RACK Packet Mechanism for Asymmetric Communication Reliability
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Solution Overview
Problem
In communication systems, especially over the Internet or wireless networks, asymmetric availability in communication directions leads to issues where transmission data may disappear, and acknowledgement packets (ACK) from the opposite direction can still arrive, causing inefficiencies in retransmission control, particularly when a large number of data packets vanish consecutively, leading to delayed recovery and reduced throughput.
Innovation Solution
A communication system that employs a reception terminal to set an unarrival determination time for retransmission requests and repeatedly sends retransmission acknowledgement (RACK) packets if no next data packet arrives within this time, allowing the transmission terminal to specify and retransmit missing data packets using time difference information from ACK and RACK packets, which includes timestamps for accurate packet timing.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the retransmission timer set time is extended to accommodate packet round trip time variations, then reliability of retransmission control is improved, but communication efficiency deteriorates due to delayed detection of missing packets
Solution Approach 1:
The invention applies preliminary action by having the reception terminal proactively send RACK packets before the transmission terminal's retransmission timer expires. This allows the transmission terminal to detect missing packets earlier and initiate retransmission without waiting for the timer to timeout, thus resolving the contradiction between reliable detection (requiring extended timer) and communication efficiency (requiring quick detection).
Solution Approach 2:
The invention implements feedback by introducing a new RACK packet mechanism where the reception terminal provides feedback about expected sequence numbers to the transmission terminal. This feedback loop enables the transmission terminal to adjust its retransmission behavior based on real-time network conditions rather than relying solely on timer-based passive detection, improving both reliability and efficiency.
2Reliability
If time out retransmission is used to ensure reliable delivery, then reliability is improved, but communication efficiency deteriorates due to unnecessary retransmissions when delay occurs
Solution Approach 1:
The RACK packet mechanism provides continuous feedback from the reception terminal to the transmission terminal about which packets are expected. This allows the transmission terminal to distinguish between packets that are delayed (but will arrive) and packets that are truly lost, enabling selective retransmission only when necessary and avoiding unnecessary retransmissions that would occur with traditional time-out-based mechanisms.
Solution Approach 2:
By having the reception terminal send RACK packets in advance before the transmission terminal's retransmission timer expires, the system performs preliminary detection of missing packets. This allows the transmission terminal to take preliminary action (retransmission) only when actually needed, rather than waiting for timer expiration which may trigger unnecessary retransmissions.
3Device complexity
If conventional ACK packet mechanisms are used for retransmission control, then device complexity is minimized, but the ability to handle asymmetric communication availability deteriorates
Solution Approach 1:
The invention applies asymmetry by introducing a unidirectional RACK packet mechanism where only the reception terminal sends these special packets to the transmission terminal. This asymmetric approach allows the system to handle asymmetric communication availability (where one direction may have better reliability than the other) without requiring complex bidirectional modifications to both ACK and retransmission mechanisms, thus maintaining simplicity while improving adaptability.
Data Source
AI summary
A receive terminal setting a non-delivery determination time for determining that a next data packet is not delivered after transmitting an acknowledgement (ACK) packet for a received data packet; when the next data packet is not delivered within the non-delivery determination time, the receive terminal repeatedly transmits a retransmission request (RACK) packet prompting the transmission of the next data packet; a transmit terminal specifies a non-delivered data packet using time difference information based on the time-of-day information of the received ACK packet and RACK packet and retransmits the specified data packet to the receive terminal; the time-of-day information here is a time stamp added by the receive terminal to each of the ACK packet and RACK packet when transmitted, or a time stamp added by the transmit terminal to each of the ACK packet and RACK packet when received.