Introduction Computer Networks Introduction 1 Network Definitions and

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) P&D slide Computer Networks: Introduction 4

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 P&D slide Computer Networks: Introduction 6

internet Figure 1. 4 Interconnection of networks P&D slide Computer Networks: Introduction 7

Network P&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

T X W Y Host L 2 W 3 AP 3 W 4 4 5 nodes 16 14 11 Host J 17 12 15 6 13 10 Host D W 2 1 Host B Host C Z Host M Host A W 1 Host H 7 9 Host E 8 Host G Host F Computer Networks: Introduction 9

Sample Application Paradigms Computer Networks: Introduction 10

Client-Server Applications Figure 1. 1 A network with two clients and one server. Tanenbaum slide Computer Networks: Introduction 11

Client-Server Model Figure 1 -2. The client-server model involves requests and replies. Tanenbaum slide Computer Networks: Introduction 12

Peer-to-Peer Applications Figure 1. 3 In a peer-to-peer system there are no fixed clients and servers. Tanenbaum slide Computer Networks: Introduction 13

Mobile Network Users Figure 1 -5. Combinations of wireless networks and mobile computing. Tanenbaum slide Computer Networks: Introduction 14

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 Figure 1 -6. Classification of interconnected processors by scale. Tanenbaum slide Computer Networks: Introduction 16

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 Copyright © 2000 The Mc. Graw Hill Companies Ethernet hub Leon-Garcia & Widjaja: Communication Networks Figure 1. 17 Tanenbaum slide Computer Networks: Introduction 18

Wireless LANs Figure 1 -35. (a) Wireless networking with a base station. (b) Ad hoc networking. Tanenbaum slide Computer Networks: Introduction 19

Metropolitan Area Networks Figure 1 -8. A metropolitan area network based on cable TV. Tanenbaum slide Computer Networks: Introduction 20

MAN 1* a 2 3 b 4 A c Metropolitan network A consists of access subnetworks a, b, c, d. d Hierarchical Network Topology A g Copyright © 2000 The Mc. Graw Hill Companies Leon-Garcia & Widjaja: Communication Networks Computer Networks: Introduction National network consists of regional subnetworks , , g. Metropolitan network A is part of regional subnetwork . Figure 1. 8 21

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 Mc. CLELLAN BOULDER GWC CASE RADC ILL CARN LINC USC AMES MITRE UCSB STAN SCD ETAC UCLA RAND TINKER BBN HARV NBS ARPAnet circa 1972 a point-to-point network Copyright © 2000 The Mc. Graw Hill Companies Leon-Garcia & Widjaja: Communication Networks Computer Networks: Introduction Figure 1. 16 23

Wide Area Networks (WANs) Figure 1 -10. A stream of packets from sender to receiver. Tanenbaum slide Computer Networks: Introduction 24

G net 1 net 3 G G = gateway G net 2 Copyright © 2000 The Mc. Graw Hill Companies G net 5 G net 4 G internet - a network of networks Leon-Garcia & Widjaja: Communication Networks Computer Networks: Introduction Figure 1. 18 25

Network Classification by Topology Bus flow of data Bidirectional flow assumes baseband cable Repeater Computer Networks: Introduction 26

Network Classification by Topology Ring Repeater Note - a ring implies unidirectional flow Computer Networks: Introduction 27

Network Classification by Topology Tree Headend Computer Networks: Introduction 28

Network Classification by Topology Star hub, switch or repeater Computer Networks: Introduction 29

Network Classification by Topology Star W 1 W 2 AP W 3 W 4 Wireless Infrastructure Computer Networks: Introduction 30