ABSRTACT
Mobile telephony allowed us to talk on
the move. The Internet turned raw data into helpful services that people found
easy to use. Now, these two technologies are converging to create third
generation mobile services. In simple terms, third generation (3G) services
combine high-speed mobile access with Internet Protocol (IP)-based services.
But this doesn’t just mean fast mobile connection to the world wide web.
Rather, it means whole new ways to communicate, access information, conduct
business, learn, and be entertained -- liberated from slow, cumbersome
equipment and immovable points of access.
Mobile computing is being heralded as the new “killer app” for the
Internet.
While 3G hasn’t
arrived yet 2.5G is here! The technologies at the forefront of 2.5G push are
GPRS (General Packet Radio Service), EDGE (Enhanced Data rates for Global
Evolution.), WCDMA (Wideband Code Division Multiple Access), and WAP (Wireless
Application Protocol).
On
the road to 3G, we shall have an insight into the blossoming of 3G from 2G, the
technologies involved, & their areas of application.. GRPS and WAP are
definite stepping-stones on 3G wireless networks. Separately their improvements
are useful upgrades and together they are a significant departure from 2G
systems. A gradual transition and user acceptance for 3G could be a reality.
INTRODUCTION
Imagine
having a combined camera, video camera, computer, stereo, and radio included in
your mobile phone! It's possible with 3G, the future of wireless communications.
We will soon have high-speed access to a host of mobile multimedia services.
With access to any service anywhere, anytime, from one
terminal, the old boundaries between communication, information, media, and
entertainment will disappear. Services will truly converge.
"Mobility" will be offered with many services
that we currently regard as "fixed" -- indeed, Ericsson believes that
mobility will become the norm for many communication services. We’ll be able to
make video calls to the office and surf the Net simultaneously, or play
interactive games with friends at home -- wherever we may be. But 3G is not
just about applications that require high-speed data rates. It’s about
convenience and speed of access.
Ø
The following table gives an
overview of wireless generations from 1G of 3G :
TECHNOLOGY
|
FEATURES
|
|
First-generation wireless
|
AMPS Advanced Mobile Phone Service
|
-Analog voice service
- No data service |
Second-generation wireless
|
CDMA Call Division Multiple Access
TDMA Time Division Multiple Access
GSM Global System for
PDC Personal Digital Cellular
|
- Digital voice service
- 9.6K to 14.4K bit/sec.
- CDMA, TDMA and PDC offer one-way data transmissions only - Enhanced calling features like caller ID - No always-on data connection |
Third-generation wireless
|
W-CDMA Wide band Code Division Multiple Access
CDMA-2000 Based on the Interim Standard-95 CDMA
standard
|
- Superior voice quality
- Up to 2M bit/sec. always-on data - Broadband data services like video and multimedia - Enhanced roaming |
While 3G has not arrived yet what the industry calls
2.5G is here! The term 2.5G is an ad hoc term for migratory technologies
bridging the gap towards 3G. While one
cannot expect to see real time streaming video on the cell phone soon, 2.5G
technologies will enable e-mail management, web browsing and m-commerce (mobile
commerce). We will look at two complimentary technologies viz., GPRS and WAP,
at the forefront of 2.5G push.
GPRS (General Packet Radio Service)
It is a packet switched wireless protocol for global system for
mobile communications (GSM) that mirrors the Internet model and enables
seamless transition towards 3G networks. It transmits IP packets very
efficiently allowing profitable services to be marketed at attractive tariffs.
Hence it is an excellent platform for wireless data services and applications.
It permits burst transmission speeds of up to 115 Kbit/s (theoretically upto
even 171 Kbit/s). It is the first
transport mode to allow full instant Internet access and is an enabler for a
wide range of applications. In this sense
it truly may pave the way for UMTS (Universal Mode Telecommunication
Service ), a 3G service. As both are packet based technologies, GPRS will be
widely installed by operators as a step in the evolution towards the UMTS
world.
It works as an overlay data packet network on top of its underlying
circuit switched global system for mobile communications (GSM) radio network
which is the prevailing mobile standard in Europe
and most of Asia Pacific region. However it is also designed to work on TDMA
(Time Division Multiple Access) standard used by many mobile vendors in North America .
v
Features
:
Several features of 3G wireless networking are delivered by GPRS:
Its main features can be categorized from user perspective and
networking perspective.
·
User features :
The real advantage of GPRS is that it provides an
‘ALWAYS – ON’ connection between mobile terminal and the network. ‘Always – on’
does not mean that there is always a steady stream data connection; It just
means that, because data packets can be transmitted almost immediately i.e.,
instant IP connectivity, there is no costly connection time. Many current 2G
information services require a data connection over voice line. As a result,
users are charged by the minute for data services. This would not be necessary
with GPRS.
SPEED is main
advantage over existing networks. Using all 8 TDMA time slots in radio
interface, a maximum speeds of upto 171.2 Kbit/s are possible, that’s about 3
times faster than 56K modem and about 10 times faster CSD(Circuit Switched
Data) transfers currently used.
HIGHER BANDWIDTH enables applications such as low
quality video monitoring or music download.
·
Network features :
Packet switching replaces the circuit switched transfer
mechanism of GSM. Just like data transfers over internet, GPRS splits
information into separate related data packets that are transmitted and
reassembled at the termination. This allows the operators to implement IP
(Internet Protocol) based infrastructure for tomorrows 3G voice and data
applications.
SPECTRUM is used efficiently because GPRS resources are
only allocated when there is actual data transfer , thus sharing the same
limited radio resource among all mobile devices in a cell which frees up idle
bandwidth that would have otherwise been wasted.
v
Working
of GPRS :
Since the main goal of GPRS is to provide an
intermediate step towards 3G, it needs to be both straightforward so that it
can deploy on existing systems and also provide a logical upgrade path to 3G.
However it is very important to note that GPRS signaling and data transfer does
not in fact travel through GSM networks. The GSM network is only contacted for
table look up in Location Registers so that GPRS can find user profiles on the
existing network.
The radio spectrum in the bands 890-915 MHz for the uplink (mobile
station to base station) and 935-960 MHz for the downlink has been reserved in
Europe some regions in Asia Pacific for mobile networks. At least 10 MHz in
each band was reserved explicitly for GSM. This 2x25 MHz spectrum is divided
into 200 kHz carrier frequencies using FDMA. One or more carrier frequencies
are assigned to individual base stations, and each carrier is divided into
eight time slots using TDMA. Groups of eight consecutive time slots form TDMA
frames, with a duration of 4.615 ms. A transmission channel occupies one time
slot position within a TDMA frame. TDMA frames of a particular carrier
frequency are numbered, and both the mobile station and the base station are
synchronized on this number. Larger frames are formed from groups of 26 and 51
TDMA frames (there are also larger groups), and position within such frames
defines the type and function of a channel. GPRS sends packetized air traffic
over one to eight time slots using time division multiple access. This can be
shared with other users. The receiver takes these packets and sends them over
public land mobile networks using IP backbones. The packets can then be rooted
like any other IP datagram, onto other public data networks like the internet.
(We will see what is packet-switching mode
in the latter sessions of this paper.)
v
GPRS
network nodes :
Since existing network nodes use circuit switch technology, they
cannot handle packet traffic. Base stations for instance, would have to be
upgraded to include packet control units, mobility management, and security
features. In addition to deploy GPRS on GSM, two kinds of network nodes are needed
:
1)
Serving GPRS support node (SGSN) :
·
Delivers packets to mobile
stations within service area
·
Detects new GPRS mobile
stations
·
Queries home location register
to get user profile data
·
Keeps track of mobile stations.
2)
Gateway GPRS support node (GGSN) :
·
Interfaces with external IP
networks
·
Maintains routing information
used to tunnel packets to the right SGSN.
·
One GGSN serves many SGSNs.
GPRS PROTOCOL LAYERING
¨
GMM/SM:
The Session Management layer supports context handling of packets to
allow transparent data transport. The GPRS Mobility Management (GMM) sub layer
supports the mobility of user terminals by keeping track of location and
managing moves to other cells.
¨
LLC :
The Logical Link Control provides packet data transfer between MS
(Mobile Station) and SGSN. It also manages retransmission.
¨
RLC :
The Radio Link Control tailers the packets i.e., size etc. for the
needs of digital radio transmission.
¨
MAC :
The Medium Access Control utilizes the resources of physical radio
interface below it to send the packets.
¨
GSMRF :
This physical interface can use one to eight TDMA time slots to
transfer information at the rate of 171.2 Kbit/s.
The other side of the link through base station system include :
¨
BSSGP :
The Base Station System GPRS Protocol transports between a BSS and a
SGSN.
WAP
(Wireless Application Protocol )
The
internet and mobility are main drivers behind our economy. One comprises the
world’s biggest library while the other represents the natural way of working
the untethered way. WAP the defacto standard brings them together enabling
anywhere anytime access to information from any device over any network. It is
essentially a browsing protocol, specifically for mobile devices.
The idea
behind WAP is to take a client server approach with emphasis on the server
doing most of the work.. It is designed to deliver content in optimal format
for display on thin client devices such as mobile phones, This is done by using
a small micro browser on the mobile phone that requires only minimal resources.
Its main
feature is that it does not depend on any one specific underlying transport
standards which means that WAP complaint services and applications run over all
network types, both current and future.
v How does WAP work ?
To send or
retrieve data, the micro browser on a WAP capable phone initiates the following
events:
1)
The browser makes a request in
WML (Wireless Markup Language). The WML is derived from HTML (Hyper Text Markup
Language). This is specifically designed for mobile data transfer and mobile
screen display.
2)
The request is passed to WAP
gateway which has an access to internet ant retrieves the requested information
from the server.
3)
Requested data is then sent
back to mobile micro browser from the WAP gateway.
THE WAP MODEL
WAP AND GPRS A
GOOD MATCH
WAP has taken off rapidly and looks set to get mobile
data revolution. Users are currently accessing mobile portals using circuit
switched data links which indicates the high value they place on the content.
Thus when the same content over GPRS the user experience will be enhanced. To
become practical and useful WAP needs precisely those upgrades that GPRS
provides. GPRS is very efficient medium and it consumes far less air resources.
Therefore the result is that operator cost for WAP over GPRS services are
significantly lower than with WAP over CSD.
Ø Packet Switching vs.
Circuit Switching :
Circuit Switching was designed for voice communication.
It creates temporary dedicated links well suited for this type of
communication. But, it less well suited for data and other non-conversational
transmissions which tend to be bursty meaning that data comes in spurts with
idle gaps between them. When these links are used, the line is often idle and
its facilities wasted. Multiplexing improves line utilization but is only
minimally effective unless transmission is predictable and every user is
transmitting at same rate.
Second weakness is
its data rate. A CS link creates the equivalent of a single cable between two
devices and thereby assumes single data rate for both devices.
Thirdly, CS is
inflexible. Once a circuit has been established, that circuit is the path taken
by all parts of transmission whether or not it remains the most efficient.
Finally, CS sees
all transmissions as equal, but often with data network transmission, priority
is important. For instance, transmission X can go anytime, but transmission is
time dependent and must go immediately.
A better solution
for data transmission is Packet Switching (PS). In PS network, data is
transmitted in discrete units of potentially variable length blocks (from 200
bytes to 65,545 bytes) called packets. Longer transmissions are broken up into
multiple packets. Each packet contains data and a header with control information. The packets are sent to networks
from node to node where packet is stored briefly and then routed accordingly to
the information in its header.
A typical Packet
(A cell networking is an improvement over packet network which is
made up of 53 bytes each wherein 47 bytes reserved for data and 5 bytes for
header)
Ø Instant access :
The ‘Always – on’ feature is an excellent alternative to
circuit switched data and its associated need to set up a call for every
communication to Internet. GPRS provides immediacy , which will enable higher
interactivity and faster response time, thus lowering user frustration. In an
optimized service the user can access the first page of a WAP session in about
5 to 10 seconds and subsequent pages
will take 2 to 4 seconds. With ‘Always – on’ mode it will possible to access
the first page nearly as quickly as subsequent pages. GPRS users are on-line
via logical connections as in the internet model. Communication channels are
employed during transmission sessions only but are instantly available. Thus,
staying on-line all the day does not in itself incur any additional charges.
Ø Higher Transfer rate :
The higher transfer rates are needed to accommodate
WAP’s unusually complex and frequent network resource requirements. The
increased bandwidth will allow better and more varied applications with
pictures, movement and sound. This would be a welcome change to the current
lack luster WAP applications.
Ø Security :
Security in wap and GPRS is performed at different
protocol layers. GPRS provides security at bearer layer while WAP adds security
on top of transport layer. The first step is to authenticate the mobile
terminal with standard GSM techniques. After that all data between the mobile
terminal and serving GPRS support node (SGSN) is encrypted. WAP security is
based on wireless transport layer security which is independent of the
underlying bearer. For establishing secured connections between WAP gateway and
content servers on the internet Secure Sockets Layer (SSL) is used.
3G AROUND THE
GLOBE
In Europe , cellular
networks had cellular networks had reached relative standardization through the
GSM for most of the last decade. The natural upgrade was GPRS. Europe ’s transition to 3G technology, generically called
W-CDMA (Wide band Code Division Multiple Access) may begin this year or next,
the major hurdle being economical rather than technical.
Unlike Europe North America suffers from a lack of
standardization on 2G cellular service. Some carriers use CDMA (Code Division
Multiple Access) while others use TDMA (Time Division Multiple Access). CDMA
carriers will probably continue to upgrade their data rates until they launch
3G. While TDMA carriers will first upgrade to GPRS before going on to W-CDMA.
Because of these difficulties, 3G in north America
will roll out later than in Europe .
But, Japan Japan
CONCLUSION
The world is witnessing the
transformation of mobile phone from a voice centric communication device to a
tool fro managing business and private life and sharing and storing
experiences. In this scenario, WAP over GPRS together bring mobile services one
step forward on the road of evolution towards 3G services.
Unfortunately,
there are also shortfalls to both technologies that suggest they are merely
transition technologies. Although both standards have a lot of industry backing
there is also a lot of pressure from competing technologies. A lot depends on
whether true 3G capable technologies will emerge sooner rather than later. If
3G is deployed soon, 2.5G technologies may not have sufficient to penetrate the
market properly. Whatever happens, GPRS and WAP are useful migratory
technologies, which will be, heard a lot more.
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