Unable to use Broadband across my office

[skrao]

My set up1 Airtel BB connection with Binatone router24 port D-Link switch5 Wireless access points across the building connected to the Dlink switchInternet setupThe Airtel BB is connected through a patch cable to a port on the switch, wireless access is a key protected network working on the same 192.168.x.x series with 255.255.255.0 subnet.clients are WinXP desk and laptops with wireless access cards. Now the issueThe router is configured as the default gateway on all the clients. Internet access happens in bursts. appears and disappears with out any reset /repair or change. When it works its adequately fast and all clients (16 in total) have connectivity, ping response to our own hosted server is good. when the connection drops it stays dropped for a long time ( typically for about 45 mins to an hour) then magically reappears.We use a web app that fortunately uses a XML store and forward mechanism so work does not get affected, however it is an irritant for those needing mailing etc. Airtel support visited the site, connected a laptop directly to the router and said,our problem is to land internet till here, after this we arent responsible. Have tried everything from reboots, to resets etc no luckPlease help