Question : Trafic through dual WAN modem (bandwith)?

(This is continuation from http:Q_24192729.html, namely from http:Q_24192729.html#23787976)

We were suggested to use dual WAN modem -- in our case 2 ADSL from the same ISP. That is because the telephone centre has technical limitation 4 Mbits/s per one phone link.

The main goal is not increasing reliability but to get higher traffic throughput. Our main task is a remote administration of our customers via terminal services (Microsoft environment). Currently, we observe slowdown when more of our people do administration on more customer sites.

keith_alabaster said "... even with dual links, you will need to set a default gateway to one of the connected ISP's with the other as failover. The reason being that ISA will establish a connection (takes SSL for example) with an internet site - you will need to ensure that traffic within a session always takes the same route to its destination so be aware that you will not get a combined bandwidth." http:Q_24192729.html#23787976

Could you explain that better in our context?

Is the usage of a dual WAN modem a good approach to solve our problem? Are there any other alternatives, suggestions, comments?

Thanks,
    Petr

Answer : Trafic through dual WAN modem (bandwith)?

With dual WAN modems, you will get two logical paths where the data can usually be load balanced.
In this scenario, if you have two 4Mb lines, you could have two 4 Mb transfers going at once but you would be unable to achieve a single 8 Mb transfer.
The issue would come down to what type of layer 2 transport the modems are using.  Are you using PPP to connect to your ISP?  If so, you would have to use multilink PPP and then you could aggregate the bandwidth into one logical pipe.  Your ISP would also have to support multilink for it to work.  You can aggregate two lines with one router such as a Linksys running a special variant of Tomato/MLPPP.
http://fixppp.org/
You could also purchase a cisco router thats supports MLPPP.