DSL Bonding vs Bonding DSL with Cable

Bonded DSL vs bonding DSL with cable modem

When your branch offices are distributed over multiple geographical regions, chances are your WAN connectivity options at every branch office are not uniform and in some cases are limited. Unlike a decade ago, a single WAN connection is never going to be an acceptable network design given the fact that organizations increasingly depend on cloud-based applications that can’t perform without Internet connectivity. This dynamic creates the pressure and need for IT managers to design networks that relax the dependency on a single point of failure (i.e. a single ISP design), as much as possible. Thanks to Software Defined modern Broadband Bonding routers, organizations can now design WAN networks that can leverage 2 or more WAN resources intelligently. 

As an example, a remote office can look at bonding DSL lines to get higher performance and reliability. Or, if ISP diversity is one of the design requirements of the network, DSL can be broadband bonded with a Cable modem to provide a network that can take advantage of the best of both worlds, namely the high bandwidth (yet sometimes unreliable) specs of Cable with the more dependable, yet lower bandwidth of DSL services. The question to address for IT managers: Is bonding DSL lines with a bonded DSL modem the better option compared to combining cable with DSL?

Well, “yes and no”. If you are combining same transport types, such as bonding 2 or more DSL lines, then legacy aggregation algorithms can perform better up to a limit, without requiring more intelligent management of the resources that the modern bonding algorithms implement. In practice though, one should keep in mind that 2 identical types of DSL lines will never look and behave identically in real world setups, even when they are colocated. For a variety of reasons that we won’t get into here, the performance fluctuations in the DSL lines can be uncorrelated and therefore at any given time one of your DSL line may be better than the other when considering various performance parameters, such as bandwidth, packet loss, jitter and others. However, the chances of having somewhat similar performance metrics on the transport is more likely with 2 DSL lines (or 2 Cable lines for that matter) compared to a strategy of combining different transport types (i.e. one DSL with one Cable).

So, we need to assume that the performance fluctuations in the WAN resources are unavoidable. For those scenarios, an approach that is adaptive and molds the bonding algorithm to adapt to the WAN conditions is the best approach. With Software Defined WAN (SD-WAN) architecture, Broadband Bonding routers can effectively change the bonding algorithm on the fly and per application, to provide the best end-user experience for that application. This was a major leap forward in the WAN management sector as it opened up the ability to bring wildly different network types together and still have optimal end-user experience irrespective of the applications at hand.

In light of all this perspective, can one claim that a bonded DSL modem (i.e. bonding 2 DSL lines) is a better approach than bonding DSL with Cable? Not necessarily. As we mentioned, if you have access to an SD-WAN based Broadband Bonding router, adding carrier diversity to your branch office WAN network will tilt the scale towards ISP diversity.

Of course, speaking of diversity of ISPs and variation in WAN link performances, these variations are amplified in a cellular environment. In our next post, we will look at the approaches that are involved aggregating 3G, 4G, LTE and 5G modems.

Cahit Akin, CEO, Mushroom Networks, Inc. 

Mushroom Networks is the provider of Software Defined WAN solutions capable of Broadband Bonding that enables self-healing WAN networks that route around network problems such as latency, jitter and packet loss.



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