Network Protocols

Network Protocols

1. Layers

   • Layer 1
     • Data Link Layer
     • Passes data over the physical network
       • Responsible for how bits are sent (as electrical signals)
         • By cables
         • By wireless
     • Ethernet
   • Layer 2
     • Network Layer
     • Makes connections between data packets
     • Directs data packets
     • Handles network traffic
     • Used by routers
     • IP
       • Internet Protocol
       • Responsible for packet switching
         • Used by routers to direct data packets on the Internet
         • Sending device splits the data into packets to be sent across the network
           • Each packet is given a number to show the order of the data
           • Each router reads the packet header and decides which way to sent the packet
             • Packets may take different routes, but should all arrive
               • The packet numbers are used to reassemble the packets into their correct order
                 • Once this happens and the checksums match, a confirmation is sent back
               • If they don't, a timeout message is sent back and the packets are sent again
         • Header
           • Contains the control information
             • Destination address
             • Source address
             • Packet number
         • Payload
           • Part of a document/video/email
         • Check sum
           • A form of validation used to check the payload data hasn't been compromised/corrupted
           • Both the source device and the receiving device calculate a value
             • If these match, then the data has been received correctly
         • This is efficient as there are so many possible routes
   • Layer 3
     • Transport Layer
     • Controls the data flow
       • Splits data into packets
       • Checks packets are correctly sent and delivered
     • TCP
       • Transmission Control Protocol
       • Sets up the rules for how devices connect on the network
         • Splits the data into packets
         • Reassembles the packets back into the original data
         • Checks the data is correctly send and delivered
   • Layer 4
     • Application Layer
     • Turns data into websites (plus other applications) and vice-versa
     • HTTP
       • HTTPS
         • Hyper Text Transfer Protocol Secure
         • Encrypts all information sent and recieved
       • Hyper Text Transfer Protocol
       • Used by web browsers to access websites
       • Communicates with web servers
     • FTP
       • File Transfer Protocol
       • Used to access, edit and move files between devices on a network
         • Like accessing files on a server from a client computer
     • SMTP
       • Simple Mail Transfer Protocol
       • Used to send emails
       • Used to transfer emails between servers
     • POP3
       • Post Office Protocol version 3
       • Used to retrieve emails from a server
       • The server holds the email until you download it, then it gets deleted
     • IMAP
       • Internet Message Access Protocol
       • Used to retrieve emails from a server
       • When you download an email from the server, you only receive a copy of the email
   • Advantages
     • It breaks network communication into manageable pieces
       • This aids developers as they only have to concentrate on one area
     • Layers are self-contained so can be changed without the other layers being affected
     • Having set rules means that companies must make them compatible, so different brands will work with each other
   • Data can only be passed through adjacent layers
   • Each layer serves the layer above it