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| | | | FAQ Revisions | Editors: File Quit  , Johkal , sortofageek
Last modified on 2008-08-15 20:31:20
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2.1 Modems·How can I view my Modem's Signal Levels, Firmware Version & Log Entries?
·What should my Signal Levels be?
·What are the differences between the Motorola SB5100, SB5101 & SB5120?
·Which modem should I get?
·Can I update my modem's firmware?
·Should I lease or buy my modem?
·Should I use USB or Ethernet?
·What do messages about timeouts mean?
·Why does one device pull an IP, but my other device doesn't? It worked before!
| | | Most cable modems have built-in diagnostics for getting information on the quality of the cable signal coming to the modem. The procedures for accessing these diagnostics vary depending on the brand and model of cable modem you have. If the information below won't get you to these diagnostics, please contact the manufacturer of your cable modem (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.
1) Try this first: Open your browser and navigate to http://192.168.100.1/ (or try holding SHIFT key and clicking the links). This is the most common method of accessing the diagnostics. You may need to navigate a bit from here to access the pertinent information.
•1.A) For an Ambit cable modem, you may be prompted for a username and password. The username is root and the password is also root. Some Ambit cable modems have the information you are after on more than one web page.
•1.B) For an ARRIS Touchstone TM502G CDV Modem, you will navigate to http://192.168.100.1 to view the diagnostics.
•1.C) For a Motorola SBV5220, go to http://192.168.100.1. The username is admin and the password is motorola.
•1.D) For a RCA cable modem, you may need to navigate to http://192.168.100.1/moreInfo.html to view the diagnostics.
•1.E) For a Scientific Atlanta modem, go to http://192.168.100.1. The username is admin and the password is w2402
•1.F) For an SMC8013 gateway, (Business customers) go to http://10.1.10.1. The username is cusadmin and the password is highspeed
•1.G) For a Terayon TJ615, navigate to http://192.168.100.1 and type icu4at! at the password prompt (or copy paste it from here). To see the signals go to http://192.168.100.1/modemRfPage. If you cannot access the status page at http://192.168.100.1 (main menu) reboot the cable modem, wait for it to synch and then try. The reboot may be necessary due to the fact that the status page was an afterthought
•1.H) For a Terayon TJ715, navigate to http://192.168.100.1/diagnostics_page.html to view the diagnostics. The password is icu4at!
•1.I) For a 3Com cable modem, you may need to navigate to http://3comcablemodem.com or http://49.112.50.65 to view the diagnostics. A note about 3Com cable modems: they are notorious for reporting erroneous information, and sifting out the values you will be interested in will be difficult at best. Also, some 3Com modems will prompt you for a username and password, which are User and Password respectively.
2) If none of the above methods work, or if your cable modem does not have block sync, you may need to 'force' a connection directly to the modem. This is done by:
•2.A) Set the IP of your ethernet connection to 192.168.100.254
•2.B) Set the Subnet Mask of your ethernet connection to 255.255.255.0
•2.C) Leave the Default Gateway and DNS Servers blank.
•2.D) Reboot your PC.
•2.E) Repeat step 1) above, as necessary.
•2.F) IMPORTANT! Be sure to set your ethernet connection back to DHCP (Obtain IP and DNS automatically) and reboot when you are done checking the diagnostics or you won't be able to access the internet!
Once you have accessed the diagnostics interface in your browser, you need to know which of these statistics are important and what to watch for if you are having difficulties. See the FAQ: What should my signal levels be? for an interpretation of this information.
Thanks to mbernste and SolarPup
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by Kylemaul edited by Johkal
last modified: 2007-11-17 07:18:49 | | | 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:
-10 dBmV to +10 dBmV "Recommended".
-11 dBmV to -14 dBmv / +11 dBmV to +14 dBmV "Acceptable".
-15 dBmV & +15 dBmV "Maximum".
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.
QPSK: 12 dB minimum. 15 dB or higher recommended. (often used in upstream channels)
16 QAM: 18 dB minimum. 21 dB or higher recommended. (often used in upstream channels)
64 QAM: 24 dB minimum. 27 dB or higher recommended. (often used in downstream channels)
256 QAM: 30 dB minimum. 33 dB or higher recommended. (often used in downstream channels)
There is no upper SNR limit; however, 40 dB is the highest most people see. Going above 40 db is possible though.
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.
+8 dBmV to +58 dBmV maximum for QPSK. (DOCSIS 1.0, 1.1)
+8 dBmV to +55 dBmV maximum for 8 QAM and 16 QAM. (DOCSIS 1.0, 1.1)
+8 dBmV to +54 dBmV maximum for 32 QAM and 64 QAM. (A-TDMA DOCSIS 2.0)
+8 dBmV to +53 dBmV maximum for S-CDMA DOCSIS 2.0 (All Modulations)
Recommended upstream signal levels are +35 dBmV to +52 dBmV.
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. Make the cable run to the modem as clean as possible; the less junk in the way, the better.
Thanks to MacLeech
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by Johkal | | | Similar in appearance and features, the SB5101 & SB5120 are not repackaged versions of the SB5100.
The SB5100 uses the Broadcom chipset/processor BCM3348.
The SB5101 uses the Broadcom chipset/processor BCM3349.
The SB5120 uses the Texas Instrument chipset/processor TI4401.
Each modem has its own firmware versions unique to its model. All other product specifications are the same for all 3 models.
The SB5100 has been discontinued by Motorola, but support is available.
The SB5101 is a current model.
The SB5120 is being phased out.
You may also want to take a look at this post by Nerdtalker . ~sorto'
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by Bleek edited by Johkal
last modified: 2007-03-19 22:11:52 | | | While there is no clear-cut answer to this question, and the purpose of these FAQs is not to endorse products, multiple threads have been created on this topic that should provide some information into what most BBR users would recommend as the "best" modem for Comcast.
Polls:
2007 »[POLL] Which Cable Modem is Best for Comcast HSI?
2006 »[POLL] Which Cable Modem is Best?
2004 »[poll] What Modem is Best?
2004 »[Connectivity] What type of modem do you use?
Threads:
»Need a new cable modem
»[Connectivity] What router and modem ?
»[Connectivity] Motorola 5100 vs. 5120
»Got New Modem- It the New LINKSYS MODEM VERSION!!
NOTE: These opinions are NOT endorsed by Comcast in any way, shape or form. All opinions are respective of the poster. To see Comcast's full list of approved modems click Here.
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by Nerdtalker edited by Johkal
last modified: 2008-01-06 08:25:06 | | | No, Comcast controls what firmware is sent to your modem. Users cannot update their modem's firmware.
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by Nerdtalker edited by Johkal
last modified: 2006-02-12 14:25:52 | | | There really isn't a perfect solution to the question, so here are the Pros and Cons of each option:
Lease:
•Pros:
You are normally provided a new modem.
You can swap your present modem for a new modem, usually without any questions asked.
You don't have to spend $50+ on a new modem if your leased one breaks.
•Cons:
You have to pay a monthly fee.
You are at the mercy of Comcast as to which modem you get.
Buy:
•Pros:
The ability to choose your own modem.
You don't have to pay the monthly fee.
Retail stores will offer a free or discounted modem with a self install kit and a service subscription.
•Cons:
The modem costs $50+ upfront
If your modem breaks, it's your responsibility to replace it.
Whether you lease or buy, Comcast will provide needed firmware updates as long as the modem is on the approved list: Approved Modem List
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by Nerdtalker edited by Johkal
last modified: 2008-06-07 22:47:31 | | | While USB may seem the better, cheaper solution, Ethernet is usually faster and more stable in the long run.
Because USB 1.1 is a 12 megabit connection, when users connect other devices, they quickly consume the 12 megabits. This causes the connection to slow. Other devices also sometimes conflict with the USB-connected modem, creating instability.
Ethernet, on the other hand, is the industry small network standard. A NIC (Network Interface Card) is required. If you don't have one, they usually run $10-$20. Because this is 100 megabits full-duplex, the connection can't be fully saturated by the modem.
If you do decide that USB is the best solution for you, drivers can be found here: Drivers
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by Nerdtalker edited by Johkal
last modified: 2008-06-14 12:53:25 | | | 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 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 ( 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 ( 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.
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by Kip patterson edited by Johkal
last modified: 2008-08-10 19:05:36 | | | Inside the configuration file that each modem receives on startup, is a field called CPE=x. This value dictates exactly how many mac addresses behind the modem are allowed to pull a real, routable, Comcast IP address. This is also what they change when you purchase another IP, since it lets you pull more than one.
The solution to this problem is quite easy, simply power-cycle the modem.
Keep in mind that if you have a router, and previously had a PC connected, you will need to restart the modem, or clone the mac of the PC into the router. Also, the router only counts as that one device and not the devices behind the router.
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by Nerdtalker edited by Johkal
last modified: 2006-02-16 10:12:28 |
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