1. High Voltage!!

2. Parts of An Atom Proton Proton Neutron Neutron Electron Electron

3. Flowing Electrons Electrons are negatively charged Electrons are negatively charged Protons are positively charged Protons are positively charged Opposite charges attract Opposite charges attract Velocity of electrons keep them in orbit around nucleus Velocity of electrons keep them in orbit around nucleus Electrons pulled free from the atom is what we call electricity! Electrons pulled free from the atom is what we call electricity!

4. “Dynamic” Electricity Electricity can be viewed as a dynamic process. Electricity can be viewed as a dynamic process. Dynamic means “changing.” Dynamic means “changing.” Electrons are changing—moving from one atom to another. Electrons are changing—moving from one atom to another. This flowing of electrons is called an “electrical current.” This flowing of electrons is called an “electrical current.”

5. Static Electricity “Static” means stationary or unchanging. “Static” means stationary or unchanging. Electrons have been “loosened” from the atom and stay in one place. Electrons have been “loosened” from the atom and stay in one place. The electrons have “voltage” but lack a “current.” The electrons have “voltage” but lack a “current.” A conductor supplies the current—or path— for static electricity to discharge. A conductor supplies the current—or path— for static electricity to discharge.

6. ESD Electrostatic Discharge (ESD) is the process of static electrons jumping to a conductor. Electrostatic Discharge (ESD) is the process of static electrons jumping to a conductor. Simple experiment: Simple experiment: –Rub your shoes on a carpet (this will cause a voltage to build up around your body) –Touch a metal door knob (the metal is a conductor providing a path for the “flow of electrons”—high voltage electricity!!)

7. Conductors Conductors have a large number of loosely attached electrons. Conductors have a large number of loosely attached electrons. These electrons can easily be freed from the nucleus of the atom when voltage is applied. These electrons can easily be freed from the nucleus of the atom when voltage is applied. See this web page for a demonstration: See this web page for a demonstration: –Free the Electron! Free the Electron!Free the Electron!

8. Examples of Conductors Metals Metals –Gold –Silver –Copper (Cat 5 Cable) Water Water Humans!! Humans!!

9. Insulators Material with a high resistance to electrical current. Material with a high resistance to electrical current. Electron orbits are very close to the nucleus. Electron orbits are very close to the nucleus. Examples: Examples: –Plastic –Glass –Wood –Air and other gases

10. Semiconductors With semiconductor materials, the flow of electrons can be precisely controlled. With semiconductor materials, the flow of electrons can be precisely controlled. Examples: Examples: –Carbon –Germanium –And Silicon!! Because silicon is widely available (sand), it is the material we use for computer chips. Because silicon is widely available (sand), it is the material we use for computer chips.

11. Networking Uses All Three!! We use conductors to provide a path for the electrical current. We use conductors to provide a path for the electrical current. –For example, copper wire in our cables. We use insulators to keep the flow of electrons going in one direction. We use insulators to keep the flow of electrons going in one direction. –For example, the plastic sheathing on cables. We use semiconductors to precisely control the flow of electrons. We use semiconductors to precisely control the flow of electrons. –For example, computer chips use silicon.

12. Measuring Electricity Voltage—force or pressure caused by the separation of electrons and protons. Voltage—force or pressure caused by the separation of electrons and protons. –Unit of measurement: Volts (V) Current—the path provided for the free flow of electrons in an electrical circuit. Current—the path provided for the free flow of electrons in an electrical circuit. –Unit of measurement: Ampere (amp) Resistance—impedance or opposition to the flow of electrons: conductor=low resistance; insulators=high resistance. Resistance—impedance or opposition to the flow of electrons: conductor=low resistance; insulators=high resistance. –Unit of measurement: ohms (Ω)

13. Two Types of Current Alternating Current (AC)—electrical current flows in both directions; positive and negative terminals continuously trade places (polarity) Alternating Current (AC)—electrical current flows in both directions; positive and negative terminals continuously trade places (polarity) –Example: Electricity provided by CPL Direct Current (DC)—electrical current flows in one direction; negative to positive Direct Current (DC)—electrical current flows in one direction; negative to positive –Example: Electricity provided by batteries

14. Three Required Parts of an Electrical Circuit Source or BatteryComplete PathResistance

15. Safety Ground Wire Safety Ground Wire prevents electrons from energizing metal parts of the computer. Without grounding, severe shock and fires can occur. Safety grounds are connected to the exposed metal parts of the computer’s chassis.

16. Multimeter Basics A Multimeter is used to measure: –Voltage –Resistance –Continuity (level of resistance) When using a Multimeter, you must properly set it to either AC or DC, depending on the voltage you’re trying to measure.

17. Analog vs. Digital Signals Analog signals have a continuously varying voltage-versus-time graph

18. Analog vs. Digital Signals Digital signals have a square wave with instant transitions from low to high voltage states (0 to 1).

19. Networks Use Digital Signaling Bits are represented by either no voltage (0) or +3 to +6 Volts (1). Bits are represented by either no voltage (0) or +3 to +6 Volts (1). A Signal Reference Ground attached close to a computer’s digital circuits establishes the baseline for no voltage. A Signal Reference Ground attached close to a computer’s digital circuits establishes the baseline for no voltage. Bits must arrive at the destination undistorted in order to be properly interpreted. Bits must arrive at the destination undistorted in order to be properly interpreted. What six things can distort a bit? What six things can distort a bit?

20. Collisions Bits Are Distorted By... Let’s look at each in more detail Propagation Collisions Propagation Attenuation Reflection Noise Timing Problems Attenuation Reflection Noise

21. Bits Are Distorted By... Propagation Propagation Attenuation Attenuation Reflection Reflection Noise Noise Timing Problems Timing Problems Collisions Collisions

22. Propagation Propagation means travel Propagation means travel A bit takes at least a small amount of time to travel (propagate) down the wire. A bit takes at least a small amount of time to travel (propagate) down the wire. If the receiving device cannot handle the speed of the arriving bits, data will be lost. If the receiving device cannot handle the speed of the arriving bits, data will be lost. To avoid data loss, the computer either... To avoid data loss, the computer either... –Buffers the arriving bits into memory for later processing, or –Sends a message to the source to slow down the speed of propagation.

23. Bits Are Distorted By... Propagation Propagation Attenuation Attenuation Reflection Reflection Noise Noise Timing Problems Timing Problems Collisions Collisions

24. Attenuation Attenuation is the loss of signal strength. Attenuation is the loss of signal strength. The signal degrades or losses amplitude as it travels (propagates) along the medium The signal degrades or losses amplitude as it travels (propagates) along the medium Loss of amplitude means that the receiving device can no longer distinguish a 1 bit from a 0 bit. Loss of amplitude means that the receiving device can no longer distinguish a 1 bit from a 0 bit. Attenuation is prevented by: Attenuation is prevented by: –Not exceeding a medium’s distance requirement (100 meters for Cat 5 cable) –By using repeaters that “amplify” the signal

25. Bits Are Distorted By... Propagation Propagation Attenuation Attenuation Reflection Reflection Noise Noise Timing Problems Timing Problems Collisions Collisions

26. Reflection Reflection refers to reflected energy resulting from an impedance mismatch between the NIC and network media. Reflection refers to reflected energy resulting from an impedance mismatch between the NIC and network media. Impedance is the resistance to the flow of current in a circuit provided by the insulating material. Impedance is the resistance to the flow of current in a circuit provided by the insulating material. When impedance is mismatched, the digital signal can “bounce back” (reflect) causing it to be distorted as bits run into each other. When impedance is mismatched, the digital signal can “bounce back” (reflect) causing it to be distorted as bits run into each other.

27. Bits Are Distorted By... Propagation Propagation Attenuation Attenuation Reflection Reflection Noise Noise Timing Problems Timing Problems Collisions Collisions

28. Noise Noise is unwanted additions to the signal Noise is unwanted additions to the signal Noise is unavoidable Noise is unavoidable Too much noise can corrupt a bit turning a binary 1 into a binary 0, or a 0 into a 1, thus destroying the message. Too much noise can corrupt a bit turning a binary 1 into a binary 0, or a 0 into a 1, thus destroying the message. There are five kinds of noise: There are five kinds of noise: –NEXT A; Thermal Noise; Impulse/Reference Ground Noise; EMI/RFI; & NEXT B

29. Noise Our signaling is usually strong enough to override the effects of thermal noise. Our signaling is usually strong enough to override the effects of thermal noise. Reference Ground Noise can usually only be solved by an electrical contractor. Reference Ground Noise can usually only be solved by an electrical contractor. Noise threats we can control directly include: Noise threats we can control directly include: –NEXT (Near End Cross Talk) whether at the source (A) or the destination (B) –EMI/RFI

30. NEXT Noise Near End Cross Talk (NEXT) originates from other wires in the same cable. Near End Cross Talk (NEXT) originates from other wires in the same cable. Crosstalk is avoided by a network technician using proper installation procedures including: Crosstalk is avoided by a network technician using proper installation procedures including: –Strict adherence to RJ-45 termination procedures (Chapter 5); –Using high quality twisted pair cabling

31. EMI/RFI Noise EMI (Electromagnetic Interference) and RFI (Radio Frequency Interference) attack the quality of electrical signals on the cable. EMI (Electromagnetic Interference) and RFI (Radio Frequency Interference) attack the quality of electrical signals on the cable. Sources of EMI/RFI include: Sources of EMI/RFI include: –Fluorescent lighting (EMI) –Electrical motors (EMI) –Radio systems (RFI)

32. EMI/RFI Noise Example Source computer sends out a digital signal. Along the path, the signal encounters EMI noise. Along the path, the signal encounters EMI noise. The digital signal and EMI combine to distort the signal. The digital signal and EMI combine to distort the signal. Digital Signal EMI Distorted Signal

33. EMI/RFI Noise Two ways to prevent EMI/RFI Noise: Two ways to prevent EMI/RFI Noise: –Through shielding the wires in the cable with a metal braid or foil. (Increases cost and diameter of the cable) –Through cancellation the wires are twisted together in pairs to provide self-shielding within the network media.

34. Canceling EMI/RFI Noise UTP Cat 5 has eight wires twisted into four pairs. In each pair, one wire is sending data and the other is receiving. As the electrons flow down the wire, they create a small, circular magnetic field around the wire.

35. Since the two wires are close together, their opposing magnetic fields cancel each other. They also cancel out outside magnetic fields (EMI/RFI). Twisting of the wires enhances cancellation Canceling EMI/RFI Noise

36. Bits Are Distorted By... Propagation Propagation Attenuation Attenuation Reflection Reflection Noise Noise Timing Problems Timing Problems Collisions Collisions

37. Timing Problems Dispersion—similar to attenuation; is the broadening of a signal as it travels down the media. Dispersion—similar to attenuation; is the broadening of a signal as it travels down the media. Jitter—caused by unsynchronized clocking signals between source and destination. This means bits will arrive later or earlier than expected. Jitter—caused by unsynchronized clocking signals between source and destination. This means bits will arrive later or earlier than expected. Latency—is the delay of a network signal caused by: Latency—is the delay of a network signal caused by: –Time it takes a bit to travel to its destination –Devices the bit travels through

38. Bits Are Distorted By... Propagation Propagation Attenuation Attenuation Reflection Reflection Noise Noise Timing Problems Timing Problems Collisions Collisions

39. Collisions Collisions occur in broadcast topologies where devices share access to the network media. Collisions occur in broadcast topologies where devices share access to the network media. A collision happens when two devices attempt to communicate on the shared- medium at the same time. A collision happens when two devices attempt to communicate on the shared- medium at the same time. Collisions destroy data requiring the source to retransmit. Collisions destroy data requiring the source to retransmit. The prevention of collisions will be discussed in more detail later in the semester. The prevention of collisions will be discussed in more detail later in the semester.

40. Final Topic: Encoding Encoding is the process of converting binary data into a form that can travel on a physical communications link. Encoding is the process of converting binary data into a form that can travel on a physical communications link. For our purposes, you only need to know the two types of encoding schemes most commonly used: For our purposes, you only need to know the two types of encoding schemes most commonly used: –Manchester –NRZ (non-return to zero)

41. Good Luck on the Test!!