How to setup seamless wireless roaming ?

There are a few different ways one can accomplish wireless roaming with more than one access point (or multiple routers set as access points) in a way that wireless clients can connect to either AP, without noticing and without having to connect to a different WiFi network.

Multiple APs
The simplest setup involves setting up multiple APs (or routers set as APs) of any brand, connecting them to the same WiFi network with the same DHCP server, same SSID, same security type (i.e. WPA2-AES, etc.), same passphrase, but different channels.
This type of setup allows for clients to roam around the coverage area, and switch between APs without noticing interruptions in most cases. It is suitable for most home setups, however it has a couple of limitations: clients will only switch to another AP when the signal degrades enough so that it is not usable, they will not use the stronger signal when in range of two APs. Also, a VoIP/Skype call may be dropped in the split second when switching between APs.

Seamless Roaming
If you need to have clients use the stronger signal when in range of two APs, you need a feature called "seamless handoff", a.k.a seamless handover, seamless roaming, zero-handoff. It must be supported by the APs, since it is not part of the WiFi specs. Seamless roaming allows for communication between the APs, so that clients will use the stronger/better signal when in range of multiple APs, and clients will not notice any connection interruptions when switching between APs, even with VoIP. This type of setup does not work with most routers set as APs, it usually requires enterprise level APs that suppor the feature. The cheaper decent option for setting up seamless roaming is usually with Ubiquiti APs.

Mesh Wi-Fi
Mesh Wireless systems consist of multiple hardware devices of the same type connected wirelessly and communicating with each other, serving clients similarly to APs, extending the wireless range of a single AP without the limitations and speed disadvantages of repeaters/extenders. There are several new mesh systems on the market that include three devices in a package deal for under $500. We have several such WiFi systems listed in the broadband hardware section. This is also an option for an extended coverage with seamless roaming.