Multicast Retransmission via MAC Header Modification
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Solution Overview
Problem
In wireless networks, especially 802.11 WIFI networks, the lack of retries in broadcast and multicast transmissions leads to duplicate frames due to legacy receivers' inability to distinguish retransmissions, causing issues in encrypted environments where modifying destination addresses or BSSID to indicate retries results in costly re-encryption processes.
Innovation Solution
Modifying MAC header fields, particularly setting the retry bit and altering locally administered bits in MAC addresses, to prevent legacy systems from decrypting and thus discarding retransmissions, while allowing non-legacy systems to recognize and handle retransmissions without re-encryption.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the destination address or BSSID is modified to indicate retries in multicast transmissions, then legacy receivers can distinguish retransmissions from new transmissions, but re-encryption is required which consumes excessive processor resources
Solution Approach 1:
The solution segments the problem by treating legacy and non-legacy receivers differently. The access point modifies MAC header fields (such as setting the locally administered bit) specifically for legacy receivers to prevent them from processing retransmissions, while non-legacy receivers use the retry bit mechanism. This segmentation allows each receiver type to be handled with the most appropriate method, avoiding unnecessary re-encryption for all transmissions.
Solution Approach 2:
The invention changes parameters in the MAC header fields (such as the locally administered bit in destination address or BSSID) to create a distinction that legacy receivers can detect. These parameter changes are made in a way that does not require re-encryption of the frame body, as they are detected at the MAC layer before decryption attempts. Non-legacy receivers ignore these parameter changes and rely on the retry bit instead.
2Reliability
If retries are introduced in multicast transmissions, then transmission reliability improves, but legacy receivers generate duplicate frames because they cannot distinguish retransmissions from new transmissions
Solution Approach 1:
The solution applies preliminary anti-action by proactively preventing legacy receivers from processing retransmission frames. The access point modifies MAC header fields (such as setting the locally administered bit) in retransmitted frames before transmission, which causes legacy receivers to automatically discard these frames without attempting to process them as new transmissions. This preliminary modification prevents the harmful effect of duplicate frame generation at its source.
Solution Approach 2:
The modified MAC header fields act as an intermediary mechanism between the retransmission function and legacy receivers. By setting specific bits in the MAC header (such as the locally administered bit), the system creates an intermediate signal that legacy receivers can detect and use to identify retransmissions without requiring them to understand the retry bit mechanism or require re-encryption of the frame body.
3Productivity
If MAC header fields are modified to prevent legacy systems from decrypting retransmissions, then re-encryption costs are avoided, but compatibility with legacy systems must be maintained
Solution Approach 1:
The invention applies local quality by making specific, targeted modifications to certain fields within the MAC header (such as the locally administered bit in destination address or BSSID) rather than modifying the entire frame structure or requiring re-encryption. These localized modifications are sufficient to prevent legacy receivers from processing retransmissions while maintaining overall frame integrity and compatibility with the 802.11 standard.
Solution Approach 2:
Instead of trying to make legacy receivers understand and handle retransmissions correctly (the conventional approach), the invention inverts the approach by making retransmissions unrecognizable to legacy receivers through MAC header field modifications. This causes legacy receivers to automatically discard these frames, while non-legacy receivers that understand the retry bit mechanism can properly handle them. The problem is solved by making the solution work around legacy limitations rather than trying to overcome them.
Data Source
AI summary
Systems and methods for broadcast and multicast retransmissions within a protected wireless communications system are described. Retransmitted broadcast or multicast frames are designated by modification of fields or subfields in the MAC header of the frame which are constituent parts of the additional authentication data used to generate encryption keys. Such modifications cause legacy receivers to disregard the retransmitted frames or render legacy receivers to be unable to decrypt the retransmitted frame, avoiding the generation of duplicate frames. Non-legacy receivers recognizing the modification conventions can restore the MAC header to the original state and can reconstruct the original encryption keys and decrypt the retransmitted frames. A non-legacy transmitter can retransmit a frame without the need to re-encrypt the frame.