In this paper we study a constraint-based routing strategy using label switching in a multi-layered hierarchical satellite constellation such as Transformational Communications Architecture. Both quality (Bit Error Rate on free space optical and radio inter-satellite links) and bandwidth availability on a satellite link are taken into account when setting up routes for high priority real-time traffic such as VoIP, which is sensitive to delay and jitter. To protect the real-time traffic from being swamped by bursty best-effort traffic we propose to have a separate queue for high priority traffic. Packets from several real-time flows are aggregated onto the same LSP (Label Switched Path) based on destination and priority, and are shielded from each other by a proportional dropping policy, where packets from flows exceeding their Committed Information Rate (CIR) have high dropping probability during congestion. The performance of the prioritized load balancing routing algorithm on a multi-layered satellite network is simulated and analyzed.

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