— In this study, Voice over IP (VoIP) performance in multi-layered satellite IP networks with on-board processing (OBP) capability is investigated. With on-board processing, a satellite can process the received data, and according to the nature of application, it can decide on the transmission properties. Specifically, considered OBP includes error-correcting coding to combat adverse channel conditions and priority queueing mechanisms for efficient use of the system resources. After a brief overview of relevant aspects of satellite networks to VoIP, VoIP performance for Non-Geostationary Earth Orbit (NGEO) single layer and multi-layered constellations are examined using a network simulation tool. The outcome of these simulations justifies the premise for the multi-layered architecture for delay-sensitive and real-time traffic such as voice. Subsequently, the effects of some quality-of-service (QoS) mechanisms in multi-layered architecture are tested using various simulation param...