How to connect analog devices to Microsoft Teams?

In this post I give you an architectural overview on how you can connect analog devices, e.g. fax machines, analog phones, door bells, intercoms etc. to Microsoft Teams.


First of all, I’d recommend to please get rid of your analog devices. Let me guess you are probably reading this because you have some of these poor and legacy analogs which you cannot get rid of for some reasons?

  • If this is the case:
    Well, ok, let’s go ahead to keep your existing investments in analog devices and get it to work.
  • If not, i.e. you can get rid of them:
    Skip this post and read something more interesting. 😉


The goal is to add analog devices to a Microsoft Teams voice/telephony deployment.

Use Cases – Analog Telephony with Teams user and PSTN

The uses cases are defined as follows:

  1. call from an analog device to a Teams user
  2. call from a Teams user to an analog device
  3. call from an analog device to a PSTN (external) phone (number) [e.g. mobile phone]
  4. call from a PSTN (external) phone to an analog device

Architecture Overview

In this architectural sketch you can see a high level Microsoft Teams Direct Routing deployment including an analog device which is connected via an anlog [device] gateway.

It includes

  • [left] PSTN sip trunk [from your PSTN provider of choice],
  • [center] a (certified) session border controller (SBC),
  • [center] a analog [device] gateway
    • sip trunk between analog gateway and SBC
    • analog link (FXS, RJ11) between analog gateway and analog device
  • [center-right] analog device [connect to analog gateway]
  • [right] a Microsoft Phone System sip trunk
  • [right] a Microsoft Teams User


What are the requirements for this? To keep it short, you need:

  1. Teams Direct Routing (TDR) [for details, please see Plan Direct Routing]
  2. Analog [Device] Gateway

Note: In case you have Microsoft Teams and utilize calling plans for telephony already but need these analog devices added you can add Teams Direct Routing to what you’ve got already.

Conclusion, opinion and summary

To sum this up, to connect analog devices to your Microsoft Teams deployment you need Teams Direct Routing (TDR). Then you can attach an analog device to an analog (device) gateway which is linked to a certified SBC for Direct Routing which handles the voice routing (from/to PSTN/Microsoft Phone System/analog gateway).

Additional resources


  1. Quick question – If we use MS Teams calling plan at the same time can we also integrate with on-prem SBC to route calls to other PBXs within the network. The SBC will nto route calls to PSTN, just to internal devices.

    Liked by 1 person

    • Yes, you can combine both Teams Direct Routing and Calling Plans.
      You need to create and assign a Voice Routing Policy incl. PSTN usage with the phone numbers for the analogs which are behind the SBC and the analog device gateway/s. In the Voice Routing Policy and PSTN usage only the numbers for the analogs should be included. and if a Teams users makes an internal call to the analogs the assigned Voice Routing Policy incl. PSTN usage… is applied and the analog rings. Otherwise a PSTN call is made if the user has a domestic or international calling plan assigned.

      For details please see
      There is a slide deck regarding “Direct Routing” from Microsoft available it also depicts the voice routing in this scenario on slide number 32 “Voice routing basics” (July 2020).


  2. Is it possible to explain a little bit this comment: “Note: In case you have Microsoft Teams and utilize calling plans for telephony already but need these analog devices added you can add Teams Direct Routing to what you’ve got already.”

    We are moving to Teams and moving all our users online to use Calling Plans on Microsoft Phone System. We don’t have an existing PSTN and all I want to do is be able to use an Audiocodecs SBC + ATA to allow our existing fax machines to function. The idea is that Microsoft Teams + Calling Plans are our phone system, with a few FAX machines attached with an ATA to this environment. Is that actually possible? All documentation points to the need for a PSTN service or some SIP trunk, but our end goal is to be full Microsoft Phone System + few devices through ATA. We don’t even need these devices on the ATA to be “callable” from within Teams, they just need to be able to call our and be called to for FAX.


    • Hello Dmitri,
      what you read is right, you need a PSTN SIP Trunk from a provider.
      I.e. you need to connect a PSTN SIP Trunk to the SBC and the ATAs, too.
      On the SBC you’ll have to configure the connection and routing between both, the PSTN SIP Trunk and the ATAs with the attached fax machines.
      The SIP trunk to Teams is not needed if you don’t want to call to/from analogs to/from Teams.
      You cannot route calls from Microsoft 365 Phone System Phone Numbers (calling plan-based) to onpremise analog devices, at least I’m not aware that this is possible at the moment. You can assign a calling plan only to a user or a service (call queues/…) not to a analog or something.
      The described approach in this comment also means that if you need to configure this with a PSTN SIP Trunk and that you get new phone numbers and need to use those for the fax machines, analogs etc. which are attach to this PSTN SIP Trunk via SBC and ATAs.The question here is how many analogs / fax machines do you have and did you consider to migrate those devices to a Fax2Mail/Mail2Fax service? There are cloud based fax services. Nevertheless you’ll have different phone numbers for these fax “machines” and you cannot use the numbers which you have on the Microsoft 365 Phone System.
      I hope this helps and explained the architecture a bit better?
      Best Regards


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