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 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.
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 the steps of:
determining at a plurality of nodes in the access network, an urgency class of pending packets according to a scheduling algorithm;
using class-differentiated arbitration times, as idle time intervals required before transmission is attempted following a busy period on the medium; and
assigning shorter arbitration times to higher urgency classes.
2 . 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 the steps of:
determining at a plurality of nodes in the access network, an urgency class of pending packets according to a scheduling algorithm;
using class-differentiated arbitration times, as idle time intervals required before a backoff counter is decreased; and
assigning shorter arbitration times to higher urgency classes.
3 . The method for a distributed medium access protocol of claim 2 , which further comprises:
adjusting backoff probability functions in real time based on congestion estimates derived from a number of re-transmissions attempted by a node.
4 . The method for a distributed medium access protocol of claim 3 , which further comprises:
adjusting backoff probability functions in real time, based on congestion estimates derived from a number of re-transmissions attempted by each of its neighbor nodes.
5 . The method for a distributed medium access protocol of claim 2 , which further comprises:
adjusting backoff probability functions in real time based on class-specific congestion estimates derived from a number of re-transmissions attempted by a node.
6 . The method for a distributed medium access protocol of claim 3 , which further comprises:
adjusting backoff probability functions in real time based on class-specific congestion estimates derived from a number of re-transmissions attempted by each of its neighbor nodes.
7 . The method for a distributed medium access protocol of claim 2 , which further comprises:
adjusting backoff probability functions in real time at a node based on congestion estimates derived from the time spent by packets waiting for transmission.
8 . The method for a distributed medium access protocol of claim 7 , which further comprises:
adjusting backoff probability functions in real time at a node based on congestion estimates derived from the time spent by packets waiting for transmission at each of its neighbor nodes.
9 . The method for a distributed medium access protocol of claim 2 , which further comprises:
adjusting backoff probability functions in real time at a node based on class-specific congestion estimates derived from the time spent by packets of different classes waiting for transmission.
10 . The method for a distributed medium access protocol of claim 9 , which further comprises:
adjusting backoff probability functions in real time at a node based on class-specific congestion estimates derived from the time spent by packets of different classes waiting for transmission at each of its neighbor nodes.
11 . The method for a distributed medium access protocol of claim 1 , which further comprises:
further differentiating packets into urgency classes based on probability density functions of backoff counters whose superposition yields a uniform composite density function, thus achieving efficient dispersion of contending stations' backoff time.
12 . The method for a distributed medium access protocol of claim 2 , which further comprises:
further differentiating packets into urgency classes based on probability density functions of backoff counters whose superposition yields a uniform composite density function, thus achieving efficient dispersion of contending stations' backoff time.
13 . The method for a distributed medium access protocol of claim 1 , which further comprises:
further differentiating packets into urgency classes based on different persistence probabilities, by which permission is granted for transmission, for different packets that are assigned the same urgency arbitration time.
14 . The method for a distributed medium access protocol of claim 2 , which further comprises:
further differentiating packets into urgency classes based on different persistence probabilities, by which permission is granted for transmission, for different packets that are assigned the same urgency arbitration time.
15 . An apparatus 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:
means for determining at a plurality of nodes in the access network, an urgency class of pending packets according to a scheduling algorithm;
means for using class-differentiated arbitration times, as idle time intervals required before a backoff counter is decreased; and
means for assigning shorter arbitration times to higher urgency classes.
16 . The apparatus for a distributed medium access protocol of claim 15 , which further comprises:
means for adjusting backoff probability functions in real time based on congestion estimates derived from a number of re-transmissions attempted by a node.
17 . The apparatus for a distributed medium access protocol of claim 16 , which further comprises:
means for adjusting backoff probability functions in real time, based on congestion estimates derived from a number of re-transmissions attempted by each of its neighbor nodes.
18 . The apparatus for a distributed medium access protocol of claim 15 , which further comprises:
means for adjusting backoff probability functions in real time based on class-specific congestion estimates derived from a number of re-transmissions attempted by a node.
19 . The apparatus for a distributed medium access protocol of claim 16 , which further comprises:
means for adjusting backoff probability functions in real time based on class-specific congestion estimates derived from a number of re-transmissions attempted by each of its neighbor nodes.
20 . The apparatus for a distributed medium access protocol of claim 15 , which further comprises:
means for adjusting backoff probability functions in real time at a node based on congestion estimates derived from the time spent by packets waiting for transmission.