ICT 2a

LAN: local area network (relatively limited area)        e.g. office, building, campusPeer-to-peer (P2P)  NetworkEach PC access the resources which are share by all the other peer workstations ,e.g. homes, some companies+ve: relatively low cost-ve: drop in performance when large and heavily loaded P2P network-ve low network loading limitWAN: wide area network *wide geographical area)         e.g. across cities, countries, continents connect different lanes tgt via telephone lines, leased lines, microwave, satellites and optical fiber cables. 

Client/Serverconnected to a central server or a host computer.e.g. schools, large companies+ve better security controls+ve large-scale network environment+ve high network loading limit-ve high set-up cost

Network services1. Internal communication2. Hardware sharing3. Centralized data Management (firewalls, virtual private networks)4. Software sharing5. Internet Access service sharing6. Network conferencing7. Information backup

Network interface card (NIC)An expansion board for connecting PC to network. It has a unique media access control (MAC) address. Connector: RJ-45Expansion Bus : ISA, PCI, PCMCIA, USBBandwidth: 10, 100, 1000 MbpsConnecting DevicesSwitch and HubSwitch , hub provide a central connection point for cables on a network.Switch: One or more PC are connected to a switch via network cables and it in turn is connected to a server.speed: 10,100 Mbps/ 1GbpsHub:handle low transmission traffic, efficiency drops under heavy network. Repeaters: amplifies the received signals + remove unwanted noise. Prevent actuation.Bridge: interconnect two or more LansRouter: translates signals from different networks.              Connect different types of Lans and between a Lan and the InternetModem: Demodulation Digital->Analogue             Modulation     A->DCable Modem : Cable TV line Turnradio-frequency signals for transmission and demodulates A->D signals Digital Subscriber line (DSL) modem: Residential telephone cable.Network Cables:Unshielded twisted-pair (UTP) cables/ STP cables :RJ-45 connector on both endsCoaxial Cable: BNC connector on both ends usage: VCR and cable television.Optical Fiber Cable: +ve greater signal carrying capacity+ve faster data transmission+ve Susceptibility to noise or interference from other device+ve better security for signal transmission.-ve High cost-ve Relatively more difficult installation process -ve special device is needed to convert digital signals to optical light beams-ve once installed it can hardly be changed

Radio connections:1. Satellite Broadband    requires: dedicated satellite + satellite dish2. Microwave broadband    AP r usually mounted on top of buildings, because each subscriber unit must have a line-of sight to AP3. Wi-Fi Connections    Wireless NIC is needed   based on IEEE 802.11 WLAN standard.      Type                      Radio frequency  Cost 802.11a 54 Mbps   5GHz                  High     unpopular 802.11b 11 Mbps   2.4GHz               Low      pop 802.11g 54 Mbps   2.4GHz               Low      pop 802.11n 600 Mbps  2.4/5GHz           Highest    +ve Low cost of building up network+ve Network can be extended to an outdoor area+ve Network structure can be modified-ve effective data transfer is affected by surrounding environment-ve risk of intrusion is high-ve max. data transmission speed is lower than wired network-ve limited coverage-ve high cost of building up large wireless network

TPC              10/100Mbps   cheap                  electrical coaxial cable      299Mbps   expensive             electrical optical fibre     >100Mbps    most expensive     opticalWiFi             11-600Mbps  depend the size    radio waves                                         coverageInfra-red       115K-4Mbps   1-2 m               PDA, mobile phonebluetooth         1-10 Mbps   1 - 10 m            PDA, mobile phoneWiFi                                  Indoor 70m        PDA, printer                                         out    250m

ISP:1. Dial-up connection: Require dial-up modem+ telephone line (56kbps)2. Integrated Services Digital Network: (ISDN)Lease line 128 kbps+ve high security lv3. Broadband connections+ve higher transmission speed+ve constant availability without dialing +ve stimulate use of data + voice connectionsA. Asymmetric digital subscriber line (ADSL)Dl: 1.5-9 Mbps Upload:16-40 Kbpse.g. PCCW/ netvigatorB. SDSL identical upstream+ downstream (Max. 24 Mbps)e.g. HKBBC. Cable modem cable TV network Max:30 Mbps being shared -> 1.5 Mbpse.g iCable

Wireless1. WiFi hot spot11-600 Mbps2. WAP area covered by mobile phone network10-153 Kbps3. GPRSMax: 11.52 Kbps

Communication software:+ve instant or much higher transmission speed+ve much lower cost of transmission +ve support multimedia+ve transmitted information is reusable Types: Email (E-mail client application/ web browser ->MS outlook, Lotus Notes) Video Conferencing (Video Conferencing software iVisit, Meeting Space) Internet phone (Internet phone client application -> skype, Net2Phone) Instant Messaging (Instant messaging software ->ICQ, MSN, Yahoo messenger) Chat room (web browser) Newsgroup (\ /) Discussion forum (\ /) Communication Protocol: Set of rules abt data formatting or signalling tht is understood by all communication software.  Transmission Control Protocol/ Internet Protocol: internet access, network communication in an intrant Simple Mail Transfer Protocol (SMTP) : transfer email msg Wireless Application Protocol (WAP): Wireless communication i.e. smart phones Internet Fax Protocol (IFP) : send+ receive fax Voice over Internet Protocol (VoIP):voice data transmission by internet phone 

Open system interconnection -> 7 layers Application layerInterface/ ApplicationControlling data integrity, error recover, coordinates partnering, error recovery  PresentationFormatting/ Data translation/ Encryption/ Decryption  Session layerData formating/ Grouping/ Managing terminating session of different application Transport layerTCP Transport head+ data ->Segement Divided into smaller packets b4 transmitting to the next layerreliable communcation, establishing, controlling the flow of info., segments, reassembles data Network layerNetwork Header (network address info.)+ Segment -> packet Routing: Find the best path to the destination IP, Adress Resolution Protocol (IP->MAC), RARP (reverse)  Data link layer DLH+Packet +DLT -> FrameData link header: physical address_ method of error Data link Trailer: indicating the end of the packet Physical layerMaking interaction between communication devices  Frame-> LAN 1-3: software oriented 4: intermediate layer 5-7 hardware oriented1-5: IP address 6-7: MAC address

Function:TCP: File is divided into packets and then forward one by one to IP layer. Transport layer reassembles the received data packets into a single data fileIP: 1.adding the destination IP address to every packet.2. Packet fragmentation3. Select shortest path to the destination/ alternative path to avoid network congestion.Issued by Internet Corporation for Assigned Names and Numbers (ICANN)IP = Network address (same), host address (different)Class A          Class B               Class C0-127            128-191                92-223

Uniform Resource Locator:http://www.abc.com.hkhttp= protocol www= host recordabc= Second level domaincom.hk = top level domainabc.com.hk = domain namewww.abc.com.hk = Fully Qualified Domain Nameport no. 21 FTP23 Telnet protocol25 SMTP80 HTTP443 HTTPsDomain Name systemTranslate(name resolution) domain names -> IP address If DNS X cant find the data requested, it will find other DNS on the internet.

HTTPhypertext transfer protocol:Application protocol tht is used to transfer hypertext doc. from HTTP server to the client through the Internet. 

Search engine1.Spiderprogram tht searches throughout the Internet, extracts info. + updates its search engine index accordingly. Different search engine return different search lists.2.Databasecatalgoues and store the information searched by the spider.3.Access programAccepts search request from users, compare with database and return search results.Type:General                                            GoogleSpecialized                                       Medline PlusGeneral searches using natural lang:  Ask Jeeves!SkillsCan use * wildcard for searching Quality Information: Completeness  Accuracy Authority Objectivity Timeliness Legality  Word Wide Web (WWW) widely used Internet service. Multimedia:1. Graphics Bitmap/vectorGIF :vecotr2. Audio Uncompressed: (sound eff)WAV,WMA (support streaming)Compressed: MP3, AAC (portable)3. Animation SWF: Vector-based animationWMF (can not edited extensively)(allow re-scaling)EPS (allow re-scaling)Plugs-in:small program tht is integrated into web browser to provide additional functionality+ve keep the web browser efficient _ small file size+ve browser is up-to-date to handle latest multimedia e.g. flash player, quicktime, realplayer, shock player (computer animation format)FTP: Requires user authentication/ support CLU

Email:transfer signals between mail servers. user ID @ Mail server domain nameabc      @ hotmail.comSMTP: unable to authenticate email sender -> spam mailsOrginally designed for ASCII text-based msgPOP: dl all the email from server.IMAP: stores all read+ unread emails in mail server.+ve more than one user can access the same mail box at the same time+ve users can access mail boxes from any computers.Webmails:+ve : free webmail service+ve: no need to install and configure additional software+ve no restriction exist on system platforms, location or ways of internet connection-ve low acess speed-ve forced to view advertisement-ve extra charges for addition mail box capacity-ve  higher security risk -ve require to stay onlineNewsgroupdiscussion forumonline chatRemote Logon. Telnet(no encryption) -> Secure Shell (Port no. 22)Support streaming: server sds small portion of the media file to pc, media player start playing.e.g. wmv rm, qt   , mpeg4, wma , aacWeb casting: broadcasting of multimedia contents like vdovoice mailvideo conferencing qualtiy affected by comprassion ratio of vdo + audio and frame size/ratee.g. lectures, telemedicine/ telenursing/ business meetingE-commerce models Business =b consumer =CB2B: online technical support, online market research, credit card payment....C2C: buy and sell items through an auction process :eBay/ Yahoo Auction+ve acess wordwide market+ can find hard to get items-ve unable to interact face to face=ve difficult to promote to the non-internet user-ve pay for delivery-ve cant feel the products b4 purchasing 

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Web Authoring:establish a web sitedesign the stricture + layout1. plandesign the contentaudienceobjectivedesign info2. buildkeep website updatedavoid lengthy pagescategorize3. publishing and testing using FTPidentify hyperlink (broken/ miss)scan for outdated files

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