On Mon, 17 Apr 2006, Kem Cook wrote: > I'm sorry I wasn't present for whole telecon, but I would really be > interested in an explanation of: > > >> - asking each night for everything that we might need > >> is not an option: too expensive, don't have enough bandwidth > > I would think this is mandatory. Conditions change, sometimes with little > or no warning. Planning is fine, but being prepared is better. And I > don't see why this is hard. 5 bands of template images and some synthesis > of the light curve database should be all that is needed.
I believe what this note was referring to is the following: If for a given night we know we are going to observe some well know portion of the sky, then we can just issue a query for all of the data we need from that portion of the sky and send it to the base facility--regardless of whether any of those records are already there. The point being made here is that we may not be able to afford to be this frivolous with our bandwidth; rather, a more efficient scheme for transfering the needed database data may be needed. The difficulty here is that there are too many unknowns at this stage to calculate a detailed bandwidth budget. We have a handle on some numbers, but many are guesses, untested, or simply unspecified. (E.g. how big is a synthesis of a light curve database?) What I think the numbers are telling us is that we're likely to be working close to capacity. For example, we know we won't have bandwidth to transfer both raw and processed products from base to AC (29 Gbps). If we can get 2 Gbps sustained, then we can get the raw data to the AC in 8.3 hours. We'll be sending Alert packets--the alert announcement and supporting data--in real time, so that cannot exceed 10 hours to transmit; there is certainly an interest to include as much information as possible here. That leaves less than 6 hours for other purposes (instrumental data, non-alert related light curve data, and back-transfer of results from archive center). (This doesn't address how long it will take to recover if the network is down for some amount of time.) So, maybe this is all do-able and we won't have to worry about bandwidth limitations, but at this stage, it's prudent to plan for the harder problem. The more efficient we can be, the more bandwidth we'll have for moving the data you want. cheers, Ray _______________________________________________ LSST-data mailing list [email protected] http://www.lsstmail.org/mailman/listinfo/lsst-data
