Your feeling is probably correct. I have seen these errors for years, using multiple modems (Ambit, Arris, RCA and Motorola) at multiple locations. I dug up a link I referenced a year and a half ago that kind of explains possible causes of these errors.
T3 and T4 Timeouts
I wanted to close this topic with a discussion on T3 and T4 timeouts as I have received many questions on what causes T3 and T4 timeouts? Fundamentally, a T3 timeout occurs when the cable modem fails to receive a RNG-RSP from the CMTS within 200 msec (after sending a RNG-REQ). A T4 timeout occurs when a cable modem fails to receive a RNG-REQ transmit grant MAP from the CMTS within 35 sec on the downstream channel (after receiving the previous RNG-RSP). There are number of reasons that these could occur and I will list a couple below for each and help guide you the root cause, but understand this is not and exhaustive list.
T3 Timeout No RNG-RSP in 200 msec Typically an Upstream Problem
Most likely cause is upstream impairments preventing the RNG-REQ from reaching the CMTS, therefore the CMTS never transmits a RNG-RSP
May occur because the RNG-REQs from multiple cable modems collided, again the CMTS does not receive the RNG-REQ (now from multiple modems) and fails to process multiple RNG-RSP messages resulting in multiple T3 timeouts
CMTS over-utilization unable to process RNG-REQ and/or RNG-RSP within T3 time frame (200 msec)
Can also be a downstream problem due to plant impairments i.e. RNG-RSP is transmitted, but corrupted in route and the cable modem never receives the message
Look for low MER at the cable modem
T4 Timeout No RNG-REQ Grant MAP Received by Cable Modem in 35 sec Typically a Downstream Problem
T4 timeouts can usually be identified with downstream impairments causing the cable modem to miss receiving the RNG-REQ grant MAP transmitted to it
If T4 errors are impacting many modems off of a common leg, trouble shoot that leg
If T4 errors are just associated with one modem, look for low MER/level at that modem
T4 timeouts can also be associated with a CMTS that has extremely high utilization i.e. >95% depending on the vendor and firmware version
Rule of thumb for CMTS utilization is 80% to allow for peak usage periods
It is highly unlikely that T4 timeouts are associated with any upstream impairments
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volpefirm.com/blog/docsi ··· tenance/I register multiple T3 or T4 errors and disconnects daily at my current location. Just something I've gotten used to...
Here's my current specs:
Model Name: SB6141
Vendor Name: Motorola
Firmware Name: SB_KOMODO-1.0.6.3-SCM03-NOSH
Boot Version: PSPU-Boot(25CLK) 1.0.12.
Hardware Version: 7.0
Serial Number: ************************
Firmware Build Time: Aug 18 2011 10:27:53
Downstream Bonding Channel Value
Channel ID 68 65 66 67
Frequency 561000000 Hz 543000000 Hz 549000000 Hz 555000000 Hz
Signal to Noise Ratio 38 dB 37 dB 38 dB 38 dB
Downstream Modulation QAM256 QAM256 QAM256 QAM256
Power Level
The Downstream Power Level reading is a snapshot taken at the time this page was requested. Please Reload/Refresh this Page for a new reading
0 dBmV 0 dBmV 0 dBmV 0 dBmV
Upstream Bonding Channel Value
Channel ID 4
Frequency 34600000 Hz
Ranging Service ID 72
Symbol Rate 2.560 Msym/sec
Power Level 48 dBmV
Upstream Modulation [5] 16QAM
Ranging Status Success
Signal Stats (Codewords) Bonding Channel Value
Channel ID 68 65 66 67
Total Unerrored Codewords 652831645 652839864 652847258 652856236
Total Correctable Codewords 14 0 0 1
Total Uncorrectable Codewords 646 575 1363 570