The two methods of bandwidth aggregation used by the multiport analog routers we tested--Multilink PPP (MLPPP) and proprietary load-sharing--work from different network levels. MLPPP multiplexes individual packets down two or more connection links. Load-sharing, which Ramp Networks calls COLT (Connection Optimized Link Technology) and Multi-Tech employs in a similar form, multiplexes whole TCP sessions down the various PPP links. If you have only one TCP session, as you would with FTP, MLPPP provides increased bandwidth; COLT does not.

You should consider using a device that supports MLPPP, such as the Multi-Tech, Netopia or 3Com routers, if your remote office will be connecting to a central site where your company controls the connection equipment or to an ISP that supports that protocol. ISPs that offer multichannel ISDN should have no problem offering MLPPP for analog lines, but few actually do.

Ramp Networks' COLT, on the other hand, doesn't require special support, and the same holds true for Multi-Tech's version. In fact, you can use different ISPs for each modem's connection. The advantage here is increased fault tolerance in the event of disrupted service to one ISP. However, because COLT requires the use of NAT (Network Address Translation), only a select number of machines in a remote office are individually addressable by an outside source. In addition, COLT supports only the IP protocol. Unless your company uses a tunneling protocol, you won't be able to run multiple protocols from a remote office to a central office.

In making the decision whether to choose a device that uses load-sharing or MLPPP, consider your network topology. Does it route to a remote network or use NAT? Either aggregation technology can use NAT, which allows all the remote-office machines to share a single user account (one IP address). If you choose a load-sharing device, you have to use NAT. MLPPP connections can be configured either way.