PBCCH relative to BCCH

Hi All,

In Nokia Gsm/Gprs network, there are a channel oranization between PBCCH with BCCH, they call it a MPBCCH, its TRX TSL
is something like below :

TSL 0 : BCCH
TSL 1 :
TSL 2 : PBCCH
TSL 3 :
TSL 4 :
.
.
TSL 7 :

They said this structure can make operator easily to enable bsc_gprs_param_enabled is in use,
use PBCCH/PCCCH as a standard feature.

Is any one have detail information about MPBCCH ?