Dynamic Retransmission Timer for Vehicular Ad Hoc Networks
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Solution Overview
Problem
Existing packet retransmission algorithms in TCP do not account for network operating conditions, leading to inefficient retransmission strategies in opportunistic ad hoc networks, such as vehicular ad hoc networks, which can result in network overload due to multiple copies of unacknowledged packets.
Innovation Solution
A method for operating opportunistic relaying networks that involves transmitting payload data to a selected device based on local conditions, including buffer vacancy, using an opportunistic routing algorithm to set a retransmit timer period as a minimum value multiplied by an inverse function of the buffer vacancy of the selected device, and repeating the process for unacknowledged packets.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the standard TCP backoff algorithm is used for retransmission, then the risk of overloading the network with multiple copies of retransmitted packets is reduced, but the retransmission strategy does not account for network operating conditions leading to inefficiency
Solution Approach 1:
The retransmission timer period is made dynamic by adjusting it based on the buffer vacancy of the selected device. The timer period is set to a minimum value multiplied by an inverse function of the buffer vacancy, allowing the system to adapt retransmission timing to current network conditions rather than using a fixed backoff algorithm
Solution Approach 2:
The system implements feedback by monitoring the buffer vacancy of receiving devices and using this information to adjust retransmission timing. The source device receives status data including buffer vacancy indications from responding devices, and this feedback is used to calculate the appropriate retransmission timer period
2Speed
If retransmission timer period is set to minimum value, then retransmission speed is improved, but network overload may occur due to multiple unacknowledged packet copies
Solution Approach 1:
The retransmission timer period parameter is changed dynamically based on network conditions. Instead of using a fixed minimum timer period, the system calculates the timer period as a minimum value multiplied by an inverse function of the selected device's buffer vacancy, adjusting the parameter to balance speed and network load
3Quantity of substance
If the retransmission timer period is increased to reduce network overload, then the number of packet copies is reduced, but retransmission efficiency decreases
Solution Approach 1:
The system dynamically adjusts the retransmission timer period parameter based on real-time buffer vacancy information. By setting the timer period to minimum value multiplied by an inverse function of buffer vacancy, the system optimizes the parameter to achieve both reduced network overload and maintained retransmission efficiency
Solution Approach 2:
The system uses feedback from buffer vacancy status to intelligently adjust the retransmission timer period. This feedback mechanism allows the system to increase the timer period only when necessary (when buffer vacancy is low) and maintain minimum period when conditions allow, thus balancing network load reduction with retransmission efficiency
Data Source
AI summary
A number of data relay devices, e.g. mobile telephones, (10, 20, 30, 40, 50, 60, 70, 80), are conveyed by vehicles and move relative to each other. They form a vehicular ad hoc wireless network (19, 29, 39, 49), etc in which data stored by a device (20) (either own-generated or relayed from another device (10) is transmitted either directly or by means of one or more other devices (30) to a network access point (90) which interfaces with a cellular network. When two devices (20, 30) come into proximity to each other, they use an opportunistic routing algorithm to determine a forwarding direction for the data. A retransmit timer is triggered on transmission of data, and messages which are unacknowledged at the expiry of the timer period are retransmitted. The timer period dynamically follows local congestion conditions and is recalculated at each transmission by the expression, timer minimum period/recent forwarding success(t). The current recent forwarding success at time t, RFS(t), is calculated from the RFS(t−1) calculated for the immediately preceding transmission and from the current forwarding success, CFS, by the expression RFS(t)=4/5 RFS(t−1)+1/5 CFS(t) where CFS is the square of the ratio of the available buffer space in the target device to the size of the payload in the source device.