## 5 Conclusions  
In this paper, we present a novel SDN-based integrated satellite-terrestrial network architecture, in terms of a label-based AOS frame switching mechanism and optimized network protocols as follows:  
1. The label-based AOS frame switching mechanism is proposed to replace the unnecessary on-satellite time-energy-cost process of data unpacking-repacking caused by IP forwarding. In addition, a data communication network overhead is used for the managing and controlling message communication between nodes;
2. Distributed routing and label switching path setup is designed to realize terrestrial-terrestrial, satellite-terrestrial, and intra-satellite data transmission using the optimized OSPF protocol (i.e., flood-restraint and routing path computation under uni-directional link) and the constraint CSPF protocol and LDP protocol (i.e., under the multiple QoS requirements of port cost, port priority, link duration time, forward/backward bandwidth, and link latency);
3. A semi-physical platform constitutes a software platform and hardware that is used to validate the proposed mechanisms and optimized protocols. Still, there will be more work to do in the future:  
1. Source-destination SCIDs are still needed for the ingress-egress label edge routers in the label switching path setup. We aim to use the neighbor discovery protocol (NDP) for IP/MAC address learning, and thus fetch terminal IP addresses for the network management system, which qualifies source-destination IP addresses for label switching path setup without the source-destination SCIDs;
2. The **OAM** field in the **extended control field** of the AOS frame will be upgraded for fast link connection detection, enabling 1+1, 1:1, and 1:n working path protection with fast rerouting;
3. The completely optical switching approach will be used for high-speed data flows (e.g., 10/40/100 Gbps) without the necessity of optical-electronic transformation;
4. Since the ISTNs are primarily composed of GEO satellites, MEO satellites, and terrestrial networks, LEO satellites are the primary access network utilized by terrestrial terminals. Thus, the orbital speed and direction of LEO constellations need to be considered. In addition, the locations of multiple ground stations are critical for ISTNs;
5. Recent innovations and research on satellite communication will be studied, such as semantic routing, semantic addressing, and variable-length addressing for space-based infrastructure. Conceptualization, W.Z., X.J., Q.L., S.H., B.G. and S.L. ; methodology, W.Z. and B.G. ; software, W.Z., X.T. and M.M. ; hardware, T.F. ; validation, W.Z. and X.S. ; writing-original draft preparation, W.Z. ; writing-review and editing, X.J. and X.S. ; supervision, X.J. ; project administration, W.Z. All authors have read and agreed to the published version of the manuscript. This research is fully supported by GUET Excellent Graduate Thesis Program (Grant No. 19 YJPYBS03), Innovation Project of Guangxi Graduate Education (Grant No. YCBZ2022109), and New Technology Research University Cooperation Project of the 34 th Research Institute of China Electronics Technology Group Corporation, 2021 (Grant No. SF2126007). \begin{table}
\begin{tabular}{c c c c} \hline  & **vx\_simulator\_01** & **vx\_simulator\_02** & **vx\_simulator\_03** \\ \hline Forward LSP & Out-port: **3**1  & In-port: 1 \\  & Out-label: 0x00D2 & In-label: 0x00D2, Out-label: 0 xFFFF & In-label: 0 xFFFF \\ Backward LSP & In-port: **4**1  & Out-port: **4**, In-port: 1 \\  & In-label: 0 xFFFF & Out-label: 0x0054 & Out-label: 0x0054 \\ \hline \end{tabular}
\end{table} 
Table 6: The bi-directional label switching path under QoS requirements and the circumstances of uni-directional link between node vx_simulator\_01 and node vx_simulator\_03 in the semi-physical platform. **Institutional Review Board Statement:** Not applicable. **Informed Consent Statement:** Not applicable.