Random medium access methods with backoff adaptation to traffic
Using low PF values in conjunction with traffic-adapted contention windows leads to substantial decreases in delay and jitter. In general, adaptation to traffic reduces contention or delay: opening up the contention window in congestion and closing it on relief. Residual backoff adaptation provides for the reduction of the already decremented backoff values of stations that interrupted the backoff countdown process due to a transmission. It is good to adapt both the contention window and the residual backoff in order to avoid jitter. Otherwise, if the contention window is reduced but residual backoffs stay unchanged, new arrivals will enjoy shorter backoff delays than older ones, resulting in greater jitter. Adjusting both preserves the relative ordering of backoff counter values, which implies also some form of age ordering. Different adjustments can be applied to different priority traffic.
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 at a plurality of nodes in a network, an urgency class for each of a plurality of pending packets according to a scheduling algorithm;
transmitting pending packets in a given urgency class before transmitting packets of a lower urgency class;
remembering a number of transmission attempts by a node for a last transmission of same node;
estimating from said number of transmission attempts a current congestion level that is experienced; and
adjusting a backoff counter to the current congestion level to provide a dispersion of packet traffic bursts.
2. The method for a distributed medium access protocol of claim 1 , which further comprises:
broadcasting with each transmission the number of transmission attempts by a node;
estimating from said number of transmission attempts received from other nodes the current congestion level that is experienced; and
adjusting a backoff counter to the current congestion level to provide a dispersion of packet traffic bursts.
3. The method for a distributed medium access protocol of claim 1 , which further comprises:
remembering the number of transmission attempts for packets of every urgency class by a node for the a last transmission in that class of same node;
estimating from said number of transmission attempts the current congestion that is experienced by the an urgency class of a pending packet; and
adjusting a backoff counter for the pending packet to the current congestion level to provide a dispersion of packet traffic bursts.
4. The method for a distributed medium access protocol of claim 1 , which further comprises:
broadcasting with each transmission the number of transmission attempts by a node and the assigned urgency class;
estimating from said number of transmission attempts received from other nodes the current congestion level that is experienced by an urgency class of a pending packet; and
adjusting a backoff counter of the pending packet to the current congestion level to provide a dispersion of packet traffic bursts.
5. The method for a distributed medium access protocol of claim 1 , which further comprises:
initializing backoff counters with a relatively longer value, and then decreasing the value upon transmission failure and retrial.
6. The method for a distributed medium access protocol of claim 1 , which further comprises:
remembering the number of transmission attempts by a node for the last transmission of same node;
estimating from said number of transmission attempts the current congestion level that is experienced; and
adjusting a persistence probability to current congestion level to provide a dispersion of packet traffic bursts.
7. The method for a distributed medium access protocol of claim 1 , which further comprises:
broadcasting with each transmission the number of transmission attempts by a node;
estimating from said number of transmission attempts received from other nodes the current congestion level that is experienced; and
adjusting a persistence probability to the current congestion level to provide a dispersion of packet traffic bursts.
8. The method for a distributed medium access protocol of claim 1 , which further comprises:
remembering the number of transmission attempts for packets of every urgency class by a node for a last transmission in that class of same node;
estimating from said number of transmission attempts the current congestion level that is experienced by an urgency class of a pending packet; and
adjusting a persistence probability for the pending packet to current congestion level to provide a dispersion of packet traffic bursts.
9. The method for a distributed medium access protocol of claim 1 , which further comprises:
broadcasting with each transmission the number of transmission attempts by a node and the assigned urgency class;
estimating from said number of transmission attempts received from other nodes the current congestion level that is experienced by an urgency class of a pending packet; and
adjusting a persistence probability of the pending packet to the current congestion level to provide a dispersion of packet traffic bursts.
10. The method for a distributed medium access protocol of claim 1 , which further comprises:
initializing a persistence probability with a relatively lower value, and then increasing the value upon transmission failure and retrial.
11. The method for a distributed medium access protocol of claim 1 , which further comprises:
establishing criteria for cancellation of transmission of a packet associated with packet delay.
12. The method for a distributed medium access protocol of claim 1 , which further comprises:
applying backoff prior to attempting any transmission.
13. The method for a distributed medium access protocol of claim 1 , which further comprises:
checking for permission to transmit by using a specified persistence probability prior to attempting any transmission.
14. The method for a distributed medium access protocol of claim 1 , wherein said network is a wireless network.
15. The method for a distributed medium access protocol of claim 1 , wherein said network is a cellular packet network.
16. The method for a distributed medium access protocol of claim 1 , wherein said network comprises one or more multi-channel air interface systems in accordance with at least one of: Frequency Division Multiple Access (FDMA), Time Division Multiple Access (TDMA), Orthogonal Frequency Division Multiplexing (OFDM) or Code Division Multiple Access (CDMA).