1 Chapter 15 Network Properties (Ownership, Service Paradigm, Measures of Performance)

1

Chapter 15

Network Properties

(Ownership, Service Paradigm, Measures of Performance)

2

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

3

Advantages and Disadvantages

Advantages and Disadvantages

PrivateComplete controlInstallation and operation costs

PublicNo need for staff to install/operate networkDependency on carrierSubscription fee

4

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

5

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

6

Virtual Private NetworkVirtual Private Network

7

Network Service ParadigmNetwork Service Paradigm

Fundamental characteristic of networkUnderstood by hardwareVisible to applications

Two basic types of networksConnectionlessConnection-oriented

8

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

9

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

10

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

11

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

12

TerminologyTerminology

In conventional telephone systemCircuit

In CO data networkVirtual CircuitVirtual Channel

13

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

14

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

15

Examples of Service Paradigm

Various Technologies Use

Examples of Service Paradigm

Various Technologies Use

16

Connection MultiplexingConnection Multiplexing

Typical computer has one physical connection to network

All logical connections multiplexed over physical interconnection

Data transferred must include connection identifier

17

Connection IdentifierConnection Identifier

Integer valueOne per active VCNot an addressAllows multiplexing

Computer supplies when sending dataNetwork supplies when delivering data

18

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

19

Illustration of ATM VCIllustration of ATM VC

Switch maps VPI/VCIs17 to 1296 to 8

20

Two PrimaryPerformance Measures

Two PrimaryPerformance Measures

DelayThroughput

21

DelayDelay

Time required for one bit to travel through the network

Three types (causes)Propagation delaySwitching delayQueuing Delay

Intuition: “length” of the pipe

22

ThroughputThroughput

Number of bits per second that can be transmitted

CapacityIntuition: “width” of the pipe

23

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

24

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

25

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

26

Practical ConsequencePractical Consequence

Any network that operates with a utilization approaching 100% of capacity is doomed

27

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”

28

SummarySummary

Network can bePublicPrivate

Virtual Private NetworkUses public networkConnects set of private sitesAddressing and routing guarantee isolation

29

Summary (continued)Summary (continued)Networks are

ConnectionlessConnection-oriented

Connection typesPermanent Virtual CircuitSwitched Virtual Circuit

Two performance measuresDelayThroughput

30

Summary (continued)Summary (continued)

Delay and throughput interactQueuing delay increases as utilization

increasesDelay * Throughput

Measured in bitsGives total data “in transit”