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1.3 Exchanging data (1.3.3 Networks (Topologies (Star: Advantages: If one…
1.3 Exchanging data
1.3.3 Networks
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Internet registries: Five global organisations governed by the Internet Corporation for Assigned Names & Numbers.
Internet registrars: Hold records of all existing website names and the details of those domains that are currently available to purchase.
DNS (Domain Name System): A domain name identifies the area or domain that an Internet resource resides in. These are organised into a hierarchy of smaller domains.
e.g. Top level domain: .com or .uk; Second level domain: .co, .gov; Third level domain: .bbc, .ebay
IP Address: A unique address that is assigned to a network device. It indicates where a packet of data is to be sent or has been sent from.
WANs: Made up of LANs, covers a large geographical area.
LANs: Consists of multiple devices connected through cables in a small geographical area or single site.
Topologies
Star: Advantages: If one cable fails, only one node is affected. Consistent use even during heavy network traffic. No data collisions. Easy to add more devices to the network. More secure as data can't be seen by other devices.
Mesh: Advantages: If a connection is blocked or broken, the data can circumvent it with another route. Faster communication since data packets do not need to travel via a central switch.
Bus: Advantages: Inexpensive to install as it requires less cable than a star topology and does not require any additional hardware.
Disadvantages: If the main cable fails, network data can no longer be transmitted to any node. Performance degrades with heavy traffic. Low security, all computers see all data transmissions.
Disadvantages: May be costly to install because of the length of cable required, if the central device goes down, the whole network goes down.
Disadvantages: Maintenance is very difficult and costly. Set-up cost is expensive and difficult to set up.
Wi-Fi: Is a local area wireless technology that allows you to connect to devices via a wireless network access point (WAP).
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Packet Switching: Is a method of communicating packets of data across a network on which other similar communications are happening simultaneously.
Packet:
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Header: Contains the protocol, the sender & receiver IP, and the packet number.
Media Access Control (MAC): A unique identifier set by the manufacturer. The address is 48 bits and is written in 12 Hex digits.
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Protocols
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POP3: is responsible for retrieving emails from a mail server that temporarily stores your incoming mail. Email is not synchronised between devices.
IMAP: is another email protocol that is designed to keep emails on a server, email is synchronised between devices.
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Proxy Server: Intercepts all packets entering and leaving hiding the true network addresses of the source from the recipient.
Viruses and worms: have the ability to self-replicate by spreading copies of themselves. Viruses rely on a host on other files whereas Worms can be executed without any intervention.
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1.3.2 Databases
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One-to-many: Examples include Mother and Children, Borrower and library book.
Many-to-many: Examples include Student & Course, Film & Actor.
Flat file database: Is a database consisting of only one table. Useful for storing limited amount of data.
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Secondary Key: If searches are needed to be made, more than one index may be need to be searched. These will be made secondary keys. For example, patients are unlikely to know their CustomerID, so a second name would be the secondary key.
Foreign Key: An attribute where it is a primary key in one table and a normal entity in another allowing a connection to happen.
Referential integrity: Means that no foreign key in one table can reference a non-existent record in a relate-able table.
1.3.1 Compression, Encryption and Hashing
Lossless Compression: It works by finding patterns in data, meaning no actual data is loss.
Lossy Compression: Works by removing unnoticeable and non-essential information. Audio / Images will however lose a bit of quality.
Encryption: The transformation of data from one form to another to prevent unauthorised third parties from being able to understand. Plain text is the original data or message, The encrypted data is known as Ciphertext. The thing used to encrypt and decrypt is known as the key.
Symmetric (private key) encryption: Uses the same key to encrypt and decrypt data. This means the key must be transferred which is known as key exchange
Asymmetric (Public key) encryption: Uses two separate keys that are related. The public key is seen by everyone that wants to send you data by encrypting it. The private key is known only by you and is used to decrypt the data.
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