802.1q and cisco switches

Hi,
I have a couple of questions on VLAN config in cisco:
1)In cisco switches ,once a port is configured as VLAN Trunk will it accept or send untagged frames ?Is it that all frames are tagged(well, thats what i think) ?

2)If all frames are going to be tagged why do we require the TPID field in the IEEE802.1q frame format?All frames are tagged and hence is it not possible for the trunk port to interpret that the field following Source address is VLAN ID ?

thanks and regards,
prashant

Hi all,
i have clarified myself.
In cisco the frames from VLAN 1 or the Native VLAN are sent untagged over the trunk port!!!
whereas frames from ports belonging to other VLANs are sent tagged.
So this explains why you really require TPID field of IEEE802.1q
Regards,
Prashant[/b]