Star Network refers to the network each node device through a network focused on devices (such as the hub or switch HUB Switch) connected together, each node star-shaped distribution network connection.Â This topology is mainly used in IEEE 802.2, IEEE 802.3 Ethernet standard.Â
Easy to implement, but the installation and maintenance workload, cost more: it is generally used in the transmission medium using common twisted pair or coaxial cable.Â But each site must be focused on the central network device connected directly and requires a lot of cable, and installation and maintenance workload has increased sharply.Â
Node extension, mobile convenience: node extensions only concentrated from the hub or switch and other devices to pull a cable, but just need to move a node corresponding to the new node to node equipment.Â
Fault diagnosis and isolation easy: a node failure will not affect other nodes connection, can take any failed nodes removed;Â heavier burden on the central node, easily become a bottleneck; capacity of each site, the lower the distribution: the central node in the event of failure, the entire network was affected.
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Label 1.2 Ring Network topology
RingÂ topologyÂ isÂ aÂ networkÂ topologyÂ whereÂ eachÂ nodeÂ is connectedÂ toÂ twoÂ other nodes, formingÂ aÂ singleÂ routeÂ for theÂ transmissionÂ lineÂ directlyÂ toÂ eachÂ node.Â The dataÂ will go throughÂ fromÂ eachÂ nodeÂ toÂ everyÂ nodeÂ in turn,Â eachÂ nodeÂ routesÂ traveledÂ willÂ receive eachÂ dataÂ packet.
Because theÂ ringÂ topologyÂ providesÂ onlyÂ oneÂ pathÂ betweenÂ twoÂ nodes,Â the topologyÂ is likelyÂ to beÂ disruptedÂ in the event ofÂ failureÂ ofÂ aÂ link.Â A nodeÂ failureÂ orÂ cable damage occursÂ causingÂ allÂ nodesÂ toÂ separateÂ fromÂ the ringÂ topology.Â FDDIÂ networksÂ can overcome theÂ shortcomingsÂ ofÂ the data transmissionÂ clockwiseÂ andÂ counter clockwise to formÂ a ring:Â in the eventÂ of failureÂ dataÂ toÂ be sentÂ backÂ toÂ completeÂ the ringÂ beforeÂ he arrivedÂ at the end ofÂ the cable,Â itÂ actsÂ conductedÂ duringÂ each ofÂ the nodesÂ such as "ring C".Â 802.5Â networkingÂ protocolÂ -Â alsoÂ known asÂ theÂ IBMÂ token ring networkÂ -Â also avoidÂ theseÂ disadvantages:Â they use aÂ starÂ topologyÂ at theÂ physical layerÂ access toÂ the variousÂ stationsÂ andÂ unitsÂ toÂ mimicÂ the ringÂ at theÂ dataÂ link layer.
ManyÂ ringÂ networksÂ to addÂ aÂ "counterÂ rotatingÂ ring"Â toÂ formÂ aÂ redundantÂ topology.
ThisÂ does notÂ require aÂ computerÂ networkÂ server
NetworksÂ can beÂ builtÂ widerÂ useÂ token ring
AÂ computerÂ malfunctionÂ causedÂ the problemÂ in theÂ network
NotÂ easyÂ to repairÂ ifÂ damage occurs
MAUÂ expensiveÂ type ofÂ networkÂ cardÂ from theÂ cardÂ type ofÂ EthernetÂ network
SlowerÂ thanÂ Ethernet
Label 1.3 Bus Network topology
Bus topology,Â alsoÂ knownÂ as aÂ linearÂ bus,Â theÂ networkÂ topologyÂ isÂ the simplest.Â It consistsÂ ofÂ aÂ cable, knownÂ asÂ segmentsÂ orÂ spinal cord,Â whichÂ connectsÂ all the computersÂ in theÂ networkÂ inÂ aÂ row. Three conceptsÂ should be takenÂ into accountÂ so thatÂ computersÂ canÂ communicateÂ onÂ theÂ bus network. The dataÂ in theÂ networkÂ isÂ inÂ the form ofÂ electronic signals,Â it isÂ sentÂ toÂ allÂ computersÂ in theÂ network.Â This informationÂ will only beÂ acceptedÂ by theÂ computerÂ thatÂ has an addressÂ that matchesÂ theÂ addressÂ thatÂ is encodedÂ by theÂ original signal.Â OnlyÂ one computerÂ canÂ onlyÂ sendÂ signalsÂ orÂ dataÂ withinÂ a periodÂ of time.
What are three (3) basic modes used in MAC to control access to medium by devices? Describe one of the modes.
The MAC (Medium access control) is a sub-layer to closely associate with the physical layer. The three basic modes use in the MAC there are Reservation, Contention and Round Robin.
Reservation is reserveÂ a stationÂ to sendÂ the dataÂ slotsÂ for future expansion, or even indefinitely.
Explain CSMA/CD with the help of a diagram.
Label 1.4 Simplified Algorithm of CSMA/CD
Carrier Sense Multiple Access / Collision Detection (Carrier Sense Multiple Access with Collision Detection, CSMA / CD)Â
This program requires the device to send the frame at the same time listens to the channel to determine whether a conflict if the process of sending data conflict is detected, then the following conflict management operations:Â
Always on Time
Marked to Standard
Send a special block and stopped sending data information: Special block a few bytes of information are all one continuous signal, a move intended to strengthen the conflict in order to allow other devices to detect the conflict as quickly as possible.Â At a fixed time (the beginning is 1 contention period times) to wait a random time, once again sent.Â If you still crash, the use of truncated binary exponential algorithm to avoid sending back.Â Stop within the previous ten second "fixed time" and then double time to send a random ten times to stop before a "fixed time" and then sent randomly.Â Even after 16 times trying to give up the transmission failure.Â This program applies toÂ Ethernet (DIX Ethernet V2) standard, IEEE 802.3 standard.
IEEE 802.3 Ethernet standard allows different types of cables to be used with a data transfer rate of 10 Mbps. Explain the Ethernet implementations which use coaxial cable, UTP cable. Use a proper diagram with appropriate topology.
EthernetÂ is a dataÂ communications frameworkÂ consisting of aÂ series ofÂ standardÂ way ofÂ wiringÂ and signalÂ generated andÂ sentÂ acrossÂ the cable.Â Ethernet standardÂ is to maintainÂ theÂ Electrical and Electronics EngineersÂ IEEE 802.3Â working groupÂ to developÂ a standard,Â Ethernet-basedÂ local areaÂ network.Â Use an Ethernet cable, including thoseÂ with copperÂ coreÂ and those withÂ fiber core,Â forÂ faster dataÂ transfer rate.
Label 2.1 is Star topology in UTP.
CategoryÂ 5eÂ UTPÂ cable
10Â baseÂ TÂ Ethernet usesÂ UTPÂ (5eÂ category)Â unshielded twisted pairÂ (UTP)Â cable, which isÂ commonly usedÂ and relativelyÂ inexpensiveÂ cablesÂ to otherÂ network solutions, such asÂ 100 Base TÂ EthernetÂ networkÂ Optical fiber network.Â Category 5Â cable consists of copperÂ coreÂ encapsulated inÂ an insulatingÂ materialÂ made â€‹â€‹ofÂ PVC.Â Two-coreÂ copper wire,Â insulation and PVCÂ packaging, isÂ twistedÂ around each otherÂ along the lengthÂ of theÂ cable.Â What is the meaningÂ of theÂ term "twisted pair"Â of theÂ twisted pairÂ Twisted pairÂ ofÂ insulated wire, then coveredÂ withÂ insulationÂ jacket,Â and then from polyvinyl chlorideÂ to make up forÂ theÂ CAT 5Â cable.Â WindingÂ wiresÂ aroundÂ each other along the cableÂ to protect dataÂ fromÂ electromagnetic interferenceÂ may come from other nearbyÂ cables orÂ electrical equipment.Â Maximum length ofÂ aÂ segmentÂ of theÂ CAT 5 UTPÂ cableÂ isÂ 328 feet (100Â meters).Â After this,Â the length of theÂ signalÂ along the cableÂ drop.Â 10 baseÂ TÂ network dataÂ transferÂ speed of 100Â megabitsÂ per second. UTP is using for Star topology all wiring is done from a central point (the server or hub) and normally STP or UTP are four wires. The star topology has the greatest cable lengths of any topology (and thus uses the most amount of cable). The advantage for the star topology is easy to add new workstations and easy centralized control the network or monitoring the hub. The disadvantages is if hub failure cripples all workstations connected to that hub and hubs are more expensive than thin-Ethernet. Twisted pairÂ ofÂ quality mayÂ vary fromÂ veryÂ high-speedÂ cableÂ telephoneÂ gradeÂ wire.Â The cableÂ hasÂ four pairs ofÂ wireÂ inside theÂ jacket.Â Each pairÂ isÂ twistedÂ a different number of twistsÂ per inchÂ to helpÂ eliminateÂ interference withÂ adjacentÂ pairsÂ and other electrical equipment.Â EIAÂ /Â TIAÂ (ElectronicÂ Industries AssociationÂ /Â Telecommunications Industry Association)Â has establishedÂ standards ofÂ UTPÂ and scoring,Â six linesÂ (the other categoriesÂ are emerging.)
Coaxial cable can be used in long distance connection example the building to building or bus network topology.
Label 2.1.1 is bus network topology
Coaxial cableÂ 10BASE 2
EarlyÂ implementation ofÂ Ethernet, calledÂ EthernetÂ 10BASE 2,Â often usedÂ coaxial cableÂ network equipment.Â RG58Â coaxial cable,Â because of the needÂ to use other types ofÂ coaxial cableÂ may have differentÂ electrical characteristics,Â may not workÂ in the dataÂ transmission environment.Â RG58Â coaxial cableÂ typically includesÂ aÂ solid copperÂ core, withÂ 20 AWGÂ copper wire.Â This coreÂ is covered withÂ solidÂ polyethylene shield,Â wrapped inÂ aluminum foilÂ and polyethyleneÂ insulationÂ along the lengthÂ of the cable.Â TheÂ cable isÂ then covered with aÂ flame-retardantÂ PVCÂ jacket.Â Maximum length ofÂ coaxial cable for aÂ 10BASE 2Â is 607 feet (185 meters). Coaxial - two conductors separated by insulating layers, such as TV 75 ohm cables. Maximum lengths is 185-500 meters. Thin - thin cable interfaces with the British Navy (BNC) at the end of the year.Â Thin is part of the RG - 58 series cable *. Maximum cable length is 185 meters.Â Transfer rate of 10Mbps.Â thin cable should have 50 ohm impedance, the termination impedance of 50 ohms.Â T or barrel connector has no impedance.
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Thicket - inch semi-rigid cable.Â The maximum cable length is 500 meters.Â Transfer rate of 10Mbps.Â Expensive and not commonly used.Â (The RG - 11 or RG - 8).Â A vampire tap or piercing tap water for a transceiver connected to the computer connected to the cable.Â 100 connections may be made.Â The computer has an attachment unit interface (AUI connector) in its network card, is a 15-pin DB, 15 connector.Â Computer is connected to the transceiver AUI cable from the card using the DROP on its network cable.
Coaxial cable type:
The RG - 58 / ü - 50 ohms, with a solid copper core.
The RG - 58 / ü * - 50 ohms, and the core wire.
The RG - 58 of the C / ü * - Military version of RG - 58 / United States
The RG - 59 - 75 ohms, broadband transmission, such as cable TV.
The RG - 62 - 93 ohm, mainly for the Arc Net.
The RG - 6 - for satellite cable (if you want to run the satellite cable!).
* Only these are part of IEEE standard for Ethernet networks.
Label 2.1.2 is Coaxial cableÂ 10BASE 2
Explain two different implementations of Fast Ethernet
Fast Ethernet is use CSMA/CD in star wire bus topology to run UTP data or fiber optical cable. It also similar with 10baseASE-T cable are attach to a hub. It provides compatibility with existing 10BASE-T system and it also upgrade from 10BASE-T. Fast Ethernet is referrer to 100 BASE-X and the X is a placeholder for the FX and TX variants.
The 100 media type designation is refers to the transmission speed of 100Mbit/s.
The "BASE" is refers to the baseband signaling, which means that only Ethernet signals are carry on the medium. The TX FX and T4 are referring to the physical medium that carries the signal. The fast Ethernet adapter can be logically divide into MAC which deals with the higher level of medium and PHY (Physical Layer Interface). The MAC can be link to the PHY by the 4 bit 25 MHZ synchronous with the parallel interface as a MII or 2 bit 50 MHZ variant (RMII).
The 100 BASE-T is several for the fast Ethernet for twisted pair cables, this will including 100BASE-TX (100 Mbit/s over two pair Cat5) 100BASE-T4 (100 Mbit/s over 4 pair Cat3), 100BASE-T2 (100 Mbit/s over 2 pair Cat3). The section length for a 100BASE-T cable is limit to 100Â meters. All are standards underÂ IEEE 802.3. Almost all 100BASE-T installations are 100BASE-TX. Ethernet work over a cable is deemed acceptable for most networks had to be rewiring for 100 megabit speed whether or not there had supposedly been CAT3 or CAT5 cable.
Version of Fast Ethernet overÂ optical fiber is 100BASE-FX, 100BASE-SX, 100BASE-BX and 100BASE-LX10.
The version 100BASE-FX is use 1300nm near-infrared (NIR) light wavelength transmit via to 2 strands of fiber optical, one is for receive (RX) and other is for transmit (TX). The maximum length is 400 Meters for half-duplex connections and 2 KM for full-duplex over multi-mode fiber optical.
The version for 100BASE-SX is use two stands of multi-mode fiber optical to receive and transmit. It is a lower cost alternative, because it use short wavelength. The 100BASE-SX can operate distances is up to 550 Meters. The 100BASE-SX is the shorter wavelength use 850nm and the shorter distance it can support, and use less optical components.
The version for 100 BASE-BX is single strand of fiber optical. the single mode fiber is use along with a special multiplexer splits the signal to transmit and receive wavelengths. The 2 wavelengths is use for transmit and receive is 1310/1550nm. The terminals each side is not equal, as the one transmitting "downstream" use 1550nm wavelength, and other side is "upstream" use the 1310 nm wavelength the distances can be 10 , 20 or 40 KM.
The version for 100BASE-LX10 is two single mode fibers optical. Is also can support 10KM and wavelength is 1310nm. It can describe in IEEE 802.3.
C. Differentiate between a hub and a switch. Also use a diagram to show the difference.
Label 2.3 is OSI Model for switch and hub
Label 2.3.1 is Micro segmentation (Switch) and no Micro segmentation (Hub)
A hub is rather device in operates on the Physical Layer of the OSI model. Switch is on other hand is more intelligent and it operates on the Data Layer of the OSI model.
A hub will receive the information on one port, information is then broadcast to all ports. This will not be a good plan, if it does not waste bandwidth and causing the collision. Imagine ifÂ two computersÂ transmitÂ dataÂ at the same time:Â theÂ impactÂ of informationÂ and informationÂ packageÂ will beÂ destroyed. We will have toÂ relayÂ theÂ data throughÂ the process ofÂ EthernetÂ Carrier Sense MultipleÂ Access with Collision Detection, but you can call it aÂ CSMA / CD. In simple terms, it is the protocol we resend the data after a collision occurs.
Collision is clearly a problem with hubs. More importantly the hub is notorious waste the bandwidth. Hubs are operating in half-duplex, the mean is that data can only flow in one direction at a times. As compare with full-duplex where can send and receive the data between two devices at the same times. Since we are operating in half-duplex, the bandwidth will be share between each port on the hubs. For example you haveÂ a 20-portÂ hub withÂ 20KBÂ ofÂ / sÂ lineÂ sharing.Â ButÂ you can only getÂ 1k-bitÂ / sÂ to each computerÂ on the network.
Switch is operates on the Data Link Layer of the OSI model. This means the switches are quite intelligent than hubs this is because they can route the data in a dynamic level. For example if the information is belonging to computer C, the switch will only send the data to computer C. For example the Label 2.3.1 there are many collision domains for the switch network. If the computerÂ 1Â and computerÂ 2Â to send dataÂ to each otherÂ at the same time, for example,Â you might have aÂ collision. ComputerÂ 1Â and ComputerÂ 3Â orÂ 4,Â however, willÂ not experienceÂ the collisionÂ process. In the hub network, only have one collision domain. This mean if the first computer wants to transmit a data it can be interrupt by any other computer on the network. Switch can keep track of which computer address are belong to a specific port. If you have information want deliver to computer A, it will only pass thought the computer A port. Micro segmentation allowsÂ us to maintainÂ the highest possibleÂ bandwidthÂ for each computer. If you have a 20KBÂ ofÂ / sÂ lineÂ in,Â each computerÂ can haveÂ theÂ fullÂ 20KBÂ / s (Note, ifÂ two orÂ more computersÂ using aÂ cableÂ at the same time, theyÂ must be shared.Â Nevertheless, itÂ is farÂ better thanÂ a hub,Â it canÂ automaticallyÂ splitÂ the bandwidth of theÂ port,Â you might not evenÂ use!).
Hubs, was chiefly because the priceÂ forÂ cheap,Â easy to install.Â Fortunately,Â on the "dumb"devicesÂ is that theyÂ do not needÂ too muchÂ configuration orÂ maintenance.
Switch is more expensive than hubs, but they allow more configuration options. They can be programmed as routers, something hubs can not be completed.
Describe frame exchange protocol in IEEE 802.11. Explain how the physical layer specifications for IEEE 802.11 have been issued.
The current 802.11 standard defines the "frame" type used in the transmission of data, and the management and control of the wireless link.
A frame is divided into very specific parts and specifications.Â Each frame has a MAC header, payload and frame check sequence (FCS).Â Some frames may be not part payload.Â The first 2 bytes of MAC header is the frame control field, providing detailed information framework.Â The frame of sub-areas, the area proposed to control the order.
Protocol Version: This is the two representatives in size and protocol version.Â Current version of the protocol is zero.Â Other values â€‹â€‹are reserved for future use.
Type: This is the size of the two bits, to help determine the type of wireless LAN frames. Control, data and management of various frame types are defined in IEEE 802.11.
Sub-Type: This is the 4-bit size.Â Type and subtype combined to determine the exact frame.
ToDS and FromDS: Each is one bit in size.Â They indicate whether a data frame is to a distributed system.Â Control and management frames set these values â€‹â€‹to zero.Â All of the data frame will have one bit set.Â However, in the communication network in the IBSS bit is always set to zero.
More clips: more fragments bit is set to a higher level, the most obvious package is divided, and for all non-final part.Â Some management framework, and may need to split.
Retry: sometimes need to retransmit the frame, and this has a retry bit is set to a re-send.Â This helps in the elimination of duplicate frames.
Power Management: Power Management Power Management bits that the sender of the state to complete an exchange.Â Access points are required to manage the connection will not be set up power-saving bit.
More data: The more data than the buffer frames received for a distributed system. The access point to facilitate is use of the station's power-saving mode.Â This suggests that at least one station is available and processing of all connections.
WEP: WEP bit after processing a change.Â This is a framework to switch to one another has been decrypted, or if no will has been one of the encryption settings.
Order: This bit is only set when the "strict orders" transfer method is employed. Frame and the fragments are not always sending the command; it will result in transmission performance.
The next two bytes are reserved in the ID field during this period.Â This field can take the following three forms: the duration of contention free period (CFP qualified) and the associated ID (aid).
802.11 up to four address fields.Â Each can carry the MAC address.Â Address 1 is the receiver, the transmitter address 2, address 3 is the receiver for filtering purposes.
Sequence control field is part of a two-byte message is used to determine the order and the elimination of duplicate frames.Â The first 4 bits the number of fragments, the last 12 bits are serial number.
An optional two-byte control area is the quality of service added to 802.11.
Frame body field size is variable, from 0 to 2304 bytes, plus any overhead from security package and contains information from the higher level.
Frame Check Sequence (FCS) is the last 4 bytes, in the standard 802.11 frame. Often referred to as cyclic redundancy check (CRC), which allows retrieval framework integrity check?Â Since the frame will be calculated and sent additional FCS.Â When a receiver one can calculate the FCS is the framework and compare it to a home. Management framework allows the maintenance of communication.Â Some of the common subtypes 802.11 include:
Authentication Frame: 802.11 certification began in the WNIC sends an authentication frame of the access point contains its identity.Â With open system authentication WNIC sends an authentication frame and the only access point responds with an authentication accept or reject the frame itself.Â With shared key authentication, the initial WNIC sends an authentication request, will receive an authentication framework that contains the text from the access point challenges.Â The WNIC sends an authentication frame containing challenge text to the encrypted version of the access point.Â The results of this process determine the WNIC the authentication state.
Association request frame: it is sent from the station to the access point to allocate resources and synchronization.Â Information about the framework, including support for WNIC data rate and the network SSID station would like to agree.Â If the request is accepted, the reserved memory of the access point, the establishment of an association ID WNIC.
Association response frame: from one access point to send a station that contains a group to accept or reject the request.Â If it is an accepted framework will include an associated ID and other information, and supports data transfer rates.
Beacon frames: sent from an access point periodically announce their existence and provide the SSID, and other parameters WNICs range.
Deauthentication frame: terminates the connection from the station hopes to send from another station.
Divorce framework: Send wishes to terminate the connection from the station.Â This is an elegant way for the access point, to give up the memory allocation and deletion WNIC from the association table.
Probe Request frames: from the bottom station, the requested information to another station.
Probe Response frames: sent from an access point that contains features, supported data rates, receiving Probe Request frames.
Re-association request frame: WNIC sends a request, drop weight combination, from the current range of related and found another access point access point with a stronger signal.Â The coordinates of the new access points to forward any information that may still be included in the buffer before the access point.
Re-association response frames: sent from one access point to accept or reject the WNIC containing re-association request frame.Â The framework includes the necessary data is related, such as association ID and supported data rates.
Control framework for the exchange of data frames between stations.Â Some of the common 802.11 control frame include:
Acknowledge (ACK) frame: the receipt of a data frame, the receiving station will send an ACK frame transmission station, if no errors were found.Â If the sending station does not receive the ACK frame at a predetermined period of time, the sending station will resend the frame.
Request to Send (RTS) frame: RTS and CTS frame provides an optional collision mitigation plan and the access point hidden station.Â A station sends a first step in real-time strategy framework for the two shake hands, you need to send data frames.
Clear to Send (CTS) of the framework: a station in response to a RTS frame by frame tour.Â It provides the required clearance stations send data frames.Â CTS provides collision control and management, including time value, all other stations are held, and requests the transmission station transmission.
Data frame to carry the package from the website and documents in the body.
InÂ IEEE802Â Executive CommitteeÂ approved twoÂ projects toÂ a higherÂ rate ofÂ physical layerÂ (PHY)Â extensionÂ toÂ 802.11.Â The firstÂ extension, IEEE 802.11a, andÂ definesÂ the requirementsÂ for aÂ physical layerÂ operatingÂ in theÂ 5.0Â GHzÂ U -Â NIIÂ frequency andÂ data rates fromÂ 54 MbpsÂ toÂ 6 MbpsÂ of. In the secondÂ extension, IEEE 802.11b, andÂ defines the physicalÂ layerÂ specifications setÂ work in theÂ 2.4 GHz ISMÂ bandÂ up toÂ 11 Mbps.Â BothÂ physical layers areÂ definitions of operation andÂ the existingÂ MAC. The physical layer of the 802.11 consistent three wireless data exchange method, they if infrared (IR), frequency hopping spread spectrum (FHSS) and direct sequence spread spectrum (DSSS). 802.11Â Wireless LANÂ radio operatorsÂ in theÂ 2.4GHz (2.4Â è‡³Â 2.483 GHz)Â unlicensed radio frequencyÂ (RF)Â band.Â IsotropicÂ maximum transmit powerÂ allowedÂ in this bandÂ in theÂ U.S. FederalÂ Communications CommissionÂ 1WTÂ type,Â but theÂ equipmentÂ is usually limited toÂ 100mWtÂ 802.11Â values.
In theÂ 802.11Â physical layersÂ is divided intoÂ the physical layerÂ convergence protocol (PLCPÂ report)Â and physicalÂ medium dependentÂ (PMD)Â sub layer.Â Be reportedÂ in the PLCPÂ /Â parse the dataÂ unitÂ to sendÂ / receiveÂ using a variety ofÂ 802.11Â media access technology.Â PMDÂ ofÂ theÂ data transmissionÂ / receptionÂ and modulationÂ /Â demodulation ofÂ direct access, under the guidanceÂ of airÂ PLCPÂ reported.Â 802.11 MACÂ layerÂ is subjectÂ to the greatÂ extension ofÂ the nature ofÂ the media.Â For example, itÂ implements a second layer ofÂ relativelyÂ complexÂ brokenÂ PDU.
For the infrared (IR) for wireless are not been acceptable by public, this is because there are no successful commercial implementations on 802.11 IR technology.
For the FHSS is use RadioÂ frequencyÂ for transmissionÂ toÂ the rapidÂ change in theÂ transmission process. The first short rupture is transmitted at one frequency, the secondÂ on anotherÂ frequency, and so on.Â The amountÂ ofÂ time spentÂ at aÂ particular frequencyÂ known as theÂ residence time,Â change theÂ frequencyÂ hoppingÂ sequence isÂ known. According toÂ FCCÂ regulation, allÂ in theÂ 900Â MHz bandÂ FHSSÂ systemsÂ hopÂ must beÂ 50 channels,Â can not spendÂ more than fourÂ into a secondÂ frequencyÂ inÂ aÂ transmission time every 20Â seconds.Â FHSSÂ system in theÂ 2.4 GHzÂ bandÂ toÂ jumpÂ between theÂ 15 channels, the maximumÂ output powerÂ can not beÂ more than 124Â mW. FHSS isÂ not widelyÂ used inÂ wireless LANÂ system, butÂ the BluetoothÂ does notÂ use itÂ in the 2.4Â GHzÂ frequency.Â BluetoothÂ change frequencyÂ 1600times.
For the Direct Sequence Spread Spectrum (DSSS) is a inflection technique.Â Like all the other spread-spectrum technology, the transmitted signal takes up more bandwidth than the information signal is modulated.Â This technique makes use of pseudo-random string of consecutive PN code symbols called "chips." These chips have a shorter duration than one bit of information, because this method of information transmission regulatory sequences of the chip.Â Also uses a spread spectrum signal sequence structure, in which the chip is generated by a transmitter called the a priori receiver.Â The receiver can use the same PN sequence offset the impact of the PN sequence in the received signal to reconstruct the information signal.
Makes use of pseudo-random sequence spread spectrum transmission 1 and -1 values â€‹â€‹and the data being transmitted multiplied by a "noise" signal.Â This will create a transmission frequency is much higher than the original signal, which spread the energy of the original signal into a wider band.Â This will create a similar "white noise" or static, the only real difference is that with the actual static, the receiver can extract meaningful data is multiplied by the same pseudo-random sequence.Â This process is called "to spread."
For the cancellation spread to work, send and receive sequences must be synchronized.Â This requires the serial receiver and transmitter synchronization sequence through some form of search time.Â However, this obvious shortcoming, it is obvious benefits: if the sequence number of transmitters synchronized relative to each other so that they must be synchronized between the receiver can be used to determine the relative time, which in turn can be used to calculate the receiverposition, if the transmitter's position is well known.Â This is the basis for many of the satellite navigation system.
The resulting effect of channel noise ratio is called processing gain.Â This influence can be through the use of larger and longer PN sequence chips per bit more, but the actual physical device used to generate the PN sequence impose limitations to the processing gain.
If do not want to send the transmitter, but in the same channel using a different PN sequence (or no order) in the communication process to achieve the results did not get a signal.Â This effect is based on Code Division Multiple Access (CDMA) spread-spectrum property, which allows multiple transmitters to share the same channel within the limits of cross-correlation properties of PN sequences.
As this description suggests that the emission waveform of a conspiracy to have a general bell-shaped envelope concentrated in the carrier frequency, just like a normal morning transmission, but the increase in noise to a wider distribution than a morning transmission.
In contrast, pseudo-random frequency hopping spread spectrum re-tune the carrier, rather than pseudo-random noise added data, results in a uniform frequency distribution, the width of the output range from pseudo-random number generator.
The advantages of spread-spectrum resistance to intentional or unintentional interference, sharing a single channel for multiple users, and reduce the spread of opportunities, one will be blocked.
a. Explain circuit switching and the phases used in it with the help of a diagram.
Label 3.1 Circuit Switching
Circuit-switchedÂ (Circuit Switching)Â isÂ aÂ relativeÂ concept ofÂ packet switching.Â Circuit switchingÂ requirementsÂ must firstÂ establish a connectionÂ between the two partiesÂ in the communicationÂ channel.Â AfterÂ theÂ connection is established, the two sidesÂ of the communication activitiesÂ can begin.Â Both sides need toÂ communicateÂ the message throughÂ a goodÂ connectionÂ has been establishedÂ for delivery, butÂ the connectionÂ has-beenÂ maintained untilÂ theÂ end of the communicationÂ of both sides.Â Communication activitiesÂ at aÂ timeÂ throughout the process,Â the connectionÂ will alwaysÂ occupyÂ the beginning ofÂ the connection is established, communication systemÂ resourcesÂ allocated to itÂ (channel, bandwidth,Â time slot, code, etc.), whichÂ reflects theÂ difference between circuit switchingÂ onÂ the essential characteristics ofÂ packet switching. In thisÂ networking, the connectionÂ betweenÂ two devicesÂ is calledÂ the circuit, which issued throughout theÂ communication.Â Nature of the information, the circuitÂ isÂ the maintained by the network.Â The circuit may also be able to be fix one that is always present, or it may be a circuit that is created on an as-needed basis.Â Even thoughÂ many potentialÂ pathsÂ through theÂ intermediate device may haveÂ communication betweenÂ two devices, only oneÂ will beÂ used forÂ any particular dialogue. In theÂ circuit-switchedÂ network, communicationsÂ can occurÂ betweenÂ two devicesÂ in front ofÂ theÂ circuits.Â This isÂ shown asÂ a thickÂ blueÂ lineÂ of theÂ pipelineÂ dataÂ from the deviceÂ deviceÂ AÂ to Device B and matchingÂ purpleÂ line fromÂ device B back to device A. OnceÂ established, all communication betweenÂ these devicesÂ inÂ this circuit,Â even if there areÂ other possible waysÂ can beÂ envisage through theÂ dataÂ between devicesÂ on the network. The most typical exampleÂ of theÂ circuit-switchedÂ is telephone networkÂ system.Â When you call, theyÂ answer, youÂ establishÂ a circuitÂ connectionÂ between the dataÂ youÂ can,Â ifÂ needs a steady flow.Â ThisÂ circuit functionsÂ the same way,Â no matter how manyÂ intermediate devices areÂ used toÂ your voice.Â You can useÂ it,Â as long as youÂ need it, and then terminate theÂ circuit.Â The next time youÂ call,Â you will get aÂ new circuit, which may be use a differentÂ hardwareÂ than the first circuit, depending onÂ whatÂ can beÂ timeÂ in the network.
b. What is packet switching? Describe Datagram and Virtual circuits in packet switching with the diagrams
Label 3.2 Packet Switching
InÂ computer networks andÂ communications, packet switchingÂ is a communications paradigm, groupÂ (messageÂ or messageÂ fragments) in a singleÂ routeÂ between nodes, noÂ previously establishedÂ communication path. Packet switchingÂ data communicationsÂ isÂ a newÂ andÂ important concept,Â is nowÂ the world'sÂ data and voiceÂ communicationsÂ in theÂ most importantÂ foundation.Â Previously, data communicationÂ is based onÂ the idea ofÂ â€‹â€‹circuit switching, as inÂ traditional telephoneÂ circuits,Â in a callÂ needs to occupyÂ a proprietaryÂ circuit, communicationÂ in bothÂ ends ofÂ the circuit. In thisÂ network type,Â there is no specificÂ path isÂ used for dataÂ transmission.Â Instead, the data isÂ choppedÂ into small piecesÂ calledÂ packets andÂ sent over the network.Â Packets can beÂ routed, combinedÂ or distributedÂ as requiredÂ toÂ their finalÂ destination.Â At the receiving end, this process isÂ the opposite,Â read dataÂ packetsÂ and re-assembled into theÂ form ofÂ raw data.Â Packet switching networkÂ similar toÂ the postal systemÂ moreÂ than itsÂ telephoneÂ system (albeitÂ not perfect.)Â An example is shown in Label 3.2. In theÂ packet-switchingÂ network,Â noÂ circuitÂ is establishment prior ofÂ transmission the dataÂ between devices.Â BlocksÂ of data,Â even fromÂ the sameÂ document or communication,Â can takeÂ any number ofÂ paths, because it'sÂ journeyÂ from oneÂ device to another.Â Compare this with Label 3.1. InÂ packet switching, aÂ system canÂ beÂ assembled intoÂ packetsÂ of dataÂ usingÂ a communication linkÂ withÂ more than one machineÂ communication.Â Not only theÂ linkÂ is shared,Â and eachÂ packetÂ independent of otherÂ packetsÂ canÂ be routed.Â This is theÂ main advantage ofÂ packet switching.