CRM: How to get Work Center (Assignment) value of a service line item of Order

Dears,

Following is my scenario:

CRM IDoc (CRMXIF_ORDER_SAVE_M) ----PI ---- File.

CRM IDoc will have Service Order details along with Service Item details.

Issue: The current IDoc does't have the Work Center entries for each Item

Requirement: Need to get work center of each service item and pass into IDoc or create RFC and send back to PI

Note: I don't know how to identify whether assignment has been done for each item or not...

could you please help me if you have any BAPI, RFC or code to get work center details of each service line item....?

Thanks-
Rams