Transmission Systems

Overview
In this area adventurer, you will traverse the obstacle course of Transmission Systems. Successfully master each obstacle and you will find yourself well on your way to exploring this area of TC201.

Fundametals of Transmission Systems

 * Wired vs. Wireless
 * Understand application requirements
 * Optimal balance between
 * Transmission characteristics
 * Propagation delay
 * Security
 * Mechanical strength
 * Physical dimension
 * Cost

Transmission Characteristics

 * Throughput: amount of data system can transmit in a unit of time
 * Factors affecting throughput:
 * Bandwidth
 * Error performance
 * Distance
 * Characteristics are related
 * bandwidth and distance
 * error performance and distance
 * bandwidth and error performance
 * Security Propdelay.png
 * Protection of data from interception
 * Mechanical Strength
 * Physical limits to the amt. of bending, twisting, expanding …..
 * Physical Dimension
 * size, weight….
 * Cost
 * Acquisition, deployment, operation & maint., upgrade & replacement

Propagation Delay

 * Time it takes for signal to travel through the transmission system from sender to receiver
 * Factors influencing propagation delay:
 * Nature of medium
 * Length of circuit
 * Number of network elements on path
 * Amount of processing done on signal

Wired Media

 * Shielded vs. unshielded
 * Protect from external sources of interference (EMI, RFI)
 * Minimize signal loss


 * Gauge Gauge.png
 * Thickness of the conductor
 * Thicker wire
 * More bandwidth
 * Less resistance
 * Greater break strength
 * American Wire Gauge (AWG) – used mostly in U.S.

Unshielded Twisted Pair (UTP)

 * Twisting - Reduce radiation - more twists the better
 * No outer conductorUtp.png
 * Capacity: 1 MHz to 200 MHz
 * Higher category #, better performance
 * Applications: Telephone, ISDN, Token Ring,Ethernet, ADSL
 * Inexpensive for line, expensive for trunk
 * UTP usually ubiquitous in buildings
 * Low to medium capacity
 * Prone to interference, which limits capacity and distances
 * Medium to high loss
 * Easy to intercept

Shielded Twisted Pair

 * Shield protects from EMI, reduce emission
 * better error performance, less attenuationSto.png
 * High cost
 * Applications: high-noise environment, highspeed LAN

Coaxial Cable

 * Consist of a single two conductor wire
 * Better error performance because of shielding
 * Thicker than TP
 * Capacity
 * DistanceCoaxial.png
 * Cost
 * Better security
 * Applications:
 * CATV: old systems: 330 MHz, 40 Ch.
 * past decade: upgraded to 750 MHz, 116 Ch.
 * Older Local Area Networks for computers

Optical Fiber

 * Light source: turn electrical to optical
 * Light Emitting Diode (LED): Cheaper, but multimode, broadly-defined signals
 * Laser Diode: less attenuation, tightly defined signals enabling WDM
 * CableOptical.png
 * Light detector: turn optical to electrical
 * Modal dispersion & Pulse dispersion
 * Refractive index: Step-index vs. graded-index
 * Core diameter: MultiMode vs. SingleMode

Fiber Optics

 * High bandwidth (Gbps – Tbps)
 * Good error performance
 * No EMI/RFI, almost error free (10-9 - 10-14 )Fiboptw.png
 * Can go long distance
 * Highly secure
 * High cost
 * Fragile
 * Used for backbones

Microwave Transmission

 * UHF - EHF frequency ranges
 * substantial bandwidth: T1, T3, >6GbpsMicro.png
 * prone to attenuation & environmental interference
 * more like light than radio, requires line-of-sight
 * use for point-to-point application
 * Antenna centered in reflective dish which can focus the radio beam;
 * Larger dish, higher gain
 * Higher frequency, smaller dish
 * Cost: cheaper than coaxial in long haul application, need licensing
 * Application:
 * Was used for long-haul application (MCI)
 * Is used for private network, carrier bypass, temporary use, alternative to CATV

Satellites

 * Microwave system
 * Highly regulated because of wide footprint, limited number of orbital slots
 * Bandwidth: MHz - GHz
 * Error performance
 * Prone to environmental interference (Sunspot activity)Sats.png
 * Significant propagation delay (.64 sec)
 * Hybrid approach
 * Cheaper than cable in point-to-multipoint application
 * Application
 * Voice, data, private network (VSAT), GPS, DBS

Types of Satellites

 * Low Earth Orbits (LEO)
 * Hundreds to thousands of kilometers
 * Requires inter-satellite links, handoffs like a mobile phone net
 * Medium Earth Orbits (MEO)
 * Tens of thousands of kilometers
 * One revolution every couple hours
 * Geostationary Earth Orbits (GEO)
 * 36,000 miles
 * Largest footprint


 * http://science.nasa.gov/Realtime/JTrack/

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