Networking and Telecommunications 1/16/2019

Transmission Characteristics Medium Air Waves – (satellite, microwaves, wireless lans (infrared, radio waves) Electrical /Copper (Twisted Pair, Coax) Light (fiber optic via glass/plastic cable) 1/16/2019

Transmission Signals Transmission Types Parallel - all 8 bits at same time serial – 1 bit at a time (rs232), sequential Transmission Types Asynchronous – start/stop bits, one character at a time Synchronous – fast, multiple characters in a block of data. No start/stop bits. 1/16/2019

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Analog (continuous sine wave) Watch (with hands),speedometer digital transmissions (discrete pulses of 0 or 1) Computers/binary TV-discrete channels 1/16/2019

Analog vs. Digital Internal to Computer (digital, binary) Transmissions – originally analog Phone systems – analog totally at first Computers – used modems to talk over analog phone lines (and connections between CO were analog) Today – Connections between CO are digital. Connections between home and CO (last mile) are still mostly analog Cable Modems and DSL – connections from home becoming Digital 1/16/2019

Why Digital better then Analog? Faster (higher capacity) 56k vs. Mbps+ Better data integrity (less errors), distortion of pulses easier to correct Better Security Lower Costs Today No analog to digital conversion needed (no modem) Easier to integrate voice, video, data 1/16/2019

Transmission Codes = Encoding (Morse Code) EBCDIC (8 bit) ASCII (8bit vs 7bit) Parity – Even vs. Odd Half Duplex vs. Full Duplex 1/16/2019

EBCDIC vs. ASCII (link) A 1100 0001 0100 0001 B 1100 0010 0100 0010 Z Character EBCDIC ASCII A 1100 0001 0100 0001 B 1100 0010 0100 0010 Z 1110 1001 0101 1010 5 1111 0101 0011 0101 ! 0010 0001 1/16/2019

Morse Code 1/16/2019

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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 1/16/2019

Speed (modems) Baud vs. BPS 300, 1200, 2400, 9600, 14.4, 28.8, 56k 1/16/2019

Modems 1/16/2019

Circuit Switching Networks “Temporary", "dedicated", communications channel Voice (phone) 1/16/2019

Packet Switching Networks Store and forward, non-dedicated Shared communications channel (packets interleaved on same line) Packets may take different paths, arrive in different order (reassemble at end) X.25 – old WAN standard for PSN Useful for data 1/16/2019

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Telecom Hardware Hosts (mainframe, mini) Micros, workstations (desktop systems) Terminals (vt100, 3270, X-terminals) Automatic Teller Machines (ATM - Banks) POS (Point of Sales - cash registers) Fax Satellite Dishes, Satellites, radar towers Terminal Server (Access Server) MUX (multiplexer) - TDM and FDM Modems 1/16/2019

Satellite Dish ATM Machine Fax Machine Terminal 1/16/2019

Terminal Servers/Access Servers Connect modem pool to internal network Allows outside users to connect in And internal users to dial-out Authentication is normally used 1/16/2019

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Multiplexers Allows multiple systems to share single common communications channel Often used with mainframes/terminals, as well as phone systems 2 Main Methods used: TDM – Time Division Multiplexing FDM – Frequency Division Multiplexing 1/16/2019

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Transmission (telecom.) Media electrical/copper: Phone wire TP - 2 pair (4 wire, RJ-11), 4 pair (8 wire, RJ- 45) Coax rs232 light: fiber optic (glass/plastic) air: satellite/microwave 1/16/2019

Fiber Optics Cable Phone Cable (RJ-11) 1/16/2019

Leased lines - digital, dedicated, often fiber-based Dial-up lines - analog, non-dedicated, (POTS -Plain Old Telephone Service) Leased lines - digital, dedicated, often fiber-based 56k T1 - 1.544 Mbps T3 - 44 Mbps OC3/OC12 1/16/2019

Modems POTS (Plain Old Telephone Service) Modulator/demodulator, digital-->analog-->digital Carrier wave (base, neutral wave) Amplitude modulation (am), frequency modulation (fm) Phase modulation (like radio, am/fm) 1/16/2019

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Frequency Modulation of a Carrier Wave 1/16/2019

Baud vs. bps - detectable events (signaling events) Detect changes in carrier wave Types of modems - internal/external 1/16/2019

Modem Terms Standards - V.32 (9600), V.32bis (14,400 or 14.4) V.34 (28.8), V.90 (56k) ---> 56k max speed Data compression Error detection (parity, checksum) Encryption 1/16/2019

Internal Modem External Modem 1/16/2019

Cable and DSL Modems Also called broadband Sometimes 56k and below is referred to as narrowband Higher speeds then 56k and always online (may be security risk) 1/16/2019

DSL Modem Cable Modem 1/16/2019

Cable Modems Cable- digital modem, higher speeds (500k to 2 meg) Different upload/download speeds Shared technology Uses Cable TV coax cable Security Concerns 1/16/2019

DSL Digital Subscriber Line - digital modem Fast speeds but typically less then cable modems Different upload/download speeds switched/dedicated technology Uses new installed line or existing phone line with filters Speeds of 144k up to 6 meg Typically 144k to 600k for home users 1/16/2019

Bandwidth Speed Info carrying capacity of a transmission facility Range of frequencies, given in hertz (hz), Cycles/sec, that can be accommodated without signal degredation voice lines 3000 hz (300 to 3300 hz) 1/16/2019

Note – DSL and Cable Modems range from 500,000 bps to 2,000,000 bps and thus would be in the around the T1 range (2-4 lane highway). (wireless is similar) 1/16/2019

Transmission Problems Attenuation - loss of signal strength over a distance Crosstalk - interference from neighboring wires EMI/RFI - electro magnetic interference- radio frequency interference Line noise Solutions - amplifiers, repeaters, shielding, twisted pair, fiber 1/16/2019

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RS-232 Asynch. serial communications standard (1969) 25 pins (DB-25), copper based (electrical signal) Handshaking (modems) DCE/DTE Null modem connection 50 feet max Used with modems, printers, terminals Typical 2,3,7 (send, receive, ground) 1/16/2019

RS-232 1/16/2019

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RS-232 1/16/2019

RS-232 1/16/2019

RS-232 1/16/2019

Summary 1/16/2019

Telecommunications Low level Bits Encoding Parity Duplex Serial Asynch etc.. 1/16/2019

Hardware Modems Mux T1 T3 terminal server rs232 etc.. (access server) 1/16/2019

Software Connect to host File transfer telnet/tn3270/ssh terminal emulation log into host windows terminal hyperterminal File transfer ftp/sftp 1/16/2019

Fun Facts 1876 – Bell “electrical speech machine” 1878 – 1st phone book New Haven Conn., 1 page (50 names) 1883 – 1st yellow pages. Why yellow? 1929 – 1st President with phone in White House ?? (Herbert Hoover) 1/16/2019

Herbert Hoover 1/16/2019

More Fun Facts Alexander Graham Bell – 29 telephone Photophone (speech via light waves) Bell and Elisha Gray (2 hours apart) First Rotary Phone (non crank) – 1929 First mobile phone – 1924 NYC police 1/16/2019

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THE END 1/16/2019