Method and arrangement to maintain a TCP connection

• US 8,751,669 B2
• Filed: 12/20/2007
• Issued: 06/10/2014
• Est. Priority Date: 12/20/2007
• Status: Active Grant

• Current Assignee: Telefonaktiebolaget LM Ericsson
• Original Assignee: Telefonaktiebolaget LM Ericsson
• Inventors: Eriksson, Anders
• Primary Examiner(s): NGUYEN, PHUOC H
• Application Number:
  US12/808,555
• Publication Number:
  US 20110131308A1
• Time in Patent Office: 2,364 Days
• Field of Search: 709/220, 709/222, 709/227, 709/228
• US Class Current: 709/228
• CPC Class Codes: H04L 67/04 specially adapted for terminals or networks with limited capabilities; specially adapted for terminal portability
• CPC Class Codes: H04L 67/14 Session management for real-time applications in data packet communications networks H04L65/1066
• CPC Class Codes: H04L 67/145 avoiding end of session, e.g. keep-alive, heartbeats, resumption message or wake-up for inactive or interrupted session
• CPC Class Codes: H04L 69/16 Implementation or adaptation of Internet protocol [IP], of transmission control protocol [TCP] or of user datagram protocol [UDP]
• CPC Class Codes: H04L 69/163 In-band adaptation of TCP data exchange; In-band control procedures

Abstract

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).

Claims

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 L_probe;

receiving either a corresponding acknowledge packet ACK or a corresponding time-to-live exceeded packet;

decrementing the probe value L_probe if an acknowledge packet ACK is received or incrementing the probe value L_probe if a time-to-live exceeded packet is received;

repeating the steps using a binary search algorithm until a hop value L_HV 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 L_HV is equal to log 2(L_max), wherein L_max 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 L_HV.

2. The method as in claim 1, wherein the step of sending the keep-alive packet is repeated at regular time intervals.

3. The method as in claim 1, wherein the set of steps of determining the hop value L_HV is repeated at regular time intervals.

4. The method as in claim 1, wherein the probe packet is a payload carrying packet.

5. The method as in claim 1, wherein the connection is a TCP connection, the network node is a Network Address Translation function (NAT), the first host is a server and the second host is a mobile terminal.

6. The method as in claim 1, wherein the hop value L_HV is unique for each connection.

7. The method as in claim 1, wherein the keep-alive packet is configured to start a timer.

8. The method as in claim 1, wherein the first host is a server including a processor.

9. A host adapted to maintain a connection established in a multi-hop network with another host passing through a network node that is designed to release the connection after a certain time of inactivity, comprising:

a processor, configured to;

provide a probe packet having a time-to-live information field set a probe value L_probe;

receive either an acknowledge packet ACK or a time-to-live exceeded packet;

decrement the probe value L_probe if the acknowledge packet ACK is received or increment the probe value L_probe if the time-to-live exceeded packet is received;

perform a binary search algorithm to determine a hop value L_HV that is less than a number of hops the probe packet needs to make to reach the another host but greater than or equal to the number of hops the probe packet needs to make to reach the network node;

wherein a number of probe packets that need to be sent in order to determine the hop value L_HV is equal to log 2(L_max), wherein L_max is equal to a maximum number of hops; and

provide a keep-alive packet for the another host designed to delay a release of the connection and having a time-to-live information field set to the hop value L_HV.

10. The host as in claim 9, wherein said processor is configured to provide the keep-alive packet at a regular interval.

11. The host as in claim 9, wherein the processor is configured to determine the hop value L_HV at a regular time interval.

12. The host as in claim 9, wherein the probe packet is a payload carrying packet.

13. The host as in claim 9, wherein the connection is a TCP connection and the network node is a Network Address Translation (NAT) function.

14. The hoot as in claim 9, wherein the host is a server.

15. The host as in claim 9, wherein the another host is a mobile terminal.

16. The host as in claim 9, further comprising a transmitter device configured to send the probe packet toward the another host and send the keep-alive packet toward the another host.

17. The host as in claim 9, further comprising a receiver device configured to receive either the acknowledge packet ACK or the time-to-live exceeded packet.

18. The host as in claim 9, wherein the hop value L_HV is unique for each connection.

19. The host as in claim 9, wherein the keep-alive packet is configured to start a timer.

20. The host as in claim 9, wherein the processor is configured to employ a history of acknowledge packets ACK or time-to-live exceeded packets to set the probe value L_probe.