GPRS PCU Implementation

8/12/2019 GPRS PCU Implementation

1/22

GPRS PCU implementation for OpenBTS

Ivan Kluchnikov

[email protected]


2/22

GPRS architecture

CCU

CCU

CCU - Channel Codec UnitPCU - Packet Control UnitSGSN - Serving GPRS Support NodeGGSN - Gateway GPRS Support Node


3/22

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


4/22

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


5/22


6/22

GPRS Transmission Plane

OpenBTS (CCU) + PCU OsmoSGSN OpenGGSN


7/22

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


8/22

GPRS Additional Logical Channels


9/22

GPRS Capacity on Demand

TS

01

2

3

4

5

6

7

time

Circuit switched channels

Packet switched channelsPDCH

SignallingBCCH+FCCH+SCH+CCCH


10/22

GPRS Allocation of physical resource

Allocation schemes

Fixed allocation(deprecated) Dynamic allocationExtendedDynamic Allocation


11/22

GPRS Dynamic Assignment


12/22

GPRS RLC/MAC Layer


13/22

RLC/MAC Block Structure

Differences in Block Structure


14/22

GPRS Temporary Block Flow (TBF)

MS BSS

LLC PDURLC/MAC Control Block

RLC/MAC Control Block

RLC Data Block 1

RLC Data Block N



TBFEstablishment

RLC Data Block Transfer

TBF Release

TBF

Uplink TBF


15/22

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


16/22

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


17/22

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


18/22

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


19/22


20/22


21/22

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

=========================================

RlcMacDownlink 67340


22/22

==========================================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

Documents

GPRS PCU Implementation