A session is established on an existing connection, for a defined period of time, using a determined type of communication or protocol. Sessions can have specific bandwidth , and time to live (TTL) parameters.

You can compare a session to a conversation. A session is established when one end point initiates a request by establishing a TCP connection on a particular port, the receiving end is listening on that port, and replies. You could telnet to port 80 even though telnet normally uses port 23, because at this level, the application being used cannot be determined.

However, the strong points of sessions and stateful protocols can also be their weak points. Denial of service (DoS) attacks involve creating so many sessions that the connection state information tables are full and the unit will not accept additional sessions.