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Self-study Material - Version 1- June 2002

CNS/ATM COURSE

PRE-COURSE

SELF-STUDY MATERIALPrepared by: Airways Engineering

Foreword

The Communications, Navigation, Surveillance / Air Traffic Management (CNS/ATM) course is an introductory course that will benefit all Airways Engineering personnel. In order to accomplish this task trainees must go from the known to the unknown. The problem is knowing where we should start and how much material can be taught. Even if we knew the background of all the trainees on a particular course it would take too many resources to tailor a specific course to the specific knowledge level determined to exist.

So this self-study material provides an overview of what the CNS/ATM system concept is, and an insight into on how computers work and communicate. It is important that you know the material well before attending the CNS/ATM course. The terms and concepts are used throughout the CNS/ATM course and you will have difficulty following the certain systems description without a basic understanding of the principles and definitions included in this pre-course study package.

A pre-course threshold knowledge test will be administered to ensure an understanding of this self-study material. You must pass this test with an average of 50% to attend the course.SECTION - 1

1. AIR TRAFFIC DEMAND

1.1Air traffic demand is increasing in all parts of the world. Although rates of growth may differ between regions, significant increases in air traffic demand are expected to continue. The current demands have already increased the pressure on air traffic service providers and users, straining airspace and airport resources. Without change, the result will be further congestion and delays due to the capacity limitations of todays system, which together with environmental considerations, could have significant economic consequences.

1.2The average annual growth rate for the period 2000-2005 was expected to be 5.2%. For the period 2005 -2010 it was projected at 4.8%. These rates of growth have fallen off and it still remains to be confirmed if the rate of growth in Air Traffic will return to the levels that existed prior to the events of September 11th, 2001.

2.SYSTEM PROBLEMS

2.1System shortcomings in the early 1980s amounted to essentially three factors:

Propagation limitations of existing line of sight systems;

The difficulty, caused by a variety of reasons, to implement current Communications, Navigation and Surveillance systems and operate them in a consistent manner in large parts of the world; and,

The limitations of voice communications and the lack of digital air-ground data interchange systems to support automated systems un the air and on the ground.

2.2

These shortcomings were reflected in problems, such as:

Schedule delays due to insufficient Air Traffic Control (ATC) capacity to meet the traffic demand in particular during peak hours.

Differences in operating concepts and procedures and the lack of co- ordination between regions and Flight Information Regions (FIRs) causing increased workloads for both ATC and flight crew.

Air Traffic Flow Management (ATFM) which prevented matching available capacity with demand over the entire route, causing the need for flying holding patterns in the sectors with the highest capacity constraints.

The inflexibility of fixed route structure systems preventing the most efficient use of airspace and most economical conduct of flight operations.

The inability to expand to meet future traffic growth, in an evolutionary fashion.

The inability to fully exploit the capabilities of advanced airborne equipment such as flight management systems.

The increasing operating costs of the present Air Traffic Services (ATS) system associated with the need to increase capacity. Without advanced automation, increases in capacity can only be achieved by decreasing the size of existing control areas and increasing the number of controllers.

2.3 Unless there were improvements to the old system, international aviation would experience a continuing increase in airport and airspace congestion, which would become progressively worse as air traffic increased. This would result in higher operating costs and a stifling of the market for the aviation industry.

3FUTURE AIR NAVIGATION SYSTEM (FANS) COMMITTEE - FANS Phase I

3.1In the early 1980s, the International Civil Aviation Organization (ICAO) recognized the increasing limitations of the existing air navigation systems and the need for improvements to take civil aviation into the 21st century. In 1983, ICAO established the Special Committee on Future Air Navigation Systems (FANS) with the following terms of reference:

3.2"To study technical, operational, institutional and economic questions, including cost/benefit effects, relating to future potential air navigation systems; to identify and assess new concepts and technology, including satellite technology, which may have future benefits for the development of international civil aviation including the likely implications they would have for users and providers of such systems; and to make recommendations thereon for an over-all long term projection for the co-ordinated evolutionary development of air navigation for international civil aviation over a period of the order of twenty five years"

3.3The committee presented to the ICAO Council and the international aviation community, a consolidated proposal for a future global air navigation system.

3.4The Committee concluded that the application of satellite, communications and computer technology was the only solution that would enable international civil aviation to overcome the shortcomings of the present CNS system and fulfill the needs and requirements of the foreseeable future on a global basis. In arriving at this concept of FANS the Committee was guided by the Objectives that a new CNS system should provide for:

Global communications, navigation and surveillance coverage from (very) low to (very) high altitudes, also embracing remote, off-shore and oceanic

Digital data interchange between the air-ground systems to fully exploit the automated capabilities of both.

Navigation/approach service for runways and other landing areas which need not be equipped with precision landing aids.

3.5The FANS I Committee completed its work in May 1988 and recommended that the ICAO Council urgently establish a new committee to advise on the overall monitoring, co-ordination of development and transition planning to ensure that implementation of the future CNS system takes place on a global basis in a cost effective manner, and in a balanced way between air navigation systems and geographical areas.

4FANS PHASE II

4.1In July 1989, the ICAO council, acting on the recommendation of the FANS Phase I Committee, established the Special Committee for the Monitoring and Co-ordination of Development and Transition Planning for the Future Air Navigation System (FANS Phase II).

4.2In October 1993, the FANS Phase II Committee completed its work. It recognized that implementation of related technologies would not arrive overnight, but would rather evolve over a period of time, depending on the existing infrastructure in the various States and Regions, and the over-all requirements and needs of the aviation community.

4.3The Tenth Air Navigation Conference - September 19914.3.1The Tenth Air Navigation Conference held in Montreal in September 1991, endorsed the FANS concept which then became known as the Communications, Navigation, Surveillance / Air Traffic Management system (CNS/ATM). CNS/ATM involves a complex and interrelated set of technologies depending largely on Satellites and including new communications and computer technologies. CNS/ATM is a vision developed by ICAO with the full co-operation of all sectors of the aviation community to accommodate future needs of international air transport. The results of the conference encapsulated a set of agreed recommendations covering the full spectrum of CNS/ATM activities that continue to offer guidance and direction to the international civil aviation community.

4.4Global Planning

4.4.1The FANS PHASE II Committee was tasked to develop a plan of action which was included in their report as an appendix (FANS Phase II - Doc 9623). In 1996 the ICAO Council directed the ICAO Secretariat to revise the Global Plan as a living document comprising technical, operational, economic, financial, legal and institutional elements. The intention was to offer guidance and advice to regional planning groups and States on implementation strategies, which include technical cooperation aspects.

4.4.2The Secretariat on the first page of the revised Global Plan included the following information on CNS/ATM:

4.2Definition

4.2.1 Communications, navigation and surveillance systems, employing digital technologies, including satellite systems together with various levels of automation, applied in support of a global air traffic management system.

4.3Strategic Vision

4.3.1To foster implementation of a global air traffic management system that will enable aircraft operators to meet their planned times of departure and arrival and adhere to their preferred flight profiles with minimum constraints and without compromising agreed levels of safety.4.4Mission

4.4.1To develop a seamless, globally co-ordinated system of air navigation services that will cope with world-wide growth in air traffic demand while:

Improving upon the present levels of safety;

Improving upon the present level of regularity;

Improving upon the over-all efficiency of airspace and airport operations, leading to increased capacity;

Increasing the availability of user-preferred flight schedules and profiles; and

minimizing differing equipment carriage requirements between regions.

5OVERALL DESCRIPTION OF THE NEW CNS/ATM SYSTEMS

5.1Communications - Navigation - Surveillance

5.1.1The main features of the global concept of the CNS systems could be summarized as follows:

5.1.2Existing Communications

Figure 1

5.1.3 The present communications environment is based on the use of Very High Frequency (VHF) and High Frequency (HF) voice transmissions with all the problems of language, slow rate of information transfer, high workload, possibility of errors etc. Due to its propagation characteristics the use of VHF is limited to line-of-sight communication and world-wide coverage is clearly not possible. Mobile HF communications were the only ones available for over-the horizon communications. Such communications have reliability limitations as a result of the variability of propagation characteristics. Though data-link can and will solve the majority of these problems it has been recognized that there is a need to compensate for the "situational awareness" that the pilot has in a voice based environment. Some of the problems with communications included:

VHF spectrum saturation in many areas of the world.

The lack of digital air-ground data interchange systems to support automated

systems in the air and on the ground.

Voice communication has slow rate of information transfer.

Voice communication problems arise due to language skill or accent of

controllers and pilots.

Possibility of errors of transmission or comprehension. High workload of a controller.5.1.4 FUTURE COMMUNICATIONS

Figure 2

5.1.5Data and voice communications are made available through direct satellite/aircraft/ground links. Initially, high frequency (HF) voice may have to be maintained in the transition period and over polar regions until such time as satellite communication is available. HF data is considered for data link coverage in the polar regions and remote continental areas as a backup or possible alternative to mobile satellite communication.

5.1.6Very high frequency (VHF) will remain in use for voice and data communication in many continental and terminal areas.

5.1.7The secondary surveillance radar (SSR) Mode S data link will be used for air traffic services (ATS) purposes in high density airspace.

5.1.8The aeronautical telecommunication network (ATN) will provide the interchange of digital packet data between endusers over various airground and groundground communication sub-networks.

5.1.9Data communication using ARINC 622 standard is available as an interim system5.1.10

BENEFITS

Table 1

5.2 Navigation

Figure 3

5.2.1LIMITATIONS

5.2.1.1Very High Frequency Omni-Directional Radio Range (VOR)

Limited coverage;

Decreasing accuracy at increasing distance from beacon;

Extensive flight inspection measurements required to reassure and maintain required accuracy.

5.2.1.2 Distance Measuring Equipment (DME)

Limited coverage;

Decreasing accuracy at increasing distance from beacon;

Limited number of users (at reaching maximum, coverage decreases);

Sometimes coverage adjustment required to prevent interference;

In order to meet Required Navigation Performance (RNP) 1 requirements with multi DME, the geometry of the location of DMEs is a constraint.

5.2.1.3Non Directional Radio Beacon (NDB)

Limited range;

Limited accuracy.

5.2.1.4Inertial Navigation System (INS) / Inertial Reference System (IRS)

Navigation information derived from INS decreases in accuracy with time (in general less than 2 NM/hr).

5.2.2 FUTURE NAVIGATION Figure 4

5.2.3Progressive introduction of area navigation (RNAV) capability in compliance with the required navigation performance (RNP) criteria.

5.2.4Global Navigation Satellite System(s) (GNSS) will provide worldwide coverage and will be used for aircraft navigation and for nonprecisiontype approaches and, with appropriate augmentation, Category I approaches. With adequate augmentation systems CategoryII and CategoryIII approaches may be available in the future.

5.2.5The global strategy for the introduction and application of non-visual aids to approach and landing is as follows:

i) continue Instrument Landing Systems (ILS) operations to the highest level of service as long as operationally acceptable and economically beneficial;

ii) implement Microwave Landing System (MLS) where operationally required and economically beneficial;

iii) promote the use of multi-mode receiver (MMR) or equivalent airborne capability to maintain aircraft interoperability;

iv) GNSS, with such augmentations as required, to support approach and departure operations, including at least Category I operations, and implement GNSS for such operations as appropriate;

v) Category II and III operations, based on GNSS technology, with such augmentations as required [e.g. Differential GNSS (DGNSS), Space Based Augmentation Systems (SBAS) such as the Wide

Area Augmentation System (WAAS), Ground Based Augmentation System (GBAS) such as Local Area Augmentation Systems (LAAS)], where operationally acceptable and economically beneficial; and

vi) enable each region to develop an implementation strategy for future systems in line with the global strategy.

vii) Nondirectional radio beacon (NDB) and VHF omnidirectional radio range/distance measuring equipment (VOR/DME) will be progressively withdrawn.

5.3BENEFITS 5.3.1"The global navigation satellite system will provide a high-integrity, high-accuracy, world-wide navigation service for the en-route, terminal, and non-precision approach phases of flight, and possibly for Category I precision approach and landing operations as well as making it possible to achieve capacity improvements at limited cost throughout the world.

5.3.2Three- and four-dimensional navigation accuracy will be improved.

5.3.3Aircraft will be able to navigate in all airspace in any part of the world using a single set of navigation avionics.

5.3.4Provider States will realise cost savings as existing ground-based navigation aids are no longer needed One of the attractions of GNSS is that it may lead to the removal of some or all ground-based radio navigation aids, such as NDB, VOR, DME etc. If Local Area Augmentation System (LAAS) meets CAT III requirements then GNSS could eventually replace ILS and MLS as a landing aid. However, this is not going to happen overnight and GNSS must prove itself before anything will happen. Nevertheless, the removal of "classical" navigation aids was recognised by FANS as one of the drivers behind the move to satellite technology..

5.3.5The new system can be used in conjunction with other systems, such as inertial navigation systems, to support operations through all phases of flight.

NLimitationsBenefits

1The propagation limitations of current line-of-sight ground-based VHF navigation systems.

Global coverage, world-wide navigation service is available. Single set of navigation avionics will allow to navigate in any part of the world.

2No full coverage of VOR/DME beacons and others as well in many regions of the world.

Global coverage, world-wide navigation service is available. Single set of navigation avionics will allow to navigate in any part of the world.

3Accuracy limitations, that does not allow to use flexible routes and area navigation (RNAV).High-accuracy navigation for all phases of flight.

Table 2

5.4Surveillance5.4.1 In areas of high traffic density, Secondary Surveillance Radar (SSR) Modes A and C currently provide the main method for surveillance and control of air movements backed up by primary radar and voice reports on VHF. As these are "line of sight" systems, for oceanic operations, remote land areas, and areas where primary and secondary radar cannot be justified economically, voice reports on HF are used for a procedural service which demands wide separation standards to ensure adequate safety.

Figure 65.4.2The key feature of the FANS surveillance concept is Automatic Dependent Surveillance (ADS), a means of extending surveillance service to oceanic airspace, remote land areas, and other areas where radar coverage is not available. Instead of having to rely on voice position reports, an aircraft operating in these non-radar areas will automatically transmit its position (and other relevant data, such as aircraft intent, speed and weather) to the air traffic centre via satellite or other communication links. The aircraft position can then be displayed in a manner similar to that of present radar displays. Used in conjunction with complementary two-way pilot-controller communications, ADS will serve as the basis for the provision of tactical air traffic services.

5.4.3SSR will continue to be used for surveillance in terminal areas and high-density continental airspace. Enhancing SSR with Mode S will provide selective address and data link capabilities to extend further the benefits of SSR for surveillance purposes. The resulting system will be characterised by reduced interference and high accuracy

5.4.4BENEFITS5.4.4.1Automatic dependent surveillance (ADS) services will be the basis for potentially significant enhancements to flight safety by reducing position report errors.

5.4.4.2ADS will provide significant early benefits in oceanic and other non-radar areas.

5.4.4.3employ of ADS, supported by direct pilot-controller communications, ill allow these non-radar areas to evolve to the point where air traffic services are provided in the same manner as in todays radar airspace.

5.4.4.4 ADS will support reductions in separation minima in non-radar airspace. These reductions will alleviate delays, minimise necessary diversions from preferred flight paths, and reduce flight operating costs.

5.4.4.5ADS will support increased air traffic control (ATC) flexibility, enabling controllers to be more responsive to aircraft flight preferences. With or without reductions in separation minima, this flexibility will contribute to cost savings for flight operations.

5.4.4.6Mode S in combination with ADS will facilitate uniform surveillance services world-wide. It will provide high-accuracy, interference-protected surveillance in high-density airspace.

5.4.4.7Cost savings to provider States will be realised through the gradual elimination of various ground systems.

5.4.4.8Mode S provides the ability to selectively address aircraft through the 24 bit Mode S code.5.5

Air Traffic Management (ATM)

5.5.1The main beneficiary of the new CNS systems will be the ATM system. The new CNS systems will enable the direct transfer of digital information between the ground and the air during all phases of flight. The deployment of the new CNS infrastructure will additionally facilitate the exchange of information between the main ATM functions, i.e. Airspace Management (ASM ), Air Traffic Flow Management (ATFM ) and Air Traffic Control (ATC ), resulting in an integrated ATM service to users from gate-to-gate.

Figure 7

5.5.2Increased Use of Automation

The future ATM system will make increasing use of automation to reduce or eliminate constraints imposed on operations by current systems, and to derive the benefits made possible by implementation of the new CNS systems. The flexibility afforded by the new CNS systems will allow for the introduction of automation capabilities from the simplest to the most advanced as required by individual States, but in a globally consistent yet evolutionary manner. For this reason, it is expected that the use of ATM automation will be most visible in the areas of:

flow management

tactical control

oceanic operations

en-route/terminal operations and

airport operations

5.5.3 Improved Flow Management

Flow Management will in future be based on sophisticated models and databases describing the current and projected levels of demand and resources. This new level of automation will make it possible to predict the possible sources of congestion and delay and formulate real-time flow management strategies to cope with demand.

5.5.4 Tactical Control

Automation will allow rapid negotiation between the service provider and aircraft to enhance tactical control. Improved tactical control will permit the accommodation of changes in a users preferred trajectory in three or four dimensions while satisfying any ATM constraints, resolving conflicts and scheduling the use of scarce resources, such as runways.

5.5.5 Oceanic Operations

International air traffic is growing much more rapidly than domestic operations. This area of ATM stands to benefit significantly from the new technologies and will experience significant improvements through the next decade. Extensive use will be made of ADS, Satellite Communications, GNSS, weather system improvements etc. to integrate ground-based ATM and airborne Flight Management Systems. The goal is to develop flexible oceanic operations which accommodate the users preferred trajectories to the maximum extent.

5.5.6 En-route and Terminal Operations

The automated flow management will monitor available capacity and demand at airports throughout the en-route and terminal airspace, and will implement strategies to prevent the development of congestion. The ATM functions will be integrated to provide smooth traffic flow into and out of terminal areas.

5.5.7 Airport Operations:

Traffic flows at airports will be structured to ensure maximum utilisation of approach and departure capacities. Curved approaches will eliminate some of the current constraints on approach capacity, and the use of new aids will permit independent Instrument Flight Rules on parallel runways spaced as closely as 2,500ft thus reducing the estate required for enlarging airports. Improved surface guidance systems at congested airports will increase capacity still further.

5.5.8The new ATM capabilities and more accurate data will make it possible to enhance safety, reduce delays, and increase airspace and airport capacity.

5.5.9Oceanic ATM operations will become much more flexible, resulting in a greater capability to accommodate user-preferred trajectories.

5.5.10 Improved flow management will prevent excessive levels of congestion.

5.5.11 Data link will transmit a variety of information from appropriately equipped aircraft to the ground, and provide enhanced information to the cockpit. It will dramatically reduce the communicators workload, and reduce the channel congestion and communications errors that characterise the current voice environment

5.5.12New capabilities will make it possible to permit flexible routing, as well as dynamic modifications to aircraft routes in response to changes in weather and traffic conditions.

5.5.13Terminal and en-route ATM functions will be integrated to provide smooth traffic flows into and out of terminal areas.

5.5.14Air traffic controllers will be able to establish efficient approach streams for parallel and converging runway configurations.

5.5.15Single-runway capacities in instrument meteorological conditions (IMC) will increase to a level approaching current single-runway capacities in visual meteorological conditions (VMC).

5.5.16Independent instrument flight rules (IFR) operations on triple and quadruple parallel runways will become routine in high density environments.

5.5.17Conflicts among departure and approach operations involving adjacent airports will be reduced.

5.5.18 Flexibility in controlling the noise footprint of airport traffic operations will be increased.5.5.19The over-all benefits of the new ATM system will derive from the combined benefits of the new communications, navigation, and surveillance systems, together with increasing use of automation.

5.5.20CONCLUSION5.5.20.1This section of the CNS/ATM self-study material has given the trainee a broad overview of what CNS/ATM is and defined some of the terms they will encounter on the course. To provide a realistic view of the systems now under consideration or being actively implemented a look at one of the CNS/ATM Charts from the Middle East Regional Plan is appropriate.

5.5.20.2The future CNS systems from the Middle East ICAO CNS/ATM Plan are presented in a condensed form in the CNS evolution table below. Included is the function they perform and the conventional systems they will eventually replace:

FUNCTIONConventional System

ElementsNew CNS System Elements

Oceanic continental en-route airspace with low density trafficCommunicationsVHF voice

HF Voice1. VHF voice/data (notes 3&4)

2. AMSS data/voice (Note 4)

3. HF data/voice (note 4)

4. ATN router/end system

NavigationLORAN-C

NDB

VOR/DME

Barometric altimetry

INS/IRS1. GNSS

2. Barometric altimetry

3. GNSS Altitude

4. INS/IRS

SurveillancePrimary radar/SSR

Voice Position ReportsADS

ADS-B

Continental Airspace with high-density trafficCommunications

VHF voice1. VHF voice/data (notes 3&4)

2. AMSS data/voice (Note 4)

3. HF data/voice (note 4)

4. ATN router/end system

NavigationLORAN-C

NDB

VOR/DME

Barometric altimetry

INS/IRS1. GNSS

2. Barometric altimetry

3. GNSS Altitude (Note 2)4. INS/IRS

SurveillancePrimary radar (Note1)

SSR Mode A/CSSR Mode A/C or S

ADS / ADS-B

Oceanic areas with high-density traffic

CommunicationsHF voiceAMSS data/voice (Note 4)

HF data/voice (Note 4)

ATN router/end system

NavigationMNPS

LORAN-C

Barometric altimetry

INS/IRS1. GNSS

2. Barometric altimetry

3. GNSS Altitude (Note 2)

4. INS/IRS

SurveillanceVoice position reportsADS

Terminal Areas with high-density trafficCommunicationsVHF voiceVHF voice/data (notes 3&4)

SSR Mode S data link

ATN router/end system

NavigationNDB

VOR/DME

ILS/MLS

Barometric altimetry

INS/IRSGNSS

ILS/MLS/DGNSS (Note 5)

Barometric Altimetry

INS/IRS

SurveillancePrimary radar (Note1)

SSR Mode A/CSSR Mode A/C or S

ADS / ADS-B

Terminal Areas with low-density trafficCommunicationsVHF voiceVHF voice/data (notes 3&4)

ATN router/end system

NavigationNDB

VOR/DME

ILS/MLS

Barometric altimetry

INS/IRSGNSS

ILS/MLS/DGNSS (Note 5)

Barometric Altimetry

INS/IRS

SurveillancePrimary radar (Note1)

SSR Mode A/CADS / ADS-B

End of Section - SECTION I - Review ExerciseAnswers found at page 24

Q1What does the abbreviation CNS/ATM stand for?

a) A term agreed on at the ICAO 10th Air Navigation Conference?

b) Central Navigation System / Air Traffic Movements

c) Communications, Navigation, Surveillance / Air Traffic Management

d) Communications, Navigation, Surveillance / Air Traffic Movements

Q2

One of the System shortcomings identified in the early 1980s was?a) The propagation limitations of existing line of sight systems.

b) The ease with which new Communications, Navigation and Surveillance systems could be implemented in large parts of the world.

c) The capability of voice communications and the availability of digital air-ground data interchange systems to support automated systems in the air and on the ground.

d) There were none.

Q3

The shortcomings identified in the early 1980s were reflected in problems, such as?

a) Air Traffic Control (ATC) needed more air traffic demand.

b) Air Traffic Flow Management (ATFM) which had the available capacity over the entire route, causing no need to fly holding patterns in the sectors with the highest constraints.

c) The flexibility of fixed route structure systems which allow the most efficient use of airspace and most economical conduct of flight operations.

d) The inability to fully exploit the capabilities of advanced airborne equipment such as flight management systems.

Q4What does FANS mean?

a) It includes all Committees of ICAO dealing with FANS

b) It relates to the Future Aeroportable Nexus System (FANS)

c) Future Air Navigation System

d) Nothing it is just a term coined by ICAO Staff

Q5In arriving at the concept of FANS the ICAO Committee was guided by the Objectives that a new CNS system should provide for?

a) VHF communications, navigation and surveillance

b) Digital data interchange between the air-ground systems to fully exploit the automated capabilities of both.

c) aircraft to maintain their own separation

d) satellite tracking and ephemerisQ6Due to its propagation characteristics the use of Very High Frequency (VHF) radios is limited to?

a) world-wide coverage

b) line-of-sight communication and world-wide coverage is clearly not possible

c) line-of-sight communication and world-wide coverage is possible

d) line-of-sight communication and oceanic areas

Q7Mobile HF communications have reliability limitations as a result of the variability of propagation characteristics and: ..?a) over the horizon communications are not available

b) were the only ones available for over-the horizon communications

c) the system has the ability to communicate far out into space

d) a High Fence (HF) must be broken down and rebuilt to make it more reliable

Q8Some of the problems with communications identified by the ICAO FANS Committee were:a) VHF spectrum saturation in many areas of the world.

b) no automated systems in the air and on the ground.

c) Voice communication has rapid rate of information transfer.

d) No possibility of errors of transmission or comprehension.

e) Low workload of a controller.

Q9Data and voice communications are made available through direct satellite/aircraft/ground links. HF data is considered for data link coverage in the polar regions and remote continental areas as a backup or possible alternative to mobile satellite communication. Name another planned data link service?

a) Very high frequency (VHF) data communication will be used in many Oceanic and Remote Areasb) (SSR) Mode S data link may be used for air traffic flow management purposes c) The aeronautical telecommunication network (ATN) will only be the airborne data service d) Data communication using ARINC 622 standard is available as an interim system

Q10What are some of the limitations of VORs?

a) Broken coverage above Flight Level (FL) 400

b) Decreasing accuracy at increasing distance from beacon

c) Few flight inspection measurements required

d) Increasing accuracy at increasing distance from beacon

Q11Which statement is NOT true about Distance Measuring Equipment (DME)a) Limited coverage

b) Decreasing accuracy at increasing distance from beacon

c) Unlimited number of users (at reaching maximum altitude, coverage decreases)

d) Sometimes coverage adjustment required to prevent interference

e) In order to meet Required Navigation Performance (RNP) 1 requirements with multi DME, the geometry of the location of DMEs is a constraint.

Q12The accuracy of INS/IRS degrades at how many nautical miles per hour?

a) 1 NM

b) 3.5NM

c) 2 NM

d) .5NMQ13 What do the letters RNP stand for?

a) Rollex Navigation Precision

b) Rollover Nightime Point

c) Required Navigation Precision

d) Required Navigation Performance

Q14The FANS Committee strategy for Navigation included the following sentence?a) Global Navigation Satellite System (GNSS), without augmentations

b) Only Category II and III operations

c) Enable each region to develop an implementation strategy for future systems in line with the global strategy

d) INS/IRS will be progressively withdrawn

e) All of the above

Q15One of the advantages of GNSS is that it may lead to:a) the removal of some or all ground-based radio navigation aids, such as NDB, VOR, DME etc.

b) the installation of ILS and MLS as a landing aid

c) less accurate navigation resulting in less accidents

d) the installation of more classical navigation aids such as NDB,VOR,DME etc.

e) All of the aboveQ16In areas of high traffic density the main method for surveillance and control of air movements is?

a) Primary & Secondary Surveillance Radar (SSR)

b) primary radar alone

c) voice reports on VHF

d) HF Voice Reports

e) All of the aboveQ17The key feature of the FANS surveillance concept is Automatic Dependent Surveillance (ADS), a means of extending surveillance service to oceanic airspace, remote land areas, and other areas where radar coverage is not available. Instead of having to rely on voice position reports, an aircraft operating in these non-radar areas will:

a) automatically transmit its position (and other relevant data, such as aircraft intent, speed and weather) to the air traffic centre via satellite or other communication links

b) Not be displayed in a manner similar to that of present radar displays

c) Not use controller-pilot-data-link-communications (CPDLC)

d) never use ADS as the basis for the provision of tactical air traffic services.

e) All of the above

Q18SSR with Mode S will provide?a) selective address and data link capabilities to extend further the benefits of SSR for surveillance purposes. ADS will support increased air traffic control (ATC) flexibility, enabling controllers to be more responsive to aircraft flight preferences. This flexibility will contribute to cost savings for flight operations. The resulting system will be characterised by reduced interference and high accuracy

b) Automatic dependent surveillance (ADS) services will be the basis for potentially significant enhancements to flight safety by reducing position report errors. ADS will provide significant early benefits in oceanic and other non-radar areas. Implementation of ADS, supported by direct pilot-controller communications, will allow these non-radar areas to evolve to the point where air traffic services are provided in the same manner as in todays radar airspace.

c) ADS will support reductions in separation minima in non-radar airspace. These reductions will alleviate delays, minimise necessary diversions from preferred flight paths, and reduce flight operating costs. Mode S in combination with ADS will facilitate uniform surveillance services world-wide.

d) Cost to provider States will be realised through the gradual elimination of various ground systems. Mode S provides the ability to selectively address aircraft through the 24 bit Mode S code. It will provide high-accuracy, interference-protected surveillance in high-density airspace.

e) All of the above

Q19The main beneficiary of the new CNS systems will be the ATM system. The new CNS systems will enable the direct transfer of digital information between the ground and the air during all phases of flight. The deployment of the new CNS infrastructure will additionally facilitate the exchange of information between the main ATM functions, which are:

a) Airspace Management (ASM ) and Air Traffic Services (ATS)

b) Surveillance, Automation, Airways and Approach

c) Airspace Management (ASM ), Air Traffic Flow Management (ATFM ), and Air Traffic Control (ATC )

d) None of the above

Q20The future ATM system will make increasing use of automation to reduce or eliminate constraints imposed on operations by current systems, and to derive the benefits made possible by implementation of the new CNS systems. The flexibility afforded by the new CNS systems will allow for the introduction of automation capabilities from the simplest to the most advanced as required by individual States, but in a globally consistent yet evolutionary manner. For this reason, it is expected that the use of ATM automation will be most visible in the areas of:a) Airspace management, Air Traffic Flow Management, Maintenance, Statistical Analysis

b) Personnel Management, Pay Services, Tower Operations, ACC Operations

c) Flow Management, Tactical Control, Oceanic Operations, En-route/Terminal Operations and Airport Operations

d) All of the above.

Q21Flow Management will in future be based on sophisticated models and databases describing the current and projected levels of demand and resources. This new level of automation will make it possible to predict:a) The number of aircraft that will cross a point in space which divided by two results in the mean average air traffic flow

b) The number of near miss incidents that will occur over the total possible flow of air traffic

c) The possible sources of congestion and delay and formulate real-time flow management strategies to cope with demand.

d) How many computers the civil aviation authority will need to make automation possible.

e) All of the above

Q22Automation will allow rapid negotiation between the service provider and aircraft to enhance tactical control. Improved tactical control will permit the accommodation of changes in a users preferred trajectory in three or four dimensions while satisfying:a) potential safety violations of aircraft and aircraft algorithms

b) required separation minima and preferred profiles of ATC

c) resolving conflicts and giving the aircrew a happy flying feeling

d) any ATM constraints, resolving conflicts and scheduling the use of scarce resources, such as runways.

e) All of the above

Q23International air traffic is growing much more rapidly than domestic operations. This area of ATM stands to benefit significantly from the new technologies and will experience significant improvements. Extensive use is made of ADS, Satellite Communications, GNSS, weather system improvements etc. to integrate ground-based ATM and airborne Flight Management Systems. The goal is to:

a) transition to satellite and OMEGA systems as quickly as possible

b) develop flexible oceanic operations which accommodate the users preferred trajectories to the maximum extent

c) terminate the use of INS/IRS operations

d) use data communications exclusively

e) All of the above

Q24The automated flow management will monitor available capacity and demand at airports throughout the en-route and terminal airspace, and will implement strategies to prevent the development of congestion. The ATM functions will be integrated

a) to assist the air traffic controller approach supervisor

b) to allow smoother landings

c) to provide smooth traffic flow into and out of terminal areas

d) to enhance straight in approaches and landings

e) all of the above

Q25Please indicate whether the following statements are true or false?

The new ATM capabilities and more accurate data will make it possible to enhance safety, reduce delays, and increase airspace and airport capacity. Oceanic ATM operations will become much more flexible, resulting in a greater capability to accommodate user-preferred trajectories. Improved flow management will prevent excessive levels of congestion.

True

False

Data link will transmit a variety of information from appropriately equipped aircraft to the ground, and provide enhanced information to the cockpit. It will dramatically reduce the communicators workload, and reduce the channel congestion and communications errors that characterise the current voice environment. New capabilities will make it possible to permit flexible routing, as well as dynamic modifications to aircraft routes in response to changes in weather and traffic conditions.

True

False

Terminal and en-route ATM functions will be integrated to provide smooth traffic flows into and out of terminal areas. Air traffic controllers will be able to establish efficient approach streams for parallel and converging runway configurations. Single-runway capacities in instrument meteorological conditions (IMC) will increase to a level approaching current single-runway capacities in visual meteorological conditions (VMC).

True

False

Independent instrument flight rules (IFR) operations on triple and quadruple parallel runways will become routine in high density environments. Conflicts among departure and approach operations involving adjacent airports will be reduced. Flexibility in controlling the noise footprint of airport traffic operations will be increased. The over-all benefits of the new ATM system will derive from the combined benefits of the new communications, navigation, and surveillance systems, together with increasing use of automation.

True

FalseANSWERS TO REVIEW QUESTIONS - SECTION I

A1c)Communications, Navigation, Surveillance / Air Traffic Management

A2a)The propagation limitations of existing line of sight systems.A3d)The inability to fully exploit the capabilities of advanced airborne equipment such as flight management systems.

A4c)Future Air Navigation Systems (FANS)

A 5b)Digital data interchange between the air-ground systems to fully exploit the automated capabilities of both.

A6b)line-of-sight communication and world-wide coverage is clearly not possible

A7b)were the only ones available for over-the horizon communications

A8a)VHF spectrum saturation in many areas of the world.

A9d)Data communication using ARINC 622 standard is available as an interim system

A10b)Decreasing accuracy at increasing distance from beacon

A11c)Unlimited number of users (at reaching maximum altitude, coverage decreases)

A-12c)2 NM

A13d)Required Navigation Performance

A14c)Enable each region to develop an implementation strategy for future systems in line with the global strategy

A15a)the removal of some or all ground-based radio navigation aids, such as NDB, VOR, DME etc.

A16a)Primary & Secondary Surveillance Radar (SSR)

A17 a)automatically transmit its position (and other relevant data, such as aircraft intent, speed and weather) to the air traffic centre via satellite or other communication links

A18e)All of the above

A19c)Airspace Management (ASM ), Air Traffic Flow Management (ATFM ), and Air Traffic Control (ATC )

A20c)Flow Management, Tactical Control, Oceanic Operations, En-route/Terminal Operations and Airport Operations

A21c)The possible sources of congestion and delay and formulate real-time flow management strategies to cope with demand.

A22d)any ATM constraints, resolving conflicts and scheduling the use of scarce resources, such as runways.

A23b)develop flexible oceanic operations which accommodate the users preferred trajectories to the maximum extent.

A24c)to provide smooth traffic flow into and out of terminal areas

A25

True, True, True, True,

SECTION - II

6.0BITS & BYTES AND COMPUTER COMMUNICATIONS6.1DATA LINK

6.1.1In oceanic areas and remote land airspace with limited ground-based air navigation facilities, surveillance of air traffic is envisioned to be provided by ADS position reporting through satellite communications. Surveillance of low-altitude traffic operations, including helicopters, will be conducted in a similar manner. In continental airspace, surveillance of air traffic may be achieved by ADS/ADS-B reports integrated with ground-based radar systems. Controller Pilot Data Link Communication (CPDLC) and the interchange of ATS messages will be carried out by satellite, Secondary Surveillance Radar (SSR) ModeS, Very High Frequency (VHF), High Frequency (HF) or other suitable data links available. There will also be DATIS, DFIS, DPDC .6.1.2Whoa! Far too much for some of us and not enough for others. Well let us back up a bit and bring all of us along to the same starting point shall we. First if we know nothing about data communications we need to know some of the very basic stuff like how bits and bytes work and how computers can talk with each other. We need to know enough of this to be able to conceptualize more advanced information. We need to bring all of you from the known (what you already know from school or other learning experiences) to the unknown (what we are trying to make you aware of.) So let us start at the beginning by going to the very basics. If you find that this is too elementary for you then you can skip the reading and go to the practice test at the end of the self study package to see just how much you do know.

6.2How Bits and Bytes Work

6.2.1If you have used a computer for more than five minutes, then you have heard the words bits and bytes. Both RAM and hard disk capacities are measured in bytes, as are file sizes when you examine them in a file viewer.

6.2.2You might hear an advertisement that says, "This computer has a 32-bit Pentium processor with 64 megabytes of RAM and 2.1 gigabytes of hard disk space." And many articles talk about bytes. In this material we will discuss bits and bytes so that later on you can understand some of the issues in CNS/ATM.

6.3Decimal Numbers

6.3.1The easiest way to understand bits is to compare them to something you know: digits. A digit is a single place that can hold numerical values between 0 and 9. Digits are normally combined together in groups to create larger numbers. For example, 6,357 has four digits. It is understood that in the number 6,357, the 7 is filling the "1s place," while the 5 is filling the 10s place, the 3 is filling the 100s place and the 6 is filling the 1,000s place. So you could express things this way if you wanted to be explicit:

(6 * 1000) + (3 * 100) + (5 * 10) + (7 * 1) = 6000 + 300 + 50 + 7 = 6357

6.3.2Another way to express it would be to use powers of 10. Assuming that we are going to represent the concept of "raised to the power of" with the "^" symbol (so "10 squared" is written as "10^2"), another way to express it is like this:

(6 * 10^3) + (3 * 10^2) + (5 * 10^1) + (7 * 10^0) = 6000 + 300 + 50 + 7 = 6357

6.3.3What you can see from this expression is that each digit is a placeholder for the next higher power of 10, starting in the first digit with 10 raised to the power of zero.

6.3.4That should all feel pretty comfortable -- we work with decimal digits every day. The neat thing about number systems is that there is nothing that forces you to have 10 different values in a digit. Our base-10 number system likely grew up because we have 10 fingers, but if we happened to evolve to have eight fingers instead, we would probably have a base-8 number system. You can have base-anything number systems. In fact, there are lots of good reasons to use different bases in different situations.

6.4Bits

6.4.1Computers happen to operate using the base-2 number system, also known as the binary number system (just like the base-10 number system is known as the decimal number system). The reason computers use the base-2 system is because it makes it a lot easier to implement them with current electronic technology. You could wire up and build computers that operate in base-10, but they would be fiendishly expensive right now. On the other hand, base-2 computers are relatively cheap.

6.4.2So computers use binary numbers, and therefore use binary digits in place of decimal digits. The word bit is a shortening of the words "Binary digit." Whereas decimal digits have 10 possible values ranging from 0 to 9, bits have only two possible values: 0 and 1. Therefore, a binary number is composed of only 0s and 1s, like this: 1011. How do you figure out what the value of the binary number 1011 is? You do it in the same way we did it above for 6357, but you use a base of 2 instead of a base of 10. So:

1 0

1 1

(1 * 2^3) + (0 * 2^2) + (1 * 2^1) + (1 * 2^0) =

(1*2*2*2) + (0*2*2) + (1*2*1) + (1) =

8 + 0 + 2 + 1 = 116.4.3You can see that in binary numbers, each bit holds the value of increasing powers of 2. That makes counting in binary pretty easy. Starting at zero and going through 20, counting in decimal and binary looks like this:0 = 0

1 = 1

2 = 10

3 = 11

4 = 100

5 = 101

6 = 110

7 = 111

8 = 1000

9 = 1001

10 = 1010

11 = 1011

12 = 1100

13 = 1101

14 = 1110

15 = 1111

16 = 10000

17 = 10001

18 = 10010

19 = 10011

20 = 101006.4.4When you look at this sequence, 0 and 1 are the same for decimal and binary number systems. At the number 2, you see carrying first take place in the binary system. If a bit is 1, and you add 1 to it, the bit becomes 0 and the next bit becomes 1. In the transition from 15 to 16 this effect roles over through 4 bits, turning 1111 into 10000.

6.5Bytes

6.5.1Bits are rarely seen alone in computers. They are almost always bundled together into 8-bit collections, and these collections are called bytes. Why are there 8 bits in a byte? A similar question is, "Why are there 12 eggs in a dozen?" The 8-bit byte is something that people settled on through trial and error over the past 50 years.

6.5.2With 8 bits in a byte, you can represent 256 values ranging from 0 to 255, as shown here:

0 = 00000000

1 = 00000001

2 = 00000010

...

254 = 11111110

255 = 111111116.5.3In the article How CDs Work, on the WEB you can learn that a CD uses 2 bytes, or 16 bits, per sample. That gives each sample a range from 0 to 65,535, like this:

0 = 0000000000000000

1 = 0000000000000001

2 = 0000000000000010

...

65534 = 1111111111111110

65535 = 11111111111111116.5.4 Bytes are frequently used to hold individual characters in a text document. In the American Standard Code for Information Interchange (ASCII) character set, each binary value between 0 and 127 is given a specific character. Most computers extend the ASCII character set to use the full range of 256 characters available in a byte. The upper 128 characters handle special things like accented characters from common foreign languages.

6.5.5You can see the 127 standard ASCII codes below. Computers store text documents, both on disk and in memory, using these codes. For example, if you use Notepad in Windows 95/98 to create a text file containing the words, "Four score and seven years ago," Notepad would use 1 byte of memory per character (including 1 byte for each space character between the words -- ASCII character 32). When Notepad stores the sentence in a file on disk, the file will also contain 1 byte per character and per space.

6.5.6Try this experiment: Open up a new file in Notepad and insert the sentence, "Four score and seven years ago" in it. Save the file to disk under the name getty.txt. Then use the explorer and look at the size of the file. You will find that the file has a size of 30 bytes on disk: 1 byte for each character. If you add another word to the end of the sentence and re-save it, the file size will jump to the appropriate number of bytes.

6.5.7Each character consumes a byte.

If you were to look at the file as a computer looks at it, you would find that each byte contains not a letter but a number -- the number is the ASCII code corresponding to the character (see below). So on disk, the numbers for the file look like this:

F o u r a n d s e v e n

70 111 117 114 32 97 110 100 32 115 101 118 101 1106.5.8By looking in the ASCII table, you can see a one-to-one correspondence between each character and the ASCII code used. Note the use of 32 for a space -- 32 is the ASCII code for a space. We could expand these decimal numbers out to binary numbers (so 32 = 00100000) if we wanted to be technically correct -- that is how the computer really deals with things.

6.6Standard American Standard Code for Information Interchange (ASCII) Character Set

6.6.1The first 32 values (0 through 31) are codes for things like carriage return and line feed. The space character is the 33rd value, followed by punctuation, digits, uppercase characters and lowercase characters.

0 NUL

1 SOH

2 STX

3 ETX

4 EOT

5 ENQ

6 ACK

7 BEL

8 BS

9 TAB

10 LF

11 VT

12 FF

13 CR

14 SO

15 SI

16 DLE

17 DC1

18 DC2

19 DC3

20 DC4

21 NAK

22 SYN

23 ETB

24 CAN

25 EM

26 SUB

27 ESC

28 FS

29 GS

30 RS

31 US

32

33 !

34 "

35 #

36 $

37 %

38 &

39 '

40 (

41 )

42 *

43 +

44 ,

45 -

46 .

47 /

48 0

49 1

50 2

51 3

52 4

53 5

54 6

55 7

56 8

57 9

58 :

59 ;

60

63 ?

64 @

65 A

66 B

67 C

68 D

69 E

70 F

71 G

72 H

73 I

74 J

75 K

76 L

77 M

78 N

79 O

80 P

81 Q

82 R

83 S

84 T

85 U

86 V

87 W

88 X

89 Y

90 Z

91 [

92 \

93 ]

94 ^

95 _

96 `

97 a

98 b

99 c

100 d

101 e

102 f

103 g

104 h

105 i

106 j

107 k

108 l

109 m

110 n

111 o

112 p

113 q

114 r

115 s

116 t

117 u

118 v

119 w

120 x

121 y

122 z

123 {

124 |

125 }

126 ~

127 DEL

6.7Lots of Bytes

6.7.1When you start talking about lots of bytes, you get into prefixes like kilo, mega and giga, as in kilobyte, megabyte and gigabyte (also shortened to K, M and G, as in Kbytes, Mbytes and Gbytes or KB, MB and GB). The following table shows the multipliers:

NameAbbr.Size

KiloK2^10 = 1,024

MegaM2^20 = 1,048,576

GigaG2^30 = 1,073,741,824

TeraT2^40 = 1,099,511,627,776

PetaP2^50 = 1,125,899,906,842,624

ExaE2^60 = 1,152,921,504,606,846,976

ZettaZ2^70 = 1,180,591,620,717,411,303,424

YottaY2^80 = 1,208,925,819,614,629,174,706,176

6.7.2You can see in this chart that kilo is about a thousand, mega is about a million, giga is about a billion, and so on. So when someone says, "This computer has a 2 gig hard drive," what he or she means is that the hard drive stores 2 gigabytes, or approximately 2 billion bytes, or exactly 2,147,483,648 bytes. How could you possibly need 2 gigabytes of space? When you consider that one CD holds 650 megabytes, you can see that just three CDs worth of data will fill the whole thing! Terabyte databases are fairly common these days, and there are probably a few petabyte databases floating around the Pentagon by now.

6.8Binary Math

6.8.1Binary math works just like decimal math, except that the value of each bit can be only 0 or 1. To get a feel for binary math, let's start with decimal addition and see how it works. Assume that we want to add 452 and 751:

452

+ 751

---

1203

6.8.2 To add these two numbers together, you start at the right: 2 + 1 = 3. No problem. Next, 5 + 5 = 10, so you save the zero and carry the 1 over to the next place. Next, 4 + 7 + 1 (because of the carry) = 12, so you save the 2 and carry the 1. Finally, 0 + 0 + 1 = 1. So the answer is 1203.

6.8.3Binary addition works exactly the same way:

010

+ 111

---

10016.8.4Starting at the right, 0 + 1 = 1 for the first digit. No carrying there. You've got 1 + 1 = 10 for the second digit, so save the 0 and carry the 1. For the third digit, 0 + 1 + 1 = 10, so save the zero and carry the 1. For the last digit, 0 + 0 + 1 = 1. So the answer is 1001. If you translate everything over to decimal you can see it is correct: 2 + 7 = 9.

6.9Quick Recap

6.9.1Bits are binary digits. A bit can hold the value 0 or 1.

Bytes are made up of 8 bits each.

Binary math works just like decimal math, but each bit can have a value of only 0 or 1.

6.9.2There really is nothing more to it -- bits and bytes are that simple!6.9.3A bit is short for "binary digit." It is the smallest possible unit of information; i.e. a bit is to information what an atom is to an element! A bit could be represented by an on-off switch. This is essentially the case for static memory chips, or RAM (random-access memory), where each of the thousands of bits is a transistor, which may be in the on or off state. Dynamic RAM uses charged or uncharged capacitors to store data. [As an aside, static RAM is faster than dynamic RAM, but is also more expensive and power-consuming. Because capacitors discharge over time, dynamic memory must be constantly refreshed.] Magnetic media (floppies, hard drives, tape, even credit cards and ATM cards, use a positively or negatively charged magnetic region for each bit.6.10Data lines

6.10.1Transferring individual bits between CPU and memory would be very time consuming, so it is customary to send a larger chunk of information. For some reason or another, memory is usually divided into eight-bit chunks called bytes. Four-bit chunks are called nibbles - no kidding! Most computers, then, will have at least 8 lines running between CPU and memory for data in and 8 lines for data out. Thus, a whole byte is transferred at once (in parallel). This also means that we only need a unique address for each byte in our memory, rather than having to have a unique address for each bit. Early IBM-type PCs had an 8-line (or 8-bit) data bus running between memory and the 8086 CPU. Later, the 80286 CPU improved on this by have a 16-bit data bus. Computers containing 80386, or 80486 have a 32-bit data bus. Pentium chips have a 64-bit external data bus.

6.10.2We also have names for larger chunks of information. Since computers work in binary, memory is usually divided up into divisions that are a power of 2. Hence,

kilobyte = 1024 bytes (1024 = 210), abbreviated KB (Kb is kilobits)

megabyte = 1024 KB = 1,048,576 bytes, abbreviated MB (Mb is megabits)

gigabyte = 1024 MB = 1,073,741,824 bytes, abbreviated GB (Gb is gigabits)

6.11Address lines

6.11.1Address lines run between the CPU and memory and are used to tell the memory which particular byte we want to read or write. Early microcomputers used 16 address lines. Each line could be [on/off; high/low; true/false; 0/1; etc.], allowing for 216 unique addresses, or 65,536 bytes of addressable memory.

6.11.2The original IBM PC had 20 address lines. Since 220 = 1,048,576, IBM PCs, and the Microsoft DOS which was written for it, could only utilize 1 MB of memory. About 360 KB was reserved for ROM BIOS, video RAM, etc. (more on this later), and the other 640 KB was available for the DOS operating system and user programs. PCs have essentially been stuck with that limitation ever since, although Windows (and other, newer, operating systems like OS/2, LINUX, Windows 95) gets around it somewhat. The CPUs themselves have advanced beyond that stage (the 80286 has 24 address lines, allowing for 16 MB to be addressed; the 80386/486 has 32 address lines to address 4 gigabytes), but in order to maintain "backward compatibility," DOS has remained a 1 MB (640 KB) world. Windows, and to a much greater extent, Windows 95, have crashed the 1 MB barrier by using protected mode, 32-bit addressing

6.12So what do we put into memory?

6.12.1Instructions and data!

6.12.1.1Instructions

6.12.1.1.1Instructions are stored as binary numbers, just as data is. For example, 10110010 (decimal 178) might be interpreted by the CPU as "get the byte of data located at the address given by the next two bytes and add it to the number in the accumulator (a part of the CPU that contains numbers to be acted on).

6.12.1.2Data: ASCII, integers, floating point real and complex, etc.

6.12.1.2.1Data are usually either numbers or letters. Of course, memory can only hold binary numbers, so we have to agree how to interpret those numbers (a kind of code) when we want them to represent letters (or numbers, for that matter). ASCII stands for American Standard Code for Information Interchange. In this system, 7 bits are used to represent 128 (27) different letters, numbers, punctuation, and special codes. When the eighth bit is used (why waste it?), we have Extended ASCII, in which 256 characters are available. The "upper" 128 characters are not as standard as the first 128. Refer to an Extended ASCII chart.

6.12.2Not all computers use this system. IBM, on their mainframes, stubbornly sticks with EBCDIC, which means something but I have tried very hard to forget what. Unicode is a new system which use 2 bytes, allowing many more characters to be represented (how many, class?), such as Kanji, Cyrillic, Hebrew, etc. Unicode is backwards compatible with ASCII, meaning that operating systems using Unicode, such as Windows 95, can still make sense of ASCII files.

6.12.3Earlier it was mentioned that 10110010 equals decimal 178. So why do we need a "code" for representing numbers in a computer? Why not just use binary (converted back to decimal when we type it in or read it, of course)? Well, how would we represent negative numbers? What about fractions? What about numbers larger than 8 bits can represent (28 = 256)? You see the problem. The solution, shortened a bit (no pun intended) is to use more than one byte, and, for floating point numbers, to use some of the bits for an exponent and the rest for the mantissa. The table below shows some of the more common data types. The exact details depend on the particular program used (which, in turn, usually depends on the compiler used to create the program).

6.13 Common Data TypesData TypeApproximate RangeSignificant

(from)(to)BitsDigits

logicalFalse (0)True (1)8NA

characteraZ (sort of!)8NA

short integer-128.00127.0082

integer-32,768+32,767164

long integer-2 x 109+2 x 109329

single precision IEEE real-3.4 x 10+38 to -1.2 x 10-38+1.2 x 10-38 to +3.4 x 10+38326

double precision IEEE real-1.8 x 10+308 to -2.2 x 10-308+2.2 x 10-308 to 1.8 x 10+3086415

single precision complexlike single precision real, for both real and imaginary partslike single precision real, for both real and imaginary parts

double precision complexlike double precision real, for both real and imaginary partslike double precision real, for both real and imaginary parts

7.1Personal Computers (PC)

7.1.1When you mention the word "technology," most people think about computers. Virtually every facet of our lives has some computerized component. The appliances in our homes have microprocessors built into them, as do our televisions. Even our cars have a computer. But the computer that everyone thinks of first is typically the personal computer, or PC.

7.1.2A PC is a general purpose tool built around a microprocessor. It has lots of different parts -- memory, a hard disk, a modem, etc. -- that work together. "General purpose" means that you can do many different things with a PC. You can use it to type documents, send e-mail, browse the Web and play games.

we will talk about PCs in the general sense and all the different parts that go into them. You will learn about the various components and how they work together in a basic operating session. You'll also find out what the future may hold for these machines.

Motherboard - This is the main circuit board that all of the other internal components connect to. The CPU and memory are usually on the motherboard. Other systems may be found directly on the motherboard or connected to it through a secondary connection. For example, a sound card can be built into the motherboard or connected through PCI.

Power supply - An electrical transformer regulates the electricity used by the computer.

Hard disk - This is large-capacity permanent storage used to hold information such as programs and documents.

Operating system - This is the basic software that allows the user to interface with the computer.

Integrated Drive Electronics (IDE) Controller - This is the primary interface for the hard drive, CD-ROM and floppy disk drive.

Peripheral Component Interconnect (PCI) Bus - The most common way to connect additional components to the computer, PCI uses a series of slots on the motherboard that PCI cards plug into.

SCSI - Pronounced "scuzzy," the small computer system interface is a method of adding additional devices, such as hard drives or scanners, to the computer.

AGP - Accelerated Graphics Port is a very high-speed connection used by the graphics card to interface with the computer.

Sound card - This is used by the computer to record and play audio by converting analog sound into digital information and back again.

Graphics card - This translates image data from the computer into a format that can be displayed by the monitor.

7.2Defining a PC

7.2.1Here is one way to think about your PC: "A PC is a general-purpose information processing device. It can take information from a person (through the keyboard and mouse), from a device (like a floppy disk or CD) or from the network (through a modem or a network card) and process it. Once processed, the information is shown to the user (on the monitor), stored on a device (like a hard disk) or sent somewhere else on the network (back through the modem or network card)."

7.2.2We have lots of special-purpose processors in our lives. An MP3 Player is a specialized computer for processing MP3 files. It can't do anything else. A Global Positioning Satellite (GPS) is a specialized computer for handling GPS signals. It can't do anything else. A Gameboy is a specialized computer for handling games, but it can't do anything else. A PC can do it all because it is general-purpose.

7.3On the Inside

7.3.1Let's take a look at the main components of a typical desktop computer.

Central processing unit (CPU) - The microprocessor "brain" of the computer system is called the central processing unit. Everything that a computer does is overseen by the CPU.

Memory - This is very fast storage used to hold data. It has to be fast because it connects directly to the microprocessor. There are several specific types of memory in a computer:

Random-access memory (RAM) - Used to temporarily store information that the computer is currently working with

Read-only memory (ROM) - A permanent type of memory storage used by the computer for important data that does not change

Basic input/output system (BIOS) - A type of ROM that is used by the computer to establish basic communication when the computer is first turned on

Caching - The storing of frequently used data in extremely fast RAM that connects directly to the CPU

Virtual memory - Space on a hard disk used to temporarily store data and swap it in and out of RAM as needed

7.3.2The computer you are using to read this page uses a microprocessor to do its work. The microprocessor is the heart of any normal computer, whether it is a desktop machine, a server or a laptop. The microprocessor you are using might be a Pentium, a K6, a PowerPC, a Sparc or any of the many other brands and types of microprocessors, but they all do approximately the same thing in approximately the same way.

7.3.3If you have ever wondered what the microprocessor in your computer is doing, or if you have ever wondered about the differences between types of microprocessors, then read on. In this self-study material you will learn how fairly simple digital logic techniques allow a computer to do its job, whether its playing a game or spell checking a document!

7.4Inside a Microprocessor

7.4.1To understand how a microprocessor works, it is helpful to look inside and learn about the logic used to create one. In the process you can also learn about assembly language -- the native language of a microprocessor -- and many of the things that engineers can do to boost the speed of a processor. A microprocessor executes a collection of machine instructions that tell the processor what to do. Based on the instructions, a microprocessor does three basic things:

1 Using its ALU (Arithmetic/Logic Unit), a microprocessor can perform mathematical operations like addition, subtraction, multiplication and division. Modern microprocessors contain complete floating point processors that can perform extremely sophisticated operations on large floating point numbers.

2 A microprocessor can move data from one memory location to another.

3 A microprocessor can make decisions and jump to a new set of instructions based on those decisions.

7.4.2There may be very sophisticated things that a microprocessor does, but those are its three basic activities. The following diagram shows an extremely simple microprocessor capable of doing those three things:

7.4.3This is about as simple as a microprocessor gets. This microprocessor has:

a) An address bus (that may be 8, 16 or 32 bits wide) that sends an address to memory

b) A data bus (that may be 8, 16 or 32 bits wide) that can send data to memory or receive data from memory

c) An RD (read) and WR (write) line to tell the memory whether it wants to set or get the addressed location

d) A clock line that lets a clock pulse sequence the processor

e) A reset line that resets the program counter to zero (or whatever) and restarts execution

f) Let's assume that both the address and data buses are 8 bits wide in this example.

7.4.4Here are the components of this simple microprocessor:

a) Registers A, B and C are simply latches made out of flip-flops.

b) The address latch is just like registers A, B and C.

c) The program counter is a latch with the extra ability to increment by 1 when told to do so, and also to reset to zero when told to do so.

d) The ALU could be as simple as an 8-bit adder (see the section on adders in How Boolean Logic Works for details), or it might be able to add, subtract, multiply and divide 8-bit values. Let's assume the latter here.

e) The test register is a special latch that can hold values from comparisons performed in the ALU. An ALU can normally compare two numbers and determine if they are equal, if one is greater than the other, etc. The test register can also normally hold a carry bit from the last stage of the adder. It stores these values in flip-flops and then the instruction decoder can use the values to make decisions.

f) There are six boxes marked "3-State" in the diagram. These are tri-state buffers. A tri-state buffer can pass a 1, a 0 or it can essentially disconnect its output (imagine a switch that totally disconnects the output line from the wire that the output is heading toward). A tri-state buffer allows multiple outputs to connect to a wire, but only one of them to actually drive a 1 or a 0 onto the line.

g) The instruction register and instruction decoder are responsible for controlling all of the other components.

7.4.5Although they are not shown in this diagram, there would be control lines from the instruction decoder that would:

a) Tell the A register to latch the value currently on the data bus

b) Tell the B register to latch the value currently on the data bus

c) Tell the C register to latch the value currently on the data bus

d) Tell the program counter register to latch the value currently on the data bus

e) Tell the address register to latch the value currently on the data bus

f) Tell the instruction register to latch the value currently on the data bus

g) Tell the program counter to increment

h) Tell the program counter to reset to zero

i) Activate any of the six tri-state buffers (six separate lines)

j) Tell the ALU what operation to perform

k) Tell the test register to latch the ALU's test bits

l) Activate the RD line

m) Activate the WR line

n) Coming into the instruction decoder are the bits from the test register and the clock line, as well as the bits from the instruction register.

7.5RAM and ROM

7.5.1The previous section talked about the address and data buses, as well as the RD and WR lines. These buses and lines connect either to RAM or ROM -- generally both. In our sample microprocessor, we have an address bus 8 bits wide and a data bus 8 bits wide. That means that the microprocessor can address (28) 256 bytes of memory, and it can read or write 8 bits of the memory at a time. Let's assume that this simple microprocessor has 128 bytes of ROM starting at address 0 and 128 bytes of RAM starting at address 128.

7.5.2ROM stands for read-only memory. A ROM chip is programmed with a permanent collection of pre-set bytes. The address bus tells the ROM chip which byte to get and place on the data bus. When the RD line changes state, the ROM chip presents the selected byte onto the data bus.

7.5.3RAM stands for random-access memory. RAM contains bytes of information, and the microprocessor can read or write to those bytes depending on whether the RD or WR line is signaled. One problem with today's RAM chips is that they forget everything once the power goes off. That is why the computer needs ROM.

By the way, nearly all computers contain some amount of ROM (it is possible to create a simple computer that contains no RAM -- many microcontrollers do this by placing a handful of RAM bytes on the processor chip itself -- but generally impossible to create one that contains no ROM).

7.5.4 On a PC, the ROM is called the BIOS (Basic Input/Output System). When the microprocessor starts, it begins executing instructions it finds in the BIOS. The BIOS instructions do things like test the hardware in the machine, and then it goes to the hard disk to fetch the boot sector .This boot sector is another small program, and the BIOS stores it in RAM after reading it off the disk. The microprocessor then begins executing the boot sector's instructions from RAM. The boot sector program will tell the microprocessor to fetch something else from the hard disk into RAM, which the microprocessor then executes, and so on. This is how the microprocessor loads and executes the entire operating system. Read-only memory (ROM), also known as firmware, is an integrated circuit programmed with specific data when it is manufactured. ROM chips are used not only in computers, but in most other electronic items as well. You will learn about the different types of ROM and how each works.

7.5.5Random access memory (RAM) is the best known form of computer memory. RAM is considered "random access" because you can access any memory cell directly if you know the row and column that intersect at that cell.

7.5.6The opposite of RAM is serial access memory (SAM). SAM stores data as a series of memory cells that can only be accessed sequentially (like a cassette tape). If the data is not in the current location, each memory cell is checked until the needed data is found. SAM works very well for memory buffers, where the data is normally stored in the order in which it will be used (a good example is the texture buffer memory on a video card). RAM data, on the other hand, can be accessed in any order.

Question

I know my computer uses DRAM (dynamic RAM) for the main memory. I have also heard of static RAM. What is the difference, and why are there two kinds?

Answer

Your computer probably uses both static RAM and dynamic RAM at the same time, but it uses them for different reasons because of the cost difference between the two types. If you understand how dynamic RAM and static RAM chips work inside, it is easy to see why the cost difference is there, and you can also understand the names.

Dynamic RAM is the most common type of memory in use today. Inside a dynamic RAM chip, each memory cell holds one bit of information and is made up of two parts: a transistor and a capacitor. These are, of course, extremely small transistors and capacitors so that millions of them can fit on a single memory chip. The capacitor holds the bit of information -- a 0 or a 1 (see How Bits and Bytes Work on the WEB page for more information on bits). The transistor acts as a switch that lets the control circuitry on the memory chip read the capacitor or change its state.

A capacitor is like a small bucket that is able to store electrons. To store a 1 in the memory cell, the bucket is filled with electrons. To store a 0, it is emptied. The problem with the capacitor's bucket is that it has a leak. In a matter of a few milliseconds a full bucket becomes empty. Therefore, for dynamic memory to work, either the CPU or the memory controller has to come along and recharge all of the capacitors holding a 1 before they discharge. To do this, the memory controller reads the memory and then writes it right back. This refresh operation happens automatically thousands of times per second.

This refresh operation is where dynamic RAM gets its name. Dynamic RAM has to be dynamically refreshed all of the time or it forgets what it is holding. The downside of all of this refreshing is that it takes time and slows down the memory.

Static RAM uses a completely different technology. In static RAM, a form of flip-flop holds each bit of memory. A flip-flop for a memory cell takes 4 or 6 transistors along with some wiring, but never has to be refreshed. This makes static RAM significantly faster than dynamic RAM. However, because it has more parts, a static memory cell takes a lot more space on a chip than a dynamic memory cell. Therefore you get less memory per chip, and that makes static RAM a lot more expensive.

So static RAM is fast and expensive, and dynamic RAM is less expensive and slower. Therefore static RAM is used to create the CPU's speed-sensitive cache, while dynamic RAM forms the larger system RAM space.

7.6How ROM Works

7.6.1Read-only memory (ROM), also known as firmware, is an integrated circuit programmed with specific data when it is manufactured. ROM chips are used not only in computers, but in most other electronic items as well. In this trainee handbook you will learn about the different types of ROM and how each works.

7.6.1.1Let's start by identifying the different types of ROM.

7.6.2ROM Types7.6.2.1There are five basic ROM types:

ROM

PROM

EPROM

EEPROM

Flash memory

7.6.2.2Each type has unique characteristics, which you'll learn about in this article, but they are all types of memory with two things in common:

Data stored in these chips is nonvolatile -- it is not lost when power is removed.

Data stored in these chips is either unchangeable or requires a special operation to change (unlike RAM, which can be changed as easily as it is read).

7.6.2.3This means that removing the power source from the chip will not cause it to lose any data.

7.6.3ROM at Work

7.6.3.1Similar to RAM, ROM chips (Figure 1) contain a grid of columns and rows. But where the columns and rows intersect, ROM chips are fundamentally different from RAM chips. While RAM uses transistors to turn on or off access to a capacitor at each intersection, ROM uses a diode to connect the lines if the value is 1. If the value is 0, then the lines are not connected at all.

7.6.3.2A diode normally allows current to flow in only one direction and has a certain threshold, known as the forward breakover, that determines how much current is required before the diode will pass it on. In silicon-based items such as processors and memory chips, the forward breakover voltage is approximately 0.6 volts. By taking advantage of the unique properties of a diode, a ROM chip can send a charge that is above the forward breakover down the appropriate column with the selected row grounded to connect at a specific cell. If a diode is present at that cell, the charge will be conducted through to the ground, and, under the binary system, the cell will be read as being "on" (a value of 1). The neat part of ROM is that if the cell's value is 0, there is no diode at that intersection to connect the column and row. So the charge on the column does not get transferred to the row.

7.6.3.3As you can see, the way a ROM chip works necessitates the programming of perfect and complete data when the chip is created. You cannot reprogram or rewrite a standard ROM chip. If it is incorrect, or the data needs to be updated, you have to throw it away and start over. Creating the original template for a ROM chip is often a laborious process full of trial and error. But the benefits of ROM chips outweigh the drawbacks. Once the template is completed, the actual chips can cost as little as a few cents each. They use very little power, are extremely reliable and, in the case of most small electronic devices, contain all the necessary programming to control the device. A great example is the small chip in the singing fish toy. This chip, about the size of your fingernail, contains the 30-second song clips in ROM and the control codes to synchronize the motors to the music.

7.6.4 PROM

7.6.4.1Creating ROM chips totally from scratch is time-consuming and very expensive in small quantities. For this reason, mainly, developers created a type of ROM known as programmable read-only memory (PROM). Blank PROM chips can be bought inexpensively and coded by anyone with a special tool called a programmer.

7.6.4.2 PROM chips have a grid of columns and rows just as ordinary ROMs do. The difference is that every intersection of a column and row in a PROM chip has a fuse connecting them. A charge sent through a column will pass through the fuse in a cell to a grounded row indicating a value of 1. Since all the cells have a fuse, the initial (blank) state of a PROM chip is all 1s. To change the value of a cell to 0, you use a programmer to send a specific amount of current to the cell. The higher voltage breaks the connection between the column and row by burning out the fuse. This process is known as burning the PROM.

7.6.5You Need Connections

7.6.5.1No matter how powerful the components inside your computer are, you need a way to interact with them. This interaction is called input/output (I/O). The most common types of I/O in PCs are:

Monitor - The monitor is the primary device for displaying information from the computer.

Keyboard - The keyboard is the primary device for entering information into the computer.

Mouse - The mouse is the primary device for navigating and interacting with the computer

Removable storage - Removable-storage devices allow you to add new information to your computer very easily, as well as save information that you want to carry to a different location.

Floppy disk - The most common form of removable storage, floppy disks are extremely inexpensive and easy to save information to.

CD-ROM - CD-ROM (compact disc, read-only memory) is a popular form of distribution of commercial software. Many systems now offer CD-R (recordable) and CD-RW (rewritable), which can also record.

Flash memory - Based on a type of ROM called electrically erasable programmable read-only memory (EEPROM), Flash memory provides fast, permanent storage. CompactFlash, SmartMedia and PCMCIA cards are all types of Flash memory.

DVD-ROM - DVD-ROM (digital versatile disc, read-only memory) is similar to CD-ROM but is capable of holding much more information.

Ports

Parallel - This port is commonly used to connect a printer.

Serial - This port is typically used to connect an external modem.

Universal Serial Bus (USB) - Quickly becoming the most popular external connection, USB ports offer power and versatility and are incredibly easy to use.

Firewire (IEEE 1394) - Firewire is a very popular method of connecting digital-video devices, such as camcorders or digital cameras, to your computer.

Internet/network connection

Modem - This is the standard method of connecting to the Internet.

Local area network (LAN) card - This is used by many computers, particularly those in an Ethernet office network, to connected to each other.

Cable modem - Some people now use the cable-television system in their home to connect to the Internet.

Digital Subscriber Line (DSL) modem - This is a high-speed connection that works over a standard telephone line.

Very high bit-rate DSL (VDSL) modem - A newer variation of DSL, VDSL requires that your phone line have fiber-optic cables. 7.7From Powering Up to Shutting Down

7.7.1Now that you are familiar with some of the parts and workings of a PC, let's see what happens in a typical computer session, from the moment you turn the computer on until you shut it down:

i) You press the "On" button on the computer and the monitor.

ii) You see the BIOS software doing its thing, called the power-on self-test (POST). On many machines, the BIOS displays text describing such data as the amount of memory installed in your computer and the type of hard disk you have. During this boot sequence, the BIOS does a remarkable amount of work to get your computer ready to run.

The BIOS determines whether the video card is operational. Most video cards have a miniature BIOS of their own that initializes the memory and graphics processor on the card. If they do not, there is usually video-driver information on another ROM on the motherboard that the BIOS can load.

The BIOS checks to see if this is a cold boot or a reboot. It does this by checking the value at memory address 0000:0472. A value of 1234h indicates a reboot, in which case the BIOS skips the rest of POST. Any other value is considered a cold boot.

If it is a cold boot, the BIOS verifies RAM by performing a read/write test of each memory address. It checks for a keyboard an