DSL line redundancy - is this setup a good solution?

[AndyCan]

I'm no longer working in a school, i've moved onto a new job in the private sector, but from the amount i used to come on here when i worked in a school i thought id see if anyone can offer any advice on the following.

 

I've been tasked with upgrading a company's internal network. They currently have 2 dsl lines coming in from 2 different suppliers (the thinking being that if 1 company has network problems) its unlikely the other will. While it sounds a good idea im sure there is a better way of doing this, could the one company set something up to be able to guarantee at least 1 line is always up and working?

 

These lines come into the standard routers provided which dont appear to be up to much then both go into a SonicWall TZ 210. I'm not familiar with SonicWall equipment but my next job is to determine whether or not the TZ 210 is suitable for 150 users or if i'll have to upgrade to something a little more robust. Anyone with any SonicWall knowledge please feel free to interject here!

 

So i guess i'm asking, does this setup sound like a good solution or could it be improved. any thoughts?

[glennda]

There are various options available depending on cost which vary from Leased lines with ADSL backup, EFM(Ethernet for the first mile), Bt infinity could also be an option.