Is it possible to build shipment by fetching rates from external system throu integration interfaces??

Scenario : Order releases will be bulk planned to build shipment. During the process of building (planning), OTM needs to send an interface xml to an external system and get the rates again throu an interface xml, then it should use those values to build shipment with actual rates..

Is this scenario is possible? If possible then what are the interfaces i should use??

I looked at the interface types in integration guide but not sure which interface and how OTM works in this case??

Immediate response is really appreciated.