1. Networking and Telecommunications
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2. Transmission Characteristics
Medium
Air Waves – (satellite, microwaves, wireless lans (infrared, radio waves)
Electrical /Copper (Twisted Pair, Coax)
Light (fiber optic via glass/plastic cable)
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3. 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.
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8. Analog (continuous sine wave)
Watch (with hands),speedometer
digital transmissions (discrete pulses of 0 or 1)
Computers/binary
TV-discrete channels
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9. 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
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10. 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
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11. Transmission Codes = Encoding
(Morse Code)
EBCDIC (8 bit)
ASCII (8bit vs 7bit)
Parity – Even vs. Odd
Half Duplex vs. Full Duplex
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12. EBCDIC vs. ASCII (link) A 1100 0001 0100 0001 B 1100 0010 0100 0010 Z
Character
EBCDIC
ASCII A B Z 5 !
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13. Morse Code
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15. Waves Sound, Electrical, Radio, Electromagnetic
Sine Wave, measured in Hertz (Hz)
Characteristics – Amplitude and Frequency
Bandwidth – difference from high to low frequency range
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16. Speed (modems) Baud vs. BPS 300, 1200, 2400, 9600, 14.4, 28.8, 56k
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17. Modems
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18. Circuit Switching Networks
“Temporary", "dedicated", communications channel
Voice (phone)
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19. 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
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21. 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
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22. Satellite Dish
ATM Machine
Fax Machine
Terminal
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23. 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
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25. 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
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28. 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
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29. Fiber Optics Cable
Phone Cable
(RJ-11)
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30. 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
T Mbps
T Mbps
OC3/OC12
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31. 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)
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35. Frequency Modulation of a Carrier Wave
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36. Baud vs. bps - detectable events (signaling events)
Detect changes in carrier wave
Types of modems - internal/external
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37. 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
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38. Internal Modem
External Modem
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39. 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)
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40. DSL Modem
Cable Modem
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41. Cable Modems Cable- digital modem, higher speeds (500k to 2 meg)
Different upload/download speeds
Shared technology
Uses Cable TV coax cable
Security Concerns
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42. 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
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43. 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)
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44. 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)
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45. 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
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48. 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)
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49. RS-232
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52. RS-232
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53. RS-232
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54. RS-232
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55. Summary
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56. Telecommunications Low level Bits Encoding Parity Duplex Serial Asynch
etc..
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57. Hardware Modems Mux T1 T3 terminal server rs232 etc.. (access server)
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58. Software Connect to host File transfer telnet/tn3270/ssh
terminal emulation
log into host
windows terminal
hyperterminal
File transfer
ftp/sftp
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59. 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)
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60. Herbert
Hoover
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61. 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
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64. THE END
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