TDMA slots on each carrier: 8
Channel allocation: 1 to 8 time slots per TDMA
One time slot (Physical channel) : 0.577 ms
Frame Interval: 4.615 ms
Asymmetric data traffic: different time slots for Uplink and
9. Frequency Hopping: 217 hops/s
10. Connectivity: Packet switched data networks such as IP and
11. Extra nodes:
Gateway GPRS Support Node (GGSN) and
Serving GPRS Support Node (SGSN)
• Offers end-to-end packet switched data transfer
• Bearer Services
• PTP - Point-To-Point service
• PTM - Point-To-Multipoint service
• PTM-M Multicast service (News,whether
• PTM-G Group call service (conferencing