Emergency call handling in contention-based wireless local-area networks

• US 20040151144A1
• Filed: 09/29/2003
• Published: 08/05/2004
• Est. Priority Date: 02/03/2003
• Status: Active Grant

• Current Assignee: Avaya Incorporated
• Original Assignee: Avaya Incorporated
• Inventors: Benveniste, Mathilde
• Granted Patent: US 7,539,168 B2
• Time in Patent Office: Days
• US Class Current: 370/336
• CPC Class Codes: H04M 11/04 with alarm systems, e.g. fire, police or burglar alarm systems
• CPC Class Codes: H04M 2242/04 for emergency applications
• CPC Class Codes: H04W 28/06 Optimizing the usage of the radio link, e.g. header compression, information sizing , discarding information system modifying transmission characteristic according to link quality by modifying frame length H04L1/0007; dynamic adaptation of the packet size for flow control or congestion control H04L47/365
• 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 72/02 Selection of wireless resources by user or terminal
• CPC Class Codes: H04W 74/04 Scheduled access hybrid access H04W74/02
• CPC Class Codes: H04W 74/085 collision avoidance
• CPC Class Codes: H04W 76/50 for emergency connections
• CPC Class Codes: H04W 84/12 WLAN [Wireless Local Area Networks]

Abstract

An apparatus and methods for handling emergency message frames (e.g., “911” call frames, etc.) sent by a station in a wireless local-area network are disclosed. The illustrative embodiment increases the probability with which an emergency message frame is accorded the highest quality-of-service by modifying one or more IEEE 802.11e parameters (e.g., back-off contention window length, Arbitration Inter-Frame Space [AIFS], etc.) for a station or access point that transmits an emergency message frame.

Claims

1. A method comprising:

selecting one of a plurality of time slots in a back-off contention window; and

transmitting a frame via a shared-communications channel at the selected time slot;

wherein the length of said back-off contention window is based on the destination of said frame.

2. The method of claim 1 wherein the length of said back-off contention window is less than K only when the destination of said frame is associated with an emergency call center, wherein K is a positive real number.

3. The method of claim 1 wherein said shared-communications channel is for wireless communications in a local-area network.

4. The method of claim 3 wherein said local-area network is an IEEE 802.11 local-area network, and wherein the length of said back-off contention window is less than CWmin[AC] for every access category AC when the destination of said frame is associated with an emergency call center.

5. A method comprising:

(a) transmitting a frame via a shared-communications channel;

(b) selecting one of a plurality of time slots in a first back-off contention window when (a) is unsuccessful;

(c) re-transmitting said frame via said shared-communications channel starting at the time slot selected at (b);

(d) selecting one of a plurality of time slots in a second back-off contention window when (c) is unsuccessful; and

(e) re-transmitting said frame via said shared-communications channel starting at the time slot selected at (d);

wherein said second back-off contention window is shorter than said first back-off contention window when said first back-off contention window exceeds a minimum length.

6. The method of claim 5 wherein said shared-communications channel is for wireless communications in a local-area network.

7. A method comprising alternately

(a) selecting one of a plurality of time slots in a back-off contention window, and

(b) re-transmitting a frame via a shared-communications channel starting at the time slot selected at (a);

wherein the length of said back-off contention window decreases with each successive re-transmission of said frame until said length equals a minimum length.

8. The method of claim 7 wherein said shared-communications channel is for wireless communications in a local-area network.

9. A method comprising:

(a) determining when a shared-communications channel has been idle for a time interval; and

(b) transmitting a frame via said shared-communications channel after said time interval;

wherein the length of said time interval is based on the destination of said frame.

10. The method of claim 9 wherein the length of said time interval is less than L only when the destination of said frame is associated with an emergency call center, wherein L is a positive real number.

11. The method of claim 10 wherein said shared-communications channel is for wireless communications in a local-area network.

12. The method of claim 11 wherein said local-area network is an IEEE 802.11 local-area network, and wherein the length of said time interval equals the Point Coordination Function Inter Frame Space when the destination of said frame is associated with an emergency call center.

13. The method of claim 9 further comprising:

(c) selecting one of a plurality of time slots in a back-off contention window when (b) is unsuccessful; and

(d) re-transmitting said frame via said shared-communications channel at the selected time slot;

wherein the length of said back-off contention window is based on the destination of said frame.

14. A method comprising:

receiving a first frame and a second frame for transmission via a shared-communications channel, wherein said first frame comprises a first source address and wherein said second frame comprises a second source address; and

transmitting said first frame and said second frame via said shared-communications channel in an order based on said first source address and said second source address.

15. The method of claim 14 wherein said order is based on whether said first source address is associated with an emergency call center and on whether said second source address is associated with an emergency call center.

16. The method of claim 14 wherein said shared-communications channel is for wireless communications in a local-area network.

17. A method comprising:

receiving a first frame and a second frame for transmission via a shared-communications channel, wherein said first frame comprises a first destination and wherein said second frame comprises a second destination; and

transmitting said first frame and said second frame via said shared-communications channel in an order based on said first destination and said second destination.

18. The method of claim 17 wherein said order is based on whether said first destination is associated with an emergency call center and on whether said second destination is associated with an emergency call center.

19. The method of claim 17 wherein said shared-communications channel is for wireless communications in a local-area network.

20. An apparatus comprising:

a processor for selecting one of a plurality of time slots in a back-off contention window; and

a transmitter for transmitting a frame via a shared-communications channel at the selected time slot;

wherein the length of said back-off contention window is based on the destination of said frame.

21. The apparatus of claim 20 wherein the length of said back-off contention window is less than K only when the destination of said frame is associated with an emergency call center, wherein K is a positive real number.

22. The apparatus of claim 20 wherein said processor and said transmitter operate in accordance with an IEEE 802.11 specification, and wherein the length of said back-off contention window is less than CWmin[AC] for every access category AC when the destination of said frame is associated with an emergency call center.

23. An apparatus comprising:

a processor for determining when a shared-communications channel has been idle for a time interval; and

a transmitter for transmitting a frame via said shared-communications channel after said time interval;

wherein the length of said time interval is based on the destination of said frame.

24. The apparatus of claim 23 wherein the length of said time interval is less than L only when the destination of said frame is associated with an emergency call center, wherein L is a positive real number.

25. The method of claim 24 wherein said shared-communications channel is for wireless communications in an IEEE 802.11 local-area network, and wherein the length of said time interval equals the Point Coordination Function Inter Frame Space when the destination of said frame is associated with an emergency call center.

26. An apparatus comprising:

a host computer for generating a data block; and

a wireless terminal for;

selecting one of a plurality of time slots in a back-off contention window; and

transmitting a frame based on said data block via a shared-communications channel at the selected time slot;

wherein the length of said back-off contention window is based on the destination of said frame.

27. The apparatus of claim 26 wherein said wireless terminal operates in accordance with an IEEE 802.11 specification, and wherein the length of said back-off contention window is less than CWmin[AC] for every access category AC when the destination of said frame is associated with an emergency call center.

28. An apparatus comprising:

a host computer for generating a data block; and

a wireless terminal for;

determining when a shared-communications channel has been idle for a time interval; and

transmitting a frame based on said data block via said shared-communications channel after said time interval;

wherein the length of said time interval is based on the destination of said frame.

29. The apparatus of claim 28 wherein the length of said time interval is less than L only when the destination of said frame is associated with an emergency call center, wherein L is a positive real number.

30. The method of claim 29 wherein said wireless terminal operates in accordance with an IEEE 802.11 specification, and wherein the length of said time interval equals the Point Coordination Function Inter Frame Space when the destination of said frame is associated with an emergency call center.