• General Information
• What does SAXTA stand for?
• What are SAXTA's System requirements?
• Can the SAXTA project host the data I want to share?
• How is technical support handled?


• Technology
• What data formats are supported by SAXTA?
• Can I "unshare" my data?
• Do I need a firewall?
• Can I just modify our ftp site?


• Security
• Who can access my data?
• How does SAXTA ensure that only the data that I shared are visible?
• How do you prevent illegal content from being shared on SAXTA?

• Question: What does SAXTA Stand for?
  Answer: SAXTA is an acronym derived from combinbing "SAtellite" with "JXTA". SAXTA's purpose is to facilitate the sharing and distribution of Satellite data and is based on the Open Source JXTA Technology. JXTA is both a standardized set of XML-based protocols and a JAVA™ reference implementation designed to support and empower Peer-to-Peer and Grid Computing.
  



• Question: What are SAXTA's System requirements?
  Answer: SAXTA is meant to be platform independent. SAXTA is written in JAVA 5, and is packaged as a servlet integrated within a JAVA Web Server. Every platform running JAVA 5 and supporting a JAVA Web Server (Servlet v2.4, JSP v2.0) can run SAXTA. Specifically, the SAXTA application in designed to operate within most common operating systems, including MS Windows (XP, 2000, 2003 ...), Linux, Unix (multiple ) flavors, and Apple OS X.
  
  In future releases, SAXTA will make use of "native" Hierarchical Data Format (HDF) libraries in order to read the metadata associated with satellite data packaged in HDF files. Sharing HDF files will be restricted to the HDF-supported platforms. Search and download functions, in future releases of SAXTA, will not be affected.
  
  SAXTA requires 15 Mbytes of local disk space for the SAXTA servlet or 119 Mbytes for the fully bundled win32 version. Network traffic and bandwidth usage associated with SAXTA is comparable to that of a typical web server.
  



• Question: Can the SAXTA project host the data I want to share ?
  Answer: Our philosophy is to let the user maintain complete autonomy over their data, something that could be lost if an intermediary hosts and distributes the users data. SAXTA is designed to be as easy as possible to install and use. It does not require network/firewall reconfiguration, and it automatically extracts and externalizes the metadata associated with the satellite images intended for sharing. It takes approximately 5 minutes to install the software, join the network, and start sharing data.
  
  It is not the SAXTA project's goal to serve as the physical data center. Instead, we provide the community with the infrastructure of a network and the user with the capabilities to create their own data-sharing node.
  However, if it is difficult to do so in your environment, please contact SAXTA's outreach coordinator and we will work with you to find a solution.
  



• Question: How is technical support handled ?
  Answer: As with most open source software, SAXTA is provided "as is" under NASA's open source license. While we don't provide technical support per say, if you have any issues or comments about the software, please feel free to direct you inquires to SAXTA's outreach coordinator who will work with you to address your concerns.
  
  
• Question: What data formats are supported by SAXTA ?
  Answer: The SAXTA architecture can accommodate multiple types of image data. Saxta V1 Beta only allows sharing of Landsat 7 L1G, Aster L1A and L1B data. The system is designed to be extensible to additional data types such as Landsat Data Continuity Mission and derived products. Specifically the following metadata formats are currently supported:
  • Aster L1B, Aster L1A HDF  as well as Aster L2 "AST_07" formats.
  • Landsat 7 Orthorectified (EarthSat), where the Landsat 7 scene metadata are located in a ".met" files.
  • Landsat 7 FAST-L7A Format.
  • Landsat 7 NLAPS Format.
  • Landsat 7 "MTL" format, where the  Landsat 7 scene metadata are located in a "._MTL*" file. Usually the metadata file bears the "_MTL.TIF", "_MTL.TIF.txt", "_MTL.L1G" or "_MTL.L1G.txt" extension, and is "null" padded to a size of 64K.
    
  
  
  
• Question: Can I "unshare" my data ?
  Answer: Yes, unsharing is as easy as sharing the data in the first place. In order to do this, the user selects the "My Data Holding" tab from the SAXTA web based GUI. SAXTA then displays the satellite data currently being shared. Select the data you want to stop sharing, and click the "Remove" button at the bottom of the screen. This change will take effect immediately, even though the data will continue to appear present within the SAXTA network as the change message propagates throughout. During this period, any attempt to download the "remnant" data will be unsuccessful.
  
  
  
• Question: Do I need a firewall ?
  Answer: No, SAXTA can operate securely without needing a firewall. Nevertheless, many users will prefer to install SAXTA inside their firewall. In either case, no special network reconfiguration is necessary. To optimize performance, we suggest allowing incoming SAXTA queries on port 9700 and 9701.
  
  
  
• Question: Can I just modify our ftp site ?
  Answer: The data being shared within an existing ftp site can also be shared via SAXTA. The advantage of SAXTA in this configuration is that it adds an important new data discovery service; the users do not need to know the desired ftp site name or URL. A further benefit is that SAXTA allows for search on standardized metadata, an improvement over simple ftp file browse.
  
  To share data via an ftp site and SAXTA, just install SAXTA on you ftp server and share your ftp directories in your SAXTA software by using the "My Data Holdings" tab.
  
  
  
• Question: Who can access my data ?
  Answer: SAXTA currently uses 2 different mechanisms to ensure that a user's shared data is only available to the SAXTA community. For starters, SAXTA uses a private JXTA "Net Peer Group" as well as private Super, Rendez-Vous and Relay Peers, which separate and hide SAXTA from the rest of the JXTA network. In addition, within this private network, SAXTA creates another specific "Saxta Community " Peer Group that uses JXTA Personal Security Environment (PSE) Authentication and Security Framework. The "SAXTA Community" peer group is protected by JXTA's PSE membership which relies on a chain of trusted X509 Digital Certificates and private keys. Currently all SAXTA members share a digital certificate. In the future, individual Digital Certificates will fully individualize access control.
  
  
  
• Question: How does SAXTA ensure that only the data I shared are visible ?
  Answer: SAXTA does not recognize or identify a file by its file name. SAXTA shared file information is stored in a "hash table" whose key is the file's unique 128 bit md5 "fingerprint". In order for SAXTA to serve a file, its md5 needs to be generated and registered into SAXTA's shared file table. It is impossible to generate a counterfeit md5 without having complete access to the original file. Hence, for someone to generate a valid SAXTA identifier for a given file, they will have to have an exact copy, and that will allow him/her only to download that exact file, no other.
  



• Question: How do you prevent illegal content from being shared on SAXTA ?
  Answer: Blocking of the sharing of illegal content is a serious technical challenge. Many solutions have been attempted by a network-sponsoring organizations and companies. Few solutions have been entirely successful, and much investment has been squandered in the process. We propose to address the problem from an old-fashioned angle: accountability. Unlike other Peer to Peer networks, SAXTA is not anonymous, and each file shared on the SAXTA network can be easily traced to a unique source. Upon completion of the SAXTA's PSE Membership implementation, each file and actually each message will be digitally signed and thus authenticated. While we can't pretend that it will be impossible to share inappropriate content on SAXTA, this traceability allows for the enforcement of the file sharing rules. An added benefit is for the provider to be credited with the contribution of legitimate data. We believe that the robust tracking of file provenance, coupled with enforcement of the rules, will act as a strong deterrent to illegal file sharing.
  

SAXTA is an open source software and we invite you to participate in the project.  You could for instance be contributing in helping us develop additional data type support capabilities for SAXTA. Please contact our outreach coordinator to get you started.