| reply to jsmiddleton4
Re: [AZ] More Friday night node overload..... The errors being received (SYNC Timing Synchronization failure - Failed to acquire QAM/QPSK symbol timing) indicates the modem is having trouble discerning the modulation type to use in order to transmit and receive data.
The CMTS transmits data via 256-QAM (Quadrature Amplitude Modulation) signals over the RF plant to the subscriber's home cable modem. With 256-QAM modulation it is able to encode 8 bits per symbol averaging a bandwidth of about 40 Mbps. The cable modem transmits data to the CMTS on the upstream over the RF plant via 64-QAM modulation. With 64-QAM modulation it is able to encode 6 bits per symbol averaging a bandwidth of about 30 Mbps. The higher the modulation the higher the speed, but it is less tolerant to link degradation as the symbols are closer together and difficult for the receiver to demodulate.
When the symbol timing can't be established this points to an issue somewhere in the RF plant either somewhere in the home or further back. This kind of problem can many times be caused by poor shielding in consumer electronics on the same drop if the modem is not split from the other drops.
The CMTS sends out a SYNC broadcast message about every 200 msec which is used for system timing. Along with this a UCD (Upstream Channel Descriptor) is sent every 2 seconds which tells the modem the upstream frequency to transmit on, symbol rate, modulation profile and any other parameters it needs in order to communicate on the network. The CMTS also sends out Media Access Protocol (MAP) messages in order to allocate "talk time" to each cable modem. Since there are many cable modems and only one upstream frequency, the cable modems must "time-share" the upstream channel, which is called Time Division Multiple Access (TDMA).
When the modem successfully locks on to a QAM channel it looks for all three, the SYNC, UCD, and MAP messages. If the modem doesn't find all three it assumes the DOCSIS channel is either offline or it is on a video QAM channel and continues searching.
The message stating - SYNC Timing Synchronization failure - Failed to acquire FEC framing is related. FEC means Forward Error Correction which is a mechanism that looks at the packet trailer Frame Check Sequence (FCS) checking it for symbol errors. If symbol errors are found then FEC will try to correct as many of the errors as it can.
So what does all this mean? Basically, those error messages are just the messages as the modem is searching for a QAM channel to lock on to. So since it can't acquire the QAM symbol timing (most likely because it didn't receive a UCD on the forward path [modem's receive or Rx]) it then moves on to the next frequency and then it finally finds one. Once it finds one to lock on to then it starts the ranging process with the CMTS. Once ranging is complete that is the end of the DOCSIS protocol communications and it then moves on to the IP layer communications requesting an IP from the DHCP server, Time of Day (ToD), and downloading the config file. ToD was required with DOCSIS 1.0, but now with DOCSIS 2.0 and 3.0 is just an option and no longer required and in many cases has been replaced with Network Time Protocol (NTP).
All in all, the errors being received do not relate to node saturation. However, if they are something that your modem is experiencing often and you see your modem dropping offline it definitely could warrant a technician coming out to the home to check things out. |
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 dvd536as Mr. Pink as they comePremium
join:2001-04-27
Phoenix, AZ
kudos:4 | reply to jsmiddleton4
said by jsmiddleton4:"What happens when everyone has a D3..." Then cablelabs comes up with DOCSIS 4.0 
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Eventually cablecos will ditch HFC and go pure FTTH and end the endless +1 upgrade cycles. |
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dvd536as Mr. Pink as they comePremium
join:2001-04-27
Phoenix, AZ
kudos:4 | reply to AZHSISUPPRT2
Thanks for the very detailed explanation. answers all those things we see in logs[well moto people anyway] but were afraid to ask about.
I never knew time of day was required with D1.0 |
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 bbeesleyVIP
join:2003-08-07
Richardson, TX
kudos:4 | reply to dvd536
said by dvd536:Eventually cablecos will ditch HFC and go pure FTTH and end the endless +1 upgrade cycles.
not likely...the costs to replace the network at the last few hundred feet will prevent that for some time.....probably at least ten years...and by then we will probably see high-speed wireless instead of fixed infrastructure FTTH as a preferred mechanism as it allows better mobility and eliminates drop and feeder infrastructure costs.
even Verizon appears to be focusing on LTE rather than FIOS most likely because it costs so much to pull fiber to every subscriber and future subscribers aren't going to want to be tied to their home for content...they will want to take it with them
what you will more likely see in the new few years is a migration to PON over HFC which will allow higher bandwidth than DOCSIS especially in the return, while allowing the cable providers to continue to use their existing fiber-deep architecture
EPoC is currently in standards review at both Cablelabs and in the IEEE and indicators are that deployments will start as early as 2014 for SOHO installations
»www.lightreading.com/document.as···lr_cable |
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dvd536as Mr. Pink as they comePremium
join:2001-04-27
Phoenix, AZ
kudos:4 | said by bbeesley:said by dvd536:Eventually cablecos will ditch HFC and go pure FTTH and end the endless +1 upgrade cycles.
not likely... Well its nice to dream anyway.
imagine a world without RF issues |
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bbeesleyVIP
join:2003-08-07
Richardson, TX
kudos:4 | said by dvd536:Well its nice to dream anyway.
imagine a world without RF issues
fiber is not a panacea for technical problems...it just has different ones than RF
noise is typically the biggest issue in RF and it can be hard to troubleshoot and find but good practices and training go a long ways to mitigating this.
fiber has it's own set of quirks that require well trained techs, quality tools, and good procedures and practices to ensure consistent service |
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| reply to m8trix
Having a low upstream power level is usually an indicator of a nice quiet plant. The modem doesn't have to yell to be heard. Add a couple of splitters and its very easy for him to get that "sweet 45 db," would it better his connection--NO.
As someone that had to deal with 52 DB upstream for 18 months, over 20 truck rolls, contractors/empoyees(comcast) not knocking but saying that they did, having a low upstream powerlevel is a godsend. Only way I actually got it fixed, is during primetime I would send noise and feedback into the cable plant to knock everyone offline, only for a few minutes, 3 days of this and they had the trucks rolled all up and down the street fixing the problem that 18 months worths of calls and technician visits could not do.
Now I am running a nice clean 35-37 db, and whenever there is a congestion issue, the first thing that I hear is-- "your upstream power level is very low..." ... "Oh would you like me to add a splitter to fix that..possibly expose a RG6 cable to my remote controlled car that operates in the 20-40mhz range?" They move on to a different topic after that.
But seriously, I'd just get a D3 modem and see if it fixes your problem first. My experiences with Brighthouse, Cox, and Comcast have shown me that no one listens until the little old lady cannot access her email anymore, or the city commissioner next-door has trouble loading weather.com. |
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dvd536as Mr. Pink as they comePremium
join:2001-04-27
Phoenix, AZ
kudos:4 | said by thedunlap:Only way I actually got it fixed, is during primetime I would send noise and feedback into the cable plant to knock everyone offline, only for a few minutes, 3 days of this and they had the trucks rolled all up and down the street fixing the problem that 18 months worths of calls and technician visits could not do. How did you do that? sounds like something that would get a 8:30 to 11am issue actually looked into for me. |
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 Fubar
join:2001-02-20
Phoenix, AZ
kudos:2 | said by dvd536:said by thedunlap:Only way I actually got it fixed, is during primetime I would send noise and feedback into the cable plant to knock everyone offline, only for a few minutes, 3 days of this and they had the trucks rolled all up and down the street fixing the problem that 18 months worths of calls and technician visits could not do. How did you do that? sounds like something that would get a 8:30 to 11am issue actually looked into for me. And would also be Illegal!
Good luck with that. |
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Reviews:
 ·Cox HSI
| said by Fubar:said by dvd536:said by thedunlap:Only way I actually got it fixed, is during primetime I would send noise and feedback into the cable plant to knock everyone offline, only for a few minutes, 3 days of this and they had the trucks rolled all up and down the street fixing the problem that 18 months worths of calls and technician visits could not do. How did you do that? sounds like something that would get a 8:30 to 11am issue actually looked into for me. And would also be Illegal! Good luck with that. LOL exactly what I was thinking, sadly I know how people feel dealing with issue's like this. Because I am still currently dealing with one. But I would never attempt to push noise into the lines to have an issue fixed. Because I have dealt with an on and off again noise issue it seems like forever now. As I type this, I am getting ready to give customer support a call to setup a tech visit. So everything home side can be checked over again to make sure no issue's are coming from my home. |
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| reply to AZHSISUPPRT2
Re: [AZ] More Friday night node overload..... "All in all, the errors being received do not relate to node saturation."
Except that they only happen at peak use times. Never during low use times.
But thanks for your explanation. Seems to me the reason my modem is having issues finding a connection that will "work" is because there are so many other people using those connections.
"if the modem is not split from the other drops."
It is split from the other drops. |
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| reply to thedunlap
"until the little old lady cannot access her email anymore, or the city commissioner next-door has trouble loading weather.com."
Yep. Kinda sad but true. |
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| reply to jsmiddleton4
Looks like no one from Cox is going to take any action.
Another thing that is sad but true. |
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m8trix
join:2003-12-24
Phoenix, AZ
kudos:3 Reviews:
·Cox HSI
1 edit | reply to jsmiddleton4
a suggestion has aleady been given to you,but does not seem that you have followed that advice,you have posted low upstream power myself, AZHSISUPPORT2 and others suggested a tech vist, a field tech visit should also be able to see what the other modems are doing on your node and if they are not resetting like yours and have long up times guess what it something at your home |
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bbeesleyVIP
join:2003-08-07
Richardson, TX
kudos:4 | reply to jsmiddleton4
you are "guessing" at what might be wrong and asking Cox to take an action based on your assumptions?
Several techs have come on here and patiently tried to explain to you that you are correlating your symptoms to a cause based on a misunderstanding of how DOCSIS works. One has even gone into great technical detail on the subject.
I concur with what the techs posted - your issue is most certainly noise related, not congestion.
The best way to have "Cox...take any action" is to work with them and have a tech come out and start the process of finding the source of the noise. |
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| reply to jsmiddleton4
Re: [AZ] More Friday night node overload..... What's sad is you continue to believe you're correct in your assumptions about COX's network.
You've been given suggestions by several knowledgeable people that either work at COX or have worked for COX, yet you do not take their advice or suggestions.
You continue to waste your time attempting to persuade COX that you know more about their network than they do. Instead of attempting any of the suggested resolutions, you just post useless whining..
I really don't understand what more you expect COX or any of it's employees to do when you won't cooperate or attempt any suggestions they have provided. |
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| jsmiddleton4,
I took a look at your modem and the Tx levels are pretty low at 34.7 dBmV right now. I also checked out the other 3 neighbors that are connected to the same tap as yourself and they seem to be having some Tx level issues as well. I created a ticket to have our plant maintenance techs check it out and see if the tap is bad. I'll keep an eye on it and let you know what they say.
Thanks,
--
Chris@Cox Communications Arizona |
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