Semester 1 Module 3 Networking Media

1. Semester 1 Module 3 Networking Media Andres, Wen-Yuan Liao Department of Computer Science and Engineering De Lin Institute of Technology andres@dlit.edu.tw http://www.cse.dlit.edu.tw/~andres

2. Overview • Discuss the electrical properties of matter • Define voltage, resistance, impedance, current, and circuits • Describe the specifications and performances of different types of cable • Describe coaxial cable and its advantages and disadvantages compared to other types of cable • Describe STP cable and its uses

3. Describe UTP cable and its uses • Discuss the characteristics of straight-through, crossover, and rollover cables and where each is used • Explain the basics of fiber-optic cable • Describe how fiber-optic cables can carry light signals over long distances • Describe multimode and single-mode fiber • Describe how fiber is installed

4. Describe the type of connectors and equipment used with fiber-optic cable • Explain how fiber is tested to ensure that it will function properly • Discuss safety issues related to fiber optics

5. Outline • Copper Media • Optical Media • Wireless Media

6. Atoms and electrons • The atom(原子) is comprised of: • Electrons(電子) – Particles with a negative charge that orbit the nucleus. • Nucleus(核子) – The center part of the atom, composed of protons and neutrons. • Protons(質子) – Particles with a positive charge. • Neutrons(中子) – Particles with no charge (neutral). • Coulomb‘s(庫侖) Electric Force Law • The opposite charges react to each other with a force that causes them to be attracted to each other. • Like charges react to each other with a force that causes them to repel each other. • The force is inversely proportional to the square of the separation distance.

9. Bohr’s(波爾 ) model • Protons are positive charges and electrons are negative charges. There is more than 1 proton in the nucleus. • Loosened electrons that do not move and have a negative charge are called static electricity (靜電). • If these static electrons have an opportunity to jump to a conductor, this can lead to electrostatic discharge (ESD). • ESD, though usually harmless to people, can create serious problems for sensitive electronic equipment. • A static discharge can randomly damage computer chips, data, or both.

10. Voltage • Voltage is sometimes referred to as electromotive force (EMF)(電動勢). • EMF is related to an electrical force, or pressure. • Voltage can also be created in three other ways: • By friction(摩擦), or static electricity. • By magnetism(磁力), or electric generator. • By light, or solar cell(太陽能蓄電). • Voltage is represented by the letter V, and sometimes by the letter E. • The unit of measurement for voltage is volt (V).

11. Resistance and impedance • The materials through which current flows offer varying amounts of opposition, or resistance to the movement of the electrons. • Conductors(導體) : The materials that offer very little, or no, resistance. • Insulators(絕緣體) : Those materials that do not allow the current to flow, or severely restrict its flow. • The letter R represents resistance. • The unit of measurement for resistance is the ohm(歐姆). • The symbol comes from the Greek letter, omega. (Ω)

12. Semiconductors are materials where the amount of electricity they conduct can be precisely controlled. • The most important semiconductor which makes the best microscopic-sized electronic circuits is silicon (Si)(矽). • Silicon is very common and can be found in sand, glass, and many types of rocks.

14. Current • In electrical circuits, the current is caused by a flow of free electrons. • When voltage, or electrical pressure, is applied and there is a path for the current, electrons move from the negative terminal along the path to the positive terminal. • The letter “I” represents current. • The unit of measurement for current is Ampere (Amp or A)(安培). • Amp is defined as the number of charges per second that pass by a point along a path.

15. As an example, • Static electricity has very high voltage, so much that it can jump a gap of an inch or more. However, it has very low amperage and as a result can create a shock but not permanent injury. • The starter motor in an automobile operates at a relatively low 12 volts but requires very high amperage to generate enough energy to turn over the engine.

17. Circuits • Current flows in closed loops called circuits. • Voltage causes current to flow. • Resistance and impedance oppose it. • An electric appliance(設備) has a plug with three prongs(分支), one of the three prongs serves as the ground, or zero volts. • The ground provides a conducting path for the electrons to flow to the earth. • A water analogy helps to explain concepts of electricity.

19. Ohm’s law • V=I*R • Voltage (V) equals current (I) multiplied by resistance (R). • Two ways in which current flows are alternating current (AC) and direct current (DC): • AC: flows in one direction, then reverses its direction and flows in the other direction, and then repeats the process. • DC: always flows in the same direction. • Power lines carry electricity in the form of AC because it can be delivered efficiently over large distances.

21. Cable specifications • Cables have different specifications and expectations pertaining to performance: • What speeds for data transmission can be achieved using a particular type of cable? • What kind of transmission is being considered? Digital? Analog? • How far can a signal travel through a particular type of cable before attenuation of that signal becomes a concern? • Some examples of Ethernet specifications which relate to cable type include: • 10BASE-T (100m) • 10BASE5 (500m) • 10BASE2 (200m)

23. Coaxial cable • Coaxial cable consists of a copper conductor surrounded by a layer of flexible insulation.(銅包鋼導體)(發泡聚乙烯絕緣) • Over this insulating material is a woven copper braid or metallic foil that acts as the second wire in the circuit and as a shield for the inner conductor. (編織屏蔽) • Covering this shield is the cable jacket.(聚氯乙烯護套)

25. Advantages: • It can be run longer distances than STP, UTP, ScTP cable without the need for repeaters. • Repeaters regenerate the signals in a network so that they can cover greater distances. • Coaxial cable is less expensive than fiber-optic cable and the technology is well known. • It has been used for many years for many types of data communication such as cable television.

26. Disadvantages: • Coaxial cable is more difficult to work. • Coaxial cable is more expensive to install than twisted-pair cable. • A solid electrical connection at both ends is important to properly ground the cable. Poor shield connection is one of the biggest sources of connection problems in the installation of coaxial cable.

27. STP cable • STP cable combines the techniques of cancellation, shielded, and twisted wires. • Each pair of wires is wrapped in metallic foil.(鋁箔屏蔽) • The two pairs of wires are wrapped in an overall metallic braid or foil.(編織層)

29. A new hybrid of UTP is Screened UTP (ScTP), which is also known as foil screened twisted pair (FTP).

31. UTP cable • UTP is a four-pair wire medium used in a variety of networks. • Each of the eight copper wires in the UTP cable is covered by insulating material.(聚乙烯絕緣) • In addition, each pair of wires is twisted around each other. • This type of cable relies on the cancellation effect produced by the twisted wire pairs to limit signal degradation caused by EMI and RFI. • To further reduce crosstalk between the pairs in UTP cable, the number of twists in the wire pairs varies.

32. TIA/EIA-568-B contains specifications that govern cable performance. • Category 5 is the cable most frequently recommended and implemented in installations. • However, Category 6 cable will supersede Category 5 cable in network installations. • The fact that Category 6 link and channel requirements are backward compatible to Category 5e makes it very easy for customers to choose Category 6 and supersede Category 5e in their networks. • Applications that work over Category 5e will work over Category 6.

34. STP reduces electrical noise within the cable such as pair to pair coupling and crosstalk. • STP also reduces electronic noise from outside the cable such as electromagnetic interference (EMI)(電磁波) and radio frequency interference (RFI)(無線電波). • However, STP is more expensive and difficult to install than UTP.

35. Advantages • It is easy to install and is less expensive than other types of networking media. • Disadvantages • UTP cable is more prone to electrical noise and interference than other types of networking media • The distance between signal boosts is shorter for UTP than it is for coaxial and fiber optic cables.

37. Three types of cable connections used between internetwork devices: • Straight-through: The cable that connects from the switch port to the computer NIC port. • Crossover: The cable that connects from one switch port to another switch port. (pins #1, #2 to pins #3, #6) • Rollover: The cable that connects the RJ-45 adapter on the COM port of the computer to the console port of the router or switch. (RJ-45 to DB9)

41. Outline • Copper Media • Optical Media • Wireless Media

42. The electromagnetic spectrum • The light used in optical fiber networks is one type of electromagnetic(電磁) energy. • This energy in the form of waves can travel through a vacuum(真空), the air, and through some materials like glass. • An important property of any energy wave is the wavelength(波長).

44. Radio, microwaves, radar, visible light, x-rays, and gamma rays seem to be very different things. However, they are all types of electromagnetic energy. • If all the types of electromagnetic waves are arranged in order from the longest wavelength down to the shortest wavelength, a continuum called the electromagnetic spectrum(電磁波譜) is created.

46. Human eyes were designed to only sense electromagnetic energy with wavelengths between 700 nanometers and 400 nanometers (nm). (visible light) • A nanometer is one billionth of a meter (0.000000001 meter) in length. • The longer wavelengths of light that are around 700 nm are seen as the color red. • The shortest wavelengths that are around 400 nm appear as the color violet(紫). • This part of the electromagnetic spectrum is seen as the colors in a rainbow.

48. Wavelengths that are not visible to the human eye are used to transmit data over optical fiber. • These wavelengths are slightly longer than red light and are called infrared(紅外線) light. • Infrared light is used in TV remote controls. • The wavelength of the light in optical fiber is either 850 nm, 1310 nm, or 1550 nm. • These wavelengths were selected because they travel through optical fiber better than other wavelengths.

49. Ray model of light • When electromagnetic waves travel out from a source, they travel in straight lines. • These straight lines pointing out from the source are called rays(射線). • In the vacuum of empty space, light travels continuously in a straight line at 300,000 kilometers per second. • However, light travels at different, slower speeds through other materials like air, water, and glass. • When a light ray called the incident(入射) ray, crosses the boundary from one material to another, some of the light energy in the ray will be reflected(反射) back.

50. The light energy in the incident ray that is not reflected will enter the glass. • The entering ray will be bent at an angle from its original path. This ray is called the refracted(折射) ray. • The index of refraction(折射率) is defined as the speed of light in vacuum divided by the speed of light in the medium. .