Introduction

Computer Networks: Introduction 1

Network Definitions and Classification

• Preliminary definitions and network terminology

• Sample application paradigms• Classifying networks by transmission

technology• Classifying networks by size (or scale)• Classifying networks by topology

Computer Networks: Introduction 2

Preliminary Definitions

computer network :: [Tanenbaum] a collection of “autonomous” computers interconnected by a single technology.

[LG&W] communications network ::a set of equipment and facilities that provide a service.

[PD] {low level definition} A network can consist of two or more computers directly connected by some physical medium such as coaxial cable or an optical fiber. Wireless connectivity needs to be included in this definition.

Computer Networks: Introduction 3

Network Building Blocks• Nodes and Hosts: computers, routers,

switches• Links: coaxial cable, optical fiber, wireless

communication– point-to-point

– multiple access

(a)

(b)

Computer Networks: Introduction 4

P&D slide

Preliminary Definitions

In a distributed system the collection of independent computers appears to its users as a single coherent system.

Namely, the distinctions lie in the transparency in assigning tasks to computers.

Computer Networks: Introduction 5

Switched Networks

Figure 1.3

Computer Networks: Introduction 6

P&D slide

internet

Figure 1.4 Interconnection of networks

Computer Networks: Introduction 7

P&D slide

NetworkP&D recursive definition::i. two or more nodes connected by a

link.

or

ii. two or more networks connected by a node {an internet}.

Computer Networks: Introduction 8

Computer Networks: Introduction 9

12

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145

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HostB

HostC

HostL

HostD

HostE

HostG

HostJ

HostA

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HostF

HostM

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T X

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nodes

AP

W1

W2

W3

W4

Sample Application Paradigms

Computer Networks: Introduction 10

Client-Server Applications

Computer Networks: Introduction 11

Figure 1.1 A network with two clients and one server.

Tanenbaum slide

Client-Server Model

Figure 1-2. The client-server model involves requests and replies.

Computer Networks: Introduction 12

Tanenbaum slide

Peer-to-Peer Applications

Figure 1.3 In a peer-to-peer system there are no fixed clients and servers.

Computer Networks: Introduction 13

Tanenbaum slide

Mobile Network Users

Figure 1-5. Combinations of wireless networks and mobile computing.

Computer Networks: Introduction 14

Tanenbaum slide

Classifying Networks by Transmission Technology

broadcast :: a single communications channel shared by all machines (addresses) on the network.

Broadcast can be either a logical or a physical concept(e.g. Media Access Control (MAC) sublayer ) .

multicast :: communications to a specified group.This requires a group address (e.g. – multimedia

multicast).

point-to-point :: connections are made via links between pairs of nodes.

Computer Networks: Introduction 15

Network Classification by Size

Computer Networks: Introduction 16

Figure 1-6. Classification of interconnected processors by scale. Tanenbaum slide

Network Classification by Size

• LANs {Local Area Networks}– Wired LANs: typically physically broadcast at

the MAC layer (e.g., Ethernet, Token Ring)– Wireless LANs

• MANs {Metropolitan Area Networks}– campus networks connecting LANs logically or

physically.– often have a backbone (e.g., FDDI and ATM)

Computer Networks: Introduction 17

Wired LANs

transceivers

Ethernet bus Ethernet hub

Leon-Garcia & Widjaja: Communication Networks

Copyright ©2000 The McGraw Hill Companies

Figure 1.17

Computer Networks: Introduction 18

Tanenbaum slide

Wireless LANs

Figure 1-35. (a) Wireless networking with a base station. (b) Ad hoc networking.

Computer Networks: Introduction 19

Tanenbaum slide

Metropolitan Area Networks

Computer Networks: Introduction 20

Figure 1-8. A metropolitan area network based on cable TV. Tanenbaum slide

MAN

Computer Networks: Introduction 21

Metropolitan network Aconsists of access subnetworks a, b, c, d.A

1*a

c

b

d

2

34

Hierarchical Network Topology

National network consists of regional subnetworks α, β, γ.

Metropolitan network A is part of regional subnetwork α.

A

γ

α

β

Copyright ©2000 The McGraw Hill Companies

Leon-Garcia & Widjaja: Communication Networks

Figure 1.8

Network Classification by Size

• WANs {Wide Area Networks}– also referred to as “point-to-point” networks.– ARPANET Internet– usually hierarchical with a backbone.– Enterprise Networks, Autonomous Systems

(ASs)– VPNs (Virtual Private Networks).

Computer Networks: Introduction 22

AMES UTAH BOULDER GWC CASEMcCLELLAN

Computer Networks: Introduction 23

UCLA RAND TINKER

USC

SCDSTAN

AMES

MIT

ILLLINC

RADC

CARN

MITREUCSB

ETAC

BBN HARV NBS

ARPAnet circa 1972a point-to-point network

Copyright ©2000 The McGraw Hill Companies

Leon-Garcia & Widjaja: Communication Networks

Figure 1.16

Wide Area Networks (WANs)

Computer Networks: Introduction 24

Figure 1-10.A stream of packets from sender to receiver. Tanenbaum slide

G

G

G

GG

net 1

net 2

net 3

net 4

net 5G = gateway

G

internet - a network of networksCopyright ©2000 The McGraw Hill Companies

Computer Networks: Introduction 25

Figure 1.18Leon-Garcia & Widjaja: Communication Networks

Network Classification by TopologyBus

Computer Networks: Introduction 26

flow of data

RepeaterBidirectional flowassumes baseband cable

Network Classification by Topology

Repeater

Repeater

Ring

Note - a ring implies unidirectional flow

Computer Networks: Introduction 27

Network Classification by Topology

Tree

Headend

Computer Networks: Introduction 28

Network Classification by TopologyStar

hub, switch or repeater

Computer Networks: Introduction 29

Network Classification by TopologyStar

AP

W1 W2

W3

W4

Computer Networks: Introduction 30

Wireless Infrastructure