Preemptive packet transmission
Disclosed herein is technology to reduce latency of frames through a network device supporting various priorities. In an implementation, a method comprises configuring one or more priorities with a preemptive right over other one or more of said plurality of priorities; receiving frames in a sequence, each of the frames having a frame priority comprising of one of said plurality of priorities; queuing the received frames in a predetermined order based on a frame arrival time and the frame priority; transmitting a current frame based on a current frame priority and current frame arrival time; stopping transmission of the current frame when a later frame in the sequence is received that has a later frame priority with preemptive right over the current frame priority; transmitting an invalid frame check sequence; transmitting the later frame; and restarting the transmission of the current frame after transmitting the later frame.
1. A method to reduce latency of frames through a network device supporting a plurality of frame priorities, the method comprising:
configuring said plurality of frame priorities, wherein each frame priority of said plurality of priorities specifies a preemptive right, a priority right or no right over each of the other frame priorities of said plurality of priorities;
receiving frames in a sequence, wherein each of the frames is associated with a frame priority comprising of one of said plurality of frame priorities;
queuing each of the received frames in a predetermined order based on a frame arrival time and the frame priority associated with the received frame;
transmitting a current frame;
stopping transmission of the current frame when a later frame in the sequence is received that is associated with a frame priority specifying a preemptive right over the frame priority associated with the current frame;
transmitting an invalid frame check sequence;
transmitting the later frame; and
restarting the transmission of the current frame after transmitting the later frame.
2. The method of claim 1 further comprising ordering the transmission of the frames based at least in part on the sequence prior to stopping the transmission.
3. The method of claim 1 wherein restarting the transmission of the current frame after transmitting the later frame comprises restarting the transmission of the current frame when there are no other later frames awaiting transmission associated with a frame priority specifying a priority right over the frame priority associated with the current frame.
4. The method of claim 1 further comprising monitoring for later frames in the sequence associated with a frame priority that specifies a preemptive right over the frame priority associated with the current frame.
5. The method of claim 4 wherein transmitting the invalid frame check sequence comprises transmitting the invalid frame check sequence in response to detecting the later frame associated with the frame priority having preemptive right over the current frame.
6. The method of claim 1 further comprising, after stopping the transmission of the current frame, retaining the current frame in queue.
7. The method of claim 1 further comprising, after completing the transmission of the current frame, deleting the current frame from the queue.
8. A network device comprising:
a network interface that receives frames in a sequence, wherein each frame is associated with a frame priority of a plurality of frame priorities, and each frame priority of said plurality of frame priorities specifies a preemptive right, a priority right or no right over each of the other frame priorities of said plurality of frame priorities, and transmits the frames to a downstream network device;
a controller operatively coupled with the network interface that stops transmission of a current frame in the sequence when a later frame in the sequence is received that is associated with a frame priority that specifies a preemptive right over a frame priority associated with the current frame, instructs the network interface to transmit an invalid frame check sequence, instructs the network interface to transmit the later frame, and instructs the network interface to restart the transmission of the current frame after transmitting the later frame.
9. The network device of claim 8 wherein the controller orders the transmission of the frames based at least in part on the sequence prior to stopping the transmission.
10. The network device of claim 8 wherein the controller restarts the transmission of the current frame after transmitting the later frame when there are no other later frames awaiting transmission associated with a frame priority that specifies a preemptive right over the frame priority associated with the current frame.
11. The network device of claim 8 wherein the controller monitors for later frames in the sequence associated with a frame priority that specifies a preemptive right over the frame priority associated with the current frame.
12. The network device of claim 11 wherein the controller instructs the network interface to transmit the invalid frame check sequence in response to detecting the later frame associated with the frame priority that specifies a preemptive right over the frame priority associated with current frame.
13. The network device of claim 8 wherein the controller maintains the current frame in the queue until the current frame is completely transmitted.
14. The network device of claim 8 wherein the controller removes the current frame from the queue after it is completely transmitted.
15. The network device of claim 8 wherein the upstream network device retains the current frame in queue and, when restarting the transmission of the current frame, restarts the transmission of all bits of the current frame.
16. A system comprising:
an upstream network device that receives frames in a sequence, wherein each frame is associated a frame priority of a plurality of frame priorities, and each frame priority of said plurality of frame priorities specifies a preemptive right, a priority right or no right over each of the other frame priorities of said plurality of frame priorities, transmits the frames, stops transmission of a current frame in the sequence when a later frame in the sequence is received that is associated with a frame priority with preemptive right over a frame priority associated with the current frame, transmits an invalid frame check sequence, transmits the later frame, and restarts the transmission of the earlier frame after transmitting the later frame; and
a downstream network device that receives the frames and the invalid frame check sequence.
17. The system of claim 16 wherein the upstream network device orders the transmission of the frames based at least in part on the sequence prior to stopping the transmission.
18. The system of claim 16 wherein the upstream network device restarts the transmission of the current frame after transmitting the later frame when there are no other later frames awaiting transmission that are associated with a frame priority with preemptive right over the frame priority associated with the current frame.
19. The system of claim 16 wherein the upstream network device monitors for later frames in the sequence associated with a frame priority with preemptive right over the frame priority associated with the current frame.
20. The system of claim 19 wherein the upstream network device transmits the invalid frame check sequence in response to detecting the later frame associated with the frame priority with preemptive right over the frame priority associated with the current frame.