1 chapter 15 network properties (ownership, service paradigm, measures of performance)
TRANSCRIPT
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Chapter 15
Network Properties
(Ownership, Service Paradigm, Measures of Performance)
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Network Ownership And Service Type
Network Ownership And Service Type
PrivateOwned by individual or corporationRestricted to owner’s useTypically used by large corporations
PublicOwned by a common carrierIndividuals or corporations can subscribe“Public” refers to availability, not data
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Advantages and Disadvantages
Advantages and Disadvantages
PrivateComplete controlInstallation and operation costs
PublicNo need for staff to install/operate networkDependency on carrierSubscription fee
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Public Network Connections
Public Network Connections
One connection per subscriberTypical for small corporation or individualCommunicate with another subscriber
Multiple connections per subscriberTypical for large, multi-site corporationCommunicate among multiple sites as well as
with another subscriber
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Virtual Private NetworkVirtual Private Network
A serviceProvided over public networkInterconnects sites of single corporationActs like private network
No packets sent to other subscribersNo packets received from other subscribersData encrypted
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Virtual Private NetworkVirtual Private Network
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Network Service ParadigmNetwork Service Paradigm
Fundamental characteristic of networkUnderstood by hardwareVisible to applications
Two basic types of networksConnectionlessConnection-oriented
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Connectionless ( CL )Connectionless ( CL )
SenderForms packet to be sentPlaces address of intended recipient in packetTransfers packet to network for delivery
NetworkUses destination address to forward packetDelivers
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Characteristics of Connectionless Networks
Characteristics of Connectionless Networks
Packet contains identification of destinationEach packet handled independentlyNo setup required before transmitting dataNo cleanup required after sending dataThink of postcards
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Connection-Oriented (CO)Connection-Oriented (CO)
SenderRequests “connection” to receiverWaits for network to form connectionLeaves connection in place while sending dataTerminates connection when no longer needed
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Connection-Oriented (CO)(continued)
Connection-Oriented (CO)(continued)
NetworkReceives connection requestForms path to specified destination and informs
senderTransfers data across connectionRemoves connection when sender requestsThink of telephone calls
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TerminologyTerminology
In conventional telephone systemCircuit
In CO data networkVirtual CircuitVirtual Channel
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Comparison of CO and CLComparison of CO and CL
COMore intelligence in networkCan reserve bandwidthConnection setup overheadState in packet switchesWell-suited to real-time applications
CLLess overheadPermits asynchronous useAllows broadcast / multicast
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Two Connection TypesTwo Connection Types
Permanent Virtual Circuit (PVC)Entered manuallySurvives rebootUsually persists for months
Switched Virtual Circuit (SVC)Requested dynamicallyInitiated by applicationTerminated when application exits
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Examples of Service Paradigm
Various Technologies Use
Examples of Service Paradigm
Various Technologies Use
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Connection MultiplexingConnection Multiplexing
Typical computer has one physical connection to network
All logical connections multiplexed over physical interconnection
Data transferred must include connection identifier
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Connection IdentifierConnection Identifier
Integer valueOne per active VCNot an addressAllows multiplexing
Computer supplies when sending dataNetwork supplies when delivering data
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Example Connection Identifier (ATM)
Example Connection Identifier (ATM)
24 bits long (The full address is 160 bits)Divided into two parts
Virtual Path IdentifierVirtual Channel Identifier
Known as (VPI/VCI)Different at each end of connection
Mapped by switches
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Illustration of ATM VCIllustration of ATM VC
Switch maps VPI/VCIs17 to 1296 to 8
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Two PrimaryPerformance Measures
Two PrimaryPerformance Measures
DelayThroughput
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DelayDelay
Time required for one bit to travel through the network
Three types (causes)Propagation delaySwitching delayQueuing Delay
Intuition: “length” of the pipe
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ThroughputThroughput
Number of bits per second that can be transmitted
CapacityIntuition: “width” of the pipe
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Components of DelayComponents of Delay
Fixed (nearly constant)Propagation delaySwitching delay
VariableQueuing delayDepends on throughput
If delay is changing rapidly, we refer to it as Jitter
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Relationship BetweenDelay and ThroughputRelationship BetweenDelay and Throughput
When network idleQueuing delay is zero
As load on network increasesQueuing delay rises
Load defined as ration of throughput to capacity
Called utilization
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DefineD0 to be the propagation and switching delayU to be the utilization (0 U 1)D to be the total delay
Then
High utilization known as congestion
Relationship BetweenDelay and UtilizationRelationship BetweenDelay and Utilization
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Practical ConsequencePractical Consequence
Any network that operates with a utilization approaching 100% of capacity is doomed
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Delay-Throughput ProductDelay-Throughput ProductDelay
Time to cross networkMeasured in seconds
Throughput CapacityMeasured in bits per second
Delay * ThroughputMeasured in bitsGives quantity of data “in transit”
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SummarySummary
Network can bePublicPrivate
Virtual Private NetworkUses public networkConnects set of private sitesAddressing and routing guarantee isolation
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Summary (continued)Summary (continued)Networks are
ConnectionlessConnection-oriented
Connection typesPermanent Virtual CircuitSwitched Virtual Circuit
Two performance measuresDelayThroughput
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Summary (continued)Summary (continued)
Delay and throughput interactQueuing delay increases as utilization
increasesDelay * Throughput
Measured in bitsGives total data “in transit”