Reliability Class field in PDP Context messages

Hello everyone,
I am new to GPRS and trying to understand impact of QOS profile in PDP
Context Creation/Respone messages. I am specifically interested in
Reliability Class (RC) filed in QOS profile. I have following
questions:
1) Who determines/dictates the RC in the network?
2) What is the standard (best practice) RC used these days in the GPRS
world?
3) Can GGSN force the RC to a certain value (lets say 3)? What's the
impact in doing that?
4) Does RC play any role in providing services on the phone?

I would appreciate if anyone can comment on these. Thanks in advance.


Abu Hamzah