Method and arrangement to maintain a TCP connection

摘要

The present invention relates to a method and an arrangement to maintain a TCP connection (230) between two hosts (140, 250) in a multi-hop network (110,120). If the connection (230) is inactive (no IP packets sent or received) during a certain period of time, it may happen that the connection (230) is released by certain intermediate network entities such as a Network Address Translation NAT function (130). The current invention overcomes this problem by sending keep-alive packets (210) from one of the hosts (250) towards the other (140) at regular intervals. Said packets (210) prevent the NAT (130) from releasing the connection (230). In order to not disturb the other host (140) e.g. a mobile terminal in a sleeping mode, the keep-alive packets (210) are adapted in such way that they are sent far enough to reach the NAT (130) but not all way to the other host (140).

主权项

1. A method of maintaining a connection established in a multi-hop network between a first host and a second host and passing through at least one network node that is designed to release the connection after a certain time of inactivity the method comprising the steps of:
sending from the first host towards the second host at least one probe packet having a time-to-live information field set to a probe value Lprobe; receiving either a corresponding acknowledge packet ACK or a corresponding time-to-live exceeded packet; decrementing the probe value Lprobe if an acknowledge packet ACK is received or incrementing the probe value Lprobe if a time-to-live exceeded packet is received; repeating the steps using a binary search algorithm until a hop value LHV has been determined that is less than the number of hops the probe packet needs to make in order to reach the second host but greater than or equal to the number of hops the probe packet needs to make in order to reach the network node; wherein a number of probe packets that need to be sent in order to determine the hop value LHV is equal to log 2(Lmax), wherein Lmax is equal to a maximum number of hops; and sending a keep-alive packet from the first host towards the second host where the keep-alive packet is designed to delay the release of the connection and having a time-to-live information field set to the hop value LHV.