Acessing existing router and other devices on network

Thr Router is a TP-Link Archer C2300.   The home network looks like this:  Home networked devices > Router > T-Mobile Gateway (ethernet cable).  Laptop is connected:  Laptop > T-mobile Gateway (ethernet cable) (using both ethernet ports on the gateway).  The Router is using one of the gateway’s ethernet ports and the Laptop is using the other. The router is located in a networking closet and is ethernet connected through in-wall cabling and is actually located two floors below the gateway. The laptop is located 5’ from the gateway. I would like for the Laptop to be connected on the home network and to have visibility to all of the connected devices on the network.  I don’t know how to do this when going through the T-Mobile gateway and would like instructions.

I appreciate your response but that answer doesn’t solve my problem.  My laptop and T-mobile gateway are two floors away from the router and supplimentary switches for all of my ethernet connections.  I only have one Cat5e cable running through ther walls from the network closet to the office where the laptop and gateway are located.  Previously, when I was using cable for internet, my laptop was connected via ethernet, to the router through that in-wall cat5e cable.  Now the T-moble gateway uses that single cat5e cable to connect to the router two floors below.  Because the t-mobile gateway is now using the cat5e cable connection to the router, I have lost the ethernet connection to my laptop.  My current solution is to connect my laptop directly to the t-Mobile gateway via cat5e cable an using the 2nd ethernet (RJ45) port at the back of the gateway.  

My issue is that the T-moble Gateway is not acting like a switch and is not allowing me to access my router and home networked devices.  Is there a way to configure the T-Mobile gateway so that it acts like a network switch and allows for one connected device to have visibility and access to another connected device, when both devices are connected to the gateway by ethernet (hardwired devices)?    I prefer not to use wifi connections for my computers when connected to my home network.

@206-369-5787 

“My issue is that the T-moblie Gateway is not acting like a switch and is not allowing me to access my router and home networked devices.  - True, the gateway is just a dumb gateway, providing the user access (or a gateway to the T-Mobile cellular network). 

Is there a way to configure the T-Mobile gateway so that it acts like a network switch and allows for one connected device to have visibility and access to another connected device, when both devices are connected to the gateway by ethernet (hardwired devices)?  - No, this is where you need a router to move traffic between devices. 

  I prefer not to use wifi connections for my computers when connected to my home network.” - Then you need a take the time to install cat5 cables between your router (they usually have 4-5 cat5 ports) and where your devices will be used (upstairs or downstairs). 

I hope this helps.