Networks Chapter 9

Objectives Describe the basic components of a network Explain the methods of data transmission, including types of signals, modulation, and choices among transmission modes Differentiate among the various kinds of communications links and appreciate the need for protocols Describe various network configurations List the components, types, and protocols of a local area network Appreciate the complexity of networking Describe some examples of networking MIS105: Networks

Contents Data Communications Network Data Transmission Communications Media Network Topology Local Area Network Wide Area Network Organization of Resources Protocol Software Communication Applications MIS105: Networks

Send and receive information over communications lines Data Communications Send and receive information over communications lines MIS105: Networks

Centralized Data Processing All processing, hardware, software in one central location Inefficient Inconvenient MIS105: Networks

Distributed Data Processing Computers at a distance from central computer Can do some processing on their own Can access the central computer MIS105: Networks

Distributed Data Processing

Network Uses communication equipment to connect two or more computers and their resources PC based LAN – shares data and resources among users in close proximity WAN – shares data among users who are geographically distant MIS105: Networks

Sending device Communications link Receiving device Basic Components Sending device Communications link Receiving device MIS105: Networks

Network Design Data Transmission (Analog or Digital) Media (Modem, Routers etc) Topology – Physical layout of components Protocol – Rules governing communication of data Distance LAN WAN Technology Peer-to-peer File server Client/server MIS105: Networks

Data Transmission Digital Transmission Sends data as distinct pulses Data is represented as an electromagnetic signal Need digital line Analog Transmission Sends a continuous electrical signal in the form of a wave Conversion from digital to analog needed Telephone lines, coaxial cables, microwave circuits

Digital Transmission Asynchronous and Synchronous Sending and receiving devices must work together to communicate MIS105: Networks

Asynchronous Transmission Contains start/stop bits Start signal Generally one character at a time (8 bits) Stop signal Low-speed communications

Synchronous Transmission Blocks of data transmitted at a time Send multiple characters at a time Align internal clock of sending / receiving devices Send error-check bits More complex More expensive Faster transmission MIS105: Networks

Analog Transmission Data is transmitted through alteration of the carrier wave (a basic frequency) Amplitude Modulation (AM) – height of the wave is increased to represent 1; higher amplitude means higher strength of sound or pixel Frequency Modulation (FM) – number of times wave repeats during a specific time interval can be increased to represent a 1 Low cost Good for shorter distance Still very popular MIS105: Networks

Modem Modem = Modulation + Demodulation Modulate Demodulate Convert from digital to analog Demodulate Convert from analog to digital Speeds up to 56,000 bps (56K)

Modem Transmission process Modulation – Computer digital signals converted to analog Sent over analog phone line Demodulation – Analog signal converted back to digital

Types of Modems Direct-connect PCMCIA External Internal Personal Computer Memory Card International Association Notebook and laptop computers

Types of Modems DSL: Digital Subscriber Line Uses conventional telephone lines Uses multiple frequencies to simulate many modems transmitting at once No industry standard Cost Speed (usually upto 3Mbps) Phone line shared between computer and voice MIS105: Networks

Types of Modems Cable Modem Coaxial cables Does not interfere with cable TV reception Up to 10 million bps Always on Shared capacity Security problem 05: Networks

Types of Modems Cellular Modems Uses cellular telephone system Slower speed MIS105: Networks

ISDN Integrated Services Digital Network One of the oldest Digital broadband transmission Speeds upto 128 Kbps Connect and talk at the same time Need Adapter Upgraded phone service Initial costs high Ongoing monthly fees may be high Not available in all areas MIS105: Networks

Types of Communication Channels Direction of data flow Simplex One direction Television broadcasting Arrival/departure screens at airport Half-duplex Either direction, but one way at a time CB radio Bank deposit sent, confirmation received Full-duplex Both directions at once Telephone conversation Point to Point (P2P or Pt2Pt) Connection restricted to 2 endpoints Eg, 2 computers connected directly using their interface cards MIS105: Networks

Communications Media Physical means of transmission Bandwidth Range of frequencies that the medium can carry Measure of capacity MIS105: Networks

Network Cable Twisted pair Coaxial cable Fiber optic cable Wireless MIS105: Networks

Twisted Pair Cable Inexpensive Susceptible to electrical interference (noise) Telephone systems Physical characteristics Requires two conductors Twisted around each other to reduce electrical interference Plastic sheath Shielded twisted pair Metallic protective sheath Reduces noise Increases speed MIS105: Networks

Coaxial Cable Higher bandwidth Less susceptible to noise Used in cable TV systems Physical characteristics Center conductor wire Surrounded by a layer of insulation Surrounded by a braided outer conductor Encased in a protective sheath MIS105: Networks

Fiber Optics Transmits using light Higher bandwidth Less expensive Immune to electrical noise More secure – easy to notice an attempt to intercept signal Physical characterizes Glass or plastic fibers Very thin Material is light MIS105: Networks

Wireless Transmission Uses infrared or low-power radio wave transmissions No cables Easy to set up and reconfigure Slower transmission rates Small distance between nodes MIS105: Networks

Microwave Transmission Line-of-site High speed Cost effective Easy to implement Weather can cause interference Physical characteristics Data signals sent through atmosphere Signals cannot bend of follow curvature of earth Relay stations required MIS105: Networks

Satellite Transmission Microwave transmission with a satellite acting as a relay Long distance Components Earth stations – send and receive signals Transponder – satellite Receives signal from earth station (uplink) Amplifies signal Changes the frequency Retransmits the data to a receiving earth station (downlink)

Satellite Transmission

Network Topology Physical layout Star Ring Bus Node – any device connected to the network Server Computer Printer Other peripheral MIS105: Networks

Network Topologies Packets Pieces of data transmitted over a network Packets are created by sending node Data is reassembled by receiving node Packet header Sending and receiving address Packet payload Number and size of data Actual data Packet error control Teaching tip For technical students take the time to draw the packet structure on the board. The typical structure is destination address | sending address | packet number | total packets | data size | payload | error control. MIS105: Network Basics

Network Topologies Star topology All nodes connect to a hub Advantages Packets sent to hub Hub sends packet to destination Advantages Easy to setup One cable can not crash network Disadvantages One hub crashing downs entire network Uses lots of cable Most common topology MIS105: Network Basics

Star Topology MIS105: Network Basics

Network Topologies Ring topology Nodes connected in a circle Tokens used to transmit data Nodes must wait for token to send Advantages Time to send data is known No data collisions Disadvantages Slow Lots of cable One node can crash the entire network MIS105: Network Basics

Network Topologies Ring topology MIS105: Network Basics

Token Ring Ring topology No danger from collisions Token passing Token has an address Node looks at token as it passes Addressed to me? Retrieve data Pass it on if not my address Send Empty token? Attach message Pass it on if not empty MIS105: Networks

Network Topologies Bus topology Also called linear bus One wire connects all nodes Terminator ends the wires Advantages Easy to setup Small amount of wire Disadvantages Slow Easy to crash Teaching tip Pages 352 and 353 have diagrams of each network topology MIS105: Network Basics

Network Topologies Bus topology MIS105: Network Basics

Network Topologies Mesh topology All computers connected together Internet is a mesh network Advantage Data will always be delivered Disadvantages Lots of cable Hard to setup rk Basics

Network Hardware Hubs Center of a star network All nodes receive transmitted packets Slow and insecure MIS105: Network Basics

Network Hardware Switches Replacement for hubs Only intended node receives transmission Fast and secure Insider information Twisted pair networks cannot achieve higher than 10 Mbps using a hub. Switches are necessary to achieve 100 Mbps or higher. MIS105: Network Basics

Network Hardware Bridge Connects two or more LANs together Packets sent to remote LAN cross Other packets do not cross Segments the network on MAC addresses MIS105: Network Basics

Network Hardware Router Connects two or more LANs together Packets sent to remote LAN cross Network is segmented by IP address Connect internal networks to the Internet Need configured before installation Discussion point Ask who in the class has high speed Internet. Then determine if anyone is sharing this to the rest of the house or dorm. If they are, see if they can describe the setup. Most likely, the sharing is done with a router. MIS105: Network Basics

Network Hardware Gateway Connects two dissimilar networks Connects coax to twisted pair Most gateways contained in other devices Gateway MIS105: Network Basics

Connections over short distances through communications media LAN Local Area Network Components PCs Network cable NIC Connections over short distances through communications media MIS105: Networks

LAN Network Interface Card (NIC) Connects computer to the wiring in the network Circuitry to handle Sending Receiving Error checking MIS105: Networks

WAN Wide Area Network Link computers in geographically distant locations

Hybrid Network Types Campus Area Networks (CAN) A LAN in one large geographic area Resources related to the same organization Each department shares the LAN MIS105: Network Basics

Hybrid Network Types Metropolitan Area Network (MAN) Large network that connects different organizations Shares regional resources A network provider sells time Teaching tip An example of a regional resource is a supercomputer. For example, Pittsburgh has the Pittsburgh Super Computing center (www.psc.edu). The various colleges in Pittsburgh connect to the center through a MAN in Pittsburgh. MIS105: Network Basics

Hybrid Network Types Home Area Network (HAN) Small scale network Connects computers and entertainment appliances Found mainly in the home MIS105: Network Basics

Hybrid Network Types Personal Area Network (PAN) Very small scale network Range is less than 2 meters Cell phones, PDAs, MP3 players Insider information PAN is very new. Few devices support PAN. High end cell phones include Bluetooth technology. Once the technology matures, Bluetooth will allow the creation of a PAN. MIS105: Network Basics

Communication Services Common carriers licensed by FCC (Federal Communications Commission) Switched / dial-up service Temporary connection between 2 points Ex: plain old telephone service (POTS) Dedicated service Permanent connection between 2 or more locations Ex: Build own circuits, Lease circuits (leased lines) MIS105: Networks

High Capacity Digital Lines 1.54 Mbps 24 simultaneous voice connections T3 28 T1 lines 43 Mbps Expensive High-volume traffic MIS105: Networks

Multiplexer Combines data streams from slow-speed devices into single data stream Transmits over high-speed circuit (ex T1) Multiplexer on receiving end needed to restore to component data streams MIS105: Networks

Organization of Resources Client/Server Controls the network Hard disk holding shared files Clients Other computers on network Thin client – no processing MIS105: Networks

Organization of Resources Client/Server and File Server MIS105: Networks

Organization of Resources File Server Server transmits file to client Client does own processing MIS105: Networks

Organization of Resources Client/Server How it works Client sends request for service to server Server fulfills request and send results to client Client and server may share processing Benefits Reduces volume of data traffic Allows faster response for each client Nodes can be less expensive computers MIS105: Networks

Organization of Resources Peer-to-Peer (P2P) Peer to peer networks (P2PN) All nodes are equal Nodes access resources on other nodes Each node controls its own resources Most modern OS allow P2PN Distributing computing is a form Kazaa Common with up to 12 computers Disadvantage – slow transmission MIS105: Networks

Organization of Resources Hybrid Contains elements of various organizations to optimize transmission speed and organizational needs MIS105: Networks

Protocol Set of rules governing the exchange of data Assists with coordination of communications; ie, was the message received properly? TCP/IP Transmission Control Protocol / Internet Protocol Internet standard All computers in world speak same language MIS105: Networks

Carrier sense multiple access with collision detection Ethernet CSMA/CD Carrier sense multiple access with collision detection Tries to avoid 2 or more computers communicating at the same time Computer listens and transmits when cable is not in use Collision results in waiting a random period and transmitting again Performance degrades with multiple collisions Dominant protocol Bus or star topology Uses CSMA/CD MIS105: Networks

File Transfer Software Download Receive a file from another computer Upload Send a file to another computer

Terminal Emulation Software PC imitates a terminal for communication to mainframe Micro-to-mainframe link MIS105: Networks

Office Automation Communication Applications E-mail Facsimile (Fax) Groupware Teleconferencing Video conferencing ATM Electronic fund transfers Telecommuting Online services The Internet Electronic data interchange (EDI) MIS105: Networks