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Morac
Cat god

join:2001-08-30
Riverside, NJ
kudos:1
Reviews:
·Comcast

3 edits

[Connectivity] Modem is reporting continuous T4 errors.

My connection appears to be working currently, but my modem has been reporting the following every 30 seconds pretty much all day today:

"Received Response to Broadcast Maintenance Request, But no Unicast Maintenance opportunities received - T4 time out;"

Any idea what's going on here? I have a Zoom Telephonics 5341.

My signals are:

 
Channel Frequency: 668999756 Hz651000488 Hz657001709 Hz662998535 Hz
Modulation: 256 QAM256 QAM256 QAM256 QAM
Signal strength: -5.9741 dBmV-5.5496 dBmV-5.7347 dBmV-5.4211 dBmV
Signal noise ratio: 37.093 dB36.844 dB37.093 dB37.093 dB
 
Upstream
Channel Id: 101112
Upstream Frequency: 36200108 Hz29399949 Hz22000000 Hz
Upstream bandwidth: 6400000 Hz6400000 Hz3200000 Hz
Transmission signal strength: 50.2500 dBmV50.2500 dBmV50.0000 dBmV 
 
 

edit:

I rebooted my modem and it's still happening. It also took a very long time to come up. Here's what was reported in the logs:

 
1406/21/12 19:41:43Z00.0warningMIMO Event MIMO: Stored MIMO=0 post cfg file MIMO=0;CM-  MAC=00:05:ca:xx:xx:xx;CMTS-MAC=00:01:5c:xx:xx:xx;CM-QOS=1.1;CM-VER=3.0;
1506/21/12 19:42:36R02.0criticalNo Ranging Response received - T3 time-out;CM-MAC=00:0  5:ca:xx:xx:xx;CMTS-MAC=00:01:5c:xx:xx:xx;CM-QOS=1.1;CM-VER=3.0;
1606/21/12 19:42:43U102.0warningTCS Partial Service;CM-MAC=00:05:ca:xx:xx:xx;CMTS-MAC=  00:01:5c:xx:xx:xx;CM-QOS=1.1;CM-VER=3.0;
1706/21/12 19:42:44U103.0warningInitializing Channel Timeout Expires - Time the CM can   perform initial ranging on all upstream channels in the TCS has expired;CM-MAC=00:05:ca: x x:xx:xx;CMTS-MAC=00:01:5c:xx:xx:xx;CM-QOS=1.1;CM-VER=3.0;
1806/21/12 19:42:46E115.0noticeAdded MAC address [00:12:3f:e0:60:fe]
1906/21/12 19:42:52R05.0criticalStarted Unicast Maintenance Ranging - No Response rece  ived - T3 time-out;CM-MAC=00:05:ca:xx:xx:xx;CMTS-MAC=00:01:5c:xx:xx:xx;CM-QOS=1.1;CM-VER= 3 .0;
2006/21/12 19:48:52R04.0criticalReceived Response to Broadcast Maintenance Request, Bu  t no Unicast Maintenance opportunities received - T4 time out;CM-MAC=00:05:ca:xx:xx:xx;CM T S-MAC=00:01:5c:xx:xx:xx;CM-QOS=1.1;CM-VER=3.0; 
 
 

Edit 2:

Is it possible for one of the 3 upstream channels to be having T4 errors, but the other 2 work okay?

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TechnoScott
Premium
join:2003-03-25
00000

T3 and T4 timeouts occur when the return path is impaired. Since you have a D3 modem the problem could be on any of the upstreams but is most likely the worst on the 22MHz upstream. You can't do much about it as an end user except call for a service call and hope the repair guy knows how to look at Pathtrak. If he/she sees a noise problem in Pathtrak they can escalate the issue to the maintenance department.

You'll have working service with T3 and T4 timeouts but you'll see some packet loss until the T3/T4 problem gets fixed.



EG
The wings of love
Premium
join:2006-11-18
Union, NJ
kudos:10

said by TechnoScott:

T3 and T4 timeouts occur when the return path is impaired.

FWIW, they happen for downstream issues as well. Any RF impairment which causes a loss of "handshake" / communication between a modem and the CMTS will yield them.

TechnoScott
Premium
join:2003-03-25
00000

Maybe in your system they're a downstream problem - but where I'm at its 99.9% an upstream issue.



Morac
Cat god

join:2001-08-30
Riverside, NJ
kudos:1
Reviews:
·Comcast
reply to TechnoScott

said by TechnoScott:

You'll have working service with T3 and T4 timeouts but you'll see some packet loss until the T3/T4 problem gets fixed.

The odd thing is did a high packet ping test for about 5 minutes and didn't see any packet loss, despite continuous T4 errors every 30 seconds. That would lead me to believe only one of the channels is having a problem, which to me would point to a headend problem over a line problem.

When calling support, they basically run ping tests and the like. Since I'm not seeing any symptoms of a problem, other than the T4 errors, they probably won't do anything.
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Morac
Cat god

join:2001-08-30
Riverside, NJ
kudos:1
Reviews:
·Comcast
reply to EG

said by EG:

FWIW, they happen for downstream issues as well. Any RF impairment which causes a loss of "handshake" / communication between a modem and the CMTS will yield them.

I'm inclined to believe they are upstream for a few reasons:

1. Historically the majority of issues with Internet are upstream signal problems.
2. I'm not seeing problems with my cable channels which are all digital.
3. The signal level and SNR for my downstream channels is very good.

From what I've read the T4 time out is 30 seconds and that's what I'm seeing every 30 seconds since yesterday I get a "Received Response to Broadcast Maintenance Request, But no Unicast Maintenance opportunities received - T4 time out" error in my log. So this is a continuous problem.
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Zizoo

join:2010-05-12
PA
reply to Morac

NJ and parts of PA are experiancing an outage issue since about 7am with phone and internet intermittent connectivity issues.



Morac
Cat god

join:2001-08-30
Riverside, NJ
kudos:1
Reviews:
·Comcast

1 edit

said by Zizoo:

NJ and parts of PA are experiancing an outage issue since about 7am with phone and internet intermittent connectivity issues.

I don't think that's my issue since I've had this problem since around 2:30 AM yesterday (after my modem went offline and came back up after about 10 minutes).

One of the Comcast twitter team is looking into it currently.

Edit:

ComcastWill confirmed one of the upstream channels looks to be having issues. He forwarded it to the local network group so hopefully they can fix it.

That brings up an interesting question. What does the modem do if one of the three upstream channels is having trouble. Will it just use the other two or will it sometimes still use the bad channel?

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EG
The wings of love
Premium
join:2006-11-18
Union, NJ
kudos:10
reply to TechnoScott

said by TechnoScott:

Maybe in your system they're a downstream problem - but where I'm at its 99.9% an upstream issue.

Quote;

"3-Critical H501.8 HFC: T4 Timer Expired:

Explanation. The cable modem did not receive a station maintenance opportunity in which to transmit a Ranging Request (RNG-REQ) message within the T4 timeout period (30 to 35 seconds). The cable modem is resetting its cable interface and restarting the registration process. Typically, this indicates an occasional, temporary loss of service, but if the problem persists, check for possible service outages or maintenance activity on this particular headend system.
Recommended Action for your Provider: Check the configuration on the CMTS. Check the cable plant for RF connector or cabling issues that could be generating noise on the downstream and upstream."

"T4 ( Received Response to Broadcast Maintenance Request, But no Unicast Maintenance opportunities received )

Explanation: The cable modem did not receive a station maintenance opportunity in which to transmit a Ranging Request (RNG-REQ) message within the T4 timeout period (30 to 35 seconds). The cable modem is resetting its cable interface and restarting the registration process. Typically, this indicates an occasional, temporary loss of service, but if the problem persists, check for possible service outages or maintenance activity on this particular headend system. This error message is DOCSIS event message is R04.0, Ranging Request.

Quote;

"Why Do Cable Modems Drop Offline?
A Cable Modem requires three main things to remain online once it is connected and operational:

Clean RF plant with a carrier-to-noise consistently above 30dB in the Upstream, and above 33dB in the downstream.

Unicast polls from the CMTS every 30 seconds (keepalives). These are unicast transmit opportunities for this modem's assigned SID, in which it can send a RNG-REQ to the CMTS. If the cable modem does not receive a unicast transmit opportunity within T4 seconds (30 seconds) it has to time out and re-initialise it's MAC layer. So if there is a problem (RF) in the downstream, the cable modem might not "see" this unicast transmit opportunity, and drop offline.

If the CMTS does not get a reply from the CM to the unicast transmit opportunity, the CMTS will poll the modem 16 times in short succession in order to try and get an answer. The modem is considered offline by the CMTS if there is no reply after these retries."

RouterRooter

join:2001-11-22
Rockville, MD
reply to Morac

Morac,

Had sporadic connectivity problems over last few days here -- good RF stats (4/3 channels down/up with good levels) but either no Internet or extremely slow. Same modem as you and essentially identical log:

13 06/22/12 08:28:50 Z00.0 warning MIMO Event MIMO: Stored MIMO=0 post cfg file MIMO=0;CM-MAC=00:26:5b:4b:26:a0;CMTS-MAC=00:01:5c:22:b5:cf;CM-QOS=1.1;CM-VER=3.0;
14 06/22/12 08:29:35 R02.0 critical No Ranging Response received - T3 time-out;CM-MAC=00:26:5b:4b:26:a0;CMTS-MAC=00:01:5c:22:b5:cf;CM-QOS=1.1;CM-VER=3.0;
15 06/22/12 08:29:51 U102.0 warning TCS Partial Service;CM-MAC=00:26:5b:4b:26:a0;CMTS-MAC=00:01:5c:22:b5:cf;CM-QOS=1.1;CM-VER=3.0;
16 06/22/12 08:29:51 U103.0 warning Initializing Channel Timeout Expires - Time the CM can perform initial ranging on all upstream channels in the TCS has expired;CM-MAC=00:26:5b:4b:26:a0;CMTS-MAC=00:01:5c:22:b5:cf;CM-QOS=1.1;CM-VER=3.0;
17 06/22/12 08:29:54 R05.0 critical Started Unicast Maintenance Ranging - No Response received - T3 time-out;CM-MAC=00:26:5b:4b:26:a0;CMTS-MAC=00:01:5c:22:b5:cf;CM-QOS=1.1;CM-VER=3.0;
18 06/22/12 08:33:54 R04.0 critical Received Response to Broadcast Maintenance Request, But no Unicast Maintenance opportunities received - T4 time out;CM-MAC=00:26:5b:4b:26:a0;CMTS-MAC=00:01:5c:22:b5:cf;CM-QOS=1.1;CM-VER=3.0;
19 06/22/12 08:34:05 E115.0 notice Added MAC address [00:26:f2:a1:57:6b]
20 06/22/12 11:43:24 R04.0 critical Received Response to Broadcast Maintenance Request, But no Unicast Maintenance opportunities received - T4 time out;CM-MAC=00:26:5b:4b:26:a0;CMTS-MAC=00:01:5c:22:b5:cf;CM-QOS=1.1;CM-VER=3.0;

POPOed modem a few times and took ~ 5 minutes to fully connect with several drop-backs from finding upstream back to finding downstream (based on LEDs) before success..

Problem cleared up about 9 AM today. So ... I assume this is a problem at the plant and nothing to do with our equipment or local lines.

RR

mistical

join:2003-03-05
Chicago, IL
reply to Morac

I've been having the same problem for the past 2 months now, happens more than 10 times a day and only started to happen again since 3 upstream bonded channels was introduced again in my area after 2 years since they last tried it.



Morac
Cat god

join:2001-08-30
Riverside, NJ
kudos:1
Reviews:
·Comcast

2 edits
reply to RouterRooter

The weird thing is other than jitter being a bit higher than usual (some large packet pings are slow to return, but that's been that way since upstream channel bonding was added), I'm not seeing any problems. No packet loss, no slowdowns, nothing. Despite getting the T4 errors constantly for at least 24 hours now.

From what I was told only one of my 3 channels is having problems (which is odd in itself since if there was a line problem you'd think it would affect all three). I guess the modem can work okay with 2 of the 3 channels up and running. I'm not sure how the modem decides which channel to send packets out over, but it must not being using the bad one.
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TechnoScott
Premium
join:2003-03-25
00000

1 edit
reply to Morac

edited



flwpwr

@comcast.net
reply to EG

T3/T4 explained in a lot more techy detail than most arm chair techs will ever remember.

FWIW - »volpefirm.com/docsis-101/docsis1···tenance/



EG
The wings of love
Premium
join:2006-11-18
Union, NJ
kudos:10

I've seen that before. It's a good article, thanks.


instigator

join:2012-06-24
Fort Lauderdale, FL
reply to Morac

Morac - Have you seen this issue resolved?

I'm in south florida and am seeing the exact same issue with the T3/T4 errors on channel 10 of my upstream. The other two bonded channels are fine.




I tried calling Comcast today to see if they have noticed anything, but apparently I need to contact my local office regarding something this detailed.


pclover

join:2008-08-02
Santa Cruz, CA
Reviews:
·Comcast

said by instigator:

Morac - Have you seen this issue resolved?

I'm in south florida and am seeing the exact same issue with the T3/T4 errors on channel 10 of my upstream. The other two bonded channels are fine.

[att=1]

I tried calling Comcast today to see if they have noticed anything, but apparently I need to contact my local office regarding something this detailed.

More then likely a noise issue. 22.6 MHz is low so bound to have issues when you go that low.

You could also call comcast and ask what your uSNR is.


Morac
Cat god

join:2001-08-30
Riverside, NJ
kudos:1
Reviews:
·Comcast

1 edit
reply to instigator

said by instigator:

Morac - Have you seen this issue resolved?

Nothing as yet. Last I heard it was forwarded to the local networking group (I trust that the Twitter guy did this). It's not affecting my speeds and I was able to play online games (COD:MW3) all weekend without issue. It would be nice to get this fixed though.

BTW, is that the Moto Surfboard? I wish my modem displayed status of individual channels. It would have made things a lot easier to diagnose. I actually originally bought a Surfboard 6120, but it crippled my upload speeds (there was some kind of incompatibility issue with Comcast at the time) so I switched to the Zoom. It works great, but reported status is a bit lacking. I know there's a constantly occurring T4 timeout, but not on which channel.

Edit:

I just asked ComcastWill for an update and was told there are intermittent channel fluctuations on multiple channels, all on the same control card, so the card may be going bad. They are going to try tweaking the frequencies and if that doesn't work, they're going to try to swap the card.

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instigator

join:2012-06-24
Fort Lauderdale, FL

1 edit

Thanks for the update Morac. It is the Moto Surfboard 6120. I just ordered the Zoom last night because I found out that my area actually has the 8 channel bonding!!

I'm not sure who to contact at Comcast with this issue because it is so specific and it seems to have happened out of the blue (1.5 years without a single issue until now). I'm seeing sever speed issues because of the uploads. Downloads are fine, speed tests showing 30M+. The uploads are ~0.2M which even hinders web browsing. I think the modem is using that bad channel.

Who is this ComcastWill you are speaking of?

EDIT - didn't see pclover's response:
pclover - what is the uSNR? I like to know what I'm asking for so I can explain to them when they as me



Morac
Cat god

join:2001-08-30
Riverside, NJ
kudos:1
Reviews:
·Comcast

said by instigator:

Who is this ComcastWill you are speaking of?

EDIT - didn't see pclover's response:
pclover - what is the uSNR? I like to know what I'm asking for so I can explain to them when they as me

First ComcastWill is one of Comcast's Twitter support team.

Second, if you are seeing upload issues, it could be an upstream signal problem. uSNR is upstream signal to noise ratio. If you call into Comcast support they can check that (as can the Twitter support team).
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EG
The wings of love
Premium
join:2006-11-18
Union, NJ
kudos:10

said by Morac:

Second, if you are seeing upload issues, it could be an upstream signal problem.

FWIW, due to the way TCP ACK (Acknowledgement) works, upstream / return impairments can affect the downstream as well.


Morac
Cat god

join:2001-08-30
Riverside, NJ
kudos:1
Reviews:
·Comcast

said by EG:

said by Morac:

Second, if you are seeing upload issues, it could be an upstream signal problem.

FWIW, due to the way TCP ACK (Acknowledgement) works, upstream / return impairments can affect the downstream as well.

True but ACK packets are normally much smaller than upstream data packets so unless things are really bad, they are less likely to be affected.
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Morac
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join:2001-08-30
Riverside, NJ
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Reviews:
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1 edit
reply to Morac

Just mentioning that despite this "being looked into", the constant T4 errors on one channel continue. Fortunately it's not affecting speeds or latency, but it's kind of like skydiving without a backup chute.
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instigator

join:2012-06-24
Fort Lauderdale, FL
reply to Morac

Thought I'd follow up since I posted in here... My zoom modem came in the mail last Friday. Once I connected it I had 8 channels bonded DS 3 channels bonded US (including the channel I was/am seeing with errors), but had absolutely terrible connection speeds...less than 1M. I followed the wire in the attic and found an extra splitter that was unnecessary so I put a straight-through connector in it.

BOOM! I instantly saw constant 35M+ download speeds and 5M+ uploads on the speed test.

Everything seems to be running smooth



Morac
Cat god

join:2001-08-30
Riverside, NJ
kudos:1
Reviews:
·Comcast
reply to Morac

I checked into the status of this since it's been about a month and I was told that "maintenance has been completed to stabilize channels", but I'm still getting the T4 errors though.

I'm having ComcastWill look at it, but while he was looking at it, the modem rebooted. He said he didn't do that, but I haven't seen a reboot the entire time this has been happening.

He's going to try pinging my local network group to look at the CMTS again, but I'm guessing they aren't really doing anything about it since one or more of the channels is still working.

Is there for support to actually see if the CMTS is having problems (other than looking at signals)?
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threadsent

join:2012-09-08

any updates? i have the exact same problem. i get t4 errors all day every minute on my log.
i have near optimal power/signal levels.



Morac
Cat god

join:2001-08-30
Riverside, NJ
kudos:1
Reviews:
·Comcast

said by threadsent:

any updates? i have the exact same problem. i get t4 errors all day every minute on my log.
i have near optimal power/signal levels.

I had a service outage in the middle of the night about 2 or 3 weeks ago. When it came back up, the problem was fixed. My guess is they finally replaced the bad part.

Functionally, I haven't noticed a difference. Upload speed might be a tiny bit faster, but nothing else changed.
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DrDrew
That others may surf
Premium
join:2009-01-28
SoCal
kudos:15

1 edit

1 recommendation

reply to Morac

said by Morac:

pstream Frequency: 36200108 Hz29399949 Hz22000000 Hz
Upstream bandwidth: 6400000 Hz6400000 Hz3200000 Hz
...
Is it possible for one of the 3 upstream channels to be having T4 errors, but the other 2 work okay?

Yes.

For example your middle upstream channel is centered on 29.4 mhz and is 6.4 mhz wide. 29.4 - 3.2 (half the channel width) is 26.2 mhz. The CB radio frequencies are from 26.965 to 27.405 MHz, so the entire CB radio band is within that lower half of your middle upstream channel.

It's possible a crack in the cable is letting local CB interference or a local CB radio placed close to cable equipment is overpowering it's shielding.

This is a pretty common problem with cable systems running along major trucking routes.

It would've been better if the 29.4 Mhz channel was 3.2 Mhz wide and the 22 Mhz upstream was 6.4 Mhz wide... that would've left a gap from 25.2 to 27.8 Mhz for the CB band to fit into.
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Morac
Cat god

join:2001-08-30
Riverside, NJ
kudos:1
Reviews:
·Comcast
reply to Morac

Problem is back again as of yesterday. My signals look good.


Downstream
Channel Frequency: 675000488 Hz 657001099 Hz 668999146 Hz 681001709 Hz
Modulation: 256 QAM 256 QAM 256 QAM 256 QAM
Signal strength: 8.8028 dBmV 8.8512 dBmV 9.2323 dBmV 8.1789 dBmV
Signal noise ratio: 37.356 dB 36.844 dB 37.356 dB 37.356 dB

Upstream
Channel Id: 7 8 9
Upstream Frequency: 36200215 Hz 29399984 Hz 22000000 Hz
Upstream bandwidth: 6400000 Hz 6400000 Hz 3200000 Hz
Transmission signal strength: 43.2500 dBmV 43.5000 dBmV 43.2500 dBmV


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EG
The wings of love
Premium
join:2006-11-18
Union, NJ
kudos:10
reply to Morac

Don't forget about the uSNR (upstream Signal to Noise Ratio) number that can only be read from their end. It should be at least 30 dB and higher is better. Call in when you are experiencing the problem and see if it is in spec.