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CHAPTER 4 Hardware Architecture
The WFO-Advanced system installed in Denver in May 1996 comprises four full function graphics workstations, two text-only workstations, two data servers, an application processor, and several smaller processors for data acquisition. The system configuration is flexible and can easily be extended to include more workstations, application processors, or acquisition processors.
The hardware architecture for the WFO-Advanced system is illustrated in Figure4.1. With minor exceptions, the system configuration and hardware for the WFO-Advanced are as specified for AWIPS by the AWIPS contractor. The function, description, and fail-over concept for each system component is described at a high level in this chapter.
Figure4.1
The network provides the interconnection between the various processors in the system and for this discussion does not include external communications interfaces.
The WFO-Advanced network consists of two major components: the 100 megabit/second FDDI ring and the 10 megabit/second ethernet bus. All of the graphic workstations, database and application computers, and Plaintree ethernet switches are connected to the FDDI ring. To simplify reconfiguration, the actual FDDI connections are made to a patch panel that is wired to provide the ring architecture. Optical bypass switches are provided for all computers (except the Plaintree switches) to allow FDDI communications automatically to bypass failed computers. The ethernet is implemented within a Plaintree ethernet switch box that also provides the interconnection between the ethernet and the FDDI.
Two Plaintree ethernet switches are connected to the network, each having connections to all ethernet devices. Should one switch fail, the second will automatically take over control of the network. Should failure of the ethernet switch not be detected by the backup ethernet switch, then the faulty switch may need to be manually shut down.
Refer to Figure4.2 for an overview and additional detail of the acquisition processors.
Figure4.2
The SBN provides GOES satellite images and national guidance products to all AWIPS sites. The data are transmitted over two separate channels and are received at each site by a communications processor (CP) that handles the communications protocols and forwards the data to the database computer.
The CP is a Hewlett Packard 743 computer executing the RT operating system. Inside the CP is a communications board manufactured by SBE that handles the incoming SBN protocol. Each CP performs communications functions for the NESDIS (GOES satellite images) and NWS/TG (national guidance products) channels. Data are transmitted from the CP to the WFO-Advanced database over the ethernet. The communications processor and software were provided by the AWIPS contractor. Figure4.3 provides a detailed diagram of the SBN communications hardware and links.
Figure4.3
Two CP processors, each with its own connection to the incoming signal, provide the desired redundancy. Each processor routinely sends data to its assigned database. If a CP fails, data from the operating CP needs to be routed to the second database in order for both databases to have current data.
The WSR-88D radar product generator is the source of radar data for the weather forecast office. The data are received and processed for storage and display by the WFO-Advanced system.
The Simpact Freeway performs the X.25 communications protocol conversion. It is a commercial system that can receive data through several ports concurrently using a choice of protocols. In Denver, the Freeway handles the dedicated line to the primary WSR-88D radar and also dial-up lines to associated radars. Radar images are received from the radar product generator (RPG) in compressed form and sent over the ethernet to the WFO-Advanced database. Figure4.4 provides the detailed configuration of the radar acquisition components.
Figure4.4
A second Simpact Freeways is used to receive the input signal if the primary system fails. A manual switch is used to connect the radar signal to the back-up Freeway.
WFO-Advanced has two other external links for receipt and transmission of data. Experimental observations and products are received from FSL over a T1 line, and forecast products prepared on the workstation are sent to other locations through the AFOS system. A Local Data Acquisition and Distribution (LDAD) system is scheduled to be installed in the near future. It will receive additional local data sets and distribute weather products to external users.
An RS232 line connects the AFOS system to the WFO-Advanced database computer. The line can be switched manually to connect to either database computer. In addition, the output of local forecast models and other data collected at FSL is transmitted over a T1 link through a CISCO 4500 communications router to the WFO-Advanced ethernet. Routine transmissions from FSL through this link use the Local Data Manager (LDM) protocol developed by Unidata. The proposed LDAD hardware consists principally of two Pentium PC servers, two network servers, and several modems. In order to provide the required network security, the LDAD system and FSL's T1 link are planned to be isolated from the WFO-Advanced system through a TIS communications firewall.
Since FSL's data are considered experimental, no backup is provided for the link with FSL. The AFOS connection is critical for dissemination of forecast products, and the line has a switch that can connect AFOS to either one of the database machines. For the LDAD system, redundant processors and network servers will provide the desired backup capability.
The database computer performs all of the data management and some data acquisition tasks. In addition, each database computer runs the X server software for half of the text workstations. The purpose of the application processor is to execute meteorological applications such as event monitors, routine product preparation, data analyses, and local forecast models.
Each database computer is a Hewlett Packard K200 server equipped with two PA7200 processors, 256 megabytes of random access memory, and 8 gigabytes of disk storage. Hydrometeorological products and data are allocated 6 GB. The application processor is identical except that it has only 128 megabytes of memory and 4 gigabytes of disk storage. These computers connect to the FDDI network. The Informix relational database management software is used to store a limited set of hydrometeorological data in the database.
To provide the desired redundancy, the system is configured with two database computers. Each stores a complete set of all data on its local disks. Half of the workstations (including text processors) use the database on one computer and the remainder use the database on the other. Should one computer fail, half of the workstations would temporarily be without data. A UNIX shell script needs to be executed to reconfigure the system so that the affected workstations can access the other database. An alternate configuration that used data mirroring and dual-porting of disks resulted in occasional catastrophic corruption of data on the primary and back-up disks. This resulted in neither database computer being able to access the database.
The workstation provides the capability for the user to display graphical information and interact with the data. Each workstation runs two independent copies of the menu and display software, one for each monitor. Each workstation includes an associated X terminal for display and editing of text products.
The workstation consists of a Hewlett Packard J200 computer with two 19 inch color monitors. Each monitor is controlled by an HCRX24 graphics controller that supports four concurrent color tables: 24-bit true color, 8-bit image underlay, 8-bit graphics overlay, and 8-bit transparency. To support long animation loops, the workstation requires a minimum of 256 megabytes of random access memory. Each workstation is equipped with a four gigabyte disk drive for storing the operating system and workstation software. The user input devices are two sets of keyboards, mice, and touchpads. The workstation can easily be configured to operate with either a single set of input devices for both monitors or separate input devices for each monitor. The J200 connects directly to the FDDI network.
The text editor runs on a Hewlett Packard black-and-white X terminal with 12 megabytes of memory. The X terminal has an ethernet connection.
The two color graphics monitors on the workstation operate independently; each has its own input devices. If one display screen fails, the other screen can perform all of the workstation functions. In the event of a complete workstation or text processor failure, another workstation or text processor in the system would need to assume its functions.
The WFO-Advanced hardware architecture is being evaluated at the NWS Forecast Office in Denver, Colorado.
As of this writing, several of the backup systems described in this section are not in place. The backup CP is currently undergoing testing in Boulder, and is expected to be installed in Denver before the end of January. At that time, the redundant data feeds and databases described earlier will be implemented, and the workstations will be split between the two databases, with two workstations and three text stations on each server.
It is likely that as the evaluation of the system proceeds, minor changes to the architecture may be made.
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Wakefield. Last updated 9 Jan 97.