Basic Concepts

1. Basic Concepts • We will define basic telecommunication terms, such as: • analog • digital • bandwidth • compression • protocols • codes and bits

2. The architecture or protocol suite is the umbrella under which the devices communicate with each other

3. Congestion • All networks are limited in how many peripherals they can support without experiencing too much degradation • Today more and more peripherals are being added to networks • New ways to eliminate congestion on a network have been developed

4. Eliminating Congestion • Multiplex: • to transmit two or more signals over a single channel • Compression: • reducing the representation of the information, but not the information itself • reducing the bandwidth or number of bits needed to encode information or a signal

5. Multiplexing • Several devices can share a telephone line • T-1 telephone line will carry 24 communication paths on one high-speed link • T-3 provides 672 communication paths on one link

6. Compression • Applications such as: graphics, x-ray images, video are bit intensive • Thus require high bandwidth when transmitting • Compression reduces the number of bits needed to transfer

7. Analog and Digital • Telephone system developed to transmit speech • Spoken words are transmitted as analog sound waves • People speak in an analog format, in waves • Telephone system was completely analog until 1960

8. Analog Components • Telephones plugged into your home jacks • Most TV signals and telephone lines from home to provider • Most cable drops

9. Digital Components • ISDN lines • Fiber optic lines between telephone company offices

10. Analog Signals • Move down telephone lines as electromagnetic waves • The way it travels is expressed in frequency • Frequency refers to the number of times per second that a wave oscillates or swings back and forth in a complete cycle from its starting point to its ending point

11. Analog Signals • A complete cycle occurs when a wave starts at a zero point of voltage, goes to the highest positive point of the wave, down to the negative voltage portion, and then back to zero voltage

12. Analog Signals • The higher the speed or frequency, the more complete cycles of a wave are completed in a period of time • This speed or frequency is measured in Hertz • Hertz: a measurement of frequency in cycles per second, 1 hertz is 1 cycle p/sec

13. Hertz • A wave that oscillates or swings back and forth 10 times per second has a speed of 10 hertz or cycles per second • Bandwidth or range of frequencies a service occupies is determined by subtracting the lower range from the higher range • 300-3300Hz (voice)= 3300-300= 3000Hz

14. Analog Services • Voice (300 -3300 Hz) • Microwave Radio (2-12 GHz) • Analog cable TV signals (54-750 MHz) • Oscillate between a specific range of of frequencies

15. Analog versus Digital • Analog system can no longer handle the increase in the number of calls that are being generated, was designed for lower volume • Digital networks are faster, have more capacity, and are more reliable

16. Impairments on Analog Services • Analog signals loose their power the longer they travel • Signal meets resistance in the media (copper, coaxial cable, air), causes fading of the signal or attenuation of the signal • Analog signals also pick up noise or electrical energy while travelling from power lines, light sources, and electrical machinery • Requires: amplification to inhibit attenuation

17. Amplification • To overcome resistance in a signal, analog signals are amplified while they travel over a medium • Drawbacks amplification: • also increases level of noise in signal

18. Digital Signals • Advantages digital signals: • higher speeds • clearer voice quality • fewer errors • less complex peripheral equipment required

19. Digital Signals • No waves are transmitted • Digital signals are transmitted in the form of binary bits • Binary = being composed of two parts • In telecommunications this means only on or off, one or zero piece(s) of information transmitted

20. Digital Signals • Less error, because on-off easier to recreate than an analog signal or sine wave • Easier to repair than analog signals • When digital signals fade, are easy to REGENERATE (not amplify) over distance • Noise is discarded along the digital path

21. Digital TV • Great example of how digital transmission enhances clarity, because: • noise in signal eliminated • error detection high in digital systems, so distance from signal not a factor • signal lost altogether if it is not in range • provides studio quality voice and image • began in 1998, 100% in 2006

22. Digital Phone Services • Digital technology first implemented in 1962 in the long distance network • 1975: Northern Telecom introduces the first digital telephone switch (PBX) • 1976: ATT #4ESS toll office switch • 1977: NT installs first digital switch • 1982: #5ESS calls digitally switched to end-users

23. Channel Banks • Introduction of digital transmission between central offices in 1960’s • Analog to digital conversions necessary • Channel banks served this purpose • Expensive to maintain, cumbersome, and expensive • Led to development of digital switches

24. Basics • Computers exchange bits to communicate with each other • Bits are arranged in a predefined format to make them readable • ASCII: American Standard Code for Information Interchange • EBSDIC: Extended Binary Coded Decimal Interexchange

25. Basics • Baud rate: is a measure of transmission speed over an analog phone line • Baud rate measured differently than bit rate • Bits are measured in seconds • Baud rate measures the number of changes per second in an analog sine wave signal

26. Baud and Bit Rates • A baud is one analog electrical signal • One wave or cycle equals one baud • 1200 baud line means that the analog wave completes 1200 cycles in one second • 56,000 bits per second lines, carry 56,000 bits in one second, or 56Kbps

27. Codes • ASCII code is limited to 128 characters • upper case • lower case • numbers • punctuation • Does not include: • bold, underlining, font changes, tables, etc.

28. Attachments • Word processors add their own codes to perform fancy word processing • Easier to send the entire documents as attachment than to come up with coding schemes for all such specialized documents • MIME: (multipurpose mail extension) mail protocol used send attachments

29. Bandwidth • Refers to capacity • Carrying capacity expressed differently for analog and digital transmissions • analog capacity measured in Hertz • digital capacity measured in bytes

30. Hertz • Measure of frequency of analog services • Example: • Co-axial cable with bandwidth of 400 MHz • means 400 million cycles per second • difference between lowest and highest frequency, within which the medium carries traffic

31. Hertz • Cabling which carries between 200MHz and 300 MHz has a bandwidth or frequency of 100 MHz • The greater the difference between highest and lowest frequency the greater the bandwidth or capacity of the medium

32. Bits • ISDN, T-1, T-2, ATM are digital services • speed is stated in the number of bits transmitted per second • T-1: 1.54 million bits p/s (Mbps) • ISDN: 64Kbps • ATM: 622 Mbps, or 13.22 Gbps

33. Narrowband T-1 at 1.54Mbps Analog phone lines at 3,000 Hz BRI ISDN at 64Kbps Wideband Broadcast TV 6MHz per channel Cable TV 700MHz ATM at 13.22 Gbps SONET up to 13.22G T-3 at 44.7Mbps Narrow/Wideband

34. Applications • Wideband: • TV • Cable • Connections between telephone offices • Narrowband: • phone connection to end users

35. Protocols • Enable computers to communicate with each other • Spell out the rules of interaction between two or more computers • Handle error detection and correction and file transmission

36. Examples of Protocols • Who transmits first? • What is the structure of the addresses of devices such as computers? • How are errors fixed? • How long to wait before disconnecting? • How to package data to be sent?

37. Architecture • Ties computers and peripherals together into a coherent whole • Forms the network which connects all devices together • Layers within architectures have protocols to define functions such as routing, error checking and addressing

38. Examples of Architectures • SNA: developed by IBM to tie together all their devices • OSI: Open Standards Interconnection, developed by International Standards Organization, to allow devices from various vendors to communicate with each other

39. OSI • Not widely implemented • Laid foundation for the concept of open communications among vendors • Basic concept of layering of groups of functions into 7 layers • Each layer can be changed and developed independently

40. Layers • 1: physical layer • 2: data link layer • 3: network layer • 4: transport layer • 5: session layer • 6: presentation layer • 7: application layer

41. Compression • White spaces & redundant images removed • Letter abbreviation • Only changed part of image transmitted • Many types of compression methods • Based on mathematical algorithms • Codec (coder/decoder) devices used to perform the algorithm

42. Streaming Media • Software used to speed up transmission of video and audio over the Internet • When graphics and text sent to your screen, text immediately available, graphs later • Important feature of browsers to make material available as it downloads • MPEG standards are used for streaming

43. Streaming Media • ITU formed the Moving Picture Experts Group (MPEG) in 1991 to develop compression standards • Made standard that more processing power needed to encode than to decode material • RealNetworks Inc. • Microsoft Corporation

44. Multiplexing • Combines traffic from multiple telephones or data devices into one stream • Allows many devices to share the same communication path • Makes more efficient use of telephone lines • Does not alter actual data sent • Consists of special equipment, hardware

45. Networks • LAN (local area network) • WAN (wide area network) • MAN (metropolitan area network)

46. Network Terminology • Hub: wiring center to which all devices are connected within a segment of a LAN, connections with twisted pair cabling • Switching Hub: allows multiple transmissions on a LAN segment • Backbone: connects hubs together • Bridge: connects multiple LAN’s together

47. Network Terminology • Layer 2 switch: bridges with multiple ports, switch data between LAN segments • Router: connects multiple LAN’s together, more complex than bridges, handle more protocols • Routing Switches: fast router • Server: centrally located computer which houses set of files, documents, data, etc.

48. Bridges • Used to connect a small number of LAN’s • Provide one common path to connect several LAN’s • Easy to configure, all data sent to all devices on a network, appropriate device picks it up, broadcast feature • Lack routing and congestion control

49. Routers • Used to connect multiple LAN’s over large distances (differing buildings, cities) • More sophisticated than bridges • Can handle differing protocols from various LAN’s

50. Routers • Capabilities: • flow control: if path congested holds data until capacity is available • path optimization: selects best available path with use of tables • sequencing: sends data in orderly packets • receipt acknowledgement: receiver send a message back to verify receipt of file