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Chapter 29
TM/TC Link reference
29.1
Introduction
With EuroSim the possibility exists to model a telemetry/telecommand link at run time either between
two sub-models within a EuroSim simulator, or between EuroSim and another (external) computer.
The main feature of this library is to simulate the bandwidth and time-delay that characterize a longrange communication link, such as the TM/TC link between a ground station and a satellite. By default
this delay is disabled and packets are forwarded without any delay. Note that the TM/TC link interface
is included in the C++ Batch interface (see Chapter 27) which for external clients may be a preferable
interface for setting up and establishing the TM/TC connection.
The TM/TC mechanism uses a central server process running within EuroSim, via which the two terminators (or clients) can communicate. The server can maintain one or more client-to-client links; links
are bidirectional and can be established between any two internal clients or between an internal and an
external client. For the latter, use is made of TCP/IP. No link can be established between two external
clients.
EuroSim has the flexibility to handle any data structure as a packet: “packets” do not have to be compliant
with ECSS PUS [Sec03] standards in order to be sent and received over the TM/TC link. An ECSS PUS
support library to pack and unpack PUS packets however is included with EuroSim. In Figure 29.1 a
schematic of a TM/TC link between an external simulator and a EuroSim simulator is provided.
OnBoard Thermal Model (EuroSim)
Ground Station
ethernet
Input
cmd(s)
Process
TC
TC packets
Process
TC
Ground station commands
Thermal
Control
Model
Operator
Display
data
Process
TM
TM packets
Process
TM
Temperature readings
Figure 29.1: External TM/TC Link Schematic
In the case of an internal TM/TC link, i.e. between two or more sub-models within an EuroSim application,
the link needs to be set up, customized and then used.
In the case of an external TM/TC client, the only difference is first to connect the external client over
TCP/IP to the EuroSim server. Then the setting up and use of the link uses exactly the same routines. The
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