DSL Redundancy and Failover Options

DSL services do not carry an SLA (Service Level Agreement) so, if having a broadband connection is important to your business these options will be of interest. The solution which best suits your business is dependant on a combination of factors including:

  • How 'mission critical' is the connection
  • Level of technical expertise on site
  • Cost of the solution

This document starts off with the least cost solutions and works up to 'the best' DSL redundancy options.

Options with a Single DSL Line

The diagram below shows a basic setup (click to enlarge). There is no physical redundancy on the customer site and no mitigation against provider and DSLAM issues. While Gconnect has multiple redundant connections to the internet, and multiple, geographically diverse connections to our provider networks, the area which causes most issues (the phone line and local exchange) is not covered.

Gconnect Single ADSL Line Diagram

Keep some spare hardware

We would always recommend having a spare (new and tested) microfilter and DSL router. If you do not have the technical know-how to configure the spare router, we would encourage getting your IT support company to do this for you in advance.

Just one DSL line, what can be done?

With a single broadband line there is not much redundancy available on the line itself, however you can elect to have BT Total care on the PSTN line (Public Switched Telephone Network) and BT Enhanced Care on the DSL service. These services will provide an elevated level of support should a fault arise. Under normal circumstances there is no SLA (service level agreement) on the DSL service so the provider is under no obligation to repair the fault in a fixed time frame. If a continuous broadband connection is required for your business a second line should be considered.

Options with 2 DSL Lines

Once the decision to install a backup line or second DSL line has been made there are several ways to deploy the line which will depend on your businesses circumstances and level of expertise.

This diagram shows a single router connected to 2 DSL lines, from 2 different providers. Gconnect can provide BT based DSL and O2 based DSL services to provide 'provider level' redundancy. The local telephone exchange equipment is normally different with different 'back haul' across the provider cloud, which terminates in the Gconnect network in different equipment in different locations. The copper pair from the telephone exchange to the PSTN box in your office, while being different may still be in the same physical cable, so a digger in the street could still render both lines useless, however this occurrence is very rare.

Gconnect Dual ADSL Line Diagram

Option 1 - Single Standard DSL router

While still using two DSL lines, a standard DSL router can connect to a single DSL line, and in the event of a connection problem can be moved to the backup line by simply unplugging the router from one phone line and plugging into the other. To make this easy, you would need to have either a multiply router or, more likely use a spare router for the backup line. The reason for this is that in order to provide provider redundancy the username and password would need to be different on each line.

Option 2 - Dual WAN DSL Router

Some DSL routers can support dual DSL connections and will manage the failover from one provider to the other. Some will even load share over the two lines which gives the best of both worlds. This setup while giving connection redundancy, does not give 'in-situ' hardware redundancy. Again, we would always recommend having a spare (new and tested) microfilter and DSL router. As with any router, if you do not have the technical know-how to configure the spare router, we would recommend getting your IT support company to do this for you and test it in advance. Dual WAN DSL routers are more expensive than most, so it may be reasonable to use a standard DSL router as a spare, which should be a temporary measure, but this depends on your business requirements.

Option 3 - Two active DSL Routers

This diagram illustrates two DSL routers connected to two different providers simultaneously.

Gconnect Dual ADSL Line Diagram

Both lines should be up and running, and providing your PC/server supports it, multiple gateways can be configured to use the primary, and should that fail, the secondary service. If that setup is not possible, one line can be kept with the LAN connection disconnected until needed. When using this sort of solution the requirement for keeping spare equipment is diminished, so long as the business can survive on one line. There are many network design variations available with this model including splitting the LAN into 2 groups and using 2 gateways or policy routing.

Option 4 - Two Cisco DSL routers

The 'Rolls-Royce' solution to redundant DSL is to use 2 routers, 'in-situ' with seamless failover between them which is invisible to the network users. Similar to the above scenario, however the Cisco routers can act as a 'pair' using HSRP (Hot Standby Routing Protocol) and both lines can be utilised to send different types of traffic (policy routing), yet failover to one of the lines if needed. Failover is seamless and requires no intervention from staff on site. Gconnect provide a Cisco device management service for this sort of setup.

Next Steps

Our sales team and technical support team will be glad to discuss options with you to get the best solution for your business.

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