STP queries

Salam,

I have two queries regarding STP 802.1d

1 - the STP states from disabled->blocking->listening->learning->forwarding.
If all the switches and its port are in blocking state then how they
initiate the process of sending BPDU as blocking port is allowed to receive
only BPDUs so that the switch can hear from other neighboring switches.

2 - Cisco recommends that if the changes needs to be made, only the network
diameter value should be modified on the Root Bridge Switch, When the
diameter is changed, the switch calculates new values for all three STP
timers automatically. So, how can we change the diameter value ???

-- 
Regards,
M. Faisal.
Blogs and organic groups at http://www.ccie.net