Methods and systems for providing priority access to 802.11 endpoints using DCF protocol

• US 7,826,472 B2
• Filed: 02/18/2005
• Issued: 11/02/2010
• Est. Priority Date: 02/18/2005
• Status: Active Grant

• Current Assignee: Avaya Incorporated
• Original Assignee: Avaya Incorporated
• Inventors: Krishnan, Parameshwaran, Krishnakumar, Anjur S., Kappes, Martin
• Primary Examiner(s): Sefcheck, Gregory B
• Assistant Examiner(s): Kang, Suk Jin
• Application Number:
  US11/062,262
• Publication Number:
  US 20060187952A1
• Time in Patent Office: 2,083 Days
• Field of Search: 370/209, 370/351, 370/447, 370/465, 370/338, 370/445, 370/349, 370/448, 370/347, 370/329, 370/252, 370/230, 455/452.1, 709/232, 709/222
• US Class Current: 370/445
• CPC Class Codes: H04M 2242/04 for emergency applications
• 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 72/12 Wireless traffic scheduling
• CPC Class Codes: H04W 74/0816 with collision avoidance
• CPC Class Codes: H04W 74/0875 with assigned priorities based access
• CPC Class Codes: H04W 76/50 for emergency connections
• CPC Class Codes: H04W 84/12 WLAN [Wireless Local Area Networks]

Abstract

A method for providing priority access to 802.11 endpoints. The method includes the steps of sending a Clear To Send (CTS) frame from a designated station, without requiring a Request to Send (RTS) frame from a first station. The CTS frame includes a field identifying the first station for commencing transmission, and a field indicating a duration of transmission. A deferring step is also performed for deferring any transmissions of stations other than the first station until after the duration indicated in the CTS frame has passed.

Claims

1. A method for providing priority access to 802.11 endpoints comprising the steps of:

sending an unsolicited Clear To Send (CTS) frame from a designated station without requiring a Request to Send (RTS) frame from a first station, said CTS frame including a field identifying said first station for commencing transmission, and a field indicating a duration; and

deferring any transmissions of stations other than said first station until after said duration indicated in said CTS frame has passed, wherein the sending and deferring occur during a contention period wherein said duration is set to;

w =(DIFS+ω

+CW_min·

t_slot·

I(busy))

wherein ω

is the range of symmetric jitter in T₀;

I (busy) is an indicator function that is 1 if the medium is busy at the scheduled beginning of an invitation window and 0 otherwise;

w is an invitation window;

DIFS is a DCF interframe space;

CW_min is a minimum contention window size; and

t_slot is a slot time and t zero is a first packetization interval.

2. The method as recited in claim 1, wherein said designated station is an access point (AP).

3. The method as recited in claim 2, further comprising the steps of:

seizing wireless medium by said AP; and

transmitting a frame after said wireless medium has been idle for a Point Interframe Space (PIFS) using Coordination Function between said first station and said designated station.

4. The method as recited in claim 3, wherein the step of seizing wireless medium further comprises the step of the period indicated in said field indicating a duration, said designated station providing a transmission opportunity for said first station after conclusion of any ongoing frame exchange sequence on said wireless medium.

5. The method as recited in claim 1, wherein said first station includes a voice over internet protocol (VoIP) endpoint transmitting frames at regular packetization intervals, T₀.

6. The method as recited in claim 1, further including a step of setting minimum contention window size (CWmin) to a low value.

7. The method as recited in claim 1, wherein said first station includes a voice over internet protocol (VoIP) endpoint transmitting frames at regular packetization intervals, T₀.

8. The method as recited in claim 7, further comprising the steps of:

estimating T₀ at a signaling server; and

estimating a frame inter-arrival time.

9. The method as recited in claim 8, wherein the step of estimating said frame inter-arrival time further comprises using a mart (martingale) heuristic.

10. The method as recited in claim 8, wherein the step of estimating frame inter-arrival time comprises using a wavgeo (geometric weighted average) heuristic.

11. The method as recited in claim 8, wherein the step of estimating frame inter-arrival time comprises using the wavuni (uniform weighted average) heuristic.

13. The method as recited in claim 1, wherein said CTS frame of said identified station identifies an emergency call.

15. The method as recited in claim 5, further comprising the steps of:

transmitting a frame from said VoIP endpoint after waiting an interval period of DIFS; and

scheduling next invitation to said VoIP endpoint to a future time T₀ that is a packetization interval.

16. The method as recited in claim 15, wherein said designated station is able to transmit an invitation CTS at said scheduled future time T₀.

17. The method as recited in claim 16, further comprising the step of repeating said method until all frames from said VoIP endpoints are transmitted.

12. A method for providing priority access to 802.11 endpoints comprising the steps of:

sending an unsolicited Clear To Send (CTS) frame from a designated station without requiring a Request to Send (RTS) frame from a first station, said CTS frame including a field identifying said first station for commencing transmission, and a field indicating a duration;

deferring any transmissions of stations other than said first station until after said duration indicated in said CTS frame has passed, wherein the sending and deferring occur during a contention period; and

inviting said first station to transmit by transmitting a Clear to Send (CTS) directed to said first station at a time immediately prior to an invitation window that is before said first station has gone into a back-off mode,

wherein said invitation window w is set to;

w =(DIFS+ω

+CW_min·

t_slot·

I(busy))

wherein ω

is the range of symmetric jitter in T₀,;

I (busy) is an indicator function that is 1 if the medium is busy at the scheduled beginning of an invitation window and 0 otherwise;

w is an invitation window;

DIFS is a DCF interframe space;

CW_min is a minimum contention window size; and

t_slotis a slot time and t zero is a first packetization interval.

14. The method as recited in claim 12, wherein said invitation window w is as small as a DCF Interframe Space (DIFS).

18. A method for providing priority access to 802.11 endpoints comprising the steps of:

sending an unsolicited Clear To Send (CTS) frame from a designated station without requiring a Request to Send (RTS) frame from a first station, said CTS frame including a field identifying said first station for commencing transmission, and a field indicating a duration;

deferring any transmissions of stations other than said first station until after said duration indicated in said CTS frame has passed, wherein the sending and deferring occur during a contention period, wherein a signaling protocol is used to detect a first frame of a transmission;

identifying a frame that is transmitted without back-off using a synchronization algorithm P; and

using said frame as a reference for scheduling invitation windows for subsequent frames occurring after said frame without any collision, wherein said synchronization algorithm P defines the width of an invitation window in a steady state as;

Δ

=PIFS+Tcrs+w, wherein Tcts is the time to transmit a CTS frame, wherein PIFS is a point interframe space in a coordination function and w is an invitation window.

19. The method as recited in claim 18, further comprising the steps of:

signaling a successful completion of call establishment as soon as a signaling message to an endpoint indicating successful call establishment is observed; and

starting to protect said wireless medium by transmitting CTS frames to said endpoint.

20. The method as recited in claim 19, further comprising the steps of:

setting the duration of a CTS to cover free periods between already scheduled invitations to other voice terminals, the duration of CTS being divided into windows of width ≦

PIFS+Tcrs+DIFS+CW_mintslot;

continuing protection until a first media frame from an endpoint in said first station is observed; and

setting T_sched to be the end of an immediately preceding invitation window for said endpoint in said first station.

21. The method as recited in claim 20, further comprising the steps of:

scheduling a next invitation window at the beginning of a new scheduled window of width Δ

+d starting at a time T₀−

ω

/2−

DIFS into a future T_sched, wherein d is the interval between said future T_sched and the time a first media frame appeared on said wireless medium; and

setting said future T_sched to the beginning of said new scheduled window.

22. The method as recited in claim 21, further comprising the steps of:

wherein when said medium is not busy at said future T_sched, said endpoint will not go into a back-off mode, transmitting said frame at DIFS after said wireless medium becomes ready; and

scheduling the beginning of a next invitation window of width Δ

, at T₀−

ω

/2−

DIFS into a future time, as measured from the time said frame appeared on said wireless medium.

23. The method as recited in claim 21, further comprising the steps of:

wherein when said wireless medium is busy at said future T_sched, and if said endpoint has gone into back-off, said designated station reserving said wireless medium when a current transmission ends;

said designated station providing said new scheduled invitation window to said endpoint in said first station; and

scheduling another next invitation window at the beginning of a second new scheduled window of width Δ

+d’

starting at a time T₀−

ω

/2−

DIFS into a second future T_sched, wherein d′

is the interval between said second future T_sched and the time another media frame appeared on said wireless medium; and

setting said second future T_sched to the beginning of said second new scheduled window.

24. The method as recited in claim 22, further comprising the steps of:

scheduling subsequent invitation windows with window width Δ

at T₀ into the future from the start of a current window in a steady state.

25. The method as recited in claim 19, further comprising the steps of:

observing a signaling message which indicates the end of a call; and

stopping the step of scheduling subsequent invitation windows.

26. The method as recited in claim 23, further comprising the steps of:

observing a signaling message which indicates the end of a call; and

stopping the step of scheduling subsequent invitation windows.

27. The method as recited in claim 18, further comprising the steps of:

identifying a signaling frame indicating an emergency call sent from said VoIP endpoint in a signaling server;

identifying a frame transmitted without back-off and using said frame as a reference to schedule invitation windows for subsequent frames without any collision; and

protecting said medium by transmitting CTS frames to said VoIP endpoint.