Networking and Telecommunications 2 Telecommunications 6202021 1 Transmission

Networking and Telecommunications 2. Telecommunications 6/20/2021 1

Transmission Characteristics o Medium n n n 6/20/2021 Air Waves – (satellite, microwaves, wireless lans (infrared, radio waves) Electrical /Copper (Twisted Pair, Coax) Light (fiber optic via glass/plastic cable) 2

o Transmission Signals n Parallel - all 8 bits at same time n serial – 1 bit at a time (rs 232), sequential o Transmission Types n Asynchronous – start/stop bits, one character at a time n Synchronous – fast, multiple characters in a block of data. No start/stop bits. 6/20/2021 3

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o Analog (continuous sine wave) n Watch (with hands), speedometer o digital transmissions (discrete pulses of 0 or 1) n n 6/20/2021 Computers/binary TV-discrete channels 8

Analog vs. Digital o Internal to Computer (digital, binary) o Transmissions – originally analog n Phone systems – analog totally at first n Computers – used modems to talk over analog phone lines (and connections between CO were analog) n Today – Connections between CO are digital. Connections between home and CO (last mile) are still mostly analog n Cable Modems and DSL – connections from home becoming Digital 6/20/2021 9

Why Digital better then Analog? o Faster (higher capacity) n 56 k vs. Mbps+ o Better data integrity (less errors), distortion of pulses easier to correct o Better Security o Lower Costs Today o No analog to digital conversion needed (no modem) o Easier to integrate voice, video, data 6/20/2021 10

o Transmission Codes = Encoding n n n (Morse Code) EBCDIC (8 bit) ASCII (8 bit vs 7 bit) o Parity – Even vs. Odd o Half Duplex vs. Full Duplex 6/20/2021 11

EBCDIC vs. ASCII Character 6/20/2021 EBCDIC (link) ASCII A 1100 0001 0100 0001 B 1100 0010 0100 0010 Z 1110 1001 0101 1010 5 1111 0101 0011 0101 ! 0101 1010 0001 12

Morse Code 6/20/2021 13

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Waves • Sound, Electrical, Radio, Electromagnetic • Sine Wave, measured in Hertz (Hz) • Characteristics – Amplitude and Frequency • Bandwidth – difference from high to low frequency range 6/20/2021 15

o Speed (modems) n Baud vs. BPS p 300, 1200, 2400, 9600, 14. 4, 28. 8, 56 k 6/20/2021 16

Modems 6/20/2021 17

Circuit Switching Networks o “Temporary", "dedicated", communications channel o Voice (phone) 6/20/2021 18

Packet Switching Networks o Store and forward, non-dedicated o Shared communications channel (packets interleaved on same line) o Packets may take different paths, arrive in different order (reassemble at end) o X. 25 – old WAN standard for PSN o Useful for data 6/20/2021 19

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Telecom Hardware o Hosts (mainframe, mini) o Micros, workstations (desktop systems) o Terminals (vt 100, 3270, X-terminals) o Automatic Teller Machines (ATM - Banks) o POS (Point of Sales - cash registers) o Fax o Satellite Dishes, Satellites, radar towers o Terminal Server (Access Server) o MUX (multiplexer) - TDM and FDM o Modems 6/20/2021 21

Satellite Dish ATM Machine Fax Machine Terminal 6/20/2021 22

Terminal Servers/Access Servers o Connect modem pool to internal network o Allows outside users to connect in o And internal users to dial-out o Authentication is normally used 6/20/2021 23

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Multiplexers o Allows multiple systems to share single common communications channel o Often used with mainframes/terminals, as well as phone systems o 2 Main Methods used: n n 6/20/2021 TDM – Time Division Multiplexing FDM – Frequency Division Multiplexing 25

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Transmission (telecom. ) Media o electrical/copper: n Phone wire n TP - 2 pair (4 wire, RJ-11), 4 pair (8 wire, RJ- 45) n Coax n rs 232 o light: fiber optic (glass/plastic) o air: satellite/microwave 6/20/2021 28

Fiber Optics Cable Phone Cable (RJ-11) 6/20/2021 29

o Dial-up lines - analog, non-dedicated, (POTS -Plain Old Telephone Service) o Leased lines - digital, dedicated, often fiber-based n n 6/20/2021 56 k T 1 - 1. 544 Mbps T 3 - 44 Mbps OC 3/OC 12 30

Modems o POTS (Plain Old Telephone Service) o Modulator/demodulator, digital-->analog-->digital o Carrier wave (base, neutral wave) n Amplitude modulation (am), frequency modulation (fm) n Phase modulation (like radio, am/fm) 6/20/2021 31

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Frequency Modulation of a Carrier Wave 6/20/2021 35

o Baud vs. bps - detectable events (signaling events) n Detect changes in carrier wave o Types of modems - internal/external 6/20/2021 36

Modem Terms o Standards - V. 32 (9600), V. 32 bis (14, 400 or 14. 4) o V. 34 (28. 8), V. 90 (56 k) ---> 56 k max speed o Data compression o Error detection (parity, checksum) o Encryption 6/20/2021 37

Internal Modem External Modem 6/20/2021 38

Cable and DSL Modems o Also called broadband o Sometimes 56 k and below is referred to as narrowband o Higher speeds then 56 k and always online (may be security risk) 6/20/2021 39

DSL Modem Cable Modem 6/20/2021 40

Cable Modems o Cable- digital modem, higher speeds (500 k to 2 meg) o Different upload/download speeds o Shared technology o Uses Cable TV coax cable o Security Concerns 6/20/2021 41

DSL o Digital Subscriber Line - digital modem o Fast speeds but typically less then cable modems o Different upload/download speeds o switched/dedicated technology o Uses new installed line or existing phone line with filters o Speeds of 144 k up to 6 meg o Typically 144 k to 600 k for home users 6/20/2021 42

Bandwidth o Speed o Info carrying capacity of a transmission facility o Range of frequencies, given in hertz (hz), Cycles/sec, that can be accommodated without signal degredation o voice lines 3000 hz (300 to 3300 hz) 6/20/2021 43

Note – DSL and Cable Modems range from 500, 000 bps to 2, 000 bps and thus would be in the around the T 1 range (2 -4 lane highway). (wireless is similar) 6/20/2021 44

Transmission Problems o Attenuation - loss of signal strength over a distance o Crosstalk - interference from neighboring wires o EMI/RFI - electro magnetic interferenceradio frequency interference o Line noise o Solutions - amplifiers, repeaters, shielding, twisted pair, fiber 6/20/2021 45

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RS-232 o Asynch. serial communications standard (1969) o 25 pins (DB-25), copper based (electrical signal) o Handshaking (modems) o DCE/DTE o Null modem connection o 50 feet max o Used with modems, printers, terminals o Typical 2, 3, 7 (send, receive, ground) 6/20/2021 48

RS-232 6/20/2021 49

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RS-232 6/20/2021 52

RS-232 6/20/2021 53

RS-232 6/20/2021 54

Summary 6/20/2021 55

Telecommunications o Low level n Bits n Encoding n Parity n Duplex n Serial n Asynch n etc. . 6/20/2021 56

Hardware o Modems o Mux o T 1 o T 3 o terminal server n (access server) o rs 232 o etc. . 6/20/2021 57

Software o Connect to host n telnet/tn 3270/ssh n terminal emulation n log into host n windows terminal n hyperterminal o File transfer n ftp/sftp 6/20/2021 58

Fun Facts o 1876 – Bell “electrical speech machine” o 1878 – 1 st phone book n New Haven Conn. , 1 page (50 names) o 1883 – 1 st yellow pages. Why yellow? o 1929 – 1 st President with phone in White House ? ? o (Herbert Hoover) 6/20/2021 59

Herbert Hoover 6/20/2021 60

More Fun Facts o Alexander Graham Bell – 29 telephone n n Photophone (speech via light waves) Bell and Elisha Gray (2 hours apart) o First Rotary Phone (non crank) – 1929 o First mobile phone – 1924 NYC police 6/20/2021 61

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THE END 6/20/2021 64