Two routers, two modems

While I'd like to think of myself as an above average individual when it comes to understanding residential networks, that may not be the case with respect to commercial applications. I'm hoping this forum may provide me with some further knowledge.

The situation I'm hoping can be resolved here involves two cable modems and two airport extremes. Being a large stucco building where cat 5e is not in place throughout, the current setup includes the following...

On the main floor there is a cable modem connected to an airport extreme with two additional airport expresses located at other areas to create full coverage. In the attic is another cable modem connected to a second airport extreme with two additional airport expresses connected via cat 5e cable. Each airport extreme currently has a different SSID and password therefore creating two separate networks, one upstairs and one down.

My question is given that two cable modems are present, is it possible to create one roaming network rather than have two separate or will that cause problems with the devices that try and connect? If in fact this is a problem, are there any ways to accomplish the roaming network? Would a mesh network be any different?

Thanks to any and all for taking the time and your help.

The simplest way is to get rid of one of the cable modems and use the extreme and expresses it was servicing to extend the network you have from the other cable modem and network. In doing so you could get rid of the subscription to the second cable supplier.

In order to roam across wireless hotspots you need the same SSID throughout the network. You also need to be able to maintain the same IP address (to maintain a continuous connection). This means having one router acting as the DHCP server. There are ways to configure two or more routers as dhcp servers but that wouldn't really serve your roaming requirement.

Mrplow...

Thanks for the reply.

I believe the reason that a second cable modem is in place is due in part because of the different variables at play (i.e. thick stucco walls, second floor hallway w/ rooms, etc.). By adding additional expresses to the second floor would possibly cause a weak signal to those respective devices along with reducing speed and/or overall performance. I have no idea whether or not what I've mentioned is true with respect to your suggestion, but from the information I have had an opportunity to gather from the internet, the belief is that for every additional express, your network performance is diminished...slightly. By adding as many as this situation would require, I'm concerned that it may not work and ultimately cause frustration for the guests and ownership alike for this bed & breakfast location.

I truly appreciate your response and certainly welcome any feedback you have. Thanks again for all of your time and enjoy the day.

It's hard to advise fully without being on site but I'll go ahead and say that two separate and distinct incoming Internet connections are not going to come together in one bonded network very easily if at all in this scenario.

IMO you're better off looking at ways to get a single network distributed throughout.

Obviously cabling to a wireless access point(s) is ideal but not always practical.

But that doesn't mean there aren't more options. Perhaps consider Ethernet over power adapters (power line). It depends on how the ring main is wired in the property but power line adapters, especially those with wireless hotspots built in can get a network connection anywhere there's power. Consider those that have a power pass through and wireless capability. Like these:
Amazon.com: Linksys Powerline AV Wireless Network Extender (PLWK400): Computers & Accessories

Lets assume that you can connect to both first floor and second floor SSIDs from either floor. Would this be correct?

If running Mountain Lion or Mavericks option click on the WIFI icon in the menu bar and select open Wireless Diagnostics.
Select the Window menu and then Utilities. Then select Performance.

As the graph fills in you are looking to have and SNR value of 20 or higher. This constitutes an Excellent connection. Anything lower than 5 is unacceptable. 10-20 would be the minimum and deemed a Good connection.

This will help you place the Airport Expresses as to not saturate a location and under serve another. This is not the Apple best practice, but it is a supported one that does not require wiring each AE location.

Mesh in this case would be achieved by placing the AE devices to maintain the highest SNR value. Keep in mind that wireless traffic is not full duplex. This means that AEs that are only connected wirelessly versus back fed to the Airport Extreme will perform slower simply because they can only transmit or receive data and not both at the same time.

Wi-Fi base stations: Extending the range of your wireless network by adding additional Wi-Fi base stations