# Delay-Sensitive Service Provisioning in Software-Defined Low-Earth-Orbit Satellite Networks
## 1 Introduction  
Entering the second decade of the 21 st century, low-Earth-orbit (LEO) constellation networking has entered a second wave of development after more than 10 years of dormancy. The emergence of LEO giant constellations such as Starlink, Oneweb, and Lightspeed has driven the rapid development of space-based networks. LEO satellite networks can provide global low-latency and broadband network access through hundreds to tens of thousands of satellites. Networks characterized by LEO giant constellations and hybrid network architectures are developing rapidly. Massive satellites are usually deployed at multiple orbit heights, using a deployment method mainly based on low-inclination constellations and including a small number of near-polar orbit satellites to achieve global coverage. Additionally, the deployment of inter-satellite links has become very common, especially with significant advancements in laser inter-satellite link technology, greatly improving the data transmission capacity between satellites. This allows the LEO constellation network to be completely independent of the ground network, achieving the \"non-landing\" transmission of massive data. Consequently, LEO satellite networks are rapidly evolvinginto multi-functional, composite space-based networks for global communication, mobile internet, and more. Compared to high-Earth-orbit satellites, LEO satellites offer advantages such as low latency, low transmission loss, high speed, and lower cost. They are considered a vital solution for improving network coverage and communication efficiency. With the rapid development of LEO satellite networks, LEO constellation networks have emerged as a viable option for numerous application scenarios and service requirements. However, as the demand for delay-sensitive services like global sensing, emergency communications, remote sensing, and remote control continues to increase, the performance requirements for transmission in LEO satellite networks are becoming more stringent [1]. Currently, the mainstream technology for solving real-time transmission problems is time-sensitive networking (TSN) technology proposed by the IEEE 802.1 working group. TSN integrates key technologies such as time synchronization, resource management, gate control scheduling, preemption mechanism, and seamless redundancy. It not only enables the real-time transmission of delay-sensitive services based on traditional Ethernet but also ensures compatibility with non-delay-sensitive service. Currently, TSN technology is mainly applied to wired networks such as industry and vehicular networks and is gradually expanding to fields such as Wi-Fi, 5G fronthaul networks, and space networks. However, compared to ground networks, the propagation delay of inter-satellite links in space networks is usually larger and rapidly changing due to the long distance and constant variation of inter-satellite links. For this reason, it is very difficult to achieve time-deterministic service guarantees based on precise time gate control scheduling strategies in LEO satellite networks. Therefore, based on existing literature, current solutions for real-time transmission in space missions mainly focus on the wired networks within satellites and lack end-to-end transmission solutions for inter-satellite links. However, with the increase in the number of nodes in low-orbit satellite networks and the continuous reduction in inter-satellite link propagation delay, supporting delay-sensitive services on LEO satellite networks is feasible through the support of satellite nodes and effective network management strategies. In order to effectively support delay-sensitive services in LEO satellite networks, three requirements must be met: first, satellite nodes need to have a bandwidth guarantee strategy to meet service bandwidth requirements and avoid bandwidth contention between services. Second, network traffic distribution should be balanced to avoid network link congestion.