SIP registration reliability

Some customers have had problems using all their SIP “trunks” that are registered with an upstream provider, so I came up with a hand-waving algorithm to compare these boxes’ registration time outs. I’m curious about how often other boxes out there have registration timeouts, so here’s the formula:

[Relative Registration Reliability] = [registration timeout event logged] / [SIP trunks registered w/ provider] / [sample timeout period]

Example: 1338 time outs / 3 trunks / 31 days = 14.4 (rounded to 10th) means that on any given day, a single SIP registration will have a little over 14 secs where the trunk is essentially unusable (because it looks like Asterisk retries every sec for every registrant). A simple grep grabs the time out events for Jan. '08:

Here are some of our cutomers’ RRR factors (awful pun on that acronym, hehe):


Is this a ballpark figure? Or does someone have 0 timeouts during a month …