Solution : https://service.sap.com/sap/support/notes/384077 (SAP Service marketplace login required)
Key words : 
dispatcher und gateway parameter settings, cost based optimizer statistics, send large amounts, parameter rdisp/rfc_min_wait_dia_wp, parameter rdisp/rfc_max_own_used_wp, achieve optimum performance, guarantee secure communication, symptom problems occur, data transfer performance, avoid online users
Related Notes : 
       
| 438015 | Latest qRFC version and supplement for 3.x, 4.x, 6.10, 6.20 | 
| 436687 | Composite SAP note: APO integration performance | 
| 430725 | Inbound queueus for PI.2001.1 | 
| 416475 | APO CIF: Customizing for inbound queues | 
| 400330 | Outbound Scheduler/qOUT Scheduler | 
| 384971 | System parameters for high interface load | 
| 375566 | Large number of entries in tRFC and qRFC tables | 
| 370601 | Composite SAP note: APO 3.0 and 3.1 performance | 
| 74141 | Resource Management for tRFC and aRFC |