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Home » Kerio User Forums » Kerio Operator » Gigaset C470 + C610 - rtp lost packet - voice droupouts

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Kerio Operator 2.4.5 build 5285 running in Hyper-V environment.

We are using Grandstream phones and now we addedd couple of Gigaset C470IP and C610IP.

Gigaset phones suffers from dropouts during the calls.
The incomming stream is 100% correct without any packet loss.
The outgoing stream (from the phone to the Operator) is sometimes 51% RTP packet loss.


- no matter if the call is inside or outside organization
- phones reseted to factory defaults
- gigabit network
- when Gigaset configured with additional SIP account to the server in internet - call 100% correct
- no NAT between phone and Operator
- same VoIP account configured on softphone/smartphone or Gradnstream - without issue
- Gigaset phones with the latest firmware

Are the Gigaset phones known to have issues with Operator?

Please help me troubleshoot.

Filip Jenicek (Kerio)

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we have one Gigaset unit in the office and as far as I can tell, it worked fine. However, I have tried it only a few times and the base station was always just a couple of meters away.

Could it be some interference on the wireless part? Was the handset near the base station and was it in the same place while making both test calls (Operator/Internet server)?

Please try to install Operator on a physical HW or use a different virt. environment to rule out the hyper-v environment. Try, for example, virtualbox.

Brian (GFI/Kerio)

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You can also look at the call history in Kerio Operator. There you can see the "From QoS" and the "To QoS". It shows you the packet loss, total packets, and jitter for both directions. This way you can compare the results from Operator to your packet capture. It does seem though that you have some kind of network issue if you have packet loss.

Brian Carmichael
Instructional Content Architect

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Well it looks like we sorted it out.

After numerous tests we did following:

- created brand new VM for Operator
- installed latest build
- restored configuration from backup

Unfortunately no tests made after the fresh install (late night:-)

- my colleague pointed me check the network connection of Hyper-V 2012 R2 host
- we use MS network teaming of two 1Gbit copper
- switch independent NIC teaming
- on both cards we spot discarded packets


- temporarily disabled one network card of the team

The day after there were no problems with the calls made by Gigasets.

Hopefully soon will have opportunity to test the calls with fully enabled teaming to determine if the cure was reinstall or disabling the NIC teaming.

Anyway interesting is that Grandstream phones were without problem when Teaming enabled.

Are there any known problems with 2012 R2 NIC teaming feature and VoIP?


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OK now confirmed we have found the cause of the problems.

Kerio Operator as Virtual Machine in Hyper-V 2012 R2

Hyper-V server connected to the network via 2x1Gbit network cards joined by feature "Nic teaming - switch independent" into one 2Gbit NIC - and thats the cause of the problems.

When 2 or more cards in nic team ---> Gigaset phones have problem with call dropouts.
Only one direction (from Gigaset to Operator) is affected
Doesnt matter if Legacy or Modern NIC is being used in the Operator VM.

Immediately when Operator is connected only via one physical line - calls are clear and ok.

The desk phones - Grandstream are not affected with same problem.
Filip Jenicek (Kerio)

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Thank you for sharing your findings. It is strange indeed.

Perhaps the hyper-v is doing some load balancing and decided to send the traffic for the Gigaset IP over the second interface.
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