Physical Layer - Chapter 2 Physical Layer Transmission...

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7.1 Chapter 2 Physical Layer Transmission Media Physical Layer
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7.2 Figure 2/1 Transmission medium and physical layer Physical Layer Introduction Introduction 1. Computers and other telecommunication devices use signals to represent data. 2. These signals are transmitted from one device to another in the form of electromagnetic energy. 3. Electromagnetic signals can travel through vacuum, through air, or through other transmission media.
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7.3 Figure 2.2 Classes of transmission media Physical Layer Transmission media can be broadly classified in to two categories: 1. Guided media 2. Unguided Media
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7.4 2-1 GUIDED MEDIA 2-1 GUIDED MEDIA Guided media, which are those that provide a conduit Guided media, which are those that provide a conduit from one device to another, include twisted-pair cable, from one device to another, include twisted-pair cable, coaxial cable, and fiber-optic cable. coaxial cable, and fiber-optic cable. Twisted-Pair Cable Coaxial Cable Fiber-Optic Cable Topics that will be discussed in this section: Topics that will be discussed in this section: Physical Layer
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7.5 Figure 2.3 Twisted-pair cable Physical Layer Twisted-pair cable Comes in two forms: Unshielded and Shielded Figure 2.4 UTP and STP cables
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7.6 1. A twisted pair consists of two conductors (usually copper), each with its own coloured plastic with insulation. 2. The plastic insulation is colour-banded for identification. 3. Colours are used to identify specific conductors in a cable, and to indicate which wires belong in pairs and how they relate to other pairs in a larger bundle. Twisting reduces interference and noise. Advantages of UTP are cost, and ease of use. UTP is cheap, flexible, and easy to install. UTP comes in five grades or categories: Category 1 – The basic twisted-pair cabling used in telephone systems. This level of quality is good for voice, but inadequate for all but low-speed data communication. Category 2 – The next higher grade, suitable for voice and for digital transmission of up to 4 Mbps. Category 3 – Required to have at least three twists per foot and can be used for data transmission of up to 10 Mbps. Category 4 – Provides transmission rate up to 16 Mbps. Category 5 – Used for data transmission up to 100 Mbps. Physical Layer
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7.7 Shielded Twisted-Pair (STP) cable It has a metal foil or braided-mesh covering that encases each pair of insulated conductors. The metal casing prevents the penetration of electromagnetic noise. It can also eliminate a phenomenon called crosswalk, which is the undesired effect of one circuit (or channel) on another circuit (or channel). It occurs when one line (acting as a kind of receiving antenna) picks up some of the signals travelling down another line (acting as a kind of sending antenna). This effect can be experienced during telephone conversations when one can hear
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This note was uploaded on 02/23/2012 for the course CS 101 taught by Professor Martand during the Spring '10 term at Punjab Engineering College.

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Physical Layer - Chapter 2 Physical Layer Transmission...

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