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Transmission medium We can say that transmission media belong to layer zero.

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Presentation on theme: "Transmission medium We can say that transmission media belong to layer zero."— Presentation transcript:

1 Transmission medium We can say that transmission media belong to layer zero

2 Transmission medium Transmission media can be divided into two broad categories: – Guided media include twisted-pair cable, coaxial cable, and fiber-optic – Unguided media is usually air

3 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. A signal traveling along guided media is directed and contained by the physical limits of the medium Twisted-pair and coaxial cable use metallic (copper) conductors that accept an transport signals in the form of electric current Optical fiber is a glass cable that accepts and transports signals in the form of light

4 Twisted-Pair Cable Consists of – two conductors (normally copper) – each with its own plastic insulation – twisted together

5 Twisted-Pair Cable One of the wires is used to carry signals to the receiver And the other is used as a ground reference Receiver uses the difference between the two level Interference (noise) and crosstalk may affect both wires and create unwanted signals Receiver operates only on the difference between these unwanted signals – If the two wires are affected by noise or crosstalk equally Receiver is immune (the difference is zero) – If the two wires are parallel The effect of these unwanted signals is not the same in both wires (one close and one farther) – By twisting the pairs, a balance is maintained

6 Twisted-Pair Cable The number of twists per unit of the length (e.g. inch) determines the quality of the cable – More twists mean better quality

7 Unshielded versus Shielded Two common twisted-pair cable used in communications – Unshielded twisted-pair (UTP) – Shielded twisted-pair (STP) STP has a metal foil or braided-mesh covering – Preventing the penetration of noise or crosstalk – It is bulkier and more expensive

8 Categories EIA: the Electronic Industries association classifies unshielded twisted- pair cable into seven categories which determined by quality (1 lowest and 7 highest)

9 Connectors Most common UTP connector is RJ45 – R J stands for Registered Jack

10 Performance One way measure performance is to compare – attenuation vs. frequency and distance. – A twisted-pair can pass a wide range of frequencies. – Figure 7.6 shows with increasing frequency, attenuation in decibels per kilometer (dB/km), sharply increase with frequency above 100 kHz. – Gauge is a measure of the thickness of the wire.

11 Application Used in telephone Lines (UTP) DSL lines (UTP) Local area networks

12 Coaxial Cable Carries signals of higher frequency ranges than twisted-pair cable Coax has a central core conductor of solid or stranded wire (usually copper) Encased in an outer conductor of metal foil, braid, or a combination of the two The outer metallic wrapping Outer conductor is also enclosed in an insulating sheath Whole cable is protected by a plastic cover

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14 Coaxial Cable Standards Coaxial cables are categorized by their radio government (RG) ratings Each RG number denotes a unique set of physical specifications – Wire gauge of the inner conductor – Thickness and type of the inner insulator – Construction of the shield – Size and type of the outer casing Each RG ratings is adapted for a specialized function

15 Coaxial Cable Connectors Coaxial cable connector is BNC (Bayone-Neill-Concelman) Figure shows the BNC connector, the BNC T connector, and the BNC terminator

16 Applications It was used in analog and digital telephone networks (replaced by fiber-optic) Cable TV networks (replaced by fiber-optic) Traditional Ethernet Lans

17 Fiber-Optic Cable It is made of glass or plastic and transmits signals in the form of light If a ray pf light traveling through one substance and enters another (more or less dense), the ray changes directions Optical fibers use reflection to guide light through a channel

18 Fiber-Optic Cable Glass or plastic core is surrounded by a cladding of less dense glass or plastic

19 Propagation Modes Current technology supports two modes (multimode and single mode) for propagating light along optical channels Multimode: multiple beams from a light source move through the core in different paths Multimode can be implemented in two forms: – Step-index – Graded-index

20 Propagation Modes

21 Fiber Sizes By the ratio of the diameter of their core to the diameter of their clading [micrometers]

22 Cable compostion

23 Fiber-Optic Connections Fiber-optic use three different type of connectors 1. Subscriber Channel (SC) connector Used in cable TV and it uses a push/pull locking system 2. The Straight-Tip (ST) connector – Used for connecting cable to networking devices 3. MT-RJ in new connector with the same size as RJ45

24 Fiber-Optic Connections Applications It used in backbone networks For cable TV with coaxial cable (a hybrid network)

25 Advantages and Disadvantages of Optical Advantages over twisted-pair and coaxial – Higher bandwidth Less signal attenuation –Signal with fiber-optic can run for 50 km with requiring regeneration –5 km for coaxial or twisted-pair cable Immunity to electromagnetic interference –Electromagnetic noise cannot affect fiber-optic cables Resistance to corrosive materials –Glass is more resistant to corrosive materials than copper Light weight More immune to tapping –Fiber-optic cables definitely more immune to tapping than copper cables

26 Advantages and Disadvantages of Optical Disadvantages – – Installation/maintenance Because it is new technology, need expertise – – Unidirectional If we need bidirectional we need two fibers – – Cost The cables and interfaces are expensive

27 UNGUIDED MEDIA: WIRELESS Unguided media: transport electromagnetic waves without using a physical conductor (wireless communication) – Signal broadcast through air

28 UNGUIDED MEDIA: WIRELESS Unguided signals can travel from the source to destination in several ways: – Ground propagation – Sky propagation – Line-of-sight propagation

29 UNGUIDED MEDIA: WIRELESS Ground propagation (below 2 MHz) – Radio waves travel through the lowest portion of atmosphere – Waves emanate in all directions from the transmitting antenna – Distance depends on the amount of power in the signal Sky propagation ( MHz) – Higher frequency radio waves radiate upward into ionosphere where they reflected back to earth – This type of transmission allows for greater distance with lower power output

30 UNGUIDED MEDIA: WIRELESS Line-of-sight propagation (above 30 MHz) – Very high-frequency signals are transmitted in straight lines directly from antenna to antenna – Antennas must be directional – Facing each other – Either tall enough or close enough

31 UNGUIDED MEDIA: WIRELESS Electromagnetic spectrum defined as radio waves and microwaves is divided into eight ranges, called bands:

32 UNGUIDED MEDIA: WIRELESS Wireless transmission can be divided into: – Radio waves – Microwaves – Infrared waves

33 UNGUIDED MEDIA: WIRELESS Radio waves – Radio waves: waves range in frequencies between 3 KHz and 1 GHz – Microwaves: waves ranging in frequencies between 1 and 300 GHz – Radio waves are omnidirectional (propagated in all directions) – The sending and receiving antennas do not have to be aligned – Disadvantage One antenna interferences another antenna when they using same frequency – Radio waves that propagate in the sky mode, can travel long distance [AM radio] – Radio waves [low and medium frequencies] can penetrate walls inside a building Advantage: an AM radio can be received inside a building Disadvantage: we cannot isolate a communication to just inside or outside a building Applications – Useful for multicasting: Radio, television. Cordless phones and paging system

34 UNGUIDED MEDIA: WIRELESS Microwaves – Microwaves are unidirectional – Antenna need to be aligned – Advantage: pair of antenna can be aligned without interfering with another pair – Microwave propagation is line-of-sight – For long distance communication Very tall towers Repeater – Very high-frequency microwaves cannot penetrate walls Disadvantage if receiver inside a building

35 UNGUIDED MEDIA: WIRELESS Applications – Due to unidirectional properties, microwaves useful when unicasting (one-to-one) communication Cellular phones Satellite networks Wireles LANs

36 UNGUIDED MEDIA: WIRELESS Infrared – From 300 GHz to 400 THz (wavelengths from 1 mm to 770 nm) – Use for short-range communication – It has high frequency, cannot penetrate walls Prevents interference between one system and another –Remote control not interfere with our neighbors – Can not be used outside because suns rays contain infrared waves (interference) – (IrDA) Infrared Data Association established standards for communicating between devices: Keyboards, mice, PCs and printers


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