TDC 461: Basic Telecommunications DePaul University Winter 2001 LoriLee M. Sadler

Agenda: Welcome to TDC 461 Course Overview Syllabus Overview Intro to Telecommunications Brief History of Telecom Voice Characteristics Analog vs. Digital Telephone Set Modems Fax Machines

Course Overview What you’ll get out of this course –basic concepts and info –sense of the real world application of telecom –heightened awareness of legal/social issues surrounding telecom technologies –ability to use your knowledge to evaluate proposed systems for feasibility and “fit”

Course Overview, cont. –What do you want to get out of this course?

Syllabus Overview Instructor Info Course Logistics Grading –Homeworks –Exams –Academic Integrity Class schedule

Class Tools Web site 461 Web tools

What is Telecommunications? Voice Data Video Integrated

Why Telecommunications Technology? Helps solve communications problems of physical distance. Helps solve communications problems of physical barriers.

Quality Measures of Telecommunications Systems Cost: Efficiency: Quality: Time: Ease of Use:

Problems in Telecom Legacy systems Interoperability: public standards vs. proprietary standards Costs

Communications Networks What are they? – Why do we have them? – What is required to make them work?

Network Structure POP = Point of Presence PBX = Private Branch Exchange

Telecom History Technologies continuously improving: – Regulatory Issues: Who pays for all this? How much competition? Business Issues: How much does it cost? What services are available?

History of Transmission Technology Through history, voice and data transmission systems are getting –Higher capacity –Lower cost

Analog Trunk Technology

Digital Trunk Technology (T-Carrier hierarchy)

Digital Trunk Technology Synchronous Optical Network (SONET)

Switching History

Regulatory History Alexander Graham Bell said:... and the lawsuits began. Watson, Come Here! I need you!

Regulatory History

Modified Final Judgement Regional Holding Companies (RHCs) or Regional Bell Operating Companies (RBOCs) formed Each RHC composed of multiple Local Exchange Companies (LECs) Interexchange Carriers (IXCs) provide long- distance service.

Regional Holding Companies Ameritech Bell Atlantic NYNEX (Bell Atl) Bell South SBC Pacific Telesis (SBC) US West

Modified Final Judgement 1984 Examples: –Ameritech, SBC, Southwestern Bell, etc. are Local Exchange Carriers (LECs) –AT&T, MCI, Sprint, etc. are Interexchange Carriers (IXCs)

Network Structure POP = Point of Presence PBX = Private Branch Exchange

Modified Final Judgement (1984) 231 Local Access and Transport Areas (LATAs) defined in US. LECs can provide only intra-LATA service. IXCs provide only inter-LATA service. LECs must give customers equal access to all IXCs.

Problems with MFJ of 1984: No single company (LEC or IXC) can provide all communications services for its customers. This is inefficient. LATA boundaries limit LEC services. Many other companies (Cable TV, Competitive Access Carriers, etc.) are not constrained by MFJ.

The Solution? Deregulation! Telecommunications Act of 1996 –Allows IXCs to offer local service –Allows LECs to offer long-distance service (when they can show competition) –Allows Competitive LECs (CLECs) to share LEC facilities (for fair competition). –Allows combination of voice, data, video service packages.

Telecommunications Act (1996) LECs must give competitors: –All services at wholesale prices. –Access to telephone numbers, operator services, directory listings. –Access to poles, ducts, and right-of-ways. –Physical co-location of equipment within LEC buildings.

Telecommunications Act (1996) A LEC can offer inter-LATA services when substantial competition exists on its network. –The courts are still deciding exactly what this means...

Telecommunications Act (1996) Universal Service LECs must provide “affordable access” for Schools, Libraries, Health Departments, Hospitals, etc.

Problems - Telecom Act 1996: IXCs are moving slowly on providing local service due to wiring costs. LECs are still in court deciding: – Cable TV carriers find it expensive to offer voice services over cable.

The Telephone Set Telephone Set: Handset: Dial Pad:

What is Speech? = Speech is a continuous change in air pressure over time generated by a vibrating larynx. –It is an analog waveform (can take any value). –It is a periodic waveform (repeats itself in time)

Periodic Signals Amplitude (A) = signal height = volume –Measured in volts Frequency = # of signal cycles/sec –Measured in Hertz (cycles per second)

Periodic Signals Example: For the signal above: –Amplitude = 3 volts –Fundamental Frequency = 100 Hz

Voice Characteristics

Bandwidth-Limited Circuits analog bandwidth=> telephone circuit bandwidth=> filtering=>

Why is Filtering done? To save money – Quality is still good –

Speech Transmission Varying Air Pressure Varying Electrical Current Person produces changes in air pressure via vibrating larynx. Carbon granules in telephone receiver produce varying resistance in response to changes in air pressure

Speech Reception Varying Electrical Current Varying Air Pressure Changes in air pressure move ear drum and are interpreted as speech. Electromagnet in earpiece moves a diaphragm in response to electrical current changes and produces varying air pressure.

Analog vs. Digital Information Analog information contains a continuously changing stream of values. – Digital information contains bits (binary digits) representing 0 or 1. –

Analog vs. Digital Signals Analog signals vary continuously and can take any value. Digital signals change at discrete times and take only fixed discrete values.

Analog vs. Digital Transmission Analog repeater circuits take weak signals and amplify them. Digital repeater circuits analyze signals, amplify and remove accumulated noise. Repeater Regenerator

49 Analog Signaling of Digital Data Information Source (DTE) Transmitter (DCE) Receiver (DCE) Information Destination ( DTE) Transmission Network Digital Data Analog Network (e.g. PSTN) MODEM Analog Signal

50 Analog Signaling of Digital Data Analog POTS in the PSTN Digital ISDN in the PSTN Analog Signal Analog Network (e.g. PSTN) CO Analog Signal Digital Network (e.g. ISDN) CO ISDN MODEM Digital Data ISDN MODEM Digital Data CODEC located in MODEM CODEC located in CO Switch

51 Digital Signaling of Analog Data Analog Data (e.g.voice) needs to be converted to/from a digital signal –for ISDN service, conversion performed in phone (or ISDN modem at desk top) –for analog POTS, conversion performed within line card at CO (in switch) Conversion is performed by a CODEC (Coder / Decoder) Desired qualities in a analog signaling scheme include: –minimal data rate –minimal quantization noise –retention of voice fidelity

52 CODEC Operation CODEC Process samplerquantizer analog signal PAM digital signal (PCM) F SAMPLE Sampler “samples” the analog signal at fixed intervals defined by the sampling frequency, F SAMPLE. Quantizer digitizes PAM samples into discrete levels and encodes a n bit binary pattern for each quantized sample

53 CODEC Operation - analog -> digital - Resulting data rate = F SAMPLE x n time Amplitude Quantization interval Binary code -4 to-3 -3 to to to 0 0 to to 2 2 to 3 3 to PAM signal PCM signal

54 CODEC Operation - digital -> analog - PCM digital bit stream is collected into eight bits sample is placed in the middle of quantization interval defined by binary code –resulting quantization error lead to quantization noise, Q NOISE signal is sent through a LPF[F MAX ]

Modems Essentially a CODEC MOdulate/DEModulate Standard Interface:

56 MODEM Features Half duplex vs full duplex Synchronous vs asynchronous Loopback testing is normally integrated into modem Modems accept commands to provision and operate (e.g. FDX|HDX or dial number) using the “Hayes Command set” –driver software uses the commands to provision the modems

57 MODEM standards

Fax Machines Operation Regulation: ITU Group 3 Group 4