VoIP calls drop after 30 seconds

You may experience an issue with VoIP where calls are dropped after no response (typically 30 seconds). The VOIspeed PBX is forced to end the call if it fails to get the required response according to SIP standards.

Typically VoIP calls follow the sequence below:

  • PBX gets the INVITE message from the service provider (Incoming SIP request “INVITE” FROM 83.211.227.21:5060).
  • The PBX sends reply to the device that it is trying to connect the call with the message 100 Trying (Outgoing SIP response “100 Trying” to request INVITE TO 83.211.227.21:5060).
  • When the call is answered then PBX sends reply to device with the message 200 OK (Outgoing SIP response “200 Ok” to 83.211.227.21:5060 TO INVITE request). You can check the IP address to which device must respond. This IP address is not the public IP address of the PBX. You can check the IP address by looking at the Contact packet field.
  • After the 200 OK message the PBX expects the acknowledgment message ACK from the device which suggests that the device has acknowledged that the call has been accepted.

SIP/2.0 200 OK
Via: SIP/2.0/UDP 35.14.14.30:5060;received=35.14.14.30;rport=5060;branch=z9hG4bKFB9835A2
Record-Route:
From: <sip:343242354@@voispeed.com>;tag=7CDD5F05
To: <sip:010982343240@ voispeed.com>;tag=as060f4802
Call-ID: E65610FD3FD33367
CSeq: 36 INVITE
Server: voip
Allow: INVITE, ACK, CANCEL, OPTIONS, BYE, REFER, SUBSCRIBE, NOTIFY, INFO
Supported: replaces
Contact: <sip:CALL-67081598-01098234324@343242354:5061>
Content-Type: application/sdp
Content-Length: 247

Below is a brief checklist of common causes of malfunctioning:

  • Most issues are caused by the router having multiple IP addresses and the service provider sending a reply to the wrong IP address.
  • Another possibility is that the router/firewall is blocking SIP traffic – you must make sure that the router allows VoIP traffic. With some routers you need to disable the SIP/ALG field to allow VoIP traffic.
  • Another thing to check is that the right IP address has been entered for mapping the router i.e. the router is not programmed correctly to send the VoIP traffic to the PBX and is sending the VoIP traffic to the wrong machine.
HOW TO DIAGNOSE:

To do the diagnostics from the log is simple. You just to need to look at the diagnostics of the call and capture the some of the 200 OK messages sent by the PBX and check the response from the device to the PBX. Below you’ll see that the responses show that the PBX is sending the 200 OK messages constantly but not receiving any acknowledgments.

Today 11:14:52.332 Outgoing SIP response “200 Ok” to request INVITE TO 83.211.227.21:5060
Today 11:14:52.472 Outgoing SIP response “200 Ok” to request INVITE TO 83.211.227.21:5060
Today 11:14:52.873 Outgoing SIP response “200 Ok” to request INVITE TO 83.211.227.21:5060
Today 11:14:53.679 Outgoing SIP response “200 Ok” to request INVITE TO 83.211.227.21:5060
Today 11:14:55.284 Outgoing SIP response “200 Ok” to request INVITE TO 83.211.227.21:5060
Today 11:14:58.529 Outgoing SIP response “200 Ok” to request INVITE TO 83.211.227.21:5060
Today 11:15:02.551 Outgoing SIP response “200 Ok” to request INVITE TO 83.211.227.21:5060
Today 11:15:02.551 Outgoing SIP response “200 Ok” to request INVITE TO 83.211.227.21:5060
Today 11:15:06.598 Outgoing SIP response “200 Ok” to request INVITE TO 83.211.227.21:5060
Today 11:15:10.697 Outgoing SIP response “200 Ok” to request INVITE TO 83.211.227.21:5060
Today 11:15:18.916 Outgoing SIP response “200 Ok” to request INVITE TO 83.211.227.21:5060

TO REMEDY THIS:

You must ensure that Public IP address of the PBX matches the Contact field of 200 OK messages, if the issue remains then you’ll need to check the path of the call with a network sniffer (e.g. Wire shark) which allows you to analyse the packet contents in detail. After using a network sniffer you will have full control over your router and VoIP configuration.
Please see the steps below for troubleshooting:

  • Disable all functions related to VoIP/SIP (e.g. ALG).
  • Reconfigure the port forwarding and make sure that ports are correctly pointing towards the PBX.
  • Make sure that router is set up correctly if it has more than one IP address.
  • Restart the router after making changes and then verify that all changes have been implemented.
1 Comment
  • Daniel
    Posted at 07:18h, 30 April Reply

    Very useful information. Appreciate 🙂

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