The avnserver process stores the names and locations of all objects used by AvnFPS servers, and it provides these names and locations to all other AvnFPS processes. Additionally, avnserver other task is to provide a notification mechanism between servers and clients. Thus, avnserver combines PYRO's name and event servers. One and only one instance of avnserver should run within a WFO cluster. A client first connects to avnserver to get information about the locations of the data request server and to subscribe for notifications. Client processes do not have to run on hosts at the same WFO as the data servers. An access list of valid hosts, maintained in a configuration file, is used to provide access control. avnserver must be running before any other AvnFPS servers or clients can be successfully started.

The application avninit is used to launch AvnFPS servers and in a certain order. Users typically do not have to be concerned about the servers. It is avninit's job to ensure that all servers are running and restart them if they fail.

An instance of avndis monitors AWIPS data directories using gamin [Gamin]. avndis is a threaded application: for each data source, there is a dedicated thread that processes the data. Which server instance processes which data is determined by the server configuration file etc/server.cfg. avndis receives a notification from the gamin server when a file in a monitored directory is created or modified. The server, or parent process, then passes the file name to appropriate thread. The thread processes the file's content, writes data to AvnFPS database and returns information back to the parent process. The parent process then sends notification to avnserver. A client that subscribed to the server will then receive this notification. Currently implemented threads are:

Every 30 seconds avndis sends an ALIVE message that is used by clients to monitor the state of AvnFPS servers and to alert users if something goes wrong.

avndrs is mainly responsible for providing data to AvnFPS clients. The data source is the AvnFPS database, however, it can also directly access AWIPS files such as NetCDF data in the /data/fxa tree. The other function of avndrs is to write forecasts prepared by the clients to a queue where they are then processed by the transmission server avnxs. Each instance of avndrs is capable of processing all data sources.

Every 30 seconds avndrs sends an ALIVE message that is used by clients to monitor state of AvnFPS servers and alert users when something goes wrong.

The transmission server, avnxs, provides a bridge between AvnFPS and the AWIPS transmission system. avnxs supports delayed transmissions, i. e., issuing forecasts that have been prepared by the forecaster before the transmission window opens.

Data flow diagram: Transmission Server

Forecasts prepared by the AvnFPS forecast editor are written to the directory xmit/pending as text files with a particular naming convention. The filename is then used to determine the disposition of the product. Files in the xmit/pending directory are named as follows:

fid-ccccnnnxxx-wmoid-wfoid-ymmddhhmm-typ-tttttttttt

where

avnxs monitors files in the xmit/pending directory to the current system clock. The requested transmission time, T_xmit, and the creation time, T_post, are retrieved from the filename and from the OS, respectively. If the current time T_cur is within range: T_xmit < T_cur < T_post + N hours, avnxs will call an AWIPS program (currently handleOUP.pl) to send the forecast out to the WAN. N, the number of hours before a pending file is considered 'old', is now a configurable item in etc/xmit.cfg file. If the forecast file is too old, it will be moved to xmit/bad directory. The value of N (usually 3 hours) is set in transmission server configuration file. Files that do not match transmission file format are discarded. avnxs checks for the return code from handleOUP.pl. The status is written to a file xmit/DoW, where DoW is a 3-letter abbreviation for the Day Of the Week. Here is a sample entry from xmit/DoW:

The first word is either SUCCESS or FAILnnn, and nnn is the error code returned by handleOUP.pl. If handleOUP.pl fails to transmit the forecast, the file will be moved to xmit/bad. The transmission status will be announced via avnserver to all client GUIs, see Section 4, “Forecast Transmission”.

The transmission server also collects information on forecasts sent by the office for verification purposes. A special product is send periodically to the Performance Branch within OCWWS at NWS Headquarters that contains information that identifies which forecaster is responsible for which forecast. A configuration file etc/xmit.cfg specifies WMO and AWIPS headers and the frequency of transmission.

AvnWatch is the main client application. It provides forecast preparation and monitoring functionality. Avnclimate is a set of GUIs accessing archived climatological data. Current functionality provides display of historical data and statistics that can help by producing a short-term forecast based on current weather conditions. These applications are described in much greater detail in Chapter 2.