Course Introduction

v Introduction§ Matthew Green, Professor§ Teaching Assistants: Venkatesh Gopal (head TA), Eyal Foni, Shikha

Fadnavis and Praveen Malhan (maybe more soon!)v Registration: 60-80 students

§ If you’re waitlisted, come and see me next Monv Prerequisites

§ Intermediate programmingv My teaching style

§ PPT lecture slides• Made available after lecture

§ Off script lecturing on whiteboard• Just as important towards exams, etc.

§ Do not like late arrivals to classv A word about academic integrity

Course Introduction

v WireShark labs (15% of course grade)§ May do with one partner (cannot be same partner for

programming assignments)§ Due at 10pm the night before the first lecture of the week§ Upload PDF solution via blackboard

v Homework assignments (15% of course grade)§ Assigned problems from the textbook§ Also due 10pm the night before the first lecture of the week§ Upload PDF solution via blackboard

v Programming Projects (20% of grade)§ May work in groups of 2 students§ Use Python programming language

v Late assignments, 10% per day, up to 3 daysv Review syllabus

Course intro, cont.

v Course website/syllabus etc.§ https://isi.jhu.edu/~mgreen/600.444/§ Piazza Signup: piazza.com/jhu/spring2017/en600344

v Office Hours§ Mine: Mon 2-4pm (excepting this afternoon)§ Tues or Weds by appointment§ TAs will post something

Introduction 2-3

How many of you (show of hands):

v Understand the difference between TCP and UDP?v Are familiar with the OSI reference model?v Understand packet encapsulation?v Have looked at raw TCPDump output?v Can analyze raw TCPDump output?v Have used WireShark before?v Know what a DNS zone transfer is?v Could draw an accurate picture of IP header with all fields

from memory?v Have done socket programming before?v Know the difference between link state and distance

vector routing?v Are family with Scapy?

Introduction 2-4

How many of you (show of hands):

v Are freshman?v Sophomores?v Juniors?v Seniors?v Graduate students in CS?v MSSI Graduate students?v Non-Computer Science majors?

Introduction 2-5

v Someone, please remind me when there are 10 minutes left in class, to go over the Wireshark Lab and the Homework assignment!

Introduction 2-6

Introduction 1-7

Chapter 1Introduction

Computer Networking: A Top Down Approach 6th edition (or 7th) Jim Kurose, Keith RossAddison-WesleyMarch 2012

Introduction

Chapter 1: roadmap1.1 what is the Internet?1.2 network edge

§ end systems, access networks, links1.3 network core

§ packet switching, circuit switching, network structure1.4 delay, loss, throughput in networks1.5 protocol layers, service models1.6 networks under attack: security

1-8

Introduction

What’s the Internet: �nuts and bolts� view

vmillions of connected computing devices: § hosts = end systems§ running network apps

vcommunication links§ fiber, copper, radio,

satellite§ transmission rate:

bandwidth

vPacket switches: forward packets (chunks of data)§ routers and switches

wiredlinks

wirelesslinks

router

mobile network

global ISP

regional ISP

home network

institutionalnetwork

smartphone

PC

server

wirelesslaptop

1-9

Introduction

Internet appliances

IP picture framehttp://www.ceiva.com/

Web-enabled toaster +weather forecaster

Internet phonesInternet refrigerator

IP-enabled cameraDDoS your friends for fun

1-10

Tweet-a-watt: monitor energy use

Introduction

v Internet: �network of networks�§ Interconnected ISPs

v protocols control sending, receiving of msgs§ e.g., TCP, IP, HTTP, Skype, 802.11

v Internet standards§ RFC: Request for comments§ IETF: Internet Engineering Task

Force

What’s the Internet: �nuts and bolts� view

mobile network

global ISP

regional ISP

home network

institutionalnetwork

1-11

What’s the Internet: a service view

v Infrastructure that provides services to applications:§ Web, VoIP, email, games, e-

commerce, social nets, …v provides programming

interface to apps§ hooks that allow sending

and receiving app programs to “connect” to Internet

§ provides service options, analogous to postal service

mobile network

global ISP

regional ISP

home network

institutionalnetwork

Introduction 1-12

What’s a protocol?

Introduction

What’s a protocol?

human protocols:v �what�s the time?�v �I have a question�v introductions

… specific msgs sent… specific actions taken

when msgs received, or other events

network protocols:v machines rather than

humansv all communication activity

in Internet governed by protocols

protocols define format, orderof msgs sent and receivedamong network entities,

and actions taken on msg transmission, receipt

1-14

Introduction

a human protocol and a computer network protocol:

Q: other human protocols?

Hi

Hi

Got thetime?2:00

TCP connectionresponse

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

<file>time

TCP connectionrequest

What�s a protocol?

1-15

Introduction

A closer look at network structure:

v network edge:§ hosts: clients and servers§ servers often in data

centers

v access networks, physical media: wired, wireless communication links

v network core: § interconnected routers§network of networks

mobile network

global ISP

regional ISP

home network

institutionalnetwork

1-16

A little bit of history

POTS

A little bit of history

(plain old telephone service)POTS

POTS

Question: given a town of many people, how do we wire them together?

=

POTS (“fully connected” network)

Option: connect each subscriber to every other subscriber?

POTS (“fully connected” network)

Circuit switching

Option: connect each subscriber to a central switchboard

=

Circuit switching

Option: connect each subscriber to a central switchboard

=

Question: limitations?

Introduction

Circuit switchingend-end resources allocated

to, reserved for �call�between source & dest:

v In diagram, each link has four circuits. § call gets 2nd circuit in top

link and 1st circuit in right link.

v dedicated resources: no sharing§ circuit-like (guaranteed)

performancev circuit segment idle if not used

by call (no sharing)v Commonly used in traditional

telephone networks1-24

Introduction

Circuit switching: FDM versus TDM

FDM

frequency

timeTDM

frequency

time

4 usersExample:

1-25

A bit more history

A bit more history

Idea: don’t reset circuits, let’s keep them up 24/7. And let’s

route data in “packets”.

Host: sends packets of data

host sending function:v takes application messagev breaks into smaller

chunks, known as packets, of length L bits

v transmits packet into access network at transmission rate R§ link transmission rate,

aka link capacity, aka link bandwidth

R: link transmission ratehost

12

two packets, L bits each

packettransmission

delay

time needed totransmit L-bit

packet into link

L (bits)R (bits/sec)= =

1-28

Network Layer 4-29

Packet switchingforwarding: move packets from router�s input to appropriate router output

routing: determines source-destination route taken by packets

§ routing algorithms

routing algorithm

local forwarding tableheader value output link

0100010101111001

3221

123

dest address in arrivingpacket�s header

Introduction

Packet switching versus circuit switching

example:§ 1 Mb/s link§ each user:

• 100 kb/s when �active�• active 10% of time

vcircuit-switching:§ 10 users

vpacket switching:§ with 35 users, probability >

10 active at same time is less than .0004

packet switching allows more users to use network!

Nusers

1 Mbps link

Q: what happens if > 35 users?

1-30

Introduction

Packet-switching: store-and-forward

v takes L/R seconds to transmit (push out) L-bit packet into link at R bps

v store and forward: entire packet must arrive at router before it can be transmitted on next link

one-hop numerical example:§ L = 7.5 Mbits§ R = 1.5 Mbps§ one-hop transmission

delay = 5 sec

more on delay shortly …1-31

sourceR bps destination

123

L bitsperpacket

R bps

v end-end delay = 2L/R (assuming zero propagation delay)

Introduction

Packet Switching: queueing delay, loss

A

B

CR = 100 Mb/s

R = 1.5 Mb/s D

Equeue of packetswaiting for output link

1-32

queuing and loss: v If arrival rate (in bits) to link exceeds transmission rate of

link for a period of time:§ packets will queue, wait to be transmitted on link § packets can be dropped (lost) if memory (buffer) fills up

Introduction

v great for bursty data§ resource sharing§ simpler, no call setup

v excessive congestion possible: packet delay and loss§ protocols needed for reliable data transfer, congestion

controlv Q: How to provide circuit-like behavior?

§ bandwidth guarantees needed for audio/video apps§ still an unsolved problem (chapter 7)

is packet switching a �slam dunk winner?�

Q: human analogies of reserved resources (circuit switching) versus on-demand allocation (packet-switching)?

Packet switching versus circuit switching

1-33

Introduction

Protocol �layers�Networks are complex,with many �pieces�:

§ hosts§ routers§ links of various

media§ applications§ protocols§ hardware,

software

Question:is there any hope of organizing structure of

network?

…. or at least our discussion of networks?

1-72

Introduction

An analogy

1-73

Writing

Transcription

Coding

Boxing

Delivery

Introduction

An analogy

1-74

Reading

Transcription

Decoding

Unboxing

Receiving

Introduction

An analogy

1-75

Introduction

An analogy

1-76

Introduction

An analogy

1-77

Introduction

An analogy

1-78

Introduction

Why layering?

1-79