Tiered contention multiple access (TCMA): a method for priority-based shared channel access
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.
1. A method for transmitting a packet, the method comprising:
determining, at a node having a buffer, an urgency class for the packet according to a schedule, wherein each of a plurality of urgency classes is assigned a plurality of differentiating parameters with values that are different from values of other urgency classes, the plurality of differentiating parameters comprising a backoff window for drawing an initial backoff counter for the packet and a persistence factor, wherein the persistence factor is different for each urgency class of the plurality of urgency classes, and wherein the persistence factor is to derive a subsequent backoff window having a range of values from which a subsequent backoff counter value for the packet is drawn randomly from the range of values upon a transmission retrial of the packet; and
transmitting, by the node, the packet in the urgency class before transmitting another packet of a lower urgency class.
2. The method of claim 1 , further comprising:
remembering a number of transmission attempts by the node for a last transmission of the node;
estimating, from the number of transmission attempts, a current congestion level; and
adjusting the initial backoff counter for the packet responsive to the current congestion level.
3. The method of claim 1 , further comprising:
broadcasting, with each transmission attempt, a number of transmission attempts by the node of the packet;
estimating, from a number of transmission attempts received from other nodes, a current congestion level experienced by the other nodes for the urgency class of the packet; and
adjusting an initial backoff counter for a pending packet of the urgency class responsive to the current congestion level experienced by the other nodes for the urgency class of the packet.
4. The method of claim 1 , further comprising:
remembering a number of transmission attempts by the node for a last transmission in each urgency class of the plurality of urgency classes;
estimating, from the number of transmission attempts by the node, a current congestion level for the urgency class; and
adjusting an initial backoff counter for a pending packet of the urgency class responsive to the current congestion level.
5. The method of claim 1 , further comprising:
broadcasting, with each transmission attempt, a number of transmission attempts by the node of the packet and the urgency class of the packet;
estimating, from a number of transmission attempts received from other nodes, a current congestion level experienced by the other nodes for the urgency class of the packet; and
adjusting the initial backoff counter for the packet responsive to the current congestion level experienced by the other nodes for the urgency class of the packet.
6. The method of claim 4 , further comprising:
broadcasting, with each transmission attempt, a number of transmission attempts by the node of the packet and the urgency class of the packet;
further estimating, from a number of transmission attempts received from other nodes, the current congestion level experienced by the other nodes for the urgency class of the packet; and
further adjusting the initial backoff counter for the packet responsive to the current congestion level experienced by the other nodes for the urgency class of the packet.
7. The method of claim 1 , further comprising:
initializing the initial backoff counter and the subsequent backoff counter with a value, and then changing the value upon a transmission failure and retrial.
8. The method of claim 1 , further comprising:
remembering a number of transmission attempts by the node for a last transmission of the node;
estimating, from the number of transmission attempts, a current congestion level; and
adjusting a persistence probability responsive to the current congestion level.
9. The method of claim 1 , further comprising:
broadcasting, with each transmission attempt, a number of transmission attempts by the node of the packet;
estimating, from a number of transmission attempts received from other nodes, a current congestion level experienced by the other nodes; and
adjusting a persistence probability responsive to the current congestion level experienced by the other nodes.
10. The method of claim 8 , further comprising:
broadcasting, with each transmission attempt, a number of transmission attempts by the node;
further estimating, from a number of transmission attempts received from other nodes, the current congestion level experienced by the other nodes; and
further adjusting the persistence probability responsive to the current congestion level experienced by the other nodes.
11. The method of claim 1 , further comprising:
remembering a number of transmission attempts by the node for a last transmission in each urgency class of the plurality of urgency classes;
estimating, from the number of transmission attempts, a current congestion level for the urgency class of the packet; and
adjusting a persistence probability for the packet responsive to the current congestion level for the urgency class of the packet.
12. The method of claim 1 , further comprising:
broadcasting, with each transmission attempt, a number of transmission attempts by the node of the packet and the urgency class of the packet;
estimating, from a number of transmission attempts received from other nodes, a current congestion level experienced by the other nodes for the urgency class of the packet; and
adjusting a persistence probability of the packet responsive to the current congestion level experienced by the other nodes for the urgency class of the packet, in order to provide a dispersion of packet traffic bursts.
13. The method of claim 11 , further comprising:
broadcasting, with each transmission attempt, a number of transmission attempts by the node of the packet and the urgency class of the packet;
further estimating, from a number of transmission attempts received from other nodes, the current congestion level experienced by the other nodes for the urgency class of the packet; and
further adjusting the persistence probability of the packet responsive to the current congestion level experienced by the other nodes for the urgency class of the packet.
14. The method of claim 1 , further comprising:
initializing a persistence probability with a value, and then increasing the value upon a transmission failure and retrial.
15. The method of claim 1 , further comprising:
establishing a criterion for cancellation of transmission of the packet associated with a packet delay.
16. The method of claim 1 , further comprising:
applying a backoff prior to attempting the transmitting.
17. The method of claim 1 , further comprising:
checking for a permission to transmit by using a persistence probability prior to attempting the transmitting.
18. A non-transitory computer-readable medium storing a plurality of instructions which, when executed by a processor of a node having a buffer, cause the processor to perform operations for transmitting a packet, the operations comprising:
determining an urgency class for the packet according to a schedule, wherein each of a plurality of urgency classes is assigned a plurality of differentiating parameters with values that are different from values of other urgency classes, the plurality of differentiating parameters comprising a backoff window for drawing an initial backoff counter for the packet and a persistence factor, wherein the persistence factor is different for each urgency class of the plurality of urgency classes, and wherein the persistence factor is to derive a subsequent backoff window having a range of values from which a subsequent backoff counter value for the packet is drawn randomly from the range of values upon a transmission retrial of the packet; and
transmitting the packet in the urgency class before transmitting another packet of a lower urgency class.
19. An apparatus for transmitting a packet, the apparatus comprising:
a processor of a node; and
a computer-readable medium storing a plurality of instructions which, when executed by the processor, cause the processor to perform operations, the operations comprising:
determining an urgency class for the packet according to a schedule, wherein each of a plurality of urgency classes is assigned a plurality of differentiating parameters with values that are different from values of other urgency classes, the plurality of differentiating parameters comprising a backoff window for drawing an initial backoff counter for the packet and a persistence factor, wherein the persistence factor is different for each urgency class of the plurality of urgency classes, and wherein the persistence factor is to derive a subsequent backoff window having a range of values from which a subsequent backoff counter value for the packet is drawn randomly from the range of values upon a transmission retrial of the packet; and
transmitting the packet in the urgency class before transmitting another packet of a lower urgency class.
20. The apparatus of claim 19 , the operations further comprising:
remembering a number of transmission attempts by the node for a last transmission of the node;
estimating, from the number of transmission attempts, a current congestion level; and
adjusting the initial backoff counter for the packet responsive to the current congestion level.