Ok, I am back. I am getting a lot of good input to my original post, and I have more questions, but first let me try and answer all the questions put to me.
Firstly, my internet connection, all devices on my AirPort network are wireless, and each device is visible on the AirPort Extreme Utility App device pop up screen. These devices include, Mac Pro laptop, El Capitan, HP laptop, Win.10, 2 iPhones, 2 mini iPads, Directv, HP Printer, and 3 undefined Home Theatre connections. I need to get clarification on the latter 3 connections. All of these devices, absent a power outage, are connected 24/7. We have had several outages over the past year and, in each instance, when the power came back all device connected to the internet with no action on my part, other than, maybe, selecting the network to connect to, being required.
I now understand that my network configuration includes two routers in series, the combined ATT Modem / Net Gear Router and the AirPort Extreme router. I also understand that my Airport setting in this type of configuration is incorrect and should be set at "Bridge." This "serial" set up is attributable to my stupidity.
In previous networks in a Comcast ISP environment. I had a Modem and a router providing wired and wireless connectivity to the internet. The most recent router with Comcast was the Airport. In this new set up with ATT I dismissed, without thought, the Net Gear component and installed the Airport. When each device,as detailed above, joined the network, without so much as a hiccup, I assumed all was well. It was always evident, when a device needed a reconnect, that in addition to the AirPort network and neighborhood networks, there was a ATT network and a Directv.network available. I never attempted to use either of these networks.
Now comes the Samsung BD-J5700 Blue Ray Device which I am attempting to wirelessly connect to my network. There is a internet connection set up function within the overall blue Ray set up procedure that I am using. One of the screens looked for and located my wireless networks and it displayed, among several, the AirPort and ATT networks. I selected AirPort and I kept getting various messages that indicated "unable" to connect to the network and the internet or connected to the network but unable to connect to the internet. I should note here that this was all after I had entered an IP address, gateway etc manually. The auto connect function had failed repeatedly so I tried the manual route. I looked at the settings of several connected devices and used those settings changing only the last box on the IP address to a new number. In most instances the failed message also suggested I contact the ISP provider.
I called Samsung and the best they could do was to advise that I contact my ISP provider. I then contacted ATT and at first they didn't want to talk to me because of the AirPort being between the device and the ATT Modem/Router. It was suggested that I could try to set the device up on the ATT network. We did this and lo and behold it worked. I now have 2 active networks in play and how that plays out over time I don't have a clue. The Blue Ray is connected to the internet but I would prefer having all devices on the same network, hence my post for help.
Given what I have heard so far I have a few questions:
Since I am not using the AirPort as a repeater and the AirPort and the ATT modem/router sit side by side, should I consider moving all the devices to the ATT network and then simply disconnect the AirPort?
Does the AirPort bring any advantages to the table otherwise not inherent in the ATT Net Gear device
If I leave the AirPort in place and change its setting to "Bridge" what will happen to the connected devices? Will there be a transparent shift to ATT addresses and no required action on my part?
Lastly, thanks to all who have responded to my post.