Transcript Chapter One
Chapter Four Transmission Basics and Networking Media 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 Transmission Basics Figure 4-1: Example of an analog signal Transmission Basics Amplitude Measure of a signal’s strength (height of the wave) Frequency Number of times a signal’s amplitude changes over a period of time Expressed in hertz (Hz) (Heinrich Hertz) Wavelength Distances between corresponding points on a wave’s cycle Inverse to frequency Freq 1,000,000 cycles/second (1MHz) – WL 300m Freq 2,000,000 cycles/second (2MHz) – WL 150m Transmission Basics Phase Refers to progress of a wave over time in relationship to a fixed point Figure 4-2: Phase differences Transmission Basics Figure 4-3: A complex analog signal representing human speech Transmission Basics Binary system encodes using 1s and 0s Bits (binary digit) can only have a value of either 1 or 0 Eight bits together form a byte Byte “01111001” = “121” on digital network Noise or any interference that may degrade signals affects digital signals less than analog signals Transmission Basics Figure 4-4: Example of a digital signal Transmission Basics Digital more reliable than analog Digital is less effected by noise However, digital requires many pulses to transmit the same info an analog signal can transmit with a single wave Higher reliability/efficiency make the extra digital signaling worth it Data Modulation Modem Name reflects function as modulator/demodulator Digital to analog – analog to digital 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 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 Used by modern Ethernet networks 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 Commonly used to increase the amount of data that can be transmitted in a time period Transmission Direction Time division multiplexing (TDM) Divides channel into multiple intervals of time (time slots) Figure 4-7: Time division multiplexing Transmission Direction Statistical multiplexing Similar to TDM Assigns slots to nodes according to priority and need instead of in succession Figure 4-8: Statistical multiplexing Transmission Direction Wavelength division multiplexing (WDM) New technology Used only with fiber-optic cable Data is transmitted as pulses of light Fiber-optic modem (FOM) is a mux/demux 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 Throughput Table 4-1: Throughput measures Baseband and Broadband Baseband Transmission form in which (typically) digital signals are sent through direct current (DC) pulses applied to the wire DC requires exclusive use of wire’s capacity Example: Ethernet networks Broadband Transmission form in which signals are modulated as radiofrequency (RF) analog pulses that use different frequency ranges 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 Transmission Flaws Figure 4-11: An analog 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 Process of retransmitting a digital signal Repeater Device used to regenerate a digital signal (physical layer) Figure 4-14: A digital signal distorted by noise, and then repeated Media Characteristics Determining transmission media for your network: Throughput Perhaps most significant factor in choosing a transmission medium is throughput Cost Cost of installation – yourself vs. contractors Cost of new infrastructure versus reusing existing infrastructure Cost of maintenance and support Cost of a lower transmission rate affecting productivity – wait times Cost of obsolescence Media Characteristics Size and scalability Specifications determining size and scalability: Maximum nodes per segment Maximum segment length Maximum network length Latency is the delay between the transmission of a signal and its receipt Media Characteristics Connectors Connects wire to network device Noise immunity Thicker cables are generally less susceptible to noise Installation location very important Conduits can protect cabling from noise Coaxial Cable Consists of central copper core surrounded by an insulator, braiding, and outer cover called a sheath Figure 4-15: Coaxial cable 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 10Base5 Designation explanation: 10 – throughput (10 Mbps) Base – Baseband transmission 5 – maximum segment length (500 meters) 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 In Thicknet networking, the transceiver is a separate device and may also be called a media access unit (MAU) Figure 4-16: Thicknet cable transceiver with detail of a vampire tap 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 BNC barrel connectors are used to join two Thinnet cable segments together