GPRS Architecture

Packet-switched technique vs. circuit-switched

In circuit-switching, resources (e.g. a channel) are allocated to user for duration of connection
Inefficient use of resources
User pays for the whole connection
High QoS: channel maintains real-time connection
In packet-switching, resources are allocated to user only for the time it takes to send each packet
A channel can serve many users
User pays by the packet
Ideal for bursty data connections

Packet-switched

1.High bit rates
2.Shared bandwidth
3.Variable access times
4.Friendly bill (based on volume)
5.Robust application support
6.Frequent transmission of small volumes


Circuit-switched
1.Low bit rates
2.Reserved bandwidth
3.Fixed access time
4.Unfriendly bill (based on duration)
5.Limited application support
6.Large volumes


GPRS network architecture is built on top of the existing GSM network infrastructure.
To support packet switched functionality, GPRS introduces several new nodes in addition to the network nodes in the GSM.
There exist a Gateway GPRS Support Node (GGSN) and a Serving Support Node (SGSN). There is a backbone network that connects the SGSN and GGSN node together. Some of the existing GSM nodes should be upgraded with GPRS functionality.

PACKET AND CIRCUIT-SWITCHED DATA TRANSFER

In any kind of network the information can travel using either packet-switched (PS) or circuit-switched (CS) mode.
In general, circuit-switched mode is better for a connection set up for the purpose of a constant information flow.
A dedicated resource for this purpose is allocated throughout the connection.
Packet-switched mode is better for “bursty” connections in which short amounts of data are exchanged between the users over long time periods or for infrequent transmissions of big data volumes.
In this case no physical resources are dedicated for the purpose of the connection.
In principle, every burst of data will be routed separately within the network.
it takes to send each packet
A channel can serve many users
User pays by the pacIn circuit-switching, resources (e.g. a channel) are allocated to user for duration of connection
Inefficient use of resources
User pays for the whole connection
High QoS: channel maintains real-time connection
In packet-switching, resources are allocated to user only for the time ket
Ideal for bursty data connections

General Packet Radio Service (GPRS)

Introduction
Part I
GPRS Architecture
Part II
Bearer Services and Supplementary Services
Mobility Management
GPRS Limitations

introduction

Around 1994, the GSM phase 2 standards were enhanced to include a number of new and improved services.
These enhancements became known as GSM Phase 2 Plus.
One of the new features proposed in 1994 was a new service, true packet radio service known as GPRS
The purpose of GPRS (General Packet Radio Service) is to provide an efficient system aimed at data transfer for mobile users.
GPRS allows a user with suitable mobile station to occupy multiple time slots on a TRX, there by making it possible to occupy of all 8 timeslots if they are available.
The GSM system will be largely reused, though new hardware needs to be integrated in the existing network.
GPRS (General Packet Radio Service)
Reuse the existing GSM infrastructure (not standalone)
Introduce packet-switched routing functionality
Better data transfer rates due to multi-slot operation
Low cost and connectivity-oriented
Migration Path to 3G Networks

BTS–Base Transceiver Station

BTS provides physical connection of an MS to the network in the form of Air Interface.
On the other side BTS connected to BSC thru Abis-interface.
Cabinet size is reduced substantially from 1991 to current.
Functionality and basic structure largely unchanged.
A BTS cabinet can have up to 16 TRX (GSM recommendation)

TRX – Most important module of BTS from signal processing point of view

Consists of a low frequency part for signal processing and a high frequency part for modulation/demodulation.

Both parts are connected by a separate or integrated Frequency hopping unit.
All other parts of BTS are associated with TRX and perform auxiliary or admin tasks.

Base Station System (BSS)

The Base Station System (BSS) is responsible for all the radio related functions in the system, such as:
Radio communication with the mobile units
Handover of calls in progress between cells
Management of all radio network resources and cell configuration data.


A BSS consists of the following elements:

• One or more BTSs (base transceiver station)

• One BSC (base station controller)

• One TRAU (transcoding rate and adaptation unit).

Capacity and Frequency Re-use

It is the number of frequencies in a cell that determines the cell’s capacity.
However, a cellular network can overcome this constraint and maximize the number of subscribers that it can service by using frequency re-use.
Each company with a license to operate a mobile network is allocated a limited number of frequencies.
Depending on the traffic load and the availability of frequencies, a cell may have one or more frequencies allocated to it.
It is important when allocating frequencies that interference is avoided.
Frequency re-use means that two radio channels within the same network can use exactly the same pair of frequencies, provided that there is a sufficient geographical distance.
The tighter frequency re-use plan, the greater the capacity potential of the networkInterference can be caused by a variety of factors.
A common factor is the use of similar frequencies close to each other. The higher interference, the lower call quality.
To provide coverage to all the subscribers, frequencies must be reused many times at different geographical locations in order to provide a network with sufficient capacity.
The same frequencies can not be re-used in neighboring cells as they would interfere with each other so special patterns of frequency usage are determined during the planning of the network.

These frequency re-use patterns ensure that any frequencies being re-used are located at a sufficient distance apart to ensure that there is little interference between them.
The term “frequency re-use distance” is used to describe the distance between two identical frequencies in a re-use pattern.
The lower frequency re-use distance, the more capacity will be available in the network.

Cell Characteristics

The Basic Union In The System
defined as the area where radio coverage is given by one base station.
A cell has one or several frequencies, depending on traffic load.
Frequencies are reused, but not used in neighboring cells due to interference.
Each served by its own antenna
Served by base station consisting of transmitter, receiver, and control unit
Use multiple low-power transmitters
Cell sizes from some 100 m in cities to, e.g., 35 km on the country side (GSM)
Pico cells covering building interiors, Micro cells covering selected outdoor areas, and Macro cells for more wider area

CELLS

A cell may be defined as an area of radio coverage from one BTS antenna system.
It is the smallest building block in a mobile network and is the reason why mobile networks are often referred to as cellular networks.
Typically, cells are represented graphically by hexagons.

SOLUTIONS TO TRANSMISSION PROBLEMS

Some solutions to the problems described in previous sections are

1. Channel Coding
2. Interleaving
3. Diversity
   

Although many of these do not entirely solve all problems on the radio transmission path, they do play an important part in maintaining call quality for as long as possible

Channel Coding
In digital transmission, the quality of the transmitted signal is often expressed in terms of how many of the received bits are incorrect.
This is called Bit Error Rate (BER).
BER defines the percentage of the total number of received bits which are incorrectly detected.
This percentage should be as low as possible. It is not possible to reduce the percentage to zero because the transmission path is constantly changing.
This means that there must be an allowance for a certain amount of errors and at the same time an ability to restore the information, or at least detect errors so the incorrect information bits are not interpreted as correct.
Channel coding is used to detect and correct errors in a received bit stream.

Mobile Radio Propagation Effects

Signal strength must be strong enough between base station and mobile unit to maintain signal quality at the receiver must not be so strong as to create too much interference with channels in another cell. Attenuation due to rain presence of raindrops can severely degrade the reliability and performance of communication links trees near subscriber sites can lead to multipath fading Loss of strength of signal due to absorption by trees, plants, parks (greenary) is called vegetation losses

RF Propagation

Basic propagation models
Reflection
Diffraction
Scattering

• Reflection

Reflection occurs when a propagating electromagnetic wave is incident upon an object which has very large dimensions when compared to the wavelength of the propagating wave
Reflection occurs from the surface of the earth and from buildings and walls

• Diffraction

Diffraction occurs when the radio path between the transmitter and receiver is obstructed by a surface that has sharp irregularities (edges)
Building edges, roof tops

• Scattering

Scattering occurs when the medium through which the wave travels consist of objects with dimensions that are small compared to the wavelength .
Rough surfaces , Sign posts
Essentially, the radio waves interact with the physical environment along each of these paths.
There are typically (unless you are in free-space) many paths from the transmitter to the receiver.
Each path is called a multipath.

• Fading

Fading occurs when there is more than one transmission path to the MS or BTS, and therefore more than one signal is arriving at the receiver.
This may be due to buildings or mountains, either close to or far from the receiving device.

• Rayleigh Fading

This occurs when a signal takes more than one path between the MS and BTS antennas.
In this case, the signal is not received on a line of sight path directly from the Tx antenna.
Rather, it is reflected off buildings, for example, and is received from several different indirect paths.

TRANSMISSION PROBLEMS

Many problems may occur during the transmission of a radio signal.
Some of the most common problems are described below.
Path Loss
Shadowing
Fading


PATH LOSS
Path loss occurs when the received signal becomes weaker and weaker due to increasing distance between MS and BTS, even if there are no obstacles between the transmitting (Tx) and receiving (Rx) antenna.
The path loss problem seldom leads to a dropped call because before the problem becomes extreme, a new transmission path is established via another BTS.

Shadowing
Shadowing occurs when there are physical obstacles including hills and buildings between the BTS and the MS.
The obstacles create a shadowing effect which can decrease the received signal strength.
When the MS moves, the signal strength fluctuates depending on the obstacles between the MS and BTS
A signal influenced by fading varies in signal strength.
Drops in strength are called fading dips.

RADIO FREQUENCY

The term Radio Frequency (RF or rf) refers to the electromagnetic field that is generated when an alternating current is input to an antenna. This field, also called an RF field or radio wave
This can be used for wireless broadcasting and communications and many other purposes over a significant portion of the electromagnetic radiation spectrum
In vacuum, all electromagnetic waves travel at the speed of light: c = 3x108 m/sec.

Mobile Station characteristics

Technical Marvel
Falling Prices
Availability of different devices
Interaction with BTS
Channel negotiation ,modulation/demodulation and coding/decoding functionality
Efficient use of battery power
Communicates directly with MSC and VLR as well via MM (mobility management) and CC (call control)
Different types of MSs have different output power capabilities and therefore different ranges.
Hand-held phones generally have a lower output power and consequently a shorter range than a vehicle-mounted phone.
According to GSM specifications, MSs are categorized into five classes according to MS output power.
The location of the MS also affects the received power of the transmitted signal.
An MS located at the top of a high building has a greater range than one that is located at or below ground level

Subscriber Identity Module (SIM)

SIM is a microchip
Except for emergency calls, a GSM mobile phone cannot be used without the SIM.
In GSM terminology, the term MS refers to the combination of a SIM and an ME
The SIM stores three types of subscriber related information:
Fixed data stored before the subscription is sold: e.g. IMSI, authentication key and security algorithms
Temporary network data: e.g. the location area of the subscriber and forbidden PLMNs
Service data: e.g. language preference etc..,
A SIM contains information for GSM network operations.
This information can be related to the mobile subscriber, GSM services or PLMN.
The data storage requirements of a SIM are divided into two categories: mandatory and optional.
The major task of a SIM is to store data.
The SIM has an area of non-volatile memory which is used to store information specific to a particular subscriber and this includes the subscriber’s unique international mobile subscriber identity (IMSI) number.
This number is used to identify each individual subscriber within the GSM network
The SIM will also contain the subscriber’s secret authentication key, Ki, the authentication algorithm, A3, and the cipher key generation algorithm, A8.
The language preference indicator is also located in the SIM and this is used to indicate the language to be used on the MS screen.
The items described above are mandatory and must be present in any SIM that conforms to the GSM specifications.
The SIM may also contain a number of optional items which will include the subscriber’s abbreviated dialling numbers.
The SIM may also contain a list of the last number(s) that the subscriber has dialled and an area of storage for the subscriber’s short messages.
Inserting an SIM card into an ME effectively personalises the equipment to the particular subscriber.

Pulse Code Modulation -PCM

Pulse code modulation (PCM) is the worldwide process for transmission
of digital signals.PCM is used to transmit both signaling data and payload.
PCM is categorized into hierarchies, depending on the transmission rate.
Consider a 2Mbps PCM link be partitioned in 32 independent channels of 64kbps each
One 64-Kbps time slot out of a 2-Mbps PCM link typically is used for signaling data
A call setup consumes about 1 to 2 Kbps.

Overview of GSM architecture- Subsystems

Mobile Station – MS
Subscriber Identity Module –SIM
Base transceiver station (BTS)
Base station controller (BSC)
Transcoding rate and adaptation unit (TRAU)
Mobile services switching center (MSC)
Home location register (HLR),
Visitor location register (VLR)
Equipment identity register (EIR).
Together, they form a
public land mobile network (PLMN).

System Architecture of GSM

GSM makes use of Cellular Structure
The basic idea of cellular network is to partition the available frequency range – allocate only part of frequency spectrum to BTS – keep the range of base station small to reuse the frequency.
One more important aspect of network planning is to reduce interference between different base stations.

GSM frequency Ranges

For GSM 900 system
890-915 MHz is uplink range (MS transmit)
935-960 MHz is downlink range (MS receive)
Bandwidth is 25 MHz.
For GSM 1800 system
1710-1785 MHz is uplink frequency range (MS transmit)
1805-1880 MHz is downlink frequency range (MS receive)
Bandwidth is 75 MHz

GSM PHASES

In the late 1980s, the groups involved in developing the GSM standard realized that within the given time-frame they could not complete the specifications for the entire range of GSM services and features as originally planned.
Because of this, it was decided that GSM would be released in phases with phase 1 consisting of a limited set of services and features.

History Of GSM

In the early 1980s, many countries in Europe witnessed a rapid expansion of analog cellular telephone systems. However, each country developed its own system, and interoperability across borders became a limiting factor.
In 1982, the Conference of European Post and Tele communications (CEPT), established a working group called the Groupe Spécial Mobile (GSM).
The task of GSM is to define a new standard for mobile communications in the 900 MHz range using digital technology.
1986
Field tests were held in Paris to select which digital transmission technology to use.
The choice was Time Division Multiple Access (TDMA) or Frequency Division Multiple Access (FDMA).
1987
A combination of TDMA and FDMA was selected as the transmission technology for GSM.
Operators from 12 countries signed a Memorandum of Understanding committing themselves to introducing GSM by 1991.
1988
CEPT began producing GSM specifications for a phased implementation.
Another five countries signed the MoU.
1989
European Telecommunication Standards Institute (ETSI) took over responsibility for GSM specification.
1990
Phase 1 specifications were frozen to allow manufacturers to develop network equipment.
1991
The GSM standard was released.
An addition was made to the MoU allowing countries outside CEPT to sign.
The year 1991 also saw the definition of the first derivative of GSM, GSM 1800 or DCS 1800, which more or less translates the GSM system in to the 1800MHz frequency band.
The meaning of acronym GSM was changed to Global System for Mobile communications the same year.
1992
Phase 1 specifications were completed.
First commercial Phase 1 GSM networks were launched.
The first international roaming agreement was established between Telecom Finland and Vodafone in UK.

histroy of telecommunication

The need for reliable long-distance communication systems has existed since antiquity.
Over time, the sophistication of these systems has gradually improved, from smoke signals to telegraphs and finally to the first coaxial cable, put into service in 1940.
As these communication systems improved, certain fundamental limitations presented themselves.
Electrical systems were limited by their small repeater spacing (the distance a signal can propagate before attenuation requires the signal to be amplified), and the bit rate of microwave systems was limited by their carrier frequency.
In the second half of the twentieth century, it was realized that an optical carrier of information would have a significant advantage over the existing electrical and microwave carrier signals.
However, no coherent light source or suitable transmission medium was available.
After the development of lasers in the 1960s solved the first problem, development of high-quality optical fiber was proposed as a solution to the second.
Optical fiber was finally developed in 1970 by Corning Glass Works with attenuation low enough for communication purposes (about 20dB/km).
At the same time GaAs semiconductor lasers were developed that were compact and therefore suitable for fiber-optic communication systems.
After a period of intensive research from 1975 to 1980, the first commercial fiber-optic communication system was developed, which operated at a wavelength around 0.8 µm and used GaAs semiconductor lasers.
This first generation system operated at a bit rate of 45 Mbit/s with repeater spacing of up to 10 km.
The second generation of fiber-optic communication was developed for commercial use in the early 1980s, operated at 1.3 µm, and used InGaAsP semiconductor lasers.
These systems were initially limited by dispersion.
In 1981 the single-mode fiber was revealed to greatly improve system performance.
By 1987, these systems were operating at bit rates of up to 1.7 Gb/s with repeater spacing up to 50 km.
Third-generation fiber-optic systems operated at 1.55 µm and had loss of about 0.2 dB/km.
They achieved this despite earlier difficulties with pulse-spreading at that wavelength using conventional InGaAsP semiconductor lasers.
Scientists overcame this difficulty by using dispersion-shifted fibers designed to have minimal dispersion at 1.55 µm or by limiting the laser spectrum to a single longitudinal mode.
These developments eventually allowed 3rd generation systems to operate commercially at 2.5 Gbit/s with repeater spacing in excess of 100 km.
The fourth generation of fiber-optic communication systems used optical amplification to reduce the need for repeaters to increase fiber capacity.
This improvement caused a revolution that resulted in the doubling of system capacity every 6 months starting in 1992 until a bit rate of 10 Tb/s was reached by 2001.
Recently, bit-rates of up to 14 Tbit/s have been reached over a single 160 km line using optical amplifiers.

Telecommunication-introduction

Introduction
The use of light to send messages is not new. The idea of using glass fibre to carry an optical communications signal originated with Alexander Graham Bell. However this idea had to wait some 80 years for better glasses and low-cost electronics for it to become useful in practical situations.
Fiber-optic communications is based on the principle that light in a glass medium can carry more information over longer distances than electrical signals can carry in a copper or coaxial medium. With few transmission losses, low interference, and high bandwidth potential, optical fiber is an almost ideal transmission medium.
Among the tens of thousands of developments and inventions that have contributed to this progress three stand out as milestones:
1. The invention of the LASER (in the late 1950's)
2. The development of low loss optical fibre (1970's)
3. The invention of the optical fibre amplifier (1980's)
In initial time, portion of electro magnetic spectrum was used to convey information in communications systems.
The data is transferred over the communication channel by superimposing the information onto a sinusoidally varying electromagnetic wave, which is known as “carrier”.
At the destination information is removed from the carrier wave and processed as desired.
More the information to be carried, higher the carrier frequency there by increasing the transmission bandwidth.

Fulcrum Participates In RS3G Workshop @ EUNIS 2010

RS3G (Rome Student Standards and Systems Group) is a self-established group of software implementers and stakeholders in the European Higher Education domain which is focused on contributing to the definition and adoption of electronic standards for the exchange of student data.
This is supported by European University Information Systems organization (EUNIS).

EUNIS Congresses are international events that attract a large audience from Higher Education Institutions (HEI). It is a chance for international specialists, users, researchers, decision–makers and academic teachers from all over Europe to share their experience. This edition of the annual EUNIS Congress, hosted by the University of Warsaw, took place on 23-25 June 2010 in Warsaw, the capital of Poland.

Fulcrum’s CEO, Rajesh Sinha, was invited in this event as a speaker. Rajesh walked an audience through the pioneering solution developed by Fulcrum for Higher Education sector. The solution developed has the capability to track various activities of students who are migrating to UK to pursue higher education.

The solution Fulcrum thus developed was collaboration between two different Universities that run on completely different applications / systems. The challenge was to implement two completely different Enterprise Services Buses in the Universities and implement connectors to 4 different types of applications and then to demonstrate that a SINGLE reporting program could retrieve data from two Universities WITHOUT any change to the logic of the report.

This solution is termed as one of the ground breaking solutions by Microsoft. Rajesh also focused on Interoperability of services across Institutions over the Cloud environment, thereby leading the discussion to the need of Standards and Protocols within HE Sector. This was highlighted by some of the solutions that Fulcrum is building around ‘Enterprise Service Bus in the Cloud’ as ‘Internet Service Bus’.