Interactive operating systems are evaluated differently. Often the measure of success for interactive
operating systems is response time; when a user enters a command, how much time elapses before
the user receives the first response from the system?
204 ANSWERS TO REVIEW QUESTIONS
NETWORKING
7.1 Explain how an IP packet might become duplicated and arrive twice at its destination.
Suppose a TCP message is sent from Host A to distant Host Z. Because of network congestion,
Host A does not get a confirmation from Host Z within its timeout period for the message confirmation.
Therefore, Host A assumes the message was lost, and it sends the message again. Perhaps all of
the IP packets will eventually arrive at Host Z, and that will mean that many or all packets are
duplicated at Host Z.
It??™s also possible that an error in a router??™s routing table could result in a packet being sent twice by
different paths to the distant host.
7.2 Some researchers in networking complain that networking protocols have become ???ossified.??? What do
they mean by that, and why might that be so? Who benefits from ???ossified??? protocols?
As the Internet and its protocols have become central to many business applications, the consequences
of any change to the protocols have become much more serious.
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