Thread: T3 Timeouts.
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Old 28-02-2010, 00:45   #10
Sephiroth
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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!
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