Communication Networks Review Question/Answer - Lecture 11

Communication NetworksReview Question/Answer Lecture 11OverviewLANs WANs DifferentiationPath ReliabilityCircuit Switching Driven example networkCircuit Switching Routing TypesSemi-Permanent Connection TypeISDN Review QuestionDatagram and Virtual Circuit Operational DifferentiationLimitations of Circuit Switching for Data TransmissionVirtual Channel and Virtual Path Difference2WANs and LANsQ:-Differentiate between WANs and LANs3High Speed WANs and LANsScope of High Speed LANs and WANs (backbone)WANs and LANs scope in case of wireless communication (Mobility)4Overview of Wireless LANswireless transmission mediumissues of high prices, low data rates, occupational safety concerns, & licensing requirements now addressedkey application areas:LAN extensioncross-building interconnectnomadic accessad hoc networking5Single Cell LAN Extension6Multi Cell LAN Extension7Cross-Building Interconnectused to connect wired or wireless LANs in nearby buildingspoint-to-point wireless link usednot a LAN per seconnect bridges or routers8Nomadic Accessalso useful in extended environment such as campus or cluster of buildingsusers move around with portable computersaccess to servers on wired LANlink LAN hub & mobile data terminal laptop or notepad computerenable employee to transfer data from portable computer to server9Infrastructure Wireless LAN10Ad Hoc Networkingtemporary peer-to-peer network11Wireless LAN RequirementsTHROUGHPUT – should make efficient use of mediumNUMBER OF NODES- hundreds of nodes across multiple cellsCONNECTION TO BACKBONE LAN – use of control modulesSERVICE AREA – coverage area of 100 to 300mBATTERY POWER CONSUMPTION – reduce power consumption while not in useTRANSMISSION ROBUST AND SECURITY– reliability and privacy/securityCOLLOCATED NETWORK OPERATION – possible interference between LANsLICENSE-FREE OPERATION – not having to secure a license for the frequency band used by the LANHANDOFF/ROAMING– enable stations to move from one cell to anotherDYNAMIC CONFIGURATION- addition, deletion, relocation of end systems without disruption12Wireless LANsspread spectrum LANsmostly operate in ISM (industrial, scientific, and medical) bandsno Federal Communications Commission (FCC) licensing is required in USAOFDM LANsorthogonal frequency division multiplexingsuperior to spread spectrumoperate in 2.4 GHz or 5 GHz bandinfrared (IR) LANsindividual cell of IR LAN limited to single roomIR light does not penetrate opaque walls13WAN MAN and LANQ:-Differentiate between WANs and LANsAns:- Wide area networks (WANs) are used to connect stations over very large areas that may even be worldwide while local area networks (LANs) connect stations within a single building or cluster of buildings. Ordinarily, the network assets supporting a LAN belong to the organization using the LAN. For WANs, network assets of service providers are often used. LANs also generally support higher data rates than WANs.1415Q:-Differentiate between WANs and LANs Ans:- Wide area networks (WANs) are used to connect stations over very large areas that may even be worldwide while local area networks (LANs) connect stations within a single building or cluster of buildings. Ordinarily, the network assets supporting a LAN belong to the organization using the LAN. For WANs, network assets of service providers are often used. LANs also generally support higher data rates than WANs.Wide-Area Wireless Computing 16Q:-Why is it useful to have more than one possible path through a network for each pair of stations?17More than one PathQ:-Why is it useful to have more than one possible path through a network for each pair of stations?Ans:-It is advantageous to have more than one possible path through a network for each pair of stations to enhance reliability in case a particular path fails.18LahoreKarachiPacket 2Packet 1Islamabad19Review QuestionQ:- What is the principal application that has driven the design of circuit-switching networks?20Switching TechniquesData transmitted through a network of intermediate switching nodes, which are not concerned with contentEnd devices receiving data are stations; switching devices are nodesA collection of nodes is a communication networkA switched communication network routes data from one station to another through nodes21Switched Network CharacteristicsSome nodes connect only to other nodes for switching of data; other nodes have one or more stations attached as well.Node-station links are generally dedicated point-to-point links; ode-node links are usually multiplexed linksUsually, the network is not fully connected; however, it is desirable to have more than one possible path through the network for each pair of stations to enhance reliability22Types of Switched NetworksTwo different technologiesCircuit switchingPacket switchingDiffer in the way the nodes switch information from one link to another between source and destination23Circuit-Switching StagesCircuit establishmentData transferpoint-to-point from endpoints to nodeinternal switching/multiplexing among nodesCircuit disconnect24Circuit EstablishmentStation requests connection from nodeNode determines best route, sends message to next linkEach subsequent node continues the establishment of a pathOnce nodes have established connection, test message is sent to determine if receiver is ready/able to accept message25Data TransferPoint-to-point transfer from source to nodeInternal switching and multiplexed transfer from node to nodePoint-to-point transfer from node to receiverUsually a full-duplex connection throughout26Circuit DisconnectWhen transfer is complete, one station initiates terminationSignals must be propagated to all nodes used in transit in order to free up resources27Circuit Switching CharacteristicsChannel capacity is dedicated for the duration of a connection, even if no data are being transferredOnce the circuit is established, the network is effectively transparent to the users, resulting in negligible delaysDeveloped to handle voice traffic but is now also used for data traffic28Circuit Switching ApplicationsPublic Telephone Network (PSTN)Private Branch Exchanges (PBX)Private Wide Area Networks (often used to interconnect PBXs in a single organization)Data Switch29Public Switched Telephone Network (PSTN)SubscribersSubscriber Line (“local loop”) Connects subscriber to local telco exchangeExchanges (“end office”)Telco switching centers>19,000 in USTrunksConnections between exchangesCarry multiple voice circuits using FDM or synchronous TDMManaged by IXCs (inter-exchange carriers)30Control SignalingManage the establishment, maintenance, and termination of signal pathsIncludes signaling from subscriber to network, and signals within networkFor a large public telecommunications network, a relatively complex control signaling scheme is required31 Signaling FunctionsAudible communication with the subscriberTransmission of the number dialedInformation between switches that a call cannot be completedInformation between switches that a call has ended and the path can be disconnectedTelephone ring signalTransmission of billing informationTransmission of equipment and trunk status informationTransmission of system failure diagnostic informationControl of special equipment (e.g. satellite channel equipment)32Types of Control SignalsSupervisoryAddressCall InformationNetwork Management33Supervisory SignalsBinary character (true/false; on/off)Deal with the availability of the called subscriber and of the needed network resourcesUsed to determine if a needed resource is available and, if so, to seize it. Also used to communicate the status of requested resources.34Address SignalsIdentify a subscriberInitially generated by a calling subscriber when dialing a telephone numberResulting address may be propagated through the network to support the routing function and to locate and ring the called subscriber's phone35Call Information SignalsProvide information to the subscriber about the status of a callIn contrast to internal signals (which are analog or digital electrical messages), these are audible tones that can be heard by the caller or an operator with the proper phone set36Network Management SignalsUsed for the maintenance, troubleshooting, and overall operation of the networkThese signals cover a broad scope, and it is this category that will expand most with the increasing complexity of switched networks37In-Channel SignalingTraditionally, control signals were carried on the same channel as the call to which the control signals relateDrawbacksInformation transfer rate limitedDelay between entering a number and establishing a connection38Common-Channel SignalingControl signals are carried over paths completely independent of the voice channelsOne independent control signal path can carry the signals for a number of subscriber channels (i.e. is a “common control channel” for these channels)39Softswitch ArchitectureA general-purpose computer running specialized software that turns it into a smart phone switchCost significantly less and can provide more functionalityCan convert digitized voice bits into packets, opening transmission options (e.g. voice over IP)Physical switching function: media gateway (MG)Call processing logic: media gateway controller (MGC)40Traditional Circuit Switching Illustration 41Softswitch Architecture Illustration42Review AnswerQ:- What is the principal application that has driven the design of circuit-switching networks?43Ans:- Telephone Communications.44Review Question (Routing)Q:- Distinguish between static and alternate routing in a circuit-switching network.45Routing in Circuit Switched NetworksRoutingThe process of selecting the path through the switched network.Two RequirementsEfficiency --ability to handle expected load of traffic using the smallest amount of equipment.Resilience--ability to handle surges of traffic that exceed the expected load of traffic.46Routing in Circuit-Switched NetworksMany connections will need paths through more than one switchNeed to find a route based onEfficiencyResiliencePublic telephone switches are a tree structureStatic routing uses the same approach all the timeDynamic routing allows for changes in routing depending on traffic conditionsUses a peer structure for nodes47Routing in Circuit Switched NetworksTraditionally Circuit Switched Networks routing has been static hierarchical tree structure with additional high usage trunks.But today, a dynamic approach is used, to adjust to current traffic conditions.48Alternate RoutingAlternative routing is a form of routing in circuit-switching networksPossible routes between end offices are predefinedOriginating switch selects appropriate routeRoutes are listed in preference orderDifferent sets of routes may be used at different times49Routing in Circuit Switched NetworksAlternate RoutingApproach where possible routes between end offices are predefined.The alternate routes are sequentially tried, in order of preference, until a call is completed.Fixed Alternate Routing--only one set of paths provided.Dynamic Alternate Routing--different sets of preplanned routes are used for different time periods50AlternateRoutingDiagramSwitch X has 4 possible routes to destination switch Y.Direct route is tried first.If this trunk is unavailable (busy, out of service), the other routes will be tried in a particular order depending on the time period.Eg, during weekday mornings, route b is tried next.51Review Answer (Routing)Q:- Distinguish between static and alternate routing in a circuit-switching network.Ans:- Static routing involves the use of a predefined route between any two end points, with possible backup routes to handle overflow. In alternate routing, multiple routes are defined between two end points and the choice can depend on time of day and traffic conditions.5253Review Question:Semi-Permanent Connection Q:- What is a semipermanent connection?54Protocol Architecture (diag)55Reference Model PlanesUser planeProvides for user information transferControl planeCall and connection controlManagement planePlane managementwhole system functionsLayer managementResources and parameters in protocol entities56ATM Logical ConnectionsVirtual channel connections (VCC)Analogous to virtual circuit in X.25Basic unit of switchingBetween two end usersFull duplexFixed size cellsData, user-network exchange (control) and network-network exchange (network management and routing)Virtual path connection (VPC)Bundle of VCC with same end points57ATM Connection Relationships58Advantages of Virtual PathsSimplified network architectureIncreased network performance and reliabilityReduced processingShort connection setup timeEnhanced network services59VP/VC CharacteristicsQuality of serviceSwitched and semi-permanent channel connectionsCall sequence integrityTraffic parameter negotiation and usage monitoringVPC onlyVirtual channel identifier restriction within VPC60Review Answer:Semi-Permanent Connection Q:- What is a semi-permanent connection?Ans:-This is a connection to another user set up by prior arrangement, and not requiringa call establishment protocol. It is equivalent to a leased line.6162Review Question: ISDN Data RatesQ:- What data rates are offered for ISDN primary access63ISDNKnown as the Integrated Services Digital Network (ISDN) Data, audio, image and video transmissionIt is a switched digital telecommunication line that can be delivered over regular copper wiresPossible to provide end-to-end digital communications64ISDN Basic CharacteristicsSignalingDataDataDataD Channel16-64 KbpsB Channels64 Kbps65ISDN Service ConnectionsThere are two different types of ISDN services that are widely availableOne is known as the Basic Rate Interface or BRI Used for home or SOHO connectionThe other is known as the Primary Rate Interface or the Used in large businesses 66BRI Characteristics2 B Channels1 D Channel67Channels in BRI ServiceB channels are known as bearer channelsCarry informationD channel is known as the Delta channelUsed for signaling purposes2B + D channel service68The B Channel64k bps per channelThe two B channels can be inverse multiplexed or boded together Achieve a maximum aggregate communication speed of 128 Kbps69The D Channel16 KbpsEntire bandwidth is not used for signaling purposeExcess of 9.6 Kbps is available for packet switched data transmission applicationsExcess bandwidth usageClimate control, security alarm system etc.70PRI ServiceMore sophisticated service compared to BRIPRI service offers 23 B channels and 1 D channel71Properties of B Channels in PRIEach B channel operates at a speed of 64K bps The B channels are used for carrying dataB channels can be combined together to increase the aggregate communication speed72Properties of D Channel in PRIEach D channel operates at a speed of 64 KbpsConsiderably faster than the D channel in BRI23 B channels share a D channel for signaling purpose73Review Question: ISDN Data RatesQ:- What data rates are offered for ISDN primary accessAns:-PRI channels are delivered over a T1 lineT1 speed1.544M bpsAggregate speed of PRI from all 23 B channels and the single D Channel is computed as follows:23 * 64 K+ 1* 64K + = 1.536 MbpsIn North America and Japan, 23B+D Primary Rate Access operates at 1.544 Mbps and offers 23 B channels plus 1 64-Kbps D channelIn most of the rest of the world, 30B+D Primary Rate Access operates at 2.048 Mbps and offers 30 B channels plus 1 64-Kbps D channel (located in time-slot 16) 7475Review QuestionDatagram Vs. Virtual Circuit OperationQ:-Explain the difference between datagram and virtual circuit operation.7677Around 1970, research began on a new form of architecture for long distance communications: Packet Switching.Packet SwitchingIntroductionPacket Switching refers to protocols in which messages are divided into packets before they are sent. Each packet is then transmitted individually and can even follow different routes to its destination. Once all the packets forming a message arrive at the destination, they are recompiled into the original message.78Packet Switching OperationData are transmitted in short packets. Typically an upper bound on packet size is 1000 octets.If a station has a longer message to send it breaks it up into a series of small packets. Each packet now contains part of the user's data and some control information. The control information should at least contain:Destination AddressSource AddressStore and forward - Packets are received, stored briefly (buffered) and past on to the next node79AdvantagesLine efficiencySingle node to node link can be shared by many packets over timePackets queued and transmitted as fast as possibleData rate conversionEach station connects to the local node at its own speedNodes buffer data if required to equalize ratesPackets are accepted even when network is busyDelivery may slow downPriorities can be used80Switching Technique - Virtual Circuits and DatagramsStation breaks long message into packetsPackets sent one at a time to the networkPackets handled in two waysDatagramVirtual circuit81Datagram Packet SwitchingIn datagram approach each packet is treated independently with no reference to packets that have gone before. No connection is set up.Packets can take any practical routePackets may arrive out of orderPackets may go missingUp to receiver to re-order packets and recover from missing packetsMore processing time per packet per nodeRobust in the face of link or node failures.8283Packet Switching Datagram ApproachVirtual Circuit Packet SwitchingIn the Virtual Circuit approach a pre-planned route is established before any packets are sent. There is a call set up before the exchange of data (handshake). All packets follow the same route and therefore arrive in sequence.Each packet contains a virtual circuit identifier instead of destination addressMore set up timeNo routing decisions required for each packet - Less routing or processing timeSusceptible to data loss in the face of link or node failureClear request to drop circuitNot a dedicated path8485Packet Switching Virtual Circuit ApproachVirtual Circuits vs. DatagramVirtual circuitsNetwork can provide sequencing and error controlPackets are forwarded more quicklyNo routing decisions to makeLess reliableLoss of a node looses all circuits through that nodeDatagramNo call setup phaseBetter if few packetsMore flexibleRouting can be used to avoid congested parts of the network86Packet switching - datagrams or virtual circuitsInterface between station and network nodeConnection orientedStation requests logical connection (virtual circuit)All packets identified as belonging to that connection & sequentially numberedNetwork delivers packets in sequenceExternal virtual circuit servicee.g. X.25Different from internal virtual circuit operationConnectionlessPackets handled independentlyExternal datagram serviceDifferent from internal datagram operation87External Virtual Circuit andDatagram Operation88InternalVirtualCircuit andDatagram Operation89Q:-Explain the difference between datagram and virtual circuit operation.Ans:-In the datagram approach, each packet is treated independently, with no reference to packets that have gone before. In the virtual circuit approach, a preplanned route is established before any packets are sent. Once the route is established, all the packets between a pair of communicating parties follow this same route through the network.90Review AnsDatagram Vs. Virtual Circuit Operation91Review Question:Limitations of Circuit Switching for Data TransmissionQ:-What are some of the limitations of using a circuit-switching network for data transmission?92Circuit Switching (e.g., Phone Network)Establish: source creates circuit to destinationNode along the path store connection infoNodes may reserve resources for the connectionTransfer: source sends data over the circuitNo destination address, since nodes know pathTeardown: source tears down circuit when done9394Timing in Circuit Switching95Q:-What are some of the limitations of using a circuit-switching network for data transmission?Ans:- It is not efficient to use a circuit switched network for data since much of the time a typical terminal-to-host data communication line will be idle. Secondly, the connections provide for transactions at a constant data rate, which limits the utility of the network in interconnecting a variety of host computers and terminals.Review Ans:Limitations of Circuit Switching for Data TransmissionMoreover circuit switching is designed for voiceBut for data, the shortcomings are:`Resources dedicated to a particular callMuch of the time a data connection is idleData rate is fixedBoth ends must operate at the same rate96Review Ans:Limitations of Circuit Switching for Data Transmission97Review QuestionVirtual Channel and Virtual PathQ:-What is the difference between a virtual channel and a virtual path?98Review QuestionVirtual Channel and Virtual PathQ:-What is the difference between a virtual channel and a virtual path?Ans:-A virtual channel is a logical connection similar to virtual circuit in X.25 or a logical channel in frame relay. In ATM, virtual channels that have the same endpoints can be grouped into virtual paths. All the circuits in virtual paths are switched together; this offers increased efficiency, architectural simplicity, and the ability to offer enhanced network services.99SummaryLAN WAN differenceReliability via having more than one pathConventional PSTN network: A circuit-switching driven designMore bits and pieces of ATM: semi-permanent connectionISDN data rates showing different schools of thoughts of US and EUDatagram Vs. Virtual ChannelWhat if data has to be transmitted on circuit switched networkVCC Vs. VPC100101