topic Re: Webex calling migration/HA in Webex Calling

Webex calling migration/HA

momosebi — Tue, 19 Aug 2025 17:39:53 GMT

Hello all,

So I have a customer that wants to migrate from their on-premise UCM infrastructure to Webex calling. However, they have a concern regarding the cloud hosting platform of the webex calling. If for some reason, an internet disconnection event occurs in their office, then they would essentially lose access to the Webex cloud, and in-turn this would result in a disruption of their internal calling services. A problem that doesn't exist with the existing on-prem CUCM infrastructure.

Hence, my question is this, is it possible in a Webex calling infrastructure, to have it so that they can still make calls internally, even without cloud access? I think I read somewhere that it is possible by placing a router to route the calls internally. But I don't really know much about it and would appreciate some guidiance here.

Thanks.

Re: Webex calling migration/HA

Vaijanath Sonvane — Tue, 19 Aug 2025 17:48:07 GMT

Hi @momosebi,

Similar to CUCM, Webex Calling supports survivability mode using on-premise router (Survivability Gateway) .

By default, Webex Calling endpoints operate in Active mode, connecting to the Webex cloud for SIP registration and call control. However, if the network connection to Webex breaks, endpoints switch automatically to Survivability mode and registrations fall back to the Survivability Gateway within the local network. While endpoints are in Survivability mode, the Survivability Gateway provides a basic backup calling service for those endpoints. After the network connection to Webex resumes, call control and registrations revert to the Webex cloud.

While endpoints are in Survivability mode, you can make the following calls:

Internal calling (intrasite) between supported Webex Calling endpoints
External calling (incoming and outgoing) using a local PSTN circuit or SIP trunk to external numbers and E911 providers

Please check below document for more details:

https://help.webex.com/en-us/article/d68vi1/Site-survivability-for-Webex-Calling

Re: Webex calling migration/HA

momosebi — Tue, 19 Aug 2025 19:03:27 GMT

Thank you very much for this, really does address my concern.

If you would be so kind, I've got another question.

For external calls, the customer uses a Yeaster GSM device, that connects to the CUCM servers, and routes external calls.

Can this be migrated to Webex calling, and how?

Re: Webex calling migration/HA

Vaijanath Sonvane — Tue, 19 Aug 2025 19:41:57 GMT

Hi @momosebi,

For PSTN services, Webex Calling has number of options to choose from:

1. You can go with Cisco Calling Plan. In this case, Cisco acts as your PSTN carrier, simplifying number provisioning and management within Control Hub.

https://help.webex.com/en-us/article/nousk9ab/Get-Started-with-the-Cisco-Calling-Plans

2. Or You can choose one of the Cloud Connected Service Provider. Check below URL for list of providers:

https://www.webex.com/products/calling-global-availability.html

Re: Webex calling migration/HA

momosebi — Wed, 20 Aug 2025 08:35:23 GMT

Thank you @Vaijanath Sonvane.

However, I though Webex offered an option that allows one to maintain existing PSTN services, and easily migrate it to the Webex cloud.

Also from the link you shared earlier, I understand that to implement the survivability mode, you need a survivability gateway, which has to be an IOS XE device like the C8200 router. However, I'm unsure of the necessary router physical configuration, like in terms of the necessary modules (NIM/Voice modules), or the necessary software or subscriptions (like maybe DNA subscriptions), or other necessary accessories for the router. I don't know if you or anyone has an idea about this.

Re: Webex calling migration/HA

kellysmith9312 — Mon, 01 Sep 2025 07:03:18 GMT

Yes, it is possible to keep internal calling running even if the internet goes down. Webex Calling can be paired with a Local Gateway or SRST (Survivable Remote Site Telephony) so that phones can still call each other internally and even make critical PSTN calls during an outage. For more complex needs, some companies opt for a hybrid setup or Webex Calling Dedicated Instance to maintain full resiliency.

We have helped businesses set up this kind of failover-ready Webex Calling solution. If you would like to see how it works in practice, you can check us out here: sparxitsolutions.com

Re: Webex calling migration/HA

kerneltech — Tue, 10 Feb 2026 12:59:28 GMT

Thanks for sharing this scenario — Webex Calling migrations in HA environments can definitely get tricky, especially when downtime and call continuity are critical.

From experience, the safest approach is to treat the migration as a phased transition rather than a single cutover. Start by validating number assignments, device mappings, and routing behavior in a test location or subset of users. This helps surface issues early, particularly around call routing, survivability, and failover behavior.

It’s also important to double-check dependencies like SBC configuration, PSTN connectivity, and user feature parity before moving production traffic. Clear rollback steps and proper monitoring during the migration window make a big difference in avoiding service disruption.

We’ve handled similar web and communication platform migrations where stability and minimal downtime were the top priorities. Sometimes a small adjustment in sequencing or validation saves hours of troubleshooting later.

If anyone’s interested in structured migration planning or needs technical support beyond Cisco docs, you can also find practical implementation insights here:

https://kerneltech.net/