Radio Service (GPRS)
|GPRS protocol is a packet-switch protocol; define for
web applications in GSM network. In other words Internet
on GSM network is standardized as GPRS network.
GPRS has digital structure and this structure based on
Time Division Multiple Access (TDMA) technique.
One TDMA frame has 8 time slots (TSs). These TSs
can be allocated to users, and single TS can be shared
by several active users for uplink and downlink purposes.
Different coding schemes are used to enhance data rate
from 9Kbps to 150 Kbps per user, and it takes 0.5 to 1
second. Security features in GPRS is provided by GSM network.
GPRS Architecture Global System for Mobile Communication
(GSM) circuit-switch architecture does not support the GPRS
packet-switch architecture. Thus, GPRS requires its own
network architecture. Several networks and databases e.g.
Mobile Station (MS), Base Station Subsystem (BSS),
Home Location Register (HLR), Visitor Location Register
(VLR) in existing GSM network are modified in GPRS network.
GPRS architecture introduces the following network
nodes to GSM architecture.
Serving GPRS Support Node (SGSN)
Gateway GPRS Support Node (GGSN)
Mobile Station (MS)
Base Station System (BSS)
Home Location Register (HLR)
Visitor Location Register (VLR)
1.Serving GPRS Support Node (SGSN): In GPRS network
SGSN is equivalent to MSC. Packets of data between MSC
and Public Switch Data Network (PSDN) are transferred and
received by SGSN.
2.Gateway GPRS Support Node (GGSN): GSM databases
e.g. HLR and VLR are supported by GGSN. It also interacts
with external packet-switch networks.
3.Mobile Station (MS): In GPRS network MS consists of
Mobile Terminal (MT) and Terminal Equipment (TE).
A computer attached to MT is called a ME. Through air,
MT communicates with the BSS.
4.Base Station System (BSS): In BSS, Base Transceiver
Station (BTS) and Base Station Controller (BSC) are modified
to support GPRS channel coding schemes BTS is modified
while to forward calls to Mobile Switching Centre (MSC)
and data to SGSN through Packet Control Unit (PCU),
is supported by BSC. One SGSN is served by one BSC.
5.Home Location Register (HLR): In GPRS, HLR
contains information about routing. To map an MS to
one or more GGSNs, update the SGSN and to store
the Internet Protocol (IP) address, this information is
accessed by both SGSN and GGSN.
6.Visitor Location Register (VLR): In GPRS.
VLR contains the SGSN number and this number
indicates the MS currently served by the SGSN.
GPRS Interfaces Different interfaces are used
for routing between network nodes in GPRS.
Um interface provides communication between MS and BSS.
Gb interface provides connection between BSS and SGSN.
Gn interface provides connection between SGSN and GGSN
within the same GPRS network.
Gp interface provides connection between SGSN and GGSN
when they are in different GPRS network.
Gi interface provides connection between GGSN and external
Gs interface provides communication between MSC
GPRS functional Groups The functions which are defined in
GPRS are following.
Network access function: Point to point data transfer,
registration of MS with packet data protocols,
radio resources for MS communication and
charging information about packet transmission,
is provided by this function.
Packet routing and transfer function: Routing of
data between an MS and destination, conversion of
GPRS address to external address and forwarding of
packets between an MS and GGSN, is provided by this function.
Logical link management function: The communication
between an MS and the GSM network is maintained by it.
Radio resources management function: Radio
communication paths are allocated by it.
Mobility management function: Current location
of an MS is kept by it. When an MS is entered to a
new area, all routing and location in formations are also updated by it.
Network management function: If provides mechanisms
to support network functions related to GPRS.
Advantages The major advantage of GPRS is that, to access data
no dial-up connection is required. It is an inexpensive mobile data
service as compared to Short Message Service (SMS) in GSM.