SEPT, 2005 CSI 4118 1

Part 2.1

Network Properties

(Ownership, Service Paradigm, Measures of Performance)

Robert Probert, SITE, University of Ottawa

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Network Ownership And Service Type

Private Owned by individual or corporation Restricted to owner’s use Typically used by large corporations

Public Owned by a common carrier Individuals or corporations can subscribe “Public” refers to availability, not data

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Advantages and Disadvantages

Private Complete control Installation and operation costs

Public No need for staff to install/operate network Dependency on carrier Subscription fee

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Public Network Connections

One connection per subscriber Typical for small corporation or individual Communicate with another subscriber

Multiple connections per subscriber Typical for large, multi-site corporation Communicate among multiple sites as well as

with another subscriber

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Virtual Private Network

A service Provided over public network Interconnects sites of single corporation Acts like private network

No packets sent to other subscribers No packets received from other subscribers Data encrypted

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Network Service Paradigm

Fundamental characteristic of network Understood by hardware Visible to applications

Two basic types of networks Connectionless Connection-oriented

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Connectionless ( CL )

Sender Forms packet to be sent Places address of intended recipient in packet Transfers packet to network for delivery

Network Uses destination address to forward packet Delivers

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Characteristics of Connectionless Networks

Packet contains identification of destination Each packet handled independently No setup required before transmitting data No cleanup required after sending data Think of postcards

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Connection-Oriented (CO)

Sender Requests “connection” to receiver Waits for network to form connection Leaves connection in place while sending data Terminates connection when no longer needed

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Connection-Oriented (CO)(continued)

Network Receives connection request Forms path to specified destination and informs

sender Transfers data across connection Removes connection when sender requests Think of telephone calls

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Terminology

In conventional telephone system Circuit

In CO data network Virtual Circuit Virtual Channel

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Comparison of CO and CL

CO More intelligence in network Can reserve bandwidth Connection setup overhead State in packet switches Well-suited to real-time applications

CL Less overhead Permits asynchronous use Allows broadcast / multicast

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Two Connection Types

Permanent Virtual Circuit (PVC) Entered manually Survives reboot Usually persists for months

Switched Virtual Circuit (SVC) Requested dynamically Initiated by application Terminated when application exits

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Examples of Service ParadigmVarious Technologies Use

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Connection 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 Identifier

Integer value One per active VC Not an address Allows multiplexing

Computer supplies when sending data Network supplies when delivering data

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Two PrimaryPerformance Measures

Delay Throughput

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Delay

Time required for one bit to travel through the network

Three types (causes) Propagation delay Switching delay Queuing Delay

Intuition: “length” of the pipe

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LatencyQueueTransmitnPropagatioLatency

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cablea in /102.3

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light of Speed8

8

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Bandwidth/SizeTransmit

light of Speed / DistancenPropagatio

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Throughput

Number of bits per second that can be transmitted

Capacity Intuition: “width” of the pipe

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Throughput

imeTransfer t / sizeTransfer Throughput

sizeTransfer h1/Bandwidt RTT imeTransfer t

(effective end-to-end throughput)

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Components of Delay

Fixed (nearly constant) Propagation delay Switching delays constant

Variable Queuing delay Depends on throughput

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Relationship BetweenDelay and Throughput

When network idle Queuing delay is zero

As load on network increases Queuing delay rises

Load defined as ration of throughput to capacity Called utilization

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Define D0 to be the propagation and switching delay U to be the utilization delay D to be the total delay

Then

High utilization known as congestion

Relationship BetweenDelay and Utilization

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Practical Consequence

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

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Delay-Throughput Product

Delay Time to cross network Measured in seconds

Throughput Capacity Measured in bits per second

Delay * Throughput Measured in bits Gives quantity of data “in transit”

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Delay x Bandwidth

Bandwidth

Delay

This product is analogous to the volume of a pipe or the number of bits it holds. It corresponds to how many bits the sender must transmit before the first bit arrives at the receiver.

Delay may be thought of as one-way latency or round-trip time (RTT) depending on the context.

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Jitter

Network

Interpacket gap

Packetsource

Packetsink

1234 1234

Jitter is a variation (somewhat random) of the latency from packet to packet. Jitter is most often observed when packets traverse multiple hops from source to destination.

Question: What is the cause of jitter?

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Summary

Network can be Public Private

Virtual Private Network Uses public network Connects set of private sites Addressing and routing guarantee isloation

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Summary (continued)

Networks are Connectionless Connection-oriented

Connection types Permanent Virtual Circuit Switched Virtual Circuit

Two performance measures Delay Throughput

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Summary (continued)

Delay and throughput interact Queuing delay increases as utilization

increases Delay x Throughput

Measured in bits Gives total data “in transit”