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 BTS MS BTS MS BSC MSC GMSC MS EIR VLR HLR AUC PSTN PDN ISDN

GPRS Architecture BTS MS BSC Gb SGSN Gf Gs Gr D EIR MSC/VLR HLR Gc Gn GGSN Gi PDN Gp GGSN Other GPRS PLMN

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 Security Functions Activate PDP Context Accept Create PDP Context Request Create PDP Context Response PDP type,PDP Address QoS Requested,Access Point,… PDP type,PDP Address QoS Negotiated,Access Point,… PDP type,QoS Negotiated,… PDP type,PDP Address QoS Negotiated,…

Routing PLMN1 PLMN2 MS BTS BSC SGSN Gn Intra-PLMN GPRS Backbone Gn SGSN GGSN Gi Packet Data Network(PDN) Eg.Internet,Intranet Border Gateway Gp Inter-PLMN GPRS Backbone Border Gateway Intra-PLMN GPRS Backbone GGSN Router LAN Host 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 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

PLL RFL Phy Layer MAC Network Service Relay RLC BSSP Phy Layer Network Data Link Service BSSGP IP LLC TCP/UDP Relay SNDCP GTP Phy layer Data Link Layer IP TCP/UDP Network Layer (IP or X.25) GTP RLC :Radio link control BSSGP:BSS GPRS Application protocol PLL :Physical link layer GTP :GPRS tunneling protocol RFL :Physical RF layer TCP :Transmission control protocol MAC:Medium access control UDP :user datagram protocol IP :Internet Protocol Transmission Plane BSSSGSNGGSN GmGb Gi

PLL RFL RLC MAC LLC SNDCP Network Layer Application PLL PHY RFL Layer MAC Network Service Relay RLC BSSGP MS BSS SNDCP:Subnetwork dependent convergence protocol LLC :Logical link control RLC :Radio link control Um

Application LLC RLC MAC GSM/RF GMM/SM GSM RF Physical layer MAC Network service Relay RLC BSSGP Phy Layer Network layer BSSGP LLC GMM/SM MS BSS SGSN GMM/SM:GPRS Mobilty Management and session Management Protocol GSM/RF:GSM physical layer(radio interface) I.e.PLL and RFL Signalling Plane:MSSGSN UmGb

BSSAP SCCP MTP3 MTP2 Phy Layer MTP2 MTP3 SCCP BSSAP Signalling Plane SGSN MSC/VLR SGSN MSC/VLR Gs

MAP TCAP SCCP MTP3 MTP2 Phy Layer MTP2 MTP3 SCCP TCAP MAP MAP :Mobile Application Part TCAP :Transaction capabilities and application part SCCP :Signalling connection control part MTP :Message transfer part SGSN HLR(and EIR) Signalling Plane SGSNHLR/SGSNEIR Gr

GSM TDMA Frame Slots and Bursts MHz MHz 960 MHz MHz 200 KHz MHz MHz 915 MHz MHz 200 KHz Data Burst = bit periods TDMA Frame Uplink Downlink Time Slot

GPRS Air Inteface Uplink Downlink Voice User1 Voice User2 GPRS User1 GPRS User2 GPRS User3 F1 F2 F3 F4 F1 F2 F3 F4 Time Slot Number Carrier Frequency

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 GroupChannel Function Direction Packet data Traffic channel PDTCHData TrafficMS BSS Packet broadcast control channel PBCCHBroadcast ControlMS BSS Packet common Control Channel (PCCCH) PRACH PAGCH PPCH PNCH Random Access Access Grant Paging Notification MS BSS Packet Dedicated Control Channels PACCH PTCCH Associated Control Timing Advance Control MS BSS

Uplink Data Transfer MSBSS PRACH or RACH PAGCH or AGCH Random Access Transmission Packet channel Request 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 request PPCH or PCH MSBSS

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 stetter.html “Wireless Internet Access based on GPRS”, IEEE Personal Comm. April 2000.