cs 1.4

understand the factors that affect network performance

network performance refers to how well data is transmitted throughout the network. the speed of a network is measured in bits per second this is also known as the bit rate kbps = a thousand bits per second mbps = a million bits per second bgps = a billion bits per second bandwidth describes how much data can be transferred over the network in a given time. bandwidth is not about how fast data travels. it is measured in bits per second (bps) often called the bit rate. for example, a bandwidth of 8 mbps means that 8 megabits of data can be transferred at once every second. a higher bandwidth means that more data can flow per second which has a positive effect on the speed of data transfer as data is likely to arrive more quickly. the more frequencies available on a channel then the more data that can travel at once. the higher the bandwidth, the faster data can flow per second. networks can support many users. the bandwidth has to be shared amongst the users. however, bandwidth isn't always shared equally. too many users or devices on the same network can cause the network to slow down if there is not enough bandwidth for the data. contention ratio is the number of users sharing the same data capacity. it is used to measure the ratio of users compared to the available bandwidth. the lower the contention ratio the higher the quality of service. for example, a 50:1 contention ratio means that up to 50 broadband customers are sharing the same bandwidth at any one time. the lower the contention ratio, the higher the quality of service. transmission media refers to the cables or wireless connections that carry data around the networks. the type of cable chosen can affect the network performance. copper cables tend to be used on lans. there are different types of copper cables. more expensive cables can carry additional data at a faster speed. so there is a decision between cost and speed. on wans, fibre optic cables are often used and these provide very high bandwidth. the disadvantage is that they are more expensive compared to standard ethernet cables. wireless technology, or wi-fi can be used to transmit data over a lan. however, wi-fi has a lower bandwidth compared to ethernet cables. less data can be supported and it may be transmitted at a slower rate, thus affecting network performance. the more expensive cables, the faster it can carry additional data. the number of errors that occur during data transmission is another factor which can affect the network performance. this is called the 'error rate'. an error can happen when, for example, a binary 1 is sent across the network, but instead, a binary 0 is received. there are two reasons why this can happen like interference. if a cable, or switch, is placed near to electrical equipment, then interference from the equipment may cause the bits to flip randomly. shielded cables can be used to reduce the problem. or a weak signal could increase the error rate. as the cable length gets longer, the signal can become too weak and errors can begin to creep in. the longer the cable length, the weaker the signal so there is more error rate. latency describes how much time it takes for a packet of data to travel across the network. on a small lan, latency is not really a problem as all of the nodes are near to one another. but on larger networks, latency can become more of an issue. every cable, switch and router on the network adds a delay (latency), to the connection. networks with long delays are called high latency networks. the more nodes there are, and the further away they are from each other, the higher the latency/delays

explain the different roles of computers within the client-server and peer-to-peer networks

all client server networks rely on a central server. a server is a powerful, specialist computer which is designed to allow multiple users to access it. a server can perform many tasks. but its primary role is to store and serve files and resources to users whenever they are requested. servers can manage printing jobs, access to the internet, email services and data backups. large networks may have multiple servers which are dedicated to performing a specific task. for example, file, print or email servers. computers on the network connect to the server through a central hub or switch. in order to use the network, a person has to log in and the server checks that the username matches the password. once a user has logged in, they can request files and resources stored on the server. peer to peer networks are usually found in homes and small offices. they can support up to a maximum of 10 workstations. hence why they're not found or are suitable for larger organisations. there is no central file server on a p2p network. instead files are stored on the hard disk of each individual workstation. files and folders which are to be shared with other users on the network are assigned shared permissions users can then access them from the workstation they are on. on p2p networks, users on it are not required to log in. users can allow others to freely access all of their resources on their workstation. or they can assign a password to a file of folder. that way only those who know the password can open the file. with a p2p, if one peer is switched off or unavailable, other users can still use the network. they will be able to access their own files and resources stored on the other peers. however, they will not be able to access their files from the unavailable peer

describe local and wide area networks

local area network is a network where network devices are located near one another. typically, a lan includes computers and peripherals connected to a server within some geographical area . they may be in the same building or lots of buildings that are close together. devices are connected together by either copper ethernet cables or wifi. each device is called a node. the organisation who owns the lan also owns the cables and the wireless access point (wap). they are responsible for the cost of setting up, and maintaining, all parts of the lan. a wan is a communications network that spreads across a large geographic area such as across cities, states, or countries. a company wan will enable staff from different offices to share files and resources stored on the network. the largest wan in existence is the internet. this connects billions of lans together to form the largest, and most diverse, network. lans are connected to form wans using different methods. some examples are fibre optic cables. leased telephone lines. satellite communication links and microwave links

explain the hardware needed to connect stand-alone computers into a local area network: wireless access points, routers/switches, nic and transmission media

network interface card: sometimes known as a network interface controller. every device on the network needs a nic. it is found inside the device, sometimes as a dedicated card, sometimes as a chip on the motherboard. each nic has its own individual mac address (media access control). the mac address enables every device on the network to be uniquely identified. because of this, data can be sent to the correct device. the nic converts data from the nodes into a format that is compatible with the network, following the network protocols. protocols means set of rules hub: a hub is a small box which links nodes together to form a network. every node on a wired network is connected to the hub by a cable. hubs transmit data from one node, to another, in the form of data packets. a data packet is a small chunk of data. it has a destination address included. when a data packet arrives at the hub, it is transmitted to every other node on the network. this is not very secure as every node can view the data, whether it was intended for them, or not. another issue with using a hub is the high risk of a data collision. data collisions happens because a network cable can only have one data packet in it at any instant. so, if two or more computers on the network transmit data at exactly the same time, a data collision will occur. the collided data is marked as unusable and the data has to be transmitted again. this can lead to a delay and the network slowing down switch: for larger networks or networks where security is important, a switch is a better option than a hub. a switch is similar to a hub as it allows computers to be linked together to exchange data. but, unlike a hub, a switch sends the data packet only to the intended node. it does this by reading the destination information within the data packet. the switch knows the location of every node on the network because of their individual mac addresses. because data is only sent to the intended devices, security is improved. there is also a much lower risk of data collisions when switches are used. the disadvantage of switches are that they cost more than hubs. so they only tend to be used in high bandwidth and high performance networks router: a router is a device which transfers data from one network to another i.e. between networks. routers are used to connect lans together to form a wan. without a router, you would not be able to connect to the internet. how a router works: a data packet arrives from the node or hub. the router reads the data packet's destination ip address (internet protocol address) - this is not the same as the mac address. the router uses a database to look up where the ip address is located. it identifies all of the different routes that could be used to send the data packet through. it checks how busy each route is at that very moment. it sends the data packet via the fastest route/ path. cables: using cables in a network is otherwise known as a 'wired connection'. wired networks have a higher bandwidth than wireless networks. ethernet: network cables are used to join individual nodes together to form lans. the wired connections are made of pairs of wires twisted together to reduce interference. these cables are referred to as: shielded twisted pair, unshielded twisted pair utp, ethernet cables, CAT-5 or CAT-6. using these cables ensures maximum bandwidth, security and reliability. there are sets of wires for transmitting data and a set of wires for receiving data coaxial cable: coaxial cable is a type of copper cable specially built with a metal shield and other components engineered to block signal interference. it is the cable used to connect tv to a top box or freeview box to an aerial. it is an older networking standard and has become less popular in computer networking. fibre optic: fibre optic cables can be used to connect wans together. fibre optic cables use light to transmit data. they provide extremely high bandwidth and are commonly used to connect large lans together. fibre optic cables are able to cover much longer distances than copper cables without losing their signal. they are used in undersea cables to carry internet traffic between continents. wap and wifi: a wireless access point (wap) is used to connect wifi devices to a wired network, without the need for physical cables. to access a wifi hotspot you need the name of the network and the correct password. waps are commonly found in homes and also in public areas e.g. cafes, airports, offices etc. on larger networks, a wap can provide access to the network without the need to be physically connected with cables. as long as people are within range of the wap, they can move about from room to room and still be able to access the network. wireless access point: waps are similar to hubs. they do not read the destination address of the data packet. they simply broadcast the data to every device connected to the wifi network. this is a security issue as anyone connected to the network can access the data. another disadvantage of waps are that the bandwidth on a wireless network is less than a wired or cable network. internet service provider: on a home network there is a single box that has the role of a wap, router and a switch. it is connected to the telephone network and is usually provided by the internet service provider (isp). examples of isps are: virgin media, bt, plusnet and sky broadband

decribe the internet as a worldwide collection of computer networks: dns, hosting and the cloud

the internet: the Internet is a global system of computer networks. these networks connect together using the transmission control protocol and the Internet protocol. this protocol enables every device on the Internet to connect together. the Internet isn't only about with websites. in fact the websites are just one of the many services available on the Internet. other services include: video streaming. instant messaging. email services, peer to peer and file transfer protocol internet service providers: isp stands for Internet service provider. isp is a company that provides you with access to the Internet. you might hear them referred to as Internet provider. some examples of isps are: bt internet, talk talk, plus net, virgin, sky and ee. isps normally charge a monthly fee for this service. if you don't pay the fee or you cancel your contract you won't be able to use Internet except in public wifi hotspots uniform resource locator: url stands for uniform resource locator. there are many billions of webpages on the Internet. there has to be a way of identifying every single one of them. each website has a unique address. this address is called the web page url. no other website on the Internet has the same address. example: www.pledis-17.com ip address: every hardware device connect to the Internet has its own unique address. this is called an ip address (short for Internet protocol). the ip address enables every device on the network to be identified and located. an ip address is made up of a set of four numbers. each of the four numbers are separated by a dot. example: 76.215.67.190. ip addresses can be static or dynamic. static ip addresses is one that never changes. the dynamic ip address is temporary and changes each time the device access is the Internet. this is safer domain name system: dns stands for domain name system. the dns is the Internet equivalent of a phonebook. it acts as a directory of every domain name and its corresponding ip address . this directory is actually a database. the database is stored on a number of servers through the Internet which is called the domain name servers. ww.bbc.co.uk is easy for you to remember. however if you want to view the website you need to know the ip address of the device that is hosting it. would you be able to remember 212.58.224.0? no you won't. and that is just one ip address for one website. imagine how many other hundreds of websites that you visit. you couldn't possibly remember all of those ip addresses. but luckily because of the dns you don't need to know them. the browser uses the ip address to locate the server hosting the website. it then sends a request to the server asking it to deliver a copy of the webpage to your browser. the server sends a copy of the webpage (broken to data packets) over the Internet back to your browser. your web browser reassembles the data packets and displays the webpage on your screen hosting: websites need to be hosted on a web server. there are two different methods of hosting. local hosting and external hosting local hosting: you can host a website on your own computer. this is called local hosting. if you plan to do this you need to set your computer up as a web server. this will enable people to connect to your computer to access the website and any related files advantages: speed: hosting your website locally on your computer means that it will run much faster than if we were hosted on a server in a different country. it is less expensive than external hosting as there is no rental charge. it gives you full control of your website. privacy - you may want a website for your own use disadvantages: you need technical knowledge to host a website locally your computer always needs to be switched on otherwise the site will be unavailable. bandwidth can be an issue especially if your website is popular. you are responsible for the backups external hosting: most people choose to host their website externally. external hosting is where you pay up a web hosting company and monthly fee to host your website one of their servers advantages: you don't have to worry about running out of bandwidth. however you may be charged for additional bandwidth the hosting company will maintain the server and insure that it is always available. the hosting company perform regular backups virus and malware scans disadvantages: external hosting can be expensive. if the company server goes offline your website will be unavailable. if the company upgrades their software it might mean that some of the code used on the website is incompatible. this can cause parts of your website to break the cloud: the cloud or cloud computering refers to a range of software and services that are run on the Internet examples of cloud services are: streaming services. eg. netflix or spotify, online applications. eg. google docs or office 365, online storage. eg. dropbox or amazon, web services and online backups. eg. mozy, hosting a web page. eg. fast hosts or 1&1 advantages: you can access data from any device with an Internet connection, it is easy to share files with other users multiple people can work on the same file simultaneously, your work is automatically backed up disadvantages: if you don't have an Internet connection you can't login and access your files, if you forget your login details you can't access any of your files and media, there is a risk of hackers being able to access your private data and files, some cloud services charge an ongoing monthly or annual fee