Use an SIP provider to setting up a VoIP service might cause several problems, include the lack of standardization. Different parameters are required to use the same SIP client with various SIP providers. If different clients want to connect to the same SIP provider, they will need new pieces of information. Sometimes, many of new users who are getting into the field of SIP VoIP for the first time are being confuse of this problem. They need to set a few parameters which are confusing, such as authentication username, outbound proxy servers, STUN servers, codec, etc. Users like us might be able to set those parameters in proper way, if we can figure out for ourselves or wait for connection to an SIP server has standardized interface. It’s easy to figure out how to automatically provision the SIP client. Simply contact the ITSP, if you have obtained a plan of hosted PBX.
The network administrator and the ISPs may be imposing settings for the local security and firewalls. But, you can bypass it by using the outbound proxy server. This is because an ISP will block the most commonly used port to restrict VoIP call on its network. The SIP client cannot use regular means to initiate VoIP calls to a server of SIP, without this being accessible. In order to do it, workaround is required. STUN server is a one well known way to achieve it. Make sure that your outbound proxy has configured is the other way to the SIP server
The SIP client will send a request to the outbound proxy and it doesn’t have a VoIP call appearance. It is merely the proxy itself which will act as a go between and communicate with the server. It’s named “proxy” due to the same appearance like a VPN or a Virtual Private Network.
However, an outbound proxy server may not be so important for you at all. But, this field also entrusted by some SIP clients and providers. If you need to configure your clients but you didn’t get the proper settings from your provider, this can be complicated. Since an outbound proxy server would just be a waste when making use of a STUN server, you don’t need to configure it at all.
Visit your provider’s website (Internet Call Services) and spend your time on it to search for the information of what your proxy settings are. Or simply call your SIP provider. They will give you the details of how to automatically configure the VoIP phone of your clients.