T3 Timeouts.
 

Hi all,

I posted a message on VM's broadband support newsgroup today as I've been experiencing fluctuations in download speeds, downstream power levels, and intermittent pauses in transmission for a couple of months. The problems have been a minor annoyance, so I've been in no rush to report them; however, with the imminent closure of the newsgroups I thought I'd get in now!

The support guy has said he's had a look at my connection and can see some T3 timeouts and has booked an engineer for me.

I have no idea what a T3 timeout is and I like to have a few facts to hand before an engineer visits so I was hoping somebody would be kind enough to answer a couple of questions:

• What is a T3 timeout?
• Would there be any evidence of T3 timeouts in my modem's event logs?
• What are the possible causes/remedies of T3 timeouts?

If anyone can offer any information I'd appreciate it.

Cheers,

Ed.

Re: T3 Timeouts.
 

You could past your full stats and event logs here (minus your CM IP address) and we'll try to take you forward from there (and explain the causes/remedies).

We're gonna specuulate anyway without the proper tools so we might as well be better informed of your case.

Re: T3 Timeouts.
 

I "might" find this is a network issue and not local and to do with the ongoing BSR issues if ur on the motorolla kit.

Re: T3 Timeouts.
 

T3 timeouts? I get them all the time in the CM log, however my connection has always (touches wood) worked as expected so I never felt the need to go crying to tech support :/

Re: T3 Timeouts.
 

Not all faults revolve around BSR's.;)

Re: T3 Timeouts.
 

did i say they were?

Dont twist what was said and re read the post once again.

Re: T3 Timeouts.
 

No twist Chris hence the smiley, it was a joke, remember them.;):p:

Re: T3 Timeouts.
 

Thanks for the offers of assistance guys. I've posted the relevant bits of my post to the VM newsgroups below, including modem info and traceroute results.

There seems to be this sequence of events cropping up every couple of days...

Cheers,

Ed.

Re: T3 Timeouts.
 

No twisting required. You have absolutely no idea what the OP's problem is, and yet you choose to post a line of complete and utter speculation which, by a massive coincidence, is the same piece of complete and utter speculation that you have posted in a great many threads over the last few months.

In all seriousness, and in the interests of getting the actual problem fixed, I would advise the OP to just ignore you completely and instead take advice from someone who knows what they're talking about.

Re: T3 Timeouts.
 

My 20 meg modem records T3 timeouts - but yours hasn't. The cribbed definition taken from the DSLInfo is:

T3 ( Ranging Request Retries Exhausted )

The cable modem has sent 16 Ranging Request (RNG-REQ) messages without receiving a Ranging Response (RNG-RSP) message in reply from the CMTS. The cable modem is therefore resetting its cable interface and restarting the registration process. This typically is caused by noise on the upstream that causes the loss of MAC-layer messages. Noise could also raise the signal-to-noise ratio (SNR) on the upstream to a point where the cable modem's power level is insufficient to transmit any messages. If the cable modem cannot raise its upstream transmit power level to a level that allows successful communication within the maximum timeout period, it resets its cable interface and restarts the registration process. This error message is DOCSIS event message is R03.0, Ranging Request.

Bearing in mind that without tools, opinions here are speculation, it seems to me that focus on downstream power is not unreasonable.

I say this because there isn't evidence of upstream impairment; true, the upstream SNR is read at the CMTS end, but unless this is an intermittent problem (your event log implies intermittency), your upstream power level is normal and doesn'tr fit the T3 event profile.

In winter, you can expect a +2 dB (IMO) variance from the summer reading. But if it has fallen on a colder day, then things may be happening on your circuit. Varying downstream power can arise because an SNR impairment can be varying as well. From my knowledge of this phenomenon, I'm not talking about RF noise ingress; I'm thinking about more physical effects. The CMTS punts out at a fixed 50 dBmv and by the time it reaches your modem, all the losses on the way should ideally bring it into a -5 to +6 dBmv range. There is argument on the forum about the range, but when power rises it has the tendency to carry noise which can cause corrupted data and knock-on re-requests to the other end - slowing your download speed.

So, when the engineer comes, you'd need to provide evidence or your record of the fluctuating power levels so that he might arrange or do tests between the cabinet and your house. If you don't really have this, start collecting!

Re: T3 Timeouts.
 

Thank you Seph. I see small fluctuations in downstream power all the time - usually of the order of 0.1 dBmV to 0.2 dBmV. If I sit and just keep hitting F5 I can see the figure change each time. Same thing happens with the downstream SNR. I gather these small fluctuations are normal though. The drop of nearly 2 dBmv in the space of a couple of days is the biggest I've ever seen though (I'm sorry to say I'm sad enough to monitor these things fairly closely, even when I have no problems :) ).

I shall start logging power levels over the next week or so. I take it there is no way I can get these values other than accessing the config pages via my browser? It would be nice if I could automate it so I can take regular readings throughout the day...

Something else occurs to me that may be relevant:

When we first moved into this property we had a lot of problems with the TV reception. We were told it was because we are a fair distance from the cabinet and the cable used was insufficient for that kind of distance. This meant power levels were too low (IIRC). We had a repull done (eventually) which left power levels to the modem too high so they had to come out and fit an attenuator. Not sure whether this has any bearing on the situation...

Ed.

Re: T3 Timeouts.
 

The minor fluctuations are totally normal for this type of network.

A drop of 2 dBmv is also nothing to worry about IMO. Less noise amplified.

The bit I highlighted in blue is important. From that I take it you're in an ex-Telewest area where they provided each house with a private cable to the street box. So your SNR to the cabinet isn't the issue. But another house on the cabinet could be injecting noise for a number of reasons and this could affect your downstream speed when that happens - and everyone else's. Have you spoken to anyone else with VM service?

The power level too high? If you're a long distance from the cabinet he might have moved you up to a block with less attenuation. If the power went too high, he may have moved you up more than one block on the frame. IMO, it means he didn't really know what he was doing in some respects. There are amplifiers every 100m and if they're working properly, he should have needed to move you up in the frame. If they're not working properly, that could be where the problem lies.

Finally, the TV. You can go to the Menu/settings and see your power and SNR levels. They should be comparable with the broadband.

HTH

Re: T3 Timeouts.
 

Yep, I'm ex-Telewest. I'm not even sure there is anybody else on my street who has VM broadband. I shall do some asking around, although I suspect a lot of people wouldn't have noticed anything amiss, other than things being a bit slower than usual. Thanks for the suggestion.

To be fair it could well be me mis-remembering the details of what I was told - this last issue was a couple of years ago. We had a number of engineers out and several attempts at solving it though and I'm absolutely positive some of them didn't know what they were doing because they told me conflicting things about the power levels I was seeing at the time. This was one of the things that prompted me to post here this time - so I stand a chance of spotting when I'm being fed a line. :)

We never had a single problem with our service in our previous house for the 4 years we had it. Since moving into this property its been one thing after another and they've all been a real sod to get sorted out. I'd just put it down to bad luck...

TV STB is currently showing the following:

SNR - 33.308dB
AGC Signal Level (whatever that is!) - 8dBmV
Return Power - 45dBmV

I also noticed a Timers section. I assume this is the same kind of thing as VM referred to seeing on my connection? (A cable STB is basically still a cable modem, isn't it?). The Timers section had a T1 count of 1 and a T4 count of 25. All other counters were zero.

Thanks again for taking the time to reply.

Ed.

Re: T3 Timeouts.
 

Addressing the TV p[henomenon: IMO, -8 dBmv is on the low side of acceptable but if you're no longer having TV problems, should do. The SNR shows lower usually because of the run from first wall box to the cable tv box. The higher Return Power backs this up - the CMTS at the VM end requests higher power for any data the STB returns.

If the errors log shows zero, then there's no TV problem IMO.

I believe the TV signal is modulated at 256QAM (others may know better) and 33 dB SNR is at the low end of tolerance. The single occurrence of T1 and 25 occurrences of T4 are not a worry, IMO. If you go through the stats, you'll see the number of occasions that something has been downloaded or rest in your STB instigated from the CMTS end. The number of such occasions would exceed the number of T4 timeouts. On my STB I have 36 dB SNR and AGC SL of -4 dBmv, -3 dbMv and -2 dBmv with no problems. (there are three tuners in the V+ box).

Regarding your neighbours: I'm not 100% sure about Telewest cabling, but I think I might be wrong about the amplifiers. The street box has the frame I mentioned with different attenuation values and this should get round the issues of distance from the street box. Further away, the higher up the frame you'd be. You can usually tell who's got cable by the line of the duct showing on asphalt pavement or a box on the outer wall of a subscribing house. I admit there's some work to be done there, but it really is worthwhile.

HTH.

Re: T3 Timeouts.
 

:no:

:p: :D