Communication Systems PDF

Communication Systems By Dr. Reham Abobeah Chapter Two Transmission Media Types of Transmission Media  Guided Transmission Media Guided transmission media is also known as wired / bounded transmission media. The electromagnetic signals travel between the communi...

Communication Systems By Dr. Reham Abobeah Chapter Two Transmission Media Types of Transmission Media  Guided Transmission Media Guided transmission media is also known as wired / bounded transmission media. The electromagnetic signals travel between the communicating devices through a physical medium/conductor. As the medium for transmission is a physical conductor, it provides a direction to the signal. However, there are physical limitations of the conductor in the guided media, like the conductor length, its installation cost, its maintenance, etc.  Un-Guided Transmission Media The unguided media is also called wireless communication. The unguided media is also called unbounded media as it does not have any border limitation. It does not require any physical medium to transmit electromagnetic signals, instead, the electromagnetic signals are broadcasted through air to everyone. These signals are available to one who has the device capable of receiving those signal. In unguided media, as the communication is wireless, the user is allowed to be connected all the time from anywhere to the network. Types of Transmission Media Guided Transmission Media  Twisted Pair The twisted pair cable has two wires of copper twisted with each other and each surrounded by an insulating material. One of the wires carries the signal, while the other is used as a ground reference. It is flexible and easy to install. It is limited in distance, bandwidth, and data rate and provides less protection from interference. Twisted pair cable are of two types shielded and unshielded twisted pair cable.  What is Crosstalk? Crosstalk is a form of interference in which signals in one cable induce electromagnetic interference (EMI) in an adjacent cable. Crosstalk is a feature of copper cables only – fiber-optic cables do not experience crosstalk.  The message may be (zero becomes one or one becomes zero) distorted due to the electromagnetic fields that can be propagated surrounding the wire.  How the Twisted-Pair Cable has solved the crosstalk problem?  Interference from devices such as a motor car creates unequal noise over two parallel lines.  The line that is closer to the device receives more interference than the one that is farther.  If, however, the wires are twisted around each other at regular intervals, each wire is closer to the noise source for half of the time and farther for the other half.  Both receive the same amount of noise, hence, the noise from two wires cancel each other out at the receiver.  The twisting in twisted-pair cabling reduces the amount of crosstalk that occurs, and crosstalk can be further reduced by shielding cables or physically separating them.  Twisted Pair Cable Types In unshielded twisted pair (UTP) In shielded twisted pair (STP) There is only a plastic cover over There is a metal shield called the copper wire. Copper Mesh over the copper wire. Uses RJ-45 connector Not commonly used Special connecters are required.  Twisted Pair Cable Types Parameter UTP STP Data Range 10-100 Mbps 150 Mbps Cable length 100 meters max. 500 meters max. Electrical Interference Most susceptible to Less susceptible to interference or cross talk interference or cross talk Installation Easy to install Very easy to install Cost Lowest Little costly Connecting your Device through UTP Materials Required:  *UTP cable:  *RJ-45 Connector: (Register jack)  *Crimper Tool: T-568A Standard: Connecting your Device through UTP  UTP Categories UTP comes in several categories that are based on the number of twists in the wires, the diameter of the wires and the material used in the wires. CAT 1, CAT 2, CAT 3, CAT 4, CAT 5, Enhanced CAT 5, CAT 6 and now CAT 7. CAT 3 is the wiring used primarily for telephone connections. Category 5e and Category 6 are currently the most common Ethernet cables used. Guided Transmission Media--Co-axial Cable  Guided Transmission Media--Coaxial Cable  Coaxial cable or sometimes known as coax cable: carries signals of higher frequency ranges (higher Bandwidth) than twisted pair.  There are three outer layers out of inner copper wire:  Inner conductor is at center of the cable, made of copper, carries signal.  Insulation: nonconductor around copper wire which is made up of Teflon.  Copper mesh: serves both as a shield against noise and as the second conductor, which completes the Circuit-- supply ground for the copper wire ).  Outer insulation or Jacket : is an outer shield , made up of rubber/Teflon/Plastic.  Types of Coaxial Cables Thin Coaxial Cable Thick Coaxial Cable Diameter 0.25 inch 0.5 inch Max distance 185m 500m It connect 100 devices with Max devices 30 100 range 500m Practical name RG-58 RG-11 Cost Cheap More expensive  Coaxial cable Categories  mainly being used to connect satellite antenna facilities to homes and businesses  There are different types of coaxial cable, which vary by gauge and impedance.  Gauge refers to the cable’s thickness and is measured by the radio guide measurement or RG number.  The higher the RG number, the thinner the central conductor core is.  Each RG number denotes a unique set of physical spec. (wire gauge of inner conductor, thickness and type of inner insulator, etc.).  BNC connectors  To connect coaxial cable to device, we need BNC = Bayonet-Neill-Concelman.  BNC Connector is used to connect the end of the cable to a device BNC -T is used in networks to branch out a cable for connection to a computer or other device. BNC Terminator is used at the end of the cable to prevent the reflection of signal. How the Coaxial Cable Cable has solved the crosstalk problem?  Fiber Optic Cable  A fiber optic cable is made of glass or plastic and transmit signals in the form of light.  It has fibers which are long, thin, made of pure glass, about the diameter of human hair.  Optical fibers are faster, lighter, and suitable for transferring large amount of data.  Core is of glass or plastic surrounded by Cladding  Cladding is another layer of less dense glass or plastic that reflects light back into the core  Coating: Silicon coating  Strengthening Fibres: to give extra strength to cladding  Cable Jacket, the cable is surrounded with very strong plastic material such as Kevlar.   Fiber Optic Cable uses reflection to guide light through a channel.  Figure illustrates propagation of light through fiber optic cable How the Fiber optic cable has solved the crosstalk problem? It changes the copper core to a glass one so, it is hard to any electromagnetic field to affect on such cable. Fiber Optic Advantages  Greater capacity (bandwidth of up to 2 Gbps).  Distance of transferring data is from 1-3 km.  Smaller size and lighter weight.  Lower attenuation.  More resistance to corrosive materials  immunity to environmental interference.  highly secure due to lack of signal radiation. Attenuation is the loss of signal strength in networking cables or connections. This typically is measured in decibels (dB) or voltage and can occur due to a variety of factors. It may cause signals to become distorted or indiscernible.  Fiber Optic Disadvantages  Installation and maintenance need expertise.  Much more expensive.  requires highly skilled installers.  adding additional nodes is difficult.  Types of Connectors ST, SC, SMA, MIC AnyQuestions?