Diffrence Between Direct Org Transfer and Internal Sales Order Process?

Hi All,

I have few querrys related to Direct Org Transfer and IRISO Process

1) In both Direct org transfer and IRISO we transfer item from org to org?

2)Direct org very simple process than IRISO, then why we have to do IRISO?

3)Is it possible to tranfer item between orgs in Diffrent Operating units in both Direct Org Transfer and IRISO Process?

4)In rela time at what cases we use Direct Org Transfer and IRISO Process?

5)Accounting for  both Direct Org Transfer and IRISO Process?