Regarding SLA violations

I request a few moments of your time for your invaluable input on the
following questions that I am wondering about:
1. a) How often does a service provider network incur SLA violations?
    b) Which SLA parameter is the most probably violated (bandwidth, delay,
packet loss or others)?
    c) Apart from link failures, what are other likely causes of this
2. If a service provider provisions a 2 Mbps data pipe between two customer
sites, how often does the customer traffic go beyond 2 Mbps?

Thanks and best regards