http://info.gb.nrao.edu/GBT/MC/doc/designReview/designReview.html
Last modified on August 8, 1997
Along with co-op students:
While we are responsible for the content of this review, we wish to acknowledge the contributions of many.
This meeting is intended to review whether the Monitor/Control and Data Analysis hardware architecture will support the software necessary to support Operators, Engineers, and Observers. There is a vary large amount of information to cover, so we should try to limit the discussion to:
The M&C software is a distributed system consisting of numerous software modules running on multiple computers (Sun SPARC workstations and mv167 single-board computers) communicating over Local Area Networks (LANs). Drawing D35501K011 shows all of the software modules and their interface and communication needs. The mapping of software modules to computers is shown at the end of this section. The system is designed to minimize real-time software dependencies between subsystems, e.g., the only communication needed for control purposes (Manager/Panel Interface). takes place prior to a scan's onset. When stricter real-time deadlines exist between subsystems (Corrector-Correction, Corrector-Focus Tracking, RSI Ethernet Spec Interfaces), a dedicated communication link is used.
A LAN is also used to provide feedback to users in the form of discrete messages (Error & Warning Message Interface) and streams of monitor data (Sampler/Monitor Interface).
Backends which generate low enough data rates (currently the DCR and holography backends) write their data to remote disks using a LAN. Faster backends write their data directly to disk.
Coordinated Universal Time for software use is distributed independently via a network using IRIG to all single-board computers. Network Time Protocol (RFC 1305) is used to distribute time to workstations.
Telescope internal LANs and the site LAN will be separated by a gateway machine whose physical access will be limited to the operator. All control traffic to GBT software will be controlled by the operator. If, by GBT completion the site LAN is not secure, it will be an administrative decision whether to allow remote access to the GBT Control Room computers.
Observer workstations will be capable of running both analysis and telescope interface programs.
The telescope M&C system is distributed over several physically separated rooms on the telescope. Each of these rooms communicates with the others over the Local Area Network.
The following is a list of computers, their locations, and associated software modules.
The Control Room M&C equipment is used by operators and observers to specify and control observations. Provisions are also made for data reduction and analysis. The equipment specified for the Control Room is:
And the winner is:
Fast Ethernet
Fast Ethernet's main advantage is familiarity. It is the same protocol as standard ethernet, only faster. It is also wildly growing, meaning that the technology is sound, and the prices are coming down on Fast Ethernet equipment. There is a limit, however, on the amount of usable bandwidth. Estimates are that you can get between 50-75 Mb/s out of it. There is an IEEE standard on Fast Ethernet. This is the cheapest solution, but one we may well grow out of. We have chosen a switched ethernet system with a migration path to Gigabit Ethernet
For background information on the various network technologies, the University of New Hampshire's InterOperability Lab has much to offer.
High-speed backends, like the Spectral Processor, and the Spectrometer, will dump data directly into the RAID via their assigned SCSI ports. If data rates allow, the data will be formatted into FITS files before storage, otherwise, it be dumped to the disk raw, and formatted off-line. Data from low-rate backends, such as the DCR and the Holograhpy backend, will be sent over the network to the Data Acquisition Machine, where it will be formatted into FITS files and written to the RAID. All FITS formatting is done by the Data Acquisition computer, except in the case of the Spectral Processor and the Spectrometer.