MBMS (Multicast Broadcast Multicast Service)

Hello,

Concerning MBMS (Multicast Broadcast Multicast Service), I'd like to know
what channels are used and how we are sure the streams are not duplicated
for each end users that ask the multicast service, as I've read that when
the radio
ressources are allocated, it's possible to switch from point to point
(p-t-p) to point to
multipoint (p-t-m) or p-t-m to p-t-p depending on the numbers of users in
the network
in order to optimize the radio ressources . Is someone has an idea about it?
How point to
multipoint works ?

I've noticed that if IP multicast in 3GPP (R99) is implemented, there is one
GTP-U tunnel per terminal, and multicast flow, SGSN and APN (may be use of
dedicated channels) whereas with MBMS there is one GTP-U tunnel per
multicast flow,
SGSN and APN. In IP Multicast in 3GPP (R99) have you have a copy of each
streams for
each users? In MBMS how p-t-p and p-t-m works as we have one GTP-U tunnel
per multicast
flow ?

I'm thanking you in advance