an overview of gprs - scarlet
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An Overview of GPRS
Shourya RoyPradeep 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
BTSMS
BTS
BTS
MSBSC
BSC
MSC
GMSC
MS
EIR
VLRHLR
AUC
PSTNPDN
ISDN
GPRS Architecture
BTS
BTSMS
BSC GbSGSN
GfGs
Gr
DEIR
MSC/VLR
HLR
Gc
Gn
GGSN Gi PDN
Gp GGSN
Other GPRSPLMN
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 NodeA mobile station must register itself
with GPRS network. GPRS attach GPRS detachGPRS detach can be initiated by the
MS or the network.
Session ManagementAfter 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
GGSNActivate PDP Context Request
Security Functions
Activate PDP Context Accept
Create PDP Context Request
Create PDP Context Response
PDP type,PDP AddressQoS Requested,Access Point,…
PDP type,PDP AddressQoS Negotiated,Access Point,…
PDP type,QoS Negotiated,…PDP type,PDP AddressQoS Negotiated,…
Routing
PLMN1 PLMN2
MS
BTS
BSC
SGSNGnIntra-PLMN
GPRS Backbone
Gn
Gn
SGSNGGSN
GiPacket Data Network(PDN)
Eg.Internet,Intranet
Border Gateway
Gp
Inter-PLMNGPRS Backbone
Border Gateway
Intra-PLMNGPRS Backbone
GGSN
RouterLANHost
SGSN
BSC BTS
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
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
Protocol Architechture
Transmission PlaneGPRS 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 MSData link layer
LLC(MS-SGSN) RLC/MAC(MS-BSS)
Physical layerPLL:channel coding,detection of errors, forward error correction, interleaving, detection of physical link congestionRFL:modulation and demodulation
PLL RFL Phy Layer
MAC Network Service
RelayRLC BSSP
Phy Layer Phy Layer
Network Data Link Service Service
BSSGP IP
LLC TCP/UDP
RelaySNDCP GTP
Phy layer
Data Link Layer
IP
TCP/UDP
Network Layer(IP or X.25)
GTP
RLC :Radio link control BSSGP:BSS GPRS Application protocolPLL :Physical link layer GTP :GPRS tunneling protocolRFL :Physical RF layer TCP :Transmission control protocolMAC:Medium access control UDP :user datagram protocol IP :Internet Protocol
Transmission Plane
BSS SGSN GGSNGm Gb Gi
PLL
RFL
RLC
MAC
LLC
SNDCP
Network Layer
Application
PLL PHY RFL Layer
MAC Network Service
RelayRLC BSSGP
MSBSS
SNDCP:Subnetwork dependent convergence protocolLLC :Logical link controlRLC :Radio link control
Um
Application
Application
LLC
RLC
MAC
GSM/RF
GMM/SM
GSM RF Physical layer
MAC Network service
Relay RLC BSSGP
Phy Layer
Networklayer
BSSGP
LLC
GMM/SM MS BSS SGSN
GMM/SM:GPRS Mobilty Management and session Management ProtocolGSM/RF:GSM physical layer(radio interface) I.e.PLL and RFL
Signalling Plane:MSSGSN
Um Gb
BSSAP
SCCP
MTP3
MTP2
Phy Layer Phy Layer
MTP2
MTP3
SCCP
BSSAP
Signalling Plane SGSN MSC/VLR
SGSN MSC/VLR
Gs
MAP
TCAP
SCCP
MTP3
MTP2
Phy Layer Phy Layer
MTP2
MTP3
SCCP
TCAP
MAP
MAP :Mobile Application PartTCAP :Transaction capabilities and application partSCCP :Signalling connection control partMTP :Message transfer part
SGSN HLR(and EIR)
Signalling Plane SGSNHLR/SGSNEIR
Gr
GSM TDMA Frame Slots and Bursts
1
123
21
124
. . .
. . .
935 MHz935.2 MHz
960 MHz959.8 MHz
200 KHz
1
123
2
124
. . .
. . .
890 MHz890.2 MHz
915 MHz914.8 MHz
200 KHz
1 2 3 4 5 6 7 8
Data Burst = 156.25 bit periods
11 2 3 4 5 6 7 8
TDMA Frame
TDMA Frame
Uplink
Downlink
Time Slot
GPRS Air Inteface0 1 2 43 5 6 7 0 1 2 3 40 1 2 43 5 6 7 0 1 2 3 4
0 1 2 43 5 6 7 0 1 2 3 40 1 2 43 5 6 7 0 1 2 3 4
Uplink
Downlink
Voice User1
Voice User2
GPRS User1
GPRS User2
GPRS User3
F1F2F3F4
F1F2F3F4
Time Slot Number
CarrierFrequency
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 ChannelsGroup Channel Function Direction
Packet data Traffic channel PDTCH Data Traffic MS BSS
Packet broadcast control channel PBCCH Broadcast Control MS BSS
Packet commonControl Channel(PCCCH)
PRACH
PAGCH
PPCH
PNCH
Random Access
Access Grant
Paging
Notification
MS BSS
MS BSS
MS BSS
MS BSS
Packet DedicatedControl Channels
PACCH
PTCCH
Associated Control
Timing Advance Control
MS BSS
MS BSS
Uplink Data TransferMS BSS
PRACH or RACH
PAGCH or AGCH
Random Access
Transmission
Packet channel Request
PACCH
PACCH
PDTCH
PACCH
PDTCH
PACCH
Packet Immediate assignment
Packet resource Request
Packet resource assignment
Frame Transmission
Negative Acknowledgement
Retransmission of blocks in error
Acknowledgement
Downlink Data Transfer
PRACH or RACH
PAGCH or AGCH
Paging
Transmission
Packet channel Request
PACCH
PACCH or PAGCH
PDTCH
PACCH
PDTCH
PACCH
Packet Immediate assignment
Packet paging response
Packet resource assignment
Frame Transmission
Negative Acknowledgement
Retransmission of blocks in error
Acknowledgement
Packet paging requestPPCH or PCH
MS BSS
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/bettstetter.html
http://www.wsdmag.com/2000/aug2200/38-45.html
“Wireless Internet Access based on GPRS”, IEEE Personal Comm. April 2000.