Module 5 GPRS and Edge.ppt

8/14/2019 Module 5 GPRS and Edge.ppt

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GSM Network Evolution


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VEDANG Telecom Training

GSM Network Evolution


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Data Connection through GSM


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Data connection through GSM

The output from the laptop is a maximum of 9.6kbps of data and RS232 controlsignals. The control signals must also be carried to the modem and increase thebit-rate to 12kbps.

Typically a Data Card inserted into a PCMCIA slot of the laptop will convertthese signals (data and control) into a 12kbps serial bit stream for connecting toa mobile phone.

The mobile phone adds on bits for error protection and transmits across the AirInterface at 33.8kbps. This occupies one complete timeslot, as does a normalvoice link.

At the BSS (BTS/BSC) the error protection bits are removed and the 12kbps ofdata are transferred to the XCDR at 16kbps (as with speech, a padding processfor transfer over E1 links).

The XCDR rate adapts this to 64kbps (padding) for transfer to the MSC.

Finally the MSC relays the signal to a GSM network entity known as theinterworking function (IWF). This contains a Rate Adapter which will remove the64kbps padding, reconvert the serial 12kbps into the original 9.6kbps data pluscontrol signals and feed to the modem (also situated in the IWF).


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High Speed circuit Switched Data ( HSCSD)


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Need for GPRS

The need for faster, cheaper, smarter and bettermanaged servicesclearly exists with the key service being the mobile intranet i.e. securewireless access to the corporate environment over the Internet.

There were four main reasons for the slow takeup of wireless data systems:

The notebook PC/phone link was proprietary, so the PC card is expensive.

Voice and data required a user to use two devices, and carrying a phoneabout is irrelevant to a datacentric worker.

The transfer rate of 9.6kbit/s, albeit with robust error correction, wasperceived as too low and the cost of mobile email and faxing as too high.

The industry was not marketing a true solution mobile data involves a

convergence of communications and computing technologies, and untilrecently users had to apply the glue themselves.


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Circuit and Packet Switching

Circuit switching provides a fixed bandwidth channel over a unique

path from user to user for the duration of the call. It is therefore

inefficient when dealing withburstyor Variable Bit Rate (VBR)

traffic (e.g. data) as the maximum required bit rate must bemaintained throughout the duration of the call therefore leaving

resources under-utilized for much of the time.


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Packet switching can be used for data traffic that is generated inbursts and is therefore ideal for Variable Bit Rate data transport.

The paths taken by successive packets may not be the same.Overhead information is added to the data to enable the network toroute it correctly and the recipient has to assemble the packets in

the correct sequence. GSM has, until GPRS, used circuit switched connections. A bi-

directional traffic channel is established and therefore chargeable,to the user for the duration of the call whether traffic is actuallybeing transferred or not.

Packet switching divides the data into individual, limited size

containers (packets) and sends them through the network alongcommunication lines being shared by other channels.



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Using Spare GSM Capacity


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Dedicated and Switchable Timeslots


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GPRS Network Entities


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GGSNGateway GPRS Support Node

The GGSN is the node that is accessed by the Packet Data Network (PDN)due to appropriate evaluation of the Packet Data Protocol (PDP) address(e.g. X.25 or IP address).

The GGSN is linked to the external PDNs via the Gi interface or to GPRSnetworks in different Public Land Mobile Networks (PLMN) via the Gpinterface. As such, the GGSN is the first point of interconnection.

The GGSN may also connect to the Home Location Register (HLR) whichallows routing information to be passed back down to the GGSN which inturn allows the Packet Data Units (PDU) to be tunneled towards the MS.

On the other side of the GGSN, the Gn interface provides the connectiontowards the Serving GPRS Support Node (SGSN).


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SGSN and PCU

SGSN The Serving GPRS Support Node (SGSN) offers very similar

functionality to that of the MSC in a GSM network.

The SGSN will establish a PDP context to allow PDUs to betransferred between the MS and the GGSN that the MS is

currently utilizing.

PCU

The PCU attaches to existing the Base Station Controller (BSC).

The PCU is responsible for all functions of GPRS radio protocols

and communications with the SGSN.


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GPRS MS Class Capabilities


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GPRS MS Class Capabilities

A GPRS MS can operate in one of three modes of operation. Themode of operation will depend upon the services that the MS isattached to, i.e., only GPRS or both GSM and GPRS. The threedifferent modes of operation are defined in terms of mobileclasses and can be defined as such:

Class A will support simultaneous attach, simultaneousactivation, simultaneous monitor, simultaneousinvocation and simultaneous traffic..

Class B will support simultaneous attach, simultaneousactivation, simultaneous monitor.

Class C will support only nonsimultaneous attach, i.e.alternate use only.


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GPRS Mobility Management

3 different positions for the mobile:- Idle

- Ready

- Stand by


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GPRS Features

Speed Theoretical max speed is 171.2 kbps using all 8 time

slots at the same time.

GPRS data speeds are likely to average about 56kbps.

Immediacy

No dial up modem connection is necessary.

GPRS users are always connected

New applications, Better applications

The higher data rates will allow users to take part in videoconferences and interact with multimedia websites


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Limitations in GPRS

Speed much lower in reality: the network operator willnot allow all timeslots to be used by a single GPRSuser.

Sub optimal modulation:GPRS is based on amodulation GMSK (Gaussian minimum shift keying)modulation.

Transit delay: GPRS packets are sent in all differentdirections to reach the same destination.


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Mobile Evolution


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Enhanced Data Rates for GSM Evolution (EDGE)

The idea behind EDGE is to obtain even higher data rates on thecurrent 200KHz GSM carrier by changing the type of modulationused.

GPRS is based on the GMSK.

EDGE is based on 8PSK which allows a much higher bit rate

across the air interface. One symbol for every 3 bits so Rate EDGE=3 x Rate GPRS

EDGE was formerly called GSM384, because it allows datatransmission speeds of 384 Kbps.


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EDGE


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EDGE and GSM Comparison


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Introduction to 3 G services


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Fast Forward to the future


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UMTSR99(3G) Network Architecture

The first deployment of the universal mobile telecommunicationssystem (UMTS) is the release 99 (R99) architecture.

The major change is in the radio access network (RAN) with theintroduction of code division multiple access (CDMA) technology forthe air interface, referred to as wideband CDMA (WCDMA), andasynchronous transfer mode (ATM) as a transport in the

transmission part.

These changes have been introduced principally to support thetransport of voice, video and data services on the same network.

The core network remains relatively unchanged, with primarilysoftware upgrades. However, the IP pushes further into the

network, with the radio network controller (RNC) now transferringdata with the 3G SGSN using IP.


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UMTS99 (3G) Network Architecture


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The next evolution step is the release 4 (R4) architecture. Here,the GSM core is replaced with an IP network infrastructure basedaround voice over IP (VoIP) technology.

The MSC evolves into two separate components: an MGW and anMSC server (MSS).

This essentially breaks apart the roles of connection andconnection control. An MSS can handle multiple MGWs, makingthe network more scalable.

Since there are now a number of IP clouds in the 3G network, itmakes sense to merge these together into one IP or IP/ATMbackbone

This extends IP right across the whole network, all the way tothe BTS. This is referred to as the all-IP network, or the release5 (R5) architecture.

UMTSR4 & R5(3G) Network Architecture


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Maximum Data Rates in 3G networks


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Mobile Data Services


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3 steps to 3 G


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The End

Module 5 GPRS and Edge.ppt

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