Gprs
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AN OUTLINE
• •
PAKET SWITCHING RATHER THAN CIRCUIT SWITCHING (VOICE). UPGRADATION REQUIRED IN BTS,BSC AND CORE NETWORK.
•
GGSN– CONNECTS TO EXTERNAL DATA NETWORK,
– – – – – •
ACTS LIKE A ROUTER ENCAPSULATES DATA PACKETS FORWARDS PACKETS TO RIGHT SGSN ROUTING OF MS ORIGINATING PACKETS TO RIGHT DESTINATION COLLECTING CHARGING INFO ETC.
SGSN– AUTHENTICATION,CIPHERING,COMPRESSION,MOBILITY MANAGEMENT,SESSION MANAGEMENT – INTERACTION WITH HLR,MSC/VLR:JUST LIKE AN MSC FUNCTIONS IN VOICE CALL – CHARGING
GPRS ENABLED MOBILES • •
CLASS A: SIMULTANEOUS VOICE & DATA. CLASS B: SIMULTANEOUS SIGNALLING FOR VOICE & DATA: DATA COMMUNICATION SUSPENDED IF A CALL ARRIVES: MOST COMMON. • CLASS C: VOICE/DATA: ONE AT A TIME THROUGH SELECTION. • GPRS ENABLED MOBILES SUPPORT FOLLOWING CODING SCHEMES & DATA RATES PER TIME SLOT: – – – –
CS1: 9 KBPS : MOST ROBUST AGAINST ERROR. CS2: 13.4 KBPS :GOOD ERROR PERFORMANCE. CS3:15.6 KBPS: GOOD ERROR PERFORMANCE. CS4: 21.4 KBPS:VERY LESS PROTECTION AGAINST ERROR. • HIGHER DATA RATES ACHIEVED BY ALLOCATING MULIPLE TS TO ONE MOBILE.
UPGRADATION IN BTS & BSC • BTS TO BE EQUIPPED WITH » CAPABILITY TO SUPPORT CODING SCHEMES. » ADDITIONAL CHANNELS TO DEAL WITH PACKET TRAFFIC. » SPECIAL TIMING ADVANCE SCHEME. • BSC TO BE EQUIPPED WITH » CAPABILITY TO MANAGE PACKET DATA, PACKET CONTROL & PACKET BROADCAST CHANNELS: GRANTING ACCESS,SCHEDULING OF DATA BLOCKS, POWER CONTROL, CONGESTION CONTROL ETC AS IN NORMAL CHANNELS IN VOICE. » SEGMENTATION OF PACKET DATA TOWARDS BTS INTO RADIO BLOCKS,ACKNOWLEDGEMENT & RETRANSMISSION. » MANAGING INTERFACE WITH SGSN,SENDING DATA IN BLOCKS.
GPRS CHANNELS • PBCCH: BROADCASTS PACKET SPECIFIC SYSTEM INFO; – FOR LIGHT DATA TRAFFIC,FUNCTION IS PERFORMED BY BCCH.
• PCCH: COMMON CONTROL CHANNEL: » PPCH:PAGING; » PRACH:ACCESS, » PAGCH:ACCESS GRANT
• PDCH:DATA CHANNEL: » PDTCH:CARRIES USER DATA. » PACCH: SHARES TS WITH PDTCH,DEDICATED CHANNEL FOR PACKET ACK/NACK » PTCCH:USED FOR CONTINOUS TIMING ADVANCE.
MULTIPLEXING MSs ON THE SAME TIME SLOT • DNLINK: » » » »
TFI FIELD IN PDCH IS UNIQUE FOR AN MS. IF TFI MATCHES, MS ACCEPTS THE DATA. 16 MS CAN BE MULTIPLEXED IN ONE TS: EFFICIENT UTILISATION OF RESOURCES WHEN TRAFFIC IS LIGHT.
• UPLINK: » USF FIELD IN DNLINK PDCH: » MSs WHICH ARE SHARING THE PDCH READ USF VALUE TO CHECK WHICH MS CAN TRANSMIT ON CORRESPONDING UPLINK PDCH. » 7 MS CAN BE MULIPLEXED IN UPLINK. » TOTAL 16 MS IN UPLINK+DOWNLINK. » RESTRICTION IMPOSED BY TIMIMNG ADVANCE.
GPRS MULTISLOT CLASS • IT IS POSSIBLE TO ALLOCATE MORE THAN ONE TS TO A PARTICULAR MS TO INCREASE DATA SPEED. • DEPENDS ON TRAFFIC & BTS RESOURCE(CHANNELS) & CAPABILITY OF MS. • VOICE CALLS GENERALLY GET PRIORITY IN RESOURCE ALLOTTMENT. • CAPABILITY OF MS : MULTISLOT CLASS. • MOST COMMON: CLASS 10: 4 TS IN DN LINK,2 TS IN UPLINK,TOTAL NOT EXCEEDING 5.
MULTIFRAME FOR GPRS AIR INTERFACE • • • • • •
1 MULTIFRAME = 52 TDMA FRAMES 12 BLOCKS EACH OF 4 FRAMES 2 IDLE FRAMES FOR MEASUREMENT 2 FRAMES FOR TIMING ADVANCE EACH TS IN A FRAME CARRIES 114 DATA BITS. FOR CS1 181 USERBITS---AFTER CODING 456 BITS--SENT OVER 4 FRAMES (18.464 ms) • EFFECTIVE DATA RATE = (181/18.464) x 48/52 = 9.046 KBPS PER TS • SIMILARLY EFFECTIVE DATA RATES FOR CS2/CS3/CS4 MAY BE CALCULATED.
GPRS MOBILITY MANAGEMENT STATES
• EACH LA (LOCATION AREA) IS FURTHER DIVIDED INTO SEVERAL RA (ROUTING AREA) • RAI = MCC+MNC+LAC+RAC • IN PACKET IDLE MODE MS LISTENS TO PBCCH FOR PAGING. • MS REGISTERS WITH SGSN AND IS ALLOCATED P-TMSI. • THIS IS KNOWN AS GPRS ATTACH STATE. • SGSN KNOWS RA OF MS, AND MS MULTISLOT CLASS & CAPABILITY . MS MAKES REGULAR RA UPDATE. • IN ATTACH MODE MS ANSWERS THE PAGING THROUGH PRACH. • RADIO RESOURCES ARE ALLOCATED & DATAPATH IS ESTABLISHED BETWEEN MS & SGSN. • THIS IS CALLED ACTIVATION OF PDP (PACKET DATA PROTOCOL) CONTEXT.
• PDP CONTEXT CONTAINS MAPPING & ROUTING INFO FOR TRANSFERRING DATA. • ON PDP CONTEXT ACTIVATION MS OBTAINS IP ADDRESS FROM THE NETWORK(GGSN). • SERVICE PARAMETERS LIKE QOS ARE NEGOTIATED. • QOS IS ENSURED BY ALLOCATING DIFFERENT LEVELS OF RADIO PRIORITY (4 LEVELS) TO DETERMINE RADIO ACCESS & SERVICE PRECEDENCE. • TBF:TEMPORARY BLOCK FLOW: IS A PHYSICAL CONNECTION BETWEEN MS & THE NETWORK TO SUPPORT UNIDIRECTIONAL DATA ON ONE OR MORE PDCH. • TBF SPECIFIES TIMESLOTS,TFI,USF & ARFCN TO BE USED BY MS & ALSO CODING SCHEME. • TBF IS TEMPORARY AND IS MAINTAINED ONLY FOR THE DURATION OF DATA TRANSFER.
GPRS PROTOCOL STACK
• • •
GSM RF : PHYSICAL RADIO CHANNEL MAC: ALLOCATION OF CHANNEL. RLC: – – – –
ALLOTMENT OF TBF SUBMULTIPLEXING OF MULTIPLE MS IN ONE TS TS COMBINING FOR ONE MS SEGMENTATION & REASSEMBLY OF LLC FRAMES TOWARDS SGSN.
•
LLC:LOGICAL COONECTION BETWEEN MS & SGSN EVEN WHEN NO PHYSICAL CONNECTION EXISTS.
•
BSSGP: TRANSFERS LLC FRAMES WITH RELATED INFO LIKE QOS & ROUTING INFO FROM BSC TO SGSN. SNDCF:
•
» ENCRYPTION,COMPRESSION » SEGMENTATION/REASSEMBLY » MULTIPLEXING OF SIGNALLING INFO & DATA TO FORM LLC FRAMES
•
GTP: GPRS TUNNELING PROTOCOL: ENCAPSULATION OF IP PACKETS INTO DATA UNITS THAT ARE TRANSPORTED TRANSPARENTLY ACROSS GPRS SYSTEM FROM SGSN TO MS.
ENCAPSULATION & SEGMENTATION OF DATA
MOVEMENT OF PACKETS IN GPRS NETWORK •
THE ISP SENDS IP DATA PACKETS INTO GPRS NETWORK USING THE IP ADDRESS ASSIGNED TO MS.
•
GGSN SEARCHES FOR THE RELEVANT PDP CONTEXT & FORWARDS TOWARDS RIGHT SGSN.IP DATA UNITS ARE ENCAPSULATED INTO NEW DATA UNTIS OF GTP & THE NEW IP ADDRESS IS THE IP ADDRESS OF THE SGSN.
•
SGSN ENCAPSULATES THE GTP DATA UNITS & BY SNDCF PROTOCOL SUBDIVIDES IT INTO A CERTAIN NO. OF LLC FRAMES.DATA IS ALSO ENCRYPTED & COMPRESSED.
•
SGSN FINDS OUT THE LOCATION OF THE MS & SENDS LLC FRAMES TO THE RIGHT BSC.PAGING PROCEDURE IS USED AS IN VOICE CALLS.
MOVEMENT OF PACKETS IN GPRS NETWORK (CONTD) •
LLC FRAMES ARE SEGMENTED INTO MAC/RLC BLOCKS SUITABLE FOR TRANSMISSION ON AIR.
•
RLC BLOCKS ARE SENT ACROSS A-bis INTERFACE TO THE RIGHT BTS
•
BTS PERFORMES BLOCK CODING,CONVOLUTION CODING,PUNCTURING,INTERLEAVING:GIVING RADIO BLOCKS-456 BITS.
•
EACH RADIO BLOCK IS SENT ON AIR INTERFACE IN 4 NORMAL BURSTS EACH CONTAINING 114 BITS.
•
ACK/NACK SENT BY MS ON UPLINK PDCH.
PACKET DATA TRANSPORT
SOME FEATURES OF GPRS • CONTINUOUS TIMING ADVANCE UPDATE: » MS SENDS ACCESS BURST IN U/L PTCCH » BSS ACCESSES REQUIRED TA AND TRANSMITS THE INFO IN D/L PTCCH.
• NO HANDOVER: » MS PERFORMS NORMAL CELL RE-SELECTION » DURING RESELECTION MS GOES TO IDLEMODE.
• LINK ADAPTATION: » DURING DATA TRANSMISSION CODING SCHEME IS CHANGED BY THE NETWORK TO SUIT RADIOENVIRONMENT. » AUTOMATIC SWITCHOVER FROM CS1-CS2-CS3-CS4 & VICE-VERSA.
• EGPRS USES 8-PSK MODULATION TO INCREASE DATARATE 3 FOLD. • BSS NEEDS UPGRADATION. • STILL HIGHER DATARATE----UMTS/3G • UMTS USES WCDMA WHICH SUPPORTS FLEXIBLE & HIGH DATA RATE. • UMTS:SMOOTH INTEGRATION OF VOICE & DATA SERVICE. • STILL HIGHER DATA RATE:OFDM • IN ANY SYSTEM HIGHER THE DATARATE,LESS IS THE COVERAGE AREA. • MORE SUBSCRIBERS ---- LESS PEAK DATARATE.
• •
PAKET SWITCHING RATHER THAN CIRCUIT SWITCHING (VOICE). UPGRADATION REQUIRED IN BTS,BSC AND CORE NETWORK.
•
GGSN– CONNECTS TO EXTERNAL DATA NETWORK,
– – – – – •
ACTS LIKE A ROUTER ENCAPSULATES DATA PACKETS FORWARDS PACKETS TO RIGHT SGSN ROUTING OF MS ORIGINATING PACKETS TO RIGHT DESTINATION COLLECTING CHARGING INFO ETC.
SGSN– AUTHENTICATION,CIPHERING,COMPRESSION,MOBILITY MANAGEMENT,SESSION MANAGEMENT – INTERACTION WITH HLR,MSC/VLR:JUST LIKE AN MSC FUNCTIONS IN VOICE CALL – CHARGING
GPRS ENABLED MOBILES • •
CLASS A: SIMULTANEOUS VOICE & DATA. CLASS B: SIMULTANEOUS SIGNALLING FOR VOICE & DATA: DATA COMMUNICATION SUSPENDED IF A CALL ARRIVES: MOST COMMON. • CLASS C: VOICE/DATA: ONE AT A TIME THROUGH SELECTION. • GPRS ENABLED MOBILES SUPPORT FOLLOWING CODING SCHEMES & DATA RATES PER TIME SLOT: – – – –
CS1: 9 KBPS : MOST ROBUST AGAINST ERROR. CS2: 13.4 KBPS :GOOD ERROR PERFORMANCE. CS3:15.6 KBPS: GOOD ERROR PERFORMANCE. CS4: 21.4 KBPS:VERY LESS PROTECTION AGAINST ERROR. • HIGHER DATA RATES ACHIEVED BY ALLOCATING MULIPLE TS TO ONE MOBILE.
UPGRADATION IN BTS & BSC • BTS TO BE EQUIPPED WITH » CAPABILITY TO SUPPORT CODING SCHEMES. » ADDITIONAL CHANNELS TO DEAL WITH PACKET TRAFFIC. » SPECIAL TIMING ADVANCE SCHEME. • BSC TO BE EQUIPPED WITH » CAPABILITY TO MANAGE PACKET DATA, PACKET CONTROL & PACKET BROADCAST CHANNELS: GRANTING ACCESS,SCHEDULING OF DATA BLOCKS, POWER CONTROL, CONGESTION CONTROL ETC AS IN NORMAL CHANNELS IN VOICE. » SEGMENTATION OF PACKET DATA TOWARDS BTS INTO RADIO BLOCKS,ACKNOWLEDGEMENT & RETRANSMISSION. » MANAGING INTERFACE WITH SGSN,SENDING DATA IN BLOCKS.
GPRS CHANNELS • PBCCH: BROADCASTS PACKET SPECIFIC SYSTEM INFO; – FOR LIGHT DATA TRAFFIC,FUNCTION IS PERFORMED BY BCCH.
• PCCH: COMMON CONTROL CHANNEL: » PPCH:PAGING; » PRACH:ACCESS, » PAGCH:ACCESS GRANT
• PDCH:DATA CHANNEL: » PDTCH:CARRIES USER DATA. » PACCH: SHARES TS WITH PDTCH,DEDICATED CHANNEL FOR PACKET ACK/NACK » PTCCH:USED FOR CONTINOUS TIMING ADVANCE.
MULTIPLEXING MSs ON THE SAME TIME SLOT • DNLINK: » » » »
TFI FIELD IN PDCH IS UNIQUE FOR AN MS. IF TFI MATCHES, MS ACCEPTS THE DATA. 16 MS CAN BE MULTIPLEXED IN ONE TS: EFFICIENT UTILISATION OF RESOURCES WHEN TRAFFIC IS LIGHT.
• UPLINK: » USF FIELD IN DNLINK PDCH: » MSs WHICH ARE SHARING THE PDCH READ USF VALUE TO CHECK WHICH MS CAN TRANSMIT ON CORRESPONDING UPLINK PDCH. » 7 MS CAN BE MULIPLEXED IN UPLINK. » TOTAL 16 MS IN UPLINK+DOWNLINK. » RESTRICTION IMPOSED BY TIMIMNG ADVANCE.
GPRS MULTISLOT CLASS • IT IS POSSIBLE TO ALLOCATE MORE THAN ONE TS TO A PARTICULAR MS TO INCREASE DATA SPEED. • DEPENDS ON TRAFFIC & BTS RESOURCE(CHANNELS) & CAPABILITY OF MS. • VOICE CALLS GENERALLY GET PRIORITY IN RESOURCE ALLOTTMENT. • CAPABILITY OF MS : MULTISLOT CLASS. • MOST COMMON: CLASS 10: 4 TS IN DN LINK,2 TS IN UPLINK,TOTAL NOT EXCEEDING 5.
MULTIFRAME FOR GPRS AIR INTERFACE • • • • • •
1 MULTIFRAME = 52 TDMA FRAMES 12 BLOCKS EACH OF 4 FRAMES 2 IDLE FRAMES FOR MEASUREMENT 2 FRAMES FOR TIMING ADVANCE EACH TS IN A FRAME CARRIES 114 DATA BITS. FOR CS1 181 USERBITS---AFTER CODING 456 BITS--SENT OVER 4 FRAMES (18.464 ms) • EFFECTIVE DATA RATE = (181/18.464) x 48/52 = 9.046 KBPS PER TS • SIMILARLY EFFECTIVE DATA RATES FOR CS2/CS3/CS4 MAY BE CALCULATED.
GPRS MOBILITY MANAGEMENT STATES
• EACH LA (LOCATION AREA) IS FURTHER DIVIDED INTO SEVERAL RA (ROUTING AREA) • RAI = MCC+MNC+LAC+RAC • IN PACKET IDLE MODE MS LISTENS TO PBCCH FOR PAGING. • MS REGISTERS WITH SGSN AND IS ALLOCATED P-TMSI. • THIS IS KNOWN AS GPRS ATTACH STATE. • SGSN KNOWS RA OF MS, AND MS MULTISLOT CLASS & CAPABILITY . MS MAKES REGULAR RA UPDATE. • IN ATTACH MODE MS ANSWERS THE PAGING THROUGH PRACH. • RADIO RESOURCES ARE ALLOCATED & DATAPATH IS ESTABLISHED BETWEEN MS & SGSN. • THIS IS CALLED ACTIVATION OF PDP (PACKET DATA PROTOCOL) CONTEXT.
• PDP CONTEXT CONTAINS MAPPING & ROUTING INFO FOR TRANSFERRING DATA. • ON PDP CONTEXT ACTIVATION MS OBTAINS IP ADDRESS FROM THE NETWORK(GGSN). • SERVICE PARAMETERS LIKE QOS ARE NEGOTIATED. • QOS IS ENSURED BY ALLOCATING DIFFERENT LEVELS OF RADIO PRIORITY (4 LEVELS) TO DETERMINE RADIO ACCESS & SERVICE PRECEDENCE. • TBF:TEMPORARY BLOCK FLOW: IS A PHYSICAL CONNECTION BETWEEN MS & THE NETWORK TO SUPPORT UNIDIRECTIONAL DATA ON ONE OR MORE PDCH. • TBF SPECIFIES TIMESLOTS,TFI,USF & ARFCN TO BE USED BY MS & ALSO CODING SCHEME. • TBF IS TEMPORARY AND IS MAINTAINED ONLY FOR THE DURATION OF DATA TRANSFER.
GPRS PROTOCOL STACK
• • •
GSM RF : PHYSICAL RADIO CHANNEL MAC: ALLOCATION OF CHANNEL. RLC: – – – –
ALLOTMENT OF TBF SUBMULTIPLEXING OF MULTIPLE MS IN ONE TS TS COMBINING FOR ONE MS SEGMENTATION & REASSEMBLY OF LLC FRAMES TOWARDS SGSN.
•
LLC:LOGICAL COONECTION BETWEEN MS & SGSN EVEN WHEN NO PHYSICAL CONNECTION EXISTS.
•
BSSGP: TRANSFERS LLC FRAMES WITH RELATED INFO LIKE QOS & ROUTING INFO FROM BSC TO SGSN. SNDCF:
•
» ENCRYPTION,COMPRESSION » SEGMENTATION/REASSEMBLY » MULTIPLEXING OF SIGNALLING INFO & DATA TO FORM LLC FRAMES
•
GTP: GPRS TUNNELING PROTOCOL: ENCAPSULATION OF IP PACKETS INTO DATA UNITS THAT ARE TRANSPORTED TRANSPARENTLY ACROSS GPRS SYSTEM FROM SGSN TO MS.
ENCAPSULATION & SEGMENTATION OF DATA
MOVEMENT OF PACKETS IN GPRS NETWORK •
THE ISP SENDS IP DATA PACKETS INTO GPRS NETWORK USING THE IP ADDRESS ASSIGNED TO MS.
•
GGSN SEARCHES FOR THE RELEVANT PDP CONTEXT & FORWARDS TOWARDS RIGHT SGSN.IP DATA UNITS ARE ENCAPSULATED INTO NEW DATA UNTIS OF GTP & THE NEW IP ADDRESS IS THE IP ADDRESS OF THE SGSN.
•
SGSN ENCAPSULATES THE GTP DATA UNITS & BY SNDCF PROTOCOL SUBDIVIDES IT INTO A CERTAIN NO. OF LLC FRAMES.DATA IS ALSO ENCRYPTED & COMPRESSED.
•
SGSN FINDS OUT THE LOCATION OF THE MS & SENDS LLC FRAMES TO THE RIGHT BSC.PAGING PROCEDURE IS USED AS IN VOICE CALLS.
MOVEMENT OF PACKETS IN GPRS NETWORK (CONTD) •
LLC FRAMES ARE SEGMENTED INTO MAC/RLC BLOCKS SUITABLE FOR TRANSMISSION ON AIR.
•
RLC BLOCKS ARE SENT ACROSS A-bis INTERFACE TO THE RIGHT BTS
•
BTS PERFORMES BLOCK CODING,CONVOLUTION CODING,PUNCTURING,INTERLEAVING:GIVING RADIO BLOCKS-456 BITS.
•
EACH RADIO BLOCK IS SENT ON AIR INTERFACE IN 4 NORMAL BURSTS EACH CONTAINING 114 BITS.
•
ACK/NACK SENT BY MS ON UPLINK PDCH.
PACKET DATA TRANSPORT
SOME FEATURES OF GPRS • CONTINUOUS TIMING ADVANCE UPDATE: » MS SENDS ACCESS BURST IN U/L PTCCH » BSS ACCESSES REQUIRED TA AND TRANSMITS THE INFO IN D/L PTCCH.
• NO HANDOVER: » MS PERFORMS NORMAL CELL RE-SELECTION » DURING RESELECTION MS GOES TO IDLEMODE.
• LINK ADAPTATION: » DURING DATA TRANSMISSION CODING SCHEME IS CHANGED BY THE NETWORK TO SUIT RADIOENVIRONMENT. » AUTOMATIC SWITCHOVER FROM CS1-CS2-CS3-CS4 & VICE-VERSA.
• EGPRS USES 8-PSK MODULATION TO INCREASE DATARATE 3 FOLD. • BSS NEEDS UPGRADATION. • STILL HIGHER DATARATE----UMTS/3G • UMTS USES WCDMA WHICH SUPPORTS FLEXIBLE & HIGH DATA RATE. • UMTS:SMOOTH INTEGRATION OF VOICE & DATA SERVICE. • STILL HIGHER DATA RATE:OFDM • IN ANY SYSTEM HIGHER THE DATARATE,LESS IS THE COVERAGE AREA. • MORE SUBSCRIBERS ---- LESS PEAK DATARATE.
