network topology network topology
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Network TopologyNetwork Topology
SETHALAT RODHETBHAISETHALAT [email protected]@su.ac.th
COCOmputermputer NENEtworktwork REREsearchsearch LLaboratoryaboratoryComputer Science, Computer Science, SilpakornSilpakorn UniversityUniversity
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Updated: 01/11/2002Updated: 01/11/2002
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COMPUTER SCIENCE COMPUTER SCIENCE ▪▪ SILPAKORN UNIVERSITYSILPAKORN UNIVERSITY
Physical TopologiesPhysical Topologies
The term topology can be confusing. A networkThe term topology can be confusing. A network’’s s physical topologyphysical topology is the physical layout of the networking is the physical layout of the networking components. components. There is also a There is also a logical topologylogical topology that is discussed later.that is discussed later.The three most common topologies are the The three most common topologies are the busbus, , starstar, , and and ringring. . There are other physical topologies such as the There are other physical topologies such as the meshmeshand and treetree, however, we explores only the three mentioned , however, we explores only the three mentioned above.above.
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Bus TopologyBus Topology
A bus topology connects all stations in a linear fashion. SometiA bus topology connects all stations in a linear fashion. Sometimes it mes it is called is called daisydaisy--chainingchaining. . The wire on a bus network has two distinct end points, which areThe wire on a bus network has two distinct end points, which arecapped by terminators. capped by terminators. Terminators absorb electronic signals so that they are not refleTerminators absorb electronic signals so that they are not reflected cted on the network. on the network. The termination requirement of the bus topology is extremely The termination requirement of the bus topology is extremely important and is revisited quite often in discussions of networkimportant and is revisited quite often in discussions of networktopology and troubleshooting.topology and troubleshooting.On a bus topology, all stations receive the signals transmitted On a bus topology, all stations receive the signals transmitted by by other stations. Network signals travel in both directions along other stations. Network signals travel in both directions along the the bus and each station checks the data frame as it passes by.bus and each station checks the data frame as it passes by.
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Bus Topology Bus Topology (cont.)(cont.)
Although the stations are all on Although the stations are all on one cable segmentone cable segment, the bus , the bus continues to work when stations are off line because the media dcontinues to work when stations are off line because the media does oes not actually pass through the individual stations.not actually pass through the individual stations.The bus topology has several advantages: The bus topology has several advantages:
It is inexpensive.It is inexpensive.It is easy to design and implement (you simply daisyIt is easy to design and implement (you simply daisy--chain the stations chain the stations together).together).
The bus topology has its disadvantages: The bus topology has its disadvantages: It is difficult to troubleshoot. If a cable break occurs at any It is difficult to troubleshoot. If a cable break occurs at any location on location on the bus, the entire bus fails and it can be difficult to locate the bus, the entire bus fails and it can be difficult to locate the point of the point of failure.failure.It requires termination. If the last computers on the chain are It requires termination. If the last computers on the chain are not not correctly terminated, stations cannot transmit.correctly terminated, stations cannot transmit.Traffic problems and collisions are commonTraffic problems and collisions are common
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Bus Topology Bus Topology (cont.)(cont.)
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Star TopologyStar Topology
The star network configuration is the most popular topology.The star network configuration is the most popular topology.In a star configuration, all computers or stations are wired dirIn a star configuration, all computers or stations are wired directly to a ectly to a central location, which is usually a central location, which is usually a hubhub or a or a MAUMAU..Depending on the type of networking device used at the center ofDepending on the type of networking device used at the center of the star the star network, collisions can be a problem. network, collisions can be a problem. A data signal from any station goes directly to this central devA data signal from any station goes directly to this central device, which ice, which transmits the signal according to the established network accesstransmits the signal according to the established network access method for method for the type of network. the type of network. The star topology has several advantages: The star topology has several advantages:
A break in one cable does not affect all other stations as in buA break in one cable does not affect all other stations as in bus technologies, s technologies, because there is only on station per segment. This means the stabecause there is only on station per segment. This means the star is generally r is generally more reliable.more reliable.In a star, problems are easier to locate because symptoms often In a star, problems are easier to locate because symptoms often point to one point to one station.station.The star is the secondThe star is the second--easiest topology to design and install. Only the bus is easiest topology to design and install. Only the bus is easier.easier.The star does not require manual termination. The media is termiThe star does not require manual termination. The media is terminated in the nated in the station at the transceiver on the NIC, and in the hub or MAU. station at the transceiver on the NIC, and in the hub or MAU.
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Star Topology Star Topology (cont.)(cont.)
The star topology has its disadvantages: The star topology has its disadvantages: Hubs are more expensive than bus connectors.Hubs are more expensive than bus connectors.A failure at the hub can affect the entire configuration.A failure at the hub can affect the entire configuration.Star topologies use more cable than bus topologies because Star topologies use more cable than bus topologies because separate wires run to each individual station.separate wires run to each individual station.
Hubs typically function as repeaters in a star Hubs typically function as repeaters in a star configuration. configuration. These hubs are active hubs because they repeat the These hubs are active hubs because they repeat the signal before passing it on. Active hubs, the most signal before passing it on. Active hubs, the most common kind in use today, require their own source of common kind in use today, require their own source of electricity. electricity.
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Star Topology Star Topology (cont.)(cont.)
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Extended Star Topology Extended Star Topology (cont.)(cont.)
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Ring TopologyRing Topology
Ring topologies are most often seen in Ring topologies are most often seen in Token RingToken Ring and and FDDIFDDI networks.networks.Stations on a ring are wired to one another in a circle Stations on a ring are wired to one another in a circle around the entire network. It looks like a bus network around the entire network. It looks like a bus network except there are except there are no terminationno termination points. points. Data is passed around the ring and unlike a bus network, Data is passed around the ring and unlike a bus network, stations in a ring regenerate the signal before passing it stations in a ring regenerate the signal before passing it along. along. This makes the ring topology active, as opposed to the This makes the ring topology active, as opposed to the passive bus topology.passive bus topology.
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Ring Topology Ring Topology (cont.)(cont.)
The ring topology has these advantages:The ring topology has these advantages:It prevents network collisions due to the media access method orIt prevents network collisions due to the media access method orarchitecture required. architecture required. Each station functions as a repeater, so the topology does not Each station functions as a repeater, so the topology does not require additional network hardware, such as hubs.require additional network hardware, such as hubs.
However, as with any topology, disadvantages exist:However, as with any topology, disadvantages exist:Similar to a bus network, a failure at one point can bring down Similar to a bus network, a failure at one point can bring down the network.the network.Since all stations are wired together, to add a station, the Since all stations are wired together, to add a station, the network must be temporarily shut down.network must be temporarily shut down.Maintenance on a ring is more difficult than on a star topology Maintenance on a ring is more difficult than on a star topology because an adjustment or reconfiguration affects the entire ringbecause an adjustment or reconfiguration affects the entire ring..
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Ring Topology Ring Topology (cont.)(cont.)
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Tree TopologyTree Topology
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Irregular TopologyIrregular Topology
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Complete (Mesh) TopologyComplete (Mesh) Topology
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Cellular TopologyCellular Topology
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Logical TopologyLogical Topology
Logical topology defines how the signal travels, not the Logical topology defines how the signal travels, not the physical layout. physical layout.
A logical bus means that the signal will go out from the A logical bus means that the signal will go out from the sending station in all directions to every host. sending station in all directions to every host.
The physical topology may be a bus or a star. The physical topology may be a bus or a star.
In a physical star that uses a logical bus, the central In a physical star that uses a logical bus, the central device will be a hub. This may be referred to as a stardevice will be a hub. This may be referred to as a star--bus topology. bus topology.
The first part (star) represents the physical topology and The first part (star) represents the physical topology and the second part (bus) represents the logical topology.the second part (bus) represents the logical topology.
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IEEE 802IEEE 802
IEEE 802 covers issues concerning all types of networks: IEEE 802 covers issues concerning all types of networks: local area, metropolitan, and wide area. local area, metropolitan, and wide area.
As originally written, it only addressed issues related to the As originally written, it only addressed issues related to the first two layers of the OSI networking model: Physical and first two layers of the OSI networking model: Physical and Data Link. Data Link.
Several different specifications in the 802 standard are of Several different specifications in the 802 standard are of particular interest in basic networking architectures. Ex.particular interest in basic networking architectures. Ex.
802.2 802.2 -- Logical Link ControlLogical Link Control802.3 802.3 -- EthernetEthernet802.4 802.4 -- Token BusToken Bus802.5 802.5 -- Token RingToken Ring802.12 802.12 -- 100VG100VG--AnyLAN; Demand PriorityAnyLAN; Demand Priority
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Network MediaNetwork Media
Modern networks can utilize several types of network media. Modern networks can utilize several types of network media. Most networks use some type of cable for the connection media Most networks use some type of cable for the connection media however, air is sometimes used. however, air is sometimes used. Wireless technologies, such as infraWireless technologies, such as infra--red and satellite red and satellite communications, will become increasingly important at present. communications, will become increasingly important at present.
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Media DegradationMedia Degradation
In general, media is susceptible to degradation. The sources of In general, media is susceptible to degradation. The sources of the the degradation can be internal or external. When signals degrade ovdegradation can be internal or external. When signals degrade over er distance, it is called distance, it is called attenuationattenuation. Three internal factors can cause . Three internal factors can cause attenuation: attenuation:
Resistance: Opposition to the flow of electrons in a wireResistance: Opposition to the flow of electrons in a wireInductance: Opposition to the changes of electrical current in tInductance: Opposition to the changes of electrical current in the wirehe wireCapacitance: Opposition to voltage changes in the wireCapacitance: Opposition to voltage changes in the wire
When these internal opposition forces are combined and measured,When these internal opposition forces are combined and measured,the measure is called the measure is called impedanceimpedance. .
Each type of cabling has its own impedance rating, which is partEach type of cabling has its own impedance rating, which is part of of its specification. its specification.
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Media Degradation Media Degradation (cont.)(cont.)
If all cabling on a network does not have the same If all cabling on a network does not have the same impedance, the network can suffer from transmission impedance, the network can suffer from transmission errors or a reduction in the total usable segment length. errors or a reduction in the total usable segment length. In addition to the internal opposition of the wire to the In addition to the internal opposition of the wire to the signal, external forces can act upon network signals. signal, external forces can act upon network signals. These external forces come in two main categories: These external forces come in two main categories:
Electromagnetic Interference (EMI)Electromagnetic Interference (EMI)Radio Frequency Interference (RFI)Radio Frequency Interference (RFI)
Both types of interference can degrade and corrupt Both types of interference can degrade and corrupt network signals as they travel through the wire. network signals as they travel through the wire. Electrical lighting, generators, elevators, machinery, and Electrical lighting, generators, elevators, machinery, and other electromagnetic equipment can be sources of EMI. other electromagnetic equipment can be sources of EMI.
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Media Degradation Media Degradation (cont.)(cont.)
Crosstalk Crosstalk is a form of EMI. is a form of EMI.
Radio transmitting devices cause RFI.Radio transmitting devices cause RFI.
In order to reduce EMI/RFI on network cabling, you can In order to reduce EMI/RFI on network cabling, you can do the following: do the following:
Keep network media away from sources of EMI, such as lights, Keep network media away from sources of EMI, such as lights, generators, and high voltage electrical wiring.generators, and high voltage electrical wiring.Ensure that network media is properly installed. Ensure that network media is properly installed. Use shielded cabling, which is more resistant to external Use shielded cabling, which is more resistant to external interference. interference. Use repeaters, which amplify and cleanUse repeaters, which amplify and clean--up networking signals. up networking signals. Ensure that you install good quality cabling.Ensure that you install good quality cabling.
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TwistedTwisted--Pair CablingPair Cabling
Most networks are connected with twistedMost networks are connected with twisted--pair cabling.pair cabling.The cable that runs from telephone to the wall is The cable that runs from telephone to the wall is probably twistedprobably twisted--pair. pair. Different types and categories of twistedDifferent types and categories of twisted--pair cable exist, pair cable exist, but they all have two things in common:but they all have two things in common:
The wires come in pairs.The wires come in pairs.The pairs of wires are twisted around each other.The pairs of wires are twisted around each other.
The twisting of wires reduces crosstalk, which is the The twisting of wires reduces crosstalk, which is the bleeding of a signal from one wire to another and which bleeding of a signal from one wire to another and which can corrupt signals and cause network errors. can corrupt signals and cause network errors.
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CancellationCancellation
Transmitting cables have a naturally created magnetic Transmitting cables have a naturally created magnetic field around them. field around them. When two wires are placed in close proximity, their When two wires are placed in close proximity, their electronically created magnetic fields cancel each other electronically created magnetic fields cancel each other out. This cancellation actually insulates the signal from out. This cancellation actually insulates the signal from the effects of signal bleeding. the effects of signal bleeding. When the wires are twisted around one another, the When the wires are twisted around one another, the magnetic cancellation is enhanced. magnetic cancellation is enhanced. The twisting of the wires not only protects the signal The twisting of the wires not only protects the signal inside from internal crosstalk, but it also protects it from inside from internal crosstalk, but it also protects it from other external forms of signal interference.other external forms of signal interference.
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Unshielded Twisted Pair Unshielded Twisted Pair ((UTPUTP))
Unshielded twisted-pair cable (UTP) is a four-pair wire medium - composed of pairs of wires - used in a variety of networks. Each pair of wires is insulated from the others. This cable relies solely on the cancellation effect produced by the twisted wire pairs to limit signal degradation caused by EMI and RFI. To further reduce crosstalk between the pairs in unshielded twisted-pair cable, the number of twists in the wire pairs varies. Like shielded twisted-pair cable, UTP cable must follow precise specifications as to how many twists or braids are permitted per foot of cable.
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Unshielded Twisted Pair Unshielded Twisted Pair ((UTPUTP) ) (cont.)(cont.)
UTP cabling is used for a variety of electronic communications. UTP cabling is used for a variety of electronic communications. UTP cable supports data transmissions of 4, 10, 16, 100 and 1000UTP cable supports data transmissions of 4, 10, 16, 100 and 1000 Mbps. Mbps. The maximum segment length for UTP is 100 meters. The maximum segment length for UTP is 100 meters.
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Unshielded Twisted Pair Unshielded Twisted Pair ((UTPUTP) ) (cont.)(cont.)
When used as a networking medium, unshielded twistedWhen used as a networking medium, unshielded twisted--pair cable has four pairs of pair cable has four pairs of either 22 or 24 gauge copper wire. UTP used as a networking meeither 22 or 24 gauge copper wire. UTP used as a networking medium has an dium has an impedance of 100 ohms. This differentiates it from other types impedance of 100 ohms. This differentiates it from other types of twistedof twisted--pair wiring pair wiring such as that used for telephone wiring. Because UTP has an extesuch as that used for telephone wiring. Because UTP has an external diameter of rnal diameter of approximately .17", its small size can be advantageous during iapproximately .17", its small size can be advantageous during installation. Since nstallation. Since UTP can be used with most of the major networking architectureUTP can be used with most of the major networking architectures, it continues to s, it continues to grow in popularity. grow in popularity. The advantages of UTP cable include:The advantages of UTP cable include:
Easy installation: It is a thin, flexible cable that is easy to Easy installation: It is a thin, flexible cable that is easy to string between walls.string between walls.PrePre--installation: Most modern buildings come with CAT 5 UTP already installation: Most modern buildings come with CAT 5 UTP already wired into the wall wired into the wall outlets, or at least run between the floors.outlets, or at least run between the floors.Size: Since UTP is small, it does not quickly fill up wiring ducSize: Since UTP is small, it does not quickly fill up wiring ducts.ts.Inexpensive: UTP costs less per foot than any other type of LAN Inexpensive: UTP costs less per foot than any other type of LAN cable.cable.
Using UTP does have its disadvantages: Using UTP does have its disadvantages: Susceptibility to interference: It is more susceptible to interfSusceptibility to interference: It is more susceptible to interference than most other types of erence than most other types of cabling. The pair twisting does help, but it does not come closecabling. The pair twisting does help, but it does not come close to making the cable to making the cable impervious to electrical noise.impervious to electrical noise.Limited segment length: It is limited to segments of 100 meters.Limited segment length: It is limited to segments of 100 meters. The distance between signal The distance between signal boosts is shorter for unshielded twistedboosts is shorter for unshielded twisted--pair than it is for coaxial cable.pair than it is for coaxial cable.Once considered slower at transmitting data than other types of Once considered slower at transmitting data than other types of cable. Today, UTP is cable. Today, UTP is considered the fastest copperconsidered the fastest copper--based media. based media.
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Shielded Twisted Pair Shielded Twisted Pair ((STPSTP))
Another type STP cable is for token-ring installations. In this type of STP cable, known as 150 ohm STP, not only is the entire cable shielded to reduce EMI and RFI but each pair of twisted wires is shielded from each other in order to reduce cross-talk. requires an increased amount of insulation and a larger amount of shielding. These factors combine to increase the size, weight, and cost of the cable. It also requires the installation of large wiring closets and large wiring ducts, luxuries that many older buildings cannot provide.
Shielded twisted-pair cable (STP)100 ohm combines the techniques of shielding (each group of wires are surrounded by a shield), cancellation, and twisting of wires. Resistance to both EMI and RFI without significantly increasing the weight or size of the cable.
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Shielded Twisted Pair Shielded Twisted Pair ((STPSTP) ) (cont.)(cont.)
STP is similar to UTP in that the wire pairs are twisted STP is similar to UTP in that the wire pairs are twisted around each other inside the cable. around each other inside the cable. STP also has shielding around the cable to further STP also has shielding around the cable to further protect it from external interference. protect it from external interference. The shielding of the individual pairs of wires further The shielding of the individual pairs of wires further reduces the chance of crosstalk.reduces the chance of crosstalk.Shielding the individual wire pairs increases the overall Shielding the individual wire pairs increases the overall diameter and weight of the cable. diameter and weight of the cable. The maximum segment length of STP cable is 100 The maximum segment length of STP cable is 100 meters.meters.
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Shielded Twisted Pair Shielded Twisted Pair ((STPSTP) ) (cont.)(cont.)
The advantage of STP over UTP is:The advantage of STP over UTP is:Greater protection from interference and crosstalk due to Greater protection from interference and crosstalk due to shielding.shielding.
The disadvantages to STP include the following:The disadvantages to STP include the following:Cost: STP has a higher cost per foot. Cost: STP has a higher cost per foot. Grounding: The STP Shield must be grounded at both ends; if Grounding: The STP Shield must be grounded at both ends; if grounded improperly, it can cause serious interference.grounded improperly, it can cause serious interference.Difficulty in installation: Heavier and less flexible, STP is moDifficulty in installation: Heavier and less flexible, STP is more re difficult to install.difficult to install.Thickness: Because of its thickness, STP may not fit down Thickness: Because of its thickness, STP may not fit down narrow cable ducts.narrow cable ducts.No segment length advantage: Despite the heavier and thicker No segment length advantage: Despite the heavier and thicker cable, there is no increased segment length.cable, there is no increased segment length.
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RJ45 ConnectorsRJ45 Connectors
TwistedTwisted--pair wiring is fitted with a plastic connector and pair wiring is fitted with a plastic connector and inserted into a wall connector. inserted into a wall connector. These connectors are known as These connectors are known as Registered Jacks (RJ)Registered Jacks (RJ). . Typically, RJTypically, RJ--45 connectors connect UTP networks. 45 connectors connect UTP networks. The RJThe RJ--45 connectors look much like the typical RJ45 connectors look much like the typical RJ--11 11 connectors that connect telephone to the wall. connectors that connect telephone to the wall. The difference between the RJThe difference between the RJ--45 connectors and the 45 connectors and the RJRJ--11 connectors is that the former has 8 wire traces (411 connectors is that the former has 8 wire traces (4--pair) and the latter has only 4 (2pair) and the latter has only 4 (2--pair).pair).
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Coaxial CablingCoaxial Cabling
Coaxial cable consists of a solid inner Coaxial cable consists of a solid inner core, usually copper, or wire strand core, usually copper, or wire strand conductor that is surrounded by conductor that is surrounded by insulation. insulation. Just outside of the insulation is a Just outside of the insulation is a shield, which is a foil or copper braid shield, which is a foil or copper braid that protects the inner conductor. that protects the inner conductor. A protective jacket surrounds the A protective jacket surrounds the outside of the cable. outside of the cable. Coaxial cable supports data Coaxial cable supports data transmission rates of 10 Mbps. The transmission rates of 10 Mbps. The two most commonly used types of two most commonly used types of coaxial cable are coaxial cable are ThicknetThicknet and and ThinnetThinnet. . ThicknetThicknet is a thicker form of coaxial is a thicker form of coaxial cable than cable than ThinnetThinnet. . Outside diameter of Outside diameter of ThinnetThinnet is 0.18is 0.18““..ThicknetThicknet segments can be up to 500 segments can be up to 500 meters long while meters long while ThinnetThinnet segments segments are limited to 185 meters. are limited to 185 meters.
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Coaxial CablingCoaxial Cabling (cont.)(cont.)
The advantages to using coaxial cabling on a LAN The advantages to using coaxial cabling on a LAN include the following: include the following:
longer segment lengths than UTP or STPlonger segment lengths than UTP or STPbuiltbuilt--in shieldingin shieldinghubs between stations are not requiredhubs between stations are not required
Coaxial cable does have its disadvantages:Coaxial cable does have its disadvantages:not as easy to run as UTP, because it is not as flexible or thinnot as easy to run as UTP, because it is not as flexible or thinmore expensive than UTPmore expensive than UTPrequires more room in wiring ducts than UTPrequires more room in wiring ducts than UTP
ThinnetThinnet is sometimes referred to as is sometimes referred to as cheapernetcheapernet..Thinnet is no longer commonly used in Ethernet networks.
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ThinnetThinnet ConnectorsConnectors
The most common connectors for RGThe most common connectors for RG--58 cabling on 58 cabling on thinnetthinnetnetworks are networks are barrel connectorsbarrel connectors, , T connectorsT connectors, and , and terminatorsterminators. . These connectors are known as British Naval Connectors or just These connectors are known as British Naval Connectors or just BNC connectorsBNC connectors. . A barrel connector connects two sections of coaxial cabling. A BA barrel connector connects two sections of coaxial cabling. A BNCNC--T connector fits on the end of the network interface card and T connector fits on the end of the network interface card and connects a station to two sections of RGconnects a station to two sections of RG--58 cabling. 58 cabling. Terminators are placed on each end of a Terminators are placed on each end of a ThinnetThinnet network segment network segment to absorb signals as they reach the end of the wire. to absorb signals as they reach the end of the wire. This absorption keeps the signals from reflecting and preventingThis absorption keeps the signals from reflecting and preventingother stations from transmitting. other stations from transmitting.
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SETHALAT RODHETBHAISETHALAT RODHETBHAI
CONEREL 35
COMPUTER SCIENCE COMPUTER SCIENCE ▪▪ SILPAKORN UNIVERSITYSILPAKORN UNIVERSITY
ThinnetThinnet Connectors Connectors (cont.)(cont.)
SETHALAT RODHETBHAISETHALAT RODHETBHAI
CONEREL 36
COMPUTER SCIENCE COMPUTER SCIENCE ▪▪ SILPAKORN UNIVERSITYSILPAKORN UNIVERSITY
ThinnetThinnet Connectors Connectors (cont.)(cont.)
A common problem in the past on A common problem in the past on ThinnetThinnet networks has networks has been the substitution of 75been the substitution of 75--ohm terminators designed for ohm terminators designed for RGRG--59 broadband cable for the 5059 broadband cable for the 50--ohm terminators ohm terminators designed for RGdesigned for RG--58 58 basebandbaseband networks (networks (ThinnetThinnet).).The terminators look identical but can't be substituted The terminators look identical but can't be substituted without network problems occurring. without network problems occurring. Most terminators today have Most terminators today have ““5050--ohmohm”” etched on them etched on them for easier identification.for easier identification.
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SETHALAT RODHETBHAISETHALAT RODHETBHAI
CONEREL 37
COMPUTER SCIENCE COMPUTER SCIENCE ▪▪ SILPAKORN UNIVERSITYSILPAKORN UNIVERSITY
Fiber Optic CablingFiber Optic Cabling
Fiber optic cable carries light pulses Fiber optic cable carries light pulses along its fibers rather than electrical along its fibers rather than electrical signals. This cable is made of glass or signals. This cable is made of glass or plastic fibers, rather than copper wire plastic fibers, rather than copper wire like most other network cabling.like most other network cabling.The core of the cable is usually pure The core of the cable is usually pure glass. Surrounding the glass is a layer glass. Surrounding the glass is a layer of cladding made of glass or plastic. It of cladding made of glass or plastic. It traps the light in the core. traps the light in the core. The cladding is surrounded usually by The cladding is surrounded usually by Kevlar, which is the strong substance Kevlar, which is the strong substance used in bulletproof vests. There is an used in bulletproof vests. There is an outer protective jacket made of Teflon outer protective jacket made of Teflon (plenum grade) or PVC.(plenum grade) or PVC.The light pulses originate from a laser The light pulses originate from a laser (single(single--mode cable) or light emitting mode cable) or light emitting diode (multimode cable). This type of diode (multimode cable). This type of cable supports data transmission rates cable supports data transmission rates of 100 Mbps to 2 of 100 Mbps to 2 GbpsGbps. Fiber optic . Fiber optic segments can span up to 100 km. segments can span up to 100 km.
SETHALAT RODHETBHAISETHALAT RODHETBHAI
CONEREL 38
COMPUTER SCIENCE COMPUTER SCIENCE ▪▪ SILPAKORN UNIVERSITYSILPAKORN UNIVERSITY
Fiber Optic Cabling Fiber Optic Cabling (cont.)(cont.)
The advantages of fiber optic cabling include: The advantages of fiber optic cabling include: Can transmit over long distances, farther than any other networkCan transmit over long distances, farther than any other network media. media. Is not susceptible to electromagnetic interference.Is not susceptible to electromagnetic interference.Is immune from crosstalk.Is immune from crosstalk.Supports extremely high transmission rates.Supports extremely high transmission rates.Has a small diameter and can be used in narrow wiring ducts.Has a small diameter and can be used in narrow wiring ducts.Is not susceptible to eavesdropping.Is not susceptible to eavesdropping.
To its disadvantage, fiber optic cable:To its disadvantage, fiber optic cable:Is more expensive than other types of networking media.Is more expensive than other types of networking media.Is more difficult and expensive to install than other types of nIs more difficult and expensive to install than other types of network etwork media. The ends of each cable must be polished perfectly flat anmedia. The ends of each cable must be polished perfectly flat and d scratch free before they are inserted into the connection devicescratch free before they are inserted into the connection devices.s.Is fragile and must be installed carefully and protected after iIs fragile and must be installed carefully and protected after installation.nstallation.
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SETHALAT RODHETBHAISETHALAT RODHETBHAI
CONEREL 39
COMPUTER SCIENCE COMPUTER SCIENCE ▪▪ SILPAKORN UNIVERSITYSILPAKORN UNIVERSITY
Wireless CommunicationWireless Communication
The medium for wireless The medium for wireless communication is the communication is the atmosphere. Wireless signals are atmosphere. Wireless signals are electromagnetic waves, were electromagnetic waves, were proven to travel through space, proven to travel through space, empty of all matter. This feature empty of all matter. This feature means that networks can be built means that networks can be built in places where it would normally in places where it would normally be difficult, or impossible to install be difficult, or impossible to install wires or cables. wires or cables. The most common application of The most common application of wireless data communications is wireless data communications is for mobile users. for mobile users.
SETHALAT RODHETBHAISETHALAT RODHETBHAI
CONEREL 40
COMPUTER SCIENCE COMPUTER SCIENCE ▪▪ SILPAKORN UNIVERSITYSILPAKORN UNIVERSITY
Criteria for Media SelectionCriteria for Media Selection
Media selection is probably the most important Media selection is probably the most important consideration in LAN design.consideration in LAN design.
We must consider several factors when determining We must consider several factors when determining what type of cable to use in a network installation. These what type of cable to use in a network installation. These factors include:factors include:
cost limitationscost limitationsthe distance the signal must travelthe distance the signal must travelspeed considerationsspeed considerationsthe need for securitythe need for securitythe person who will do the installationthe person who will do the installationpotential interference problemspotential interference problems
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CONEREL 41
COMPUTER SCIENCE COMPUTER SCIENCE ▪▪ SILPAKORN UNIVERSITYSILPAKORN UNIVERSITY
Media ComparisonsMedia Comparisons
Type Max Length Bandwidth Install Cost InterferenceUTP 100 m 100 MBPS easy cheapest highSTP 100 m 500 MBPS moderate moderate moderate
Thinnet 185 m 10 MBPS easy cheap moderateThicknet 500 m 10 MBPS hard moderate low
Multimode 2 km 100 MBPS very hard expensive noneSingle-Mode 100 km 2 GBPS very hard expensive none