Packet Switching and Routers

• Circuit switching is creating a continuous communication connection between 2 endpoints for the duration of a transfer of data
• Packets are data that has been broken down into smaller pieces and to be reassembled when received
• Packets are often sent across networks with multiple routes to a destination
• Routers forward data packets from one network to another
• How routers send data?

  • Each router stores data about the available routes to the destination node
  • Looks up the destination IP address in its routing table to find the best router to which to forward the packet
  • Each forwarding by (or transfer across) a router is known as a hop
  • Routers continue to forward the packet until it reaches its destination node
• How do routers avoid typing up the internet?

  By having a hop limit which destroys the packet after a certain amount of hops
• What are packets made up of?

  • Header
  • Payload
  • Trailer
• What is the in header of a packet?

  • Sender's IP address
  • Recipitent's IP address
  • Protocol
  • Packet number (n of total)
• What is in the payload of a packet?

  • Data
• What is in the trailer of a packet?

  • End of packet flag
  • Checksum - recalculated at destination to ensure data isn't corrupt
• What is the purpose of gateways?

  Where data is travelling to a different network with a different protocol
• What is done at gateways?

  The header is removed and reapplied using the format of the new network
• What is done if a packet reaches its TTL?

  If a packet reaches it's time to live (TTL) it is destroyed and then requested again