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Using two or more DSL lines

Fri, 10/09/2009 - 12:50 — JP Hebert

elfiq cable modem dslA common customer request is to use two or more low-cost DSL lines, balanced by an Elfiq appliance for uptime and performance.  This approach is quite common and has its pros & cons, here is an overview of what to expect doing such a project: 

Pros:
  • DSL are low-cost lines, budgets are not very much impacted compared to multiple T1s/E1s
  • DSL is widely available in most regions
  • In the same region DSL can be offered by multiple carriers
  • DSL is fairly fast, where it is now common to get 6Mbps+ of download throughput
Cons:
  • Single point of failure: using two DSLs will drive performance but not reliability for the first 100 yards. Usually DSL lines connect to the same CO’s so if the connection to the CO is severed, all DSL lines will have the same downtime.  Most DSL infrastructures are owned by one carrier in a specific region so if you sign up with multiple DSL providers, you still have the same 100 yard point of failure
  • Upload speed: if your organization uploads large files, bear in mind that most DSLs are 768Kbps for upload speed. Link balancers are by nature session-based balancers to maintain persistence and prevent session resets, so your upload can go as fast as your fastest link only
In regards to the first con, the best approach is to diversify by adding another carrier in the region (should it be available) like a cable modem link (and dowload speeds reach up to 45Mbps in some regions).  The idea is to break away from connecting all circuits to the same CO, and cable providers have their own infrastructure parallel to the telcos.  If you cannot get another wired connection, consider WiMAX should it be available in your region or 3G wireless to have bandwidth in case of complete DSL signal loss.

 

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