Layers

• Layers


  Application

  Transport

  Internet

  Link
• Application layer


  applications such as email clients and web browsers create data to send in this layer

  e.g. a browser connecting to a banking website uses HTTP

  an email program used to send a message uses SMTP (also uses POP or IMAP to receive mail)
• Transport layer


  creates the connection between 2 computers or hosts

  data is then divided into packets and given a packet number

  packets are reassembled by the recipients transport layer

  lost packets are resent
• What protocol does the transport layer use

  uses TCP - Transmission Control Protocol
• Internet Layer


  responsible for routing packets

  source and destination addresses are written on to the packets ready for transmission
• What protocol operates on the Internet Layer

  IP - Internet Protocol
• What protocol operates in the Link Layer

  MAC (Media Access Control)

  Ethernet

  Wi-Fi
• Sending Data 


  Terminal A:

  Application layer (computer application produces data for sending)

  Transport Layer (splits data into packets )

  Internet Layer (sends and routes the packets)

  Link Layer (physical hardware and cables)

  Router:

  From Link Layer in Terminal A to Link Layer in Router

  Link to Internet Layer in Router

  Internet Layer to Link in Router

  Link Layer to receiver
• Receiving Data


  From Link layer to Internet Layer in Router

  Internet Layer to Link Layer in Router

  Link Layer in router to Link layer in Terminal B

  Terminal B

  Link Layer: removes MAC address and passes packets up to Internet Layer

  Internet Layer: removes IP addresses and passes packets up to Transport Layer

  Transport Layer: reassembles the packets and passes the data to Application Layer

  Application Layer: uses correct protocol to correctly display the data for user (webpage or email)
• Advantages of Layers


  self contained - functionality of one layer can be changed without affecting the others

  different hardware or software operates on a particular layer providing interoperability between providers and systems
• benefits of layers

  manufactures can focus on the layer they are interested in and not need to know the whole protocol stack

  one layer can change with the others staying the same