## 4 Related Work
### Multipath Transmission  
In recent years, researchers have been exploring ways to improve transmission security and reliability in heterogeneous network environments. Heterogeneous networks, such as satellite networks, the wired Internet, and mobile communication networks, face numerous challenges in data transmission due to their complex and variable characteristics. Multipath transmission protocols use multiple available paths to meet strict quality of service (QoS)constraints, achieving goals such as low latency while completing reliable transmission [41]. However, the traditional TCP protocol can only achieve single point-to-point transmission, and can only re-establish the connection after encountering threats such as attacks that cause transmission interruption. Therefore, researchers optimized TCP multipath transmission and proposed algorithms such as SCTP [42] and CMT [43] that can transmit the sender's data concurrently through different paths. However, these algorithms still have problems such as inappropriate packet scheduling, unnecessary packet retransmission, unnecessary congestion window (CWND) reduction, and receiver buffer blocking (RBB) [44]. In order to solve these problems, researchers further optimized the traditional TCP algorithm and proposed MPTCP [45] to use multiple paths to improve the resource utilization of the transmission path. MPTCP can not only transmit data packets through different paths according to different strategies, but also has a congestion control (CC) mechanism to manage network load and avoid congestion. [PERSON] et al. [46] proposed an SCTP extension to mitigate the impact of packet loss in lossy environments and limit redundant data transmission on different paths, thereby minimizing network congestion. [PERSON] et al. [47] proposed a selective redundant multipath transmission (SRMT) strategy that uses the primary path to transmit data and the secondary path to transmit redundant data. [PERSON] et al. [48] proposed an efficient SCTP multipath scheme (MPSCTP) that transmits packets on multiple paths simultaneously. MPSCTP solves the problems of packet reordering and invalid CWND growth and improves the efficiency of multipath transmission. MPSCTP was later enhanced to include full path delay, taking into account the data rate on each channel, thereby minimizing block delays on different channels. Similar to SCTP, MPTCP is a connection-oriented multi-host standard protocol designed to distribute traffic between different routes and provide transparency at the application layer. In MPTCP, a session to be transmitted is usually divided into multiple different data substreams for transmission, and packet loss on different paths can be detected and reordered at the receiving end. [PERSON] et al. [49] further optimized the MPTCP algorithm to address the problem that the system often misjudges random packet loss as congestion loss, and proposed a flow-based transmission model to improve the stability of the transmission system. [PERSON] et al. [50] proposed a packet-differentiated OLIA (D-OLIA) based on packet loss, combining the delay jitter and CWND jitter eigenvalues to determine the type of packet loss, making up for the shortcomings of simply judging by delay or CWND. [PERSON] and [PERSON] [51] proposed a new heterogeneous network multipath transmission algorithm, which uses the MPTCP algorithm and the receiving end buffer scheduling strategy to estimate out-of-order packets and allocate packets accordingly based on the performance differences of each sub-flow, effectively balancing network throughput and delay performance. [PERSON] et al. [52] studied how to minimize data transmission time in time-varying networks. The authors proposed a one-time solver that can solve the MDDT problem in polynomial time and verified the effectiveness of the proposed algorithm. [PERSON] et al. [53] proposed an IMPNC transmission scheme to solve the problem of traditional TCP single-path transmission delay in low-orbit satellite networks.