3.1b: Network Hardware & Internet
When sending data across a network, files are broken down into smaller parts called data packets.
Whole files are too large to transfer as one unit so data packets allow data to be transferred across a network quickly.
Each packet of data is redirected by routers across networks until it arrives at its destination. Data packets may split up and use alternative routes to reach the destination address.
When all the packets have arrived at the destination address the data is reassembled back into the original file.
Wireless Access Point
A Wireless Access Point (WAP) provides a link between wireless and wired networks. It creates a wireless local area network that allows WiFi-enabled devices to connect to a wired network.
Examples of a WAP in a public space could be a WiFi or Bluetooth hotspot, for example a WiFi hotspot in a coffee shop or airport to provide access to the internet.
A WAP may be a separate device or built into another device such as a router.
Routers are used to transfer data packets between networks.
Routers receive data packets and use the IP address in the packet header to determine the best route to transmit the data.
Data is transferred from router to router across the internet towards the destination.
A router stores the IP address of each computer connected to it on the network and uses a list called a routing table to calculate the quickest and shortest route to transfer data.
A switch is used to connect devices together on a LAN.
It receives data packets from a connected node, reads the destination address in the packet header and forwards the data directly to its destination.
A switch will generate a list of the MAC addresses of all devices connected to it when it receives data, and must scan for a matching destination address before sending.
An alternative to a switch is a hub but a hub is slower and less secure at it forwards a copy of received data to all connected nodes.
Network Interface Controller / Card
A Network Interface Controller (NIC) commonly also known as a Network Interface Card is an internal piece of hardware that is required for the computer to connect to a network.
The card includes a MAC address which is used when sending data across a LAN.
An ethernet cable is plugged into the network card to allow data to be exchanged between the device and a network.
A NIC used to be a separate expansion card but is now typically embedded on the motherboard.
Although not technically a device, the communication channel along which data is transferred will affect performance. Three common types of transmission media include:
Ethernet cables - used typically on a LAN to transfer data between nodes and hardware such as switches. Examples include Cat5e and Cat6.
Fibre Optic cables - very fast but more expensive and fragile cables typically used to send data quickly along a WAN. Data is sent as pulses of light.
Coaxial cables - older, slower, copper cables that are not used as much in modern times as they can be affected by electromagnetic interference.
The internet is a global network of interconnected networks.
The world wide web (WWW) is not the same as the internet. It is a way of accessing information, using protocols such as HTTPS to view web pages.
Servers provide services on the internet, such as a web server which responds to the web browser (client) request to display a web page. The web server processes the client request to prepare the web page and return it so the web browser can display it to the user.
A website must be hosted (stored) on a web server so that it can be accessed by others using the internet.
A unique domain name (e.g. csnewbs.com) must be registered with a domain registrar – this is a company that checks the name is valid and not already taken.
What is the Internet?
A DNS (Domain Name System) server stores a list of domain names and a list of corresponding IP addresses where the website is stored.
The first thing to understand is that every web page has a domain name that is easy for humans to remember and type in (such as www.csnewbs.com) as well as a related IP address (such as 18.104.22.168) which is a unique address for the device that the web page is stored on.
The steps taken to display a web page:
A domain name is typed into the address bar of a browser.
A query is sent to the local DNS server for the corresponding IP address of the domain name.
The local DNS server will check if it holds an IP address corresponding to that domain name. If it does it passes the IP address to your browser.
The browser then connects to the IP address of the server and accesses the web site.
If the local DNS server does not hold the IP address then the query is passed to another DNS server at a higher level until the IP address is resolved.
If the IP address is found, the address is passed on to DNS servers lower in the hierarchy until it is passed to your local DNS server and then to your browser.
The cloud refers to networks of servers accessed on the internet. Cloud computing is an example of remote service provision. Cloud servers can have different purposes such as running applications, remote processing and storing data.
When you store data in 'the cloud', using services such as Google Drive or Dropbox, your data is stored on large servers owned by the hosting company. The hosting company (such as Google) is responsible for keeping the servers running and making your data accessible on the internet.
Cloud storage is very convenient as it allows people to work on a file at the same time and it can be accessed from different devices. However, if the internet connection fails, or the servers are attacked then the data could become inaccessible.
Cloud Storage Characteristics:
✓ - Huge CAPACITY and you can upgrade your subscription if you need more storage.
✓ / X - Cloud storage is difficult to rank in terms of PORTABILITY, DURABILITY and ACCESS SPEED because it depends on your internet connection. A fast connection would mean that cloud storage is very portable (can be accessed on a smartphone or tablet) but a poor connection would make access difficult.
✓ - Cloud storage is typically free for a certain amount of storage. Users can then buy a subscription to cover their needs - Dropbox allows 2 GB for free or 2 TB for £9.99 a month.
3.1b - Network Hardware & Internet:
1a. Explain how a switch works. 
1b. Describe the purpose of a router. 
1c. State what WAP stands for and why it is used. 
1d. State what NIC stands for and why it is required. 
1e. State the differences between the three main types of transmission media. 
2a. State what the internet is and how it is different to the world wide web. 
2b. What is web hosting? 
3a. What is a DNS server? 
3b. Describe, using a mix of text and icons / images, how a DNS server is used to display a web page. 
3c. Describe how a DNS server searches for an IP address if it is not found on the local DNS server. 
4a. Describe what cloud computing is. 
4b. State two advantages and two disadvantages of the cloud.