maximum difference or ratio between 2 consecutive bid/ask

Hi. I need to remove possible outlier in bid / ask due to possible
transmission
  errors over the internet of the price tick events, in an automatic
trading system I am tuning.

  I'd like to ask your opinion about what is the most reasonable
choice for
  a threshold beyond which I should discard the values.

  For instance  if     BID  > previous BID  + 1% previous BID or
                             BID  < previous BID  - 1% previous BID
  then discard the last BID event. Same for ASK.


 Here I have used, by example, a 1% threshold and the ratio of
consecutive values.

 Based on your experience, what do you think is an appropriate value
for the threshold, in order to spot
 say "impossile" values, which can be attribute almost certainly to
transmission errors ?

 Any idea or suggestion is much appreciate.

 Thanks a lot.

Tommaso