Uses layered protocols in which a layer adds header information to the
payload or protocol data unit from the layer above.
In the example shown in Figure 5-1, and using Internet
terminology, an application header is added to a message on the application
layer (for example, an email). This message is passed to the TCP/UDP layer,
where it gets a TCP or UDP header (TCP in the case of an email). On the IP
layer, it receives the necessary information to find its destination, and, most
important, the IP Address of the destination. On the link layer, a header is
prepended that contains the physical addresses for a Local Area Network,
mainly, the Ethernet addresses of the sender and the receiver, and a trailer
that contains error-checking information. The physical layer represents the
actual signal on the media.
Electronic Mail or Email; Ethernet; Internet; Internet Protocol (IP); IP
Address; Local Area Network (LAN); Message; TCP/IP or Transmission Control
Protocol/Internet Protocol; User Datagram Protocol (UDP).