Actix Training Module - E_ GPRS Introduction.pdf

7/29/2019 Actix Training Module - E_ GPRS Introduction.pdf

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Actix Training Module

E/GPRS technology introduction


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All contents of this document are the property of Actix

and are provided for information purposes only. Theinformation in this document is subject to change withoutnotice. Actix will not be held liable for technical oreditorial omissions made herein, and will not be heldliable for incidental, consequential or other similardamages resulting from the use of its products.Copyright Actix 2006. All Rights Reserved


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GPRS Network Overview

Fundamental E/GPRS network structure


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GPRS Network- GGSN

Gateway GPRS Support Node

Inter-working Node to external IP network

Main Functions: Routing of incoming packets to SGSN

Access point to PDN for outgoing packets

Security/Firewall

Billing support

Session Management and Communication Setup to external network


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GPRS Network-SGSN

Serving GPRS Support Node

Forwards Incoming Packets to BSC/PCU Forwards Outgoing Packets to GGSN

Primary Functions are Ciphering and Authentication

Billing/creation of charging data records (CDR)

Mobility Management- Routing Area Updates (GMM)

Session Management- Handled in conjunction with GGSN (SM)


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GPRS Networks- GMM

GPRS Mobility Management (GMM)

Required to enable mobility of GPRS Mobile Station (MS)

SGSN informs Home Location Register (HLR) of MS under its control

MS informs network of its location by performing Routing Area (RA) updates

SGSN updates GGSN of MS location


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GPRS Networks- GMM

Three Possible GMM states


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GPRS Networks- GMM

GMM Idle Last known MS location in HLR MS not accessible for packet transfer MS detached from GPRS network

GMM Standby No data can be transferred Network resources assigned for GMM- aware of MS location RA updates and cell reselections performed MS can be paged for packet services

GMM Ready Paging received in MS and response in GGSN Can activate/deactivate PDP contexts MS attached to GPRS network


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GPRS Networks- SM

GPRS Session Management

Upon PDP Context Activation, the SGSN establishes a PDP context with GGSN

Used for Routing of packets


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GPRS GMM/SM Statistics

GMM/SM are end to end functions controlled from Core

Network GMM statistics evaluated from GPRS attach analysis

GPRS Attach Failures Occur due to GPRS Sleeping Cell GPRS not enabled on cell Poor Radio

SM Statistics evaluated from PDP context activation analysis

PDP Context Activation Failures occur due to SIM not provisioned for GPRS

No PDCH or PCU resources available Poor radio

Therefore the analysis of these statistics forms an important part of the GPRSnetwork troubleshooting process


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GPRS Attach Procedure Attach request sent by MS to SGSN Authentication is undertaken unless an MM session is already underway The SGSN indicates the MS location to the HLR The SGSN sends an Attach Accept message to the MS, in addition to a Packet TMSI (P-

TMSI) The MS acknowledges the received P-TMSI with an Attach Complete message


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PDP Context Activation Procedure

The MS sends an Activate PDP Context Request message to theSGSN. Security functions may be executed. The SGSN validates the Activate PDP Context Request , and assigns

an IP address The SGSN sends an Activate PDP Context Accept message to the MS.


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GPRS Network-BSC/PCU

Packet Control Unit Controls Air Interface Resources Controls Setup, Supervision and Disconnection of PS Calls


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GPRS Network-BTS and MS

Base Transceiver Station transmits and receives

information over air interface GPRS capable MS connects to GPRS networkand transmits and receives packet data

Class A MS can have simultaneous CS connection and PS transfer Class B MS can have simultaneous attachment to CS and PS domain,

but must suspend PS transfer if paged for CS connection Class C can attach to CS or PS but not simultaneously

GPRS capable MS can have different multi-slotcapability. The most common:

1+2 1+3 1+4 2+4


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Logical Link and Radio Resource

Logical Link from SGSN to MS

Logical link management functions concerned with themaintenance of a communication channel between anindividual MS and the PLMN . The logical linkestablishment, maintenance and release is used for:

MS attach Link status supervision and control link changes De-allocation of resources


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Logical Link and Radio Resource

Radio resource management (RR or GRR) functions

concerned with the allocation and maintenance of physical channels and the maintenance of the airinterface.

Two GPRS RR modes Packet Idle Mode - Can still be in GMM ready mode Packet Transfer Mode- when data transfer is ongoing

The RR sub-functions are Cell reselection- GRR in packet idle mode on cell re-selection Power Regulation


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GPRS Protocol Stack For GPRS the TDMA frame as structured for the GSM is always used, but

the physical channels (that is, the radio resources) are managed differently. The transmission (payload) protocol architecture for the GPRS system isshown in figure below.


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GPRS Protocol Stack The protocol stack pertaining to the MS


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GPRS Protocol Stack

Application Layer Packet data units generated by client software in MS

Sub-Network Dependent Convergence Protocol Single protocol supports data links from various network layer protocols (IP/X25) Multiplexes data from different network layers to single LLC

Logical Link Control Protocol The Logical Link Control (LLC) protocol provides a reliable logical link between

the MS and its SGSN New LLC connection created on RA update LLC performs

Sequential reassembly of frames to/from the SNDCP & RLC/MAC layer. Control flow between the MS & SGSN Ciphering Error detection, recovery (where possible) and notification of unrecoverable errors, by

means of the Frame Check Sequence (FCS)


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GPRS Protocol Stack

RLC/MAC layer

The RLC/MAC layer contains two functions Radio Link Control (RLC) The RLC provides a radio-solution-dependent reliable link. The RLC segments

and codes LLC-PDU frames for transmission across the air interface .

Medium Access Control (MAC) The MAC function defines procedures that enable a number of MS to share the

Um interface by using different physical channels it controls the access signalling (request and grant) procedures for the radio

channel, and the mapping of LLC-PDU frames onto the GSM physical channel


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GPRS Protocol Stack

Physical Layer Functions

Forward Error Correction

Interleaving

Congestion Detection

Synchronisation and Timing Advance Control

Monitoring Radio Link Quality

Power Control Procedures


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GPRS Protocol Stack


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RLC/MAC Block

The multiplexing of packet data over the physical air

interface is handled by the RLC/MAC layer DL limit 32 users per TRX UL Limit 6 users per TS PDCH Resources are either reserved or dynamic PDCH allocated per TRX as a Packet Set (P-SET) Each TBF can utilise PDCH from 1 P-SET only A summary of the key header information fields and

modes associated with this process


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RLC/MAC Block Temporary Block Flow (TBF)

The TBF is a physical connection between two RR entities which allow theunidirectional flow of upper layer PDUs over the air interface. An MS can have a

TBF in one or both directions

Temporary Flow Indicator (TFI) Each TBF is assigned a TFI (or address) for the duration of that TBF.

When a TBF is assigned, the MS is informed of which time slot(s) to useand its TFI address. A number of MSs can be assigned resources onthe same time slot(s). The header of every downlink traffic blockcontains a TFI that shows which MS the radio block is addressed to,thus the addressed MS will use that traffic block.

Uplink State Flag (USF) The header of every downlink traffic block also contains the Uplink State Flag(USF). The USF is used to notify the MS with uplink TBFs on that time slot,which one of them that may send an uplink radio block in the next group of fourbursts.


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RLC/MAC Block Coding Schemes

Prior to transmission over air interface, RLC/MAC blocks

are coded Four Schemes are defined; CS1-CS4 Link adaptation schemes controlled allow change in

coding scheme according to radio channel quality CS1- rate convolution coding

3USF + 181 bits + 40 BCS + 4 tail = 228 bits * 2 = 456 bits/4 = 114 bits Max RLC throughput per Timeslot is 181bits/20ms= 9.05kbps

CS2- rate convolution coding 6USF + 268 bits + 16 BCS + 4 tail = 294 bits * 2 = 588 -132 = 456 Max RLC throughput per Timeslot is 268 bits/20ms= 13.4kbps


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RLC/MAC Block Coding Schemes

For BLER < 10% CS 1 C/I < 10.3, 9.05kbps CS 2 C/I < 12.6, 13.4kbps CS 3 C/I < 14, 15.6kbps CS 4 C/I < 18.3, 21.4kbps


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EDGE

Enhanced Data for Global Evolution

GSM uses GMSK modulation: +/- Phase = 0 or 1 1 bit per symbol EDGE utilises GMSK and 8-PSK 8PSK has 8 phase states

3 bits per symbol ~ Triple the rate of GMSK


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EDGE GPRS has 4 coding schemes

EDGE has 9 modulation and coding schemes MCS1: GMSK, 8.8kbps MCS2: GMSK, 11.2kbps MCS3, GMSK, 14.8kbps MCS4, GMSK, 17.6kbps MCS5, 8PSK, 22.4kbps MCS6, 8PSK, 29.6kbps MCS7, 8PSK, 44.8kbps MCS8, 8PSK, 54.4kbps MCS9, 8PSK, 59.2kbps


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EDGE Link Quality Control

2 Modes, Link Adaptation and Incremental Redundancy UL is always Link Adaptation DL uses either

IR is a more complex algorithm

Actix Training Module - E_ GPRS Introduction.pdf

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