Each accepted CLTU is sent to the CMM-S model individually over a TCP/IP socket. The T501 emulator will convert the ASCII hexadecimal values into binary format, locate any and all CLTUs in the bytestream, and perform some basic sanity checks. One of the parameters for the send_cltus directive is the CLTU bytestream represented as ASCII hexadecimal values. In the command pathway, the TCTS software sends one or more CLTUs wrapped in an RTL (Run-Time Library) message specifying the send_cltus directive. Each service represents a particular facet of the T501 operation. Depending on the session type, access may be granted to zero or more services. Each session in the T50l opens exactly one TCP/IP socket. The T501 emulator to TCTS interface is broken down into two main classes: sessions and services. In the software-only testbed, the T501 emulator replaces the physical T501 and, instead of LVDS signals, provides a simple, easy-to-use, TCP/IP socket interface. In the JWST test bed, the TCTS software communicates with the T501 over TCP/IP, and the T501 converts the TCP/IP packets into LVDS signals for the CMM-S card. The T501 emulator provides two simple TCP/IP interfaces: the first interface conforms to the JWST TCTS specification, and the second interface provides a simple mechanism to downlink Virtual Channel Data Units (VCDUs) and receive uplinked Communications Link Transmission Units (CLTUs) from TCTS. The T501 emulator implements the behavior of the RT Logic Telemetrix T501 processor using only software. The as-is solution requires the utilization of commercial off-the-shelf hardware (RT Logic Telemetrix T501 processor) and custom CMM-S hardware. In order to develop a software-only test environment for the James Webb Space Telescope (JWST) mission, a solution was needed to send commands and receive telemetry between the TCTS (Telemetry and Command Test Set) and CMM-S card. Goddard Space Flight Center, Greenbelt, Maryland
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