How to connect a landline through the optical modem dial? If you plug in the phone without dialing sound, don't rush to change the phone—it's almost always stuck in voice registration

my mom's landline had been used for over ten years. Last year, when I renewed my broadband and switched to a fusion plan, the installer just said, 'Connect the landline via the fiber modem' and left. I plugged the phone cable into the narrow port behind the optical modem, and when I took it off, there was no dialing sound. My first reaction was that the phone was broken. I pulled out another cordless phone and tried it, but it still didn't work. After fiddling all night, I realized the phone was perfectly fine, but the issue was stuck in the voice registration layer on the optical modem. This article will clearly explain the path I've traveled all at once.

first identify the port: the narrow port behind the optical modem is not the network port

the row of ports on the back of the optical modem, from left to right, usually the round power port, optical port (with silkscreen PON or optical modem graphics), four or five network ports (LAN), and some even have a USB port. Mixed in, there's a phone port that is one way narrower than the network port, usually marked with TEL, PHONE, or POTS.

you don't need to carry silk screen prints—just look at the crystal head. The telephone cable uses an RJ11 connector, either 4-core or 2-core, which is a size smaller than the RJ45 (8-core) network cable. Small heads inserted into large holes cause wobbling and poor contact. The narrow opening that can be inserted firmly is this one, and physically it's hard to insert it wrong. My mom's TEWA-750G has one telephone port, and the Huawei 8145 series also has one common one. Some models have two, but the second one usually doesn't send data or gets any response. Make sure to use the first one.

by the way, the network port is a different matter—if you plug in the gigabit or hundred-gibit port incorrectly, the speed drops to 93 Mbps. I previously wrote an article specifically about how to distinguish between gigabit and hundred-gigabit ports telecom optical modem, gigabit and hundred-gigabit ports. If you can't tell if this unit is an optical modem, check out this article: Is 192.168.2.1 an optical modem or a router ?

The premise for using it as soon as you plug it in

: fixed-line services must be included in the plan

fiber optic has been installed in households, fixed-line wires have long stopped using copper wires. The analog sound coming from the phone is converted to digital signal by the optical modem and taken out by a broadband car. This system is called VOIP. The optical modem stores a set of SIP account passwords, which are responsible for "checking in" with the data center's voice server. Only when you check in with your number are you considered alive. This configuration is remotely issued by ITMS; you don't need to fill it out, and you won't be asked to fill it out.

there's only one prerequisite for plugging in and it works: number is activated . Nowadays, most fusion plans come with a landline. My mom's 129 plan comes with a landline number, zero monthly fee, and local calls are charged by the minute; If you want to secure a single broadband, you have to go to a service center to add a voice pack, which can't be done in the app. The phone side is zero-threshold; regular phones, cordless mother-to-child phones, and senior phones with large buttons all work, and caller ID works fine.

one situation to watch out for: after replacing the modem or restoring the system, landlines lose sound, most likely because voice data hasn't been sent again. Restoring the factory will reset the SIP configuration to zero. Wait for ITMS to reboot, or call 10000 directly to have the technician remotely re-register. Don't mess around with it yourself. I've stepped into the cost of factory reset once and wrote a detailed article: Telecom optical modem can't access the network after restoring factory settings. I've also written about the temperament of the ITMS system being changed back to midnight: What should I do if the Telecom's optical modem configuration is changed back to midnight

before dialing the phone, check the phone light first; don't rush to change the phone

went back to the night my mom did. The troubleshooting starts with just one thing: look at the telephone light on the front of the modem (marked with TEL or PHONE, some machines call it VOICE). This light has three states, each with completely different meanings:

My mom's desk lamp is out. Step one: Restart the optical modem, unplug it, wait 30 seconds before plugging it in, and then just wait. From power-on to the phone light stays on, sometimes one or two minutes, sometimes five or six minutes. Don't try it out right after powering on—trying it out is just a waste of worry. I lost here in my first round—after one minute of powering on, the light went off, so I had to restart three times. The more I restarted, the less it registered. I waited patiently, and after five minutes, the light came on on by itself.

restarting the two-wheel lights, they still won't turn on. Check two things. First, light decay. If the received optical power is between -8 and -27, it's considered healthy. If it exceeds -28, voice registration will fail. Logging into 192.168.2.1 (a regular useradmin account is enough) can be seen on the status page. How to handle high light degradation? I've written: What to do if the Telecom optical modem has high light degradation Second, for overdue fees, you have the same account as a landline and broadband. If you have a connection to the bill, the system will be suspended together. After paying the fee, restart the fiber modem and wait for registration. For plans and billing, check out this article: How to change your Telecom broadband plan to make worthwhile.

I had already cleared my floor and it still wasn't enough, I called 10,000 to report 'voice registration failed.' The technician remotely reissued the data, and my mom's last step was this. About ten minutes after the call, the light came on. If you find making calls troublesome, you can also report a fault with one click in the Xiaoyi Butler app: what use is the Xiaoyi Butler app ? If you catch the LOS red light flashing in the light language section, that's a matter of the light path. There's another article: What does it mean to keep flashing red light on light modem LOS .

three pitfalls: losing power means being mute, which is the most fatal problem

After moving

fixed phone to the optical modem, there are three pitfalls that are completely different from the old copper wire era.

Pitfall 1: Power outage, internet connection, and landline completely shut down. the ONT doesn't turn on power, the landline instantly becomes a decoration. Don't expect to make emergency calls—it's out of power at all. In 2024, China Unicom made headlines because of this, with customer service saying, "After fiber optic integration into the home, both landlines and networks rely on the optical modem." If you have elderly people at home, don't plug the modem into a power strip that can be turned off easily, and don't try to save electricity by cutting off the power on schedule. If you're particular about it, equip the optical modem with a small UPS. The UPS in my NAS also comes with the optical modem router. After a power outage, the landline can last over forty minutes, enough to make several repair calls: NAS should I install a UPS?

pit two: when switching to bridge, don't touch the VOICE one. the optical modem has two independent WAN connection records: the internet channel and voice channel are two separate WAN connection records. When switching to bridging, only touch the INTERNET channel; don't touch the VOICE channel. If you turn on the landline, there will be no response immediately. The process for using the super password to enter the backend and change the bridge is here. Which one is marked inside: how to get the telecom admin super password for the telecom modem.

pitfall three: Call forwarding calls disappear without a trace. set the phone to unconditionally transfer to a landline, so during outages, incoming calls go unanswered without leaving a trace, and there won't be missed call notifications when you go back. If your landline at home often loses power, use this transfer with caution.

Fax machine, don't forcibly connect

readers have asked about fax machines. You can hear the dialing sound through the phone port, and you can dial too, but the success rate of fax calls depends on luck. VOIP line faxing uses the T.38 protocol, which requires support from both the carrier side and the optical modem. Old fax machines operate according to the copper wire era timing; out of ten faxes, six or seven can be transmitted, which is considered a great loss. The more complex the file, the easier it is to break up.

nowadays, fax needs have basically been replaced: scanned paper documents into electronic WeChat and sent over, or if the recipient wants a fax number, just ask if the email is okay. If your employer strictly requires faxing, first call 10000 to ask if T.38 is available on the current line. Don't repeatedly redial to waste phone credit.

Who would need a landline to be used? Here's the screening order

it's not that the old word is useless, but its use has narrowed. There are three groups of people worth continuing to use: elderly family members who can call with a landline earpiece without unlocking or finding apps; Residential community access control or building intercom must be secured with phone numbers; Banks and hospitals that leave landline contact info are troublesome to bind and save trouble. If you don't have these issues, just keep the number in the plan. If you don't pick up the phone, you won't spend a penny.

the end provides a complete inspection order, following the order from top to bottom:

there's another easily overlooked point: if you ever want to cancel your broadband, your landline will disappear along with it. If you want to keep your number, you have to first apply for a landline or bind it to a mobile plan, then uninstall broadband. If you reverse the order, the number will be gone. What equipment must be returned when canceling, and how are penalties calculated? I accompanied my mother-in-law to handle it, and all the accounts were settled here: Telecom broadband is no longer used, how do you cancel and disassemble the phone? .