Chapter Four Transmission Basics and Networking Media Transmission

Chapter Four Transmission Basics and Networking Media

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

Transmission Basics Phase n 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 1 s and 0 s 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

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

Data Modulation Modem n Name reflects function as modulator/demodulator Modulation n Technique formatting signals Frequency modulation (FM) n Method of data modulation in which frequency of carrier signal is modified by application of a data signal Amplitude modulation (AM) n 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 n Signals travel in only one direction Half-duplex n Signals may travel in both directions over a medium but in only one direction at a time Full-duplex n n Signals are free to travel in both directions over a medium simultaneously Also referred to just as duplex

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

Transmission Direction Multiplexing n n n 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) n Divides channel into multiple intervals of time

Transmission Direction Statistical multiplexing n n Similar to TDM Assigns slots to nodes according to priority and need instead of in succession

Transmission Direction Wavelength division multiplexing (WDM) n n n 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

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

Relationships Between Nodes

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

Throughput

Baseband Broadband Baseband n Transmission form in which (typically) digital signals are sent through direct current (DC) pulses applied to the wire Broadband n Transmission form in which signals are modulated as radiofrequency (RF) pulses that use different frequency ranges

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

Transmission Flaws

Transmission Flaws

Transmission Flaws Attenuation n n 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

Transmission Flaws Regeneration n Process of retransmitting a digital signal Repeater n Device used to regenerate a signal

Media Characteristics Throughput n Perhaps most significant factor in choosing a transmission medium is throughput Cost n n n Cost of installation Cost of new infrastructure versus reusing existing infrastructure Cost of maintenance and support Cost of a lower transmission rate affecting productivity Cost of obsolescence

Media Characteristics Size and scalability n Specifications determining size and scalability: Maximum nodes per segment Maximum segment length Maximum network length n Latency is the delay between the transmission of a signal and its receipt

Media Characteristics Connectors n Connects wire to network device Noise immunity n n n Thicker cables are generally less susceptible to noise Possible to use antinoise algorithms to protect data from being corrupted by noise Conduits can protect cabling from noise

Coaxial Cable Consists of central copper core surrounded by an insulator, braiding, and outer cover called a sheath

Coaxial Cable

Thicknet (10 Base 5) Also called thickwire Ethernet Rigid coaxial cable used on original Ethernet networks IEEE designates Thicknet as 10 Base 5 Ethernet Almost never used on new networks but you may find it on older networks n Used to connect one data closet to another as part of network backbone

Thicknet Characteristics Throughput n According to IEEE 802. 3, Thicknet transmits data at maximum rate of 10 Mbps Cost n Less expensive than fiber-optic but more expensive than some other types of coaxial cable Connector n Can include a few different types of connectors, which are very different from those used on modern networks

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

Thicknet Characteristics Noise immunity n 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 n Because of its high noise resistance, it allows data to travel longer than other types of cabling

Thinnet (10 Base 2) Also known as thin Ethernet Characteristics: n Throughput Can transmit at maximum rate of 10 Mbps n Cost Less expensive than Thicknet and fiber-optic cable More expensive than twisted-pair wiring n 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 (10 Base 2) Characteristics (cont. ): n Size and scalability Allows a maximum of 185 m per network segment (see Figure 4 -20) n Noise immunity More resistant than twisted-pair wiring Less resistant than twisted-pair wiring

Thinnet (10 Base 2) Signal bounce n n n Caused by improper termination on a bus network Travels endlessly between two ends of network Prevents new signals from getting through

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 n Number of twists per meter or foot known as twist ratio Alien Crosstalk n When signals from adjacent cables interfere with another cable’s transmission

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

Unshielded Twisted-Pair Consists of one or more insulated wire pairs encased in a plastic sheath Does not contain additional shielding

Unshielded Twisted-Pair To manage network cabling, it is necessary to be familiar with standards used on modern networks, particularly Category 3 (CAT 3) and Category 5 (CAT 5)

10 Base. T Popular Ethernet networking standard that replaced 10 Base 2 and 10 Base 5 technologies

10 Base. T Enterprise-wide network n n Spans entire organization Often services needs of many diverse users

100 Base. T Enables LANs to run at 100 -Mbps data transfer rate Also known as Fast Ethernet

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

RJ-45 Connector

Fiber-Optic Cable Contains one or several glass fibers at its core n Surrounding the fibers is a layer of glass called cladding

Fiber-Optic Cable Single-mode fiber n Carries light pulses along single path Multimode fiber n Many pulses of light generated by LED travel at different angles

Fiber-Optic Cable Throughput n Reliable in transmitting up to 1 gigabit per second Cost n Most expensive type of cable Connector n You can use any of 10 different types of connectors (see Figure 4 -30)

Fiber-Optic Cable Noise immunity n Unaffected by either EMI or RFI Size and scalability n n 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: n n ST connectors SC connectors

10 Base. F and 100 Base. FX 10 Base. F n Physical layer standard for networks specifying baseband transmission, multimode fiber cabling, and 10 -Mbps throughput 100 Base. FX n Physical layer standard for networks specifying baseband transmission, multimode fiber cabling, and 100 -Mbps throughput

Physical Layer Networking Standards

Cable Design and Management Cable plant n Hardware comprising enterprise-wide cabling system Structured cabling n Method for uniform, enterprise -wide, multivendor cabling systems

Cable Design and Management Entrance facilities Backbone wiring n Backbone cabling that provides vertical connections between floors of a building are called risers

Cable Design and Management Equipment room Telecommunications closet n Punch-down block is a panel of data receptors n Patch panel is a wall-mounted panel of data receptors

Cable Design and Management Horizontal wiring

Cable Design and Management Work area n Patch cable is a relatively short section of twistedpair cabling with connectors on both ends that connect network devices to data outlets

Cable Design and Management

Installing Cable

Installing Cable

Installing Cable Straight-through cable n Terminations at both ends are identical Crossover cable n Terminations locations of transmit and receiver wires on one end of cable are reversed

Installing Cable Do not untwisted-pair cables more than one-half inch before inserting them Do not strip off more than one inch of insulation from copper wire in twisted-pair cables Watch bend radius limitations for cable being installed Test each segment of cabling with cable tester Use only cable ties to cinch groups of cable together

Installing Cable Avoid laying cable across floor where it may sustain damage Install cable at least three feet away from fluorescent lights or other sources of EMI Always leave slack in cable runs If running cable in plenum, area above ceiling tile or below subflooring, make sure cable sheath is plenum-rated Pay attention to grounding requirements

Atmospheric Transmission Media Infrared transmission n 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 n Radio frequency (RF) transmission relies n 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