Professor Yashar Ganjali
Department of Computer Science
University of Toronto
yganjali@cs.toronto.edu
http://www.cs.toronto.edu/~yganjali
Announcements
 Final project proposal
 Guidelines have been posted on class website.
 Each project completed by groups of two students

Use class mailing list to find teammates if you don’t know
anyone in class.
 1 page proposal
 Due: Fri. Oct 16th at 5PM
 Intermediate report
 Key technologies
 2 pages
 Due: Fri. Nov. 13th at 5PM
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University of Toronto – Fall 2015
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Announcements – Cont’d
 Final presentation
 In class during the last two weeks
 15 minute presentation
 Final report
 Put everything together
 5 pages
 Due: Fri. Nov. 27th at 5pm
 Volunteer for lecture notes?
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University of Toronto – Fall 2015
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The Story …
• Introduction to computer networks
• Internet vs. mail
• The science of networks
• Characteristics, graphs, scale-free networks, …
• Last week: Computer networks and healthcare
• This week: Computer networks and business
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Outline
 New business opportunities
 Online shopping
 Digital content
 Online trading
 Search engines and online advertisement
 How networks benefit small and large businesses
 Efficiency, communication
 Technologies that made it possible
 Ethernet
 Virtual private networks
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Networks Create New Possibilities
 Online shopping
 Amazon, eBay, …
 Targeted advertisement
 Online banking
 Online trading
 Currency exchange
 Stocks
 e-Commerce
 Remote meetings
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Online Shopping
 Internet can help with traditional shopping
 Retail


E.g. order furniture online
Much more convenient and flexible
 Peer-to-peer

eBay, Kijiji, Craigslist, …
 Check the order status, delivery, … online
 Electronic payments
 Credit cards, PayPal, …
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Selling Digital Content
 Internet has also created new possibilities
 eBooks, mp3s, videos, TV, …
 Amazon, Apple iTunes, Netflix, …
 These are new forms of traditional books, CDs, …
 Advantages
 Faster delivery (almost instant)
 Convenience

Access your library from anywhere
 Costs less
 Targeted advertisements and marketing

Good for advertisers and customers (?)
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Advertisement on the Internet
 New form of advertising
 Advertise while people are surfing the web
 Have access to more information
 Based on past browsing history you can find out about the
user’s interests
 … and target them with more accurate ads
 Might be useful for the customer as well

And less annoying
 Can cost less
 Compared to TV, billboards, …
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Online Trading
 Stocks, stock options, currency exchange all possible
in today’s Internet
 The most important issues here are
 Network reliability: order should not be lost
 Delay: extremely tight guarantees for timing required



It’s all about timing, timing, timing
Ordinary users: seconds to minutes
Trading companies: nano seconds to micro seconds
Online Trader
ISP One
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UniversityISP
of Toronto
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Delay in Computer Networks
 Delay has three major components:
 Transmission delay: how long it takes for your machine
to inject the traffic into network
 Propagation delay: how long it takes for data to
traverse the distance between source and destination
 Queueing delay: how long your data packets sit in
queues (buffers) on Internet routers
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Outline
 New business opportunities
 Online shopping
 Digital content
 Online trading
 Search engines and online advertisement
 How networks benefit small and large businesses
 Efficiency, communication
 Technologies that made it possible
 Ethernet
 Virtual private networks
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University of Toronto – Fall 2015
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Search Engines
 You can find new things by
looking for keywords
 Not ideal but works
 Question. What is the ideal way?
 You can find new things to buy
 That’s why advertising on the
Internet is such a big success
 We spend a lot of time behind
computers these days
 Question. how do search engines
know how to sort web pages?
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Detour: Search Engines
 Question. How do search engines
find web pages related to your
search?
 They have a large number of robots
that constantly crawl the web.
 You can simply make your own
crawler.
 Write a script that downloads a given
web page.
 Extracts all the links.
 If a link has not been downloaded
before

A
B
C
D
E
Download and repeat.
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How To Find the Best Match
 There might be many pages that have the given
keyword.
 Question. How to sort these pages and find the best
match?
 Technique # 1. Show any page that has the given
keyword, sort based on how many times the keyword
appears
 Or use font size, font shape (bold or italic, …) as guides
on how important that keyword is
 Question. Does this work? Why?
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Finding the Best Match – Cont’d
 Technique # 2: Use the number of links to this page
as a clue. The more the number of links, the higher
the rank of this page.
 Question. Does this work? Why?
 Both techniques are vulnerable to attacks
 Someone can easily increase the rank of their page by


Increasing the font size, frequency of the keywords, …
Or by creating fake pages pointing to this page
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Use Reputation as the Criteria
 Basic idea: assign a credibility score
to each page.
 Repeatedly update credibility score
of each page
 Divide the credibility score by the
number of outgoing links, and
distribute it among them.
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2
2
0
0
0
0
University of Toronto – Fall 2015
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Use Reputation as the Criteria
 Basic idea: assign a credibility score
to each page.
 Repeatedly update credibility score
of each page
 Divide the credibility score by the
number of outgoing links, and
distribute it among them.
4
2
1
1
2
0
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0
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Use Reputation as the Criteria
 Basic idea: assign a credibility score
to each page.
 Repeatedly update credibility score
of each page
 Divide the credibility score by the
number of outgoing links, and
distribute it among them.
4
2
1
1
2
1
 Question. Where do we start?
2
3
 This is the basic idea behind
“PageRank” which is used by Google.
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Why This Matters
 Good search results means people will use your
search engine
 That’s why Google doesn’t charge us
 Also, you need to find good matches between search
results and advertisements
 Can enhance your return
 Question. Is it just a matter of good matching?
 Text vs. picture vs. animation
 Size of the ad
 Where it appears on a page
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University of Toronto – Fall 2015
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Outline
 New business opportunities
 Online shopping
 Digital content
 Online trading
 Search engines and online advertisement
 How networks benefit small and large businesses
 Efficiency, communication
 Technologies that made it possible
 Ethernet
 Virtual private networks
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University of Toronto – Fall 2015
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Benefits of Using Networks in Business
 Networks allow sharing the cost of peripherals
 Printers
 Scanners
 Shared data storage
 ...
 Improved communication
 Locally
 Remotely


Work from home
Or while traveling
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University of Toronto – Fall 2015
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Efficiency
 Data is readily available
 Rather than looking for a physical file
 Can serve customers faster
 And better: shared data
 Reduce errors and improve consistency
 All staff work from the same source of information
 Make standard manuals and guidelines available
 Data can be backed up and checked for consistency
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University of Toronto – Fall 2015
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Outline
 New business opportunities
 Online shopping
 Digital content
 Online trading
 Search engines and online advertisement
 How networks benefit small and large businesses
 Efficiency, communication
 Technologies that made it possible
 Ethernet
 Virtual private networks
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University of Toronto – Fall 2015
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What Technologies Made This Possible
 Ethernet is the dominant networking
technology for Local Area Networks
(LANs)
 Extremely simple to setup
 Most of the time, just plug your
computer and it works
 Very inexpensive to setup and maintain
 Supports both wired and wireless
networking
 Relatively high rates: 10Mb/s to
100Gb/s
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How Does Ethernet Work
 First, we need an address
 Remember the mail example:
 This is how other computers know how to find you
 Two ways to assign an address to your computer
 Manual setup

We call this static IP address assignment
 Automatic setup


We call this one dynamic IP address assignment
The protocol used is called DHCP (Dynamic Host
Configuration Protocol)
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How Do Nodes Talk in Ethernet
 Shared communication medium
(wired or wireless)
 Can lead to collision
 Think of two or more people talking
in the classroom
 We need some sort of coordination
to avoid collision
 Only one person speaks at a time
 How do we do this in real life?
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How Do Nodes Talk in Ethernet – Cont’d
 Here is how Ethernet solves this problem
 Listen: if nobody else is talking you can start
 Otherwise wait till they finish
Why?
 While talking keep listening
 Nobody else talks  done!
 Somebody starts talking  collision
 In case of collision
 Choose a random time in the future
 Repeat
 Question: How long should we wait before retrying?
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University of Toronto – Fall 2015
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Wireless Networking in an Office
 Easier to setup
 No need to physically connect nodes
 Inexpensive
 Very flexible
 Can handle many computers
 Different types of devices
 Mobility: computers can be moved easily
 No need to reconfigure
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… And The Problems
 Lower rate compared to wired networks
 54-100Mb/s compared to 100Mb/s 1Gb/s or higher
 Shared medium
 Limited number of wireless channels available
 All machines are on the same medium
 In wired, you can have point-to-point connection
 Less secure
 Your signal can be heard by people nearby
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Virtual Private Networks (VPNs)
 Your employees might want to connect to their
business network from home, or while traveling
 Many security concerns
 Virtual Private Networks make this possible
 Remotely connect to your work network
 As if you are sitting in your office
 Access to all resources (databases, peripherals, …)
 All communications are encrypted
 Question. How do you build a VPN?
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Remote Collaboration
 A lot of people work from home these days
 Long distance collaborations
 Researchers, students/mentors, …
 Tons of tools to make this possible
 Voice/video conferencing and presentations
 Online sharing of documents
 Collaborative writing

Google docs, MS OneNote, …
 Energy savings, impact on environment
 Makes sense financially as well; gas prices going up
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University of Toronto – Fall 2015
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Other Areas of Impact
 Outsourcing
 Computer networks bring resources closer
 Ideally, customer won’t see a difference
 Business-to-business services
 Not only you can provide service to your customers
 You can buy and sell products and services to other
businesses

E-Commerce
 Information diffusion
 Information is money
 Technologies for fast distribution and aggregation of news
 …?
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Summary and Discussion
 Computer networks have already changed the way
we do business
 Online shopping, digital content, trading, e-Commerce,
advertisements, …
 They provide many benefits for small and large
businesses
 Communication, resource sharing, …
 What other areas can you think of?
 What are the technologies we need to work on
today?
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