protocols

• 4 layers

  1. application - Allows humans and software applications to use the network e.g. browsers (HTTP/HTTPS), email (SMTP), file transfer (FTP)
  2. transport - TCP breaks data down into data packets. makes sure the data is sent and received in the correct order and reassembled at the destination without errors.
  3. internet - IP is responsible for addressing and routing data packets. The optimal route for the data to take is calculated in this layer. aka network layer
  4. link - Ethernet sets out the format of data packets. This layer handles transmission errors and passes data to the physical layer.
• Layering allows standards to be developed, but also to be adapted to new hardware and software over time. For example, different software packages (applications) may use the same transport, network and link layers but have their own application layer. The way the program encodes the message changes - the rest of communication method remains the same.
• • Networking standards are rules that allow computer systems to communicate across networks. Standards have been created to ensure devices can exchange data and work together.
  • A protocol is a set of rules that allow devices on a network to communicate with each other.
• TCP / IP is actually two separate protocols that combine together.

  • ​​TCP is a protocol that allows packets to be sent and received between computer systems. It breaks the data into packets and reassembles them back into the original data at the destination.
  • IP is a protocol in charge of routing and addressing data packets. This ensures data packets are sent across networks to the correct destination. It is also an addressing system - every device on a network is given a unique IP address so data packets can be sent to the correct computer system.
• application layer

  • http: transfer web pages over Internet so users can view in web browser
  • https: secure, transfers encrypted data
  • ftp: File Transfer Protocol, transfers files across a network. can upload / download files to/from web server
  • smtp: Simple Mail Transfer Protocol send emails to mail server n between mail servers.
  • pop and imap: Post Office Protocol and IMAP Internet Message Access Protocol receive and store emails frm a mail server. POP deletes an email once it has been downloaded to a device. IMAP syncs the message with an email server so can be accessed by different devices.
• ip

  There are two versions of IP addressing currently used - IPv4 and IPv6.

   

  IPv4 uses a 32-bit address that allows for over 4 billion unique addresses. 

   

  IPv4 uses a numeric dot-decimal notation like this: 212.58.244.66

   

  4 billion unique addresses may sound like a lot but there are nearly 8 billion people in the world. Therefore a newer version - IPv6 - was developed with a 128-bit address, represented in hexadecimal that allows for a mind-boggling number of unique addresses.
• A MAC address is a unique serial number assigned to each network interface controller (NIC). This allows a network to uniquely identify any device. The device’s IP address changes depending on the network and the MAC address is unique to device.

  • string of hexadecimal numbers:

  1A:5B:6H:98:78:35 first 3: manufacturer last 3: unique identifier

  The MAC address is assigned by the NIC’s manufacturer and cannot be easily changed, so is referred to as a physical address. If a device has more than one NIC, for example a wired NIC and a wireless NIC, each NIC will have its own MAC address.
• 1st 3 - manufacturer last 3 - unique identifier
• IP addresses can be:

  • static - always keeps the same address. easy for network managers to know which device is which on a network.
  • dynamic - different address assigned to it each time it connects to the network. allows more devices to connect than there are available addresses. When a device disconnects from the network, its address is freed up for another device to use. When the first device reconnects, it is assigned any free address.