Office network failover? [duplicate]

Possible Duplicate:
What hardware do I need to add a backup internet connection?

I have a office LAN providing internet access to several workstations. Each workstation is basically connected to the hub, which is connected to the router through ethernet.

Wat I need to do is to hire another provider and enable any method to switch user's internet connection if the active connection goes down.

How can I do this?

All you need is a router that supports multi-WAN failover. There are many of them on the market - do some research and choose one. I won't get into product recommendations here since that is off-topic.

Alternatively, you can set up a pfSense box and use that as your router - it supports multi-WAN very well and is free (if you have some spare hardware to run it on).