Hi, Raymond
GS1 functionality became core in ECC 6.0 EhP2.
You can define GLNs for your company, plants, and purchasing organizations in the GLN Table, transaction code EANGLN. However, core functionality limits your organization to those three business objects, which many customers have said is too limiting (plant is too high-level for ship-tos, and the core functionality also assumes that the bill-to and ship-to are the same GLN, which often isn't the case.
In 2009, the Healthcare IBU funded out-of-core GLN enhancements that added 14 more business objects for GLNs with enhanced GLN Table build capabilities, IDoc User Exit to utilize the new business objects, and GLN Search Help for Vendors and Customers that you can download from the SAP Market Place for Healthcare at http://service.sap.com/healthcare-guides
For details on existing and enhanced functionality, and for a good overall education on GS1 standards that also are used not only for MM and LES functions, but also for Global Data Synchronization, Traceability, and Authentication, see my ASUG presentation "SAP Support for GS1 Standards" at SAP Box Attachment
Cheers,
Jon Arck
Healthcare IBU