Module 5 GPRS and Ehidge

Vedang Radio Technology Pvt. Ltd .

105, Nirman Industrial Estate Link Road Malad (W) Mumbai -400064

GSM Network Evolution

VEDANG Telecom Training

GSM Network Evolution


Data Connection through GSM


Data connection through GSM• The output from the laptop is a maximum of 9.6kbps of data and RS232 control

signals. The control signals must also be carried to the modem and increase the bit-rate to 12kbps.

• Typically a ‘Data Card’ inserted into a PCMCIA slot of the laptop will convert these signals (data and control) into a 12kbps serial bit stream for connecting to a mobile phone.

• The mobile phone adds on bits for error protection and transmits across the Air Interface at 33.8kbps. This occupies one complete timeslot, as does a normal voice link.

• At the BSS (BTS/BSC) the error protection bits are removed and the 12kbps of data are transferred to the XCDR at 16kbps (as with speech, a padding process for 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 the

interworking function (IWF). This contains a Rate Adapter which will remove the 64kbps padding, reconvert the serial 12kbps into the original 9.6kbps data plus control signals and feed to the modem (also situated in the IWF).


High Speed circuit Switched Data ( HSCSD)


Need for GPRS • The need for faster, cheaper, smarter and better–managed services

clearly exists with the key service being the mobile intranet i.e. secure wireless access to the corporate environment over the Internet.

There were four main reasons for the slow take–up 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 phone

about is irrelevant to a data–centric worker.• The transfer rate of 9.6kbit/s, albeit with robust error correction, was

perceived 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 until recently users had to apply the glue themselves.


Industry Convergence


Circuit and Packet Switching

Circuit switching provides a fixed bandwidth channel over a uniquepath from user to user for the duration of the call. It is therefore inefficient when dealing with ‘bursty’ or Variable Bit Rate (VBR)traffic (e.g. data) as the maximum required bit rate must bemaintained throughout the duration of the call therefore leavingresources under-utilized for much of the time.


• Packet switching can be used for data traffic that is generated in bursts 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 to route 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 actually being transferred or not.

• Packet switching divides the data into individual, limited size containers (packets) and sends them through the network along communication lines being shared by other channels.



GPRS- General Packet Radio Services• GPRS is a set of new GSM bearer services that provides packet mode

transmission within the PLMN and interworks with external networks whilst not preventing the user’s operation of other GSM services.

• GPRS will allow the service subscriber to send and receive data in an end–to–end packet transfer mode, without utilizing network resources in circuit switched mode.

• This enables a more cost effective and efficient use of network resources for applications displaying one or more of the following characteristics:• Intermittent, bursty data transmissions, where the time between

successive transmissions greatly exceeds the average transfer delay.• Frequent transmissions of small volumes of data (e.g. less than 500

octets) occurring at a rate of up to several transactions per minute.• Infrequent transmissions of larger volumes of data (e.g. several

kilobytes) occurring at a rate of up to several transactions per hour.


Using Spare GSM Capacity


Dedicated and Switchable Timeslots


GPRS Network Entities


GGSN – Gateway 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 GPRS networks in different Public Land Mobile Networks (PLMN) via the Gp interface. As such, the GGSN is the first point of interconnection.

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

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


SGSN and PCUSGSN• 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 be

transferred 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.


GPRS MS Class Capabilities


GPRS MS Class Capabilities• A GPRS MS can operate in one of three modes of operation. The

mode of operation will depend upon the services that the MS is attached to, i.e., only GPRS or both GSM and GPRS. The three different modes of operation are defined in terms of mobile classes and can be defined as such:–

• Class A – will support simultaneous attach, simultaneous activation, simultaneous monitor, simultaneous invocation and simultaneous traffic..

• Class B – will support simultaneous attach, simultaneous activation, simultaneous monitor.

• Class C – will support only non–simultaneous attach, i.e. alternate use only.


GPRS Mobility Management• 3 different positions for the mobile:- Idle- Ready- Stand by


Charging for GPRS Services


GPRS FeaturesSpeed• 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 video

conferences and interact with multimedia websites


Limitations in GPRS• Speed much lower in reality: the network operator will

not allow all timeslots to be used by a single GPRS user.• Sub optimal modulation:GPRS is based on a modulation

GMSK (Gaussian minimum shift keying) modulation.• Transit delay: GPRS packets are sent in all different

directions to reach the same destination.


Mobile Evolution


Enhanced Data Rates for GSM Evolution (EDGE)• The idea behind EDGE is to obtain even higher data rates on the

current 200KHz GSM carrier by changing the type of modulation used.

• 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 data

transmission speeds of 384 Kbps.


EDGE


EDGE and GSM Comparison


Introduction to 3 G services


The Multimedia future


Fast Forward to the future


UMTS – R99(3G) Network Architecture• The first deployment of the universal mobile telecommunications

system (UMTS) is the release 99 (R99) architecture.• The major change is in the radio access network (RAN) with the

introduction of code division multiple access (CDMA) technology for the air interface, referred to as wideband CDMA (WCDMA), and asynchronous transfer mode (ATM) as a transport in the transmission part.

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

• The core network remains relatively unchanged, with primarily software upgrades. However, the IP pushes further into the network, with the radio network controller (RNC) now transferring data with the 3G SGSN using IP.


UMTS’99 (3G) Network Architecture


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

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

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

• Since there are now a number of IP clouds in the 3G network, it makes sense to merge these together into one IP or IP/ATM backbone

• This extends IP right across the whole network, all the way to the BTS. This is referred to as the all-IP network, or the release 5 (R5) architecture.

UMTS – R4 & R5(3G) Network Architecture


Maximum Data Rates in 3G networks


Mobile Data Services


3 steps to 3 G


The End

Module 5 GPRS and Ehidge

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