If you have a Cable Modem for Internet services at your home, you might have most likely seen one of these DOCSIS Timeout messages. They are typically displayed due to an issue in your wiring, bad cables, Bad node, Bad signal from your ISP, wrong configuration in ISP CMTS/Headend, plant noise, Signal interference, and many other possibilites.
Most of these errors will lead to either modem dropping offline or not even coming online at all and it is important to fix or reduce some of these errors.
There are 5 types of DOCSIS Cable Modem Timeouts Error messages:
T1 ( 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.
Occurrence: Very rare in the customer homes
Symptom: Modem will not Range Upstream and will never come online.
Fix: This cannot be fixed by the user and will need technician to check the plant and also need to call headend office to fix the signal sent to home
T2 ( 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.
Occurrence: Very rare in the customer homes
Symptom: Modem will not Range Upstream and will never come online.
Fix: This cannot be fixed by the user and will need technician to check the plant and also need to call headend office to fix the signal sent to home
T3 ( 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.
T3 timeouts result when a Cable Modem, that is locked into the downstream, transmits a Ranging Request(RNG-REQ) to the CMTS(Cable Modem Termination System) and 200 milliseconds passes without the CM receiving a Ranging Response(RNG-RSP) from the CMTS. Indeed, maintaining a PING(Packet InterNet Groper) less than 200ms is important to a healthy DOCSIS network. When 10 T3s occur in succession (a period of 20 seconds passes without the CM receiving a Ranging Response, the CM will cease attempting to communicate with the HFC(Hybrid Fiber Optic Coaxial) network and reset its DOCSIS interface. In this case the RESET statistic on the modem log will increment but not all T3s will cause a reset if communication is restored within 10 T3 periods or 20 seconds. When T3 timeouts occur, but not enough occur in succession to trigger a reset, slow speeds are often a symptom as these timeouts slow down the TCP/IP handshakes necessary to maintain internet connections.
T3 Timeouts are typically caused by Upstream Noise causing Ranging Requests to not be clearly received by the CMTS. T3 problems can often be intermittant in nature as they may be the result of noise originating in any part of the plant that shares the same line card at the CMTS with the subscriber impacted. In fact, T3s can even be caused by noise originating on other neighboring nodes if resources are shared at the headend. Speed issues and intermittant connectivity issues are some of the most common problems encounted on our Trouble Calls.
T3 Timeouts can also be encountered when the plant's noise floor is so severe that the CM cannot overtalk it (SNR is bad and Noise power level is higher than your modem's signal). This can affect a single leg of the plant or even entire nodes. When a high noise floor results in several modems resetting their DOCSIS interface because 10 T3 timeouts have occured in succession, as we covered above, this is referred to as a noise outage. Noise outages frequently occur node-wide and while some may self-clear, many continue until a Plant Maintenence Technician locates and repairs the offending source of noise. This is why we ALL must be vigilant about preventing noise from entering the plant.
Occurrence: Extremely common in the customer homes
Symptom: Will cause intermittent disconnections. If you see couple of them, it is fine. If you quite a few of them consecutively, then it will lead to disconnections.
Example:
2017-6-14, 00:05:06 Critical (3) No Ranging Response received - T3 time-out;CM-MAC=00:11:22:c1:db:09;CMTS-MAC=4c:00:82:ee:bd:62;CM-QOS=1.0;CM-VER=3.0
Fixes:
1. Check for the loose or Bad cables. This is by far most neglected and most common fix.
2. Remove extra splitters in house
3. Buy powered amplifier to boost your upstream power
4. Buy better coaxial cables
5. Call for a technician visit to inspect and fix cables outside and inside home (could be rain damage, fire damage, animal damage, construction damage, etc)
T4 ( 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.
T4 Timeouts result when a CM does not receive a Station Maintenance Opportunity in which to transmit a Ranging Request within the T4 timeout period which is approximately 30 seconds. T4s typically result from an impairment in the downstream. As they take an interruption in connectivity for 30 seconds to occur and trigger a reset, T4s can be indicative of major faults like damaged drops, or mainline suckouts but can also occur from maintenance work in the plant or at the headend as well. A low T4 count may be indicative only of repeated maintenance operations while a high T4 count may represent a severe plant or drop impairment.
Example:
2017-6-18, 09:41:36 Critical (3) Received Response to Broadcast Maintenance Request, But no Unicast Maintenance opportunities received - T4 time out;CM-MAC=00:11:22:c1:db:09;CMTS-MAC=00:11:22:ee:bd:62;CM-QOS=1.1;CM-VER=3.0;
Occurrence: Extremely common in the customer homes
Symptom: Will cause disconnections every time it occurs.
Fixes:
1. Check for the loose or Bad cables. This is by far most neglected and most common fix.
2. Remove extra splitters in house
3. Buy powered amplifier to boost your upstream power
4. Buy better coaxial cables
5. Call for a technician visit to inspect and fix cables outside and inside home (could be rain damage, fire damage, animal damage, construction damage, etc)
6. Check for any noise sources
T6 ( 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.
Occurrence: Rarely seen in the customer homes
Symptom: Modem will not come online
Fixes:
1. Ask Technician or Call center to re-provision the modem
2. Ask Technician or call center to send different boot file (or config file) to the modem