Networks & telecommunications November 11, 2015

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

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

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

Client-server model Collaboration between Client and Server program 5

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 Server Program Client Program Client Machine 6 Server

Peer-to-Peer network 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 7

Pure P2P network 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? 8

Note: Response to Init and Seach msg not shown Pure P2P viral network Init or search msg Init or search msg Init or search msg Client 2 Client 3 Client 1 Init or search msg Init or search msg P2P File download Note: Response to Init and Seach msg not shown Client 5 Client 4 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 9

P2P using Index server 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 10

Advantages of Network vs. Stand-alone PCs? 11

Why Networking ? Resource sharing High reliability 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

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

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

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

Transmission Media Physical media Wireless 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 16

Transmission Media (Continued) Twisted Pair Category Use Signal Data rate Distance Problem Category 1 Telephone Analog/Digital <100Kbps 3-4 miles Security, noise Category 2 T1, ISDN Digital <2 Mbps Category 3 LANs 10 Mbps 100 m Category 4 20 Mbps Category 5 100 Mhz Category 6 250 Mhz Category 7 600 Mhz 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 Photo receptor (LED or LD) Photo diode (LED or LD) Destination Source 17 Fiber optic cable

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

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

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

Small Network illustrated Wide Area Network Hub or Switch Media 21

(Except sending station) Hub operation (Except sending station) 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.

Switch operation Switching table MAC Address Port A1-44-D55-1F-AA-4C 1 (Station A) B2-CD-13-5B-E4-65 2 (Station B) C3-2D-55-3B-A9-4F 5 (Station C) ; ; Switches send out a single port: destination port. Most switches can efficiently handle simultaneous transmissions Switches provide a full bandwidth to all connected computers.

Network Software Network operating system Workstation 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

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

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

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

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

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

Summary Questions Book Notes 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 What is the role of (a) a modem, (b) a router, (c) a bridge? What is the difference between a Network operating system and a workstation operating system? What is a network topology? Distinguish between network topologies Distinguish between Client-server and P2P networks 30

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

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

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

Telecommunications

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

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 Reserved Capacity Reserved Capacity Circuit 36

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

Packet-Switching Data Networks 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

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