Devices not Recognized

I have a basic setup with 2 devices and 1 gateway. I am not able to see and program the devices since I am not able to see them in the network.

These the following states of devices I am using:
1.One switch: In factory state with address15.15.255 (as per manual)
2. One actuator: In factory state with address 15.15.255 (as per manual)

3. Siemens IP Interface Gateway: Programmed to 15.15.1 address.

There is only 1 line and powered with a constant 30 V power supply. I have disconnected 1 device while programming so that it does not interfere with network due factory setting address.

I am able see and program the KNX side of the gateway but I am not able to even see/detect the device in the KNX side. The device can be turned on programming mode and so on but never visible when using ETS software.

What  could be the reason?
Atleast I

should be able to see the device in the network right?