Networking

LAN - Local Area Network
Each connected device is called a node.
A LAN is installed in one site.

Advantages

• Allows communication between workers
• Allows data to be shared
• Allows peripherals to be shared
• Computers can be upgraded more easily.
• Distributed processing

Disadvantages

• Expertise required to set up large network
• Security issues from unauthorised access to network
• Measures to secure a network include: passwords, changing password frequently, encrypting network, not allowing users to install or download files.

WAN - Wide Area Network

Covers a large geographical area, sometimes an entire country. Infrastructure often provided by telecom companies due to their wide range.

VPN - Virtual Private Network

Uses internet for infrastructure and requires extra security.

NIC - Network Interface Card

• Produces the electrical signal which carries the data
• Often found in expansion cards for computers, but since the cost of Ethernet is low, and it is such a well known standard, they are often built into computer motherboards now.

Hub

• Device which connects nodes together
• Makes them act as a single segment
• Not smart - all data packets transmitted 
• Cheap devices - USB hubs in home computers

Switch

• Smart device that can create and connect to different sections of the network
• Connects devices with a form of packet switching
• More advanced than a hub as it only sends data when a node requests it.

Routers - work with data packets to send data between networks

Wireless Networking

• Advantages
• Initial setup for new nodes is faster
• Easy access for visitors
• No building or long setup required
• Disadvantages
• Security issues
• Much slower than wired

Network Types

Peer-To-Peer - Several connected devices share a network status. Can be slow due to shared processor power and data collisions.

Client server - One central computer is high powered and dedicated as a server, connects to other nodes on the network and assigns permissions, default files and settings, etc.

Network Topology - The layout of the network, how the nodes communicate with each other. Examples:

• Mesh Topology - Devices are connected with many redundant connections between nodes. Every node has a connection to every node in the topology.
• Full Mesh Topology - Every node has a circuit connecting it to every other node on the network. Most expensive to implement, but if one node fails, traffic can be easily directed to the others. Has the most redundant connections.
• Partial Mesh Topology - Some nodes are connected to every other node, while others are only connected to a few. Less redundancy.
• 
• Star Topology - Devices connected to a central computer, called the hub each node connects to each other through the hub.
• Advantage - One node isn't impacted by another node failing.
• Disadvantage - If the central computer fails, the entire network becomes useless
• 

Protocols

Protocols are the rules and accepted standards used with networks.

DNS - Domain Name System - Translates web addresses into IP addresses.
TLS/SSL - Transport Layer Secutiy/Secure Sockets Layer -  Cryptographic protocol used for security
FTP - File Transfer Protocol - Used for transferring files between various systems
HTTP - Hypertext Transfer Protocol - For distributing web pages (hypermedia files)
IMAP - Internet Message Access Protocol - For accessing emails
POP3 - Post Office Protocol 3 - More popular method for accessing emails

DNS

Notes:
DNS translates a URL into an IP address.
Browser and OS will determine if it knows the IP address from memory or cache.
If not, OS queries resolving name server for IP address
RNS communicates with root name servers for IP address
Which will link to the Top Level Domain name servers
RNS stores info from Root Name Servers in cache
Resolving queries TLD server, links to Autoritiative Name Server
ANS' controlled by registrar
Resolving Queries ANS, which provides IP.
Resolving replies to OS
which replies to Browser
Browser then loads web page

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The purpose of DNS is to translate a web address into an IP address. When the user inputs the address into the browser, first the OS and browser check the Resolving Name Server to see if the IP is stored in memory. If not, the Root Name Server, Top Level Domain name server, and Authoritative Name Server will be queried, until the ANS responds with an IP. The Resolving Name Server updates it's cache with this information and then returns it to the OS. The browser will then access the page stored at that IP.

Advantages:

• No need to memories numbers/makes the web more user friendly
• Easier for search engines

Disadvantages:

• Breakdown of DNS would destroy the WWW
• Defeats the purpose of the internet being a decentralised system