Tiered contention multiple access(TCMA): a method for priority-based shared channel access

• US 20070019665A1
• Filed: 08/21/2006
• Published: 01/25/2007
• Est. Priority Date: 11/03/2000
• Status: Active Grant

• Current Assignee: AT&T Intellectual Property II LP (AT&T, Inc.), AT&T Properties, LLC (AT&T, Inc.)
• Original Assignee: AT&T Corporation (AT&T, Inc.)
• Inventors: Benveniste, Mathilde
• Granted Patent: US 7,983,271 B2
• Time in Patent Office: Days
• US Class Current: 370/445
• CPC Class Codes: H04L 47/10 Flow control; Congestion control
• CPC Class Codes: H04L 47/2416 Real-time traffic
• CPC Class Codes: H04L 47/2433 Allocation of priorities to traffic types
• CPC Class Codes: H04L 47/245 using preemption
• CPC Class Codes: H04L 47/283 in response to processing delays, e.g. caused by jitter or round trip time [RTT]
• CPC Class Codes: H04L 47/32 by discarding or delaying data units, e.g. packets or frames
• CPC Class Codes: H04L 47/6275 based on priority
• CPC Class Codes: H04W 28/02 Traffic management, e.g. flow control or congestion control
• CPC Class Codes: H04W 28/0252 per individual bearer or channel dynamic wireless traffic scheduling H04W72/12
• CPC Class Codes: H04W 56/00 Synchronisation arrangements
• CPC Class Codes: H04W 72/542 using measured or perceived quality
• CPC Class Codes: H04W 72/569 of the traffic information
• CPC Class Codes: H04W 74/02 Hybrid access
• CPC Class Codes: H04W 8/04 Registration at HLR or HSS [Home Subscriber Server]
• CPC Class Codes: H04W 84/12 WLAN [Wireless Local Area Networks]

Abstract

Quality of Service (QoS) support is provided by means of a Tiered Contention Multiple Access (TCMA) distributed medium access protocol that schedules transmission of different types of traffic based on their service quality specifications. In one embodiment, a wireless station is supplied with data from a source having a lower QoS priority QoS(A), such as file transfer data. Another wireless station is supplied with data from a source having a higher QoS priority QoS(B), such as voice and video data. Each wireless station can determine the urgency class of its pending packets according to a scheduling algorithm. For example file transfer data is assigned lower urgency class and voice and video data is assigned higher urgency class. There are several urgency classes which indicate the desired ordering. Pending packets in a given urgency class are transmitted before transmitting packets of a lower urgency class by relying on class-differentiated urgency arbitration times (UATs), which are the idle time intervals required before the random backoff counter is decreased. In another embodiment packets are reclassified in real time with a scheduling algorithm that adjusts the class assigned to packets based on observed performance parameters and according to negotiated QoS-based requirements. Further, for packets assigned the same arbitration time, additional differentiation into more urgency classes is achieved in terms of the contention resolution mechanism employed, thus yielding hybrid packet prioritization methods. An Enhanced DCF Parameter Set is contained in a control packet sent by the AP to the associated stations, which contains class differentiated parameter values necessary to support the TCMA. These parameters can be changed based on different algorithms to support call admission and flow control functions and to meet the requirements of service level agreements.

Claims

1. A method for a distributed medium access protocol that schedules transmission of different types of packets on a channel based on a service quality specification for each type of packet, comprising:

determining in a first wireless station a first urgency class of data having a low QoS priority;

assigning a first class-differentiated urgency arbitration time to said data having a lower QoS priority;

determining in a second wireless station a second urgency class of data having a high QoS priority;

assigning a second class-differentiated urgency arbitration time shorter than said first time, to said data having a higher QoS priority; and

transmitting from said second wireless station pending packets in said second urgency class before transmitting from said first wireless station pending packets in said first urgency class.

2. The method of claim 1, wherein:

said urgency classes each have a corresponding urgency arbitration time that must expire before starting a random backoff interval for packets assigned to that urgency class.

3. The method of claim 1, which further comprises:

assigning a longer urgency arbitration time to file transfer data with a lower QoS priority; and

assigning a shorter urgency arbitration time to voice and video data with a higher QoS priority.

4. The method of claim 2, wherein:

said random backoff interval is calculated based on a contention window range which has an initial lower value and an initial upper value, which are functions of the urgency class.

5. The method of claim 2, wherein:

said random backoff interval is selected randomly from a statistical distribution, whose mean and variance are set adaptively in response to an observed traffic intensity.

6. The method of claim 2, which further comprises:

differentiating between different urgency class transmissions with class-specific parameters of the probability distribution used to generate random backoff times and class-specific backoff retry adjustment functions.

7. The method of claim 2, which further comprises:

differentiating between different urgency class transmissions with a persistence factor, pf_i, that is different for each class i, which is used to multiply a backoff window from which backoff counters will be drawn randomly upon transmission retrial.

8. The method of claim 2, which further comprises:

differentiating between different urgency class transmissions with a new backoff range determined by traffic congestion estimates.

9. The method of claim 8, wherein:

said congestion estimates are derived from data that include feedback on success or failure of a transmission attempt.

10. The method of claim 8, wherein:

said congestion estimates are derived from data that include feedback on a number of re-transmissions attempted by a node.

11. The method of claim 8, wherein:

said congestion estimates are derived from data that include feedback on a number of re-transmissions attempted by neighbor nodes.

12. The method of claim 8, wherein:

said congestion estimates are derived from data that include feedback on age of retrials of transmissions attempted.

13. The method of claim 8, wherein:

said congestion estimates are derived from data that include feedback on attempted transmissions provided in reservation messages.

14. The method of claim 8, wherein:

said congestion estimates are derived from data that include feedback on attempted transmissions provided in request to send and clear to send messages.

15. The method of claim 8, wherein:

said congestion estimates are derived from data that include feedback on attempted transmissions provided in headers of transmitted packets.

16. A method for a medium access protocol that schedules transmission of packets from a plurality of nodes on a channel, comprising the steps of:

employing a backoff countdown procedure for channel access;

monitoring traffic intensity changes continuously and providing feedback to the MAC sublayer of contending nodes;

adjusting a backoff counter of each of a plurality of contending nodes to current congestion levels in time intervals shorter than required for the completion of a transmission attempt; and

adjusting such backoff counter in a way that enables older packets to be transmitted before newer ones with high probability, thus minimizing the latency jitter.

17. The method for a medium access protocol of claim 16, which further comprises:

adjusting such backoff counter in a way that their relative ordering is preserved.

18. A method for a medium access protocol that schedules transmission of packets from a plurality of nodes on a channel, comprising the steps of:

employing a backoff countdown procedure for random channel access;

monitoring the traffic continuously and providing feedback to the MAC sublayer of contending nodes; and

adjusting the parameters of a random distribution from which the backoff counter is drawn upon initiation of a transmission attempt for each of a plurality of contending nodes to reflect current congestion levels.

19. The method for a medium access protocol of claim 18, which further comprises:

adjusting a backoff counter of each of a plurality of backlogged nodes to reflect current contention levels in time intervals shorter than required for the completion of a transmission attempt; and

adjusting such backoff counters in a way that enables older packets to be transmitted before newer ones with high probability, thus minimizing the latency jitter.

20. The method for a medium access protocol of claim 18, which further comprises:

obtaining traffic intensity measurements continuously and providing feedback to the MAC sublayer of contending nodes.

21. The method for a medium access protocol of claim 18, which further comprises:

obtaining feedback on the success status of transmissions and channel idle time continuously and providing such feedback to the MAC sublayer of contending nodes.

22. The method for a medium access protocol of claim 18, which further comprises:

employing feedback information to estimate the expected number of backlogged nodes; and

using such estimate for the purpose of backoff-related adjustments.

23. The method for a medium access protocol of claim 18, which further comprises:

employing feedback information to estimate the expected number of backlogged nodes; and

using such estimate for the purpose of backoff-related adjustments.

24. The method for a medium access protocol of claim 18, which further comprises:

employing a wireless channel; and

performing the monitoring of the channel at the access port.

25. The method for a medium access protocol of claim 18, which further comprises:

employing a wireless channel; and

performing the monitoring of the channel at each of the contending nodes.

26. The method for a medium access protocol of claim 18, which further comprises:

determining system-wide adjustments at the access port; and

supplying such adjustments to all nodes.

27. The method for a medium access protocol of claim 19, which further comprises:

adjusting such backoff counter so that the relative ordering is preserved.