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sat
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⚠️ TODO: This page needs to be updated.
The Satellite (SAT) is one of the three entities that form part of the core of OpenSAND. It emulates the satellite in a satellite communications system, and it can be either transparent or regenerative (with on-board processing). It provides the following functionalities:
- Forwarding of BBFrames and DVB-RCS2 bursts via the emulated satellite link.
- DVB-RCS2 burst des-encapsulation and on-board switching in regenerative satellites.
- Simulation of physical layer characteristics: attenuation (loss of packets).
- Emulation of some access layer mechanisms inspired by DVB-RCS2, DVB-RCS and DVB-S2, in order to correctly route the packets between GWs and spots.
The SAT entity is composed of a stand-alone binary which is launched by the OpenSAND daemon upon the start of a simulation (signalled by an OpenSAND manager). On start, it creates the necessary emulated satellite link UDP channels, and begins the emulation of the satellite.
The exact command used by the OpenSAND daemon to launch the binary is transmitted from the Manager, and stored in the file /var/cache/sand-daemon/start.ini.
Like any OpenSAND entity, the SAT is composed of several blocks, each providing functionalities at different levels. The blocks are defined by the opensand:testbed_description:core:real_time:index. TODO link
The composition of the satellite depends on whether the transparent or regenerative mode is used. The regenerative satellite is composed of the blocks pictured in the image at the right. The transparent satellite contains the same blocks except the Encapsulation.
The Encapsulation block on the regenerative satellite implements limited functionalities with respect to the Encapsulation block present in the ST and GW. It implements the desencapsulation of received packets in order to perform on-board switching. The supported encapsulation protocols are GSE), RLE. Only the protocols supported by the standard are used.
NOTE: this block is only present on the SAT when using regenerative mode.
The satellite DVB block implements limited functionalities of DVB-like access layer mechanisms, including:
- forwarding of DVB-like signaling, capacity requests, and data packets to the correct spot/GW.
- desencapsulation of received BBFrames and RCS2/RCS-like bursts for routing purposes.
The Physical Layer block simulates the physical characteristics of the link between the terminal and the satellite. The only physical characteristic simulated in the SAT is the signal attenuation, for the links between the satellite and gateway/terminals.
The Satellite Carrier block provides an interface between the emulation network, and the OpenSAND core. It is charged of packing and unpacking the emulated satellite frames on UDP datagrams. For more information about how the emulated channels work, refer to the opensand:testbed_description:core:emulated_channel:index. TODO link
The SAT shares the same Physical Layer Block as the GW and ST. Be careful, any change to this code will affect all entities.