7-Transmission Media

1. 7-Transmission Media DR. JOHN ABRAHAM UNIVERSITY OF TEXAS PANAM

2. Transmission Media • Guided – exact path – physical media • Unguided – radio transmission

3. Taxonomy by forms of Energy • Electromagnetic, light, electrical

4. Background Radiation and electrical Noise • Random electromagnetic radiation (noise). • When electrical signals propagate down a wire, electromagnetic energy is radiated (i.e., the wire acts like an antenna) • When electromagnetic radiation encounters metal, a small electrical current is induced that can interfere with signals being carried on the wire • When an electrical pulse is sent down an unterminated wire, reflection comes back • When a signal passes across the connection between two • wires, reflection and loss occur • Note: a network diagnostic tool uses reflection to find the distance to the point where a cable has been cut

6. Twisted pair Unshielded UTP Shielded STP Both wires in a twisted pair is affected equally in case of Noise giving a net difference of 0. In parallel wires the one closer to the noise source will be affected more, giving a net difference.

8. Twisted Pair Ten Base-T UTP Connector Type RJ-45 Cat 3 up to 16MHz Cat 4 up to 20MHz Cat 5 up to 100 MHz More twists per cm and teflon insulation Cat 5e noise immunity 125 mbps Cat 6 – 200 mbps Cat 7 foil shielded around the entire set of wires. 600 Mbpps

9. Twisted pair wiring scheme • 1. Orange white • 2. Orange • 3. Green white • 4. blue • 5. Blue white • 6. Green • 7. Brown white • 8. Brown

10. Crossover cable

11. Hub is a multiport repeater (operates in Layer1 OSI) Every transmission from one port is amplified and retransmitted on all other ports The maximum length of any segment is 100 meters UTP contd

12. Using FDM coaxial can carry over 10,000 voice channels When FDM is used CATV is called Broadband Good for both analog and digital signals Greater attenuation of signals, therefore amplifiers and repeaters are used frequently. 50 ohm cable is for digital transmission 75 ohm for TV Coaxial cable

13. Single line - multiple connections FDM - frequency division - most widespread A number of signals can be carried simultaneously if each signal is modulated onto a different carrier frequency Multiplexing

14. Each modulated signal requires a certain bandwidth (called a channel) Channels are separated by bands of unused portions Broadcast TV - each channel requires 6Mhz. Coaxial cable has 500 MHz bandwidth Voice only requres 4 KHz

15. Synchronous Time Division Multiplexing Possible when the available data rate of a medium exceeds the data rate of a digital signal to be transmitted. Interleave bits or blocks at a time TDM

16. Time Division Multiplexing • The general alternative to FDM is • time division multiplexing (TDM) • In TDM sources share a medium by ``taking turns'' • There are two types of TDM: • Synchronous Time Division Multiplexing (STDM) • arranges for sources to proceed in a round-robin manner • also known as Slotted Time Division Multiplexing

17. Statistical Multiplexing • Works similar to STDM, but if a given source does not have data to send, the multiplexor skips that source • Most NW use a form of statistical multiplexing because computers do not all generate data at exactly the same rate

18. Thick 10base5 up to 1650 feet -requires trnsceivers High Bandwidth - use FDM or TDM Thin Coax 10base2 - up to 607 feet T-connectors and 50 ohm resitors No more 30 devices on a segment No more than 5 segments in a single LAN Only 3 of these segments may have devices (90) others are repeaters. Coaxial cable contd

19. Greater capacity 2 Gbps over tens of kilometers Repeaters needed only every 8 KM Smaller size & weight Materials used Plastic (short haul) Glass Fused Silica (best) Fiber Optics

20. http://www.datacottage.com/nch/fibre.htm lower attenuation electromagnetic isolation Use LED or ILD light emitting diode, Injection Laser diode Use Photodiode to detect PIN photodiode APD photodiode One - short pulse of light, Zero-absence of light Fiber contd

21. Core Cladding optical properties differ between core and cladding. Cladding has lower refractive index Jacket to protect against moisture, crushing, etc. Fiber contd

22. Light propagates from one end to another in one of the following ways mono mode (straight line) the source is laser Most expensive Multimode stepped index the source is LED Bounces of cladding Multimode graded index The cladding refractive index increases as it moves away from the core Fiber contd

23. Fiber Optic Networks Taps are difficult Two types of interface Passive interface one end has an LED or laser diode The other end has photodiode Active interface incoming light is converted to electric signal Signal is generated to full strength Tap into the signal generator

24. Wireless Transmission Radio Microwave Infrared Laser light

25. Telephone We skip most of it The phone system is divided into 2 parts Outside plant Local loops and trunks Inside plant Switches

31. Stop here

32. Switching 1. Circuit Switching A physical connection (circuit) is established between the sender and the receiver. (Similar to operator plugging in – old days) This path is called an end-to-end path. Time used to find the path adds enormous overhead. Entire bandwidth is reserved even when there are gaps in communiction. 2. Message Switching No physical path is established. The data is sent to the first switching office. Stored, forwarded later, one hop at a time.

33. Switching continued. This is known as store-and-forward network. The message could be typed and saved to punched tape and forwarded later. There was no block size limit. Therefore, one sender can monopolize the system. 3. Packet Switching Block size has upper limit. No one can monopolize more than a fraction of a sec. Suited for interactive traffic. Each router should have sufficient memory to store data.

34. Switching continued In packet switching each packet can be examined and format changed if need to be. Packets may arrive at different order. Will have to be rearranged.

35. Types of switches Hierarchical Crossbar Space Division Time Division

36. ISDN Narrow band Broad band

37. Narrow Band ISDN Primary goal was integration of voice and data. Telephones can be connected to a computer for statistics. Voice and data can be sent concurrently Caller ID

38. ISDN System Architecture ISDN is a bit pipe All bits can flow in either direction. Does not matter where the bit comes from – voice, computer, fax, etc. Additional bit pipes can be added and combined.

39. ISDN continued For each ISDN service a terminating device is need at your location such as NT1. Up to 8 devices can be added to an NT1, provided you have sufficient bandwidth (pipes).

40. ISDN interface Multiple channels can be interleaved by time division multiplexing. The Channels that are standardized is given on page 142 of the text book. Basic rate comes 2B and 1 D Primary rate: 23B +1 Hybrid: 1A +1C

41. N-ISDN Narrow ISDN focused on 64Kbps channels. Directed at telephone customers Big failure

42. BROADBAND ISDN AND ATM 156 Mbps This data rate is enough for HDTV Developed based on ATM technology ATM is a packet switching technology