Grundlagen der Rechnernetze

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Grundlagen der Rechnernetze

Introduction

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Overview

• Building blocks and terms

• Basics of communication

• Addressing

• Protocols and Layers

• Performance

• Historical development

Grundlagen der Rechnernetze ‐ Introduction 2

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Building blocks and terms

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Hosts and links

H1 H2

Host

Link

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Hosts and links

H1 H2

Host

Link

Host is a computer or

more general a device that communicates with the other host on a network

Link is (in the context of computer networks) connection between two hosts

Point to point connection designates communication connection between two hosts (nodes) or endpoints

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Types of communication

• Simplex

• Half‐duplex

• Duplex (full duplex)

Source: http://mikrotik.tips/simplex‐half‐duplex‐full‐duplex/

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Medium

• Wired communication

• Wireless communication

• Light(?)

• Sound (ultrasound)

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Communication channel between the nodes

• Communication channel – refers to a physical transmission medium (wired or wireless) but it also covers logical connection over

multiplexed medium

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Message, stream, packet [1]

H1

^M

H2 H3

S

H4

P₁ P₂

…

P_n

Payload

Header Trailer

First Bit Last Bit

Bytes

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Message, stream, packet

Message

Communication primitive, usually consists of multiple packets; usually used in the higher layers of

communication

Stream

A sequence of signals that we use to transmit data

Packet

Formatted unit of data consisting of user data and control data

(header and trailer). Essentially a part of a message; several

packets together form a message

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Multiple access

H₁ H₂ H₃

…

H_n

Collision domain

A network connected by a shared medium; in this network packets may collide with one another when they are sent. A term coming from early versions of Ethernet and wireless networks

Single hop communication Basically communication within one collision domain; packet reaches destination within one hop

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Multiplexing [1]

H₁

H₂

H₃

H₄

H₅

H₆

H₁

H₂

H₃

H₄

H₅

H₆

…

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Multiplexing [2]

• Static multiplexing (predefined)

• Statistical multiplexing (can adapt over time)

• Queueing

• Packet scheduling – the way of controlling packet transmission

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Scalability of computer networks

• Scalability

• how networks adapt to the grow of load?

• how networks adapt to the increase of hosts?

• how networks adapt to the increase of links?

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Scalability of multiple access networks

H₁ H₂ H₃

…

H_n

Assuming that all node pairs communicate the same number of times. What is the share s of the medium per node pair?

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Scalability of multiple access networks

H₁ H₂ H₃

…

H_n

Assuming that all node pairs communicate the same number of times. What is the share s of the medium per node pair?

ିଵ ଶ

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Scalability of fully connected network

H1 H2

H3

H5 H9 H4

H8

H6 H7

H10

H11

What is the number of links k per node and total number of links l?

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Scalability of fully connected network

H1 H2

H3

H5 H9 H4

H8

H6 H7

H10

H11

What is the number of links k per node and total number of links l?

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Switched network

H1 H2 H3

H8

H7

H6 H5

H4 S1

S2 S3 S4

S5

Switch – a network device that provides dedicated communication between the hosts

Switched network – computer network that uses network switches

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Switched network

H1 H2 H3

H8

H7

H6 H5

H4 S1

S2 S3 S4

S5

Packet switched network – a type of network that uses packets for communication; packet switching is a form of grouping of the data sent over the network; in here network links can be shared

Circuit switched network – a dedicated communication channel (circuit) is established between two hosts; in here network links are dedicated to one specific

communication between the hosts

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Switched network

H1 H2 H3

H8

H7

H6 H5

H4 S1

S2 S3 S4

S5

Store and forward – a packet is sent to an intermediate station where it can be either kept or forwarded

Cut through switching – a bigger chunk of the data (frame) is forwarded in smaller pieces even before the whole chunk is received

Multi‐hop communication – using multiple stations to transmit data between two hosts

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Cloud representation

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Internet [1]

N1

N3 N2

R1 H1

H2

H3

R3

R2

H4

H5

H6 H9

H8

H7

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Internet [2]

• What is internet?

• Router

• Network interface

• The Internet and a internet

• Physical network

• Intranet

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Recursive use of cloud representation

N1

N3 N2

R1 H1

H2

H3

R3

R2

H4

H5

H6 H9

H8

H7

N

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Network sizes

• LAN – local‐area network

• WAN – wide‐area network

• MAN – metropolitan area network; larger than local area network (LAN) but smaller than the area covered by a wide area network (WAN).

• SAN – storage area network – is a high‐speed network of storage devices that also connects those storage devices with servers.

• CAN – Controller Area Network (also known as CAN bus) is a vehicle bus standard designed to allow microcontrollers and devices to communicate with each other in applications without a host computer.

• PAN – personal area network; network of localized and personalized devices.

• GAN – global area network; connecting everything.

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Network sizes

Source: www.cebylon.com/khi1/141‐01‐GAN‐MAN.html

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Networks and graphs [1]

N1

N3 N2

R1

H1 H2

H3

R3

R2

H4

H5

H6 H9

H8

H7

H1

H2

H3 N1

R1 R2

N2

H4

H5 H7 H6

H9

H8

N3

R3

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Networks and graphs [2]

• Nodes

• Links

• Topology

Formal definition of a network graph:

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Topology examples

Bus Tree

Star Ring Mesh