When do we use 'oracle' in create foreign server statment's hosttype?

Connectivity
Teradata Employee

When do we use 'oracle' in create foreign server statment's hosttype?

When connecting TD14 with Oracle 11 or 12, I've read that USL 15 allows connecting them with a portal server in between. When creating the foreign server, hosttype would normally be 'portal' as that's what's in the middle between TD and Oracle. In what scenario would we use hosttype 'oracle'? 

Thanks

Peter