[users@httpd] How exactly does ab -n works? Please?

[yalag]

I read so many man pages but I still don't understand this, the -n flag 
basically tells it to make n number of requests. So assuming my server can take 
10 request per second, I would expect ab -100 to take 10 seconds and ab -1000 
to take 100 seconds. But that is not the case. I find that if I do ab -n 10000 
everything works fine. But if I do ab -n 30000, the server also gives a time 
out. What is the logic here?