GSLB Server Service/Translation Service Port

Looking through the documentation, it's not clear to me how a GSLB Server uses the Port and Translation Port values.

Since DNS itself is not port-aware I'm guessing that the port definitions are only used for health monitoring of the LTM virtual server being defined.  If that's the case I can understand the use of the Service Port as defined on the LTM VS, but I can't see what the Translation Port references nor what it's purpose might be.  

Can someone clarify?