1. Computer Networks: Introduction1 Introduction

2. Computer Networks: Introduction2 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

3. Computer Networks: Introduction3 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.

4. Computer Networks: Introduction4 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

5. Computer Networks: Introduction5 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.

6. Computer Networks: Introduction6 Switched Networks P&D slide Figure 1.3

7. Computer Networks: Introduction7 internet P&D slide Figure 1.4 Interconnection of networks

8. Computer Networks: Introduction8 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}.

9. Computer Networks: Introduction9 12 1 11 8 4 7 2 6 9 10 14 5 13 15 3 Host B Host C Host L Host D Host E Host G Host J Host A Host H Host F Host M 16 17 W TX Y Z nodes AP W1 W2 W3 W4

10. Computer Networks: Introduction10 Sample Application Paradigms

11. Computer Networks: Introduction11 Client-Server Applications Figure 1.1 A network with two clients and one server. Tanenbaum slide

12. Computer Networks: Introduction12 Client-Server Model Figure 1-2. The client-server model involves requests and replies. Tanenbaum slide

13. Computer Networks: Introduction13 Peer-to-Peer Applications Figure 1.3 In a peer-to-peer system there are no fixed clients and servers. Tanenbaum slide

14. Computer Networks: Introduction14 Mobile Network Users Figure 1-5. Combinations of wireless networks and mobile computing. Tanenbaum slide

15. Computer Networks: Introduction15 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.

16. Computer Networks: Introduction16 Network Classification by Size Figure 1-6. Classification of interconnected processors by scale. Tanenbaum slide

17. Computer Networks: Introduction17 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)

18. Computer Networks: Introduction18 Ethernet bus Ethernet hub transceivers Figure 1.17 Leon-Garcia & Widjaja: Communication Networks Copyright ©2000 The McGraw Hill Companies Wired LANs Tanenbaum slide

19. Computer Networks: Introduction19 Wireless LANs Figure 1-35. (a) Wireless networking with a base station. (b) Ad hoc networking. Tanenbaum slide

20. Computer Networks: Introduction20 Metropolitan Area Networks Figure 1-8. A metropolitan area network based on cable TV. Tanenbaum slide

21. Computer Networks: Introduction21 Metropolitan network A consists of access subnetworks a, b, c, d. National network consists of regional subnetworks . Metropolitan network A is part of regional subnetwork . A A Hierarchical Network Topology 1* a c b d  2 3 4   Figure 1.8 Copyright ©2000 The McGraw Hill Companies Leon-Garcia & Widjaja: Communication Networks MAN

22. Computer Networks: Introduction22 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).

23. Computer Networks: Introduction23 UCLARANDTINKER USC NBS UCSB HARV SCD BBN STAN AMES McCLELLAN UTAHBOULDERGWCCASE CARN MITRE ETAC MIT ILL LINC RADC Figure 1.16 ARPAnet circa 1972 a point-to-point network Leon-Garcia & Widjaja: Communication Networks Copyright ©2000 The McGraw Hill Companies

24. Computer Networks: Introduction24 Wide Area Networks (WANs) Figure 1-10.A stream of packets from sender to receiver. Tanenbaum slide

25. Computer Networks: Introduction25 G G G G G net 1 net 2 net 3 net 4 net 5 G = gateway G Figure 1.18 Leon-Garcia & Widjaja: Communication Networks Copyright ©2000 The McGraw Hill Companies internet - a network of networks

26. Computer Networks: Introduction26 Network Classification by Topology flow of data Repeater Bus Bidirectional flow assumes baseband cable

27. Computer Networks: Introduction27 Network Classification by Topology Repeater Ring Note - a ring implies unidirectional flow

28. Computer Networks: Introduction28 Network Classification by Topology Headend Tree

29. Computer Networks: Introduction29 Network Classification by Topology Star hub, switch or repeater

30. Computer Networks: Introduction30 Network Classification by Topology Star AP W1W2 W3 W4 Wireless Infrastructure