when the system upon which a transport entity is running fails and subsequently reatarts，the（）information of all active connections is lost.the affected connections become half-open，as the side that did not fail does not yet realize the promble. The still active side of a half-open connections using a（）timer.this timer measures the time transport machine will continue to await an（）of a transmitted segment after the segment has been retransmitted the maximum number of times.when the timer（），the transport entity assumes that either the other transport entity or the intervening network has failed.as a result，the timer closes the connection，and signals an abnormal close to the TS user. In the event that a transport entity fails and quickly restart，half-open connections can be teminated more quickly by the use of the RST segment.the failed side returns an RST I to every segment I that it receives.when the RST I reaches the other side，it must be checked for validity dased on the （）number I，a