Download - GPRS PCU Implementation
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GPRS PCU implementation for OpenBTS
Ivan Kluchnikov
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GPRS architecture
CCU
CCU
CCU - Channel Codec UnitPCU - Packet Control UnitSGSN - Serving GPRS Support NodeGGSN - Gateway GPRS Support Node
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GPRS Core Network
SGSN Serving GPRS Support Node
Mobility management
Control of network access
Ciphering and authentication
Gateway GPRS Support Node GGSN
Interface to external packet data networks
Routing functions
Firewall
OsmoSGSN
OpenGGSN
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GPRS Base Station Subsystem
Channel Codec Unit CCU
Channel coding (CS-1 until CS-4)
Forward Error Correction
Interleaving.
Measuring of the radio parameters, signal level and quality
PCU Packet Control Unit
Radio resource assignment
Radio channel management
Segmentation and reassembly of LLC frames
Transfer of RLC blocks
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GPRS Transmission Plane
OpenBTS (CCU) + PCU OsmoSGSN OpenGGSN
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GPRS Radio Interface
GPRS physical layer is based on that of the GSM: Access scheme: TDMA Transportation unit for data: Normal Burst Modulation: GMSK
Packet data channel (PDCH): dynamically allocated in the cell by the network mapped on a 52-multiframe
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GPRS Additional Logical Channels
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GPRS Capacity on Demand
TS
01
2
3
4
5
6
7
time
Circuit switched channels
Packet switched channelsPDCH
SignallingBCCH+FCCH+SCH+CCCH
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GPRS Allocation of physical resource
Allocation schemes
Fixed allocation(deprecated) Dynamic allocationExtendedDynamic Allocation
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GPRS Dynamic Assignment
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GPRS RLC/MAC Layer
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RLC/MAC Block Structure
Differences in Block Structure
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GPRS Temporary Block Flow (TBF)
MS BSS
LLC PDURLC/MAC Control Block
RLC/MAC Control Block
RLC Data Block 1
RLC Data Block N
RLC/MAC Control Block
RLC/MAC Control Block
TBFEstablishment
RLC Data Block Transfer
TBF Release
TBF
Uplink TBF
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GPRS implementation for OpenBTSImplemented features
Open BTS side
Handling of BCCH, RACH and AGCH for GPRS support.
52-GPRS multiframe .
Logical Channels: PACCH, PDTCH.
Channel coding using Coding Scheme 1.
Channel access control functions, including access requests and grants.
OpenBTSPCU OsmoSGSN
Gb
UDP UDP
CCU
Um L1
GPRS i l t ti f O BTS
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GPRS implementation for OpenBTSImplemented features
PCU side
Segmentation of LLC PDUs into RLC data blocks and re-assembly ofRLC data blocks into LLC PDUs.
Segmentation of RLC/MAC control messages into RLC/MAC control
blocks and re-assembly of RLC/MAC control messages from RLC/MACcontrol blocks.
Minimal BSSGP protocol implementation for integration with SGSN.
Uplink TBF Establishment on CCCH.
Downlink TBF Establishment on CCCH.
OpenBTSPCU OsmoSGSN
Gb
UDP UDP
CCU
Um L1
GPRS i l t ti f O BTS
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GPRS implementation for OpenBTSTo be done
L1 interface between PCU and OpenBTS for communication.
GPRS Attach procedure
OpenBTSPCU OsmoSGSN
Gb
UDP UDP
CCU
Um L1
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TBF Uplink/Downlink management with multiple mobiles
Backward Error Correction (BEC) procedures enabling the selectiveretransmission of RLC data blocks.
PDCH scheduling functions for UL and DL data transmission.
TFI (Temporary Flow Identity) management.
Medium Access modes (Dynamic Allocation).
USF (Uplink State Flag) management.
Contention Resolution Procedure.
Paging procedures using paging subchannel on CCCH.
Improved BSSGP (SGSN integration).
GPRS implementation for OpenBTSNext steps
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Sizeof RLC/MAC control message structures(RlcMacUplink and RlcMacDownlink union) in bytes.
RlcMacUplink 1380==========================================Packet Cell Change Failure 92Packet Control Acknowledgement 28Packet Downlink Ack Nack 60EGPRS PD AckNack 288Packet Uplink Dummy Control Block 8Packet Measurement Report 212Packet Resource Request 400Packet MobileBF Status 9Packet PSI Status 40Packet Enh Measurement Report 1376
Packet Cell Change Notification 140Packet SI Status 70
Additional MS Rad Access Cap 136Packet Pause 16
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RlcMacDownlink 67340
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==========================================Packet Access Reject 64Packet Cell Change Order 67336Packet Downlink Assignment 184Packet Measurement Order Reduced 12
Packet Neighbour Cell Data 30Packet Serving Cell Data 25Packet Paging Request 85Packet PDCH Release 3Packet Polling Request 16Packet Power Controliming Advance 42Packet PRACH Parameters 15
Packet Queueing Notification 8Packetimeslot Reconfigure 160PacketBF Release 7Packet Uplink Ack Nack 148Packet Uplink Assignment 184Packet Cell Change Continue 10Packet Handover Command 340
Packet PhysicalInformation 5Packet Downlink Dummy Control Block 7PSI1 64PSI2 556PSI3 15936PSI3 BIS 11528PSI4 56
PSI13 84PSI5 80