Difference clr.AddReference('DSOffice') and clr.AddReferenceByName('Microsoft.Office.Interop.Excel, Version=15.0.0.0, ')

what is the difference between difference clr.AddReference(‘DSOffice’) and clr.AddReferenceByName(‘Microsoft.Office.Interop.Excel, Version=15.0.0.0, Culture=neutral, PublicKeyToken=71e9bce111e9429c’)