CS 3640: Introduction to Networks and Their Applications Fall 2018, - - PowerPoint PPT Presentation

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CS 3640: Introduction to Networks and Their Applications

Fall 2018, Lecture 1: The Internet Layers Instructor: Rishab Nithyanand Teaching Assistant: Md. Kowsar Hossain

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Today in class

1.

Where do I get help? What is the Internet? What does this course look like?

2. 3.

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Where do I get…

• Administrivia, slides, logistics,

assignments, references, and policies?

• Class website (https://www.rishabn.com/cs3640-f18)

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Where do I get…

• Support, discussion, etc.?
• Class forum on Piazza

(http://piazza.com/uiowa/fall2018/cs3640)

• Meet me after class if you don’t have an invite yet.

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Rules of engagement: Seating

• Occupy the front rows. Let there be

no gaps in seating.

• You will be asked to interact with the

people around you in class.

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Rules of engagement: Interaction

• Ask questions!
• I don’t want to get bored.
• Answer questions!
• I’ll wait until you do. I have no problem

with awkward silences.

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Rules of engagement: Electronics

• Avoid using your phone, computer,
• etc. (unless I ask you to)
• I will post lecture slides and references
• nline.

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Rules of engagement: Congeniality

• Collaborate and be helpful.
• You will need to work well with your peers

to do well in this class.

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Today in class

1.

Where do I get help? What is the Internet? What does this course look like?

2. 3.

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What is a network?

• An arrangement of lines that connect points.

Node Node A B C Node Edge Edge Edge

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Examples and goals of a network

• Goals: Resource sharing and communication.
• Discuss: What makes a good network?
• Well connected, high capacity, affordable, etc.

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What is a computer network?

• A network of computing devices.
• Nodes: Computing devices.
• Edges: Transmission media.
• Examples: Cellular networks, Wi-Fi, ethernets, etc.

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Computer networks

Each network uses a specific type of transmission media to interconnect a specific set of devices.

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What is the Internet?

The Internet is not a specific network. The Internet ties different networks together.

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What is the Internet?

• The Internet facilitates communication

between many different networks.

• It allows you (on a university ethernet network) to

talk to your friend (on a home Wi-Fi network).

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Design goals: Networks vs. Internet

• Networks:
• Speed, cost, reliability, etc.
• Achieved through engineering.
• How should this task get done?
• Internet:
• Interoperability, scalability, fault-tolerance, etc.
• Achieved through architectural design.
• What tasks have to get done? Who should do them?

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Let’s design a messaging app

• Scenario: No “Internet”
• Three users:
• A on ethernet
• B on Wi-Fi
• C on cellular network
• Discuss: How would you make this app? What

protocols would you have to implement?

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Let’s design a messaging app

• You’d have to design a way for your app to use ethernet, Wi-Fi,

and cellular.

• You’d have to design a way for your app to locate devices on

each network.

• You’d have to keep adding new technology support and

maintain existing code.

• Ugh! All of that sounds like a lot of work for every new app.

How does the Internet make this easier?

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The 4-layer Internet model

• The Internet has a hierarchy of operations.
• Examples of operations: writing to a medium, finding a

device in a network, etc.

• Many of these are common to every app.
• If we made the design modular, we could easily reuse

them.

• If we made layers, each operation could go in a layer.
• Each layer could provide this operation as a service to a

higher layer.

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The 4-layer Internet model

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The link layer

• Links connect end devices (phones, laptops,

etc.) to network gateways (routers).

• Links connect network gateways to each
• ther.
• The link layer is responsible for sending

packets over a link.

• The link layer is used as a service by the

network layer.

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The link layer

• The link layer carries the

packet over a single link.

• All it does is deliver data to

the next hop.

• Examples: Wi-Fi and ethernet

Source Destination Routers Packet/Header Link

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The network layer

• The network layer provides an “end-to-

end” (source to destination) service.

• It delivers packets from the source to the

destination.

• Uses the link layer as a service.
• How?
• It figures out what the next hop should be and

tells the link layer to send it there.

• It doesn’t care how.

Network Link Network Link Transport Application Router

Source End-Host

Network Link Transport Application

Destination End-Host

Network Link Router

The network layer

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The network layer

• There is only one network layer protocol for data delivery: The

Internet Protocol (IP).

• It is the glue of the Internet. There is no Internet without IP.
• Internet Control Message Protocol (ICMP) is only for error and diagnostic

functions.

• IP makes no promises that datagrams will reach the destination :
• uncorrupted.
• in the order they were sent.
• at all.
• Discuss: Why would the Internet Protocol work this way?

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The transport layer

• Interface between the application and the

network layer. It implements:

• Reliable delivery, in-order delivery, congestion

detection, and congestion control (if required).

• Discuss: Why wouldn’t these always be required?
• Makes network communication appear like inter-

process communication for applications.

• Examples: TCP (Transmission Control Protocol)

and UDP (User Datagram Protocol).

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The application layer

• This is where the logic for your application goes.
• Every app is different, but they all really only

need to use the network through the Transport layer abstraction.

• You don’t have to write any code below this layer

to make an Internet application!

• Developers are insulated from the constant evolution
• f networking technology and protocols.

Network Link Network Link Transport Application Router

Source End-Host

Network Link Transport Application

Destination End-Host

Network Link Router

Putting it all together

Network Link Transport Application

Delivers data end-to-end. Best-effort delivery – provides no guarantees. Must use the Internet Protocol (IP). Delivers data over a single link between an end host and router, or between routers. What transport properties are required? Implements reliability, in-order delivery, congestion control. Logic of the Internet application. What should the app do? How can users interact with the app?

Summary of the 4-layer Internet model

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Let’s design a messaging app (v2)

• Scenario: The Internet abstraction exists.
• Three users:
• A on ethernet
• B on Wi-Fi
• C on cellular network
• Discuss: How would you make this app? What protocols

would you have to implement? What transport properties would you use?

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Today in class

1.

Where do I get help? What is the Internet? What does this course look like?

2. 3.

• Internet architecture
• What are the principles driving Internet design?
• Engineering and protocols
• How are these principles implemented?
• Protocol overloading
• How are implementations exploited?
• Economic, legal, social, and ethical considerations
• Ongoing challenges and things to think about as computer

scientists.

High-level organization

Network Link Transport Application

IP IP Ethernet, Wi-Fi TCP CP, UD UDP HTTP, DN DNS, , SS SSH, , BGP BGP

Tentative list of protocols

• Write a simple web application.
• Scrape the web.
• Identify Internet paths taken by your packets and

performance bottlenecks in the network.

• Identify the organizations controlling the Internet.
• Exploit protocols and overload them.
• Play with censors on the Internet.

Tentative list of things you will do in projects

• https://www.rishabn.com/cs3640-f18
• Don’t forget!
• Get on Piazza and introduce yourself.
• Set up Python and Jupyter.

Let’s go over administrivia