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3.0 Troubleshooting

Cable modems have built-in diagnostic information. The procedures for accessing these diagnostics vary depending on the model of cable modem you have. If the information below won't get you to these diagnostics, please contact Motorola (be it leased or owned). A few modems may have this information in the manual that they came with. For some cable modems, you can access these diagnostics even if the cable modem hasn't obtained block sync.


•The following list is Model specific. Choose your modem & click on the provided link:


DOCSIS 2.0 Modems

Motorola SB5100______ »192.168.100.1/ ___ No Username or Password required
Motorola SB5101______ »192.168.100.1/ ___ No Username or Password required
Motorola SB5101N/U___ »192.168.100.1/ ___ No Username or Password required
Motorola SB5102______ »192.168.100.1/ ___ No Username or Password required
Motorola SB5120______ »192.168.100.1/ ___ No Username or Password required


DOCSIS 2.0 Wireless Gateway Modems

Motorola SBG901______ »192.168.0.1/ _____ Username: admin / Password: motorola
Motorola SBG941______ »192.168.0.1/ _____ Username: admin / Password: motorola

DOCSIS 2.0 Voice Modems

Motorola SBV5121_____ »192.168.100.1/ ___ Username: admin / Password: motorola
Motorola SBV5122_____ »192.168.100.1/ ___ Username: admin / Password: motorola
Motorola SBV5222_____ »192.168.100.1/ ___ Username: admin / Password: motorola
Motorola SBV5322_____ »192.168.100.1/ ___ Username: admin / Password: motorola

DOCSIS 2.0 Wireless Voice Gateway Modems

Motorola SVG1202_____ »192.168.0.1/ _____ Username: admin / Password: motorola
Motorola SVG1501_____ »192.168.0.1/ _____ Username: admin / Password: motorola
Motorola SVG2501_____ »192.168.0.1/ _____ Username: admin / Password: motorola

DOCSIS 3.0 Modems

Motorola SB6121______ »192.168.100.1/ ___ No Username or Password required
Motorola SB6141______ »192.168.100.1/ ___ No Username or Password required

DOCSIS 3.0 Wireless Gateway Modems

Motorola SBG6580_____ »192.168.0.1/ _____ Username: admin / Password: motorola
Motorola SBG6782AC___ »192.168.0.1/ _____ Username: admin / Password: motorola

DOCSIS 3.0 Wireless Voice Gateway Modems

Motorola SBV6220_____ »192.168.100.1/ ___ Username: admin / Password: motorola

At&T High-Speed DSL Gateway Modems

Motorola 3360________ »192.168.1.254/___ The Modem will prompt for a "Modem Access Code". That code can be found on a label attached to the Gateway/Modem.



*This FAQ is based on user knowledge from a volunteer core of BroadbandReports' members. This FAQ in no way constitutes official information from Motorola or any of its affiliates.



by drake See Profile edited by Johkal See Profile
last modified: 2013-09-29 13:17:10

This is quite a common issue that arises in most of our cable ISP forums. When placing a new PC onto a new cable modem, you need to make sure you've rebooted the modem for at least 30-seconds. The cable modem remembers the last MAC Address connected to it's WAN port. Rebooting it in the 30-second period should clear out the data stored within the modem, and allow other devices to connect.



*This FAQ is based on user knowledge from a volunteer core of BroadbandReports' members. This FAQ in no way constitutes official information from Motorola or any of its affiliates.

by drake See Profile edited by Johkal See Profile
last modified: 2013-09-28 16:23:49

If your "PC Activity" light is blinking rapidly, then that's normal operation.


If your "Online/Receive/Send" lights are blinking or just not on, there's something wrong. First thing you should check is your modem signal levels.


• Ref: Viewing the Cable Modem's Signal Levels, Firmware Version & Log Entries

• Ref: What should my Signal Levels be?

Next, check your cables, cable ends & splitters for issues like looseness, damage & debris.
If the issue continues or gets worse, you might want to take a look into your local ISP forum. Be sure to check their FAQs, too.



*This FAQ is based on user knowledge from a volunteer core of BroadbandReports' members. This FAQ in no way constitutes official information from Motorola or any of its affiliates.



by drake See Profile edited by Johkal See Profile
last modified: 2013-09-29 12:59:59

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.


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.


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


Explanation: The cable modem did not receive 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 ( 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.


Feedback from Ignite See Profile: "It should perhaps be made clear these messages apply when the modem is coming online, and that T3s especially are a different thing once the modem is online, becoming a non-critical message that's harmless unless rapidly incrementing."




*This FAQ is based on user knowledge from a volunteer core of BroadbandReports' members. This FAQ in no way constitutes official information from Motorola or any of its affiliates.



by Johkal See Profile

Downstream (Rx) Receive Power Level:
This is the amount of signal received by the modem from the transmitter in the cable company head-end.

For all modems:

-7 dBmV to +7 dBmV "Recommended"
-8 dBmV to -10 dBmV / +8 dBmV to +10 dBmV - "Acceptable"
-11 dBmV to -15 dBmV / +11 dBmV to +15 dBmV - "Maximum"
Lower than -15 dBmV & Higher than +15 dBmV - "Out Of Spec."

SNR (signal to noise ratio) levels:
This is how clear the signal is at either the modem receiver (downstream SNR) or the receiver in the cable company head-end (upstream SNR).

DOCSIS specifications list minimum CNR (carrier to noise ratio) levels not SNR levels. The SNR levels listed here are based on commonly recommended MER levels for digital cable signals. Not all QAM demodulator chipsets accurately calculate SNR levels that approximate actual MER levels, so these levels may vary depending on which chipset and/or firmware is used in the equipment.

*There is no upper SNR limit; however, 40 dB is the highest most people see. Going above 40 dB is possible though.

256 QAM: 30 dB minimum. 33 dB or higher recommended. (often used in downstream channels)
64 QAM: 24 dB minimum. 27 dB or higher recommended. (often used in downstream channels)
16 QAM: 18 dB minimum. 21 dB or higher recommended. (often used in upstream channels)
QPSK: 12 dB minimum. 15 dB or higher recommended. (often used in upstream channels)

Downstream SNR levels are read at the modem on the downstream data channel and can be viewed using the modem diagnostic screens.

Upstream SNR levels are read at the CMTS on the upstream data channel, not the modem or the modem diagnostic screens. The end-user cannot get the upstream SNR directly. Only the provider can read the upstream SNR level, directly from the CMTS. Also, the upstream SNR level provided by most CMTSs is not specific to any single modem, but is an averaged, aggregate level from all modems on that upstream channel on the upstream port.

Upstream (Tx) Transmit Power (a.k.a. Return Signal) level:
This is the amount of signal transmitted by the modem to reach the receiver in the cable company head-end.

*Recommended upstream signal levels are +35 dBmV to +49 dBmV.

52 dBmV maximum for A-TDMA & TDMA (DOCSIS 3.0)
53 dBmV maximum for S-CDMA DOCSIS 2.0 (All Modulations)
54 dBmV maximum for 32 QAM and 64 QAM. (A-TDMA DOCSIS 2.0)
55 dBmV maximum for 8 QAM and 16 QAM. (DOCSIS 1.0, 1.1)
58 dBmV maximum for QPSK. (DOCSIS 1.0, 1.1)

A cable modem running a higher upstream modulation rate may downgrade itself to a lower modulation rate (i.e. 64 QAM to 16 QAM or 16 QAM to QPSK) if the upstream transmit level is higher than the maximum signal level allowed for the higher modulation rate and the CMTS is configured to allow such a change. This downgrade can cause slow speed, packet loss, and connection loss issues depending on the condition of the upstream channel.

A house or drop amplifier will NOT fix an upstream signal problem because most house amplifiers don't amplify the upstream signals; they only pass the upstream signal through with some loss.

Important notes concerning signal levels:
1. Signal levels not within the specifications listed above can cause slow speeds, connection problems, and connection loss due to packet errors, packet loss, and/or constant packet retransmission.

2. It's recommended to have the modem's signal levels at least 3dB away from the maximum/minimum levels listed above due to normal temperature related signal variation. If the modem's signal levels are at the maximum or minimum limits, they may be out of spec. if the temperature changes significantly. Signal levels that vary more then 3 dB in a 24-hour period usually indicate a problem that should be looked into.

3. Excess splits, bad connectors, and/or poor quality cabling will certainly effect cable signal levels and will cause problems.



*This FAQ is based on user knowledge from a volunteer core of BroadbandReports' members. This FAQ in no way constitutes official information from Motorola or any of its affiliates.



by sashwa See Profile edited by Johkal See Profile
last modified: 2014-02-17 16:47:36

• Support can be found here: Cable Modems & Gateways



by sashwa See Profile edited by Johkal See Profile
last modified: 2013-09-28 14:22:20