Procedure for setting up an emergency call in a wireless local loop

• US 6,275,481 B1
• Filed: 10/07/1999
• Issued: 08/14/2001
• Est. Priority Date: 04/18/1997
• Status: Expired due to Fees

• Current Assignee: Nokia Networks (Nokia Corporation)
• Original Assignee: Nokia Networks (Nokia Corporation)
• Inventors: Penttinen, Simo
• Primary Examiner(s): Hsu, Alpus H.
• Assistant Examiner(s): NGUYEN, BRIAN D
• Application Number:
  US09/414,225
• Time in Patent Office: 677 Days
• Field of Search: 370/329, 370/328, 370/336, 370/337, 370/431, 370/437, 370/442, 370/443, 370/229, 370/230, 370/231, 379/37, 379/45, 455/404, 455/509, 455/464, 455/450
• US Class Current: 370/329
• CPC Class Codes: H04W 28/26 Resource reservation
• CPC Class Codes: H04W 4/90 Services for handling of emergency or hazardous situations, e.g. earthquake and tsunami warning systems [ETWS]
• CPC Class Codes: H04W 74/04 Scheduled access hybrid access H04W74/02
• CPC Class Codes: H04W 76/50 for emergency connections
• CPC Class Codes: H04W 84/14 WLL [Wireless Local Loop]; RLL [Radio Local Loop]

Abstract

Subscriber terminal units (TU) are connected over a wireless link via a base station (BS) to an access node (AN) and further from the access node to a local exchange (LE) via a standard V5.2 interface, in which, when the interface is congested and a subscriber (TU) connected to the access node (AN) is attempting to make an emergency call to a public emergency number, the call control system of the local exchange (LE) cannot at once find a free time slot for the setup of the emergency call. In the procedure, call setup requests for other than emergency calls over the V5.2 interface are disabled during a predetermined period of time t2, and attempts to allocate a time slot in the V5.2 interface for the emergency call are repeated during such predetermined period of time t2.

Claims

1. A method for setting up an emergency call in a wireless local loop, in which subscriber terminal units (TU) are connected over a wireless link via a base station (BS) to an access node (AN) and further from the access node to a local exchange (LE) via a standard V5.2 interface, in which, when the interface is congested and a subscriber (TU) connected to the access node (AN) is attempting to make an emergency call to a public emergency number, a call control system of the local exchange (LE) is unable to find a free time slot for the setup of the emergency call within a predetermined period of time t1, wherein:

a message indicating failure of an attempt to set up an emergency call is given by a V5.2 interface signalling program to a process responsible for the setup of the emergency call;

via the process responsible for the setup of the emergency call, a message indicating failure of an attempt to set up the emergency call is given to a higher-level process responsible for signalling;

call setup requests for other than emergency calls over the V5.2 interface are disabled during a predetermined period of time t2; and

attempts to reserve a time slot in the V5.2 interface for the emergency call are repeated during said predetermined period of time t2.

2. The method as defined in claim 1, wherein, when a free time slot in the V5.2 interface has been allocated for the emergency call within said predetermined period of time t2, the call setup requests over the V5.2 interface are enabled.

3. The method as defined claim 2, wherein, when a free time slot has been allocated for the emergency call in the V5.2 interface within said predetermined period of time t2:

a message indicating allocation of a time slot is given by a process responsible for the emergency call to a higher-level process responsible for signalling;

timer (T2) is stopped by the higher-level process; and

the call setup requests are enabled by the higher-level process.

4. The method as defined in claim 1, wherein, if the setup of the emergency call is interrupted when the subscriber hangs up before a time slot is released in the V5.2 interface, then the call setup requests over the V5.2 interface are enabled.

5. The method as defined claim 4, wherein, when the subscriber who initiated the emergency call hangs up before a time slot in the V5.2 interface is released;

a higher-level process responsible for signalling is given an on-hook message;

timer (T2) is stopped by the higher-level process; and

the call setup requests are enabled by the higher-level process.

6. The method as defined claim 1, wherein:

the call setup requests are disabled by a higher-level process; and

the attempts to reserve a time slot in the V5.2 interface are continued by a lower-level process responsible for the emergency call.

7. The method as defined claim 1, wherein the predetermined period of time t1 is defined using a timer (T1) controlling the time used for normal call setup, said timer being started at the beginning of call setup and/or stopped by a higher-level process responsible for signalling.

8. The method as defined claim 1, wherein the predetermined period of time t2 is defined using a timer (T2) controlling the disabled state of the call setup requests, said timer being started after time t1 if normal call setup fails.

9. The method as defined in claim 1, wherein, if the attempts to allocate a time slot in the V5.2 interface fail during said predetermined period of time t2, then the emergency call is released and the call setup requests over the V5.2 interface are enabled.

10. The method as defined claim 9, wherein, if a lower-level process responsible for the emergency call does not receive a message indicating allocation of a time slot in the V5.2 interface from the local exchange (LE) within the predetermined period of time t2, then the lower-level process is instructed by the higher-level process responsible for signalling to release the emergency call.

11. The method as defined claim 1, wherein, if the attempts to allocate a time slot in the V5.2 interface for the emergency call fail during the combined period of time t1+t2, then the emergency call is released and the call setup requests are enabled.

12. The method as defined in claim 11, wherein, if a lower-level process responsible for the emergency call does not receive a message indicating allocation of a time slot in the V5.2 interface from the local exchange (LE) within the predetermined period of time t2, then the lower-level process responsible for the emergency call is instructed by a higher-level process responsible for signalling to release the emergency call upon receipt of a next response to a failed allocation request for a time slot in the V5.2 interface if the allocation of a time slot has failed again.

13. The method as defined claim 1, wherein, after time t1;

of the ongoing calls, a call other than an emergency call is selected;

the

the selected call is disconnected via a forced process to release a time slot in the V5.2 interface;

the emergency call is set up using the released time slot; and

the call setup requests are enabled.

14. The method as defined in claim 13, wherein:

after a lapse of the predetermined period of time t2 and setup of the emergency call is unsuccessful, forced disconnection of another ongoing call other than an emergency call or the previous call selected to release a time slot is started; and

if attempts to allocate a time slot in the V5.2 interface for the emergency call fail again, the failed emergency call to the wireless network is released.

15. The method as defined in claim 14, wherein:

after the predetermined period of time t2, the forced call disconnection of another ongoing call other than an emergency call or the previous call selected to release a time slot is started by the higher-level process responsible for signalling, and

the failed emergency call to the wireless network is disconnected after forced call disconnection has failed again.

16. The method as defined in claim 13, wherein:

said call other than an emergency call is selected by a higher-level process responsible for signalling;

an instruction to disconnect the selected call is given by a higher-level process responsible for signalling to the lower-level process responsible for the selected call;

forced disconnection of the selected call is effected by the lower-level process; and

a timer (T2) controlling the disabled state of the call setup requests is started by the higher-level process responsible for signalling.

17. The method as defined in claim 16, wherein the higher-level process responsible for signalling is informed of the disconnection of the selected call by the lower-level process responsible for the selected disconnected call.

18. The method as defined in claim 13, wherein after a lapse of a second predetermined period of time t2, the emergency call is released and the call setup requests are enabled.

19. The method as defined claim 18, wherein,

after the lapse of the second predetermined period of time t2, setup of new calls is enabled by a higher-level process responsible for signalling, and a lower-level process responsible for the emergency call is instructed by the higher-level process responsible for signalling to release the emergency call.