============================================================================ THE SOUTH POLE TDRSS RELAY (SPTR) FAQ - Updated 1/12/98 ** - indicates change GENERAL INFORMATION 1. What is SPTR? The South Pole TDRSS Relay (SPTR) is a system which uses the NASA Tracking and Data Relay Satellite System (TDRSS) to provide data services to the South Pole. 2. Why is only TDRS-1 being used? TDRS-1 is the oldest of the TDRSS satellites. Its orbital inclination (how far it moves in latitude during its 24-hour orbit) has increased enough that it now has a view of the South Pole during the southern most part of its daily orbit. It is the only TDRSS satellite with an inclination high enough to see the South Pole. 3. How do I find out when the SPTR links will be active? You should check the latest TDRSS Event Schedule for the times TDRS-1 will be supporting SPTR. In order to ensure getting the latest schedule you should be on the SPTR e-mail distribution list. 4. How do I subscribe to the SPTR e-mail distribution list? Send an e-mail to majordomo@listserv.gsfc.nasa.gov and include subscribe sptr in the body of the message. 5. How come the TDRSS events are not scheduled for the full period that TDRS-1 is in view of the South Pole? The TDRS-1 satellite supports other users besides SPTR. Every attempt will be made to give SPTR as much of the time TDRS-1 is in view of the Pole as possible, but there are other TDRSS supports which will have a higher priority. 6. Where do I find out more? Check out the SPTR webpage at http://www530.gsfc.nasa.gov/SPTR/ USING THE SPTR IP CONNECTION 1. What is the data rate of the SPTR IP connection? The SPTR IP connection through the TDRS-1 satellite is a full duplex 1.024 Mbps connection. The sum of all IP traffic can be up to 1.024 Mbps, however each individual user may not see that full rate. The IP data rate between White Sands and the Internet is also 1 Mbps. 2. How come my connection to/from the South Pole doesn't get 1.024 Mbps performance? There are many factors that could be affecting your performance. If there is no bottleneck (a link less than 1 Mbps such as a modem connection) between your computer and the TDRS-1 link, the problem may be due to the round-trip delay time through the TDRS-1 satellite. Success using TCP/IP over geosynchronous satellites varies with TCP/IP implementation. See some of the links on the SPTR Webpage for more information. 3. Is there a limit imposed by SPTR to the maximum data rate for each user? No, the only limits are the 1.024 Mbps connection and the TCP/IP performance. 4. How do I know if the SPTR link is up? First, you should consult the latest TDRSS Event Schedule to find out when the link should be up. If the link is up, you should be able to ping a computer on the other side. If you are unable to ping your destination, try a traceroute to determine where the break in the connection is. USING THE SPTR K-BAND FILE TRANSFER SERVICE 1. How do I get my files transferred from the Pole? To get a file transferred it must be placed on the SPTR South Pole File Server (SPFS) using FTP. The SPFS has an IP address of 204.89.132.35. Files placed on the SPFS prior to the start of the TDRSS event will be automatically transferred to a fileserver in White Sands, New Mexico. At the present time, users should not FTP to the SPFS during TDRSS events. After a file has been transferred to White Sands, it will automatically be deleted from the SPFS. 2. Where does a transferred file end up and how do I get it? Files are transferred to a fileserver at either the White Sands Ground Terminal (WSGT) or the Second TDRSS Ground Terminal (STGT) depending on which ground terminal is supporting TDRS-1. STGT is currently supporting TDRS-1, so the transferred files can be ftp'd from 198.116.99.66. Users are responsible for deleting there files from the servers in White Sands, once they have successfully downloaded them. Files left on the server will reduce the space available for the next day's transfer. ** 3. Can I ftp my files from White Sands during TDRSS events? No. If a user logs in during TDRS , he will not know if his file is finished transfering yet. Looking to see if the file size is increasing is NOT a good idea, the file may only be partially transfered and TDRS/South Pole may be in the middle of a fade. There is also the fear of losing CPU time away from the main application, to handle ftp's instead of transfers.... 4. What is the operating data rate of the file transfers? The K-Band link is operating at 2 Mbits per second. Due to some overhead, the actual transfer rate of the files is approximately 1.8 Mbits per second. At this rate, a 10 Mbyte file is transferred in just under 45 seconds. The K-Band link has been tested up to 50 Mbps, but the file transfer is currently limited by the speed of the server hardware and their storage capacities. 5. How much data can be transferred per day? The factors limiting the amount of data which can be transferred per day are the data rate, amount of TDRS-1 visibility time, and fileserver capacity. Currently, the data rate is fixed at the 1.8 Mbps and the TDRS-1 visibility time for file transfers is about 3 hours. This sets the maximum data transfer capacity to be 2.43 Gbytes. At this time, there is only 1.4 Gbytes storage available on each fileserver, so 1.4 Gbytes is the current limit. ** 6. What are the restrictions on the files that can be transferred? File names greater than 19 characters will be truncated. File sizes should be between 1 - 100 Mbytes in size. File sizes below 1 Mbyte will greatly reduce the throughput due to fixed overhead time for each file. These smaller files should be either compressed with other files to form a larger file or sent back using ftp on the SPTR IP link. The file transfer software will not accommodate files greater than 100 Mbytes in size. ** 7. What are the IP addresses of the file servers? South Pole File Server: 204.89.132.35 Second TDRSS Ground Terminal File Server: 198.116.99.66 (active) White Sands Ground Terminal File Server: 198.116.99.82 (inactive) ** 8. What account names and passwords are there for the file servers? There are two accounts on each machine, both the same logins and passwords: Anonymous with no password for read-only and the other account, for read/write/delete (contact Andre Fortin at andre.fortin@gsfc.nasa.gov if you feel you need this information. ============================================================================