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Networks & telecommunications October 9, 2014 LEARNING GOALS • Identify the major hardware components in networks. • Identify and explain the various types of computer networks. • Identify the various types of transmission media • Describe the role of software used in networks. • Discuss telecommunications’ principles. 2 Stand-alone computers v. Network? – – – – – – – – – – 3 Why Networking ? • Resource sharing – Sharing hardware (printers, processors, etc.) – Sharing software (programs, data files) • High reliability – Can set automatic backup of programs and data at different locations – Fault tolerance (if one server is down, others can provide service. If a disk fails, data available through mirror or RAID-3 disks) • Possible cost savings • Communication tool – Internal email service – Remote Access service 4 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 5 Computer Network (cont.) • Based on the definition from the previous slide, what hardware elements are needed to implement a computer network? 6 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 7 Physical Transmission Media • Physical media Wireless – Transmission media used to physically connect nodes to the network – Transmits electrical or optical signals – Could be copper wire or fiber optic cable 8 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 3-4 miles Security, noise Category 3 LANs Digital 10 Mbps 100 m Security, noise Category 4 LANs Digital 20 Mbps 100 m Security, noise Category 5 LANs Digital 100 Mhz 100 m Security, noise Category 6 LANs Digital 250 Mhz 100 m Security, noise Category 7 LANs Digital 600 Mhz 100 m Security, noise • Fiber optic – – – – Source 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 diode (LED or LD) Photo receptor Fiber optic cable (LED or LD) Destination 9 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 10 Wireless Media issues • • • Use electromagnetic waves or electromagnetic radiation for data transmission Propagation through space, and indirectly, through solid objects Many problems: Electromagnetic Interference (EMI) from Other stations, Microwave ovens, etc 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. Shadow Zone Multipath Interference Laptop Comm. Tower Insecure: Easier to “intercept” messages + Much more attenuation: Inverse Square law 11 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 12 Small Network illustrated Hub or Switch Wide Area Network Router Media 13 Hub operation 1. Station A transmits to the Hub 2. Hub broadcasts to all stations (Except sending station) Station C must wait, or its signal will collide with Station A's signal Station A Station B Station C Station A Station B Station C 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 Switch Switching table MAC Address A1-44-D55-1F-AA-4C B2-CD-13-5B-E4-65 C3-2D-55-3B-A9-4F ; 1 2 3 4 5 6 Switch Sends Signal out a Single Port Station A Transmits to Station C Station A Port 1 (Station A) 2 (Station B) 5 (Station C) ; Station B Transmits Simultaneously Station to Station D B Station C Station D 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 – Used on servers – Used 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 16 typing 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 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 18 Bus Network 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 19 Star Network 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 20 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 21 Network Architectures/Models • Defines how the processing takes place on the network • Two primary models – Client-server – Peer-to-peer (P2P) 22 Client-server model • Nodes are either clients or servers • Clients use services • Servers provide services – File service – E-mail service – Printing service – Database service • Client software on client node cooperates with server software on server node – The WWW is the largest client server application 23 Client-server model • Collaboration between Client and Server program 24 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 Program Client Machine Server Program Server 25 Peer-to-Peer model • All nodes on the network are equal. • Any node can be both a client and a server. 26 Summary Questions Book Notes 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 27 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? 30 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 32 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 33 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 34 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 35 Packet-Switching Data Networks • Multiplexing – Packets from many conversations are mixed (multiplexed) over each trunk line Packet Switching Multiplexing on Transmission Line 36