It is very difficult to analyze those requirements because of all the variables added by FastBIT. However, the basic formula is pretty simple: Take the expected size, in MB, of the data you might see in a day, divide it by the amount of seconds in the day and divide that number by 8 to obtain MB/Sec Bandwidth. This will result in the required bandwidth (MB/Sec) needed to sustain 100% load throughout the day.
Example: If we have 500 users sending us an average of 600MB per month (this is about what we see at the Steelgate Online Center), then the formula follows: 600MB * 500Users = 300000MB (300GB) / 30days (per month) = 10000MB Per Day (10GB) / 86400seconds (1 day) = 115.74Kb/sec * 8 (to convert to MB/Sec) = .93MB/Sec or about 61% of a full T1. It typically gets a bit peaky around noon and around midnight, so to accommodate the mean, you should probably have a 30% overhead, which in the above case, would translate to just about a full T1 (1.5MB/Sec).