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Computer Science
Computer Science 1032A/B

Midterm material is only what we learn up to reading week Sunday March 10 2-4 2 hour exam chapter 1,2, 3, 4, 6 chapter extension 2a HTML XML Word Excel Multiple choice questions Short answer Textbook material is all MC HTML XML, Word and Excel is MC and short answer Mark wise – 50% textbook and 50% computer concepts (HTML, XML) MyMISLab MyITLab Need to write an XML schema and doc Networks and Collaboration Why Networks?  Computers tend to be more useful when they are connected to networks  Connection to the Internet o Part of a functioning network of networks containing millions of computers  Provides for o Sending and receiving email o Browsing web pages (globally) o Download audio and video files o Communicate (talk) Collaboration  Two or more people working tg to achieve a common goal, result or product  Produces results greater than those that could be produced by any of the individuals working alone  Coordination and communication and often makes use of computer networks Effectiveness driven by many forces:  Communication skills and culture (most important) o Part of a group, giving and receiving critical feedback  Communication systems o Email, VPNs, instant messaging  Content mgmt. o Databases and content mgmt. make sure that one user’s work doesn’t interfere with another’s  Workflow control – internally (bus process focuses externally) o Process for creating/editing/using content Not just the ability to communicate but is all of these things above Factors not always equally important for all collaborations Networks Externality  The larger the number of people using a network, the more valuable that network becomes (‘network effect/externality’)  When networks first started, people often look for the critical mass o Value for being part of the network > cost  When networks hit critical mass, the usually grow at a faster rate  Network growth may lead to congestion problems or the market may become saturated o Cycle of the network Computer Network  Network o Collection of computers o Communicate via transmission media  Physical: copper cable, optical fibre  Wireless  Radio frequencies (cellular statellite) o Types  Local area network (LAN)  Wide area network (WAN)  Internet LAN – Local Area Network  Computers connect tg at a single physical site o Any number of computers (doesn’t matter number of computers) o Own the physical nature (space) of the computer o Can connect another computer in a building that you own o One (small) geographic area o Property controlled by company operating network  Company can run cabling as necessary WAN – Wide Area Network  Connect computers in different geographical areas o Physically separated sites  Use a variety of communication networks o Licensed by gov’t  Must contract with a communications vendor that is licensed by the gov’t and already has line/has the authority to run new lines btwn the two cities The Internet and internets  Network of networks (internet)  Internets Connect LANs, WANs, and other internets  The Internet o Sending email and browsing the Web (public)  internets o Private networks of networks  (internet) Uses a variety of communication methods and conventions o Layered protocols provides a seamless flow of data  Protocol - Set of rules that communicating devices follow o In order for the two devices to communicate, they must both use the same protocol History of the Internet  The 60’s problem: o Share data  computers in many locations o The mainframes themselves didn’t talk to one another o Incompatible computers  Operating systems, hardware, software o Primitive communications technology  Solution: o ARPANET (Advanced Research Projects Agency NETwork)  1969: requested by Dep’t of Defense  Its technology spawned the Internet  Formed to meet proposal that we base the Internet on today and answered the US defense dep’ts proposal o If enemy took out Washington then no one else could communicate – not good o Everyone can talk tko everyone but if a particular machine is taken out then its not the shortest path  They wanted to be able to ensure that any one of those installations could communicate with each other o So ended up with a network that connects everyone!  Doesn’t take shortest path but it does take a path Components of a LAN  Located on a property controlled by the company that operates the LAN o Can run cables wherever meeded to connect the computers  Switch o Special purpose computer the receives and transmits messages (all instructions) on the LAN  Knows which printer you want to print to  Everything is connected by a wire o May have more than one per LAN (can have more than one switch) o Its about the amount of traffic that you want to go through  Network Interface Card (NIC) o Each device on a LAN has a hardware component (NIC) o Hardware to connect each device to the cable o Works with programs in each device to implement the protocols necessary for communication o Built-in NIC (newer machines) or expansion slot card (older machines) o MAC (Media Access Controller) address  Unique identifier  No two MAC addresses in the entire world Media Connections  Unshielded Twisted pair (UTP) Cable (short distances) o Twisted to reduce signal interference  Optical Fiber Cable (longer distances) LAN Network Protocol  All devices use same protocol  Institute for Electrical & Electronics Engineers (IEEE) o Create and publish standards o LAN protocols from IEEE 802 committee  IEEE 802.3 or Ethernet o Specifies  Hardware characteristics  Message packaging and processing  Operates at Layers 1 & 2 of TCP/IP-OSI architecture  PCs support 10/100/1000 Ethernet NICs o 10, 100 or 1000 Mbps o 1000/1024 & bits/bytes o communication speeds = k (1000), memory = 1024  M = 1 000 000 (speed) 1024x1024 (memory)  G = 1 000 000 000 (speed) 1024x1024x1024 (memory)  Communication = bits, memory = bytes  Wired and wireless allows you to switch Ethernet (physical line) and have a wireless connection in it to allow 802.11 protocol too  Wireless LAN is a computer network that allows users to connect to a network without using a network cable o Physical line = UTP cable (802.3)  Wired connections are faster and more reliable o Dashed lines = wireless signal (802.11) (wifi)  IEEE speeds up to 54 mbps LANs with Wireless Connections  Wireless NIC (WNIC)  LAN operation o NICs – 802.3 protocol o WNICs – 802.11 protocol (Wi-Fi) o WNICS connect to Access Point (AP)  Wireless LAN require one ore more access points (AP)  The AP then connects users to the wired network  AP processes both standards Connecting to the Internet  The Internet is a Wide Area Network (WAN)  Connecting computers at separate sites o Unable to use cable btwn sites o Obtain use of connections from licensed communications companies o Routers implement the protocols for WANs  Special purpose computers  Connects your computer to computers owned and operated by your Internet Service Provider o Switch = LAN o Routers = WAN  Individual Computer connection via router to an ISP  Internet Service Provider (ISP) o Provides your computer with a legitimate Internet address o Gateway to Internet o Fee for use of Internet (helps pay for the Internet)  Pay for the Internet (someone pays to be connected) Web vs. Internet  Web o Subset of the Internet o Consists of sites that process http o Use browsers to surf the web  Internet o All the applications o Communications infrastructure o Supports all application layer protocols  http, smtp, ftp Names & Addresses  Rules exist for naming sites o Top-Level Domain (TLD)  .ca, .com, .org, .biz  Address on the Internet o Uniform Resource Locator (URL) ( o These are all unique o Sometimes the name tells us about them (.ca = Canada)  Logical Address (IP address) o Comprised of four sets of numbers separated by periods  = IP Addresses  Two kinds o Public  Used on Internet  Assigned by ICANN to ISPs (individual service providers) and institutions  Internet Corporation for Assigned Names and Numbers  Each address is unique o Private  Used within private networks  Controlled by company operating network Dynamic Host Configuration Protocol Server  IP Addresses assigned dynamically  Assigns temporary IP address o Address used while connected to LAN  Plugged or wireless o When disconnected, IP made available o Re-assigns IP address as needed  Only needs enough IP addresses for what they believe will be simultaneous use  Don’t need IP addresses for each student Domain Name System  Domain Name System (DNS) o Translates URL names into IP addresses o Resolves domain name  ICANN manages resolution system  Domain Name Resolution o Conversion o Domain name  public IP address o Performed by Domain Name Resolvers Some device from telephone or cable company. That device will give us the connections we need All three connections require that the digital data in the computer be converted to an analog (wavy) signal before being sent When receiving data the analog signal must be converted to a digital signal before the computer can read it  Modems perform these conversions Three ways to get connect to internet from homes: dial up, DSL (bell), cable (rogers) Computers are digital and when we go out of our homes to get connections are analog They way we convert from digital  analog is through a modem Different modems use different protocols and speeds Modems are inside of the box you receive from the provider Dial Up Modems  Uses telephone lines (twisted pair)  Interferes with voice telephone service  Converts btwn analog and digital  Dial ISP for connection  Max transmission speed = 56 kbps DSL Modems  Digital Subscriber Line (DSL)  Operates over telephone lines (twisted pair)  No interference with voice service  Faster data transmission than dial-up  Connection always maintained  Uses its own protocols  Services and Speeds: o Assymetric digital subscriber lines (ADSL)  256 kbps – 768 kbs (upload/download different speeds) o Symmetrical digital subscriber lines (SDSL)  Up to 1.544 mbps (upload/download same speed)  Usually what business gets Cable Modems (rogers)  High speed data transmission  Cable television lines (coaxial cable) o Connects subscribers to distribution center  High-capacity optical fiber cable o Connects neighbourhood distribution centers o All the distribution centers are connected by fiber optic o The speeds are related to the number of neighbours that are connected onto Rogers  If all neighbours try and download a movie then your internet will be slower o DSL connects directly (Bell)  No interference with TV transmission  Uses its own protocols  Performance based on the # connected o Download speed up to 10 Mbps o Upload speed up to 256 kbps  Narrowband lines = transmissions speeds less than 56 kbps o Dial up  Broadband lines = speeds in excess of 56 kbps o DSL and cable Difference is not the size of the cable it is the speed of the cable Wireless WAN  WWAN differs from a wireless LAN o Covers a larger area o Use cellular networks to transfer data  Radio waves used to connect Portable computer with a wireless WAN modem to a base station a wireless network  Radio tower carries signal to a mobile switching center, where the data are passed on to the appropriate network  Wireless service provider then provides the connection to the Internet  Similar to a cell phone Securing the Network: Firewalls  Firewall: o Computer device that prevents unauthorized network access o Special-purpose computer or program o Organizations may have multiple firewalls o Used when connecting to The Internet  Restricts access via o Port number o Access control list (ACL) o Packet-filtering  Restricts access: o Port number  Identifies a particular service (ie. 80 for http, 25 for smtp)  Filter out particular port #s to restrict access  Port 22 is the port for sending files o Access control list (ACL)  Tracks IP addresses  Filter access to sites via IP address  Filter access from other sites via IP address o Packet-filtering firewalls  Examine source & destination address, & other data before allowing message to pass  Filter incoming and outgoing messages  Prohibit traffic from particular sites  Prohibit access to specific sites  Send emails in packets Controlling Access  A number of internal firewalls segment different departments  Internal firewalls restricts the data that particular employees can access  Increases security by providing separation of duties Encryption  The process of transforming normal text into coded text  Used for secure storage or communication  Common encryption algorithms o DES – Data Encryption Standard & AES – Advanced Encryption Standard  US gov’ts standard for data encryption o 3DES – Triple Data Encryption Standard  Uses a key three times as long as Standard DES  Used for banks and other orgs that transmit highly sensitive data  Banking and financial institutions will encrypt before sending out o Secure it by encryption technique o Want to get the most complicated one so its not easily cracked Encryption  Symmetric encryption o Use same key to encrypt and decrypt o Advantages:  Much faster than asymmetric encryption o Disadvantages:  Sender and receiver must both know the key  Both must ensure the key is kept secret  If key becomes publics, others will be able to decrypt  Both sides of a transaction use the same key – difficult to know who created the document o Not the best one for security purposes but it is fast  Assymetric encryption o Uses two keys:  Public key is shared/exchanged publicly  Private key is known only to the owner of that key  Don’t give out the private key o Message encoded with one, decoded with other o Advantages over symmetric keys:  Public key can be publicly distributed  Only one party has the private key, easy to know who created the document  Easy to implement over a network o Disadvantage is the speed  Slow encryption method  Too slow for large amounts of data Encryption  HTTPS Protocol o Secure communication over Internet  http that uses SSL/TLS is //https  encrypted using Secured Socket Layer (SSL)/Transport Layer Security (TLS) protocol  Encodes messages using Web site’s public key, decoded with private key o Secure f
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