The Physical Layer describes the physical properties of the various communications media, as well as the electrical properties and interpretation of the exchanged signals. Ex: this layer defines the size of Ethernet coaxial cable, the type of BNC connector used, and the termination method.
a station on earth sends signal to a satellite orbiting the earth, which has a transponder that receives the signal, amplifies the signal, changes the frequency and sends it back down to another earth station
The Session Layer describes the organization of data sequences larger than the packets handled by lower layers. Ex: this layer describes how request and reply packets are paired in a remote procedure call.
Developed by SSH Communications Security Ltd., Secure Shell is a program to log into another computer over a network, to execute commands in a remote machine, and to move files from one machine to another
It provides strong authentication and secure communications over insecure channels.
The envelopes go to the local post office, then the regional post office, then the central post office, then the local post office of the receiver. Each post office has a set of rules as to where to send certain zip codes.
The data goes through various gateways and routers. Each router has rules as to where to send certain IP addresses.
The receiving clerk collects envelopes off the local mail trucks until he has all the envelopes that make up the report. If any envelopes are missing, he calls the sending clerk and asks him to resend that envelope.
The receiving computer’s TCP stack collects all packets and puts them into order. If any are missing, it signals the sending computer to re-send the missing packet.