When the system upon which a transport entity is running fails and subsequently restarts,the(21) 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 problem.The still active side of a half-open connections can close the connection using a(22)timer. This timer measures the time the transport machine will continue to await an (23) of a transmitted segment after the segment has been retransmitted the maximum number of times.When the timer (24),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 restarts, half-open connections can be terminated 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 based on the (25) number i, as the RST could be in response to an old segment. If the reset is valid, the transport entity performs an abnormal termination.

Astute service providers realize that the continued support of legacy X.25 and asynchronous network element using separate operations network is cost(16).For example,the maintenance of multiple networks can require additional staff. Often, this staff must be trained on multiple vendor technologies, sometimes requiring parallel groups specializing in each (17) .Hence, additional maintenance procedures must be maintained and administrative records are (18) .The duplication of transport facilities to carry (19)network traffic is an inefficient use of resources. And not surprisingly, more technologies installed in a central office means the necessity for more physical space, and an increase in power connections and power consumption migration of these (20) network elements to IP-based DCns is alogical strategy.