Transmission media and switching


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guided and unguided media and switching techniques

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Transmission media and switching

  1. 1. Transmission media
  2. 2. Guided media  Those that provide a conduit from one device to another.  Types include: ◦ Twisted pair ◦ Coaxial ◦ Fiber optic  A signal travelling along these medium is directed and contained by the physical limits of the medium.  Twisted pair and coaxial cable use metallic conductors, transporting signals in electrical current  Optical fiber is a glass or plastic cable that accepts and transports signals in form of light.
  3. 3. Twisted pair Cable  Types: ◦ unshielded twisted pair(UTP) ◦ Shielded twisted pair(STP)
  4. 4. Coaxial Cable
  5. 5. Categories of coaxial cables Category Impedance Use RG-59 75 W Cable TV RG-58 50 W Thin Ethernet RG-11 50 W Thick Ethernet
  6. 6. OPTICAL FIBER  An optical fiber (or fibre) is a glass or plastic fiber (pipe) that carries light along its length.  Light is kept in the "core" of the optical fiber by total internal reflection.
  7. 7. Unguided Media: Wireless  Radio Waves  Microwaves  Infrared
  8. 8. Band Range Propagation Application VLF 3–30 KHz Ground Long-range radio navigation LF 30–300 KHz Ground Radio beacons and navigational locators MF 300 KHz–3 MHz Sky AM radio HF 3–30 MHz Sky Citizens band (CB), ship/aircraft communication VHF 30–300 MHz Sky and line-of-sight VHF TV, FM radio UHF 300 MHz–3 GHz Line-of-sight UHF TV, cellular phones, paging, satellite SHF 3–30 GHz Line-of-sight Satellite communication EHF 30–300 GHz Line-of-sight Long-range radio navigation
  9. 9. Radio waves are used for multicast communications, such as radio and television, and paging systems. Note:
  10. 10. Microwaves are used for unicast communication such as cellular telephones, satellite networks, and wireless LANs. Note:
  11. 11. Infrared signals can be used for short- range communication in a closed area using line-of-sight propagation. Note:
  12. 12. Switching  How to connect multiple devices so as one to one communication is possible?  Solution: different topologies  Drawbacks of different topologies  Switched network consists of series of interlinked nodes called switches.  Switches are hardware and/or software devices capable of creating temporary connections between two or more devices linked to the switch
  13. 13. Types of switching  Circuit switching  Packet switching  Message switching
  14. 14. Circuit Switching  Creates a direct physical connection between two devices  It may have n inputs and m inputs  May implement space division switching or time division switching
  15. 15. A circuit switch
  16. 16. Packet Switching  Drawbacks of circuit switch ◦ Less suited for data communication ◦ Data rate is slow ◦ System is inflexible  In packet switch, data are transmitted in discrete units of variable length blocks called packets  Types: ◦ Datagram approach ◦ Virtual circuit approach
  17. 17. Datagram approach  In this approach, Each packet is treated independently, here each packet is referred to as datagram  Each message is divided into several datagrams, and each datagram may go different paths to reach their destination  This can cause datagrams to arrive at destination out of order. The transport layer takes the responsibility of reordering these out of order datagrams before they are given to destination port
  18. 18. Virtual circuit approach  Here the relationship between each packet is maintained  When data is sent, all packets of the transmission travel one after the another along a dedicated route  Can be implemented in two formats: ◦ Switched virtual circuit ◦ Permanent virtual circuit
  19. 19.  Similar to circuit switching, in SVC, a virtual circuit is created whenever it is required and this connection exists only for the duration of the transmission  Only one route is established in SVC  In the case of PVC, the same virtual circuit is established between two users but on a continuous basis  Much like a dedicated link to dedicated users
  20. 20. Message switching  It is best known otherwise as STORE AND FORWARD  Here a node receives messages, stores it until an appropriate route is free and then it sends it.  Not much in use today, due to requirement of large storage capacity and delays.