Transmission Basics and Networking Media Chapter Four Transmission Basics and Networking Media

Objectives Explain data transmission concepts including full-duplexing, attenuation, and noise Describe the physical characteristics of coaxial cable, STP, UTP, and fiber-optic media Explain the benefits and limitations of different networking media Identify the best practices for cabling buildings and work areas Describe the methods of transmitting data through the atmosphere

Transmission Basics Transmission has two meanings: Refers to process of issuing data signals on a medium Refers to progress of data signals over a medium On a data network, information can be transmitted via one of two methods: Analog Digital

Transmission Basics Both analog and digital signals are generated by electrical current, pressure of which is measured in volts In analog signals, voltage varies continuously In digital signals, voltage turns off and on repeatedly

Figure 4-1: Example of an analog signal Transmission Basics Figure 4-1: Example of an analog signal

Transmission Basics Amplitude Frequency Wavelength Measure of a signal’s strength Frequency Number of times a signal’s amplitude changes over a period of time Expressed in hertz (Hz) Wavelength Distances between corresponding points on a wave’s cycle

Figure 4-2: Phase differences Transmission Basics Phase Refers to progress of a wave over time in relationship to a fixed point Figure 4-2: Phase differences

Figure 4-3: A complex analog signal representing human speech Transmission Basics Figure 4-3: A complex analog signal representing human speech

Transmission Basics Binary system encodes using 1s and 0s Bits can only have a value of either 1 or 0 Eight bits together form a byte Noise or any interference that may degrade signals affects digital signals less than analog signals

Figure 4-4: Example of a digital signal Transmission Basics Figure 4-4: Example of a digital signal

Data Modulation Modem Modulation Frequency modulation (FM) Name reflects function as modulator/demodulator Modulation Technique for formatting signals Frequency modulation (FM) Method of data modulation in which frequency of carrier signal is modified by application of a data signal Amplitude modulation (AM) Modulation technique in which amplitude of carrier signal is modified by application of a data signal

Figure 4-5: A carrier wave modified by frequency modulation Data Modulation Figure 4-5: A carrier wave modified by frequency modulation

Transmission Direction Simplex Signals travel in only one direction Half-duplex Signals may travel in both directions over a medium but in only one direction at a time Full-duplex Signals are free to travel in both directions over a medium simultaneously Also referred to just as duplex

Transmission Direction Channel Distinct communication path between two or more nodes Figure 4-6: Simplex, half-duplex, and full-duplex transmission

Transmission Direction Multiplexing Allows multiple signals to travel simultaneously over one medium To accommodate multiple signals, single medium is logically separated into subchannels For each type of multiplexing: Multiplexer (mux) is required at sending end of channel Demultiplexer (demux) separates the combined signals and regenerates them in original form

Transmission Direction Time division multiplexing (TDM) Divides channel into multiple intervals of time Figure 4-7: Time division multiplexing

Transmission Direction Wavelength division multiplexing (WDM) Used only with fiber-optic cable Data is transmitted as pulses of light Fiber-optic modem (FOM) is a demultiplexer used on fiber networks that employ WDM Figure 4-9: Wavelength division multiplexing

Relationships Between Nodes Point-to-point Transmission involving one transmitter and one receiver Broadcast Transmission involving one transmitter and multiple receivers Webcasting Broadcast transmission used over the Web

Relationships Between Nodes Figure 4-10: Point-to-point versus broadcast transmission

Throughput and Bandwidth Throughput is amount of data the medium can transmit during a given period of time Also called capacity Bandwidth measures difference between highest and lowest frequencies a media can transmit Range of frequencies is directly related to throughput

Transmission Flaws Electromagnetic interference (EMI) Interference that may be caused by motors, power lines, television, copiers, fluorescent lights, or other sources of electrical activity Radiofrequency interference (RFI) Interference that may be generated by motors, power lines, televisions, copiers, fluorescent lights, or broadcast signals from radio or TV towers

Figure 4-11: An analog signal distorted by noise Transmission Flaws Figure 4-11: An analog signal distorted by noise

Figure 4-12: A digital signal distorted by noise Transmission Flaws Figure 4-12: A digital signal distorted by noise

Transmission Flaws Attenuation Loss of signal strength as transmission travels away from source Analog signals pass through an amplifier, which increases not only voltage of a signal but also noise accumulated Figure 4-13: An analog signal distorted by noise, and then amplified

Transmission Flaws Regeneration Repeater Process of retransmitting a digital signal Repeater Device used to regenerate a signal Figure 4-14: A digital signal distorted by noise, and then repeated

Coaxial Cable Consists of central copper core surrounded by an insulator, braiding, and outer cover called a sheath Figure 4-15: Coaxial cable

Table 4-2: Some types of coaxial cable

Thicknet (10Base5) Also called thickwire Ethernet Rigid coaxial cable used on original Ethernet networks IEEE designates Thicknet as 10Base5 Ethernet Almost never used on new networks but you may find it on older networks Used to connect one data closet to another as part of network backbone

Thicknet Characteristics Throughput According to IEEE 802.3, Thicknet transmits data at maximum rate of 10 Mbps Cost Less expensive than fiber-optic but more expensive than some other types of coaxial cable Connector Can include a few different types of connectors, which are very different from those used on modern networks

Thicknet Characteristics Attachment Unit Interface (AUI) Ethernet standard establishing physical specifications for connecting coaxial cables with transceivers and networked nodes An AUI connector may also be called a DIX or DB-15 connector Figure 4-17: AUI connectors

Thicknet Characteristics N-series connector (or n connector) Screw-and-barrel arrangement securely connects coaxial cable segments and devices Figure 4-18: N-Series connector

Thicknet Characteristics Noise immunity Because of its wide diameter and excellent shielding, has the highest resistance to noise of any commonly used types of network wiring Size and scalability Because of its high noise resistance, it allows data to travel longer than other types of cabling

Thinnet (10Base2) Also known as thin Ethernet Characteristics: Throughput Can transmit at maximum rate of 10 Mbps Cost Less expensive than Thicknet and fiber-optic cable More expensive than twisted-pair wiring Connectors Connects wire to network devices with BNC T-connectors A seen in Figure 4-19, BNC barrel connectors are used to join two Thinnet cable segments together

Thinnet (10Base2) Characteristics (cont.): Size and scalability Allows a maximum of 185 m per network segment (see Figure 4-20) Noise immunity More resistant than twisted-pair wiring Less resistant than twisted-pair wiring Figure 4-19: Thinnet BNC connectors

Thinnet (10Base2) Signal bounce Caused by improper termination on a bus network Travels endlessly between two ends of network Prevents new signals from getting through Figure 4-20: A 10Base2 Ethernet network

Twisted-Pair (TP) Cable Color-coded pairs of insulated copper wires twisted around each other and encased in plastic coating Twists in wire help reduce effects of crosstalk Number of twists per meter or foot known as twist ratio Alien Crosstalk When signals from adjacent cables interfere with another cable’s transmission Figure 21: Twisted-pair cable

Shielded Twisted-Pair (STP) STP cable consists of twisted wire pairs that are individually insulated and surrounded by shielding made of metallic substance Figure 4-22: STP cable

Unshielded Twisted-Pair Consists of one or more insulated wire pairs encased in a plastic sheath Does not contain additional shielding Figure 4-23: UTP cable

Unshielded Twisted-Pair To manage network cabling, it is necessary to be familiar with standards used on modern networks, particularly Category 3 (CAT3) and Category 5 (CAT5) Figure 4-24: A CAT5 UTP cable

Comparing STP and UTP Throughput Cost Connector Noise immunity Both can transmit up to 100 Mbps Cost Typically, STP is more expensive Connector Both use RJ-45 connectors (see Figure 4-27) and data jacks Noise immunity STP is more noise-resistant Size and scalability Maximum segment length for both is 100 meters

Figure 4-27: An RJ-45 connector

Fiber-Optic Cable Contains one or several glass fibers at its core Surrounding the fibers is a layer of glass called cladding Figure 4-28: A fiber-optic cable

Figure 4-29: Single-mode and multimode fiber-optic cables Single-mode fiber Carries light pulses along single path Multimode fiber Many pulses of light generated by LED travel at different angles Figure 4-29: Single-mode and multimode fiber-optic cables

Fiber-Optic Cable Throughput Cost Reliable in transmitting up to 1 gigabit per second Cost Most expensive type of cable

Fiber-Optic Cable Noise immunity Size and scalability Unaffected by either EMI or RFI Size and scalability Network segments made from fiber can span 100 meters Signals transmitted over fiber can experience optical loss

Fiber-Optic Cable Two popular connectors used with fiber-optic cable: ST connectors SC connectors Figure 4-30: ST and SC fiber connectors

Atmospheric Transmission Media Infrared transmission Infrared networks use infrared light signals to transmit data through space Direct infrared transmission depends on transmitter and receiver remaining within line of sight In indirect infrared transmission, signals can bounce off of walls, ceilings, and any other objects in their path

Atmospheric Transmission Media RF transmission Radio frequency (RF) transmission relies on signals broadcast over specific frequencies Two most common RF technologies: Narrowband Spread spectrum

Choosing the Right Transmission Media Areas of high EMI or RFI Corners and small spaces Distance Security Existing infrastructure Growth

Chapter Summary Information can be transmitted via analog or digital methodology Throughput is the amount of data a medium can transmit during a given period of time Noise is interference that distorts an analog or digital signal Costs depend on many factors There are three specifications that dictate size and scalability of networking media Connectors connect wire to the network device

Chapter Summary Coaxial cable consists of central copper core surrounded by an insulator and a sheath Thicknet cabling is a rigid coaxial cable used for original Ethernet networks Both Thicknet and Thinnet coaxial cable rely on bus topology and must be terminated at both ends with a resistor Twisted-pair cable consists of color-coded pairs of insulated copper wires, twisted around each other and encased in plastic coating

Chapter Summary STP cable consists of twisted pair wires individually insulated and surrounded by a shielding made of metallic substance UTP cabling consists of one or more insulated wire pairs encased in a plastic sheath Fiber-optic cable contains one or several glass fibers in its core On today’s networks, fiber is used primarily as backbone cable