What is GPRS
(General Packet Radio Service)?
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 networks.
-
Gs interface
provides communication between MSC and SGSN.
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.
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