Date post: | 21-Dec-2015 |
Category: |
Documents |
View: | 236 times |
Download: | 2 times |
Network + 2
Objectives
After reading this chapter and completing the exercises, you will be able to:
Identify organizations that set standards for networking
Describe the purpose of the OSI Model and each of its layers
Network + 3
Objectives (continued)
Explain specific functions belonging to each OSI Model layer
Understand how two network nodes communicate through the OSI Model
Network + 4
Objectives (continued)
Discuss the structure and purpose of data packets and frames
Describe the two types of addressing covered by the OSI Model
Network + 5
Transmission Basics
• Transmit means to issue signals to the network medium
• Transmission refers to either the process of transmitting or the progress of signals after they have been transmitted
Network + 6
Transmission Basics
• Analog and Digital Signaling
• On a data network, information can be transmitted via one of two signaling methods: analog or digital
• Both types of signals are generated by electrical current, the pressure of which is measured in volts
Network + 7
• An analog signal, like other waveforms, is characterized by four fundamental properties: amplitude, frequency,wavelength, and phase
• A wave’s amplitude
• Frequency
• Phase
Transmission Basics (continued)
Network + 8
• Digital signals composed of • pulses
• precise
• positive voltages and zero voltages
• Data Modulation• used to modify analog signals in order to make them
suitable for carrying data over a communication path
Transmission Basics (continued)
Network + 9
• Modem reflects this device’s function as a modulator/demodulator
• Modulates digital signals into analog signals
• Modulation
• Frequency modulation (FM)
• Amplitude modulation (AM)
Transmission Basics (continued)
Network + 10
• Transmission Direction
• Simplex
• Half-duplex
• Full-duplex
• Channel
Transmission Basics (continued)
Network + 11
• Multiplexing
• Allows multiple signals to travel simultaneously over one medium
• In order to carry multiple signals, the medium’s channel is logically separated into multiple smaller channels, or sub channels
• A device that can combine many signals on a channel, a multiplexer (mux), is required at the sending end of the channel
• At the receiving end, a demultiplexer (demux) separates the combined signals and regenerates them in their original form
Transmission Basics (continued)
Network + 12
• Time division multiplexing (TDM)
• Wavelength division multiplexing (WDM)
• WDM enables one fiber-optic connection to carry multiple light signals simultaneously
• Using WDM, a single fiber can transmit as many as 20 million telephone conversations at one time
• Statistical multiplexing
Transmission Basics (continued)
Network + 13
• Throughput and Bandwidth
• Throughput is the measure of how much data is transmitted during a given period of time
• Bandwidth is a measure of the difference between the highest and lowest frequencies that a medium can transmit
• The higher the bandwidth, the higher the throughput
Transmission Basics (continued)
Network + 14
• Baseband and Broadband
• Baseband is a transmission form in which (typically) digital signals are sent through direct current (DC) pulses applied to the wire
• Supports half-duplexing
• Ethernet is an example of a baseband system found on many LANs
Transmission Basics (continued)
Network + 15
• Broadband is a form of transmission in which signals are modulated as radio frequency (RF) analog waves that use different frequency ranges
• Does not encode information as digital pulses
• Is used to bring cable TV to your home
• Is generally more expensive than baseband
• Can span longer distances than baseband
Transmission Basics (continued)
Network + 16
• Transmission Flaws
• Noise is any undesirable influence that may degrade or distort a signal
• Crosstalk occurs when a signal traveling on one wire or cable infringes on the signal traveling over an adjacent wire or cable
• Attenuation is the loss of a signal’s strength as it travels away from its source
Transmission Basics (continued)
Network + 17
• Latency is a delay between the transmission of a signal and its eventual receipt
• The most common way to measure latency on data networks is by calculating a packet’s round trip time (RTT), or the length of time it takes for a packet to go from sender to receiver, then back from receiver to sender
• RTT is usually measured in milliseconds
Transmission Basics (continued)
Network + 18
Media Characteristics
• Five characteristics are considered when choosing a data transfer media:
• Throughput
• Costs
• Size and Scalability
• Connectors
Network + 19
• Noise Immunity
• The type of media least susceptible to noise is fiber-optic cable
Media Characteristics (continued)
Network + 20
• Because of its shielding, most coaxial cable has a high resistance to noise
• Coaxial cable is more expensive than twisted-pair cable because it requires significantly more raw materials to manufacture
• The significant differences between the cable types lie in the materials used for their center cores, which in turn influence their impedance
Coaxial Cable
Network + 21
• Thicknet (10Base5) Ethernet
• Also called thick wire Ethernet, is a rigid coaxial cable approximately 1-cm thick that contains a solid copper core
• Thicknet is sometimes called “yellow Ethernet” or “yellow garden hose”
Coaxial Cable (continued)
Network + 22
• IEEE designates Thicknet as 10Base5 Ethernet
• Thicknet uses a vampire tap and must abide by the 5-4-3 rule of networking.
Coaxial Cable (continued)
Network + 23
• Thinnet (10Base2) Ethernet
• Also known as thin Ethernet
• Because of its black sheath, Thinnet may also be called “black Ethernet”
Coaxial Cable (continued)
Network + 24
• Its core is typically made of several thin strands of copper
• Thinnet is less expensive than Thicknet and fiber-optic cable, but more expensive than twisted-pair wiring
Coaxial Cable (continued)
Network + 25
• Both Thicknet and Thinnet coaxial cable rely on the bus topology, in which nodes share one uninterrupted channel
• Networks using the bus topology must be terminated at both ends
• Without terminators, signals on a bus network would travel endlessly between the two ends of the network, a phenomenon known as signal bounce
Coaxial Cable (continued)
Network + 26
Twisted-Pair Cable
• Twisted-pair cable consists of color-coded pairs of insulated copper wires
• Every two wires are twisted around each other to form pairs and all the pairs are encased in a plastic sheath
Network + 27
Twisted-Pair Cable (continued)
• The number of pairs in a cable varies, depending on the cable type
• The more twists per inch in a pair of wires, the more resistant the pair will be to all forms of noise
• The number of twists per meter or foot is known as the twist ratio
Network + 28
• Twisted-pair cable is the most common form of cabling found on LANs today
• It is relatively inexpensive, flexible, and easy to install, and it can span a significant distance before requiring a repeater (though not as far as coax)
Twisted-Pair Cable (continued)
Network + 29
• All twisted-pair cable falls into one of two categories: shielded twisted-pair (STP) or unshielded twisted-pair (UTP)
• Unshielded twisted-pair (UTP) • Consists of one or more insulated wire pairs
encased in a plastic sheath
Twisted-Pair Cable (continued)
Network + 30
• 10BaseT
• A popular Ethernet networking standard that replaced the older 10Base2 and 10Base5 technologies
• The “10” represents its maximum throughput of 10 Mbps, the “Base” indicates that it uses baseband transmission, and the “T” stands for twisted pair, the medium it uses
Twisted-Pair Cable (continued)
Network + 31
• 10BaseT
• On a 10BaseT network, one pair of wires in the UTP cable is used for transmission, while a second pair of wires is used for reception allowing full-duplex transmission
Twisted-Pair Cable (continued)
Network + 32
• 100BaseT (Fast Ethernet)
• Also known as Fast Ethernet
• Uses base band transmission
• Configured in a star topology
• 100BaseT networks do not follow the 5-4-3 rule
Twisted-Pair Cable (continued)
Network + 33
• 100BaseTX
• Requires CAT 5 or higher unshielded twisted-pair cabling
• Within the cable, it uses the same two pairs of wire for transmitting and receiving data
• Capable of full duplex transmission
Twisted-Pair Cable (continued)
Network + 34
Fiber-Optic Cable
• Contains one or several glass or plastic fibers at its center, or core
• Data is transmitted via pulsing light sent from a laser or light-emitting diode (LED) through the central fibers
• Surrounding the fibers is a layer of glass or plastic called cladding
Network + 35
• Fiber cable variations fall into two categories:
• Single-mode
• Multimode
Fiber-Optic Cable (continued)
Network + 36
• Single-mode fiber
• Uses a narrow core (less than 10 microns in diameter) through which light generated by a laser travels over one path, reflecting very little
• Allows high bandwidths and long distances (without requiring repeaters)
• Costs too much to be considered for use on typical data networks
Fiber-Optic Cable (continued)
Network + 37
• Multimode fiber
• Contains a core with a diameter between 50 and 115 microns in diameter; the most common size is 62.5 microns over which many pulses of light generated by a laser or LED travel at different angles
• It is commonly found on cables that connect a router to a switch or a server on the backbone of a network
Fiber-Optic Cable (continued)
Network + 38
• 100BaseFX standard
• The 100BaseFX standard specifies a network capable of 100-Mbps throughput that uses baseband transmission and fiber-optic cabling
• 100BaseFX requires multimode fiber containing at least two strands of fiber
Fiber-Optic Cable (continued)
Network + 39
• 1000BaseLX standard
• The most common 1-Gigabit Physical layer standard in use today, can reach 5000 meters and use one repeater between segments
Fiber-Optic Cable (continued)
Network + 40
Cable Design and Management
• Cable plant
• Demarcation point (or demarc)
• Backbone wiring
• Punch-down block
• Patch panel
Network + 41
Installing Cable
• Straight-through cable is so named because it allows signals to pass “straight through” between terminations
• Crossover cable is a patch cable in which the termination locations of the transmit and receive wires on one end of the cable are reversed
Network + 43
Wireless Transmission
• Wireless LANs typically use infrared or radiofrequency (RF) signaling
• Characteristics of Wireless Transmission
• Antennas are used for both the transmission and reception of wireless signals
• To exchange information, two antennas must be tuned to the same frequency
Network + 45
Wireless Transmission (continued)
• Signal Propagation
• Line-of-sight (LOS)
• Signal Degradation
• Wireless signals also experience attenuation
• Wireless signals are also susceptible to noise (often called “interference”)
Network + 46
Choosing The Right Transmission Medium
• Most environments will contain a combination of these factors; you must therefore weigh the significance of each
• Areas of high EMI
• Distance
• Security
• Existing infrastructure
• Growth
Network + 47
Summary
• Identify organizations that set standards for networking
• Purpose of the OSI Model and each of its layers
• Specific functions belonging to each OSI Model layer