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⚠️ TODO: This page needs to be updated.
The Satellite Terminal (ST) is one of the three entities that form part of the core of OpenSAND, and it emulates an user satellite terminal, hence its name. It provides the following functionalities:
- Transmission/reception of network packets via the emulated satellite link.
- Simulation of physical layer characteristics: attenuation (loss of packets), and propagation delay.
- Emulation of access layer mechanisms inspired by DVB-RCS2, DVB-RCS and DVB-S2, which include scheduling outgoing packets, RRM (sending capacity requests when needed), requesting log on with associated gateway, and implementing random access mechanisms.
- Encapsulation/desencaptulation of network packets to DVB-like frames, using the appropriate protocols (e.g. RLE, GSE).
- QoS on network packets arriving at the LAN interface.
The ST 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 attaches itself to the emulated interface (either opensand-tun or opensand-tap), and begins the emulation of a satellite terminal.
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 ST is composed of several blocks, each providing functionalities at different levels. The blocks are defined by the opensand:testbed_description:core:real_time:index.
The ST is composed of the blocks pictured in the image at the right.
The Lan Adaptation block provides an interface between network packets arriving from the LAN, and the DVB block. OpenSAND supports IP and Ethernet network packets.
This block also supports the utilization of plugins, such as ROHC.
The ST shares the same Lan Adaptation Block as the GW. Be careful, any change to this code will affect both entities.
The Encapsulation block implements the encapsulation of packets transmitted by the terminal, and the desencapsulation of received packets. The supported encapsulation protocols are GSE, RLE, although protocols with variable length may be encapsulated in the DVB block (e.g. RLE and GSE). Only the protocols supported by the standard are used.
The ST shares the same Encapsulation Block as the GW. Be careful, any change to this code will affect both entities. Regenerative SATs use a different version of this block.
The DVB block implements DVB-like access layer mechanisms, including:
- handling of DVB-like signaling.
- handling registration of the terminal with the corresponding gateway.
- desencapsulation of received BBFrames, and encapsulation of RCS2/RCS-like bursts.
- encapsulation of variable length protocols (RLE and GSE).
- management of radio resources: carriers, spots and categories.
- handling of DAMA, including capacity requests.
- handling of random multiple Access techniques (Slotted Aloha and CRDSA).
- handling of Fade Mitigation Techniques (e.g. variable MODCOD).
- packet scheduling with QoS functionalities.
The Physical Layer block simulates the physical characteristics of the link between the terminal and the satellite. The physical characteristics simulated in OpenSAND are the propagation delay, and the signal attenuation. On the ST, these characteristics are both simulated just for the link between the satellite and the terminal.
The GW shares the same Physical Layer Block as the GW. Be careful, any change to this code will affect both entities.
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 ST shares the same Physical Layer Block as the GW and SAT. Be careful, any change to this code will affect all entities.