17-05-2012, 03:56 PM
Overview of GPRS
gprs[1].ppt (Size: 181.5 KB / Downloads: 174)
What is GPRS?
A new bearer service for GSM that greatly improves and simplifies wireless access to packet data networks,e.g to the internet.
Motivation
Speed
Immediacy
New and better applications
User friendly billing
Protocol Architechture
Transmission Plane
GPRS specifies a tunnel mechanism to transfer user data packets .
Signalling Plane
GTP specifies a tunnel control management protocol.The signalling is used to create modify and delete tunnels.
Registration of a Mobile Node
A mobile station must register itself with GPRS network.
GPRS attach
GPRS detach
GPRS detach can be initiated by the MS or the network.
Session Management
After Successful attach a MS gets one or more Packet Data Protocol(PDP) address.This address is unique only for a particular session.
It consists of,
PDP type
PDP address assigned to MS
Requested QoS
Address of the corresponding GGSN
Session Management(Contd.)
PDP-Address allocation:
Static:Assigned by network operator of User’s home PLMN.
Dynamic:Assigned by Corresponding GGSN.
Location Management
MS frequently sends location update messages to inform the SGSN where it is.
Determining frequency of update messages is non-trivial.
The location update frequency is dependent on the state of the MS.
Protocol Architechture
Transmission Plane
The protocols provide transmission of user data and its associated signalling
Signalling Plane
Comprises protocols for the control and support of functions of the transmission plane
Transmission Plane
GPRS Backbone:SGSN GGSN
GTP tunnels the user packets and related signalling information between the GPRS support nodes.
Subnetwork dependent convergence protocol
It is used to transfer packets between SGSN and MS
Data link layer
LLC(MS-SGSN)
RLC/MAC(MS-BSS)
Physical layer
PLL:channel coding,detection of errors, forward error correction, interleaving, detection of physical link congestion
RFL:modulation and demodulation
GPRS Air Interface
Master slave concept
One PDCH acts as Master
Master holds all PCCCH channels
The rest of channels act as Slaves
Capacity on demand
PDCH(s) are increased or decreased according to demand
Load supervision is done in MAC Layer
Multi Slot Operation
GPRS allows a mobile to transmit data in up to 8 PDCHs (eight-slot operation)
3-bit USF at beginning of each radio block in downlink points to next uplink radio block
Comparison with single-slot GSM
Higher delay at higher load
Low blocking rate
Improved Throughput
Conclusion
GPRS provides efficient access to Packet Data Networks.
Multislot operation in GPRS leads to efficient channel utilization.
GPRS is more effective for long data packet transmission than short ones.