Introduction to Computer Networks

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23.08.2020

Peter Levinsky, IT Roskilde

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mobile network

global ISP

regional ISP

home network

institutionalnetwork

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Access net: home network

cable or DSL modem

router, firewall, NAT

wired Ethernet (100 Mbps)

wireless access point (54 Mbps)

wireless

devices

often combined in single box

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FDM

frequency

timeTDM

frequency

time

4 users

Example:

Circuit switching: FDM versus TDM

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Packet Switching: queueing delay, loss

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B

CR = 100 Mb/s

R = 1.5 Mb/sD

Equeue of packetswaiting for output link

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mobile network

global ISP

regional ISP

home network

institutionalnetwork

Proxy

server FirewallFirewall

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ticket (purchase)

baggage (check)

gates (load)

runway takeoff

airplane routing

ticket (complain)

baggage (claim)

gates (unload)

runway landing

airplane routing

airplane routing

Organization of air travel

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ticket (purchase)

baggage (check)

gates (load)

runway (takeoff)

airplane routing

departure

airportarrival

airport

intermediate air-traffic

control centers

airplane routing airplane routing

ticket (complain)

baggage (claim

gates (unload)

runway (land)

airplane routing

ticket

baggage

gate

takeoff/landing

airplane routing

Layering of airline functionality

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source

application

transport

network

link

physical

HtHn M

segment Ht

datagram

destination

application

transport

network

link

physical

HtHnHl M

HtHn M

Ht M

M

network

link

physical

link

physical

HtHnHl M

HtHn M

HtHn M

HtHnHl M

router

switch

message M

Ht M

Hn

frame

Encapsulation

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Sockets

• process sends/receives messages to/from its socket

• socket analogous to door• sending process shoves message out door

• sending process relies on transport infrastructure on other side of door to deliver

message to socket at receiving process

Internet

controlled

by OS

controlled byapp developer

transport

application

physical

link

network

process

transport

application

physical

link

network

processsocket

How to Program – Socket programming

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ServerClient

TcpListener listener

listener.Start

TcpClient client listener.AcceptTcpClient

SocketSocket

Read/Writ

eStreams

Read/Writ

eStreams

Connect

Send Data

Close