Candidates shuld be able t: OCR 2.1.6 (a) explain the advantages f netwrking stand-alne cmputers int a lcal area netwrk AQA 3.1.13 understand what a cmputer netwrk is and be able t discuss the advantages and disadvantages f using a cmputer netwrk A netwrk is defined as a cllectin f cmputers and peripheral devices (such as printers) cnnected tgether. A lcal area netwrk (LAN) is a netwrk that intercnnects cmputers in a limited area such as a hme, schl, cmputer labratry, r ffice building. The cnnectins can be cable, fibre-ptic, r wireless (infra-red, micrwave r radi). Advantages f netwrks Sharing resurces: Sharing flders and files s yu can access them anywhere n the netwrk frm any cmputer Sharing peripheral devices such as printers and scanners Sharing an internet cnnectin Cmmunicatin: Using email t cmmunicate with clleagues Using messaging systems t chat while yu are wrking n ther things Transferring files between cmputers Centralised management: User prfiles and security can all be managed centrally Sftware can be distributed acrss the netwrk rather than having t install it n each individual cmputer Users can use any PC n the netwrk but still see their wn files Data can easily be backed up centrally. Sme Netwrking Fantasy Read Terry Pratchett s bk 'Ging Pstal' fr a fun fantasy abut inventing and making mney frm netwrking technlgy n DiscWrld. Lads f cmputer scientists wh've read any Terry Pratchett's bks like them instantly even if they dn't read much else.
OCR 2.1.6 (b) describe the hardware needed t cnnect stand-alne cmputers int a lcal area netwrk, including hub/switches, wireless access pints A netwrk interface card (NIC) is needed in each cmputer and peripheral cnnected in a LAN. This interface allws the devices t cmmunicate ver the netwrk either by using cables r wirelessly. Cabling is needed in a nn-wireless netwrk t cnnect the cmputers and peripherals tgether, either directly r thrugh a hub/switch. The amunt f cabling needed depends n the netwrk tplgy (the way cmputers and peripherals are physically cnnected tgether). A hub is used t link cmputers and peripherals tgether in a cabled netwrk that uses a star netwrk tplgy. A hub is a srt f junctin bx but des nt manage any f the traffic that cmes thrugh it, any data packet entering any prt is bradcast ut t all the ther prts resulting in data packet cllisins which slw the netwrk cnsiderably as the amunt f data traffic rises.
A switch is used in the same way as a hub but the data entering the device is switched t the prt it is meant t g t, rather than being bradcast t all the prts. This greatly reduces data packet cllisins resulting in a faster netwrk than the equivalent ne using a hub. A wireless access pint is a device that allws cmputers and printers etc. t cnnect t a wired netwrk using radi waves rather than cabling, prvided they are equipped with a wireless NIC. This allws a netwrk t be built with few r n cables and makes it simple t add further wireless devices. Student Activity If pssible it is best t get the students t make cnstruct a simple wired netwrk. Yu need 2 cmputers (sme decmmissined nes are ideal) a switch r hub, netwrk cards and patch cables. If the students ask questins such as What is CAT 5? r What is the difference between ISA and PCI? yu can write all these dwn and set them a task t research. Yu d nt have t cnnect this t yur schl netwrk s it shuld nt present a security threat t yur administratin staff. http://windws.micrsft.cm/en-gb/windws-vista/what-yu-need-t-set-up-ahme-netwrk Hw t make a patch cable http://www.yutube.cm/watch?v=482vteszwz8
OCR 2.1.6 (c) explain the different rles f cmputers in a clientserver and a peer-t-peer netwrk AQA 3.1.13 understand the client-server mdel Client-server netwrks On a client-server netwrk there are tw types f cmputers with tw distinct rles. One r mre server cmputers have the rle f cntrlling access t shared resurces like files and printers. Multiple client cmputers are then cnnected t the server cmputers and these are where the user actually wrks. The user lgs nt a client cmputer which then cnnects t the server, verifies the user and then allws them access t the files stred n the server that they have permissin t access. All the data is stred n the servers, which generally have far greater security cntrls than the client cmputers. Since data strage is centralised, security is easier t manage, updates t the data are far easier t administer and it is far easier t backup the data centrally in cmparisn t a peer-t-peer netwrk. Other servers may have a mre specialised rle such as a print server, dedicated t cntrlling access t shared printers and queuing print jbs. Peer-t-peer netwrks In a peer-t-peer netwrk cmputers are simply linked tgether, either using cables and a hub r wirelessly. Such netwrks d nt have cmputers with particular rles; instead, each cmputer has equivalent respnsibilities and status. This means that any cmputer n the netwrk can lad infrmatin frm the hard disk f any ther cmputer and a cmputer n the netwrk can use any printer cnnected t any ther cmputer. Peer-t-peer netwrks are cheaper t set up and easier t manage than server based netwrks but they are less secure than a client-server netwrk.
OCR 2.1.6 (d) describe, using diagrams r therwise, the ring, bus and star netwrk tplgies AQA 3.1.13 be able t describe and explain the bus, ring and star netwrking tplgies and be able t discuss the advantages and disadvantages f each f these tplgies Cmputers can be cnnected tgether in different layuts, r tplgies. There are three main tplgies but these may be cmbined in a large netwrk. Ring netwrk This is typically a peer-t-peer netwrk. The ndes are cnnected in a ring and data travels in ne directin using a cntrl signal called a 'tken'. Advantages: Cnsistent perfrmance when adding further ndes r heavy netwrk traffic as nly the nde with the 'tken' can transmit data s there are n data cllisins. Relatively cheap t install and expand. Tken passing prtcl is simple and reliable. Nt dependent n a central cmputer Disadvantages: Slwer than a star tplgy under nrmal lad. If the cable fails anywhere in the ring then the whle netwrk will fail because if any nde fails then the tken cannt be passed arund the ring. The hardest tplgy t trublesht because f the difficulty f tracking dwn where in the ring the failure has ccurred. Incnvenient t mdify r expand because t add r remve a nde yu must shut dwn the netwrk temprarily. In rder fr the ndes t cmmunicate with each ther they must all be switched n. Are ring netwrks still in use? http://www.techrepublic.cm/blg/classic-tech/des-anyne-actually-still-use-tkenring/115 Bus netwrk Ndes are cnnected t a main (bus) cable. Cmputers are cnnected t a single backbne (bus) cable. The cmputers all share this cable t transmit t each ther but nly ne cmputer can transmit at any ne time. This is fine mst f the
time if the netwrk is nt t busy but if there is a lt f traffic then transmissins interfere with each ther. In an Ethernet netwrk if data is being sent between ndes then the ther ndes cannt transmit. If t many ndes are cnnected then the transfer f data slws dramatically as the ndes have t wait lnger fr the bus t be clear. Advantages: The simplest and cheapest t install and extend. Well suited fr temprary netwrks with nt many ndes. Very flexible as cmputers can be added r taken away withut disturbing the rest f the netwrk. Failure f ne nde des nt affect the rest f the bus netwrk. Simpler than a ring tplgy t trublesht if there is a cable failure because sectins can be islated and tested independently. Disadvantages: If the bus cable fails then the whle netwrk will fail. Perfrmance f the netwrk slws dwn rapidly with mre cmputers r heavy netwrk traffic. Slwer than a ring netwrk as data cannt be transmitted while the bus is in use by ther cmputers. Star netwrk A central cmputer (server) and the subsidiary cmputer are cnnected t each ther thrugh a switch r hub. Advantages: The mst reliable because the failure f a cmputer r a cable des nt affect ther cmputers. Simple t trublesht because nly ne cmputer is affected by a brken cable. Adding further cmputers des nt greatly affect perfrmance because the data des nt pass thrugh unnecessary ndes. Easily upgraded by replacing a hub with a switch. Easy t expand with extra cmputers.
Disadvantages: Uses the mst cable which makes it mre expensive t install than the ther tw tplgies. The extra hardware required such as hubs r switches further increases the cst. As the central cmputer cntrls the whle system, the whle system will be affected if it breaks dwn r if the cable link between it and the switch fails. If the switch, the link t the server r the server itself fails then the whle netwrk fails Netwrk tplgies presentatin Get students t prduce an animated presentatin shwing hw data packets are transmitted arund a ring, bus netwrk and a star netwrk with a hub r a switch. Find ut which layut is used in yur schl Get students t talk t the netwrk technicians t find ut what netwrk layuts are used in yur schl. This is usually sme srt f cmbined setup: Cmputer science fr fun www.cs4fn.rg/fundamentals/netwrks.php Slve a netwrking prblem: fix the pipes. One f the majr issues in netwrking is finding the best way fr data t travel rund the netwrk. With ld-style telephne calls, when yu made a call t a friend there was a physical link made s that everything yu said travelled alng the same path frm start t finish. With digital netwrks, yur data (whether yur vice, emails, a mvie r the cntents f a web page) desn't have t all g the same way. It is brken int parts knwn as data packets. Each part can g whichever way is best fr the netwrk r the persn. One issue is finding ways t send data between tw pints s that as many data packets can travel at nce as pssible. What is needed is an algrithm that cmputers cntrlling the netwrk can fllw that guarantees t slve this prblem. Pinky's Pipes Pickle is a game t maximise the flw in a pipe netwrk.
Cmparisn Grid Tplg y Perfrmanc e with few cmputers Perfrmanc e with many cmputers Ease f trubleshtin g Cst f installati n Ease f setting up and mdifyin g Prblems caused by cable r cmputer failure LINE (BUS) Medium Mst affected Fairly easy Lw Easy t set up and mdify Failure f the bus cable causes ttal failure. Failure f a cmputer has n affect. RING Slw Least affected Hard High Easy t set up but harder t mdify Cable r cmputer failure causes ttal netwrk failure. STAR Fast Sme affect but the switch/hub can be upgraded easily Easy High Easy t set up and mdify Cable r cmputer failure nly affects that nde. Failure f the hub/switc h r the server causes ttal netwrk failure.
OCR 2.1.6 (e) describe the differences between a lcal area netwrk and a wide area netwrk such as the Internet A Wide Area Netwrk, r WAN, is a cllectin f cmputers and netwrks ver a gegraphically wide area. The Internet is the largest WAN.. Smaller examples f a WAN wuld include a natinal ATM netwrk used by a bank t allw custmers t access cash. Many supermarkets and ther large cmpanies perate their wn natinal WANs. WANs use hired infrastructure t cnnect the LANs tgether. A business with ffices in Lndn and Manchester will lease cnnectins frm a netwrk service prvider t cnnect the ffice LANs tgether. OCR 2.1.6 (f) explain the terms IP addressing, MAC addressing, packet and prtcls AQA 3.1.13 be able t explain, in simple terms, the handshake prcess used in mst mdern netwrking prtcls IP Addressing An Internet Prtcl (IP) address is a unique 32-bit reference number that is allcated t devices n a cmputer netwrk that uses the Internet Prtcl. Althugh IP addresses are stred as 32-bit numbers, fr ur cnvenience they are usually displayed as a series f 4 decimal numbers, each ne representing 8 bits f the riginal binary address. 32-bit binary versin: 110010011010000001011011011111111 decimal versin: 201.64.182.255 Sme IP addresses are reserved fr private netwrk ranges e.g. 10.0.0.0-10.255.255.255 172.16.0.0-172.31.255.255 192.168.0.0-192.168.255.255 MAC Addressing In cmputer netwrking, a Media Access Cntrl address (MAC address) is a unique 48-bit number assigned t a netwrk interface card (NIC) t identify it n a LAN. Because they are s lng, MAC addresses are usually displayed in hexadecimal. 48-bit binary versin: 000000000000100101111100111100011111011110000101 hexadecimal versin: 00-09-7C-F1-F7-85 MAC addresses are limited t being used n a LAN while IP addresses can be used n multiple types f netwrks including the Internet. On a LAN, data packets that use a prtcl such as TCP/IP will be packaged inside data packets that use the MAC address t deliver them crrectly. Anther use fr the MAC address is as a security feature n cabled and wireless systems, nly allwing cmputers with authrised MAC addresses t have access t the netwrk. This wrks by inspecting the data packet that is sent frm a cmputer t see if its MAC address matches ne f the apprved nes in a pre-defined table.
Packets Mdern cmputer netwrks, including the Internet, carry data by breaking it dwn int a series f distinct units called packets, rather than sending it as a cntinuus stream f data. A typical packet might cntain 1,000 t 1,500 bytes and has tw parts: Cntrl infrmatin - this prvides the data that the netwrk needs t deliver the paylad, fr example the surce and destinatin addresses. It will als have errr checking data and the number f the packet s they can be reassembled in the crrect rder. The cntrl infrmatin is fund in the packet headers and fters Data - this is the user data that is t be delivered and is lcated between the packet headers and fters. In cmplex netwrks such as the Internet, a series f packets sent frm ne cmputer t anther may fllw different rutes t reach the same destinatin. This technlgy is called packet switching and makes the netwrk mre efficient because the netwrk can balance the lad acrss varius pieces f equipment and if there is a prblem with ne piece f equipment in the netwrk then packets can be ruted arund it. Prtcls A prtcl is the set f rules that define hw devices cmmunicate. As lng as the cmputers n a netwrk are using the same prtcl then they will be able t exchange data crrectly. A prtcl will cver: hw the cmmunicatin will start the transmissin speed the significance f the bits being transmitted hw the bits will be delivered (ne at a time r in grups f 16 fr example) errr checking prcedures used The Internet Prtcl is knwn as TCP/IP, named frm tw f the mst imprtant prtcls in it: the Transmissin Cntrl Prtcl (TCP) the Internet Prtcl (IP). The TCP prvides the service f exchanging data directly between tw netwrked cmputers while the IP is used t rute data packets between netwrks and ver the Internet. Accessing Websites n the Internet Websites are stred n web servers cnnected t the internet. The site will have an IP address s peple can access the pages using their brwser sftware. Hwever, when yu want t access a site yu dn t type the IP address, yu type in a dmain name such as www.bbc.c.uk. This is because humans are quite bad at remembering numbers and typing them in crrectly s the dmain name is a text reference t a site that can be translated int the numerical IP address. When yu type the dmain name, www.micrsft.cm int the brwser the web page request is sent t a Dmain Name System (DNS) server in the internet. The DNS server has a database f dmain names and IP addresses s it can translate the dmain name int an IP address. Student Research What Is the IP Address f yur schl website? What Is the IP Address f Facebk?
Handshaking When a cmputer cmmunicates with anther device like a mdem, printer, r netwrk server, it needs t handshake with it t establish a cnnectin. A simple handshaking prtcl might nly invlve the receiver sending a message meaning "I received yur last message and I am ready fr yu t send me anther ne." A mre cmplex handshaking prtcl might allw the sender t ask the receiver if he is ready t receive r fr the receiver t reply e.g. "I did nt receive yur last message crrectly, please resend it" (if the data was crrupted en rute). Establishing a nrmal TCP cnnectin requires three separate steps: 1. The first cmputer (Alice) sends the secnd cmputer (Bb) a "synchrnize" (SYN) message, which Bb receives. 2. Bb replies with a synchrnize-acknwledgment (SYN-ACK) message, which Alice receives. 3. Alice replies with an acknwledgment message, which Bb receives, and desn't need t reply t. OCR 2.1.6 (g) explain the need fr security measures in netwrks, such as user access levels, suitable passwrds and encryptin techniques Usernames/Passwrds The file server must ensure that peple can nly access files that they are permitted t. Mst file servers d this by making each user lg n with a user name and passwrd befre they can access any files. The user name that a user lgs n with will determine which files the user can access and change. Passwrds are the mst cmmn way f securing a netwrk. A user will have a public username and a private passwrd. Anyne can knw, r guess, a username, but nly the user will knw the passwrd. The passwrd shuld be smething that that the user will remember, but very difficult fr anyne else t guess (r crack). A username is smetimes likened t the address f a huse and the passwrd as the frntdr key anyne can find the address, but very few will have the frnt-dr key. A passwrd and username are a set f characters that need t be typed in. The strnger the passwrd, the harder it is fr smene else t find the passwrd. Passwrds shuld be a mixture f upper case, lwer case, digits and punctuatin marks (e.g. Hell79_?!). The numerus ways in which permanent r semi-permanent passwrds can be cmprmised has prmpted the develpment f ther techniques. Sme alternatives t passwrds: Single-use passwrds. Mst users find single use passwrds extremely incnvenient. They have, hwever, been widely implemented in persnal nline banking, where they are knwn as Transactin Authenticatin Numbers (TANs). Access cntrls based n public key cryptgraphy. The necessary keys are usually t large t memrize and must be stred n a lcal cmputer, security tken r prtable memry device, such as a USB flash drive r even flppy disk. Bimetric methds prmise authenticatin based n unalterable persnal characteristics, but currently have high errr rates and require additinal hardware t scan, fr example, fingerprints, irises, etc. Nn-text-based passwrds, such as graphical passwrds r muse-mvement based passwrds. Graphical passwrds are an alternative means f authenticatin fr lg-in intended t be used in place f cnventinal passwrd; they use images, graphics r clurs instead f letters, digits r special characters. One system
requires users t select a series f faces as a passwrd, utilizing the human brain's ability t recall faces easily. Cgnitive passwrds use questin and answer cue/respnse pairs t verify identity. Research There are lts f pprtunities fr research. Spf fingerprints: http://www2.washjeff.edu/users/ahllandminkley/bimetric/index.html Pster Create a pster n creating strng passwrds. http://www.micrsft.cm/en-gb/security/nline-privacy/passwrds-create.aspx Access levels Netwrk managers can set up grups f users with different levels f access t the netwrk. At the highest level, the netwrk manager can install and remve sftware, access all user areas and change permissins. At lwer levels, a grup f users may nly be able t access particular pieces f sftware and their files stred in their wn areas.
Different levels f access help t ensure that the netwrk remains secure and that nly licenced sftware is used n it. Yur level f access is linked t yur User ID What levels f access are there in yur schl? Netwrk Managers, The Headmaster, Teachers, Students Encryptin This is the prcess f cnverting data t be sent ver a netwrk int smething that is unreadable by a human. Data is first encrypted by sftware then sent ver the netwrk. The receiver will knw hw t decrypt the message int smething that is recgnisable. Encryptin uses very advanced mathematical techniques, cmmnly relying n prperties f prime numbers. The best encryptin (harder t crack) uses a lt f bits t stre the key (a number that is used t decipher the encrypted data). Typically 128 r 256 bits are used. When yu buy smething n the internet r use internet banking yu may have nticed that instead f HTTP in frnt f the dmain name it changes t HTTPS.It wrks in the same way as HTTP but is encrypted s yur payment details are kept secure. Firewalls A firewall is a device r set f devices designed t permit r deny netwrk transmissins based upn a set f rules and is frequently used t prtect netwrks frm unauthrized access while permitting legitimate cmmunicatins t pass. Many persnal cmputer perating systems include sftware-based firewalls t prtect against threats frm the public Internet. Many ruters that pass data between netwrks cntain firewall cmpnents and, cnversely, many firewalls can perfrm basic ruting functins. OCR 2.1.6 (h) describe and justify netwrk plicies such as acceptable use, disaster recvery, failver, back up, archiving.
Acceptable Use Plicy (AUP) An acceptable use plicy (AUP; als smetimes acceptable usage plicy r Fair Use Plicy) is a set f rules applied by the wner/manager f a netwrk, website r large cmputer system that restrict the ways in which the netwrk site r system may be used. AUP dcuments are written fr crpratins, businesses, universities, schls, internet service prviders, and website wners ften t reduce the ptential fr legal actin that may be taken by a user, and ften with little prspect f enfrcement. Acceptable Use Plicies are an integral part f the framewrk f infrmatin security plicies; it is ften cmmn practice t ask new members f an rganizatin t sign an AUP befre they are given access t its infrmatin systems. Fr this reasn, an AUP must be cncise and clear, while at the same time cvering the mst imprtant pints abut what users are, and are nt, allwed t d with the IT systems f an rganizatin. It shuld als define what sanctins will be applied if a user breaks the AUP. What is the AUP in yur schl? When d yu have t cmply with the rules? D yu think all the rules are reasnable? Shuld sme rules be added? Is it clear and cncise? What sanctins are applied if yu break the rules? Disaster Recvery Disaster recvery is the prcess, plicies and prcedures related t preparing fr recvery r cntinuatin f technlgy infrastructure critical t an rganizatin after a natural r human-induced disaster. It is estimated that mst large cmpanies spend between 2% and 4% f their IT budget n disaster recvery planning, with the aim f aviding larger lsses in the event that the business cannt cntinue t functin due t lss f IT infrastructure and data. Of cmpanies that had a majr lss f business data, 43% never repen, 51% clse within tw years, and nly 6% will survive lng-term. Disasters can be classified in tw brad categries. The first is natural disasters such as flds, hurricanes, trnades r earthquakes. While preventing a natural disaster is very difficult, measures such as gd planning which includes mitigatin measures can help reduce r avid lsses. The secnd categry is man made disasters. These include hazardus material spills, infrastructure failure, r bi-terrrism. In these instances surveillance and mitigatin planning are invaluable twards aviding r lessening lsses frm these events. Failver
In cmputing, failver is the capability t switch ver autmatically t a redundant r standby cmputer server, system, r netwrk upn the failure r abnrmal terminatin f the previusly active applicatin, server, system, r netwrk. Failver happens withut human interventin and generally withut warning, unlike switchver. Systems designers usually prvide failver capability in servers, systems r netwrks requiring cntinuus availability and a high degree f reliability. At server-level, failver autmatin takes place using a "heartbeat" cable that cnnects tw servers. As lng as a regular "pulse" r "heartbeat" cntinues between the main server and the secnd server, the secnd server will nt initiate its systems. There may als be a third "spare parts" server that has running spare cmpnents fr "ht" switching t prevent dwn time. The secnd server will immediately take ver the wrk f the first as sn as it detects an alteratin in the "heartbeat" f the first machine. Sme systems have the ability t page r send a message t a pre-assigned technician r center. Sme systems, intentinally, d nt failver entirely autmatically, but require human interventin. This "autmated with manual apprval" cnfiguratin runs autmatically nce a human has apprved the failver. Failback, cnversely, invlves the prcess f restring a system/ cmpnent/ service in a state f failver back t its riginal state (befre failure). Back up In Cmputing, a backup refers t making cpies f data s that the cpy may be used t restre the riginal after a data lss event. The primary purpse is t recver data as a reactin t data lss. Data lss is a very cmmn experience f cmputer users. 67% f internet users have suffered serius data lss. Thugh backups represent a simple frm f disaster recvery, and shuld be part f a disaster recvery plan, by themselves, backups shuld nt be cnsidered disaster recvery. Nt all backup systems and/r backup applicatins are able t recnstitute a cmputer system. Since a backup system cntains at least ne cpy f all data wrth saving, the data strage requirements are cnsiderable. Organizing this strage space and managing the backup prcess is a cmplicated undertaking. In the mdern era f cmputing there are many different types f data strage devices that are useful fr making backups. There are als many different ways in which these devices can be arranged t prvide gegraphic redundancy, data security, and prtability. Archiving Archiving means t mve files t a lng-term strage medium. Backup and archiving are tw different prcesses. The strage media used within an archive shuld be stable and lng lasting. T cmply with crprate and gvernment regulatins n data, cmpanies will archive data nt in used but may be needed. Archiving can result in tw majr benefits:
It lets yu reclaim disk space n the primary strage. Saving disk space, alng with ther factrs, can lwer strage csts. This als means a significant reductin in csts f backup media. It can imprve perfrmance. By separating inactive data frm active data, database scans and ther data access peratins becme faster.