Limited automatic repeat request protocol for frame-based communications channels
View Patent ↗In a frame-switched network, a sender sends frames to a receiver over a possibly unreliable channel. Sent frames include frame identifiers that can be used for a limited automatic repeat request. Upon receipt of a frame, the receiver determines, from the frame identifier, if frames prior to the received frame were lost in transit. If the receiver determines that it missed a prior frame, the receiver sends the sender a negative acknowledgment (nack) for the missed prior frame or frames. Otherwise, if the receiver receives a frame correctly, it does not acknowledge the frame. The frame identifiers can be a set of sequential integers with frames transmitted in sequential frame order. In some embodiments, when a receiver receives a frame out of order, the receiver buffers the out of order frame in a receiver buffer for a receive buffer period until preceding frames are received or a receive buffer period expires. The sender can send a reminder frame to the receiver to allow the receiver to detect a missed prior frame missing from an end of a frame sequence. The channel between the sender and the receiver can be a bidirectional channel over a telephone wire, a cable, a radio frequency link or a power wire. Multiple logical channels might be set up between a given sender-receiver pair, to allow for traffic of varying priorities.
1. A method comprising:
generating a frame at a send station in a network;
sending the frame from the send station to a receive station;
determining a period of inactivity that exceeds a threshold during which no further frames are sent from the send station to the receive station;
sending, in response to the determining, a reminder frame to the receive station identifying a last frame transmitted from the send station to the receive station.
2. The method of claim 1 wherein the generating comprises generating a frame at a send station in a network, the generated frame including a sequence number to identify the frame.
3. The method of claim 2 , wherein the generating comprises generating a frame at a send station in a network, the generated frame including a sequence number to identify the frame, sequence numbers being assigned to frames per destination or receive station and per priority level.
4. The method of claim 2 and further comprising:
receiving at the send station a negative acknowledgement (NACK) from the receive station indicating that one or more transmitted frames from the send station were not received by the received station; and
re-sending, in response to receiving the NACK, the one or more frames from the send station to the receive station.
5. The method of claim 1 and further comprising:
resetting a reminder timer for the after each time a frame is sent from the send station to the receive station;
wherein the determining comprises determining a period of inactivity based on an expiration of the reminder timer.
6. The method of claim 1 and further comprising:
storing a copy of the frame in a transmit buffer at the send station;
discarding the copy of the frame if a resource constraint at the send station is met.
7. The method of claim 6 wherein the discarding comprises:
discarding the copy of the frame if a maximum time for storing the frame is met.
8. The method of claim 6 wherein the discarding comprises:
discarding the copy of the frame if a maximum number of stored frames is met.
9. The method of claim 1 wherein the determining a period of inactivity comprises determining a period of inactivity that exceeds a threshold during which no further frames are sent from a send station to a MAC address of the receive station.