computer communication & networks lecture # 07 physical layer: transmission media course...
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Computer Communication & Networks
Lecture # 07Physical Layer: Transmission Media
Course Instructor:Engr. Sana Ziafat
Physical Layer Topics to CoverSignals
Digital Transmission
Analog Transmission
Multiplexing
Transmission Media
Transmission Media
Anything that carry information from source to destination.
Physical path between transmitter and receiver in data communication .
Media IssuesFrequency range
Some media support higher frequencies than others
Impairments
• Different media deform signals differently
• Some are more susceptible to noise and distortion
Cost
• We’re in the real world…
Number of receivers
• Broadcast vs. point-to-point
Transmission Medium and Physical Layer
Types of transmission media
Transmission media is divided in to two: Wired or Wireless
Wired Media (Guided Media) , Is most common and is further divided in to three different types of cabling: Coaxial, Twisted pairs and fiber optic cables.
Wireless Media (Unguided Media), which is , in a sense, no media at all, is gaining popularity. Wireless transmission use radio waves or infrared light to transmit data
Guided Media
Waves are guided along solid medium. Guided media is also known as bounded
media, since the data signals are bounded system.
Cabling technology is not limited to copper wire only. Cables can be any physical or conductive media like wires, coaxial cables or fiber optics.
Twisted-pair Cable
Categories of unshielded twisted-pair cables
Twisted Pair Cable
(a) Category 3 UTP (16MHz)(b) Category 5 UTP (100MHz)
UTP connector
Types of Twisted Pair Cable
Two types: Shielded twisted pair Unshielded twisted pair (most commonly
used)
Twisted Pair Cables (Example) ADSL
Ethernet networks
- 10BASE-T
- 100BASE-TX
- 1000BASE-T
- 1000BASE-TX (Cat5e (enhanced))
UTP Performance
Twisted Pair Cable (Pros & Cons)pro: easy to understand mass production - low cost most widely used medium
Cons: prone to electromagnetic interference
in power plants, airport buildings, military facilities, cars…
Note:In-building networks at our university are almost all
twisted pair
Coaxial Cable
It carries high frequency signals than in twisted pair cable.
Less susceptible to interference or crosstalk.
Coaxial cable
BNC connectors
Performance Coaxial Cable
Coaxial cable has much higher bandwidth, the signals weakens rapidly and requires the frequent use of repeaters.
Applications
Cable- TV Long distance telephone transmission.
Optical Fiber
Made of glass or plastic and transmits signal in form of light.
Signal is sent using internal reflection. Relies on total internal reflection
Light waves bounce of edge of fiber Channels waves to destination
A glass or plastic core is surrounded by a cladding of less dense glass or plastic.
Bending of light ray
Optical fiber
Propagation Modes
Multimode
Multiple signals, multiple rays will pass and reflected with different angles
Light waves bounce off at different angles. Two types:
1. Step Index
2. Graded Index
Modes
Fiber Types
Defined by the ratio of diameter of their core to the diameter of their cladding.
Fiber types
Fiber construction
Fiber-optic Cable Connectors
Performance Optical Fiber
Optical Fiber (Pros & Cons)
Pros: Low attenuation Large bandwidth
Cons: Relatively “new” technology “Expensive”
Comparing optical fiber to UTPPros:
Immune to electro-magnetic interference no crosstalk
Reduced need for error detection and correction Enables longer link distances Attenuation unaffected by transmission rate Easier network upgrade Can combine different services: telephony, TV, internet… Lighter than copper cables Corrosion resistant
Cons: Optical components have higher cost Expensive deploying protocols
Unguided Media: Wireless
Unguided media transport electromagnetic waves without using a physical conductor. This type of communication is often referred to as wireless communication.
Wireless
Modern wireless digital communication began in the Hawaiian Islands
What is “the best” frequency to use for communication?
Propagation Methods
Bands
Wireless Transmission Waves
Radio Waves
Electromagnetic waves ranging in frequencies between 3 kHz and 1 GHz are normally called radio waves.
They are omnidirectional (sends signal in all directions).
Radio waves are used for multicast communications, such as radio and television, and paging systems.
Omni directional Antenna
Microwaves
Having range from 1 to 300 GHz. They are unidirectional. Microwave propagation is line-of-sight. Very high frequency microwaves can not
penetrate walls. Microwaves are used for unicast communication
such as cellular telephones, satellite networks,and wireless LANs.
Unidirectional Antennas
Infrared waves
Range from frequencies 300 GHz to 400 THz.
Infrared signals can be used for short-range communication in a closed area using line-of-sight propagation.
Readings
Chapter 7 (B.A Forouzan) Section 7.1, 7.2
Q & A
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