Call Drops

Call are Dropping but only sometimes

This may indicate that the phone is not reregistering on its set interval with the Gazelle switch (3600s) . The switch will assume that the device is no longer present and will drop any calls that may be in progress.

  • Verify the latest firmware is being ran on the phone/adapter.
  • If you are running your phone behind a NAT firewall that is SIP aware, packet mangling may be occuring.
  • If you have other IP handsets or ATAs, check if they are also configured with the same phone number. This could create registration conflicts and sudden call drops while the other devices registers on the same number.

 

 

Calls are Dropping after a few seconds of being answered

This typically means there is no reply to the 200 OK from the Gazelle switch. The 200 OK indicates the call has been answered.

The phone could possibly be:

- Responding to the 200 OK but is routing to the wrong place.

- The phone is responding on the wrong port. ie: port 0

- The phone is responding back to the wrong IP address.

- A SIP aware firewall may be mangling packets or not forwarding SIP ACKs in NAT scenarios. We have seen this behavior in Juniper firewalls.

 

Calls drop 15 minutes into call

If you are a SIP trunk client and are dropping audio in your call after approximately 15 minutes, you may not be responding to the SIP re-INVITE. Our switch performs a SIP re-INVITE every 15 minutes for any active calls in your SIP Trunk. It's a way of checking if the call is indeed still active. If an appropriate 200 OK is not received back, we disconnect the call.

 

 

Calls drop 30 seconds into call

This may occur if you are using an ATA or IP Phone peered directly to Gazelle's switch.

What happens is our switch sends a SIP 'keep alive' every 30 seconds to make sure the call is still active. It does this be sending a SIP re-invite for the live call, in which we expect a 200 OK response, that we then ACK back. If no response is received, the call is terminated by the switch.

 

This could be caused by:

- A SIP aware firewall that is mangling packets.

- NAT issues on your router and does not support SIP properly

 

 

Calls drop 50 minutes into a call.

This may occur if we don't get a response to our 'keep alive'

What happens is our switch sends a SIP 'keep alive' after 50 minutes to make sure the call is still active. It does this be sending a SIP reINVITE for the live call, in which we expect a 200 OK response, that we then ACK back. If no response is receive, the call is terminated by our switch.

We would have to investigate the call logs to confirm the above and if confirmed then the settings on your PBX as to why it is not responding to reINVITEs.

If you require this investigated further please open a support ticket via http://support.gazellecorporation.com or you can contact us by phone at 416-549-5000.

 

 

Dropped calls when using a Sonicwall 2040

If you are experiencing dropped calls, this is probably the result of SIP ALG (application layer gateway) functionality being active. Basically the firewall is mangling SIP packets, of which our switch rejects. Often by canceling the phone call.

 

To fix this, disable the "Enable SIP Transformations" option in the VOIP tab in your Sonicwall's admin panel.

 

 

Dropped calls when using a Juniper firewall

Calls can be dropped about 30s or 15m into a call across our Juniper firewall. This is due to the ALG (application layer gateway) service for SIP not handling packets properly. When we send a SIP re-invite, the remote VoIP gateway responds with the proper 200/OK; however the Juniper firewall drops the 200 response and our switch hangs up the call from lack of response.

 

Disable ALG for SIP and also follow up with Juniper Support for the latest firmware/patches for your firewall.

 

 

 

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