1. Networks & telecommunications June 16, 2015

2. LEARNING GOALS Discuss networks communication models and principles of operation Identify the major hardware and software components used networks. Identify and explain the various types of computer networks. Identify the various types of transmission media Discuss LAN topology and operation 2

3. Networks communication models and operation Define how the processing takes place on the network Define the roles of each participating computer Two primary models: – Client-server – Peer-to-peer (P2P) 3

4. Client-server model Computers are either clients or servers Clients use services Servers provide services – File service – E-mail service – Printing service – Database service – Etc. Client software on client node cooperates with server software on server node – The WWW is the largest client/server network 4

5. Client-server model Collaboration between Client and Server program 5

6. Client-server model Division of Labor – Client program handles lighter work, such as user interface chores and light processing chores – Server program handles heavy work, such as database retrieval Client MachineServer Client Program Server Program 6

7. Peer-to-Peer network 7 No dedicated server Computer are equal (peers) Computers can all receive and provide service Multiple P2P models over the years – Pure P2P – P2P Viral network – P2P with index server

8. Pure P2P network 8 Each computer must have the appropriate type of protocol & software for interaction with others Each computer must have a network connection to others Each computer can connect to any participating computer to get service (e.g. download files) What can be the major issues associated with P2P networks?

9. Pure P2P viral network 9 Client connects to another client, which connects to several others, and so forth When client first connects, it sends initiation msg to introduce itself via viral networking Searches sent by a client are also passed to others through viral networking When file is found, actual file downloads are done using direct (not viral) communication Companies offering P2P viral networking service, put in place super clients that are always on with permanent IP addresses Client 1 Client 2 Client 3 Client 4 Client 5 P2P File download Init or search msg Note: Response to Init and Seach msg not shown

10. P2P using Index server 10 Most common type of P2P networking used in file sharing Introduced by Napster (now an online music store after law suits) Relies on an Index server

11. Advantages of Network vs. Stand-alone PCs? – – – – – – – – – – 11

12. Why Networking ? Resource sharing – Sharing hardware (printers, processors, etc.) – Sharing software (programs, data files) High reliability – Can easily set automatic backups of programs and data at different locations – Fault tolerance: can duplicate servers so that if one is down, others can provide service. Servers have RAID so that if a disk fails, data available on other disks) Possible cost savings Communication tool – Console messages and internal email service – Remote Access service 12

13. Computer Network An interconnection of computers and computing equipment using either wires or wireless transmission media over small or large geographical distances. “Connect to GHI” ABC DEF GHI JKL MNO Once connected to the network, the computer (or another device) becomes a network node 13

14. Computer Network (cont.) Based on the definition from the previous slide, what hardware elements are needed to implement a computer network? 14

15. Network scope Local area network (LAN): computer network where the nodes are all in close proximity spanning a room, building, or campus Metropolitan area network (MAN): network that serves an area of 3 to 30 miles - approximately the area of a typical city. Wide area network (WAN): a large network that encompasses parts of states, multiple states, countries, and the world 15

16. Transmission Media Physical media – Transmission media used to physically connect nodes to the network – Transmits electrical or optical signals – Could be copper wire or fiber optic cable Physical Wireless 16

17. Transmission Media (Continued) Twisted Pair CategoryUseSignalData rateDistanceProblem Category 1TelephoneAnalog/Digital<100Kbps3-4 milesSecurity, noise Category 2T1, ISDNDigital<2 Mbps3-4 milesSecurity, noise Category 3LANsDigital10 Mbps100 mSecurity, noise Category 4LANsDigital20 Mbps100 mSecurity, noise Category 5LANsDigital100 Mhz100 mSecurity, noise Category 6LANsDigital250 Mhz100 mSecurity, noise Category 7LANsDigital600 Mhz100 mSecurity, noise Fiber optic – Thin glass fibers surrounded by coating – Uses laser or light for data transmission – Very fast (10+ Gbps, 100 miles without any repeater) – Very secure Source Photo diode (LED or LD) Destination Photo receptor (LED or LD) Fiber optic cable 17

18. 18 Wireless transmission media Infrared light – Has many of the same characteristics as visible light – Travels in straight lines – Cannot penetrate solid objects Radio waves – Travel in straight lines – Can penetrate through nonmetallic objects – Can travel long distances

19. 19 Wireless Media issues Use electromagnetic waves or electromagnetic radiation for data transmission Propagation through space, and indirectly, through solid objects Many problems: Laptop Comm. Tower Shadow Zone Radio waves tend to bounce off objects. Receiver can receive 2 or more signals. Thick objects can block the direct path. So, Receiver will be in a Shadow zone where it cannot well receive. Insecure: Easier to “intercept” messages Electromagnetic Interference (EMI) from Other stations, Microwave ovens, etc Multipath Interference

20. Computing Equipment Network interface card (NIC): Device that – provides a computer with unique address – Converts data into signal for transmission Hub / Switch: Central collection point for transmission media that interconnect computers Modem – Converts digital data into analog signal and back again Router – special hardware that determines optimal routing path for data packets – Usually used to connect a LAN to a WAN Bridge – Forwards messages between LANs 20

21. Small Network illustrated Hub or Switch Media Wide Area Network 21

22. Hub operation Hubs split available bandwidth among computers, i.e. with a 100 Mbps hub, the network speed will be 100 Mbps / n (where n is the number of computers) Active hubs include repeater capabilities for regenerating signals. Passive hubs don't regenerate signals. Limited to a 30meter distance apart from computers. (Except sending station)

23. Switch operation Switches send out a single port: destination port. Most switches can efficiently handle simultaneous transmissions Switches provide a full bandwidth to all connected computers. Switching table MAC AddressPort A1-44-D55-1F-AA-4C1 (Station A) B2-CD-13-5B-E4-652 (Station B) C3-2D-55-3B-A9-4F5 (Station C) ; ;

24. Network Software Network operating system – Used on servers – Used by network admins for managing network resources – Examples: Novell NetWare, Windows Server 2008 Workstation operating system – Used on client PCs – Used to manage local resources & access network resources Network monitoring software – Packet sniffers – allow seeing data as it moves over network – Keystroke monitors – allow seeing what users are typing 24

25. Protocols An agreed upon set of rules that govern communication in a network All computers on a network must use same protocol for effective communication Example of protocols: Ethernet (for communication in a LAN) Token Ring (for communication in a LAN) TCP/IP suite (for communication in a LAN and the Internet) Computer 1 Rules for Task 1 Rules for Task 2 Rules for Task 3 Rules for Task 4 Rules for Task 5 Computer 2 Rules for Task 1 Rules for Task 2 Rules for Task 3 Rules for Task 4 Rules for Task 5

26. LAN network Topologies The configurations of network components – How physically the network looks like – How logically data is transferred on the network Types of network topologies: – Bus – Star – Ring 26

27. Bus topology Most simple network topology All devices connected to a common central cable called a “bus” Inexpensive If cable fails, the entire network will shut down 27

28. Star topology Centered around central device called a hub or a switch All network nodes connect to the hub/switch Easy to install and update If hub fails, network fails 28

29. Ring topology Node connected to a logical ring in a central device called MAU More reliable than bus or star – Only one node sends at a time (no collisions) Expensive and limited speed 29

30. Summary Questions BookNotes 1)Name categories of computer networks based on their scope; i.e. their range of operation 2) Name one example of: (a) WAN, (b) LAN 3) Name physical and wireless media used in networking 4)What is the role of (a) a modem, (b) a router, (c) a bridge? 5)What is the difference between a Network operating system and a workstation operating system? 6)What is a network topology? 7)Distinguish between network topologies 8)Distinguish between Client-server and P2P networks 30

31. Summary Questions (cont.) What category of network is illustrated here?

32. Summary Questions (cont.) What category of network is illustrated here?

33. Problem Four students share a dorm. They would like to set up a network in order to share programs and data files. Three of the students own PCs and the fourth student has a laptop computer. Question: What computing equipments they need to buy in order to set up the network with a star topology? 33

34. Telecommunications

35. Voice vs. Data Communication Originally, There was a Sharp Distinction: – Voice Communication – Data Communication, in which one or both parties is a computer Database Electronic mail World Wide Web Distinction is fading because voice communication is increasingly computer-based 35

36. Circuit Switching and Reserved Capacity – Circuit switching is traditionally used in telecommunications – Circuit capacity is reserved during duration of each call – At each switch – On each trunk line Circuit Reserved Capacity Reserved Capacity 36

37. Pros and cons of Reserved Capacity Nothing like the congestion on the Internet Reserved Circuit Capacity is Expensive – Have to pay for it whether you use it or not – Good for voice, because conversations are fairly constant – Bad for data, because most data transmission is bursty; e.g., in World Wide Web, download, then stare at screen for a long time until next download 37

38. Packet-Switching Data Networks Packet Switching – Large messages are broken into small pieces called packets (or frames) – Packets are short (averaging a few hundred bytes) because networking devices handle short messages more efficiently Message Packets 38

39. Packet-Switching Data Networks Multiplexing – Packets from many conversations are mixed (multiplexed) over each trunk line Multiplexing on Transmission Line Packet Switching 39