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How does the Load Balancing feature work in a capable CradlePoint router?

This article is intended to provide a high-level explanation of how the load balancing feature works in a capable CradlePoint router.  First, it is important to understand that the CradlePoint router does not perform aggregate channel bonded load balancing.  CradlePoint routers attempt to balance modem use based on available bandwidth on attached load balanced modems.  However, the CradlePoint router will not sum the available bandwidths of attached load balanced modems nor will summed bandwidth be reflected in an online speed test.

Each modem (air card) attached to the router that is load balanced has an associated bandwidth value.  For example, let’s say modem A has an available bandwidth of 1Mbps and modem B has an available bandwidth of 2Mbps.  When an IP connection (session) is generated from a computer attached to the router, the router will assess the available bandwidth of each modem and place the connection on the modem with the greatest available bandwidth (in this example, this would be modem B), then subtract the connection’s required bandwidth from the available bandwidth on modem B.  Only Modem B will be utilized for this IP connection.  As new IP connections (session) are generated from a computer, the router will again check modem A and modem B for available bandwidth.  If modem B still has more available bandwidth than modem A, then modem B will again be utilized for this new IP connection until the connection is terminated.  The available bandwidth of each modem will be checked each time new IP connections are generated, and modem A will not be ever be utilized unless it has greater available bandwidth than modem B.

Based on the above description, one can see that the attached load balanced modems are not evenly utilized, nor is the available bandwidth of the modems summed together.  This issue can be accentuated when there is a very large difference in the available bandwidth of the two attached modems, for instance, an attached 4G modem in combination with an attached 3G modem.  In cases such as this, the 3G modem may be only slightly utilized, or possibly not at all, depending on the volume of IP connections that are generated from attached computers.  However, services such as bit torrents will usually utilize both modems very well due to the fact that multiple individual IP connections are spawned while a torrent is downloading.

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