when will RNC build a "RRC CONN request" on common channel(FACH/RACH)?

[blackantt]

please explain by a demo scene
thanks

[mirc84]

Hello,
RRC connection request message is the first message sent by UE in uplink. Thus the channel in use will be RACH.
The channel on which the RRC connection setup message will be sent by RNC, depends on the establishment cause and is configurable (at least in Huawei implementation R12).
The command is SET URRCESTCAUSE.

Please do take care that if you set too may causes on FACH (i suspect is enough to set REGISTRATION on fach) you will cause a congestion on FACH signalling.

Enjoy.