Media Concept and classification of Media

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19 de Jan de 2015

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Media Concept and classification of Media

  1. Media Concept and classification of Media 1 Presenter: Purushottam Dahal
  2. Contents  Guided Media  Twisted pair overview  Coaxial cable overview  Fiber optics overview  Unguided Media  VSAT  Satellite  Transmission Characteristics  Attenuation  Noise  Signal to Noise Ratio  Propagation Delay 1/19/2015 2
  3. Guided Transmission Media  Purpose is to transfer raw bit stream  Related with physical layer  Various physical medias can be used  Magnetic media, removable medias  Transfer rate, depends upon distance and media used. Same media may contain various transfer rates with high degree of variation. 1/19/2015 3
  4. Twisted Pair  Bandwidth characteristics of Magnetic tape and other removable media is excellent, the delay characteristics is very poor.  Transmission time is measured in minutes or hours, not milliseconds.  One of the oldest and still most common transmission media is twisted pair  A cable made by intertwining two separate insulated wires together 1/19/2015 4
  5. Types of Twisted Pair UTP STP 1/19/2015 5
  6. Name Type Bandwidth Applications Level 1 0.4 MHz Telephone and modem lines Level 2 4 MHz Older terminal systems, e.g. IBM 3270 Cat3 UTP 16 MHz 10BASE-T and 100BASE-T4 Ethernet Cat4 UTP 20 MHz 16 Mbit/s Token Ring Cat5 UTP 100 MHz 100BASE-TX & 1000BASE-T Ethernet Cat5e UTP 100 MHz 100BASE-TX & 1000BASE-T Ethernet Cat6 UTP 250 MHz 10GBASE-T Ethernet Cat6a 500 MHz 10GBASE-T Ethernet Class F S/FTP 600 MHz Telephone, CCTV, 1000BASE-TX in the same cable. 10GBASE-T Ethernet. Class Fa 1000 MHz Telephone, CATV, 1000BASE-TX in the same cable. 10GBASE-T Ethernet. 1/19/2015 6
  7. Co-axial Cable  It has better shielding than twisted pairs, so it can span longer distances at higher speeds.  Two kinds of coaxial cable are widely used.  One kind, 50-ohm cable, is commonly used when it is intended for digital transmission from the start. The other kind, 75-ohm cable, is commonly used for analog transmission and CATV, but is becoming more important with the advent of Internet over cable.  The construction and shielding of the coaxial cable give it a good combination of high bandwidth and excellent noise immunity.  The bandwidth possible depends on the cable quality, length, and signal-to-noise ratio of the data signal.  Modern cables have a bandwidth of close to 1 GHz. 1/19/2015 7
  8. Coaxial Cable Cut away View 1/19/2015 8
  9. Fiber Optics  A technology that uses glass (or plastic) threads (fibers) to transmit data. A fiber optic cable consists of a bundle of glass threads, each of which is capable of transmitting messages modulated onto light waves.  An optical transmission system has three key components: the light source, the transmission medium, and the detector.  Conventionally, a pulse of light indicates a 1 bit and the absence of light indicates a 0 bit.  The transmission medium is an ultra-thin fiber of glass. The detector generates an electrical pulse when light falls on it.  By attaching a light source to one end of an optical fiber and a detector to the other, we have a unidirectional data transmission system that accepts an electrical signal, converts and transmits it by light pulses, and then reconverts the output to an electrical signal at the receiving end. 1/19/2015 9
  10. CONT……..  Fiber optics has several advantages over traditional metal communications lines:  Fiber optic cables have a much greater bandwidth than metal cables. This means that they can carry more data.  Fiber optic cables are less susceptible than metal cables to interference.  Fiber optic cables are much thinner and lighter than metal wires.  Data can be transmitted digitally (the natural form for computer data) rather than analogically. 1/19/2015 10
  11. A Bundle of Optical Fibers The structure of a typical single-mode fiber. 1. Core: 8 µm diameter 2. Cladding: 125 µm dia. 3. Buffer: 250 µm dia. 4. Jacket: 400 µm dia 1/19/2015 11
  12. VSAT  A very small aperture terminal (VSAT), is a two-way satellite ground station or a stabilized maritime VSAT antenna with a dish antenna that is smaller than 3 meters.  The majority of VSAT antennas range from 75 cm to 1.2 m.  Data rates range from 4 Kbit/s up to 4 Mbit/s; some upgraded modules can even reach a max downlink of up to 16 Mbit/s.  VSATs access satellites in geosynchronous orbit to relay data from small remote earth stations (terminals) to other terminals (in mesh topology) or master earth station "hubs" (in star topology). 1/19/2015 12
  13. Satellite  A satellite is an artificial object which has been intentionally placed into orbit.  Such objects are sometimes called artificial satellites to distinguish them from natural satellites such as the Moon.  Satellite is a specialized wireless receiver/transmitter that is launched by a rocket and placed in orbit around the earth.  There are hundreds of satellites currently in operation. They are used for such diverse purposes as weather forecasting, television broadcast, amateur radio communications, Internet communications, and the Global Positioning System(GPS). 1/19/2015 13
  14. Attenuation  Attenuation is a general term that refers to any reduction in the strength of a signal.  Attenuation is a general term that refers to any reduction in the strength of a signal.  Attenuation occurs with any type of signal, whether digital or analog.  Sometimes called loss, attenuation is a natural consequence of signal transmission over long distances.  The extent of attenuation is usually expressed in units called decibels (dBs). 1/19/2015 14
  15. Noise  Noise is unwanted electrical or electromagnetic energy that degrades the quality of signals and data.  Noise occurs in digital and analog systems, and can affect files and communications of all types, including text, programs, images, audio, and telemetry.  In a hard-wired circuit such as a telephone-line-based Internet hookup, external noise is picked up from appliances in the vicinity, from electrical transformers, from the atmosphere, and even from outer space.  Normally this noise is of little or no consequence. However, during severe thunderstorms, or in locations were many electrical appliances are in use, external noise can affect communications.  In an Internet hookup it slows down the data transfer rate, because the system must adjust its speed to match conditions on the line. In a voice telephone conversation, noise rarely sounds like anything other than a faint hissing or rushing. 1/19/2015 15
  16. Signal-to-Noise Ratio  In analog and digital communications, signal-to- noise ratio, often written S/N or SNR, is a measure of signal strength relative to background noise.  The ratio is usually measured in decibels (dB).  Communications engineers always strive to maximize the S/N ratio. 1/19/2015 16
  17. Propagation Delay  Propagation delay is the amount of time it takes for the head of the signal to travel from the sender to the receiver.  Propagation delay refers to the time lag between the departure of a signal from the source and the arrival of the signal at the destination.  It can be computed as the ratio between the link length and the propagation speed over the specific medium. 1/19/2015 17
  18. “ ” THANK YOU 1/19/2015 18