Multi-priority media access control method for multi-channel slotted ring networks
The present invention discloses a multi-priority media access control method for a multi-channel slotted ring network. In the slotted ring networks, each node has one tunable transmitter and one fixed receiver for data channels, and is able to inspect slot status on all channels. The header slot format defines the slot priorities on ring networks and limits which packets can be transmitted through the slots. By assigning slot priority based on two thresholds to raise and lower slot priority, multiple priority packets can be transmitted.
1. A multi-priority media access control method for a multi-channel slotted ring network having a plurality of nodes connected in a ring topology, a plurality of channels for transmitting data packets and control packets, and providing a plurality of slots that synchronously and circularly flow in one direction, every control packets carrying headers of slots of corresponding channels within a slot time and providing a priority value field corresponding to a slot in one channel, each node having a plurality of queues and a stack for one channel, each queue storing packets with the same priority and having a predefined high threshold and a predefined low threshold, the method comprising the steps of:
(A) setting the priority value fields of the control packets with priority values to identify a priority for each slot by:
(A1) calculating a waiting time of a queue when a node transmits a packet from the queue;
(A2) if the waiting time of the queue is larger than its high threshold, seeking a priority value field of the corresponding channel whose value is lower than the priority of the queue, pushing the value of the priority value field into its stack, and setting the priority value field with the priority of the queue; and
(A3) if the waiting time of the queue is smaller than its low threshold, seeking a priority value field of the corresponding channel whose value is the same as the priority of the queue, popping a value from the stack, and setting the priority value field with the popped value; and
(B) each node depending on the priority value fields of control packets to select a queue at every slot time in such a manner that the priority of a slot is the smallest priority of packets that can be carried by the slot.
2. The multi-priority media access control method as claimed in claim 1 , wherein the high threshold is larger than or equal to the low threshold.
3. The multi-priority media access control method as claimed in claim 2 , wherein the waiting time of a queue is an inter-transmitting interval from a transmission moment of its last packet to an event of transmitting the packet itself.
4. The multi-priority media access control method as claimed in claim 2 , wherein the waiting time of a queue is a delay time from a moment of determining to transmit a packet to a moment of starting to transmit the packet.
5. The multi-priority media access control method as claimed in claim 2 , wherein each node rechecks the waiting time of packets for a queue only after setting the priority of a slot on the corresponding channel of the queue.
6. The multi-priority media access control method as claimed in claim 2 , wherein the channels include a plurality of data channels for transmitting the data packets and a control channel for transmitting the control packets.
7. The multi-priority media access control method as claimed in claim 6 , wherein headers of slots of all data channels are carried on slots of the control channels, and every control packet carries the headers of slots of all channels within a slot time.
8. The multi-priority media access control method as claimed in claim 7 , wherein the control packet consists of a preamble field, a checksum field and a plurality of channel-reservation elements, each storing header information of the slot of the corresponding data channel at the same slot time, and the priority value field is provided in the channel-reservation element.