LEARNING OBJECTIVES
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Understand how WiFi signals are sent.
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Know and understand why encryption is important.
SUCCESS CRITERIA
Success Criteria:
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Encrypt and decrypt messages using Caesar Cipher.
1.5 Network topologies, protocols and layers
Learners should have studied the following:
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star and mesh network topologies
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LO2 WiFi:
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frequency and channels
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encryption
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ethernet
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the uses of IP addressing, MAC addressing, and protocols including:
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TCP/IP (Transmission Control Protocol/Internet Protocol
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HTTP (Hyper Text Transfer Protocol)
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HTTPS (Hyper Text Transfer Protocol Secure)
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FTP ( File Transfer Protocol
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POP ( Post Office Protocol)
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IMAP (Internet Message Access Protocol)
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SMTP (Simple Mail Transfer Protocol)
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the concept of layers
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packet switching
KEYWORDS
Channel - A communication link carried on any suitable medium such as a wire conductor, fibre-optic cable or a wireless signal; for example a bit-stream can be sent between devices on a WLAN along a channel formed by a particular sub-frequency in a WiFi frequency band.
Frequency - The rate per second at which vibration occurs, creating a wave.
Encryption - Scrambling data to make it unreadable, to add to security in transmitting data.
key points
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Ethernet is a standard used for connecting devices in LANs.
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Copper wire or fibre-optic cabling forms the transmissions media.
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Networks are often divided into segments.
Networks - LESSON 6
Network topologies and protocols
lo2-encryption
WiFi is the name given to the wireless technology that we use to connect all our devices to the Internet through the use of radio waves.
The radio waves of WiFi are mainly in two different frequency bands:
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2.4 GHz - ultra-high frequency
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5 GHz - super-high frequency
They conform to the IEEE 802.11 standards which allow for the division of a waveband into a number of separate channels. Many channels can be set up in any given waveband but there are legal constraints on how many and how much power they use. This is because if the channels overlap they can interfere with each other.
The image above shows how a large number of adjacent channels in the 2.4 GHz range can overlap. Adjacent signals can cause interference and data corruption, so it is usual to limit a waveband to a small number of non-overlapping channels such as three or four.
A single WiFi access point has to share its bandwidth among the connected devices so in some cases performance can be severely compromised.
The security of WiFi connections can be an issue because any enabled device can up the signals. This makes them more vulnerable than ethernet networks, so encryption is an important part of any WiFi installation.
lo2- WiFi
Due to the vulnerability of wireless signals being picked up by unauthorised individuals, it is necessary to protect the data on a wireless network with some form of encryption.
Encryption is the transformation of a message so that it can only be understood by its intended recipient. The transformation normally involves a data item called a key.
An old and simple method of encryption is called the Caesar cipher. Letters are displaced by a known amount; for example using the number 2 as the 'key'.
So the plaintext message "attack at dawn" would be transformed into "cvvcemcvfcyp". The message would be sent along with the key '2' to allow decryption.
This method is too simple for serious encryption. It would be easy to try out different keys in order to construct a meaningful message, so it is more common to use elaborate algorithms with much bigger keys.
A common method is to use two keys such as the public/private key method. This is an example of asymmetric key encryption. This means that the two keys are different but complement each other. One key is used to encrypt a message but a different key is necessary to decrypt it.
One key is publicly available. It is used to encrypt a message. A secret private key is linked to this and is required to decrypt this message. Only the holder of the paired private key can decrypt the message.
lo2-Ethernet
Ethernet is a very common set of technologies used to implement LANs. It is essentially a standard used for connecting computers that are located fairly close together.
Ethernet has been around in various forms since 1980, having been developed in the 1970s.
Ethernet is still the dominant local area network standard except where it has been replaced with wireless technologies. It is most often implemented using UTP (unshielded twisted pair) or fibre-optic cabling, with connections made using hubs or more often switches.
Currently ethernet networks are mostly capable of transmission rates of up to 100 Gbits per second. There is every reason this can improve and get even faster in the future.
Ethernet networks are subdivided into segments. Each segment is a group of devices on a shared medium such as a UTP cable.
If you have a few linked computers at home, they are likely to be part of just a single segment. Larger networks are commonly divided in order to improve performance, for example in a school all the computers in the computer lab might belong to one segment and the computers in the admin department will be in another.
Large networks benefit from segmentation because the nodes on a segment are chosen to be those that are most likely to be sharing information. They can still communicate with other segments but most of the traffic is likely to be local.This reduces the occurrence of data collisions. The fewer data collisions, the fewer requests there will be for resends and so the performance of the network is improved.