Since office phone systems based on VoIP typically include more than one phone or fax machine, each with a separate IP address, SIP can create multiple problems in this back and forth call retrieval. Your router will receive all return messages as coming from one device with an identical IP address and won’t be able to distribute the inbound message to the right device. VoIP server uses the public IP address to return the message back to the caller.Ĭaller’s phone system is not able to recognize the exact phone it needs to deliver the return message to, since SIP ALG removed its private IP address. Phone data is sent to the #VoIP servers in a public IP address format. The private IP address from a specific phone is modified into a public IP address by SIP ALG. What happens when SIP ALG is turned on on your router? This issues maybe not occurred when you are using one IP phone or trunk behind the NAT, but assume about 3 or more IP phones or trunk behind the NAT or some of them are using on the NAT and another are connecting via routing such as OSPF and etc, you will be crazy when you have launched a system like the solution that I mentioned, They also commonly have problems with their own internal NAT Routing Table for the messages they transformed, causing some SIP messages to be delivered to the wrong endpoint or not be delivered at all. The replacement of the private IP is done via Scripting, which can also eliminate critical parts of the SIP message. Secondly, many commercial Firewalls and Modems do not fully understand SIP and SIP Routing. The message is delivered back to the Public IP Address and Port from which it was received. Our system fully understands NAT and prefers the use of private IP addresses in SIP Messaging as opposed to the Public IP Address. To this day some still do not understand NAT. SIP ALG was built as a tool when Hosted PBX's didn't have a great NAT solution. It is a NAT tool that inspects SIP Messages and transforms the Private IP addresses and Ports to Public IP Addresses and Ports.
You will find it on many commercial and residential Firewalls, Routers, or Modems. SIP ALG stands for Application Layer #Gateway.
0 kommentar(er)
