Does IPTV freeze at night? Don't just blame the network speed. I went through the account of multicast packet loss from beginning to end.

There is a strange problem with my IPTV: It was fine to watch all day during the day, but at 7 or 8 pm, CCTV5 started to produce mosaic, with broken pieces stuck up one by one, and the sound was intermittent. But it was fine when I switched to the local station. The first time I encountered it, my first reaction was the same as that of most people - the Internet is slow. You can turn on the computer to measure the speed. It runs steadily at 940 MB, and the network speed has obviously not dropped. It took me three nights to get to the root of this problem, so I’ll put the conclusion here first.: Ninety percent of IPTV mosaics are caused not by slow broadband, but by multicast data packets being lost halfway. , and the location of packet loss is different from what you think.

Find out first: IPTV live broadcast does not use your broadband at all

This is the foundation of the whole thing. Many people think that the TV card is because the broadband is fully occupied. In fact, the live broadcast of Telecom IPTV is through a special channel, which is called multicast in jargon. The computer room sends a video stream to the outside, and whoever subscribes receives it. It does not occupy your home's broadband bandwidth. I am here Let’s talk about multicast Grabbed the bag: The TV was showing a 4K live broadcast, but the broadband speed test did not move at all, and the two lanes were separate.

Separate and separate, one thing is shared: The optical fiber from the computer room to your home optical modem. Live streaming and Internet data are squeezed into the same optical fiber, and they are separated only after entering the optical modem. Therefore, for the rule of "mosaic at night, normal during the day", the first suspect is not who is grabbing the Internet in your home, but that there is something wrong with the public channel during the evening rush hour. I ranked this main line of investigation from high to low probability, step by step.

The first suspect: Light attenuation is close to the critical line, and the evening peak is overwhelmed

The first thing to look at is the backstage of optical modem. Open browser 192.168.2.1 , log in with the ordinary account useradmin (this account is on the label on optical modem’s butt, and I can’t find what I wrote. The sticker article ), Status → Device Information, look for the line "Received Optical Power", the unit is dBm. The closer this number is to 0, the better. If it is within -27, it is considered healthy. If it exceeds -28, trouble will begin.—— Light attenuation binning There is a complete scale in that article.

The reading of my home station is -27.6, which is just fine during the day. At night, the entire PON port is crowded with users. When the bit error rate rises, multicast packets begin to be lost. This multicast thing has a terrible temper.: If lost, lost, no retransmission. If you lose a packet while surfing the Internet, the other party will shout "If you didn't receive it, try sending it again." If the web page is half a second slower, you won't notice. ； If the live stream is lost, it is lost, and it will be blurred on the screen for you to see. This is why the same packet loss occurs, the Internet access on the computer is only slow, but the TV is mosaic.—— Mosaic is a unique symptom of multicast packet loss .

The trouble with light decay is that it's not your responsibility. The line is in the wall or in the corridor. Let’s make two things for free first.: Check to see if the yellow fiber optic cable entering the home is bent at right angles by the furniture. The bending radius must be 5 cm. In my cousin's house, it was bent by the legs of the sofa. After straightening out, the light attenuation returned from -28.4 to -25.1. ； Then pull out the optical fiber head on the optical modem, wipe it with dust-free paper and reinsert it all the way. It's still over -28 after the test. Don't bother yourself. Call 10000 to report "low light". The master will bring an optical power meter to measure it in sections. I wrote about this in the article about light failure.

Second suspect: Regarding the cable, if the eight cores are not complete, Gigabit becomes 100 Mbit.

The light attenuation number is normal, check the line at the next level. The network cable from the IPTV port of the optical modem to the set-top box, regardless of its good outer cover, requires all eight cores to be connected to Gigabit. If one core is broken, it will be negotiated to cancel 100M. There is a counter-intuitive point hidden here: The IPTV port itself is a 100M port . For common optical modems such as ZTE F7015T, network port 1 is Gigabit and the IPTV port is 100M. This is not a problem at first, because the code stream of an HD channel is only 8 or 9 MB, and the 100M port is more than enough. But if one and a half of the eight cores of this cable are broken, and coupled with contact oxidation, the actual speed reaches 20 to 30 Mbit/s, and a 4K channel with a bit stream of more than 10 Mbit/s is squeezed, and packet loss occurs.

Zero cost for law checking: Unplug both ends of the network cable and plug it in again until you hear a click. ； If you have a spare cable, replace it with one for comparison. If the box is far away from the optical modem and passes the wall plug panel in the middle, the wall plug module will be hardest hit by oxidation. My colleague's house had oxidation inside the panel. He directly took a long network cable from the optical modem to connect to the box. The mosaic disappeared on the spot, and the panel was replaced later. Can't tell the difference between Gigabit and 100 Mbit ports? Recognize the article , three methods can be understood in two minutes.

By the way, there was an oolong: The box is stuffed in the dead corner of the TV cabinet. In summer, there will be mosaics due to poor heat dissipation. Touch the side of the box and if it is hot, move it out half a fist. I'm here Black screen troubleshooting There is a saying in that article that it looks the same as the mosaic of lost packets, but the root cause is completely different.

The third suspect: Not all stations are stuck, but the code rate of that station is too high.

This floor is the least popular, but this is where my home ends. observe a detail: Is the mosaic blurry for all channels, or for individual channels? My CCTV5 and 4K channels are blurry, but the local channel is clean. Later, when I looked at the channel information page, I realized that standard definition channels are 2 to 3 megabytes, HD channels are 8 to 9 megabytes, and 4K channels are 12 megabytes and upwards.—— The bit rate difference between channels is five to six times . When there is still 5 megabits left in the line, low-bit-rate stations will still see it. High-bit-rate stations will be blocked first. This is the same as when there is still a trickle of water in the water pipe, a small cup of water will be enough, and a big bucket of water will not be enough.

Therefore, "it will be clear when you switch to another station" does not mean that the line is not sick, it only means that the disease has not reached the point of complete collapse. It would be a quick way to check in reverse.: Take the 4K channel with the highest bit rate as a touchstone. When it can be viewed smoothly will it be considered truly repaired. This also explains a common debate on forums - some people say "My IPTV is good", while others say "My IPTV is cluttered". The two people may have similar line conditions, but one only watches news broadcasts, and the other only watches sports and movie channels.

The judgment method is very simple: Press the "Confirm" or "Information" button on the remote control, and most boxes will pop up the information page of the current channel, including the resolution and bit rate. If there is no such button, you can estimate the accuracy by looking at which channels the mosaic appears on and comparing HD and SD images.

For families that have changed to bridge, check the VLAN one more step

The above three items are general troubleshooting. But if your optical modem has changed the bridge connection, and the mosaic appears only after the change, the path is completely different - 80% of the time the IPTV VLAN was lost during the change, and the multicast channel is half-dead, which is manifested as some channels being able to play, others being completely black, or bursts of fragments. I have written down the complete remedy for this matter in No signal after bridging In that article, the core action is to look up the WAN connection table in the backend of optical modem, find the connection whose type is OTHER and is bound to the IPTV port, and copy the VLAN number back. Making the habit of taking a picture of this table before bridging can save you a whole night of fuss.

After checking the three things, if it still doesn’t work, bring the evidence and call 10,000.

The investigation is over. Three things in order: The background light attenuation number, the line from the IPTV port to the box, and the comparison of high and low bit rate stations. The first two methods solve 70% to 80% of the cases I have seen, and the third method helps you determine which level the disease is at. It’s still confusing after you’ve done it all. Don’t say “the TV is not clear” when you call. If the master can’t start work, report three kinds of information.: Light attenuation readings, which channels are obscured, the pattern of good times during the day and bad times at night - the last one is particularly valuable. It points to the public passage during the evening rush hour. The master will know where to check as soon as he hears it. Coupled with the sentence "multicast packet loss", the other party will basically handle it as a knowledgeable person.

At the end, a table is provided with five types of symptoms.:

My order formula is just one sentence: Check the numbers first and then move the line. Free first and then report for repair. . The mosaic problem looks scary, but in fact, there are only three variables in hand - optical fiber, network cable, and bit rate, one by one, which is much more useful than restarting the box a hundred times. Why does restarting sometimes work? Restarting the box will re-send the message to join the multicast, which is equivalent to re-subscribing to the "subscription". Occasionally, it can be correct, but the root cause of the problem at the line level has not been affected, and it will remain the same after two days.