Lecture_1_Introduction.ppt

KNT 4073 Telecommunication Networks and Services

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Telecommunication Networks and Services

Prepared byDr AL-Khalid Othman

Department Electronic and Telecommunication EngineeringFaculty of Engineering

UNIMAS


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Introduction Telecommunication Networks and Services


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The Development of Telecommunications Network Structures and Services

Standards

The success of a new services

Technology

RegulationMarket


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Factor 1: Technology Fundamental physical

considerations Technology capabilities

based on S- shaped curve

New invention of technology

Cap

abili

ty

Time


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Factor 2: Regulation

Based on Government regulation Regulation provide a framework that

determines what types of services and networks can be implemented.

Addressing the issue of which information should be available to people over a telecommunications networks.


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Factor 3: Market Determined by customer Depend on cost, usefulness, and appeal of

the service. Cost of services decrease with the size of the

subscriber base due to economies of scale Usefulness of service frequently depends on

there being a critical mass of subscribers Example: email depend on destination Appeal of service depends on comfortability

of service


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Factor 4: Standard

Basically, an agreement to ensure interoperable among equipment vendors.

Capable “talk to one another” Have a choice of buying equipment from

multiple suppliers Standard are extremely important in

telecommunications where the value of a network is to large extent determined by the size of the community that can be reached.


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Discussion

What are the criteria of designing a communication network?


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Communication Design Consideration

Range Power Cost Bandwidth Speed Reliability Convenience Accuracy


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Range The further information has to be transmitted, the

more difficult it is to get the message through uncorrupted

Wired link – require repeaters for long distances but work well at low frequencies.

Coaxial, optical fibre – work with long distance and high frequencies.

Terrestrial radio links – require different frequencies for different purposes, eg., HF (long distance ionosphere communication across the world); VHF (variety shorter rage uses); UHF (give large BW for TV); medium wave for broadcasting.


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Power Less power at sending end (Tx), simpler and cheaper

for transmitting installation but Rx can be more complex.

Radiated power may need to be kept high to allow the use of cheap receivers (radio broadcasting)


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Cost Has to be kept as low as is compatible with achieving

the desired system performance.


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Bandwidth Large BW increase of cost and complexity of system

design. Example, in telephone channel, the BW is halved at

the start by using SSB (single sided) techniques and then making what is left for the voices.

The standard voice frequency channel for telephone is 4KHz.


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Speed Cheaper system sending information – teleprinters,

facsimile, SMS. Sending faster information, more BW required but

less time.


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Reliability How much does it matter if your signal arrives

corrupted? The aim is to use the cheapest system which will give

acceptable reproducibility of signal.


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Convenience Encompasses a multitude of factors of which most

restricting technically is the need for new systems to be compatible with the existing system.

Use more comprehensive integrated circuits whereas possible (must be digital); ease for production and cheap for repairing.

Upgrading the system


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Accuracy/Quality The received signal must be accurate compared to

the original but required more complex and expensive communication system.


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THE TELEPHONE NETWORK

The Public Switched Telephone Network (PSTN)

Analog Circuits What is Sound? The Voiceband Plain Ordinary Telephone Service (POTS)


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Many communication technologies are based on the Public Switched Telephone Network (PSTN) - voice, data or networking.

It is important to have an understanding of the structure and operation of the telephone network.


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What is the basic model for the telephone network? At the top of the diagram, we have a

telephone and a telephone switch. The telephone is located in a building called a

Customer Premise (CP), and the telephone switch is located in a building called a Central Office (CO).

One could refer to the telephone as Customer Premise Equipment (CPE).


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PSTN The telephone is connected to the telephone switch

with two copper wires, often called a local loop or a subscriber loop, or simply a loop.

This a dedicated access circuit from the customer premise into the network.

We usually have the same arrangement at the other end, with the far-end telephone in a different customer premise and the far-end telephone switch usually in a different central office.


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Connection - Why copper?

Copper is a good conductor of electricity - but not perfect: it has some resistance to the flow of electricity through it.

Because of this, the signals on the loop diminish in intensity or attenuate with distance, and if the loop were too long, you wouldn't be able to hear the other person.


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PSTN The maximum resistance allowed is usually 1300 ohms, which

works out to about 18,000 feet or 18 kft, which is 3 miles or 5 km on standard-thickness 26-gauge cable, but could be as long as 14 miles or 22 km on thicker 19-gauge cable.

Thus, COs traditionally had a serving area of three miles radius around them, about 27 square miles or 75 km2.

With suburban sprawl, we can't build COs every five miles, so in practice, new subdivisions are served from remote switches, which are low-capacity switches in small huts or underground controlled environment vaults. local loop is essential.


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PSTN The remote provides telephone service locally on the

loops in the subdivision. The remote and the loops are connected back to the

nearest CO via a loop carrier system that uses fiber or radio.

Telephone switches are connected with trunks. While subscriber loops are dedicated access circuits,

trunks are shared connections between COs.


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Discuss what do understand about PSTN structure.


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To establish a connection between one customer premise and another, the desired network address (telephone number) is signaled to the network (to the CO switch or remote) over the loop, then the switch seizes an unused trunk circuit going in the correct direction and the connects the loop to that trunk - for the duration of the call.

When one end or the other hangs up, the trunk is released for someone else to connect between those two COs.


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PSTN

This method for sharing the trunks is known as circuit switching.


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Voice and data equipment which connects to the PSTN over regular telephone lines must work within the characteristics of the local loop, so an understanding of the characteristics and limitations of the local loop is essential.


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Analog Circuits

Telephones transmit information over copper wires using voltage

Voltage is a representation of analog from speaker’s voice

“Analog” circuit


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Analog Circuits

The technique for representing information on an ordinary local loop is called analog.

The term analog comes from the design of the telephone.

A microphone in the telephone handset is placed in the path of the sound pressure waves coming out of the speaker’s throat.

As the sound pressure waves hit the microphone, they change its electrical characteristics.


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Analog Circuits The electrical characteristics of the microphone

change as the sound pressure waves hit it to make a voltage on the telephone wires change.

This voltage is a representation or analog of the sound pressure waves.

This is all we mean by analog: representation. The voltage on the wires is an analog of the sound pressure waves coming out of the speaker’s throat.


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What is Sound? Sound is a wave, a longitudinal wave Sound needs a medium to travel Sound vibrates the air like a slinky An echo is a reflection of sound of an object. It's like playing

tennis Sound travels at the speed of sound, surprise! (331 m/s) The sound phenomena we hear when an ambulance passes us

by is known as the Doppler Effect


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The Voiceband In electronics, voice band means the typical human

hearing frequency range that is from 20 Hz to 20 kHz. In telephony, it means the frequency range normally

transmitted by a telephone line, generally about 200–3600 Hz.

Frequency-division multiplexing in telephony normally uses 4 kHz carrier spacing.

The rate at which the amplitude of a signal drops off near the upper and lower limits can vary with the design of the band-pass filters.


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The question of frequency spacing was addressed at an international meeting in the 1930s.

Germany and Britain favored 2 kHz spacing, while the Netherlands and some other countries preferred 6 kHz.

The question was compromised at the American position, which was the 4 kHz spacing that remained standard and also fixed the standard PCM sample rate at 8 kHz, which in turn defines what "voiceband" means for this purpose.


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Plain Ordinary Telephone Service (POTS) Plain old telephone service, or POTS, is a term

which describes the voice-grade telephone service that remains the basic form of residential and small business service connection to the telephone network in most parts of the world.

The name is a reflection of the telephone service still available after the advent of more advanced forms of telephony such as ISDN, mobile phones and VoIP.


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POTS

It has been available almost since the introduction of the public telephone system in the late 19th century, in a form mostly unchanged to the normal user despite the introduction of Touch-Tone dialing, electronic telephone exchanges and fiber-optic communication into the public switched telephone network (PSTN).


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POTS

The system was originally known as the Post Office Telephone Service or Post Office Telephone System in many countries.

The term was dropped as telephone services were removed from the control of national post offices.


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POTS services : bi-directional, or full duplex, voice path with limited

frequency range of 300 to 3400 Hz: in other words, a signal to carry the sound of the human voice both ways at once;

call-progress tones, such as dial tone and ringing signal;

subscriber dialing; operator services, such as directory assistance, long

distance, and conference calling assistance; a standards compliant analog telephone interface

including BORSCHT functions


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BORSCHT functions BORSCHT circuitry is typically located on a telecommunications

network line card and is increasingly integrated into a chipset by several semiconductor companies for low-cost implementation of a standard POTS telephone interface for non-traditional telephony networks such as cable television networks, fiber optic, VoIP and wireless local loop.

Battery feed - device or system that supplies electrical or other types of energy to an output load or group of loads.

Overvoltage protection-Used transient voltage suppressor or TVS -a general classification of an array of devices that are designed to react to sudden or momentary overvoltage conditions.

Ringing-is the sound made by a telephone to indicate an incoming call.

http://en.wikipedia.org/wiki/BORSCHT


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BORSCHT functions Supervision-a loop start is a supervisory signal given

by a telephone or PBX in response to the completion of the loop circuit, commonly referred to as 'off-hook'.

Codec- device or program capable of performing encoding and decoding on a digital data stream or signal.

Hybrid-is a single transformer that has three windings Testing

http://en.wikipedia.org/wiki/BORSCHT


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POTS- Example In the United States, the pair of wires from the central

switch office to a subscriber's home was called the subscriber loop.

It was typically powered by 48V direct current (DC) and backed up by a large bank of batteries (connected in series) in the central office, resulting in continuation of service during most commercial power outages.

The subscriber loop would typically carry a "load" of about 300 Ohms, and did not pose a threat of electrocution to human beings.


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POTS other features : Many calling features became available to POTS

subscribers after computerization of telephone exchanges during the 1970s and 1980s. The services include:

Voicemail - is a centralized system of managing telephone messages for a large group of people.

Caller ID - is a telephone service that transmits the caller's number to the called party's telephone equipment during the ringing signal or when the call is being set up but before the call is answered.


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Call waiting - If a calling party places a call to a called party which is otherwise engaged, and the called party has the call waiting feature enabled,

Speed dialing is the use of a very short series of telephone numbers to reach public services. Typically these are two or three digits, and are most commonly known as being emergency telephone numbers like 1-1-2 and 9-1-1.

Conference call (three-way calling) - is a telephone call in which the calling party wishes to have more than one called party listen in to the audio portion of the call.


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POTS-Summary The communications circuits of the PSTN continue to be

modernized by advances in digital communications, however, other than improving sound quality, these changes have been mainly transparent to the POTS customer.

The function of the POTS local loop presented to the customer for connection to telephone equipment is practically unchanged and remains compatible even with telephones built in the early 20th century.

Due to the wide availability of POTS, new forms of communications devices such as modems and facsimile machines are designed to use the POTS service to transmit digital information.


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Discussion

What is the procedure for the telephone network to be connected?


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CONNECTING TELEPHONE NETWORK


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IP-Telephony

What is Voice-over-IP? Voice-over-Internet-Protocol or Voice-over-IP

or VoIP allows one to send a voice transmission via a network instead of the standard telephone infrastructure.

Calls can be routed via the Internet, wide area network (WAN), or local area network (LAN).


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What is an IP-PBX (Internet Protocol Private Branch eXchange) ? An IP-PBX is a customer premises business phone

system that manages telephones throughout the enterprise and acts as a gateway to both voice and data networks.

An IP-PBX allows you to place calls using a network instead of standard telephone infrastructure.

Telephones can be connected to the IP-PBX via the network and calls can be routed via the network instead of the standard public switched telephone network.


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What are the advantages of an IP-PBX system?


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What are the advantages of an IP-PBX system?

Multiple Branch Offices

With VoIP, expanding your business phone system to multiple branch office sites is easy.

Integrated IP Gateways allow you to traffic calls between offices over the Internet and save on long distance charges.

Dialing branch offices is as easy as calling an extension down the hall.

Make certain that your IP-PBX has an administration tool that simplifies the process of configuring IP gateways between remote systems.


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Toll Bypass

IP-PBXs enable businesses to reduce the cost of long distance calling by routing calls inexpensively over IP networks.

If you have overseas facilities, using an IP-PBX could reduce your business's costs significantly.


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Remote Office

Even if your business has a single remote office, an IP-PBX can give you the flexibility to pick an affordable solution.

Purchasing a solution that allows for a small or large number of IP trunks might be right for you.

Work From Home

Vertical's sophisticated IP-PBX software extends easily and seamlessly to your telecommuters, contractors, and consultants and makes them part of the corporate phone system.


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SUMMARY-THE TELEPHONE NETWORK Modern telephone network provides basic

telephone service. It involves two-way, real-time transmission of

voice signals.• In basic form, service involves transfer of

analog signal of a nominal bandwidth of 4 kHz across a sequence of transmission and switching facilities.

• The digital transmission capacity of the 4 kHz channel is about 45 kbps – miniscule in relation to speed of modern computers.


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• Ubiquity and low cost make telephone network an essential component of computer communications.

Telephone network operate on basis of circuit switching.

Circuit switching involves setting up physical path from one telephone across network to other telephone.

At telephone offices operators make physical connections that allows electric current to flow from one telephone to the other.

Examples

IP Telephony PBX 3CX Etc.


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THE TELEPHONE NETWORKPhysical resources such as wires and switch connections were dedicated to the call for its entire duration.

Modern digital telephone networks combine circuit-switching with digital transmission and digital switching.

Fig 10: Circuit switching


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• In basic form, service involves transfer of analog signal of a nominal bandwidth of 4 kHz across a sequence of transmission and switching facilities.

• The digital transmission capacity of the 4 kHz channel is about 45 kbps – miniscule in relation to speed of modern computers.


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Central Office and Local Loop

Each phone user (subscriber) has a direct connection to a switch in the central office.

This is called the local loop The local loop has a length of 1 - 10 km The switches in the central office are called (local)

exchange A company which provides local telephone service is

called a local exchange carrier or LEC


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Signaling

Signaling refers to the control functions performed to setup a phone call.

Signaling between users and the local exchange in the central office is quite simple: dial-tone, punch numbers, put phone down, etc.

Signaling between exchanges/switches is more complicated and is done via a separate network, which uses packet switching.


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The switch prepares to accept dialed digits and provides user with dial tone.

• User then enter telephone number that generates sequence of pulses or sequence of tones.

• Switch equipment converts these pulses or tones into a telephone number.

• The call setup procedure involves finding a path from source to destination.


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THE TELEPHONE NETWORKFig 12 shows a typical arrangement in a metropolitan area.

Fig. 12: Routing in typical metropolitan area


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Addressing and Routing

Each subscriber has an address (telephone number) • Addresses are hierarchical • Example: Domino’s Pizza in downtown Charlottesville 1 804 979 2656 1 804 979 country code; area code; number of local exchange; 2656 Subscriber number The information contained in a telephone address is exploited

when establishing a route from caller to callee.


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Central offices are connected by high-speed digital transmission lines that correspond to a group of trunks.

If two telephones are connected to same central office, that is, two phones are attached to switch A, then they are connected directly by local switch.

If the two telephones are connected to different central offices (that is, A and B), then a route needs to be selected.


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Consider end-to-end path that is set up between source and destination telephones.

In the majority of cases, the telephones are connected to their local telephone office with a twisted pair of copper wires.

• The voice signal flows in analog form from the telephone to the telephone office.

• The voice signal is converted into digital form using PCM at line card interface where copper wires connect to local telephone switch.


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• The digitized voice signal flows from that point onward as a sequence of PCM samples over a path that has been set up across network.

This path consists of reserved time slots in transmission links that use TDM.

The transmission links connect digital switches in which TSI arrangements have been made during call set up.

Finally, at destination switch the received PCM signal is converted back to analog form and transmitted to destination telephone over the pair of copper wires.


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International standard organisations for telecommunications


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International Telecommunication Union (ITU) ITU is based in Geneva Comprises, member countries, industrial companies and

international organizations. 1st July 1994- 3 main sectors 1st sector- Telecommunication Standardization Sector

(ITU-T) responsible for setting standards for public voice and data services (formerly the remit of the Consultative Committee on International Telegraphy and Telephony or CCITT)

2nd sector-Radio Communication Sector (ITU-R) is responsible for radio frequency spectrum management for both space and terrestrial use to be performed by the International Radio Consultative Committee (CCIR).

3rd sector-The development sector (ITU-D) is responsible for improving telecommunications equipment and systems in developing countries.


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International Telecommunication Union (ITU) Organize conference on world and/or regional basis and

operate study group G-Transmission systems and media, digital systems and

networksH- Audiovisual and multimedia systemsI- Integrated services digital networkP-Telephone transmission quality, telephone installations, local line networksQ-Switching and signallingR-Telegraph transmissionS-Telegraph services terminal equipmentU-Telegraph switching

http://www.itu.int/ITU-T/publications/recs.html


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Another Organization International Organization for Standardization-

concerns on software issue Main contribution of ISO -OSI 7 layers International Electrotechnical Committee (IEC)-

hardware issue European Telecommunications Standards Institute

(ETSI)- developing wide range standards and other technical documentation as Europe’s contribution to worldwide standardization in telecommunications, broadcasting and information technology.


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