【正文】 Encoded Data 1101010 Binary Encoding Signaling 1. First, data must be converted to binary, as we have just seen 2. Second, bits must be covered Into signals (voltage changes, etc.). Voltage change, etc. 22 Figure 37: On/Off Binary Signaling Off= 0 On= 1 On= 1 Off= 0 On= 1 Off= 0 On= 1 Light Source Optical Fiber Clock Cycle During each clock cycle, light is turned on for a one or off for a zero. 23 Figure 38: Binary Signaling in 232 Serial Ports 0 Volts 15 Volts 15 Volts Clock Cycle 0 0 1 3 Volts 3 Volts 0 1 This type of signaling is used in 232 serial ports. In a clock cycle, 3 to 15 volts represents a zero 3 to 15 volts is a ONE 24 Figure 39: Relative Immunity to Errors in Binary Signaling 0 Volts 15 Volts 15 Volts Transmitted Signal (12 Volts) Received Signal (6 volts) 3 Volts 3 Volts 0 1 Despite a 50% drop in voltage, the receiver will still know that the signal is a zero 25 Binary and Binary Signaling ? In binary signaling, there are two states – This can represent a single bit per clock cycle. ? In digital signaling, there are a few bits per clock cycle—2, 4, 8, 16, 32, … ? With more states, several bits to be sent per clock cycle ? Note that all binary transmission (2 states) is digital (few states) ? But not all digital transmission is binary 11 10 01 00 10 11 00 01 01 Clock Cycle 26 ? Test Your Understanding ? P 149 ? 4 a, b, c 27 Figure 310: 4State Digital Signaling 11 10 01 00 Client PC Server 10 11 00 01 01 Clock Cycle Digital signaling has a FEW possible states per clock cycle (4 in this slide) This allows it to send multiple bits per clock cycle This increases the bit transmission rate per clock cycle It reduces error resistance because differences between states are smaller Box 28 Quiz ? Which Is Binary? Which Is Digital? 1. Calendar 2. Number of Fingers 5. Gender Male or Female 3. On/Off Switch 4. Day of the Week Box 29 Figure 310: 4State Digital Signaling, Continued ? Equation 31: Bit rate = Baud rate * Bits sent per clock cycle – Baud rate is the number of clock cycles per second ? If the clock cycle is 1/1000 of a second, the baud rate is 1,000 baud – Bit rate is then the number of clock cycles per second times the number of bits sent per clock cycle ? If the three bits are sent per clock cycle, the bit rate is 3,000 bps or 3 kbps Box 30 Figure 310: 4State Digital Signaling, Continued ? Equation 32: States = 2Bits – Bits is the number of bits to be sent per clock cycle – States is the number of states needed to send that many bits ? Doubling the number of states transmits one more bit per clock cycle. Box Bits to be sent per clock cycle Number of states required 1 2 2 4 3 8 4 16 31 Figure 310: 4State Digital Signaling, Continued ? Example: – The clock cycle is 1/100,000 second ? The baud rate is 100 kbaud (not kbauds) – You want a bit rate of 500,000 bps ? Solution: – You have to send 5 bits per clock cycle (baud) – This will require 32 states ? States = 2bits ? States = 25 ? States = 32 Box 32 Figure 310: 4State Digital Signaling, Continued ? Example: – Suppose there a system has 8 states – Suppose that the clock cycle is 1/10,000 second – How fast can the system transmit? ? Solution: – With four states, 3 information bits can be sent per clock cycle (8=2X) [Equation 32] X=3 – With a clock cycle of 1/10,000, baud rate is 10,000 baud – The bit rate will be 30 kbps (3 bits/clock cycle times 10,000 clock cycles per second). [Equation 31] Box 33 ? Test Your Understanding ? P 151 UTP Propagation Unshielded Twisted Pair wiring 35 Figure 312: 4Pair UTP Cord with RJ45 Connector 3. RJ45 Connector 2. 8 Wires Organized as 4 Twisted Pairs Industry Standard Pen 1. UTP Cord UTP Cord 36 RJ45 Jacks and Connectors RJ45 Jack RJ45 Jack RJ45 Jack RJ45 Connectors 37 Figure 311: Unshielded Twisted Pair (UTP) Wiring, Continued ? UTP Characteristics – Inexpensive and to purchase and install – Dominates media for access links between puters and the nearest switch 38 ? Test Your Understanding ? P 154 39 Figure 313: Attenuation and Noise Power Distance 1. Signal Signals in UTP attenuate with propagation distance. If attenuation is too great, the signal will not be readable by the receiver. 40 Figure 314: Decibels ? Attenuation is Sometimes Expressed in Decibels (dB) ? The equation for decibels is – dB = 10 log10(P2/P1) – Where P1 is the initial power and P2 is the final power after transmission – If P2 is smaller than P1, then the answer will be negative 41 Figure 314: Decibels, Continued ? Example – Over a transmission link, power drops to 37%