TO: All GCN Notice recipients RE: A Redundant VOEvent Ver 2.0 server now available DT: 24 Nov 2015 If you are not interested in or using GCN VOEvents, you can stop reading. INTRODUCTION: Another version 2.0 VOEvent server has been added to the constellation of VOEvent servers in GCN. For a while there has been only a single version 2.0 server (and two version 1.1 servers), but now there are 2 version 2.0 servers providing redunancy on the 2.0 stream. The table of all VOEvent servers is: Version 2.0 Servers: 68.169.57.253 8099 45.58.43.186 8099 <== The new server! Version 1.1 Servers: 209.208.78.170 8099 50.116.49.68 8099 All 4 servers have the full compliment of the publically available GCN Notices in VOEvent format. You can connect to them anonymously and get all the Notices produced by all the contributing missions and projects, or you can use a configuration file to allow filtering of the Notices. All 4 servers listen for a connection on port_number 8099. VERSION HISTORY and FUTURE: Even though the most recent version of VOEvents is 2.0, version 1.1 is still supported by GCN because a couple sites are locked into a software package that requires Ver 1.1. For the rest of the customers, you are encouraged to use 2.0 (by connecting to those two servers). EXCERPTS FROM PREVIOUS GCN VOEVENT ANNOUNCEMENTS: DEMONSTRATION CLIENT PROGRAM: To facilitate quick and easy connection to this new service, a demo client program (voevent_client_demo) is available. It can be downloaded from http://gcn.gsfc.nasa.gov/gcn/voevent_client_demo.c This GCN/TAN client is a clean, simple, standalone client written in C. It needs no additional libraries or other software packages installed on your system. It has the basic parts to (a) establish and maintain a connection to a server, (b) receive and acknowledge VOEvents, and (c) tell you when there are problems. Usage: voevent_client_demo Example: voevent_client_demo 45.58.43.186 8099 CONNECTION PROTOCOL: A connection between the client and a server is done using the so-called "vTCP" protocol. It is the standand TCP protocol with a "v"OEvent adjustment involving (a) Imalive packet exchange, (b) a 2-part writing/reading action, and (c) the explicit ack/nacking-ing of the VOEvents received. The imalives allow for both ends to monitor the vitality of the end-to-end connection, and take corrective action if nothing has been recevied within 2or3 of the 60-sec intervals the imalives are sent. The 2-part writing/reading starts with a 4-byte quantity sent first that indicates the length of the VOEvent message that will be sent next (so the client reads 4 bytes, then knows how much to read to get the message). The acking/nacking allows the server to keep track that the client has correctly received the full VOEvent message. The TCP/IP VOEvent protocol is described in http://www.ivoa.net/Documents/Notes/VOEventTransport/ . If you already have a client which implements this vTCP protocol, you can use it to connect to the GCN/TAN VOEvent servers. (The voevent_client_demo is just a bare-bones example to get people started if they have no prior experience with VOEvents. You can also use voevent_client_demo to connect to other VOEvent servers using the vTCP protocol.) FILTERING: Even though votan is a server and you can connect anonymously[1], if you register with GCN/TAN, you can receive all the regular filtering capabilities of the original GCN system. Votan is able to accomplish this by checking your IP Number (IPN) when you connect. If your IPN matches an entry in the votan sites.cfg file, then it uses that configuration to determine which Notice types you want to receive plus all 16 filtering rules. (See http://gcn.gsfc.nasa.gov/gcn/tech_describe.html#tc25 for a list of all the filtering functions available.) If you register, you can have only one client running on the specified machine (ie the IP Number), because votan uses only the IP Number to identify you (ie no additional port_number like in original GCN). Two clients on the same machine have the same IP Number. Registration is simple -- a 'configuration' is built using the same GCN/TAN config_builder webpage (see below). If you choose not to register with votan, there can be no filtering so then your connection will receive all Notices of all the types (currently ~2000 per day; this does not count the 1440 imalive transport-protocol messages sent per day). SEE ALSO: GCN has been distributing VOEvents using its own GCN-custom protocol (also TCP/IP-based) since June 2009. Information can be found at http://gcn.gsfc.nasa.gov/tech_describe.html#tc17 And for the email-based VOEvent distribution: http://gcn.gsfc.nasa.gov/tech_describe.html#tc18a These 2 distribution methods will continue (to support existing customers). ACTION ITEM: a) If, after reviewing the information above/below, you want to receive the GCN/TAN VOEvents, you need to decide if you want to have the filtering capabilities or not. If you want filtering, then go to: http://gcn.gsfc.nasa.gov/gcn/config_builder.html and select "#1 Create a new config" specifying the "VOEVENT2.0" or "VOEVENT1.1" selections in the Distribution method pull-down menu (plus making selections for all the other items that make up sites's configuration); or select "#2 Modify an existing config" and (at the least) change your current distribution method to the VO_EVENT method. Of course, if you do not want filtering, then you can just connect anonymously[2] to the server and receive all Notices the GCN/TAN produces. b) Then you need to get a client (either voevent_client_demo or another client program) and connect to one of the VOEvent servers listed above. If you do not want filtering, then just connect with a client program. Sincerely, Scott Scott Barthelmy NASA-GSFC, Code 661, Greenbelt, MD 20771 PHONE: 301-286-3106 (office) CELL: 301-346-3733 EMAIL: scott@lheamail.gsfc.nasa.gov PAGER: 3013463733@cingularme.com WEB: http://gcn.gsfc.nasa.gov/gcn FOOTNOTES: [1] Actually, "anonymously" means without any prior arrangements, no configuration set-ups, nor any entry to some "allowed to connect" list. In practice, the GCN/TAN server will always be able to obtain your IP Number when you connect (with or without a prior configuration set-up). [2] Connecting anonymously means you do not -- can not -- have a VOEvent-based entry in the sites.cfg file. Every new connection has its IP_Num checked against those in the sites.cfg file. If there is a match, then the connection immediately converts from anonymous to vetted (your identity and configuration are known and used).