Transmission Media.1 Introduction.2 Guided Media.2.1 Twisted pair cables.2.1.1 Unshielded Twisted Pair (UTP).2.1.2 Shielded Twisted Pair (STP).2.2 Coaxial Cable.2.2.1 Thicknet (Thickwire Ethernet).2.2.2 Thinnet(Thinwie Ethernet).2.2. Thinnet Cable Connectors.2. Fibre Optics.2..1 Single Mode Fibre.2..2 Multimode Fibre Objectives At the end of this chapter, students should be able to: Learn different types of transmission media Identify bounded and unbounded transmission media Know the difference between shielded twisted pairs and unshielded twisted pair Compare and contrast coaxial, STP, UTP and fibre optics Outline the characteristics of the fibre optics and its advantages Know the role played by satellites in data communication Learn about radio, terrestrial microwave and infrared communication. Unguided Media..1 Satellite Communication..2 Terrestrial Microwave communication.. Radio Communication..4 Infrared communication.4 Summary.5 Exercise
Transmission Media.1 Introduction Due to the variety of transmission media and network wiring methods, selecting the most appropriate media can be difficult task. However, considering following factors help in choosing the correct media type: Transmission Rate Distance Covered Cost and Ease of Installation Resistance to Environmental Conditions Transmission media can be categorised into two: Guided Transmission Media Unguided Transmission Media.2 Guided Media Guided Transmission Media uses a "cabling" system that guides the data signals along a specific path. Guided Media is also known as Bounded Media, since the data signals are bounded by the cabling system. Cabling here meant in a generic sense and is not meant to be interpreted as copper wire cabling only. Here cable can be any physical or conductive media like wires, coaxial cables or fibre optics. Example of Guided Transmission Media Twisted Pair Cable Figure -1 Twisted Pair Cable Figure -1 shows a twisted pair cable, which is one of the guided transmission media, is used for computer networking. There are other guided transmission media like Coaxial cable and fibre optics. Twisted Pair Cable comes in different configuration and quality. Guided Transmission Media can be one of the following types Twisted Pair Cable o Unshielded Twisted Pairs (UTP) o Shielded Twisted Pairs (STP) Coaxial Cable Fibre Optic 49
Networking Principles.2.1 Twisted pair cables Figure -2 Twisted Pair Cables Twisted pair cables got their name because pairs of wires are twisted around one another. Twisted pair consists of colour-coded pairs of insulated copper wires. Each wire has diameter of 0.4 to 0.8 mm. Two insulated copper wires are twisted together in order to reduce crosstalk and noise susceptibility. Data is transmitted in the form of electrical signal through these copper conductors. High quality twisted pair cables have about 1 to twists per inch. The number of twists per meter or foot is known as the twist ratio. For best results, the twist rate should vary significantly between pairs in a cable. Twisted-pair cable is used over several different topologies, although it is most often implemented in star or starthybrid topologies. Twisted pair can be specified as category 1 to 6 and is abbreviated as CAT 1-6. There are two types of Twisted Pair cables Unshielded Twisted Pairs (UTP) Shielded Twisted Pairs (STP) 50
Transmission Media.2.1.1 Unshielded Twisted Pair (UTP) Copper Wire Conductor Twisted Pairs As the name implies, "unshielded twisted pair" (UTP) cabling is twisted pair cabling that contains no shielding. The UTP cables in computer networking have resistance rating of 100 ohm. UTP cabling most commonly includes 4 pairs of wires enclosed in a common sheath. UTP is a very flexible, low cost media, and can be used for either voice or data communications. It is easy to install and maintain compared to fibre optic cable. UTP is widely used for cabling LAN in today s computer network. Figure - Unshielded Twisted Pair (UTP).2.1.2 Shielded Twisted Pair (STP) Figure -4 Shielded Twisted Pair Shielded Twisted Pair (STP) cabling includes metal shielding over each individual pair of copper wires. This type of shielding protects cable from external Electromagnetic Interferences (EMI). Therefore these cables can be used in noisy area. 51
Networking Principles Cable types and their uses Type Description Use Telephone Wire It is used for voice only, not for Category 1 (CAT 1) computer data. Category 2 (CAT 2) UTP cable that contains four wire pairs. It is used for carrying data at rate of 4 Mbps for Local Talk Category (CAT ) UTP cable containing 4 pair of wires. It has possible max bandwidth of 16 Mbps It is used for 10 Mbps Ethernet and 4 Mbps Token Ring. Category 4 (CAT 4) UTP cable containing 4 pair of wires. Provide more protection to crosstalk than CAT It is used to 10 Mbps Ethernet and 16 Mbps Token Ring. Category 5 (CAT 5) UTP cable containing 4 pair of wires. CAT 5E has better protection for crosstalk. It is used for 100 Mbps Ethernet(Fast Ethernet) Category 6 (CAT 6) UTP cable containing 4 pair of wires. Can carry data at rate of 1Gbps. It is used for Gigabit Ethernet that can carry data at rate of 1000Mbps Table -1 Cable types and their Uses 52
Transmission Media Connector types Twisted Pair Cable uses RJ45 connector at the end of cable to connect with computer. Figure -5 RJ 45 connector and Jack.2.2 Coaxial Cable Figure -6 Construction of Coaxial Cable Coaxial cable is basically a copper cable, mostly used by Cable TV Companies to distribute TV signals from antenna to users home. Coaxial cable was once the primary medium for Ethernet and Local Area Networks (LANs), but due to development of STP and UTP, the use of coaxial cable has almost disappeared over few years. It is commonly called as coax and carries a signal at much higher frequencies than twisted pair. Coaxial cable has a single copper conductor at its centre as a medium for transferring an electrical signal. A plastic layer provides insulation between the centre conductor and a copper mesh shield (See Figure -6). The copper mesh helps to block any outside interference from fluorescent lights, motors, and generators. 5
Networking Principles Types of Coaxial Cable Depending on the use of coaxial cable it can be categorized into two types..2.2.1 Thicknet (Thickwire Ethernet) It is the original Ethernet medium which is approximately 1-cm thick and contains a solid copper core. Thicknet uses Vampire taps and Transceiver Cable as shown in Figure -7 to connect to a computer. IEEE designates Thicknet as 10BASE-5 Ethernet. Here the "10" represents its speed (10Mbps), the base represent Baseband Transmission and "5" represent maximum segment length of Thicknet Cable which is 500 meters. It is mostly found in the older network. Figure -7 Thicknet Cable with Vampire Taps and Transceiver cable to connect to a computer 54
Transmission Media.2.2.2 Thinnet (Thinwire Ethernet) These types of medium were popular in 1980s. Thinnet uses RG-58A/U coaxial cable. Thinnet has diameter of approximately 0.64cm, which makes it more flexible and easier to install than Thicknet. IEEE has designated thinnet as 10BASE-2.Similary like thicknet, here 10 means speed of 10Mpbs using Baseband Signal with maximum segment length of 200 meters. It is not popular choice for present due to arrival of twisted pair cables. Figure -8 Thinnet Cable Connection.2.2. Thinnet Cable Connectors BNC cable connector (Figure -9) is either soldered or crimped to the end of a cable. Figure -9 BNC Cable Connector Note: BNC stands for Bayonet Neill Concelman or British Navel connector 55
Networking Principles BNC T connector (Figure -10) is used to join the Network Interface Card (NIC) in the computer to the network cable. Figure -10 BNC T Connector BNC barrel connector (Figure -11) is used to join two lengths of thinnet cable to make one longer length. Figure -11 BNC Barrel Connector 56
Transmission Media The BNC terminator (Figure -12) closes each end of the bus cable to absorb stray signals and prevent signal bouncing. Figure -12 BNC Terminator Comparison of Thicknet and Thinnet Cables Thicknet Thicknet was the original Ethernet wiring. Thinnet Thinnet replaces early thicknet. It is also called as thickwire. Thickwire, is 0.4 inches in diameter. It is also called as thinwire. Thinnet has diameter of approximately 0.64cm. Uses Vampire Taps and Transceiver cable as connectors. Uses different BNC connectors to connect cable. Since it is thick, it is heavy and difficult to bend and install. It is light, easy to install and bend. Table -2 Thicknet and Thinnet Comparison 57
Networking Principles.2. Fibre Optics Figure -1 Fibre Optics Construction Fibre optic cable consists of a centre glass core surrounded by several layers of protective materials (as shown in Figure -1). It transfer data in the form of light rather than electrical signals, thus there is no any electrical or electromagnetic inference to such cable. This makes it ideal for certain environments that contain a large amount of electrical interference. It has also made it the standard for connecting networks between buildings, due to its immunity to the effects of moisture and lightning. Fibre optic cable has the ability to transmit signals over much longer distances than coaxial and twisted pair. It also has the capability to carry information at vastly greater speed compared to other transmission media. This capacity broadens communication possibilities to include services such as video conferencing and interactive services, but cost is high as well as difficulty in installation. Fibre optics can be classified into two categories: Single Mode Fibre Multimode Fibre.2..1 Single Mode Fibre Single Mode Fibre can transfer data for longer distance without help of a repeater and has high bandwidth with small diameter of 10 micron. In Single Mode Fibre, the laser light travels over single path with little reflection. Since light does not disperse, it can travel longer distance without requiring a repeater as shown in Figure -14. Figure -14 Signal travel over Single Mode Fibre 58
Transmission Media.2..2 Multimode Fibre Multimode Fibre contains a core with a larger diameter than a single-mode fibre (between 50 to 115 microns). Due to large diameter, many pulses of light which is generated by laser can travel at different angles as shown in Figure -15. Figure -15 Signal travel over Multimode Fibre Media Comparison Chart Media Type Advantages Disadvantages Inexpensive Sensitive to noise Twisted Pair Cable Well understood Short distance Easy to add computers Limited bandwidth Security-easily tapped Coaxial Cable Optical Fibre Cable High Bandwidth Long distances Nose immunity Very high bandwidth Noise immunity Long distances High Security Small size Table - Media Comparison Chart Physical dimensions Security-easily tapped Connections T splitters Expensive High installation cost 59
Networking Principles. Unguided Media Unguided Media consists of a means (e.g. air, space) for the data signals to travel, however there is nothing to guide them along a specific path, like in wires. In such cases, the data signals are not bounded to a cabling media. Therefore such transmission media area often called as Unbound Media. Unbounded media is electromagnetic waves in form of radio, microwave, infrared or others. Wireless communication (unbound media) is used where cables are difficult to use or install. Unguided Transmission Media can be one of the following types Satellite Communication Terrestrial Microwave Radio Communication Infrared..1 Satellite Communication Figure -16 Satellite Communication An artificial satellite is a man made object placed into orbit around the Earth for the purpose of communication and scientific research. The communication satellite consists of a radio transmitter and receiver which are called transponders and usually placed about 22,00 miles above the Earth s equator. The function of transponders is to receive the incoming radio signal from the earth, amplify it and transmit back towards the earth. Satellite provides communication over longer distance compared to normal radio communication. A ground station on one side of ocean transmit a signal to the satellite, satellite receiver receives the signal and transmit back to another station on the other side. Since satellite communication is so costly, a single satellite is shared by many organizations. The most common (or useful) satellites are Geosynchronous satellites. 60
Transmission Media Satellite Communication is used for following purposes: Air Navigation Television and Radio Transmission Videoconferencing Global Positioning System (GPS) Global Positioning System(GPS) Global Positioning System (GPS) consist of one or more earth-based receivers that accept and analyse signal sent by satellite in order to determine the receiver s geographical location. A GPS receiver can be handheld or mounted on an object like automobile, boat, aeroplane, farm and construction equipment or computer. It helps scientist, farmer, pilot and rescue workers operate more productively as well as safely...2 Terrestrial Microwave communication Figure -17 Microwave Communication Terrestrial Microwave communication is used extensively in situations when physical transmission media is impractical or difficult to install, for example between high building, across rivers, mountains, jungles and remote areas. Microwaves are transmitted via earth atmosphere between two stations. It can be used for only short distance up to 50km. Repeater station is needed if transmission distance is more than 50km. Microwave transmission is line of sight transmission, the transmit station must be in visible contact with the receive station. Such type of communication can be easily affected by atmospheric changes for example weather. 61
Networking Principles.. Radio Communication Figure -18 Radio Communication Apart from public broadcast of radio and television programs, radio communication is also used for the purpose of wireless communication. It is used for private communication with devices like portable phones. Wireless communication is also used for sending and receiving computer data. Radio communication systems consist of transmitter and receiver called base stations, between which radio signal are sent and receive. Radio communication uses electromagnetic waves but operate at radio frequency range. Area covered by such communication system depends on the power of transmitter...4 Infrared communication Infrared technology allows computing devices to communicate via short-range wireless signals. With help of infrared, computers can transfer files and other digital data between each other. Infrared transmission requires line-of-sight transmissions. That means the sender and receiver must be aligning so that nothing obstructs the path of the infrared wave. Infrared communication is usually used over short distance. Today most of the consumer devices like mobile phones, Personal Digital Assistant (PDA), Computer, laptop have built in infrared port for infrared communication. One infrared device can easily recognize other infrared device nearby and communicate with easily. 62
Transmission Media.4 Summary Transmission media can be categorized into Guided or Bounded and Unguided or Unbounded transmission media. Guided Transmission media uses a cabling system to guide data signal along a specific path. Guided transmission media are twisted pairs copper wire, coaxial cable or fibre optics. There are two types of Twisted Pair Cable; Unshielded Twisted Pairs (UTP) and Shielded Twisted Pairs (STP). Shielded Twisted Pairs (STP) has metal shielding over each individual pair of copper wires, which protect from Electromagnetic Interference (EMI) compared to UTP. UTP cable range from CAT1 to CAT6 based on data transfer rates and its uses. Coaxial cable can be used for Cable TV as well as to carry data for computer networks. Coaxial cables are of Thicknet and Thinnet types. BNC Cable connector, BNC T Connector, BNC barrel connector, BNC Terminator is used for connecting thinnet cable. Fibre optics transfer data in the form of light and it is immune to Electromagnetic Inference (EMI). Fibre optics comes as Single Mode and Multimode Fibre. Unguided or Unbounded media is Electromagnetic waves in form of Radio or Microwave signals. The communication satellite consists of a radio transmitter and receiver called transponders. Communication satellites used where cable is difficult to layout. Terrestrial Microwave communication is used in adverse geographical situation like across rivers, mountains and jungle over short distance up to 50 km. Radio communication is used for public broadcast of radio and TV as well as for wireless communication. Most of the consumer device likes mobile phones, Computers and PDA uses infrared communication over short distance to communicate with each other. 6
Networking Principles.5 Exercise Fill in the blanks 1. When selecting transmission media, important facts have to be noted are, and. 2. When cabling system is used to guide the data transmission along a specific path, such media is called. Example of an unguided transmission media is 4. cable transmits data in forms of light rather than as electric signals. 5. Two types of twisted pairs are and 6. In twisted pair, wires are twisted together in order to reduce 7. Twisted pair cables have normally to twists per inch 8. STP is better than UTP because metal shielding protect signal from interference. 9. Category 1 twisted pair is used for only. 10. Category twisted pair can carry data up to Mbps and used for 11. Coaxial cable can carry a signal at much frequencies than twisted pairs. 12. cable can be used in places with high electrical and electromagnetic interferences. Questions: 1. What do you mean by guided transmission media? 2. List different types of guided transmission media.. What is difference between UTP and STP? 4. List different categories of twisted pairs indicate their usages. 5. Compare different types of cables with their advantages and disadvantages. 6. What are different forms of unguided transmission and their uses? 64