A novel LEO/MEO two-tier satellite communication system with inter-satellite links (ISLs) is proposed for providing multimedia services to global mobile users. This two-tier system architecture can reduce the transmission delay for long-distance users via MEO satellites while keeping the benefits of using LEO satellites as the service access nodes. The routing and re-routing during a handoff operation is simplified. Since the physical topology of the underlying network is time-dependent, routing is crucial for guaranteeing the delay and delay variation performance for interactive applications. We decompose the routing problem into two parts, routing in the access network and routing in the core MEO ISL network. For the access network, a new routing algorithm called the maximum holding access protocol (MHAP) is proposed for minimizing the number of LEO handoffs. For core MEO ISL network, both minimum transmission delay routing (MTDR) and minimum transmission time jitter routing (MTTJR) are investigated. Using computer simulations, we show that the proposed routing algorithms can reduce the probability of call re-routing and thus are very suitable for providing interactive multimedia services.
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