SYST5030/ FUNDAMENTAL CONCEPTS UAnalog versus Digital UBandwidth (or channel capacity) USwitched vs. leased lines UTransmission Media UTransmission mode (parallel/serial, synchronous/asynchronous UTransmission method (simplex, half-duplex, full-duplex)

SYST5030/ 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

SYST5030/ Analog Channels -designed to carry analog signals, like speech -signal again becomes weak every few miles -need AMPLIFIERS (instead of BIT REPEATERS) 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).

SYST5030/ 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 Hz.

SYST5030/ 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.

SYST5030/ Electromagnetic Spectrum Source: Tannenbaum, Computer Networks, 3rd Ed., 1996

SYST5030/ Human ear: 20 Hz to 20,000 Hz. FM radio: 50 Hz to 15 KHz. Human voice Hz to 4000 Hz. Telephone 300 Hz. To 3 KHz. Color television: 6 MHz. Bandwidth

SYST5030/ 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. Properties of Analog Signals

SYST5030/ Kai Larsen: When does switching make sense? When does leasing make sense? Kai Larsen: When does switching make sense? When does leasing make sense?

SYST5030/ Transmission Media - Copper wire - 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. STP - shielded twisted pair UTP - unshielded twisted pair Kai Larsen: Try twisting the power-cord on your clock-radio, check receptions at different levels of twisting! Kai Larsen: Try twisting the power-cord on your clock-radio, check receptions at different levels of twisting!

SYST5030/ Transmission media - Twisted Pair Copper l Bandwidth related to distance and thickness but Mbps are possible over small distance. l Two Types commonly used in networks are: Category 3 and Category 5 (UTP). l Most buildings wired before 1988 are Cat 3 (2 or 4 pairs). l After 1988 generally use Cat 5 (more twists per inch, less cross-talk). Cat 5E

SYST5030/ Outer Jacket Insulation Shielding Insulation Conductor Transmission media - Coaxial Cable Two types: 1) Baseband. 2) Broadband.

SYST5030/ Baseband l Single digital channel. l Shielding provides high bandwidth and good noise immunity. l ~2 Gbps on a 1 Kilometer cable. l Used for original Ethernet. Broadband l Divides bandwidth into multiple channels l Can transmit 300 MHz for long distances (100 km) l Uses: TV (6 MHz per channel); CD audio; data. Transmission media - Coaxial

SYST5030/ Satellites… success and failure Source: 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 3 rd 2000 they reached the pole. Ever since, the pole has been without telephone coverage… 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 3 rd 2000 they reached the pole. Ever since, the pole has been without telephone coverage… 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…

SYST5030/ Transmit signal to satellite 22,230 miles in space (GEOs) sec. delay in transmission. - Various bands between 1 and 40 GHz are used for satellite transmission MHz band at 12 GHz => 200,000 telephone channels or 100 TV channels. Other types of satellites: LEO, MEO, HALE. Transmission media - Wireless Satellite Kai Larsen: Did you know that: GEO -> Geo-stationary orbit MEO -> Medium Earth Orbit LEO -> Low Earth Orbit HALE -> High Altitude Long Endurance Kai Larsen: Did you know that: GEO -> Geo-stationary orbit MEO -> Medium Earth Orbit LEO -> Low Earth Orbit HALE -> High Altitude Long Endurance

SYST5030/ More on Satellites Various bands between 1 and 40 GHz are used for satellite transmission (C-, Ku-, Ka- frequency bands most common). L-band (1 to 2 GHz): mobile satellite services, cell phones C-band (4 to 8 Ghz): fixed satellite services, microwave Ku-band and K-band: broadcast and fixed services (12.5 to 26.5 GHz)

SYST5030/ Transmission media - Microwave l No physical medium - i.e., wireless. l Based on radio waves above 100 MHz. l Signal is beamed from transmission tower. l Microwaves travel in straight lines l Usually place 100m towers 50 miles apart. l Used for long distance telephone l Subject to weather interference (e.g., rain)

SYST5030/ Phone Coder Light Source Regenerator Decoder Phone -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. Detector Transmission media - Fiber Optics

SYST5030/ Transmission media - Fiber Optics Glass Core Cladding Plastic Sheathing Multi-mode Fiber (50 micron core/125 micron cladding)

SYST5030/ Transmission media - Fiber Optics Glass Core Cladding Plastic Sheathing Single mode Fiber (8/125 microns)

SYST5030/ l Refraction property prevents loss of light and allows the signal to travel long distances. l Multi-mode fiber - 50 micron core. Multiple paths for a given light ray. l Single-mode fiber - 8 micron core. Single path. l Multi-mode is cheaper and more common and gives about 1 Gbps at 5 to 10 miles. Transmission media - Fiber Optics

SYST5030/ Transmission media - Fiber Optics l Single-mode is more expensive and gives up to 2 Gbps to about 20 miles. l Attenuation depends on wavelength of light and there are three wavelengths that are more popular (.85, 1.3 and 1.55 micron - most devices use first or second). l Light disperses (signal smears out) especially in multi-mode since individual rays take paths of different lengths.

SYST5030/ 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 8-bit flag Control fields Control fields Data field

SYST5030/ Asynchronous Send separate start and stop bits with each character S T A R T 8-BIT CHARACTER S T O P BLANK S T A R T S T O P 8-BIT CHARACTER This is conceptually easier, but overhead is higher S T A R T 8-BIT CHARACTER S T O P S T A R T 8-BIT CHARACTER S T O P S T A R T 8-BIT CHARACTER S T O P S T A R T 8-BIT CHARACTER S T O P S T A R T 8-BIT CHARACTER S T O P S T A R T 8-BIT CHARACTER S T O P S T A R T 8-BIT CHARACTER S T O P S T A R T 8-BIT CHARACTER S T O P S T A R T 8-BIT CHARACTER S T O P S T A R T 8-BIT CHARACTER S T O P S T A R T 8-BIT CHARACTER S T O P

SYST5030/ Kai Larsen: Think about how the class situation works between professor and students Kai Larsen: Think about how the class situation works between professor and students

SYST5030/ CHANNEL AND SIGNAL TYPE COMBINATIONS Modulating a signal means to adapt it so that it can be transmitted over the type of transmission media in use. DigitalAnalog Digital Analog SIGNAL TYPE Send with slight modification Digitize signal (Pulse Code Modulation) Send as is Convert signal to analog form - Analog Modulation (modem) CHANNEL TYPE

SYST5030/ 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?

SYST5030/4030 Assignment §Please find a partner or two (or three) §Your task: l Select the home of one group member l Design a home network around the seven cable selection criteria l Write up your solution on a transparency §Select one person to present solution §Time?