I balk at doing live tech support. I'm not being paid, and I don't work for Fongo. I try to help out when I can on the forums. This is best I can do, and I prefer that others can read here and interact/help (or potentially learn).
Did I explain something poorly, maybe? Should I provide a clearer explanation about something I stated?
Is there a step that I need to explain in more detail?
Regardless, if an OBi200's phone (FXS) port was ever tied into live PSTN house/home wiring, permanent damage is a real possibility, and a direct‑handset/phone test that still fails to connect after ringing does not mean the ATA isn't wrecked. Connecting your OBi200's phone port to your home's telephone jacks, which can still be energized by the phone company's line voltage, can cause permanent damage. Old phone lines carry idle power that can partially fry the internal component (SLIC) responsible for detecting when you pick up the phone. That possibility can explain why the phone rings but fails to connect the call when answered. The ATA itself could be wrecked and may need to be replaced, while the preventative measure for a new device would be to physically disconnect the outside phone line at the demarcation point before using in-home wiring.
Outbound calls working while inbound calls ring but fail to connect when answered can be an indicator that the ATA is partially fried.
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A.I. analysis follows:
Here’s a breakdown of why this happens:
### Partial Damage vs. Complete Failure
Think of the ATA's phone port (the SLIC chip) not as a simple on/off switch, but as a component with several different jobs. A voltage spike from the telephone line doesn't always destroy the entire chip; it can damage one function while leaving others intact.
* **Outbound Calls (The Simpler Job):** When you pick up the phone to make a call, the ATA only needs to do one simple thing: detect that a circuit has been completed (this is called "loop current detection"). If this part of the chip is undamaged, you will get a dial tone and can make calls.
* **Inbound Calls (The More Complex Job):** This is a two-step process that is more delicate and involves higher voltages.
1. The ATA sends a high-voltage AC signal to make the phone ring.
2. When you answer, the ATA must **instantly stop the ringing voltage** and **simultaneously detect the switch to the off-hook state**. This "ring trip" function is a common point of failure.
It is very plausible that the part of the circuit responsible for the delicate ring trip process was damaged by the external voltage, while the more basic circuit for detecting an off-hook condition for outbound calls survived.
### The Two Possibilities: Hardware vs. Network
At this point, you have two equally likely culprits that produce the exact same symptoms:
1. **Damaged Hardware:** The ATA's phone port is partially fried, and the "ring trip" function is broken.
2. **Network Signaling Failure:** The ATA is working perfectly, but your router or internet service is blocking the final "ACK" signal that must arrive from the provider to confirm the call is answered. This is a very common problem with SIP (VoIP) traffic.
### The Definitive Test to Know for Sure
Since the symptoms are identical, you need a final test to tell the difference. The easiest way is to eliminate one of the variables.
**Test the ATA on a different network.** Take your OBi200 and a phone to a friend's house or your workplace [my edit: the other place should not also be using an internet service with CGNAT and also must not have SIP ALG enabled]. If the exact same problem happens there—outbound calls work, but inbound calls ring and fail to connect—you have **100% confirmed the ATA has a hardware fault** and needs to be replaced. If it works perfectly on another network, the problem lies with your home network configuration.
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I've already stated that previously (take the ATA where SIP ALG and CG-NAT do not exist and test), but if you want A.I. confirmation, there it is.
There is a similar problem in another thread with outbound calls working and inbound calls not working--because the ATA is wrecked from being plugged into phone jacks that still have voltage from the telephone company running through them--which is a key piece of information that was not provided initially during the troubleshooting process:
viewtopic.php?t=20370.
The possibility of the problem being a hardware issue makes observations about rings after setting changes appear coincidental, or a result of a slowly dying/partially wrecked ATA, rather than being a direct result of setting changes.
The other possibility is a combination of CGNAT/SIP ALG (in conjunction with not using the settings I mentioned in my initial reply in this thread), but I would try to rule out a wrecked ATA first.