Telecommunication Systems

1. Telecommunication Systems Engr. M Jamil Khan

2. Signal A Signal: is a function that specifies how a specific variable changes versus an independent variable such as time. Usually represented as an X-Y plot.

3. Classification of Signals • Analog vs. Digital signals: Analog signals are signals with magnitudes that may take any value in a specific range. Digital signals have amplitudes that take only a finite number of values.

4. Classification of Signals • Continuous-time vs. discrete-time:Continuous-time signals have their magnitudes defined for all values of t. They may be analog or digital.Discrete-time signals have their magnitudes defined at specific instants of time only. They may be analog or digital.

5. Classification of Signals • Periodic vs. aperiodic signals:Periodic signals are signals constructed from a shape that repeats itself regularly after a specific amount of time T0, that is:f(t) = f(t+nT0) for all integer nAperiodic signals do not repeat regularly.

6. Basic Telephone Systems POTS is the plain old telephone system that connects most homes and small businesses. POTS lines were designed to transmit the human voice, which has a bandwidth less than 4000 Hz. A telephone conversation requires two channels, each occupying 4000 Hz.

7. Assignment Of Frequencies

8. Basic Telephone Systems Limitations A 4000 Hz analog signal can only carry about 33,600 bits per second of information while a 4000 Hz digital signal can carry about 56,000 bits per second. If you want to send information faster, you need a signal with a higher frequency. POTS cannot deliver faster signals.

9. Basic Telephone Systems - Loops The local loop is the telephone line that runs from the telephone company’s central office to your home or business. The central office is the building that houses the telephone company’s switching equipment and provides a local dial tone on your telephone. If you place a long distance call, the central office passes your telephone call off to a long distance provider.

10. Local Loops

11. Trunks A trunk is a special telephone line that runs between central offices and other telephone company switching centers. A trunk is usually digital, high speed, and carries multiple telephone circuits. A trunk is typically a 4-wire circuit, while a telephone line is a 2-wire circuit. Not associated with a single telephone number like a line is. A telephone number consists of an area code, an exchange, and a subscriber extension. The area code and exchange must start with the digits 2-9 to separate them from long distance and operator services.

12. Composition Of A Telephone Number

13. Telephone Connections When the telephone company installs a line, it must not proceed any further than the demarcation point, or demarc. Modular connectors, such as the RJ-11, are commonly used to interconnect telephone lines and the telephone handset to the base. When the handset is lifted off the base (off-hook), an off-hook signal is sent to the central office.

14. Basic Telephone Systems When the off-hook signal arrives at the central office, a dial tone is generated and returned to the telephone. When the user hears the dial tone, they dial (or press) the number. The central office equipment collects the dialed digits, and proceeds to place the appropriate call.

15. Basic Telephone Systems

16. COs for Businesses When Central office Exchanges ( COs or COEs) were automated, a number of factors made it clear that this approach was less than ideal for serving businesses of any significance and with any appreciable number of terminal devices.

17. COs for Businesses • The factors including the followings • Labor intensity • Capital Intensity • Physical Functional Limitation • Personalized Service

18. Enterprise Communications • Enterprises use the following schemes for station users • Private Branch Exchanges • Key Telephone Systems • Centrex • ACD (Automatic Call Distribution • Computer Telephony

19. Key Telephone Systems • Multi-line telephone system used in SMALL office environments • Very old technology • Similar to a PBX. • Many telephone lines come into certain phones. A light comes on if the line is busy. A user takes control of a line by pressing a button.

20. Key Telephone Systems • Provided intercom capabilities. • Often 6, 12, or 25 lines would come into a phone. • In North America, these type of phones were known as 1A2. • They are still manufactured and supported today, though they are rapidly becoming outdated.

21. Key Telephone Systems

22. Private branch exchange (PBX) • A PBX is an internal telephone network. • Users share a certain number of lines for making telephone calls outside the company. • A PBX system allows calls to come in to the company from external telephone lines. • A PBX is less expensive than connecting an external telephone line to every telephone in an organization.

23. PBX A diagram of a PBX network

24. Centrex System: • In a Centrex system, a pool of telephone lines is leased at the phone company’s central office. • In this system, the telephone company owns and houses the equipment at their location. • The number of employees who may request an outside line at any given moment is not restricted.

25. Centrex System • This service is easy to set up, can easily be upgraded, and is highly reliable. • The hiring company lacks control over the system. It has little control over the quality of service provided. • It has fewer features than many PBX systems. • It costs more to lease equipment than to purchase a system over the long term.

26. Automated Call Distributors (ACDs) • ACDs are telephone systems that route calls, prioritize calls, and play recorded messages. • They record the number of calls in the system, the number of dropped calls, and the average hold time. • ACD systems offer many features and hence are in widespread use. • The most important functions of an ACD system are call routing and data collection.

27. Automated Call Distributors (ACDs) • Call routing. • Methods for routing calls. • Data collections.

28. Computer Telephony Integration (CTI) • Integration of the telephone and computer-based systems is known as computer telephony integration (CTI). • CTI is made possible by middleware applications. • Middleware application is software that connects two or more separate applications across a computer network.

29. Computer Telephony Integration (CTI) • Widespread availability. • Features and benefits. • Advantages of CTI.

30. Features and Benefits • Automatic display of caller and call details. • Routing of voice, fax, e-mail, text messaging, and live chat into a unified queue. • Retrieval of voice, fax, and e-mail from a single location. • Delivery of automated responses. • Data analysis and reporting functions.

31. Automatic Display of Caller and Call Details • Screen pop is a screen that displays information about the user. • It also shows hardware and software configuration, recent upgrades, and prior problems. • By linking information in computer databases with incoming call information, the user and the agent save their time.

32. Delivery of Automated Responses • An auto attendant is a phone system that answers calls with a recorded message and provides prerecorded solutions. • CTI can provide real-time information on the status of the entire telephone system. • It provides real-time data on every agent, every user, and every outstanding request. • Reports can be created from within the CTI programs.

33. Advantages of CTI • Provision of services such as caller identification, call routing, and automated response. • Integration of different user access methods. • Efficient use of available help desk resources. • Integration of technology systems.

34. Assignment # 2 Working of T-Carrier From DS0 to T3.

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