Introduction to Computer Networks For ECE1001 Dr. Taek Mu Kwon Department of Electrical and Computer Engineering, UMD

Outline ECE 4321 Networks Today Optical Fiber Technology Wireless Technology Conclusion

ECE 4321 Computer Networks ECE Technical Elective Course 3 Credits Network Lab (MWAH 60) Network Programming Project (3 – 4) Written Exams Course Objective: To learn about the characteristics of network transmission media, OSI model, TCP/IP, data link protocols, routing algorithms, various LAN technologies, WAN technologies, and network programming.

Integrated Digital Service Revolution ( ) 1.No boundary between public and private networks (security through virtual private network) 2.Single mode of transmission for data/voice/video: high speed multimedia 3.No difference between wired and wireless Multipurpose global network that can be accessed any time, anywhere

Required Technology Advances for Digital Service Revolution  Elimination of present multiple, complex, costly networks and integrate them into one high speed multipurpose network.  Always ON: accessible anytime from anywhere  Improved mobility by reliable wireless/wired technology  High definition multimedia to any connection  Smart network that works like power plug  High speed optical network to home and office

Why Optical Fiber? 1 lb of optical fiber can transmit information equivalent to 2 metric tons of copper A single optical fiber can carry 60 million simultaneous phone calls Can transmit the entire 30 volume Encyclopedia Britannica within a fraction second from NY to CA.

Transmission Characteristics of Guided Media Frequency Range Typical Attenuation Typical Delay Repeater Spacing Twisted pair (with loading) 0 to 3.5 kHz0.2 1 kHz 50 µs/km2 km Twisted pairs (multi-pair cables) 0 to 1 MHz0.7 1 kHz 5 µs/km2 km Coaxial cable0 to 500 MHz7 10 MHz 4 µs/km1 to 9 km Optical fiber186 to 370 THz 0.2 to 0.5 dB/km 5 µs/km40 km

Attenuation of Typical Guided Media

Who invented Optical Fiber? Invented in Aug by Dow Corning Scientists: Dr. Donald Keck, Dr. Bob Maurer and Dr. Peter Schultz Invention was motivated by space limitation of telephone wires

First Large Commercial Use Nationwide long-distance telephone network by MCI using single-mode optical fiber, 1983 Since then more than 300 million km of optical fiber lines have been deployed worldwide.

What is Optical Fiber? A thin flexible medium capable of conducting an optical ray. The basic material consists of silicon dioxide, silica, and plastic.

Snell’s Law Fused Silica Refractive index = n1 Cladding Refractive index = n2 ii tt

Internal Structure of Optical Fiber

Optical Fiber Types Multimode (Orange Color) * Stepped index * Grade index Singlemode (Yellow Color) The fiber diameter is one wavelength of light (1um)

Wavelength Division Multiplexing (WDM) Multiple beams of different wavelengths are transmitted over the same fiber Transmission of one Tbps was achieved by 100 beams each operating at 10 Gbps (1997 Bell Lab)

Wavelengths Used in Optical Fiber Wavelength (in vacuum) range (nm) Frequency range (THz) Band label Fiber typeApplication 820 to to 333 MultimodeLAN 1280 to to 222SSingle modeVarious 1528 to to 192CSingle modeWDM 1561 to to 192LSingle modeWDM

Next Revolution of Optical Fiber Optical switching and routing High bandwidth all-optical network Fiber To The Home (FTTH)

Free Space Optics

Characteristic Summary of Optical Fiber Greater bandwidth Smaller size and light weight Lower attenuation E&M isolation Greater repeater spacing Greater security

Wireless Networks Provide mobility with true any time any where access.

Wireless Transmission Frequencies 2GHz to 40GHz – Microwave – Highly directional – Point to point – Satellite 30MHz to 1GHz – Omnidirectional – Broadcast radio 3 x to 2 x – Infrared – Local

Terrestrial Microwave Parabolic dish Focused beam Line of sight Long haul telecommunications Higher frequencies give higher data rates

Satellite Point to Point Link

Satellite Broadcast Link

Wireless Propagation Ground wave Follows contour of earth Up to 2MHz AM radio Sky wave Amateur radio, BBC world service, Voice of America Signal reflected from ionosphere layer of upper atmosphere (Actually refracted) Line of sight Above 30Mhz May be further than optical line of sight due to refraction

Ground Wave Propagation

Sky Wave Propagation

Line of Sight Propagation

Line of Sight Transmission (1) Atmospheric Absorption – Water vapour and oxygen absorb radio signals – Water absorption: greatest at 22GHz, less below 15GHz – Oxygen absorption: greater at 60GHz, less below 30GHz – Rain and fog scatters radio waves Free space loss – Signal disperses with distance – Greater for lower frequencies (longer wavelengths)

Optical and Radio Horizons

Line of Sight Transmission (2) Multipath – Better to get line of sight if possible – Signal can be reflected causing multiple copies to be received – May be no direct signal at all – May reinforce or cancel direct signal Refraction – May result in partial or total loss of signal at receiver

Multipath Interference

Concluding Remark In order to advance to the next generation of always ON, anytime, anywhere access, to data/voice/video, today’s diverse complex network and protocols must be unified to a multipurpose, multimedia network. More bandwidth and significant improvement in wireless technology are needed. Evolution on computer networks will continue providing many opportunities