There are 2 IOS devices: device C and device S. They both host a service with a characteristic and both advertise themselves. Device C have found device S and connects to it. After characteristic is found, connection C -> S is established. But after it, device S wants to connect back and write ti characteristic on device C, instead of writing to local characteristic and notifying device C. That way both devices are central and peripheral at the same time. Is there a way to do this?
Yes, there is. It is possible to act simultaneously as a Central and Peripheral device, but be aware if u are using IBeacon technology, IBeacon scanner will intercept peripheral device and stop it from reaching your central scanner. (Meaning it cannot be an IBeacon and a peripheral at the same time and u would have to stop advertising beacon before becoming a peripheral)
To create a "two way connection" in that way u would neeed to implement both CBCentralManagerDelegate and CBPeripheralManagerDelegate and initiate subsequent classes. After establishing "C - > S" connection, u would need to "tell" S how to correctly identify C, then initiate your second connection.