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1.3 - Exchanging Data, Types of Network, Network Security, Section on…

- - - - An IP address can be thought of as a logical address for a device. The address is used at the internet (network) layer of the protocol stack, which encapsulates the data in an IP packet for the transport of data to its final destination. Typically, this data could be a web page request. The IP packet must be delivered to the web server that will respond to the request by sending back the web page.
  - - - A uniform resource locator (or URL) is an address assigned to files on the Internet. Different protocols can be used in URLs to access different types of files in different ways.
      - Parts Of The URL: "https://www.bbc.co.uk/news/technology/index.html "
        
        https://
        
        The protocol being used to access a file. HTTPS stands for hypertext transfer protocol secure.
        
        www
        
        Subdomain for world wide web. This will usually point to the web server hosted at the following domain. Other subdomains can be used to point to specific directories, for example: news.bbc.co.uk
        
        .co.uk
        
        Domain. UK is a top-level domain (TLD) and .co is a second-level domain (2LD)
        
        /news
        
        Directory of the file being requested.
        
        /technology
        
        Subdirectory of the file being requested.
        
        /index
        
        Name of the file being requested
        
        .html
        
        The file’s extension. Hypertext markup language (HTML) is frequently used for creating web pages.
  - - - Routers are one of the most commonly used connection devices. They are used to send data signals across the internet. Routers work by collecting knowledge of available routes to transmit data. They then determine the most suitable route for sending data.
        Routers are also commonly used in homes. These types of router usually contain additional hardware that allows a network to be formed. Additionally, they contain a modem, which allows users to connect to the internet.
    - - A wireless access point (WAP) uses a radio transceiver to allow wireless connections to a network. In effect, the WAP creates its own wireless network, which devices connect to. The WAP then sends the wireless traffic it receives on to the main wired network.
        WAPs can also be used to extend the range of a wireless network. In this case, the WAP can either receive or transmit traffic to other WAPs, or it can be connected via a cable to the main network.
    - - Transmission media carry data signals from one computer to another. Media are either wired or wireless.
        In modern networks, wired media use either twisted copper wiring, or fibre-optic cable. Each wired medium has differing characteristics.
    - - Switches are network devices that record which computers are connected to which ports. When traffic is received, the switch forwards the traffic to its intended recipient only. This improves network performance by cutting down on unnecessary transmissions from older style networks.
    - - Modem
    - - A network interface card (NIC) offers an interface port for a wired connection. A wireless NIC provides a radio transceiver for connecting wirelessly.
        Most modern PCs come with a NIC and wireless NIC built-in, providing the option of either connection method. However, mobile devices such as tablets, smartphones and many embedded devices only feature a wireless NIC, giving only wireless connection.
  - - - In an Ethernet LAN, a MAC address can be thought of as the physical address of a device. The address is used at the link (data link) layer of the protocol stack, which encapsulates the IP packet in an Ethernet frame for transport across the local network.
  - - - Post Office Protocol. Used to request any new emails for a specific email account. The server returns the emails (if there are any).
    - - Simple Mail Transfer Protocol. Used to send an email to an email server. The server returns a code indicating whether or not the email could be delivered.
    - - File Transfer Protocol. Used to upload or download a file. The server opens a data connection (over which the file will be transferred) or sends an error code if there was a problem with the request.
    - - Internet Message Access Protocol. Used to synchronise a client email account with an account on a mail server. The server returns new emails (if there are any) and deletes any emails that were deleted locally on the client application. This allows a user to use multiple devices to access their email account.
    - - Hypertext Transfer Protocol Secure. Sends an encrypted request for a webpage. The server returns the encrypted page or an error code if there was a problem with the request.
    - - Transmission Control Protocol. When data is to be sent (whether from client or server), the data is split into packets by the IP (internet protocol) and each packet is given a sequence number. This is a reliable transmission protocol. At the receiving end, the packets are checked. If any packets go missing, they will be resent.
      - Internet Protocol. Creates a new packet (imagine putting the packet from the transport layer into a new envelope). Adds the source and destination IP addresses to allow the packet to be delivered. These are the packets that are routed across the internet.
      - The TCP/IP Stack and Network Layers
        
        Transport
        
        Network / Internet
        
        Application
        
        Link / Physical
    - - Hypertext Transfer Protocol. Used to make a request for a webpage. The server returns the page or an error code if there was a problem with the request.
  - - - The user enters the URL into the address bar of the browser
        
        Step 2
        
        The client machine sends a request to the local/ISP level DNS server for the IP address of the webserver
        
        Step 3
        
        If the local DNS knows the IP address this is looked up in it's database and returned back to the client machine.
        
        Step 4
        
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  - - - Prone to error, large resistor on each end to terminate electrons
    - - Each computer has a token and a schedule to talk on the network to reduce traffic, slower time when more computers are on the network
    - - A full mesh is where every computer on the network is connected to every other computer in the network
      - In a partial mesh each computer has a connection to at least one other computer
- - - - A server is a program on a computer that shares resources with, or provides services to, any authorised client. Most servers will run 24 hours a day, 7 days a week, so that a client can send a request for resources at any time. It also manages the network
        
        There are many types of server:
        
        File servers store and provide files.
        
        Web servers store and provide webpages.
        
        Email servers store and forward emails. Some email servers filter out spam.
        
        Database servers store databases, run queries, and allow data to be manipulated.
        
        Print servers provide printing services across the network and manage print queues.
    - - A client is a program that typically runs on a device used by an end-user such as a laptop or mobile phone.
        
        A client sends a request to the server. The server processes the request and then sends a response back to the client. For example, when you want to view a webpage, you will use a web browser (which is a web client). The browser will request the page from a web server. The server will send the page back to the browser and the page will be displayed.
  - - - In a peer-to-peer network, computers must be switched on to share resources. In the image below, the computer with an attached printer would need to be left switched on (and shared) for other workstations to use the printer.