Physical Layer Part 2

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Slide 1: 

1 Physical Layer Part 2 Multiplexing and Transmission Media

Slide 2: 

2 MULTIPLEXING Whenever the bandwidth of a medium linking two devices is greater than the bandwidth needs of the devices, the link can be shared. Multiplexing is the set of techniques that allows the simultaneous transmission of multiple signals across a single data link. As data and telecommunications use increases, so does traffic. Frequency-Division MultiplexingTime-Division Multiplexing Wavelength-Division Multiplexing Topics discussed in this section:

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3 Dividing a link into channels

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4 Categories of multiplexing

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5 Frequency-division multiplexing

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6 FDM is an analog multiplexing technique that combines analog signals.

Frequency Division Multiplexing : 

Frequency Division Multiplexing Each signal is modulated to a different carrier frequency Carrier frequencies separated so signals do not overlap (guard bands) Channel allocated even if no data each channel occupies a fraction of the bandwidth of the link a channel is defined by its center frequency, and its bandwidth. Example: radio and television signal transmission

Frequency Division MultiplexingDiagram : 

Frequency Division MultiplexingDiagram

FDM of Three Voiceband Signals : 

FDM of Three Voiceband Signals

Slide 10: 

10 FDM process

Slide 11: 

8 FDM demultiplexing example

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Wavelength Division Multiplexing : 

Wavelength Division Multiplexing Multiple beams of light at different frequency Carried by optical fiber A form of FDM Each color of light (wavelength) carries separate data channel 1997 Bell Labs 100 beams Each at 10 Gbps Giving 1 terabit per second (Tbps)

WDM Operation : 

WDM Operation Same general architecture as other FDM Number of sources generating laser beams at different frequencies Multiplexer consolidates sources for transmission over single fiber Optical amplifiers amplify all wavelengths Typically tens of km apart Demux separates channels at the destination

Slide 15: 

15 Wavelength-division multiplexing

Slide 16: 

16 WDM is an analog multiplexing technique to combine optical signals.

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17 Prisms in wavelength-division multiplexing and demultiplexing

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18 TDM

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19 TDM is a digital multiplexing technique for combining several low-rate channels into one high-rate one.

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Transmission Media A transmission medium can be broadly defined as anything that can carry information from a source to a destination. The transmission medium is usually free space, metallic cable or fiber – optic cable.

Slide 21: 

21 Transmission medium and physical layer

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22 Classes of transmission media

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23 GUIDED MEDIA Guided media, which are those that provide a conduit from one device to another, include twisted-pair cable, coaxial cable, and fiber-optic cable. Out of these twisted-pair cable, coaxial cable transport signals in the form of electric signals and fiber-optic cable transport signals in the form of light. Twisted-Pair CableCoaxial CableFiber-Optic Cable Topics discussed in this section:

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24 Twisted-pair cable One of the wires is used to carry signals to the receiver, and the other is used only as a ground reference. The receiver uses the difference between the two.

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25 UTP and STP cables

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26 Categories of unshielded twisted-pair cables

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9 UTP connector

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Coaxial cable Coaxial cable carries signals of higher frequency ranges than those in twisted-pair cable, in part because the two media are constructed quite differently. 10

Slide 29: 

29 Categories of coaxial cables

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30 BNC connectors (Bayone-Neil-Concelman) BNC Connector: used to connect the end of the cable to a device, such as TV Set BNC T Connector: used in Ethernet networks to branch out to a connection to a computer or other device. BNC Terminator: used at the end of the cable to prevent the reflection of the signal.

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13 Coaxial cable performance

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32 Bending of light ray Fiber-Optic Cable A fiber-optic cable is made of glass or plastic and transmits signals in the form of light. Light travels in a straight line as long as it is moving through a single uniform substance. If a ray of light traveling through one substance suddenly enters another substance, the ray changes direction.

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33 Optical fiber

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16 Propagation modes

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35 Modes

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36 Fiber types

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37 Fiber construction Outer jacket – PVC or Teflon Kevlar – for fabrication of bullet proof vests Plastic buffer: cushioning

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38 Fiber-optic cable connectors

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Fiber-optic cable connectors Subscriber Channel (SC) Connector is used for cable TV. It uses a push/pull locking system Straight – tip (ST) Connector is used for connecting cable to networking devices. It uses a bayonet locking system and is more reliable than SC. MT-RJ is a connector that is the same size as RJ45.

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40 UNGUIDED MEDIA: WIRELESS Unguided media transport electromagnetic waves without using a physical conductor. This type of communication is often referred to as wireless communication. Radio Waves Microwaves Infrared Topics discussed in this section:

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41 Electromagnetic spectrum for wireless communication

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42 Propagation methods

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43 Bands

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44 Wireless transmission waves

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45 Omnidirectional antenna

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46 Radio waves are used for multicast communications, such as radio and television, and paging systems.

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47 Unidirectional antennas

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48 Microwaves are used for unicast communication such as cellular telephones, satellite networks, and wireless LANs.

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49 Infrared signals can be used for short-range communication in a closed area using line-of-sight propagation.

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50 CIRCUIT-SWITCHED NETWORKS A circuit-switched network consists of a set of switches connected by physical links. A connection between two stations is a dedicated path made of one or more links. However, each connection uses only one dedicated channel on each link. Each link is normally divided into n channels by using FDM or TDM.

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51 A circuit-switched network is made of a set of switches connected by physical links, in which each link is divided into n channels.

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52 In circuit switching, the resources need to be reserved during the setup phase; the resources remain dedicated for the entire duration of data transfer until the teardown phase.

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53 Delay in a circuit-switched network

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54 Switching at the physical layer in the traditional telephone network uses the circuit-switching approach.

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55 DATAGRAM NETWORKS In data communications, we need to send messages from one end system to another. If the message is going to pass through a packet-switched network, it needs to be divided into packets of fixed or variable size. The size of the packet is determined by the network and the governing protocol.

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56 In a packet-switched network, there is no resource reservation; resources are allocated on demand.

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57 A datagram network with four switches (routers)

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58 Routing table in a datagram network

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59 A switch in a datagram network uses a routing table that is based on the destination address.

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60 The destination address in the header of a packet in a datagram network remains the same during the entire journey of the packet.

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61 Delay in a datagram network

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62 Switching in the Internet is done by using the datagram approach to packet switching at the network layer.

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