ECE CS 372 introduction to computer networks lecture 1 chapter 1

Topics To Be CoveredArchitecture of the Internet, and network protocols Delay analysis Packet-switching and circuit-switching Congestion and flow control: TCP Routing algorithms: IP

Spring 2012 ECE/CS 372 Introduction to Computer Networks

Lecture 1

School of Electrical Engineering and Computer Science

Oregon State University

Course Overview

 Yousef Qassim (qassim@eecs.oregonstate.edu)

 Office hours: TR 2:30-3:20pm @KEC lounge

Lecture/Office/Lab Hours

CS or ECE 271 or an equivalent course

Basic Linux familiarity

Textbook

Prerequisite/Textbook

Textbook is Required

Computer Networking: A Top-Down Approach

Featuring the Internet, 6th Edition, Games F

Kurose, Keith W Ross

Grading Policy

 Assignments: 15%

 Each student must hand in one copy

 5 assignments: approx 1 every two weeks

 Labs: 15%

 Each student must hand in one copy

 5 labs: approx 1 every two weeks

 One midterm exam: 30%

 Final exam: 40%

Topics To Be Covered

Architecture of the Internet, and network protocols

Delay analysis

Packet-switching and circuit-switching

Congestion and flow control: TCP

Routing algorithms: IP and datagram

Data link layers and Ethernet: ARP, CSMA/CD

Medium access control and local area networks

Lectures & assignments

Objective

 Deep understanding of basic and fundamental

networking concepts, architectures, and philosophies

 IMPORTANT: this course is NOT about setting up your

router at home, or writing a twitter program!!

Approach: how to do well in this course

 Easy: attend ALL lectures and do ALL assignments

 Do your assignments individually

 Do NOT miss any Bonus Quiz (i.e., do not miss class)

Objective

 Understand how Internet protocols work

 Force network protocols to perform certain actions

 Observe and analyze protocols’ behavior

Approach

 Software tool: Wireshark

 already installed in Lab DEAR 205

 To run, type: sudo wireshark then enter your eecs psswd

 Allows you to sniff and analyze traffic

sent/received from/by your end system: real

measurement of Internet traffic

Chapter 1: roadmap

4 Internet structure and ISPs

5 Protocol layers, service models

6 Delay & loss in packet-switched networks

What’s the Internet: a “service” view

 communication infrastructure

enables distributed apps:

 Enables apps to communicate

 Web, email, games,

e-commerce, file sharing

 communication services

provided to apps:

 Offers services

What’s the Internet: “nuts and bolts” view

 millions of connected

computing devices: called

hosts or end systems

 e.g., Laptops, workstations

 running network apps

 routers & switches:

 forward packets (chunks of

regional ISP

router workstationserver

mobile

What’s the Internet: “nuts and bolts” view

 Internet standards

 IETF

(Internet Eng Task Force)

• RFC: Request for comments

 IEEE: for links/hardware

mobile

What’s a protocol?

a human protocol and a computer network protocol:

HiHi

Got the

time?

2:00

TCP connection request

TCP connection response

Get http://www.awl.com/kurose-ross

<file>

time

What’s a protocol?

human protocols:

 “what’s the time?”

 “I have a question”

protocols define (1) format,

order of msgs sent and received among network

Chapter 1: roadmap

1 What is the Internet?

2 Network edge

5 Protocol layers, service models

6 Delay & loss in packet-switched networks

A closer look at network structure:

 network edge: applications

and hosts

 network core:

 routers

 network of networks

 access networks, physical

media: communication links

The network edge: service models

 end systems (hosts):

 run application programs

 e.g Web, email

 at “edge of network”

 client/server model

 client host requests, receives

service from always-on server

 e.g Web browser/server; email

Chapter 1: roadmap

1 What is the Internet?

3 Network core

5 Internet structure and ISPs

6 Protocol layers, service models

7 Delay & loss in packet-switched networks

The Network Core

 mesh of interconnected

routers

 the fundamental

question: how is data

transferred through net?

 circuit switching:

dedicated circuit per

call: telephone net

 packet-switching: data

sent thru net in

discrete “chunks”

Network Core: Circuit Switching

Network Core: Circuit Switching

network resources

(e.g., bandwidth)

divided into “pieces”

 allocated pieces per call

 no sharing

resource piece idle if

not used by owning call

Network Core: Circuit Switching

 Two ways of dividing bandwidth into “pieces”

 frequency division

 time division

Circuit Switching: FDM and TDM

Freq Division Multiplx (FDM)

frequency

timeTime Division Multiplx (TDM)

frequency

4 usersExample:

Network Core: Packet Switching

each end-to-end data stream is divided into packets

 no dedication/reservation: all streams share resources

1.5 Mb/s

Sequence of A & B packets does not have fixed pattern,

shared on demand  statistical multiplexing.

A

B

C

100 Mb/s Ethernet

1.5 Mb/s

statistical multiplexing

queue of packets waiting for output

link

Network Core: statistical multiplexing

Packet switching versus circuit switching

Packet-switching Circuit-switching

 Congestion may lead to it admission control

 Overhead less overhead; more overhead;

no connection setup reserve resources 1st

 Guarantee Best-effort provide guarantee

no guarantee good for multimedia

Numerical example

640,000 bits from host A to host B over a

circuit-switched network?

 The link’s transmission rate = 0.64 Mbps

 Each link uses TDM with 10 slots/sec

 0.5 sec to establish end-to-end circuit

Let’s work it out! You have few minutes!

 Solution:

ECE/CS 372 – introduction to computer networks

 Lab 1 is due on Tuesday

 ALL HW and LAB ASSIGNMENTS SHOULD BE

HARD COPY, SOFT COPY IS NOT ACCEPTED

Announcements

Lab

Location: Dearborn 205

Access code: will be written on board

Approach: how to do well in this course

Easy: attend ALL lectures and do ALL assignments

Do your assignments individually

Some hw problems will be solved in class: this gives you the opportunity to clarify things further

Packet switching versus circuit switching

Packet-switching Circuit-switching

 Congestion may lead to it admission control

 Overhead less overhead; more overhead;

no connection setup reserve resources 1st

 Guarantee Best-effort provide guarantee

no guarantee good for multimedia

Packet switching versus circuit switching

Packet switching versus circuit switching

Board …

ECE/CS 372 – introduction to computer networks

Lecture 3

Announcements:

week in class.

Chapter 1: roadmap

1 What is the Internet?

4 Internet structure and ISPs

5 Protocol layers, service models

6 Delay & loss in packet-switched networks

Internet structure: network of networks

 roughly hierarchical: tier 1, tier 2, and tier 3

 at center: “tier-1” ISPs

 e.g., MCI, Sprint, AT&T, Cable and Wireless,

at public network access points

(NAPs)

Tier-1 ISP: e.g., Sprint

Sprint US backbone network

Seattle

Atlanta

Chicago Roachdale

Internet structure: network of networks

 “Tier-2” ISPs: smaller (often regional) ISPs

 Connect to one or more tier-1 ISPs, possibly other tier-2 ISPs

Tier 1 ISP

NAP

Tier-2 ISP Tier-2 ISP

Tier-2 ISP is

customer of

tier-1 provider

Tier-2 ISPs also peer privately with each other, interconnect

at NAP

Internet structure: network of networks

 “Tier-3” ISPs and local ISPs

 last hop (“access”) network (closest to end systems)

Tier-2 ISP Tier-2 ISP

Tier-2 ISP

local ISP

local ISP localISP

local ISP Tier 3

ISP

local ISP

Local and tier-

Internet structure: network of networks

 a packet passes through many networks!

Tier 1 ISP

NAP

Tier-2 ISP Tier-2 ISP

local ISP

local ISP localISP

local ISP Tier 3

ISP

Chapter 1: roadmap

1 What is the Internet?

4 Internet structure and ISPs

6 Delay & loss in packet-switched networks

Organization of air travel

intermediate air-traffic control centers

airplane routing airplane routing

ticket (complain) baggage (claim gates (unload) runway (land) airplane routing

ticket baggage gate takeoff/landing airplane routing

Layering of airline functionality

Layers: each layer implements a service

via its own internal-layer actions

Why layering?

Dealing with complex systems:

systems

transparent to rest of system

 e.g., change in gate procedure doesn’t affect rest

of system

Internet protocol stack

 application: supporting network

 IP, routing protocols

 link: data transfer between neighboring

network elements

applicationtransportnetworklinkphysical

sourceapplication transport network link physical

link physical

ISO/OSI Model: late 70’s

applicationtransportnetworklinkphysical

Chapter 1: roadmap

1 What is the Internet?

5 Protocol layers, service models

6 Delay & loss in packet-switched networks

Sources of packet delay

 1 processing:

 check bit errors

 determine output link

 2 queueing

 time waiting at output link for transmission

 depends on congestion level of router

A

 propagation delay = d/sNote: s and R are very different quantities!

A

B

propagation transmission

nodal

Sources of packet delay

Caravan analogy

of propagation)

a car (transmission time)

 Car ~ bit; caravan ~ packet

 Time to “push” entire caravan through toll booth

= 12*10 = 120 sec = 2 mns

 Time for last car to propagate from 1st to 2nd toll both: =100km/(100km/

toll booth

toll booth

ten -car caravan

Caravan analogy (more)

1000 km/hr

min to service a car

 Q: Will cars arrive to

2nd booth before all

cars serviced at 1st

booth?

 Yes! After 7 min, 1st car

at 2nd booth and 8th car still at 1st booth

 1st bit of packet can arrive at 2nd router before packet is fully transmitted at 1st router!

toll booth

toll booth

ten -car

caravan

Exercise 1

trans rate R = 1 Mbps

distance = 1 km, speed = 2x10 8 m/s Packet length = L bits

Question:

 Which bit is being transmitted at the time the first bit

arrives at Host B for

Answer:

First bit arrives after

 Propagation delay = 2x10 3 (m)/2x10 8 (m/s) = 10 -5 sec

 Transmission delay = 100x8 (bits)/R

 Prop delay = trans delay => R=10 5 x100x8 = 80 Mbps

L=48 Bytes

 Host A

 converts analog to digital at a=64Kbps

 groups bits into L=48Byte packets

 sends packet to Host B as soon it gathers a packet

 Host B

 As soon as it receives the whole pckt, it converts it to analogQuestion:

 Time to gather 1 st pkt: 48x8 (bits)/64x1000 (b/s) = 6 msec

 Time to push 1 st pkt to link: 48x8 (bits)/1x10 6 (b/s) = 0.384 msec

 Time to propagate: 2 msec

 Total delay = 6 + 0.384 + 2 = 8.384 msec

a=64Kbps

L=48 Bytes

ECE/CS 372 – introduction to computer networks

Lecture 4

Announcements:

 Lab 1 is due Tuesday 2nd week

 HW1 is due Monday 3rd week

 No class on Friday, Friday is a lab hour

1st week 1-2pm, later on 2:30-3:20pm

Nodal delay

 dproc = processing delay

 typically a few microsecs or less

 dqueue = queuing delay

 depends on congestion

 dtrans = transmission delay

 = L/R, significant for low-speed links

 dprop = propagation delay

 a few microsecs to hundreds of msecs

prop trans

queue proc

Queueing delay (more insight)

 Every second: aL bits arrive to queue

 Every second: R bits leave the router

 Question : what happens if aL > R ?

= L bits

Queueing delay: illustration

Arrival rate: a = 1/(L/R) = R/L (packet/second)

Traffic intensity = aL/R = (R/L) (L/R) = 1

Average queueing delay = 0

(queue is initially empty)

queue Link bandwidth = R bits/sec

1 packet arrives

every L/R seconds

Packet length L bits

Queueing delay: illustration

Arrival rate: a = N/(LN/R) = R/L packet/second

Traffic intensity = aL/R = (R/L) (L/R) = 1

queue Link bandwidth = R bits/sec

N packet arrive simultaneously

every LN/R seconds

Packet length L bits

Queueing delay: behavior

 La/R ~ 0 : avg queuing delay small

 La/R -> 1 : delays become large

 La/R > 1 : more “work” than can be

serviced, average delay infinite!

= L bits

 distance = d meters; speed of propagation = s m/sec

 transmission rate of link = R bits/s

 delay (one packet only)

= L/R + ½d/s + L/R + ½d/s = 2L/R + d/s

Store-and-forward & queuing delay

 Case 1: Assume R1 < R2

 distance = d meters; speed of propagation = s m/sec

 transmission rate of link = R1 and R2 bits/s

 Consider sending two packets A and B back to back

 Case 2: Assume R1 > R2

Q: is there a queuing delay? how much is this delay?

Answer (queue is empty initially):

Throughput analysis

 Suppose: Host A has huge file of size F bits to send to Host B

 File is split into N packets, each of length L bits (i.e., N=F/L)

 Ignore propagation delay for now

Throughput analysis

 Suppose: Host A has huge file of size F bits to send to Host B

 File is split into N packets, each of length L bits (i.e., N=F/L)

 Do NOT ignore propagation delay (assume prop speed = s m/s)

Introduction: Summary

Covered a “ton” of material!

 Packet-switching versus circuit-switching