Exemplar for Internal Achievement Standard. Digital Technologies Level 2

Transcription

1 Exemplar for internal assessment resource Digital Technologies for Achievement Standard Exemplar for Internal Achievement Standard Digital Technologies Level 2 This exemplar supports assessment against: Achievement Standard Demonstrate understanding of local area network technologies An annotated exemplar is an extract of student evidence, with a commentary, to explain key aspects of the standard. These will assist teachers to make assessment judgements at the grade boundaries. New Zealand Qualification Authority To support internal assessment from 2014 NZQA 2014

2 Exemplar for internal assessment resource Digital Technologies for Achievement Standard Grade Boundary: Low Excellence 1. For Excellence, the student is required to demonstrate comprehensive understanding of local area network (LAN) technologies. This involves discussing: IP (internet protocol) addressing schema, including the consequences for static addresses and dynamically obtained addresses how the access control method used in the Ethernet architecture manages Ethernet traffic on a LAN. The student has demonstrated comprehensive understanding by discussing and clearly addressing consequences of IP schema and addresses (1). The student has discussed the use of CSMA/CD in access control (2). For a more secure Excellence, the student could have given some examples of IP schema to establish the relevance to various situations, for example how the schema works within the school. NZQA 2014

3 IP Addressing Schema Public vs. Private IP 1 A public IP address is another name for a static IP address. It is an IP address available for everyone to see. Public IP s let the general public find out information about your computer and are available to see it, for example a web server. A private IP address is an IP address used on a private network (e.g. a home network) that is not routable through the public internet. So a private IP address is for security. Subnet Masks A subnet allows data traffic between devices to be split, based on their network configuration. The subnet then orders the devices (hosts) into a logical order. For example, on a network, each device that has an IP ending in 6 would be a printer and the subnet would split them from the other IP addresses. A subnet mask is not part of the IP and it can t exist separately from the IP, but it works alongside the IP. So when a subnet mask is applied, this splits the IP into 2 parts. A extended network address and a host address. A subnet mask (like an IP) is composed of 4 bytes (32 bits) and is often written the same way as an IP, in the dotted decimal system. For example, a common subnet mask is Written in binary, this is For a subnet mask to be valid, the leftmost piece must be set to 1. So is invalid, because the bit furthest left is not a 1. But also the furthest right piece must be set to 0. So is invalid. So all valid subnet masks must have the leftmost bit a 1 (a.k.a the extended network portion ) and the rightmost bit a 0 (a.k.a the host portion ). A default gateway is a device on a network that passes traffic from the subnet to devices on other subnets. The default gateway is usually that connects the local network to the internet, but internal gateways do exist. Usually there are 2 types of internet default gateways. The first is found in a home network, where there are devices connected to a router. Here, the router acts as the internet gateway. The second type is found in a home or small business that doesn t have a router. So this is usually for networks with a dial-up connection. Here, the ISP (internet service provider) acts as the internet gateway. But a router is not necessarily needed for an internet gateway to be configured. A normal computer can do the job just fine. All that is needed is 2 network adapters, one connected to the local subnet, and another connected to the outside network. This is called a gateway computer. In large businesses and networks, either routers or gateway computers can be used to network local subnets together. So, the major problem with the internet and the amount of devices connected to it at the moment is running out of IP addresses. Now, most IP s are IPv4 which is the standard 4 numeral decimal system, e.g IPv6 is just like IPv4, but it has more digits, to ensure that there are enough IP s for a long while. If a computer has an incorrect IP address entered, then the network won t recognise the computer and the device simply won t be able to connect to the network and be able to access the internet. So if a device has

4 trouble connecting to the internet, then the first troubleshoot should be (after checking the connection) is to check the IP configuration. 1 The consequences of giving a computer a public IP instead of a private IP is that, if it is a private computer (e.g. A home desktop) then everyone on the internet and the network will be able to see your IP address, which can lead to problems with security later on and as this also makes it a static IP, furthermore leaving yourself open to security issues. But on the other hand, if a server in a work environment is given a private IP, then none of the other machines are going to be able to connect to and contact the server very easily. This can also (for obvious reasons) cause major network problems in a work environment. A consequence that can arise if the subnet mask is incorrect is that all the devices on the LAN may have problems trying to communicate with each other. So each device has to agree on what the subnet mask is, otherwise the above could happen. If the default gateway is incorrectly configured, then the main consequence is that the internet won t work. This is because the LAN won t be able to connect to other networks, which may include the internet. CSMA/CD (Carrier Sense Multi Access/Collision Detection) is a protocol employed on Ethernet architecture, which monitors traffic and traffic collision on the network. So what CSMA/CD actually does is, it stops a transmission as soon as a collision is detected. This shortens the time that it takes before a re-transmission can be attempted. So its main job is to detect and stop data collision. So in simple terms, what collision detection does is detect when 2 signals are about to collide, and stops the transmission, which shortens the time before transmissions can occur again, as usually, when the data collides, the nodes re-transmit at a random time. Also carrier sense works by each Ethernet node on the network will listen to the Ethernet cable to see if a device is transmitting. If another transmission is occurring, then the node waits to transmit. CSMA/CD is multi-access, which means that many devices can be listening and waiting to transmit at once. 2 Collisions occur very simply. So imagine there is a network with only 2 nodes. Both listen to the Ethernet, and hear no transmission. Then they both transmit. The data then collides, so each node waits (independently) and re-transmits at a different time. When there are many nodes transmitting at once, the amount and the rate of collisions on a LAN rise to a very unacceptable level. Since collisions are expected on a network, but only a very small amount, there is an acceptable level of collisions. If the amount and rate of collisions rise over this acceptable level, then the bandwidth gets absolutely shattered in re-transmission. Ethernet switches help a great deal in reducing the amount of collisions that occur on a LAN. The CSMA/CD protocol gives each node a fair chance to transmit, and does not give higher priority to any other device. So all nodes on the network get a fair chance to use the Ethernet. After the data packet has been transmitted, each node uses the CMSA/CD protocol to determine which station goes next. CSMA/CD is now out-dated technology. CSMA/CD was first introduced when twisted-cable Ethernet was becoming used, but now, nobody uses it anymore, as full-duplex communication was introduced. But CSMA/CD is still occasionally used for backwards compatibility.

5 Exemplar for internal assessment resource Digital Technologies for Achievement Standard Grade Boundary: High Merit 2. For Merit the student is required to demonstrate in-depth understanding of local area network (LAN) technologies. This involves: comparing and contrasting the characteristics and the purposes of peer-topeer LANs and client/server LANs explaining the layers in the TCP/IP networking model and the role of this model in a LAN architecture explaining IP (internet protocol) addressing with reference to static addresses and dynamically obtained addresses discussing the advantages and disadvantages of the common cable, fibre and wireless technologies for connecting the components of a LAN. The student has demonstrated in-depth understanding by comparing and contrasting the characteristics and the purposes of peer-to-peer LANs and client/server LANs by providing a detailed discussion and giving advantages and disadvantages (1). The student has explained the layers in the TCP/IP networking model and the role of this model in a LAN architecture by giving a full explanation of the layers in the model (2). The student has explained IP addressing, but this is not included in this exemplar. The student has discussed the advantages and disadvantages of the common cable, fibre and wireless technologies for connecting the components of a LAN. This example shows some of the discussion around the use of wired connections (3). To reach Excellence, the student would need to demonstrate comprehensive understanding by discussing IP addressing schema and access control methods. NZQA 2014

6 The similarities between a peer-peer and server-client LAN are things such as; devices can connect to the network in a similar way, through cable, fibre or wireless technology as well as hardware that helps to build the network such as switches or hubs. Also each network can have the same types of devices connect to them, e.g. cell phones, netbooks, desktops and gaming consoles like PS3, Xbox 360 and Wii. As well as all this, both networks have network available printing when available and as long as a printer with network capabilities is connected. 1 In contrast, both of these network architectures are very different as well. For example a peer-peer network is quite basic. It is also usually only a small network, for places such as a home or small office setting. All it is (in its simplest form) is 2 or more computers (usually along with a printer) connected to an Ethernet switch wired- or to a router/modem both wired and wireless if the modem/router allows for wireless connectivity- then from the switch or router, into a modem, and from the modem, into an ISP cloud, giving you internet. Also each computer should be able to see each other and communicate, via /chat. So unlike a server-client network, usually there is total freedom over the network from each device connected to the network as well as being generally unregulated. The advantages of a peer-peer network are things such as; ease of use- most peer-peer networks are really easy to use, as there is no server to go through or anything, as well as being able to easily see what the other devices are doing. Also they are very basic and easy to set up, because it s just a few cables plugged into each other. In contrast, the disadvantages of a peer-peer network are as follows; they are a pain to keep monitoring the traffic passing through the network, there is usually no upkeep, so it would be very easy for a suspicious character to enter the network. The advantages of a client-server network are greater security of the network, more control e.g. network traffic passing through the network, being able to see what each computer is doing and limiting certain actions and preventing things such as viruses spreading, also the amount of data storage available to each computer on the network- usually in a client-server network, the server can provide much more storage space than most external storage devices that could be attached to a peer-peer network. However, a client-server network also has its disadvantages. For example, client-server networks are costly i.e. each piece of hardware (and to some extent, software) is in excess of $500 or more and the time you need to upkeep a client-server network is a big task as well, as you have to do things like update software, check the network for problems like viruses, servers are usually quite bulky so a separate room is needed with air conditioning- as servers get quite hot, so a separate room is usually needed as well. This also helps with the physical security of the network, but also you need good software security as well. So the security both physical and software- needed can be a hassle as well.

7 TCP/IP stands for Transmission Control Protocol/Internet Protocol. The TCP/IP model is a new way to look at networking other than the OSI model. TCP/IP breaks down into 4 layers. They are as follows: 2 Application: this layer defines TCP/IP application protocols. Also how host programs interact with transport layer services to use the network. Also this layer includes some of the higher level protocols, e.g.: DNS (Domain Naming System) HTTP (Hypertext Transfer Protocol) FTP (File Transfer Protocol) DHCP (Dynamic Host Configuration Protocol) Transport: the task of this layer is to permit devices on the source and destination hosts to carry on a conversation. This layer defines the level of service and status of the connection used. The 2 main protocols for this layer are: TCP(Transmission Control Protocol) UDP(User Datagram Protocol) Internet: The internet layer packs data into data packets a.k.a IP datagrams. These contain source and destination address (logical address or IP address) information that can be used to forward the datagrams across networks and from host to host. Also this layer routes IP datagrams. The Internet layer holds the whole TCP/IP model together, as its job is to allow the hosts to insert data packets into any network and have them delivered independently to their destination. At the destination, the packets may arrive in the order that they were sent, so it s the higher layers job to rearrange them into order for delivery to application protocols running on the Application layer. Network Access: This layer is where the details of how the data is physically sent through the network, e.g. electrical and optical signals. One example of a protocol on this layer is Ethernet, the most commonly used. In a network, there are a number of technologies available now to build, operate and administrate a network. The most common are wired, wireless and optics. In wired technologies now the common wire is CAT6, which allows up to 10Gbs of data transfer. Also, router/modems are as common and the majority of them incorporate wireless connectivity as well. 3 So for wired technology, the most commonly used items that you would expect to find in any type of network would be things such as CAT6 copper cable-, Router/modem, and devices to connect to the network. Also, occasionally, you would expect to find Ethernet hubs or switches and fibre (which are optical cable). The benefits of this are that Ethernet cable is quite cheap, so for large networks you can buy in bulk really easily and that it is a very durable cable. But some of the limitations are things like the range; Ethernet cable (also called copper cable) can only go for 100 meters before a relay is needed to boost the signal so the data will actually get to its destination. So any network that has copper cable and a switch is an Ethernet network.

8 Exemplar for internal assessment resource Digital Technologies for Achievement Standard Grade Boundary: Low Merit 3. For Merit, the student is required to demonstrate in-depth understanding of local area network (LAN) technologies. This involves: comparing and contrasting the characteristics and the purposes of peer-topeer LANs and client/server LANs explaining the layers in the TCP/IP networking model and the role of this model in a LAN architecture explaining IP (Internet Protocol) addressing with reference to static addresses and dynamically obtained addresses discussing the advantages and disadvantages of the common cable, fibre and wireless technologies for connecting the components of a LAN. The student has demonstrated in-depth understanding by comparing and contrasting the characteristics and the purposes of peer-to-peer LANs and client/server LANs by explaining some of the similarities and differences between the two types of LANs (1). The student has explained IP addressing with reference to static addresses and dynamically obtained addresses by explaining the differences between static and dynamic IP addresses (2). The student has explained the layers in the TCP/IP networking model and the role of this model in a LAN architecture. Examples are given here of explanation of 2 layers of the model (3). The student has discussed the advantages and disadvantages of the common cable, fibre and wireless technologies for connecting the components of a LAN. An example of the discussion showing some compare and contrast is given here (4). For a more secure Merit, explanations and discussions need to be more in-depth, and could include some conclusions. NZQA 2014

9 Peer to Peer VS Client/Server LANS There are two different types of LANs - peer to peer LANs and client/server LANs. 1 Peer to Peer In peer to peer networks, every device can communicate within the network, as long as there is access. In this case, devices are both servers and clients, as they share files over the network, whether they provide the files (server) or use the files off another device (client). There is usually a limit to how many devices can be connected to a peer to peer network as the more devices that are on this type of network, the slower it runs. Generally peer to peer networks are less secure because each user of a device handles the security of their own files. An example of a peer to peer network is my home network. I can access files from the family computer from my laptop, and when I use the family computer I can access files from my laptop (with the password of course), so my laptop can be the client and the computer be the server and vice versa. Client/Server In a client/server network, the devices can either be a client or a server - they can't be both like in a peer to peer network. As mentioned above, servers provide files and information whereas clients use the information provided by the servers. With client/server networks, data is more secure than a peer to peer network because they are commonly used in large organisations with confidential information, so the security is organised by the system administrators. In client/server networks, the serving devices usually run faster and has more storage space compared to in a peer to peer network. This is because the device will usually serve more devices as client/server networks can be much larger than peer to peer networks. Client devices usually only communicate with serving devices because they only need to receive information from servers, and no other clients. This makes client devices run faster as they do not have to communicate with any other devices besides the servers. Static IP Addresses A static IP address is an IP address that will always stay the same. It's used when the IP address needs to remain the same to access something over the network. For example, Facebook has the same IP address all the time. This is because if it changes, users will not be able to access the website. It works the same way with other websites. For this reason it is important to have static IP addresses- imagine the hassle of constantly changing your records and notify users when your IP address changes. Static ip addresses in networks are commonly used for servers and printers. 2 Dynamic IP Addresses A dynamic IP address is an IP address that will change. It is used for situations where you do not need to have the same IP address. An example of this is when you turn on a laptop and connect it to the network. You receive an IP address when you make that connection with the network and the internet. When you are disconnected from the network, that IP address is gone, and you receive a new one when you are connected again (note that this new one could be the same one again, but this is extremely unlikely). Dynamic IP addresses are received from the DHCP server that was mentioned earlier in this report.

10 TCP/IP Model Application Layer 3 The application layer is the top layer of the TCP/IP model. At this layer in the model, the data is assigned to a protocol so the correct process is used for sending and receiving the data on devices. Common protocols include HTIP (Hypertext Transfer Protocol) which is used when you use the internet, FTP (File Transfer Protocol) which is used in sharing files over networks, and SMTP (Simple Mail Transfer Protocol) which is the protocol used when sending s. For example, when you receive an , the application (Mozilla Thunderbird for example) interacts with the application layer and is assigned the appropriate protocol for sending/receiving s (in this case SMTP). Transport Layer The transport layer is the layer of the TCP/IP model below the application layer. This layer takes the data from the application layer and converts it so it can be sent to another device on the network. It also makes sure that the data is received by the intended computer, much like the transport layer in the OSI model. The transport layer follows two protocols when it sends data. These protocols are TCP (Transmission Control Protocol) and UDP (User Datagram Protocol). Cables There are two types of cables- twisted pair and coaxial. 4 Coaxial cables are rather old, and are not commonly used anymore. Twisted pair cabling is where two wires twist around each other inside the cable. An advantage of twisted pair cabling is that it is a lot cheaper than fibre-optic cables. They are also less likely to break as they are less fragile than fibre-optic cables. On the other hand, twisted pair cabling runs slower than fibre-optic, so data isn't sent across the network as fast. Wireless networking is good because you do not have to be limited by the cabling for where you can work. For example, I can still keep my internet connection on my laptop whether I'm in my room or in the lounge. It also allows the network to become quite large as you do not need to connect a lot of cables to the server to have multiple devices connected to the network. On the other hand, wireless networking is less secure than cabled networks, mainly due to the fact that anyone can access the network if the security password isn't very strong. It can also sometimes be slower due to there being multiple devices sharing the same wireless signal. With cabled networks, each device gets its own individual cable with its own signal and speed. Fibre Fibre-optic cabling is cabling made up of thin, transparent material which carries light, meaning that the data sent is traveling at the speed of light. This is an advantage as it means that the data is sent between devices really fast. A disadvantage is that the cables are very fragile, so they break easily. For this reason, fibre-optic cables are usually installed underground. This is very expensive due to the difficulty of installing these cables underground. In some cases, fibre-optic cables are installed above ground, however they are more prone to breaking, and usually need to be completely replaced, which is also quite expensive.

11 Exemplar for internal assessment resource Digital Technologies for Achievement Standard Grade Boundary: High Achieved 4. For Achieved, the student is required to demonstrate understanding of local area network (LAN) technologies. This involves: describing networking concepts explaining why the components have been used in a local area network to achieve the desired characteristics explaining how the connection technologies allow the components to function in a LAN describing the access control method used in the Ethernet architecture. The student has demonstrated understanding by describing networking concepts in particular the purpose of a LAN (1) and fully describing ICMP (internet control message protocol) (2). The student has given reasons for why and how the components have been used in a local area network to achieve the desired characteristics by explaining what a switch does and how the switch works (3). The student has some examples of discussion in this explanation. The student has given reasons for why and how the connection technologies allow the components to function in a LAN by explaining the principles of star topology networks (4). The student has described the access control method, but this is not included in this exemplar. To reach Merit the student would have to demonstrate in-depth understanding by explaining the layers in the TCP/IP Networking Model, explaining IP (internet protocol) addressing, discussing common cable, fibre and wireless technologies and comparing and contrasting peer-to-peer and client/server LANs. NZQA 2014

12 LAN (Local Area Network) 1 A LAN stands for Local Area Network. A LAN is mainly used for small areas, such as a home, office or small schools. Areas like High Schools and Universities are WAN, Wide Area Network. A LAN host is simply a computer that is connected to a network. So hosts can communicate with each other by various protocols such as . Networking devices are the hardware used to connect devices together in a network. So some typical networking devices (hardware) are things such as: Ethernet Switches/Hubs able to input and output multiple devices and data packets at any one time Routers re-routes the data to multiple devices Modems inputs the ISP into the router/hub Repeaters regenerate incoming signals. Mostly used for long distances. With copper cable (CAT6) you need a repeater every 100 metres. With fibre you don t really need repeaters. Bridges a device that filters network traffic. WAP- Wireless Application Protocol. This is simply a protocol that is a standardised way of delivering data over wireless networks. A peripheral is a device that is connected to, but separate from, a host. These are typically input/output devices, and are able to expand the capabilities of the host, but don t form part of the computer core architecture. ICMP Internet Control Message Protocol is a control protocol used in network administration and management. Because it is a control protocol, it carries no application data but it does carry information about the network. So ICMP can be used to : Report network congestion 2 Report errors in the underlying communications of network applications Report availability of remote hosts This allows the network to be able to operate more efficiently with the data sent by the ICMP. An ICMP sends its control and error messages in various ways. The 2 most common are PathPing and Tracenet. PathPing is where the ICMP sends an echo request packet at the host, and waits for the host to respond. When it does, the workstation sends the Information through. Tracenet is a piece of software that traces the message form the workstation to the host, telling you where it is at any one time Network Switches In the network I will be creating, I will be using an Ethernet switch, as a switch 3 switches/changes the paths that the data is travelling down, so the data doesn t cross, whereas with a hub, all the data gathers in one place, so it s quite easy for the data packets to collide. This will be essential, as for digital signage, you really don t want data packets to cross.

13 But nowadays, you can only really buy switches anyway, as hubs become more out-dated. So in every network, you will most likely find a switch, instead of a hub. In a home office network, a 100mbs connection should be sufficient, as the network will mainly be for , services (e.g. printers) and internet usage, so because there probably won t be HD video demand-conversation going on, 100Mbs should be plenty. Now you can only buy CAT6 cabling, which gives Gbs, so every piece of hardware, switches, cables, printers etc. Have 1Gbs connection speeds, which is more than enough for what an office LAN does. 3 However, for a gaming party, a higher connection speed is necessary, as there will need to be quick communication between the devices, and HD picture/video quality will add to the experience. Also, a higher speed internet connection is probably helpful for online play as well. Because a gaming party LAN will be used for gaming, a higher speed connection would be a good idea. So now, because of CAT6 cabling, this gives 1Gbs, so this is more than enough to play in HD, chat, exchange information, and play online when needed. LAN architecture LAN architecture describes both the physical and logical topologies of a network. 4 Physical LAN topologies refer to the way computers can be connected together in a LAN. There are 4 standard ways now that computers can be connected in. They are Star, Ring, Bus, Mesh and Tree. Star is where all computers (or devices) are connected to a central point or hub. This is either wired or wireless. This is a very secure network, as if one computer on the network gets a virus; it can be removed from the network without paralyzing the network. However, as each computer fully relies on the hub/switch to provide the connection, if this fails or receives a large amount of traffic causing it to slow down, the whole network goes down. Figure 1 Lan Model

14 Exemplar for internal assessment resource Digital Technologies for Achievement Standard Grade Boundary: Low Achieved 5. For Achieved the student is required to demonstrate understanding of local area network (LAN) technologies. This involves: describing networking concepts explaining why the components have been used in a LAN to achieve the desired characteristics explaining how the connection technologies allow the components to function in a LAN describing the access control method used in the Ethernet architecture. The student has demonstrated understanding by describing networking concepts in particular the 7 layers of the OSI Model (1) and NAT (2). The student has given reasons for why and how the components have been used in a LAN to achieve the desired characteristics by explaining the use of a file server and proxy server in a school network (3). The student has given reasons for why and how the connection technologies allow the components to function in a LAN by briefly explaining star topologies (4) and wireless connections (5). The student has described the use of CSMA/CD in a LAN for the access control method used in the ethernet architecture (6). For a more secure Achieved, the student could have provided a more detailed explanation of the components and connection technologies in the LAN. NZQA 2014

15 The Seven Layers of OSI The OSI model was created to impose a standardised from of networking, because up till the point it was introduced every computer company would have different network protocol. This meant that you couldn't buy computers from more than one company and expect them to work, because the computers wouldn't understand how each other coded and decoded the binary code that travels through the given network media. Layer 1 - Physical Layer: The physical layer encompasses all physical components and media used during data transfer in a network. This includes, but is not limited to, cables, switches, network cards and routers. Data transferred on the level of the Physical layer is in binary. Layer 2 - Data Link Layer This layer codes and decodes the bits being transferred by the physical layer. The data link layer frames the packets of data that are sent and checks for errors in the data. Layer 3 - Network Layer This layer determines the fastest route for data to travel to its destination and routes it as such. The network layer also handles a certain amount of error checking. Layer 4 - Transport Layer This layer determines the end to end transfer and it checks the data transfer was completed error free. End to end refers to the computers at each end of the cable/wi-fi. Layer 5 - Session Layer This layer establishes, manages and terminates connections between applications. The session layer also reports upper layer errors. Layer 6 - Presentation Layer This layer formats, encrypts and decrypts data to being sent and received by computers in a network. The presentation layer also serves the purpose of translating data into a format that the application layer can understand. This layer is also sometimes called the 'Syntax' layer. Layer 7 - Application Layer The application layer, as the name suggests, is the user interface side of this network model. This layer directly communicates with the applications on the computer that require network access. Network Address Translation NAT or Network Address Translation is what enables a LAN to have two separate IP addresses. How this works is that devices within the LAN have the IP address assigned by the DHCP, however the entire network has just one IP address visible to people on other networks. Data sent from other networks is sent to what is called a NAT box, where it is then translated so that the NAT box can send it to its final destination. NAT allows more IP addresses on the network. For example, you a device on your network can have the same IP as one on your neighbours, however only the external ip is able to be seen by that network, as all internal IPs are hidden. This means no conflicts will occur if you have the same internal ip as someone else on a different network because the other network will see only the external IP, and not the internal. 1 2

16 File Server A file server is a server that allows you to access files in a network. It is one place where files are stored that can be accessed by any device in a network. A file server can be found in school shared documents is a file server as all files are in that one location, which can be accessed by any user on any computer in the school network. Proxy Server A proxy server is a server that involves what information that users on the network can access on the internet. It improves the speeds of loading previously viewed websites by saving recent websites and files so that they don't need to be downloaded again. This is why when you load a video on YouTube for example, it loads faster the second time you watch it compared to the first. By using a proxy server, you can also limit what information users can access. For example, at school some websites may be blocked as they may have objectionable material in them 3 Star Connection A star connection is where each device is connected to a switch or hub using a separate cable. This is useful as it means that you can disconnect one device, and the network will still function. Collisions tend to be less frequent in a star connection. Star connections are more commonly used because they are convenient with connecting and disconnecting devices to the network. Wi-Fi Wi-Fi, or Wireless Fidelity, is what is used for wireless networking. Devices are connected to a wireless router which, along with the devices, is also connected to the network. It is commonly used to give internet access to any device connected to the wireless network. Wireless networking is good because you do not have to be limited by the cabling for where you can work. For example, I can still keep my internet connection on my laptop whether I'm in my room or in the lounge. It also allows the network to become quite large as you do not need to connect a lot of cables to the server to have multiple devices connected to the network. Access Control Access control is when devices want to communicate with each other, however they are unsure on whether another device is currently sending data over the network. The access in controlled by a MAC protocol, specifically the CSMA/CD (Carrier Sense Multiple Access with Collision Detection) protocol. This follows half duplex data transmission, so it can only send or receive data at one time. If a device has data to send, it checks to see if any other device is currently sending data. When it is clear that the cable is free, it sends the data. This can still cause a collision if multiple devices send data across the apparently free line at the same time. When this occurs, the devices wait a random amount of time before resending the data. Usually this time is different for each device, so collisions with the same data seldom occur again

17 Exemplar for internal assessment resource Digital Technologies for Achievement Standard Grade Boundary: High Not Achieved 6. For Achieved the student is required to demonstrate understanding of local area network technologies (LAN). This involves: describing networking concepts explaining why the components have been used in a LAN to achieve the desired characteristics explaining how the connection technologies allow the components to function in a LAN describing the access control method used in the Ethernet architecture. The student has identified networking components (1) and why these components have been used in the LAN. The student has described connection technologies (3). The student has described the access control method, but this is not included in this exemplar. To reach Achieved, the student would need to demonstrate understanding by describing networking concepts more fully. There needs to be more information as to how the 7 layers of the OSI work (1), along with a more detailed description of the purpose of a LAN (1) and other networking concepts (2). The student would need to move from describing to explaining why the components have been used in a LAN to achieve the desired characteristics (3). NZQA 2014

18 The characteristics and purposes of a Local Area Network (LAN). A LAN is a small network usually used for things like a home network. A LAN is often used for connecting nodes such as computers and printers and letting them share information. A LAN has a high data rate which is usually 1 to 10 Mbits/sec. A LAN is usually distributed to machines around 1 km but can go up to 10km. The Seven Layers of OSI Layer 1: The Physical layer is things that you can physically see and touch such as wires and interfaces. The data transferred is always in binary. Layer 2: The Data Link layer is the layer that makes the procedures for links between nodes. It also corrects transmit errors in the packets as well as framing them. Layer 3: The Network layer is the layer finds the fastest route for data as well as doing a certain amount of checking for transmit errors. Layer 4: The Transport layer ensures that the end to end message delivery runs smoothly, it also provides connectionless and sequential packet delivery by flow control mechanisms. Layer 5: The Session layer connects with the destination host, the computer then sends a little amount of data requesting to be connected. Layer 6: The presentation layer formats and encrypts data into a form that won't cause any problems in compatibility. Layer 7: The application layer communicates with the applications; it's the user interface side. The TCP/IP model is a set of layers much like the OSI model but it is a lot smaller and simpler. Layer 1: Network Access Layer is the things you can touch and see that data travels through such as cables, routers, switches and modems. Layer 2: Internet Layer deals with the packeting, and addressing for the data. This layer also error checks the packets for low level errors. Layer 3: Host To Host Layer deals with season management between to hosts, this includes the establishment and termination of links between computers and/or servers. Layer 4: Application Layer gives the transport layer data to the host to host layer to send to eventually be sent across the network access layer. 1 Bandwidth Bandwidth is a method of measuring bit-rate. I t is how much data can be transported per second also knows as Bits per second or bps. 1 kbitls is traditionally defined as 1,000-bit/s. 2 Duplex and Half Duplex Simplex: is a type of connection that is one way traffic. This means it only goes one way for example a mouse to commuter. Half Duplex: is a type of connection where the data can go both back and forth however it cannot do both at the same time. For example a walky talky. Full Duplex: is a type of connection where data can go both ways at the same time. For example a phone line. Ip Adressing. IP address is like the address for your computer, it gives an address for data to be sent across a network. When something is sent across a network somewhere it has the I P address data o n it.

19 DHCP or Dynamic Host Configuration Protocol is a way of dynamically giving a device the next available I P address. NAT or Network Translation is translating data traffic when it comes into a private network so it becomes safer ICMP or Internet Control Message Protocol is a method of error checking networks. For example Ping which requests an echo response which is a way of error checking. This works by requesting a response from a network device to test the connection between the end hosts. Networking Devices Things like your cable, switchers etc are what your network needs to run vie connection of nodes. However things like print servers, file servers etc enables a collaborative environment. This helps connect a well working environment with individual peripherals such as printers and scanners. This type of set up is usually an office. The main connection method is usually Ethernet. Cables Copper Wire is a medium for transporting data through electron flow down the wire. The binary comes from the fluctuation of the voltage of the electrons. 1.5 megabytes over a distance of 2.5 kms before the signal fades. Fibre Optic is similar to copper wire except it uses light instead of electrons. 2.5 gigs over a distance of 200 km before the signal fades. Wireless on the other hand sends fluctuations over radio waves, this makes it not restricted to wire. 1 1m b/s distance vary on router. Sending and receiving Data. There are different kinds of networks depending on what environment you're in for example a LAN for you home. There are different methods of connecting to a network such as phone lines, modems and DSL. The data is then sent through the OSI model. The OSI model is what converts data into binary to be converted again Reference question