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Start my making sure your Draytek units have the most current firmware. &nbsp;<br />
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It sounds like you may have a proxy issue of some sort.. &nbsp;<br />
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Start my making sure your Draytek units have the most current firmware.  

It sounds like you may have a proxy issue of some sort..  

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We found the problem and solved it
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Hello experts,<br />
<br />
We have a YeaStar MyPBX standard edition V4 in our head office. It has LAN IP 192.168.99.99/24 . There are many phones in the HO which are working well. All those phone are in the subnet 192.168.99.0/24<br />
<br />
The problem is in a remote extension YeaLink T22 IP Phone, which has IP address 192.168.41.111/24 and connects to the PBX through gateway 192.168.41.1 (DrayTek VPN router)<br />
<br />
This remote phone registers well when it boots up. But after a while, it show (Register failed) in it's status web page while still showing as registered in the PBX CLI console.<br />
<br />
Another problem is, when I try to call that remote phone from any extension, I get error 486 (Busy Here) which represents call refusing in the phone. <br />
<br />
I have double checked codecs order and everything seems to be ok. <br />
<br />
Can anybody please advice how to troubleshoot the issue?
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Hello experts,

We have a YeaStar MyPBX standard edition V4 in our head office. It has LAN IP 192.168.99.99/24 . There are many phones in the HO which are working well. All those phone are in the subnet 192.168.99.0/24

The problem is in a remote extension YeaLink T22 IP Phone, which has IP address 192.168.41.111/24 and connects to the PBX through gateway 192.168.41.1 (DrayTek VPN router)

This remote phone registers well when it boots up. But after a while, it show (Register failed) in it's status web page while still showing as registered in the PBX CLI console.

Another problem is, when I try to call that remote phone from any extension, I get error 486 (Busy Here) which represents call refusing in the phone. 

I have double checked codecs order and everything seems to be ok. 

Can anybody please advice how to troubleshoot the issue?

SIP IP Phone connectivity issue

Voice over IP (VoIP) is a methodology and group of technologies for the delivery of voice communications and multimedia sessions over Internet Protocol (IP) networks, such as the Internet. Other terms commonly associated with VoIP are IP telephony, Internet telephony, broadband telephony, and broadband phone service. The term specifically refers to the provisioning of communications services (voice, fax, SMS, voice-messaging) over the public Internet, rather than via the public switched telephone network (PSTN).  Examples of the VoIP protocols are H.323, Media Gateway Control Protocol (MGCP), Session Initiation Protocol (SIP), H.248 (also known as Media Gateway Control (Megaco)), Real-time Transport Protocol (RTP), Real-time Transport Control Protocol (RTCP), Secure Real-time Transport Protocol (SRTP), Session Description Protocol (SDP), and Inter-Asterisk eXchange (IAX).

Voice Over IP

IP telephony (Internet Protocol telephony) is a general term for the technologies that use the Internet Protocol's packet-switched connections to exchange voice, fax, and other forms of information that have traditionally been carried over the dedicated circuit-switched connections of the public switched telephone network (PSTN). Using the Internet, calls travel as packets of data on shared lines, avoiding the tolls of the PSTN. The challenge in IP telephony is to deliver the voice, fax, or video packets in a dependable flow to the user.

IP Telephony

Telecommunication occurs when the exchange of information between two or more entities (communication) includes the use of technology. Communication technology uses channels to transmit information (as electrical signals), either over a physical medium (such as signal cables), or in the form of electromagnetic waves. The word is often used in its plural form, telecommunications, because it involves many different technologies.