I am reading about openstack neutron routed provider networks.

If I understood well, using segments I can create more subnets within the same provider net vlan id. 

Correct?

In documentation seems I must use different physical network for each segment.

I am using only one physical network ...in other words I created an openvswitch with a bridge (br-ex) with an interface on which I  receive all my vlans (trunk). 

Why must I use different physical net?

Sorry, but my net skill is poor.

Ignazio