02-05-2011, 12:29 PM
GPRS Seminar.pptx (Size: 389.64 KB / Downloads: 51)
GPRS- An Introduction
In layman language,
A bearer service for GSM that greatly improves and simplifies wireless access to packet data networks, e.g to the internet.
Goals of GPRS:
Efficient bandwidth usage for bursty data traffic (e.g. Internet)
Higher data rates
New charging models
Generalities of GPRS
Based on the existing GSM infrastructure.
Packet switching functionality
Better data transfer rates
Migration Path to 3G and Higher Networks
Service Types
Point-to-Point
Internet access by user
Point-to-Multipoint
Delivery of information (e.g. news) to multiple locations or interactive conference applications
Circuit Switched Data (CSD)
Before GPRS
A channel is allocated to user for duration of connection
Inefficient use of resources
Time-based billing
Deterministic quality of service
Resources allocated to communication
Suitable to real-time applications
Comparison
CSD
Lower bit rates
14.4kbit/s
Reserved bandwidth
Fixed access time
Time-based billing
Acronyms
MS: Mobile Station
BSC: Base Station Controller
BTS: Base Transceiver Station
MSC: Mobile Switching Controller
GMSC: Gateway Mobile Switching Controller
PSTN: Public Switched Telephone Network
VLR: Visited Location Register
EIR: Equipment Identity Register
AUC: Authentication center
HLR: Home Location Register
PLMN: Public Land Mobile Network
PDN: Packet Data Network
GPRS Architecture
New components
SGSN: Serving GPRS Support Node
GGSN: Gateway GPRS Support Node
Components needing upgrade:
HLR
MSC/VLR
Mobile Station
SGSN
Delivers data packets from and to
mobile stations
Packet Routing and Transfer from MS to GGSN
Mobility Management
Logical Link Management
Authentication
Billing and maintaining user profiles
GGSN
Interfaces GPRS backbone network with external packet data networks (PDNs)
E.g., IP networks, Internet.
Translation between PDP (packet data protocol) addresses and GSM addresses.
Authentication and billing
Many-to- many relations among SGSNs and GGSNs.
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.
PDP Context Activation
MS SGSN GGSN
Routing
Packet Routing
A laptop connects with a GPRS-capable
handset
The handset communicates with GSM BS
BS sends the GPRS packets to SGSN
SGSN encapsulates packets
Handset location information is updated in
GSM components (e.g., HLR)
SGSN sends encapsulated packets to GGSN
GGSN decapsulates and sends to PDNs.
Routing(contd.)
MS roaming in PLMN1 sends IP packet to host (e.g. Web server)
Host sends reply packet to MS home PLMN2
PLMN2’s GGSN queries HLR and finds that MS is in PLMN1
Packet is encapsulated and sent to SGSN in PLMN1
Packet travels over inter-PLMN backbone not through PDN
No encapsulation-decapsulation needed on GPRS backbones
SGSN decapsulates packet and delivers to MS
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.
A MS can be in 3 states:
IDLE
READY
STANDBY
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
GSM TDMA Frame Slots and Bursts
GPRS Logical Channels
GPRS Air Inteface
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
Uplink Data Transfer
Downlink Data Transfer
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.