Send IDoc from External System to SAP system

Hi Folks,

I have a requirement to send IDocs from an external system to the SAp system. Basically the external system is a subsystem which is able to send & receive idocs. The external system is currently able to send idocs to SAP system through the ALE layer but now we have to replace it by PI. Now the external system has to send teh IDocs to the SAP ECC system through the SAP PI 7.0.

Kindly let me knowq how I can achieve it.

Regards,

Santosh