DOCSIS T1, T2, T3 and T4 Timeouts

This is a handy summary of the various DOCSIS T1, T2, T3 and T4 timeout errors you will find in a DOCSIS network.  T3 and T4 timeouts are described in much more detail elsewhere in this blog, however this post provides a high level overview of the various timeouts as a reference.  Also see DOCSIS Cable Modems how they work in detail.  Additionally, thanks to baranek110 for Cable-Modem's Blog.

T1 Timeout ( No UCD’s received )

Explanation: The cable modem has not received any periodic Upstream Channel Descriptor (UCD) messages from the CMTS within the timeout period. This error message is DOCSIS event message is U01.0, Upstream Channel Descriptor.

T2 Timeout ( No Maintenance Broadcasts for Ranging opportunities received )

Explanation: The cable modem did not receive a broadcast maintenance opportunity in which to transmit a Ranging Request (RNG-REQ) within the T2 timeout period (approximately 10 seconds). The cable modem is resetting its cable interface and restarting the registration process. This error message is DOCSIS event message is R01.0, Ranging Request.

T3 Timeout ( Ranging Request Retries Exhausted )

Explanation: 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.

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

Explanation: The cable modem did not received 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.

T6 Timeout ( Cable Interface Reset )

Explanation: The cable modem has sent 3 Registration Requests (REG-REQ) to the CMTS without receiving a Registration Response (REG-RSP) within the T6 timeout period (3 seconds). The cable modem is therefore resetting its cable interface and restarting the registration process

This problem can also occur if the DOCSIS configuration file is corrupt, or if it contains a large number of vendor-specific information fields (VSIF). If the configuration file contains a large amount of VSIF information, the cable modem might generate a Registration Request (REG-REQ) that exceeds the maximum size of DOCSIS MAC-layer management messages (1514 bytes plus the header). The CMTS considers this an invalid MAC-layer management message and drops it, without replying.

So is this a modem problem or is something else going on?

I have changed modems three times in a month, and am still having the same issues with T3 timeouts.

have had techs out as many times, have had new lines ran although I think that when they came out to bury the line from the tap they reconnected the old line and picked up the new one. I know that there is an issue on Cox's side and are seemingly unwilling to check.

I have a Arris SB8200 Docsis 3.1 and the errors hadn't been appearing for the first month I had the modem. I just found today my coaxial cable was not tight all the way.

 What modem do you have?

I read on a forum on a different community dslreports dot com they say it could be...

Upstream and downstream levels look good. One potential contributing factor to your connections issues is upstream noise/ingress. Unfortunately, it's a metric that cannot be read at the modem, so you'll need to contact support and have them check to see if the upstream SNR is going below spec.

What is your modem model #?

I have the same problem for one year!

The first time that reported the Cox support  say that the problem is the modem, I change the modem, after change the modem one cisco (the problem persist) for one Netgear they say, the problem is that no have voltage regulator, bought the voltage regulator and the problem persist, i think this is a general problem, my problem is similar to above exposed.

Atach is one sample of my log, very similar to the first post

I've read many posts of subscribers experiencing similar problems and I they all appear to be unresolved.  I'm reluctant to call a tech and they can't find the problem or they'll tell me I need a new modem and yadda yadda yadda...............