Space Network Services Over TCP/IP
NASA Integrated Services Network (NISN) provides data transport services between the WSC and customer MOCs. NISN has sought to reduce infrastructure costs by replacing the current 4800-bit-block point to point serial network with an IP based system. For legacy customers, the 4800-bit-blocks will be encapsulated into User Datagram Protocol (UDP)/IP packets.
Customers are now requesting TCP/IP data services for the communications between the ground terminal and customer facilities. While a common approach to respond to the need of these potential Space Network (SN) customers is being studied, NASA has been providing for unique implementations for the near-term missions. As examples, full support SN customers such as EOS AM-1 and Landsat 7 are installing custom interfaces at the WSC. Currently, future low data rate, limited support SN customers have been requesting total TCP/IP supported data services. The initial customer set includes New Millennium Program Earth Orbiter-1 (NMP/EO-1), Far Ultraviolet Spectroscopy Explorer (FUSE), and Gravity Probe B Relativity (GP-B).
To provide customers with a full range of TCP/IP services, the WDISC was designed and installed to allow customers to request forward service, confirmations, commands, and telemetry via TCP/IP on the Open or closed IONet.
The majority of the WDISC features are consistent with the Consultative Committee for Space Data Systems (CCSDS), an international organization of space agencies interested in mutually developing standard data handling techniques to support space research, including space science and applications. WDISC provides customers with many of the CCSDS space link functions such as frame synchronization, randomization/derandomization and RS decoding. A future enhancement under consideration is inclusion of the CCSDS Space Link Extension (SLE) services into the system.
The overall objective of the WDISC effort is to provide direct TCP/IP based telemetry and command services on the closed IONet from the WSC. By combining the requirements of several unique customers and applying knowledge of heritage systems and customers, NASA plans to leverage the commonality to design and allow for future enhancements to provide support for a variety of customers. This capability is geared toward the new SN customers, initially EO-1 and GP-B, not using the existing 4800-bit-block infrastructure.
The WDISC supports three forward and return service pairs at each ground station WSGT and STGT. The maximum data rates through WDISC are 50 Kbps Forward and 250 Kbps Return.
The WDISC comprises eight PTP units two sets of Primary and Backup PTP pairs at each of the WSC ground terminals. Each PTP had three processing "boards". Each board can handle a single forward and single return data stream for the same event, and any board can be used to fully support any of the initial customers. Appropriate switching and controls permit failovers to occur between matching boards on the Prime and Backup PTP units.
WDISC Reference Architecture
The WDISC website provides additional operational and technical information on all aspects of the WDISC
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