a packet on a network consists of 3 parts, the header, payload and trailer. The header contains instructions about the data carried by the packet, the payload is the applications data and the the trailer tells the receiving device that it has reached the end of the packet. It may also have some type of error checking. The most common error checking used in packets is Cyclic Redundancy Check (CRC).
some of the feilds within the packet are:
- Length of packet (some networks have fixed-length packets, while others rely on the header to contain this information)
- Synchronization (a few bits that help the packet match up to the network)
- Packet number (which packet this is in a sequence of packets)
- Protocol (on networks that carry multiple types of information, the protocol defines what type of packet is being transmitted: e-mail, Web page, streaming video)
- Destination address (where the packet is going)
- Originating address (where the packet came from)