Communication Media [Compatibility Mode]
Transcription
Communication Media [Compatibility Mode]
07-May-15 INTRODUCTION TO COMMUNICATION Communication Media • What is communication? - It is the process of sending information from one point (transmitter) to another (receiver). Communication media • Communication media is the actual physical path or environment through which data travel as they move from one component (transmitter) to another (receiver) and the media connects the network devices. 1 07-May-15 Communication Media • Types of Communication Media The transmission media can be classified as: - guided or - unguided Guided media provide a physical path (solid medium) along which the signals are propagated. Eg. twisted pair, coaxial cable and optical fiber Unguided media employ an antenna for transmitting the information through air, vacuum or water. Eg. Wireless communication Communication Media • Types of Communication Media The most common types of network media are – Twisted pair cable – Coaxial cable – Optical Fiber cable & – Wireless Guided media Unguided media 2 07-May-15 Communication Media Frequency Ranges of Communication Media: Sl No. Media Frequency Range 1. Twisted pair 0 to 1 MHz 2. Coaxial Cable 0 to 500 MHz 3. Optical Fiber 180 to 370 THz 4. Wireless 1GHz to 40 GHz Electromagnetic Spectrum of Communication Media 3 07-May-15 Communication Media Twisted Pair Cable - Consists of two insulated copper wires twisted together to form a pair of a regular spiral pattern. - A wire pair acts as a single communication link. - Typically, a number of these pairs are bundled together into a cable by wrapping them in a tough protective sheath. Communication Media • The twisting tends to decrease the crosstalk interference between adjacent pairs in a cable. • Neighboring pairs in a bundle typically have different twist lengths to reduce the crosstalk interference. • On long-distance links, the twist length typically varies from 5 to 15 cm. • The wires in a pair have thicknesses of from 0.4 to 0.9 mm. 4 07-May-15 Communication Media Twisted pair cables are of two types: - unshielded and - shielded Unshielded Twisted Pair (UTP) Cables UTP cables: 5 07-May-15 Unshielded Twisted Pair (UTP) Cables Advantages of UTP cables - Least expensive of all the transmission media - Used for local area networks - Small in size (diameter of approximately 0.43 cm), so does not fill up wiring ducts as rapidly as other types - Easy to install - UTP can be used with most of the major networking architectures - The oldest method of data transmission, trained manpower are easily available Unshielded Twisted Pair (UTP) Cables Disadvantages of UTP cables - Prone to external electromagnetic interferences (interference from nearby twisted pair & from noise generated in the environment) - The distance between the repeaters is shorter - Being thin in size, it is likely to break easily Some features of UTP cable: – – – – Speed and throughput—10 to 1000 Mbps Average cost per node—Least expensive Media and connector size—Small Maximum cable length—100 m (short) 6 07-May-15 Unshielded Twisted Pair (UTP) Cables Commonly used types of UTP cables: Category Uses/Data rate Category 1 Used for telephone communications. Not suitable for transmitting data. Category 2 Capable of transmitting data at speeds up to 4 Mbps. Category 3 Used in 10BASE-T networks. Can transmit data at speeds up to 10 Mbps. Category 4 Used in Token Ring networks. Can transmit data at speeds up to 16 Mbps. Category 5 Can transmit data at speeds up to 100 Mbps. Category 5e Used in networks running at speeds up to 1Gbps. Category 6 Used in networks running at speeds up to 1Gbps. Category 7 Category 7 cable is currently the fastest standard for UTP. Shielded Twisted Pair (STP) Cable STP cables: 7 07-May-15 Communication Media • Shielded Twisted Pair (STP) Cable: – Each pair of wires is wrapped in a metallic foil. – The four pairs of wires then are wrapped in an overall metallic braid or foil. Advantages of STP cables: – STP reduces electrical noise within the cable (pair to pair coupling and crosstalk) – STP reduces electrical noise from outside the cable (EMI and RFI) Shielded Twisted Pair (STP) Cable Disadvantages of STP cables: – More expensive than UTP cables – Physically larger – Difficult to install – More difficult to connect to a terminating block Some features of STP cable – Speed and throughput—10 to 100 Mbps – Average cost per node—Moderately expensive – Media and connector size—Medium to large – Maximum cable length—100 m (short) 8 07-May-15 Coaxial Cable • Coaxial Cable Coaxial Cable • In a Coaxial cable, a copper wire is surrounded by a layer of flexible insulation • Over this insulating material is a woven copper braid or metallic foil that acts both as the second wire in the circuit and as a shield for the inner conductor • This second layer or shield can help reduce the amount of outside interference • The shield is covered by a cable jacket 9 07-May-15 Coaxial Cable • Advantages of Coaxial Cable – It has better shield against electromagnetic interference – It can span longer distance at higher data bits per second (bps) – It can be used for both analog and digital data transmissions – Easy to handle – Coaxial cable emits less radiation, so less interference with the communication equipment Coaxial Cable • Disadvantages of Coaxial Cable – More expensive to install compare to twisted pair cable – The thicker the cable, the more difficult to work with 10 07-May-15 Optical Fiber Cable • An optical fiber is a cylindrical dielectric waveguide (no conducting waveguide) that transmits light along its axis, by the process of total internal reflection. • An optical fiber is a flexible, transparent fiber made of extruded glass (silica) or plastic, slightly thicker than a human hair. Optical Fiber Cable • Structure of an Optical Fiber – The fiber consists of a core surrounded by a cladding layer, both are made of dielectric materials – The refractive index of the core is greater than the refractive index cladding 11 07-May-15 Optical Fiber Cable • Types of Optical Fiber – Single mode – Multi mode Multimode fiber – has a 62.5 microns or larger in diameter – Usually used for short distance transmissions Single-mode fiber – has a small core of 8 to 10 microns in diameter – Used for long distance transmissions Optical Fiber Cable • Advantages – It can handle much higher bandwidth – Low attenuation, – Required repeaters spacing 30 Km – Fiber is not affected by electromagnetic interference, or corrosive chemicals in the air, so ideal for factory environments where electrical interference is very high – Fiber is lighter than copper – Difficult to tap, high security 12 07-May-15 Optical Fiber Cable • Disadvantages – Optical fiber is an unfamiliar technology requiring skills which may not be easily available – Optical fiber interfaces cost more than electrical interfaces Components of a Communication System 13 07-May-15 Highway Scenario GSM, 3G, WLAN, Bluetooth, ... PDA, laptop, cellular phones, GPS, sensors 14 07-May-15 Trends on Wireless Communications Making a Call 1. 2. 3. 4. 5. Scan Control Channels: Your cell phone needs to use the "closest" base station because that's the one with the strongest signal and the one that will give the best connection. To find the closest base station, your phone checks all 21 control channels and determines which has the strongest signal. Choose Strongest: Your cell phone chooses the strongest signal and decides to use that one for placing the call. Send Origination Message: Your cell phone now transmits a very short message (about 1/4 second) that contains the MIN (Mobile Identification Number, aka your cell phone number), its ESN (Electronic Serial Number), and the number you just dialed. Get Channel Assignment: After the cellular service provider verifies that you are a valid, paying customer (based on the MIN and ESN your phone sent), the base station sends a Channel Assignment message to your phone (also a short 1/4-second burst). This message tells your phone where (that is, on which channel) the conversation will take place. Begin Conversation 15 07-May-15 Wireless Networks Compared to Fixed Networks • • • • • • Higher loss-rates due to interference. Limited availability of useful spectrum. Low transmission rates. Higher delays. Lower security, simpler active attacking. Always shared medium. Cellular Data Networks Some terms: • SMS • • • • Short Message Service MMS Multimedia Message Service GPRS General Packet Radio Service HSCSD High Speed Circuit Switched Data EDGE Enhanced Data Rates for Global Evolution 16 07-May-15 Wireless Data • • • • IEEE Standard*: 802.11x Bluetooth ZigBee Ultra Wide Band WHAT ARE STANDARDS? • Standards are published documents that establish specifications and procedures designed to maximize the reliability of the materials, products, methods, and/or services people use every day. Standards address a range of issues, including but not limited to various protocols to help maximize product functionality and compatibility, facilitate interoperability and support consumer safety and public health. Thank You This PPT is downloaded from www.ec1107.weebly.com 17