For TCP judge

Night Hazy, people square static, bored people opened a boring computer to see a boring picture, think about sleeping, dream of A and people b a chat.

One day, A has something to discuss with B Ask B "have time, want to chat with you for a day", B thought for a while to find that they can take time to reply to a said "can ah, and the specific time told a", a received the message happily to arrange their time, and told B "My time is also arranged, can speak", Then A and b crackling say for a long time, finally a words finally finished, want to end chat. So

A said "My words are done", B at this time there are two possibilities: B is not finished speaking and B is finished.

1. If the words of B are not finished, b to say with a "my words are not finished, you have to listen to a while, and then I said," and then B on the crackling and a said a bunch of things, a quiet listen, finally B said, this time B and a back to the sentence "Well, my things finally finished, You can go and do something else. "Then A is ready to go to other things, but he does not know whether B is still thinking about this conversation, out of politeness and worry, a or decided to go back to a sentence let B also to busy other, so a to B back to a" I want to busy other, you also go busy your other things. " So the conversation ended happily.

2. If b is finished, B said, "Well, I said, you go to other things," a received a reply to B, A is ready to go to busy other things, but he did not know whether B is still watching this conversation, out of courtesy and don't rest assured, a or decided to return a sentence to let B go busy with the other, So a gave B a "I'm going to do something else, and you're going to be busy with your other things."

With this conversation, he thought of the world of computers, computer A to establish a link with computer B, if b just have resources to allocate a resource (build process, assign port number, etc.) to deal with a request, they pass three TCP links after the official transfer of data, processing data. Disconnection is likely to be a B request to break the link may also be a, but the process is similar, assuming that a data is passed, the request disconnects, B to give a reply there are two possible, if B and the data is not finished to break the link will be four times the TCP link, If the data of B is passed to disconnect the link actually three times the TCP link can be finished.

Due to the instability of the network, TCP reliability and the full use of computer resources and other reasons, people to the computer set a reasonable maximum waiting time limit, if the network is broken, after this time limit has not received each other reply, the two computers on the initiative to end this communication, The resource cost of terminating this communication. In the above example, a last message to B is also because B in this time limit will not voluntarily give up the resources occupied by this communication, in order to let B earlier release of these resources, a in a timely manner to send a message to tell B, let B vacate this section of resources to busy other. A after sending the last message, wait until the time is up to this time period to give up the resources occupied by this communication.

The computer is stupid, but the human is very clever, let the computer become very clever, also makes the computer become very polite, but the computer makes mankind become less polite, more and more false. Early morning dew, people gradually woke up, it was just the whole world took a nap, did a inhuman deal! "The person who woke up, rubbed his eyes, accidentally touched the keyboard, through the light, powerless to look at the front of the picture, thought:" Y, this world and this picture with me about it, but also I did not sleep well? So he went to bed with a listless stomach.

For TCP judge