An Overview of GPRS
Shourya Roy
Pradeep Bhatt
Gururaja K.
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
GSM Architecture
PSTN
ISDN
MS
BTS
GMSC
BSC
MSC
BTS
BSC
EIR
MS
AUC
HLR
BTS
MS
VLR
PDN
GPRS Architecture
Other GPRS
PLMN
Gp
Gn
SGSN
BSC
Gb
Gf
MS
Gr
Gs
BTS
BTS
EIR
GGSN
Gc GGSN
D
MSC/VLR
HLR
Gi
PDN
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
Activate PDP Context Request
PDP type,PDP Address
QoS Requested,Access Point,…
Security Functions
Create PDP Context Request
PDP type,PDP Address
QoS Negotiated,Access Point,…
Activate PDP Context Accept
PDP type,PDP Address
QoS Negotiated,…
Create PDP Context Response
PDP type,QoS Negotiated,…
Routing
BSC
BTS
BSC
BTS
SGSN
SGSN
MS
PLMN1
Intra-PLMN
GPRS Backbone
Inter-PLMN
GPRS Backbone
Gn
Border
Gateway
Gn
Intra-PLMN
GPRS Backbone
Gp
Border Gateway
Gn
GGSN
SGSN
GGSN
Gi
Packet Data Network(PDN)
Eg.Internet,Intranet
Router LAN Host
PLMN2
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.
Location Management(Contd.)
A MS can be in 3 states:
 IDLE
 READY
 STANDBY
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

Network Layer
(IP or X.25)
Relay
SNDCP
LLC
GTP
GTP
TCP/UDP
TCP/UDP
Relay
RLC
MAC
PLL
RFL
BSSP
BSSGP
IP
IP
Network
Service
Network
Service
Data Link
Service
Data Link
Layer
Phy Layer
Phy Layer
Phy layer
Phy Layer
Gm
BSS
RLC :Radio link control
PLL :Physical link layer
RFL :Physical RF layer
MAC:Medium access control
Gb
SGSN
GGSN
BSSGP:BSS GPRS Application protocol
GTP :GPRS tunneling protocol
TCP :Transmission control protocol
UDP :user datagram protocol
IP
:Internet Protocol
Transmission Plane
Gi
MS
BSS
Application
Network Layer
SNDCP
LLC
Relay
RLC
RLC
MAC
MAC
PLL
BSSGP
Network
Service
PLL
RFL
RFL
Um
SNDCP:Subnetwork dependent convergence protocol
LLC :Logical link control
RLC :Radio link control
PHY
Layer
SGSN
BSS
MS
GMM/SM
GMM/SM
LLC
Application
LLC
Application
RLC
MAC
GSM/RF
RLC
MAC
GSM RF
Relay
BSSGP
BSSGP
Network service
Network
layer
Physical layer
Phy Layer
Um
Gb
GMM/SM:GPRS Mobilty Management and session Management Protocol
GSM/RF:GSM physical layer(radio interface) I.e.PLL and RFL
Signalling Plane:MSSGSN
SGSN
MSC/VLR
BSSAP
BSSAP
SCCP
SCCP
MTP3
MTP3
MTP2
MTP2
Phy Layer
Phy Layer
Gs
Signalling Plane SGSN
MSC/VLR
SGSN
HLR(and EIR)
MAP
MAP
TCAP
TCAP
SCCP
SCCP
MTP3
MTP3
MTP2
MTP2
Phy Layer
Phy Layer
Gr
MAP
TCAP
SCCP
MTP
:Mobile Application Part
:Transaction capabilities and application part
:Signalling connection control part
:Message transfer part
Signalling Plane SGSNHLR/SGSNEIR
GSM TDMA Frame Slots and
Bursts
960 MHz
959.8 MHz
124
Time Slot
123
...
200 KHz
...
Downlink
1
2
3
4
5
6
7
2
935.2 MHz
935 MHz
TDMA Frame
1
915 MHz
914.8 MHz
1
8
Data Burst = 156.25 bit periods
124
123
...
200 KHz
...
Uplink
1
2
3
4
5
6
7
1
8
2
890.2 MHz
890 MHz
1
TDMA Frame
GPRS Air Inteface
Time Slot Number
0
1
2
3
4
5
6
7
0
1
2
3
4
F1
Uplink
F2
F3
Carrier
Frequency
F4
0
1
2
3
4
5
6
7
0
1
2
3
4
F1
F2
Downlink
F3
F4
Voice User1
GPRS User1
Voice User2
GPRS User2
GPRS User3
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
GPRS Logical Channels
Group
Channel
Packet data
Traffic channel
PDTCH
Packet broadcast
control channel
PBCCH
Packet common
Control Channel
(PCCCH)
Packet Dedicated
Control Channels
Function
Data Traffic
Direction
MS
BSS
Broadcast Control
MS
BSS
PRACH
Random Access
MS
BSS
PAGCH
Access Grant
MS
BSS
PPCH
Paging
MS
BSS
PNCH
Notification
MS
BSS
PACCH
Associated Control
MS
BSS
PTCCH
Timing Advance Control
MS
BSS
Uplink Data Transfer
MS
PRACH or RACH
PAGCH or AGCH
PACCH
PACCH
PDTCH
PACCH
PDTCH
PACCH
BSS
Packet channel Request
Packet Immediate assignment
Packet resource Request
Packet resource assignment
Random Access
Frame Transmission
Negative Acknowledgement
Retransmission of blocks in error
Acknowledgement
Transmission
Downlink
Data
Transfer
MS
BSS
Packet paging request
PPCH or PCH
PRACH or RACH
PAGCH or AGCH
PACCH
PACCH or PAGCH
PDTCH
PACCH
PDTCH
PACCH
Packet channel Request
Packet Immediate assignment
Packet paging response
Packet resource assignment
Paging
Frame Transmission
Negative Acknowledgement
Retransmission of blocks in error
Acknowledgement
Transmission
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.
References




“General Packet Radio Service in GSM”, Jian Cai and
David J. Goodman, Rutgers University, IEEE
Communications Magazine, Oct 1997
http://www.comsoc.org/pubs/surveys/3q99issue/bett
stetter.html
http://www.wsdmag.com/2000/aug2200/38-45.html
“Wireless Internet Access based on GPRS”, IEEE
Personal Comm. April 2000.