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topic 1.3 network, IP adresses, WAN, Wide area network, star networks, .,…
topic 1.3 network
what is the internet
The internet started in the 1960s as a way for US government researchers to share information. In the 60s computers were large and immovable and the storage that was used was little better with huge magnetic tapes being used to store data.
As a result of this if the researchers wanted to look at each other's work they had to travel to different sites or have the large, magnetic tapes shipped around the country- it was too inefficient. Another driving factor to the development of the internet was the Cold War with the Soviet Union as governments looked for ways to share information in the event of a nuclear attack.
The first web browsers were very simple- click on the link to view the browser developed at CERN in 1989, The first web browser.
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HTML- hypertext markup language. All web pages are based on a version of HTML, it is a standard format for webpages
URI- perhaps more commonly known as URL- Uniform Resource Locator. This is a unique address for each website.
HTTP- Hypertext Transfer Protocol. This allows for a common way of retrieving information across the web- now succeeded by HTTPS, the S standing for secure as it uses encryption to transfer the data.
DNS and URLS
DNS and URLS
Websites are stored on webpages that are connected to the internet. Each website has it's own IP address. As we have seen IP address are difficult to remember so web sites are given a domain name or a Uniform Resource Locator (URL)
When you type in a URL to the address bar this is sent as a request to the a domain name server. This is part of the Domain Name System and it controls how webpages are retrieved.
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If the IP address is not found it is passed up to the next level of Domain Name servers. If the IP address cannot at the top level (.com or co.uk etc) an error is returned to browser.
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MAC addressing
MAC addressing
A MAC address is a 48 bit address written in Hexadecimal. This makes it easier for humans to identify and communicate the devices addressing than a binary value. Each MAC address can identify the manufacturer and then the individual device.
Try finding the MAC addresses on your mobile phone. You will probably find more than one. This is because there is likely to be a WiFi adapter and a Bluetooth adapter and both have different MAC addresses.
Each device that connects to a network has a Network Interface Card (NIC). Each NIC has it's own Media Access Control address (MAC address). This is give to the device by the manufacturer. A MAC address cannot be changed, it is unique to that device.
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web protocols
Web protocols
HTTP- Hypertext transfer protocol. Requests that the web server transmits the requested web page to the viewer's web browser.
HTTPS- Hypertext transfer protocol secure. Works in a similar way to HTTP but as this data is transmitted it is encrypted. This is becoming the most common protocol on the world wide web as it gives users peace of mind when entering financial details such as banking or debit/credit card details.
To transfer files across a system based on the client server model (see here) a protocol called FTP (File transfer Protocol). It is uses separate control and data connections. This is usually to allow for transmission of files across a wide area network.
Protocols that are used in the transmission of webpages allow the transfer of HyperText Markup Language (HTML). They are:
Email protocols
There are three email protocols that you need to be aware of two are for the receiving of emails and one for sending.
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POP- Post Office Protocol. POP receives and holds emails until they are picked up by a user. When the user checks their email it is downloaded from the server and then deletes it from the server. The email is then only available locally on the device which the user downloaded it to.
IMAP- Internet Messaging Access Protocol. This method of receiving emails is more suited to users who have multiple devices. This is because it maintains a copy of the email on the server until it is deleted by the user.
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concept of layers
There are a number of different models about how data is transferred. For OCR at GCSE you need to be aware of the four layer model.
The four layer model creates a modular design with each layer being responsible for a part of the communication process. This modular design allows software developers to adapt a protocol software for specific hardware or operating systems. As the layers are separate to each other they can be altered independantly.
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The Application Layer- This encodes the data that is being sent so that it will be understandably by the recipient. This might involve formatting data and adding a header according to the protocol such HTTP or FTP.
The Transport Layer- splits the data into packets and adds the packet information. See here for packet contents.
The Network/Internet layer. This attaches the IP address of the sender so that computer that receives it knows where it has come from. It also attaches the address of the host and the destination IP address.
The Link layer. This attaches the MAC addresses of the sender and the recipient allowing for the packet to be sent to a specific device on a LAN.
encryption
Encryption is a process stat is designed to protect data from being hacked or accessed illegally. When data is transmitted over the internet it can become vulnerable to hackers and therefore it is important that data is kept safe.
Encryption does not prevent hacking but it does make the data unreadable unless the person receiving the information has the correct tools to decode it.
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Plaintext- The original, unencrypted message
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There are two types of encryption that you need to aware of. They are symmetric and asymmetric encryption.
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Symmetric encryption uses a key which can be a combination of letters, numbers and other characters. A single key is used to encrypt and decrypt the message. The key is shared with the recipient so that they can decrypt it.
client server network
client server network
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Email servers are used to distribute emails to users and can also be used to filter incoming emails for spam.
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In school we use a client server network. This means that the computers that you are working at are clients and then in another part of the building there is a server. Servers are specially designed computers that have a specific role whether it is as a file server, web server, email server or print server. They are generally more powerful than a standard computer which can provide services and resources for the clients to access.
peer to peer networks
peer to peer network
When a network is smaller it might be more practical to use a peer to peer network. In this type of set up all of the computers are equal hence the term peer. They will be cabled or connected wirelessly and resources are shared across each of the connected computers on the Local Area Network. In order for a user to access the files or services from another computer on the network the computer has to be configured to share those resources.
full mesh
Full mesh network
The other topology is the mesh network. In this type of network each node is connected to every other- a node is simply a device on the network. To connect to the internet only one of the nodes needs to be connected to a modem, this connection is then shared across the rest of the network. The nodes share information with the next nearest node and so on. As a device is added this simply adds in the extra node. Using a full mesh network allows for data frames (similar to packets) to be sent via the quickest route.
star network
In a star network all of the computers have their own connection to a hub or switch. (see here for differences)
This provides a number of advantages including that if one cable fails only that workstation is affected and the performance is consistent even when being heavily used. Conversely it can be costly to install because of the extra hardware and cabling and also if the central switch or the server fails then the whole network is affected
Local Area networks usually cover a relatively small geographic area. They consist of a single site such as a school or home. The infrastructure of a Local Area Network is owned by the company or individual, they are responsible for the issues that occur on the network.
IP adresses
Every computer in the world has a unique IP address. This IP can be changed be the user or automatically depending on the situation in which it is being used; mobile devices tend to have dynamic IP addressing meaning that it can change.
The current system is known as IPv4. It takes an address that is made up of 4 values up to 255 (8 bits).
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It is anticipated that we will run out of possible combinations for IPv4 as there may be as many as 30 billion devices in the world. To deal with more devices a new system called IPv6 has been developed. IPv6 128 bits long which are arranged in eight groups of sixteen bits. Each group is four hexadecimal values.
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WAN
Wide Area Networks (WAN) cover a large geographical area, the most famous being the internet. Some large organisations will also make use of WANs. A WAN is a collection of computers and networks connected by a third party. This third party will be a company that owns the infrastructure such as BT. A WAN will make use of this companies cables, telephones lines, satellites and radio waves to transfer the data from one site to another.
Using a Wide Area network makes it possible for resources to be shared across a large area.
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