We have use SNAP PAC R2 for wireless data transmission.
Is it possible to connect SNAP PAC R2 cpu with S7-400 plc using Ethernet prote privided on cpu.
Have you considered using Modbus? For example, this document shows Modbus/TCP: http://www.industry.siemens.com/datapool/industry/industrysolutions/services/en/Open-MODBUSTCP-for-SIMATIC-systems-en.pdf.
I strongly suggest you contact our Product Support Group (click here). They have lots of experience helping our customers get going with Modbus.