Bridges and remote phones in disaster recovery scenario

Discussion in '3CX Phone System - General' started by Matt Crouch, Oct 20, 2017.

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  1. Matt Crouch

    Oct 20, 2017
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    My company currently has a Cudatel phone system that we will most likely be replacing with 3CX. As part of our DR discussions i have some questions.

    If we have a private cloud in a local data center with the Master 3CX unit at this location and a Slave 3CX unit at our office bridged i have the following questions:

    1. If the internet goes out at the office, can i use the 3CX app on my smart phone to make and receive calls?
    2. Would i be better off not having a bridge and only a Master in the private cloud and have nearly 70 phones at the office just be remote phones?
    3. What is the impact of having that many remote phones on the internet service?

    I am open to suggestions if you guys have any other ideas for a disaster recovery scenario.

  2. NickD_3CX

    NickD_3CX Support Team
    Staff Member 3CX Support

    Jun 2, 2014
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    First I'll try to your first question:

    1. "If the internet goes out at the office, can i use the 3CX app on my smart phone to make and receive calls?"
    > The 3CX app must be able to connect to a 3CX that is accessible and has internet. I presume your question is in the scenario that you have Master 3CX (in data center) bridged with Slave 3CX (onsite), normally 3CX client will be connected to the onsite one, but if onsite internet connection goes down, will you be able to have your 3CX apps, over 3G/4G, connect to Master 3CX and make calls. The answer you be "Yes", as long as the user has an extension account on the Master 3CX.

    The other 2 questions are kind of related. Having 70 remote phones in an idle state not making calls, the bandwidth is minimal, they send a few REGISTER UDP packet every ~80 seconds and get responses each. Bandwidth is worth calculating for how many concurrent users you anticipate being on the phone at the same time. There is an old blog post about this with some information:

    The short version, for regular codecs (e.g. G711) you should calculate ~100 Kbps Up / ~100 Kbps Down per call. If you use a compressed codec (GSM, G729, Speex) it would be approximately half that per call.
    Now whether or not you should or should not have 2 3CXs, that is entirely up to you. Technically you don't need it, you could have all phones connect to the Master directly either using 2 SBCs if they deskphones or have them all as STUN (SBC requires onsite devices, STUN requires port forwarding for each and every phone are remote site).
    If you do have an onsite Slave 3CX though, even if the internet does go down, you would still be able to make calls between extensions. You could also have a local PSTN Gateway to send calls out locally for redundancy.

    The topic is not as simple as a yes or no, there are many possibilities but it all depends on what your requirements are.
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