Business Data Communications, by Allen Dooley, (c) 2005 Pearson Prentice Hall Chapter Two 1 Business Data Communications Chapter Two Physical Layer Fundamentals

Business Data Communications, by Allen Dooley, (c) 2005 Pearson Prentice Hall Chapter Two 2 Primary Learning Objectives Understand the general purpose of the physical layer Distinguish between analog and digital Signaling Describe circuit configurations and methods of data flow Identify characteristics of conducted and radiated Media Name and differentiate four types of multiplexing

Business Data Communications, by Allen Dooley, (c) 2005 Pearson Prentice Hall Chapter Two 3 Physical Layer Similar in both the OSI and TCP/IP models Specifies the physical characteristics of a network Stacked below the data link layer Transmits an “unformatted” data bit stream Has four key components: Signaling method Circuit configuration Transmission medium Devices used

Business Data Communications, by Allen Dooley, (c) 2005 Pearson Prentice Hall Chapter Two 4 Physical Layer Pin connector functions are an important physical layer responsibility

Business Data Communications, by Allen Dooley, (c) 2005 Pearson Prentice Hall Chapter Two 5 Signaling Methods -- 1 st Component of the Physical Layer Analog versus Digital Analog is continuous Digital is discrete Analog uses modulation techniques Amplitude, Frequency, Phase, for example Analog is measured in hertz Digital uses encoding schemes Manchester and Differential Manchester, for example Digital is measured in bps, or bits per second

Business Data Communications, by Allen Dooley, (c) 2005 Pearson Prentice Hall Chapter Two 6 Analog Signaling Methods Can take an infinite form Modulate a sine wave Can change a wave’s amplitude, frequency, or phase Amplitude affects the wave’s height or strength Frequency measures the waves per second Phase occurs when a wave changes direction Modulation is either Simple or Complex

Business Data Communications, by Allen Dooley, (c) 2005 Pearson Prentice Hall Chapter Two 7 Analog Signaling Methods

Business Data Communications, by Allen Dooley, (c) 2005 Pearson Prentice Hall Chapter Two 8 Analog Signaling Methods

Business Data Communications, by Allen Dooley, (c) 2005 Pearson Prentice Hall Chapter Two 9 Analog Signaling Methods A hertz is a unit of frequency. A period is measured in seconds.

Business Data Communications, by Allen Dooley, (c) 2005 Pearson Prentice Hall Chapter Two 10 Analog Signaling Methods

Business Data Communications, by Allen Dooley, (c) 2005 Pearson Prentice Hall Chapter Two 11 Analog Signaling Methods Simple signal methods use: A choice of two amplitudes, or A choice of two frequencies, or A single phase change A simple signal method has the same symbol and bit rate

Business Data Communications, by Allen Dooley, (c) 2005 Pearson Prentice Hall Chapter Two 12 Analog Signaling Methods A complex signal method occurs when the bit rate and the symbol rate are not the same: A symbol, or baud, rate can represent more than one bit per time period When more then one bit is represented within a single symbol, then the symbol and bit rates differ Complex signal methods require that more than one bit be represented per symbol Complex signal methods combine different amplitudes, frequencies, or phases, or some combination of these

Business Data Communications, by Allen Dooley, (c) 2005 Pearson Prentice Hall Chapter Two 13 Analog Signaling Methods

Business Data Communications, by Allen Dooley, (c) 2005 Pearson Prentice Hall Chapter Two 14 Analog Bandwidth Analog bandwidth is measured in hertz The bandwidth measurement is the difference between a given analog’s lowest and highest frequencies The spectrum consists of the entire range of frequencies, from lowest to highest

Business Data Communications, by Allen Dooley, (c) 2005 Pearson Prentice Hall Chapter Two 15 Analog Bandwidth and Frequency Spectrum Example

Business Data Communications, by Allen Dooley, (c) 2005 Pearson Prentice Hall Chapter Two 16 Digital Signaling Methods Are discrete, not continuous Take the value of a binary 0 or binary 1 Make use of encoding schemes such as: Manchester Ethernet Differential Manchester Token Ring

Business Data Communications, by Allen Dooley, (c) 2005 Pearson Prentice Hall Chapter Two 17 Digital Signaling Methods

Business Data Communications, by Allen Dooley, (c) 2005 Pearson Prentice Hall Chapter Two 18 Digital Signaling Methods Make use of a “bit interval”, the time required to send a single bit The sender and receiver can use this bit interval to clock their transmission with each other With the bit interval as a clocking mechanism The sender and receiver can synchronize their transmissions However, self-clocking mechanisms are more efficient A bit rate is also associated with a digital signaling method The bit rate is the number of bit intervals per second, or bps

Business Data Communications, by Allen Dooley, (c) 2005 Pearson Prentice Hall Chapter Two 19 Digital Bandwidth Digital bandwidth is typically expressed in bits per second (bps) Digital bandwidth is determined using the bit interval and the bit rate Assuming we have a digital signal with a bit interval of 60 microseconds, what is its bandwidth? The formula is expressed as: bps = 1 / (60 * ), or approximately 16.6 Kbps (thousands of bits per second)

Business Data Communications, by Allen Dooley, (c) 2005 Pearson Prentice Hall Chapter Two 20 Digital Signaling Methods

Business Data Communications, by Allen Dooley, (c) 2005 Pearson Prentice Hall Chapter Two 21 Circuit Configuration -- 2 nd Component of the Physical Layer Two major categories Point-to-point Multipoint Point-to-point circuits are dedicated links between two communicating devices Multipoint circuits are shared among several communicating devices Either could be appropriate based on network need

Business Data Communications, by Allen Dooley, (c) 2005 Pearson Prentice Hall Chapter Two 22 Point-to-point Circuit

Business Data Communications, by Allen Dooley, (c) 2005 Pearson Prentice Hall Chapter Two 23 Multipoint or Multidrop Circuit

Business Data Communications, by Allen Dooley, (c) 2005 Pearson Prentice Hall Chapter Two 24 Transmission Medium -- 3 rd Component of the Physical Layer Two major categories Conducted Radiated Conducted – Makes use of cables Twisted wire pair, coaxial cable, fiber optic Radiated – is “In the Air” Terrestrial microwave, satellite, radio, infrared

Business Data Communications, by Allen Dooley, (c) 2005 Pearson Prentice Hall Chapter Two 25 Conducted Media Use Cable An example of category 5, unshielded twisted wire pair An example of a coaxial cable, with its layered sheathing

Business Data Communications, by Allen Dooley, (c) 2005 Pearson Prentice Hall Chapter Two 26 Conducted Media Use Cable Single mode fiber Cable with Connectors Fiber cores are measured in microns Another type of fiber is multimode Fiber is composed of either glass or plastic strands

Business Data Communications, by Allen Dooley, (c) 2005 Pearson Prentice Hall Chapter Two 27 Radiated Media, Signals “in the air”

Business Data Communications, by Allen Dooley, (c) 2005 Pearson Prentice Hall Chapter Two 28 Transmission Medium Considerations Cost Bandwidth Security Transmission Impairment Distance

Business Data Communications, by Allen Dooley, (c) 2005 Pearson Prentice Hall Chapter Two 29 Transmission Medium Impairment Considerations Attenuation Cross talk Distortion Environmental factors Rain, fog, snow, cloud cover, electrical or magnetic storms Of the various media, fiber optic is the least susceptible to impairment, and the most secure But also very expensive!

Business Data Communications, by Allen Dooley, (c) 2005 Pearson Prentice Hall Chapter Two 30 Comparison of Various Media Type of MediumSecurityTransmission Distance CostError Potential Difficulty of Installation Twisted Wire PairModerateShortLowModerateLow Coaxial CableModerateShortModerateLow Fiber OpticHighModerate to LongHighVery LowHigh RadioLowShortLowModerate Terrestrial MicrowaveLowLongModerateLow to Moderate SatelliteLowLongModerateLow to Moderate

Business Data Communications, by Allen Dooley, (c) 2005 Pearson Prentice Hall Chapter Two 31 Devices at the Physical Layer -- 4th Component of the Physical Layer Hubs or Repeaters Modems Codecs Multiplexers Cabling Tools (Not devices, but still important)

Business Data Communications, by Allen Dooley, (c) 2005 Pearson Prentice Hall Chapter Two 32 Devices at the Physical Layer -- 4th Component of the Physical Layer

Business Data Communications, by Allen Dooley, (c) 2005 Pearson Prentice Hall Chapter Two 33 Multiplexing Allows slower-speed circuit devices to share a single high-speed circuit In many cases, individual devices do not need their own high-speed circuit Type of multiplexing include: Frequency division Time division Statistical time division Wavelength division

Business Data Communications, by Allen Dooley, (c) 2005 Pearson Prentice Hall Chapter Two 34 Frequency Division Multiplexing A single high-speed circuit with multiple channel frequencies The circuit is analog Bandwidth is measured in hertz Data transmitted via channels Viewed as horizontal Makes use of guardbands as overhead

Business Data Communications, by Allen Dooley, (c) 2005 Pearson Prentice Hall Chapter Two 35 Frequency Division Multiplexing

Business Data Communications, by Allen Dooley, (c) 2005 Pearson Prentice Hall Chapter Two 36 Time Division Multiplexing A single high-speed circuit carrying multiple frames Time slots may only be used by specifically allocated devices The circuit is digital Bandwidth is measured in bits per second (bps) Data transmitted via frames Viewed as vertical Unused time slots create overhead

Business Data Communications, by Allen Dooley, (c) 2005 Pearson Prentice Hall Chapter Two 37 Time Division Multiplexing

Business Data Communications, by Allen Dooley, (c) 2005 Pearson Prentice Hall Chapter Two 38 Statistical Time Division Multiplexing A single high-speed circuit carrying multiple frames Time slots can be allocated to devices as needed Time slots must carry addressing The circuit is digital Bandwidth is measured in bits per second Data transmitted via frames Viewed as vertical, not horizontal Addressing of time slots creates overhead

Business Data Communications, by Allen Dooley, (c) 2005 Pearson Prentice Hall Chapter Two 39 Statistical Time Division Multiplexing

Business Data Communications, by Allen Dooley, (c) 2005 Pearson Prentice Hall Chapter Two 40 Wavelength Division Multiplexing Makes use of fiber optics Operates in a manner somewhat similar to the way that frequency division multiplexing is used with copper Uses lasers to transmit different frequencies of light through the same fiber optic cable At the sending end, narrow bands of light are combined into a wider band The wider band is the high-speed circuit At the receiving end, the signals are separated

Business Data Communications, by Allen Dooley, (c) 2005 Pearson Prentice Hall Chapter Two 41 In Summary The physical layer: In the OSI and TCP/IP models is similar Is essential for transporting of data bits from sender to receiver Has circuits that are Conducted or Radiated Passes its unformatted data bit stream up to the Data Link Layer