entc 345 lecture 5

8/8/2019 ENTC 345 Lecture 5

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Circuit Switching and

Packet Switching

ENTC 345Dr. Ana Goulart

Assistant Professor


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Announcements Reading: Stallings

Chapter 1 and 2

Chapter 10

TA:[email protected]

Office hours: Mondays 5 to 8 pm (T 101)

Hw # 1 due today


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Review M/M/1 example incoming link information

Hw#1: Examples of simulations and

applications

How was the first lab?


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On Opnet TrafficApplications and Profiles

Application Models: generate typical application traffic patterns

Examples: FTP

Email

Remote Login

Video Conferencing

DatabaseHTTP

Print

Voice

Custom

Standard applications


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On Opnet Standard applications

Client/Server Model

Two-tier architecture

Client Server

request

response

* Sessions: single conversation

between client/server

* Traffic organized into sessions


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Applications and ProfilesApplications: simple traffic sources, or

complex protocols, or discrete set of tasks

Application Profile: users behavior

Specify application he/she uses

how long and how often


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Applications and ProfilesApplication Profile: users behavior

Example: start time, duration, repeatability,

parallel applications or serial applications

Email HTTP

FTP

Email HTTP FTP

Profile 1 : Serial

Profile 2 : Parallel

Email


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Application Model Hierarchy

Profile

Application

Tasks

Phase

Profile Object

Application Object

Task Object

(Custom applications)


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Lab 1 Small Internetwork

Application and Profile

Objects database


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Steps: Create application add row 1

Create profile set attributes

Workstation object - Assign profile to desiredworkstations

Server object assign service type (application)

Example: How would you model the traffic at thelibrarys subnet?


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A Network Configuration

R

RR

R

R

Ethernet

switch

ATM

switchFirewall

host

Private WANServer

ISP

LAN PCs

Subscriber

connection

InternetResidential

user

(page 30 - Stallings)


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Wide Area NetworkImportant concepts:

Circuit switching

Packet switching

Frame relay

ATM (Asynchronous Transfer Mode)


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Wide Area NetworksImportant concepts:

Circuit switching

- fixed routes, dedicated path between 2 stations

- on each link, a logical channel is dedicated tothe connection

- data transmitted along the dedicated path as

rapidly as possible

Packet switching - data sent in a sequence of packets

- each packet passed from node to node along

some path

- at each node, the entire packet is received,

stored briefly and transmitted to next node


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Circuit Switching

A

B

- data transmitted along the dedicated path

as rapidly as possible


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Packet Switching

AR

RR

R

B

Internet

At each node, the entire packet is received,

stored briefly and transmitted to next node

What is the primary framework to model

this behavior and analyze delays?


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Circuit switching x Packet switchingTiming of events:

Call request signal

Data

Time

Call accept

signal

A B C D

Pkt 1

Pkt 2

Pkt 3 Propagation delay

Transmission delay

Queuing delay

Time

A B C D

Circuit switching Packet switching

Circuit

establishment


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Delays in Circuit switchingTiming of events:

Call request signal

Data

Time

A B C D

Propagation delay


Circuit

establishmentAfter connection is established,

Information is transmitted at a

fixed data rate.

Node delays are negligible.

Advantages?

Disadvantages?


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Circuit switching x Packet switchingTiming of events:

Call request signal

Data

Time

Call accept

signal

A B C D

Pkt 1

Pkt 2

Pkt 3Propagation delay

Transmission delay

Queuing delay

Time

A B C D


Circuit

establishment


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Packet switching delaysPkt 1

Transmission delay

Queuing delay + Processing

A B C

Packet switching

Propagation delay

Total delay from A to B

Pkt 1

What is the Throughput?


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ThroughputPkt 1

Transmission delay

Queuing delay + Processing

A B C

Packet switching

Propagation delay

T = Total delay from A to B

Pkt 1

What is the Throughput?

L = size of packet (bits)

Throughtput = L / T


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Impact of packet size Effect of packet size on transmission time

(figure 10.11, page 314 Stallings)

Smaller packets => higher service rate (or smaller

transmission times)

Service rate on the outgoing link

= Capacity (bits/sec)

Packet size (bits/packet)


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Virtual Circuit Packet Switching Datagram packet switching

No dedicated route for the conversation or

session

Virtual Circuit Packet Switching

Dedicated route for the conversation orsession

Additional Call setup delay


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Virtual Circuit switching (internal)Timing of events: Call request signal

Data

Time

Call accept

signal

A B C D

Circuit switching

Packet switching

Circuit

establishment

Pkt 1

Pkt 2

Pkt 3


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Virtual circuits (external) Logical path (or connections) between two

stations

Example: X.25 standard

Physical level interface between station and

packet switched network

Link level reliable data transfer across the physical

link (LAP-B)

Network level virtual circuit service, enables users

to set-up logical connectionsPacket switchingNetwork


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Frame relay Designed to eliminate the overhead of X.25

Virtual circuits or logical connections carried at

the link layer

Call control signaling (separate)

No hop-by-hop flow control (error and flow

control should be taken care by another higherlayer protocol

entc 345 lecture 5

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