FUNDAMENTAL CONCEPTS

1. FUNDAMENTAL CONCEPTS • Analog versus Digital • Bandwidth (or channel capacity) • Switched vs. leased lines • Transmission Media • Transmission mode (parallel/serial, synchronous/asynchronous • Transmission method (simplex, half-duplex, full-duplex)

2. Digital or analog channel. . . . Recall there are 2 types of signals: digital and analog. Similarly, there are two types of channels... Digital Channels - designed to carry digital signals, i.e. 0's and 1's - signal becomes weak every few miles - need BIT REPEATERS to strengthen it

3. - designed to carry analog signals, like speech - signal again becomes weak every few miles - need AMPLIFIERS (instead of BIT REPEATERS) Analog Channels Digital versus Analog • Digital channels are better. • Increasingly the phone network is becoming digital. • More than 90% lines in the US telephone network are digital now (e.g., Sprint is 100% digital).

4. Bandwidth of channel Digital Channel B.W. (or channel capacity) is defined in Bits/sec. that can flow through it. (Also called DATA RATE.) Analog Channel B.W. defined in terms of cycles/sec. (or Hertz) e.g. B.W. of telephone line to carry speech is approx. 3000 Hz.

5. Note: 1) Highest frequency component in speech is about 4000 Hz. 2) Bandwidth required to transmit an analog signal across an analog channel is determined by the highest frequency component in the signal. 3) Rapid changes in signal level correspond to high frequency. gradual changes in signal level correspond to low frequency.

6. Electromagnetic Spectrum Source: Tannenbaum, Computer Networks, 3rd Ed., 1996

7. Bandwidth Human ear: 20 Hz to 20,000 Hz. FM radio: 50 Hz to 15 KHz. Human voice - 100 Hz to 4000 Hz. Telephone 300 Hz. To 3 KHz. Color television: 6 MHz.

8. Properties of Analog Signals • Amplitude (volume) is the height of a wave • Frequency (pitch) is measured in cycles per second • Phase corresponds to the wave’s relative position • Bandwidth is the difference between the lowest and highest • frequency (measured in cycles per second or Hz.) • In general, voice contains many different frequencies.

9. Kai Larsen: When does switching make sense? When does leasing make sense?

10. Transmission Media - Copper wire STP - shielded twisted pair UTP - unshielded twisted pair - Pairs of wire from home to local telephone company office - Limited bandwidth - Deteriorates at high frequency - Ubiquitous on the local loop. - Wires are twisted together in helical pattern to minimize noise and interference. Kai Larsen: Try twisting the power-cord on your clock-radio, check receptions at different levels of twisting!

11. Transmission media - Twisted Pair Copper • Bandwidth related to distance and thickness but Mbps are possible over small distance. • Two Types commonly used in networks are: Category 3 and Category 5 (UTP). • Most buildings wired before 1988 are Cat 3 (2 or 4 pairs). • After 1988 generally use Cat 5 (more twists perinch, less cross-talk). • Cat 5E

12. Conductor Insulation Shielding Outer Jacket Insulation Transmission media - Coaxial Cable Two types: 1) Baseband. 2) Broadband.

13. Transmission media - Coaxial Baseband • Single digital channel. • Shielding provides high bandwidth and good noise immunity. • ~2 Gbps on a 1 Kilometer cable. • Used for original Ethernet. Broadband • Divides bandwidth into multiple channels • Can transmit 300 MHz for long distances (100 km) • Uses: TV (6 MHz per channel); CD audio; data.

14. Kai Larsen: Two Norwegians who started skiing towards the North Pole, 255 km into their 1,741 km long journey… relying only on their Iridium satellite telephone receives the final call… Iridium was going down…Motorola, however, decided to provided mission critical service…June 3rd 2000 they reached the pole. Ever since, the pole has been without telephone coverage… Satellites…success and failure The Iridium story: Rune Gjeldnes and Torry Larsen attempting to be the first explorers to reach the North Pole completely un- supported. Start weight of sledges: 175 kilos, each… 1741 km long journey…Nine expeditions had tried before…all failed… Source: http://www.geom.umn.edu/~worfolk/SaVi/interactive.html

15. Transmission media - Wireless Satellite - Transmit signal to satellite 22,230 miles in space (GEOs) - 0.5 - 0.6 sec. delay in transmission. - Various bands between 1 and 40 GHz are used for satellite transmission. - 600 MHz band at 12 GHz => 200,000 telephone channels or 100 TV channels. Other types of satellites: LEO, MEO, HALE. Kai Larsen:Did you know that: GEO -> Geo-stationary orbitMEO -> Medium Earth OrbitLEO -> Low Earth OrbitHALE -> High Altitude Long Endurance

16. Transmission media - Microwave • No physical medium - i.e., wireless. • Based on radio waves above 100 MHz. • Signal is beamed from transmission tower. • Microwaves travel in straight lines • Usually place 100m towers 50 miles apart. • Used for long distance telephone • Subject to weather interference (e.g., rain)

17. - Latest technology, current speeds > 10 Gbps - Hair thin strands of glass, called optical fibers - Light pulses travel through high quality glass . - Need repeaters every 20 km. - Single fiber-optic cable carries several 100,000 calls. Phone Detector Transmission media - Fiber Optics Light Phone Coder Source Decoder Regenerator

18. Transmission media - Fiber Optics Plastic Sheathing Cladding Glass Core Multi-mode Fiber (50 micron core/125 micron cladding)

19. Transmission media - Fiber Optics Single mode Fiber (8/125 microns) Plastic Sheathing Cladding Glass Core

20. Transmission Modes I. Mode of Transmission Serial - bit at a time or Parallel - Byte at a time Serial is the most common mode of transmission. II. Types of serial transmissions. 1. Synchronous Synchronization character synchronizes the two ends - then, entire message is sent 8-bit flag Control fields Data field Control fields 8-bit flag

21. S S S S S S S S S S S S S S S S S S S S S S T T T T T T T T T T T 8-BIT 8-BIT 8-BIT 8-BIT 8-BIT 8-BIT 8-BIT 8-BIT 8-BIT 8-BIT 8-BIT T T T T T T T T T T T A A A A A A A A A A A CHARACTER CHARACTER CHARACTER CHARACTER CHARACTER CHARACTER CHARACTER CHARACTER CHARACTER CHARACTER CHARACTER O O O O O O O O O O O R R R R R R R R R R R P P P P P P P P P P P This is conceptually easier, but overhead is higher T T T T T T T T T T T Asynchronous Send separatestart and stop bits with each character S S S S T 8-BIT T T 8-BIT T A CHARACTER A BLANK O CHARACTER O R R P P T T

22. Kai Larsen: Think about how the class situation works between professor and students

23. CHANNEL AND SIGNAL TYPE COMBINATIONS CHANNEL TYPE Digital Analog Send with Convert slight signal to Digital modification analog form - Analog SIGNAL Modulation (modem) TYPE Digitize signal Analog (Pulse Code Send as is Modulation) Modulating a signal means to adapt it so that it can be transmitted over the type of transmission media in use.

24. Cable Selection Criteria • Bandwidth: How fast must the network be? • Budget: How much money can you spend on cabling? • Capacity: How much traffic must the network carry? How will the traffic flow? • Environmental considerations: How noisy is the deployment environment? How important is data security? • Placement: Where will the cables run? How tight are the spaces? • Scope: How many devices must be connected to the network? • Span: What kind of distance does the network need to span?

25. Assignment • Please find a partner or two (or three) • Your task: • Select the home of one group member • Design a home network around the seven cable selection criteria • Write up your solution on a transparency • Select one person to present solution • Time?