You don't need a Wireless Router. What you need is an Access point and the way you locate your access point is very important. Check the following diagram and make sure you sit your Access Point properly
Internet --> ISP (or T1) modem--> VPN or Firewall router--> LAN switch (or switches)--> Access Point
That said, your Access Point needs to be in the LAN network. If you have the Wireless router, you have to locate it at the VPN or Firewall layer and you have to dial in VPN every time access to the LAN. Therefore, Access Point is what you need.
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