## 2 Methods
### Reliable Transmission Design Mechanism
#### 2.1.2 NACK Dynamic Adjustment Transmission Mechanism  
Packet reordering occurs when the receiving order of a flow of packets (or segments) differs from the order in which they were sent. Studies have shown that packet reordering is not a rare phenomenon and can have significant implications for data integrity and application performance [20]. Most previous research focused on the transport layer, including research on out-of-order algorithms related to the TCP protocols on the receiver side. Some of these processing algorithms have certain reference value for our out-of-order scenarios. Some algorithms, like state reconciliation [21], only solve the problem of congestion window reduction caused by out-of-order packets, but they do not solve the problem of false retransmissions. We compared several algorithms [20; 22] for handling packets out-of-order packets under the same link conditions and evaluated their deviation from the actual waiting time using the Root Mean Square Error (RMSE). The Fixed K Algorithm 2 adjusts the value of K by either increasing or decreasing a fixed amount based on the previous calculation. Its advantage is its simplicity in computation, but the downside is its slow convergence, especially during sudden changes in link reordering. The Half-Growth Algorithm 3, on the other hand, converges more quickly to the actual situation by calculating the average, but it is susceptible to the impact of sudden changes, particularly during packet loss situations, where it may lead to an overestimation of the sending time due to prolonged transmission. In addition, there is a Fixed Time Algorithm that tolerates fixed sending times, meaning it does nothing to handle reordering. We perform a comparative study of these algorithms in Section 3.1. Figure 1: Processing flow of reliable transmission. We used link aggregation to scale the original bandwidth and throughput to 10 G, but it also caused some problems. It is important to note that link aggregation can also lead to the out-of-order delivery of packets, which can cause unnecessary false retransmissions, resulting in a large number of NACKs and non-essential retransmission packets consuming a lot of bandwidth. ```
1:Input: L, dupthresh
2:if L > avg then
3: avg \(\leftarrow\) avg + K
4:else
5: avg \(\leftarrow\) avg - K
6:endif
7:dupthresh \(\leftarrow\) avg
```  
**Algorithm 2** Fixed K Algorithm  
In our scenario, packet reordering caused by link aggregation often leads to spurious retransmissions, which can result in significant bandwidth consumption, especially when the packet loss rate is high. To address this issue, we have implemented a mechanism during the processing of data packets that reduces the impact of reordering. The core idea of this mechanism can be summarized as dynamically setting the transmission time for a NACK based on the average arrival time of out-of-order packets. This approach aims to minimize excessive waiting while tolerating a certain degree of reordering. Figure 2 illustrates the internal data packet processing. In particular, this system includes a process for handling out-of-order packets. The method employed in this paper effectively reduces the occurrence of spurious retransmissions to some extent. The gray boxes in the flowchart provide further clarification of Algorithms 4 and 5 that we implemented. ```
1:Input: neck_timer, dupthresh
2:if neck_timer > dupthresh then
3: call back \"send rack to outside\"
4: clear rack
5:else
6: send task back to the loop
7:endif
```  
**Algorithm 3** Half-Growth Algorithm  
```
1:Input: L, dupthresh
2:if L > avg then
3: avg \(\leftarrow\) (1 - \(\alpha\)) \(\cdot\) avg + \(\alpha\) \(\cdot\) L
4:else
5: avg \(\leftarrow\) (1 - \(\alpha\cdot x\)) \(\cdot\) avg + (\(\alpha\cdot x\)) \(\cdot\) L
6:endif
7:dupthresh \(\leftarrow\) avg
```  
**Algorithm 4** Send NACK packet to outside  
In our scenario, packet reordering caused by link aggregation often leads to spurious retransmissions, which can result in significant bandwidth consumption, especially when the packet loss rate is high.