Near Real-Time Data
Client/Server mini-FAQ

What does the NRT Client/Server software do for me?
The NRT Server System supports the real time distribution of WIND and POLAR near-real time data. Instrument major frames are packetized by the server and made available for transfer to clients. Currently connected clients recieve each requested instrument major frame as it is received by the NRT Server. NRT data is provided during every spacecraft contact for which real time science or manuever mode data is received by the ISTP Data Capture Facility. NRT clients are developed using an NRT Client library which we supply. Contrast this capability with the NRT data files that are automatically generated on the ISTP CDHF during each real-time pass.

Please read the documentation file that comes with the software. It describes (fully and clearly I hope) everything you need to know to write your own client using the NRT Client library.

Where do I get the software?
The client software, documenation, and a sample driver is available via the following sources:
• Directly on the ISTP1 system in sys$public:[nrt.client]
• Anonymous ftp from istp1.gsfc.nasa.gov

Will it work on my computer system?

The software has been successfully built and run on VAX/VMS and Dec Alpha/VMS (with Multinet tcp/ip), Sun Solaris 2.4, and SunOS. It should work on most any Unix system.

When I build the software on my system I get a bunch of compiler warnings. Is this a problem?
You can ignore the warnings. Early versions of the software would generate compiler warnings on some systems. The latest versions should not have this problem. See the notes in the source code prologs for information on building the package.

When I run the sample program I get a "Packet Type Error". What does this mean?
You specify the instrument data that you wish to receive from the NRT server by using the Rtc_SetPacket call. This routine takes as input a string specifying the type of data requested, e.g. PO_LZ_SCR for POLAR Level-Zero Housekeeping data. If you specify a type of data for which you have not been granted access Rtc_SetPacket returns an error. The sample program reports this as a "Packet Type Error".
• If you are just trying to get the sample program to work make sure you change the packet type string. In the sample program the data requested is WIND data.

• Make sure that you have properly constructed the string that you arepassing to Rtc_SetPacket.

• Make sure that the account you are using has been given access to the data you are requesting. See the "ISTP User Information and Privileges Form" in the User Interface to verify your access privileges.

I modified the sample program to provide the data I want but the data doesn't look correct. What's going on?
Be sure to change the buffer size to be the correct size for the data you have requested. In the sample driver a structure is declared that maps the packet headers and trailers, the LZ data record header, and the instrument major frame. When you change the type of data you are requesting you must also change the size of the buffer that holds the data. Otherwise the bytes will no longer align properly in the structure. See the documentation on the NRT Client library for information on the correct sizing of the buffers to receive data.

How do I know when data will be available to test with?
WIND data is available during every WIND real time pass. See the DSN schedule available in the WIND newsgroup in the NEWS utility on the CDHF. POLAR data flows using data from the spacecraft tests will be conducted several times each week until POLAR launch. Announcements of data flows will be made via email.

Who do I call when I have problems?
For problems associated with access to the CDHF computer system, data access privileges, use of the User Interface, or general use questions, contact the ISTP PAC at (301) 286-9453, pac@istp1.gsfc.nasa.gov

---

Webmaster: Natalie Jaquith

NASA Official Responsible for Web Site: John Sigwarth
NASA Goddard Space Flight Center, Code 612.3
(301) 286-0447
Greenbelt, MD 20771

Privacy Policy and Important Notices