Networking
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Networking. Introduction. Networking - Introduction. Computers are lucky… …but this is not trivial!. Networking - Introduction. RAM. CPU. Easy…. Networking - Introduction. My smartphone in Denmark. www.surf.au in Australia. Hard…. Networking - Introduction.

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Networking

Networking

Introduction


Networking introduction

Networking - Introduction

  • Computers are lucky…

  • …but this is not trivial!


Networking introduction1

Networking - Introduction

RAM

CPU

Easy….


Networking introduction2

Networking - Introduction

My smartphone

in Denmark

www.surf.au in Australia

Hard….


Networking introduction3

Networking - Introduction

  • Networking – transmitting data between physically separated computers

  • No networking – no Internet

  • The Internet is ”just another computer network”

  • We will discuss networking within the context of the Internet


Networking introduction4

Networking - Introduction

  • What does the Internet look like…?

?

My device


Networking introduction5

Networking - Introduction

  • What does the Internet look like…?

?

My device

A Computer


Networking introduction6

Networking - Introduction

  • What does the Internet look like…?

?

Client

Server


Networking introduction7

Networking - Introduction

  • Through the Internet, my device (the client) can exchange data with a remote computer (the server)

  • How is the the client ”connected” to the server?


Networking introduction8

Networking - Introduction

  • What does the Internet look like…?

C

S

Client

Server

Routers


Networking introduction9

Networking - Introduction

  • Client is connected to a router C

  • Server is connected to a router S

  • Client sends data to C

  • C sends data to another router, who in turn sends data to another router, etc.

  • At some point, data reaches the router S

  • The server gets the data from S

  • How hard can it be…?


Networking introduction10

Networking - Introduction

  • Questions…

    • How do C and S get to know each other?

    • How does data find its way from C to S?

    • What format should data have?

    • How fast will the data get there?

    • Can we be sure that the data will reach S?

    • Can we be sure that the data is not altered?

    • …?


Networking introduction11

Networking - Introduction

  • Communication requires a protocol

  • This is true for both humans and computers!

Hi

Hi

Do you have the time?

Yes, it is 4.30pm

Okay, thank you

You’re welcome


Networking introduction12

Networking - Introduction

  • What can go wrong…?

Hi

… Я не говорю по английски

Oh, I guess he doesn’t speak English…


Networking introduction13

Networking - Introduction

  • What can go wrong…?

Hi

Hmmm, maybe he didn’t hear me…

I’ll try again in a minute…


Networking introduction14

Networking - Introduction

  • What can go wrong…?

Hi

I’m busy!

I’ll try again in a minute…


Networking introduction15

Networking - Introduction

  • What can go wrong…?

Hi

Hi

Do you have the time?

Yes, it is &.3¤p?

Hmmm, I’ll have to ask him again…


Networking introduction16

Networking - Introduction

  • A protocol is about agreement

    • When has a connection been established

    • What is the proper format of the transmitted data

    • What to do when data has been sent

    • What to do when data has been received

    • What is the proper order of data

    • When can data be considered lost

    • When can a connection be considered broken


Networking introduction17

Networking - Introduction

  • What is a connection really…?

  • Logical aspect

    • Connection-oriented service

    • Connectionless service

  • Physical aspect

    • Circuit switching

    • Packet switching


Networking introduction18

Networking - Introduction

  • Connection-oriented service

  • A (logical) way of communication, with certain properties

    • All data will be delivered

    • All data will be delivered in the correct order

    • Nobody ”floods” the counterpart with data

    • No part of the connection becomes congested


Networking introduction19

Networking - Introduction

  • Connection-oriented service

Are you ready to receive data?

Sure, go ahead

OK, here is part 1 of data

OK, I got part 1

OK, here is part 2 of data

OK, I got part 2

…and so on (handshaking)


Networking introduction20

Networking - Introduction

  • Connection-oriented service

Here is part n of data

Hmmm, I have to send part n again…

Here is part n of data

OK, I got part n


Networking introduction21

Networking - Introduction

  • Connection-oriented service

Here is part n of data

OK, I got part n

Here is part n+1 of data

Whoa, slow down a bit!

OK, I will send data more slowly


Networking introduction22

Networking - Introduction

  • Connection-oriented service

  • Many good properties, BUT…

    • More control data is sent

    • Cannot ”skip” data

    • Speed of transmission is uncertain


Networking introduction23

Networking - Introduction

  • Connectionless service

  • A (logical) way of communication, with certain properties

    • No guarantee on delivery

    • No handshaking

    • No flow or congestion control

  • BUT, can potentially deliver data faster


Networking introduction24

Networking - Introduction

  • Connectionless service

Are you ready to receive data?

Sure, go ahead

OK, bla bla bla bla bla bla…


Networking introduction25

Networking - Introduction

  • Why would we ever use a connectionless service?

  • Where could it be appropriate?

    • Sending E-mail?

    • File transmission

    • Viewing a web page

    • Streaming audio

    • Streaming video


Networking introduction26

Networking - Introduction

  • Why would we ever use a connectionless service?

  • Where could it be appropriate?

    • Sending E-mail?

    • File transmission

    • Viewing a web page

    • Streaming audio

    • Streaming video


Networking introduction27

Networking - Introduction

  • On the Internet…


Networking introduction28

Networking - Introduction

  • Circuit switching

  • Like in the old days…


Networking introduction29

Networking - Introduction

  • Using circuit switching, a dedicated end-to-end circiut is set up

C

S

Client

Server


Networking introduction30

Networking - Introduction

  • Using circuit switching, a dedicated end-to-end circiut is set up

C

S

Client

Server


Networking introduction31

Networking - Introduction

  • Properties of circuit switching

    • Guaranteed transmission rate

    • Wasteful in idle periods

  • Best for transmissions with low transmission rate variation (phonecall?)

  • Very wasteful for ”burst” transmissions


Networking introduction32

Networking - Introduction

  • Packet switching

  • The postal approach…


Networking introduction33

Networking - Introduction

  • In packet switching, we no longer use dedicated connnections

  • A recipient of data has an address

  • Data is divided into packets, which are ”stamped” with the destination address

  • The magic lies in the router…


Networking introduction34

Networking - Introduction

  • Delivering a letter…

Sender

Postbox

Letterbox

Sender

Local post office

Local post office

Regional post office

Regional post office

National post center

National post center


Networking introduction35

Networking - Introduction

Router must choose a destination router…

1

R

2

68.122.87.224

(DATA)

3


Networking introduction36

Networking - Introduction

  • Router maintains a routing table of appropriate desitination routers for a given destination adress (or interval of addresses)

  • How is the routing table created…?

  • MAGIC…for now 


Networking introduction37

Networking - Introduction

  • On the Internet, the IP (Internet Protocol) uses packet switching

  • Formally, the IP implements a datagram network – a specific variant of packet switching


Networking introduction38

Networking - Introduction

  • Circuit Switching vs. Packet Switching

  • I have a 100 megabit/second (mbps) connection available (bandwidth guaranteed)

  • I want to give all my users a 10 mbps connection

  • How many users can share the connection?


Networking introduction39

Networking - Introduction

  • Circuit Switching guarantees the bandwidth at all times!

  • Everybody must be guaranteed a 10 mbit connection…

  • …so the answer must be 100/10 = 10 users


Networking introduction40

Networking - Introduction

  • In packet switching, packets are sent

    • With full transmission rate

    • Intermixed with packets from other users

  • No guaranteed bandwidth

  • We have to know about the expected use of bandwidth per user


Networking introduction41

Networking - Introduction

  • Theoretical use per day, given a 10 mbps connection:

    • 10 mbps ≈ 1 megabyte/sec

    • 1 megabyte/sec ≈ 4 gigabyte/hour

    • 4 gigabyte/hour ≈ 100 gigabyte/day

  • In practice, probably much less!


Networking introduction42

Networking - Introduction

  • Bandwidth usage for a typical (?) private user

    • 10 gigabyte/month

    • Peak: 1 gigabyte/day

    • 00-08: ≈ 10 %

    • 08-16: ≈ 20 %

    • 16-24: ≈ 70 %


Networking introduction43

Networking - Introduction

  • What is my required ”level of service”?

  • Specified bandwidth available

    • 50 % of the time?

    • 90 % of the time?

    • 99 % of the time?

    • 99,99 % of the time?


Networking introduction44

Networking - Introduction

  • We wish to cover ”peak usage”, but assume that bandwidth usage during peak time is constant…

    • Peak usage: 1 gigabyte/day, 70 % between 16-24

    • 700 megabyte within 8 hours

    • 90 megabyte within an hour

    • 25 kilobytes per second…

    • about 250 kilobits per second (0,25 mbps)


Networking introduction45

Networking - Introduction

  • A 100 mbps connection…

  • …and a ”peak average” of 0,25 mbps…

  • …gives about 400 users

  • Circuit switching: 10 users

  • Packet switching: 400 users

  • ..if our assumptions hold up!


Networking introduction46

Networking - Introduction

  • Now we know about two protocols

    • TCP – implements connection-oriented service

    • IP – implements datagram packet switching

  • Is that enough to e.g. implement a Web browser…?

  • Still too low-level, we need a protocol ”on top of” TCP

  • Enter HTTP


Networking introduction47

Networking - Introduction

  • HTTP – HyperText Transfer Protocol

  • Specifically developed for ”distributed, hypermedia-based information systems”

  • Developed by Tim Berners-Lee (and team) around 1990

  • HTTP + HTML + URL = WWW (almost )


Networking introduction48

Networking - Introduction

  • HTTP is essentially just a set of methods that can be executed within a program

  • First HTTP version – one method! (GET)

  • Current version has nine methods


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Networking - Introduction

  • Note that HTTP is not the only protocol on this level of abstraction

  • SMTP – Simple Mail Transfer Protocol

  • FTP – File Transfer Protocol

  • …and some lesser known protocols


Networking introduction50

Networking - Introduction

  • Now we know about (at least) three protocols

    • HTTP – implements hypertext-based distributed computer systems

    • TCP – implements connection-oriented service

    • IP – implements datagram packet switching

  • How are the protocols related?

  • Are other protocols needed?

  • How do we ”organise” protocols?


Networking introduction51

Networking - Introduction

  • A standard model for layering functions in a communication system exists: the OSI model

  • OSI – Open Systems Interconnection

  • Model consists of 7 layers, each of which contains specific functionality


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Networking - Introduction


Networking introduction53

Networking - Introduction

  • The OSI model is a logical model – does not necessarily map one-to-one to actual model

  • The model for the Internet is considered to have 4-5 layers

  • Kurose & Ross: 5 layers

  • For simplicity, we consider four layers

  • The set of protocols is called the Internet Protocol Stack (or Suite)


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Networking - Introduction

Hardware…


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Networking - Introduction

  • We will discuss the three top levels in the Internet protocol stack in further detail

    • Application Layer – focus on HTTP

    • Transport Layer – focus on TCP

    • Network Layer – focus on IP


Networking introduction56

Networking - Introduction


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