Method and apparatus to maintain connectivity for mobile terminals in wireless and cellular communications systems

• US 6,477,373 B1
• Filed: 08/10/2000
• Issued: 11/05/2002
• Est. Priority Date: 08/10/1999
• Status: Expired due to Fees

• Current Assignee: The Research Foundation for The State University of New York (State University of New York)
• Original Assignee: The Research Foundation for The State University of New York (State University of New York)
• Inventors: Rappaport, Stephen S., Park, Yunsang
• Primary Examiner(s): Urban, Edward F.
• Assistant Examiner(s): WASHINGTON, ERIKA ALISE
• Application Number:
  US09/636,043
• Time in Patent Office: 817 Days
• Field of Search: 455/436, 455/435, 455/423, 455/450, 455/452, 455/509, 455/510, 455/512, 455/67.1
• US Class Current: 455/436
• CPC Class Codes: H04W 36/0079 in case of hand-off failure or rejection
• CPC Class Codes: H04W 72/56 based on priority criteria
• CPC Class Codes: H04W 76/10 Connection setup

Abstract

The present invention is directed to a system and method that allows mobile platforms each supporting any of a variety of call types, and each having differing mobility characteristics, to maintain connectivity to a backbone network in spite of unreliable radio links that occasionally fail. It accomplishes this by using automatic and user-transparent reconnection attempts for appropriate call sessions when an interruption of the link occurs. The network may be supporting a variety of different call types simultaneously. Access to network connectivity resources can be provided according to call session priority based on (for example, call session type, platform mobility, hand-off status, and user class (fee-for-service)) criteria. The technology allows support of suspended sessions and uses repeated reconnection attempts with priority access to network resources. It also provides for hand-offs of suspended sessions to neighboring gateways as mobile terminals move throughout the service area. In a network that uses this technology, for example, voice calls (typical of time-sensitive stream traffic) may preempt resources of time-insensitive data calls causing suspended sessions that do not result in session failures. Priority access for hand-offs of active sessions with respect to new call sessions can be accommodated. Mobile users that have some autonomy or who are perhaps exchanging time-insensitive data with a remote site can continue to function essentially undisturbed by link failures since the connectivity and reconnection procedures are managed by the network in a manner that is transparent to the end users. Mobile computing sessions and delay-insensitive data communications, for example, will be able to continue, largely unaware of link failures.

Claims

1. A method for controlling admission to a communications network, comprising the steps of:

activating a session between a wireless terminal and the communications network;

suspending the session if a communication link between the wireless terminal and communications network fails;

automatically attempting to maintain connectivity between the wireless terminal and the communications network through transparent reconnection attempts; and

reactivating the suspended session if reconnection is effected, wherein the step of automatically attempting to maintain connectivity comprises requesting a hand-off of the suspended session to an alternative gateway,

wherein the method further comprises the step of allocating a predetermined maximum number of suspended session H that may be maintained by a gateway in the communications network, and wherein the step of suspending the session comprises the steps of;

attempting a hand-off of the active session to the gateway; and

if the hand-off fails, suspending the session if there are less than H suspended sessions in the gateway.

2. The method of claim 1, wherein the step of activating a session comprises the steps of:

receiving a session request of a session seeking admission to the communications network, wherein the session request comprises at least one attribute corresponding to a service level of the session;

determining if the session can be accommodated at the requested service level; and

admitting the session, if the session can be accommodated.

3. The method of claim 2, wherein the at least one attribute comprises session type, mobile platform mobility, priority class and a combination thereof.

4. The method of claim 2, wherein the step of determining if the session can be accommodated comprises the steps of:

determining a priority level of the session request and the amount of available resources in the communications network; and

preempting system resources and suspending an active session having a priority that is lower than the priority of the session request, if necessary, to accommodate the session request.

5. The method of claim 1, wherein the step of activating a session comprises reactivating a suspended session.

6. The method of claim 1, further comprising the step of terminating the session if there are H suspended sessions in the gateway.

7. The method of claim 1, further comprising the step of allocating a predetermined maximum number of allowable reconnection attempts N of a suspended session.

8. The method of claim 7, wherein the step of automatically attempting to maintain connectivity comprises the steps of:

performing a reconnection attempt to reactivate the suspended session;

counting the number of reconnection attempts; and

terminating the session, if the number of reconnection attempts exceeds N.

9. The method of claim 8, wherein the step of counting is performed by a counter in the wireless terminal.

10. The method of claim 9, wherein the counter is initialized when the suspended session is reactivated.

11. The method of claim 8, further comprising the step of computing a random time for a next reconnection attempt, after each failed reconnection attempt.

12. The method of claim 8, wherein the step of performing a reconnection attempt to reactivate the suspended session, comprises the step of attempting a hand-off of the suspended session to a target gateway, wherein the hand-off attempt to the target gateway is counted as a reconnection attempt.

13. A program storage device readable by a machine, tangibly embodying a program of instructions executable by the machine to perform method steps for controlling admission to a communications network, the method comprising the steps of:

activating a session between a wireless terminal and the communications network;

suspending the session if a communication link between the wireless terminal and communications network fails;

automatically attempting to maintain connectivity between the wireless terminal and the communications network through transparent reconnection attempts; and

reactivating the suspended session if reconnection is effected, wherein the step of automatically attempting to maintain connectivity comprises requesting a hand-off of the suspended session to an alternative gateway,

wherein the program storage device further comprises instructions for performing the step of allocating a predetermined maximum number of suspended session H that may be maintained by a gateway in the communications network, and wherein the instructions for performing the step of suspending the session comprise instructions for performing the steps of;

attempting a hand-off of the active session to the gateway; and

if the hand-off fails, suspending the session if there are less than H suspended sessions in the gateway.

14. The program storage device of claim 13, wherein the instructions for performing the step of activating a session comprise instructions for performing the steps of:

receiving a session request of a session seeking admission to the communications network, wherein the session request comprises at least one attribute corresponding to a service level of the session;

determining if the session can be accommodated at the requested service level; and

admitting the session, if the session can be accommodated.

15. The program storage device of claim 14, wherein the at least one attribute comprises session type, mobile platform mobility, priority class and a combination thereof.

16. The program storage device of claim 13, wherein the instructions for performing the step of determining if the session can be accommodated comprise instructions for performing the steps of:

determining a priority level of the session request and the amount of available resources in the communications network; and

preempting system resources and suspending an active session having a priority that is lower than the priority of the session request, if necessary, to accommodate the session request.

17. The program storage device of claim 13, wherein the instructions for performing the step of activating a session comprise instructions for reactivating a suspended session.

18. The program storage device of claim 13, further comprising instructions for performing the step of terminating the session if there are H suspended sessions in the gateway.

19. The program storage device of claim 13, further comprising instructions for performing the step of allocating a predetermined maximum number of allowable reconnection attempts N of a suspended session.

20. The program storage device of claim 19, wherein the instructions for performing the step of automatically attempting to maintain connectivity comprise instructions for performing the steps of:

performing a reconnection attempt to reactivate the suspended session;

counting the number of reconnection attempts; and

terminating the session, if the number of reconnection attempts exceeds N.

21. The program storage device of claim 20 further comprising instructions for performing the step of computing a random time for a next reconnection attempt, after each failed reconnection attempt.

22. The program storage device of claim 20, wherein the instructions for performing the step of performing a reconnection attempt to reactivate the suspended session comprise instructions for performing the step of attempting a hand-off of the suspended session to a target gateway, wherein the hand-off attempt to the target gateway is counted as a reconnection attempt.

23. A communications system, comprising;

a wireless terminal; and

a gateway comprising a system for controlling admission to the communications network, wherein the system comprises a lower communication layer adapted to maintain a connection of an active session between the wireless terminal and communications network through automatic and transparent reconnection attempts when a communication link between the wireless terminal and communications system fails, wherein the system for controlling admission comprises;

means for activating a session between the wireless terminal and the communications network;

means for suspending the session if a communication link between the wireless terminal and communications network fails;

means for automatically attempting to maintain connectivity between the wireless terminal and the communications network through transparent reconnection attempts, wherein the means for automatically attempting to maintain connectivity comprises means for requesting a hand-off of the suspended session to an alternative gateway; and

means for reactivating the suspended session if reconnection is effected,

wherein the system further comprises means for allocating a predetermined maximum number of suspended session H that may be maintained by a gateway in the communications network, and wherein the means for suspending the session comprises means for attempting a hand-off of the active session to the gateway; and

if the hand-off fails, suspending the session if there are less than H suspended sessions in the gateway.

24. The communications system of claim 23, wherein the communications systems comprises one of a packet-switched network and a circuit-switched network.

25. The system of claim 23, wherein the wireless terminal comprises a mobile terminal or a fixed terminal.