Hi,
How can in a communication between the Access Pt. and the Station Pts. how can I know whether the client is a mobile/PC or it is an ESP
How can in a communication between the Access Pt. and the Station Pts.
Most people use TCP/IP for this.
how can I know whether the client is a mobile/PC or it is an ESP
You cannot know. The MAC address may be an indication but you cannot be sure expect if you have some sort of authentication in the protocol you use. As you failed to provide any information about your setup, that's already more help than you could expect.