Chapter 1 V6.1 Monday - JHU Information Security Institutemgreen/600.444/Chapter_1_Mon.pdf ·...
Transcript of Chapter 1 V6.1 Monday - JHU Information Security Institutemgreen/600.444/Chapter_1_Mon.pdf ·...
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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
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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
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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
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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
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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
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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
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Introduction 1-7
Chapter 1Introduction
Computer Networking: A Top Down Approach 6th edition (or 7th) Jim Kurose, Keith RossAddison-WesleyMarch 2012
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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
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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
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Introduction
Internet appliances
IP picture framehttp://www.ceiva.com/
Web-enabled toaster +weather forecaster
Internet phonesInternet refrigerator
IP-enabled cameraDDoS your friends for fun
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Tweet-a-watt: monitor energy use
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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
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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
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What’s a protocol?
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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
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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?
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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
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A little bit of history
POTS
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A little bit of history
(plain old telephone service)POTS
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POTS
Question: given a town of many people, how do we wire them together?
=
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POTS (“fully connected” network)
Option: connect each subscriber to every other subscriber?
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POTS (“fully connected” network)
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Circuit switching
Option: connect each subscriber to a central switchboard
=
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Circuit switching
Option: connect each subscriber to a central switchboard
=
Question: limitations?
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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
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Introduction
Circuit switching: FDM versus TDM
FDM
frequency
timeTDM
frequency
time
4 usersExample:
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A bit more history
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A bit more history
Idea: don’t reset circuits, let’s keep them up 24/7. And let’s
route data in “packets”.
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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)= =
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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
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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?
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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)
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Introduction
Packet Switching: queueing delay, loss
A
B
CR = 100 Mb/s
R = 1.5 Mb/s D
Equeue of packetswaiting for output link
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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
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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
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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?
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Introduction
An analogy
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Writing
Transcription
Coding
Boxing
Delivery
Introduction
An analogy
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Reading
Transcription
Decoding
Unboxing
Receiving
Introduction
An analogy
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Introduction
An analogy
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Introduction
An analogy
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Introduction
An analogy
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Introduction
Why layering?
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