Accepted Solutions
Yes they will still be able to make calls. The recommendation would be to turn off the CMs with a gap of time in between, so that the phones have time to pickup that the node has disappeared from the network.
A device always has an active connection with two CM nodes that acts as call processing engines, one active and one standby. If one of these disappears from the network the device will form a connection with the next in line node, in your case CM3. If it’s CM1 that disappears the phone will directly make the connection with CM2 active and put CM3 as the standby. If it’s CM2 that disappears the device will keep the CM1 in active state and put CM3 as standby. With this the device always has a connection with two CPEs and will switch between these with zero interference to the service. If you were to turn off both CM1 and CM2 at the very same time there would be a period of time before the device would pick up that both CPEs has disappeared from the network and trigger the connection with the third CM in the list. This will cause a service disruption.
As you can only have three CMs selected in a CMG, Call Manager Group, the forth CPE in the list would come from the SRST configuration in CM, aka it would reference an IOS gateway that acts as a fallback device, ie SRST, Survivable Remote Site Telephony.
I think the OP meant to say that CM3 is at the time the only active cluster node that runs the Call Manager service. At least that’s how I read it.
The phone will not re-register or drop any active call as long as they have an active connection with one of the two CPEs, ie the active or standby.
I updated my original response to add some more details.
Correct. As explained as long as the device has an operational connection to one of the two CPEs, active or standby, it would not cause any service disruption.
I don’t agree with that outline from TAC. From my experience the UX of the phone would be a short blip on the display as it changes the active CPE node, but it would not have any significant noticeable effect and if there would be an active call it would not be visibly affected. In fact we’re doing this each time we do an upgrade of our CMs as we then shutdown each one of the cluster nodes in a timed sequence to create a clone of the VM. This has no visible effect on the services for end users.
Likely the best thing for you would be to see this in action yourself by scheduling a maintenance window and test it out by turning off on CPE node for a short time period. If you have the possibility to temporarily make a specific CPE active for a small amount of devices so that you have a controlled group of phones affected that would be the best, but if not it not a big deal.
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Yes they will still be able to make calls. The recommendation would be to turn off the CMs with a gap of time in between, so that the phones have time to pickup that the node has disappeared from the network.
A device always has an active connection with two CM nodes that acts as call processing engines, one active and one standby. If one of these disappears from the network the device will form a connection with the next in line node, in your case CM3. If it’s CM1 that disappears the phone will directly make the connection with CM2 active and put CM3 as the standby. If it’s CM2 that disappears the device will keep the CM1 in active state and put CM3 as standby. With this the device always has a connection with two CPEs and will switch between these with zero interference to the service. If you were to turn off both CM1 and CM2 at the very same time there would be a period of time before the device would pick up that both CPEs has disappeared from the network and trigger the connection with the third CM in the list. This will cause a service disruption.
As you can only have three CMs selected in a CMG, Call Manager Group, the forth CPE in the list would come from the SRST configuration in CM, aka it would reference an IOS gateway that acts as a fallback device, ie SRST, Survivable Remote Site Telephony.
