Broadcast
The Network Layer
Screening
If a computer sends a packet at the transport layer to another computer and no process is listening on the destination port, the receiving computer will typically respond with an error message. For TCP, it usually sends a RST (reset) packet back to the sender, indicating that the connection cannot be established because the target port is closed. In the case of UDP, the packet is simply discarded, and no acknowledgment is sent back. This behavior ensures that the sender is informed that the intended service is unavailable.
Connectionless connection ie Computer A does not care if computer B receives the Packet of data or not, Computer A simply sends the packet to computer B.
Each packet carries the address of the intended recipient. Each computer has a unique address. It works rather like the postal system.
Photons
Packet fragmentation attack
A patient information packet
The packet of electromagnetic radiation is the photon.
If we are sending a file in one go and if some error occurred in between the file transfer then the complete file has to be resend which wastes the bandwidth so to prevent this, the file to send is divided in to smaller unit which we call packet, and then send packets 1 by one so that if a packet is lost then we need to send only that particular packet not the complete file.
Any individual IP packet can be communicated electrically over cable, as optical signals over fiber, or wirelessly as radio signals.
Usually IP addressing is used.