Multipath Receiver Reordering for 3GPP ATSSS Packet Ordering
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Solution Overview
Problem
Existing multipath receivers do not adequately support non-TCP traffic splitting, leading to out-of-order delivery and performance degradation due to varying path characteristics, which is not addressed by current ATSSS-LL and MPTCP protocols.
Innovation Solution
A multipath receiver with a reorder queue and controller that reorders data packets based on sequence numbering and negotiates reordering modes during MA PDU Sessions, using criteria like static or dynamic expiration timers and path-specific characteristics to handle packet loss and retransmission.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If data packets are distributed across multiple paths for non-TCP traffic splitting, then bandwidth utilization and throughput are improved, but out-of-order delivery occurs causing performance degradation
Solution Approach 1:
The system performs preliminary actions by establishing reordering buffers and sequence number tracking mechanisms before out-of-order packets arrive. The receiver prepares reordering structures in advance during MA PDU session establishment, enabling immediate reordering when packets arrive out of sequence without causing performance degradation
Solution Approach 2:
A reordering buffer acts as an intermediary between the multipath receiver and the upper layer protocol. This intermediary component temporarily stores out-of-order packets, reorders them based on sequence numbers, and delivers them in the correct order to the application layer, resolving the contradiction between parallel path transmission and ordered delivery
2Reliability
If strict in-order delivery is enforced for UDP traffic across multiple paths, then data stream ordering is maintained, but latency increases due to packet stalling
Solution Approach 1:
The system dynamically adjusts reordering behavior based on packet arrival patterns and path characteristics. When packets arrive in order, no reordering delay is applied. When out-of-order packets are detected, the system applies minimal necessary reordering delays, and uses expiration timers to release packets dynamically rather than enforcing static strict ordering, thereby reducing unnecessary latency
Solution Approach 2:
The system changes the ordering parameter from strict sequential ordering to sequence-number-based ordering with configurable tolerance. By modifying the reordering criterion to accept packets within a certain sequence gap threshold and using dynamic expiration timers, the system maintains adequate ordering while significantly reducing latency compared to strict in-order delivery
3Reliability
If reordering is activated for MA PDU Sessions, then data packet ordering is improved, but device complexity increases due to additional negotiation and queue management
Solution Approach 1:
The reordering mechanism is designed with multi-functionality to handle multiple protocol types (UDP, MP-DCCP, MP-QUIC) and multiple path configurations through a single unified implementation. The same reordering buffer and sequence number tracking logic serves all non-TCP traffic types, reducing overall system complexity compared to having separate reordering mechanisms for each protocol
Solution Approach 2:
The system implements self-service through automatic reordering buffer management including dynamic expiration timer adjustment, automatic sequence number gap detection, and autonomous packet release decisions. The reordering mechanism monitors its own state and adjusts its behavior without external intervention, reducing the complexity of external control logic
4Reliability
If packet loss detection is implemented in multipath protocols, then reliability is improved, but productivity decreases due to retransmission stalls
Solution Approach 1:
The system performs preliminary actions by pre-establishing multiple active paths and preparing alternative routing options before packet loss occurs. When packet loss is detected on one path, the system has already have standby paths ready, enabling seamless failover without transmission stalls, thus maintaining both reliability and productivity
Data Source
AI summary
A multipath receiver includes: a reorder queue configured to queue data packets received over multiple paths; and a reorder queue controller configured to reorder the data packets in the reorder queue according to a reorder criterion. The reorder queue controller is configured to allow Multi-Access Protocol Data Unit (MA PDU) Sessions based on Access Traffic Steering, Switching, and Splitting (ATSSS). The reorder queue controller is configured to choose to activate a reordering of the data packets. The reorder queue controller is configured to negotiate the activation of the reordering of the data packets with peers of an MA PDU Session based on an ATSSS use case, wherein in case reordering is activated, the data packets are queued in a reorder queue. The reorder criterion is based on a sequence numbering of the data packets of the MA PDU Session based on the ATSSS use case.