What is Modem Doubling?

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  • Written By: Malcolm Tatum
  • Edited By: Bronwyn Harris
  • Last Modified Date: 09 October 2019
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Modem doubling is a simple means of increasing the speed of a dial-up Internet connection by essentially making use of two standard 56kbps modems to create a double link with the Internet Service Provider. The end result is a structure that not only makes it possible to receive and transmit data more quickly, but also provides an excellent backup in the event that one of the two connections is interrupted for some reason.

The actual process of modem doubling can take place in two different ways. The fist is known as modem bonding. This approach is perhaps the most commonly used method, since the vast majority of ISPs are configured to support modem bonding. Essentially, this form of modem doubling will make use of the Multilink Protocol Plus component and essentially route half of the data packet from the service provider to each modem connection. At the end user level, the two halves are seamlessly recombined. The result is a faster connection speed for the dial up user. At the same time, the dual connection to the ISP means that if one modem connection drops for any reason, the remaining modem connection simply picks up the slack and the user can continue browsing the Internet on the strength of the one modem connection.


The second form of modem doubling is known as modem teaming. This approach can be utilized when the ISP in question does not support Multilink Protocol Plus. In this scenario, the two modems will work as separate connections, but will make good use of the download capabilities that allow most FTP and HTTP servers to continue functioning when a download is interrupted for some reason. Essentially, a software component will tell the primary modem to download the first half of the data packet while simultaneously telling the second modem to download the second half of the packet.

Once received, the two halves are combined. One disadvantage of modem teaming is that in the event one modem is disconnected from the ISP, there is no automatic compensation on the part of the other modem. This means the download will stop, effectively freezing the connection until some sort of manual intervention takes place.

For people who live in areas where DSL, wireless, or cable modems are not currently available, the ability to use modem doubling to increase dial up connection speed can make it possible to enjoy streaming media and other larger applications with greater ease. An additional dial up modem, along with teaming software, can be purchased at most computer stores, as well as purchased online.


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Post 3

Does this work with DSL/DSL2 modems?

My ISP has some kind of speed-limitation for up/download. The fastest I can manage is 500KB/s. I've sometimes jumped to 550KB/s, but it inevitably falls back.

Post 2

No, I don't think you have to use two identical modems, as it is the software that effectively does the job of receiving and integrating the two data streams. But you probably do want to use two modems that offer the same or similar transmission speeds. For example, if you have a 56K dialup modem built into your tower, you would want to use an exterior (soft) modem for the second data stream that also offered a 56k capability. Word of advice here - check that soft modem to see if it is marketed as a fax modem; if so, even if it does say 56K, it probably will not give you the speed you get from your internal modem

Post 1

Interesting article! Just either of these two scenarios (bonding vs.teaming), are identical modems required in order to function properly? Also, how the connections between the modems made (are they daisy0chained or what)? Thanks in advance for your prompt reply.

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