# A Brief Review of Multipath TCP for Vehicular Networks
## 3 Congestion Control and Scheduler
### Scheduler
#### 3.2.2 Scheduler with AI
\begin{table}
\begin{tabular}{p{113.8 pt} p{113.8 pt} p{113.8 pt} p{113.8 pt}} \hline \hline
**Main Metrics or Key Idea** & **Publication** & **Research Summary** & **Limitation/Advantages** \\ \hline Queuing delays and packet drops & [PERSON] et al. [66] & ReMP duplicates packets over all subflows in order to obtain reliability by considering both queuing delays and packet drops. & Reliable transmission/High overhead \\ \hline Bandwidth & [PERSON] [67] & A proposal that selects packets from shared sending buffer and schedules packets on each subflow based on its estimated bandwidth. & Load balancing/Consider bandwidth only \\ \hline Path capacity & [PERSON] et al. [68] & A proposal that decides scheduling policy based on the estimated path capacity of the subflows. & Load balancing/More extensive experiments are needed \\ \hline Transmission data & [PERSON] et al. [70] & An algorithm that suppresses RTTs by limiting the amount of transmission data. & Suppressing RTTs/Reduction of transmission data \\ \hline Data-sorting cost and transfer time & [PERSON] et al. [71] & A data distribution method for reducing the data-sorting cost of the receiver buffer and a path-failure detection and recovery mechanism for preventing data transfer stalling. & Reducing data sorting cost and improving throughput/Without considering loss rate when distributing data \\ \hline Download time & [PERSON] et al. [72] & DEMS, a scheduler aims at reducing the data chunk download time over multiple paths, especially benefiting medium size files and small size web pages. & Reducing download time/Only focusing on two paths \\ \hline HoL & [PERSON] et al. [73] & A proposal that aims to minimize head-of-line (HoL) blocking at the receiver side in heterogeneous networks. & Minimizing HoL/More elements of heterogeneity should be considered \\ \hline RTT & [PERSON] et al. [74] & A proposal that not only estimates the arrival time of packets on transmitting path, but also estimates the data delivery time on the other paths, in order to achieve the synchronization of data reception through all paths. & Estimating the arrival time of packets on all paths/Consider RTT only \\ \hline RTT and loss rate & [PERSON] et al. [75] & An algorithm that fixes the scheduling value based on the estimated data amount on all transmitting paths. & Reducing delay difference of paths/Vulnerability in highly dynamic networks \\ \hline RTT, loss rate, and cwnd & [PERSON] et al. [76] & An algorithm that calculates the latency based on the scheduling path and the states of other transmitting paths. & Reducing delay difference of paths/Vulnerability in bursty losses \\ \hline Delay & [PERSON] et al. [77] & A proposal that freezes a slow path temporarily in order to ensure a fast transmission of data for small flows when the latency difference of the slow path and fast path is significant. & Improving overall transmission rate/Underutilization of available paths \\ \hline Data distribution way & [PERSON] et al. [78] & A generic framework that can change the data distribution way over the subflows. & Capability of testing different schedulers of MPTCP/Limited set of traffic classes \\ \hline Delay & [PERSON] et al. [79] & A proposal that improves the link utilization rate and eliminates the out-of-ordered packets in the receiver buffer. & Improving link utilization rate and in-order packets arrival rate/TCP fairness has not been tested yet \\ \hline Learning-based & [PERSON] et al. [80] & A scheduling policy that applies reinforcement learning to enable adaptive scheduling for various network conditions and traffic patterns. & Dynamically generate packet scheduling policy/Need time to train \\ \hline \hline \end{tabular}
\end{table} 
Table 3: \(Cont.\)