Back-Up, Resiliency and Redundancy: Let’s Discuss

By June 27, 2018 August 13th, 2018 No Comments

From a voice perspective Back-Up, Resiliency and Redundancy are among the most discussed topics we have with our clients, and probably some of the more complex discussions given the options available and technologies involved. I’m going to assume for the purposes of this article that the reader is using a premise-based phone system, because those users who have a hosted PBX don’t need to worry about voice redundancy in the same way.

Hosted PBX:In a hosted PBX environment the back-up and phone system is in the cloud, and in the event of a power failure, building catastrophe, or other natural disaster, the calls continue uninterrupted to the cloud phone system. If the company has lost their phones because of fire, for example, they can be up and running as quickly as they can find/buy and power up a new phone. I recall a scenario with one of our hosted PBX clients, when last winter their electrical system was shut down for almost a week because of an accident outside their building, and the users brought their IP phones home, and the calls continued uninterrupted to the hosted IP phones.


Premise-Based System:For those companies using a premise-based phone system there are many other considerations and costs involved. One of the considerations is the types of lines that the organization is using, and given that the majority of our clients are still using a PRI circuit, for the purposes of this article I will assume that the reader still has PRI lines terminating to their phone system. One of the problems with PRI is that it is not very elegant in the way it fails. Unlike a SIP trunk, which can fail seamlessly between IP addresses, a PRI circuit can not easily fail from one building to the next or from one phone system to the next. Further, in a PBX environment, if the primary PBX fails we still need to fail the PBX to an alternate PBX. So, let’s address these two issues: 1. Back-up PBX, and 2. Back-up and resiliency in the phone lines.

With regards to a back-up PBX, let’s assume the customer is using an Avaya IP Office phone system with IP phones, and has a single site. With an Avaya solution it is possible to install a second Avaya IP Office cabinet and make the phone systems redundant to one another. Let’s imagine a primary phone system at head office, and second phone system at a data center. The Avaya phone system will replicate itself to a second back-up box, in an active / back-up manner, and all applications and programming on the back-up box will reside in the back-up system and remain idle until required. Then when needed, the IP phones can fail from the active system to the back-up system. The IP phones will re-authenticate themselves automatically from the primary to the back-up, the voice mail will fail from the active to the back-up, and now full phone set call control has been moved from the primary phone system to the back-up phone system. If the company has two sites, let’s say one in Toronto and the other in Montreal, for example, the two systems can act as back-ups to one another, so the IP Phones from Toronto can fail to the phone system in Montreal, and vice versa. The one caveat to the above is that only IP phones will fail, digital phones will not.

Phone Lines:  From a phone line perspective, we now need to address how to terminate the calls to either the back-up system, or as in the example, from Toronto to Montreal and vice versa. If the company is using SIP trunks, it is quite easy to fail calls between sites / systems because the lines are addressable via IP address. Unfortunately a PRI circuit isn’t quite as elegant in the way it fails.  It isn’t very straight forward from a carrier perspective to have a PRI fail from Toronto to Montreal. In order to get around this problem we fail the PRI to SIP using extended overflow, a feature enabled on the PRI circuit itself. If the PRI fails, or, there is a D channel failure on the PRI circuit, we fail the PRI to a number of SIP trunks. If the phone lines are down and the phone system itself is fine, the PRI will fail to SIP, and the calls will continue uninterrupted.

I remember a scenario a number of months ago where Digitcom’s PRI circuit failed and practically no one noticed because the PRI failed to our SIP trunks, and all calls in and out continued to flow as normal. Now, if the phone system itself has failed, the SIP trunks have nothing to fail to, so it is possible to fail SIP trunks from one IP address to another, or in this case, from Toronto to Montreal. If the IP phones in Toronto are still working but the phone system has failed, it is possible for all IP phones from Toronto to re-authenticate to Montreal, all calls flow to Montreal, and users in Toronto can answer as normal. If the Toronto site has lost complete power, the calls will flow to Montreal and the alternate receptionist, or auto attendant, can answer calls in the interim. The key to the above is using a combination of PRI and SIP to make the solution work.  Digitcom refers to the above as SureConnect, a full fail between PRI to SIP, and from SIP to SIP.

Hosted PBX Back-Up, SureConnect:The above scenario is somewhat expensive, however, so what we have done for a number of clients who don’t want to invest in a second system is fail the PRI to our hosted PBX, enable an auto attendant with a number of extensions that have mobile twinning enabled, and for as little as $100 / month a company can have a full active back-up solution that is enabled, live and ready to go 24 X 7 X 365. We can program all users onto the hosted PBX platform and provide twinning to their cell phones, so if the auto attendant is called, an extension dialed, the call will twin to the users cell phone. We have done this for dozens of clients, and when Digitcom had a power failure in March, our PRI failed to SIP. But since our Avaya phone system was down, the calls flowed to our hosted auto attendant. Since most of our employees have hosted PBX phones working at home, we advised staff not to come to the office, and the calls continued as normal. We also refer to this solution as SureConnect AutoAttendant.

Digitcom has been selling Hosted PBX and SIP trunks from our completely redundant data center at 151 Front Street since mid 2012, and we have enabled hosted PBX and SIP for many hundreds of customers. We have been selling PRI lines since 2010, and can deliver a complete end-to-end solution. If you are interested please get in touch with someone from our sales team.



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