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2.1 Modems

No, Comcast controls what firmware is sent to your modem. Users cannot update their modem's firmware.

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

by Nerdtalker See Profile edited by Johkal See Profile
last modified: 2008-11-01 14:49:53

When viewing Comcast's Approved Modem List, you will see a column for "Certification Levels".
Please see this overview for what this certification means:

Retail DOCSIS Tiered Levels of Certification

One Star indicates that the device has undergone DOCSIS testing by Comcast and has received the relevant Underwriters Laboratory ("UL"), Federal Communications Commission (FCC), and CableLabs certifications. Comcast's DOCSIS certification supplements CableLabs testing by adding things like performance and interoperability tests. This helps to ensure that, for example, a given device can support a given service tier's speed.

Two Stars indicates that the device has undergone all of the One Star tests as well as a basic Physical and Environmental (P&E) evaluation. Such basic P&E testing indicates basic manufacturer self-certification of a subset of P&E tests.That basic P&E evaluation is intended to address a number of important performance and safety issues, which tests from UL, the FCC, and CableLabs do not address. Some of the things P&E tests check for include areas such as device performance and safety during overheating, power interruptions (including power outs), radio frequency (RF) interference, electrostatic discharge, electrical surges, and network impairments.

Three Stars indicates that the device has undergone all of the Two Star and One Star tests as well as a full Physical and Environmental (P&E) evaluation. Such full &E testing indicates that all P&E tests were performed and that these tests were overseen in person. This is the highest and most thorough level of testing available.

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

by Johkal See Profile
last modified: 2012-08-26 18:06:49

The following info provides how to Contact Comcast & the proper procedure to Bridge an Arris Gateway Modem: 

Comcast Support: 1-800-XFINITY (1-800-934-6489) 

If you can't get through after calling Comcast Support, try these methods: 

»Comcast Direct

»twitter.com/comcastcares

For anyone who is having trouble with the gateway after calling gateway support you need to have them verify the modem is in full bridge mode. For the Arris devices bridge mode can be enabled in 2 ways. There is a 1 button GUI click method, and there is a way for them to log into the modem management page to enable the bridge mode. Not the Xfinity management page by the way. So if you call in to have it bridged and your WiFi light is still on after that, they have done it wrong.

You need to have them go into the Arris management page and then go to Advanced (requires password of the day) --> MSO features --> then

Bridge Mode -- Enabled
Wifi - Disable
LAN DHCP - Disable

Then have them reset the modem. If they don't follow those specific steps chances are your modem isn't fully in bridge mode and you may continue to have problems.

Thanks to EG See Profile

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


Feedback received on this FAQ entry:
  • when calling in you can ask the CAE who answers the phone if they have access to grandslam. Most of them should since they use this tool to look at the modem and also create the truck roll if needed. Under the HSI tab is a menu called Dory/Gateway. They should select that then go to the General settings tab. This is where the option to put the device into Bridged mode. When they do this, it will present them with a warning that it will deactivate the wireless portion. That should confirm that they are doing it correctly. Again most of the CAE's should have access to this tool, but they may have never had to do this before. It should save some time on them contacting a supervisor how to do it.

    2013-07-13 20:02:29 (rendrenner See Profile)



by Johkal See Profile
last modified: 2013-09-15 07:22:32

That choice is certainly up to you, but you may find this discussion helpful in forming your opinion.

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

by sortofageek See Profile edited by Johkal See Profile
last modified: 2008-11-01 14:50:31

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 $70+ 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 $70+ 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

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

by Nerdtalker See Profile edited by Johkal See Profile
last modified: 2011-12-18 20:26:30

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

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

Feedback received on this FAQ entry:
  • Please add USB 2.0 and USB 3.0 to this FAQ! Thanks!

    2013-07-03 19:15:28 (Coelispex See Profile)



by Nerdtalker See Profile edited by Johkal See Profile
last modified: 2008-11-01 14:51:01

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.


•The following list is Manufacturer & Model specific. This info. directs you via a link & provides Username / Password where applicable.


Arris CM550A________________ »192.168.100.1 / No username or password required.
Arris CM820A_______________ »192.168.100.1/ ___ No Username or Password required
Arris TG852G (IMS/NCS)_______ Need Info.
Arris TG862G (IMS/NCS)______ »10.0.0.1/ _______ Username: admin / Password: password
Arris TM402G (IMS/NCS)______ »192.168.100.1/ ___ No Username or Password required
Arris TM402P (IMS/NCS)______ »192.168.100.1/ ___ No Username or Password required
Arris TM502G (IMS/NCS)______ »192.168.100.1/ ___ No Username or Password required
Arris TM504G (IMS/NCS/SIP)___ »192.168.100.1/ ___ No Username or Password required
Arris TM508A (NCS/SIP)_______ »192.168.100.1/ ___ No Username or Password required
Arris TM602G (IMS/NCS/SIP)___ »192.168.100.1/ ___ No Username or Password required
Arris TM604G (IMS/NCS/SIP)___ »192.168.100.1/ ___ No Username or Password required
Arris TM608G (NCS/SIP)_______ »192.168.100.1/ ___ No Username or Password required
Arris TM702G (IMS/NCS)______ »192.168.100.1/ ___ No Username or Password required
Arris TM722G (IMS/NCS)______ »192.168.100.1/ ___ No Username or Password required
Arris TM822G (IMS/NCS)______ »192.168.100.1/ ___ No Username or Password required
Arris WBM760A_______________ Need Info.

Cisco DPC3000___ »192.168.100.1/ ___ No Username or Password required
Cisco DPC3008___ »192.168.100.1/ ___ No Username or Password required
Cisco DPC3010___ »192.168.100.1/ ___ No Username or Password required
Cisco DPC3825___ Need Info.
Cisco DPC3939___ »10.0.0.1/ _______ Username: admin / Password: password
Cisco DPC3939B__ »10.1.10.1/ ______ Username: cusadmin / Password: highspeed

D-Link DCM-202___ »192.168.100.1/ __ Username: dlink / Password: dlink
D-Link DCM-202 (Comcast firmware)___»192.168.100.1/ ___ Username: admin / Password: hitron
D-Link DCM-301__ »192.168.100.1/ __ Username: admin / Password :password

Motorola SB5100____ »192.168.100.1/ ___ No Username or Password required
Motorola SB5101____ »192.168.100.1/ ___ No Username or Password required
Motorola SB5101U___ »192.168.100.1/ ___ No Username or Password required
Motorola SB5120____ »192.168.100.1/ ___ No Username or Password required
Motorola SB6121____ »192.168.100.1/ ___ No Username or Password required
Motorola SB6141____ »192.168.100.1/ ___ No Username or Password required
Motorola SB6180____ »192.168.100.1/ ___ No Username or Password required
Motorola SB6183____ »192.168.100.1/ ___ No Username or Password required
Motorola SBG6580___ »192.168.0.1/ _____ Username: admin / Password: motorola
Motorola SBG6700AC_ Need Info.
Motorola SBG6782AC_ »192.168.0.1/ _____ Username: admin / Password: motorola
Motorola SBG901____ »192.168.0.1/ _____ Username: admin / Password: motorola

Netgear CG3000DCR___ »10.1.10.1/ __ Username: cusadmin / Password: highspeed
Netgear CG814CCR-V2_ »192.168.100.1/ ____ No Username or Password required
Netgear CMD31T______ »192.168.100.1/ ____ Username: admin / Password: password
Netgear CM400_______ Need Info.
Netgear CM500_______ Need Info.
Netgear C3000_______ Need Info.
Netgear C3700_______ Need Info.
Netgear C6300_______ Need Info.
Netgear N450________ Need Info.

Scientific-Atlanta DPC2100R2__________ Need Info.
Scientific-Atlanta DPC2203 (IMS/NCS)___ Need Info.
Scientific-Atlanta DPC2203C (IMS/NCS)__ Need Info.
Scientific-Atlanta DPC2203C2 (IMSNeed Info./NCS)_Need Info.

SMCNetworks SMC8014WG-CCR_____ Need Info.
SMCNetworks SMCD3G-CCR________ »10.1.10.1/ ___ Username: cusadmin / Password: highspeed
SMCNetworks SMCD3GNV (IMS/NCS)_ »10.0.0.1/ ___ Username: admin / Password: password

Technicolor TC8305C (IMS)___ »10.0.0.1/ _______ Username: admin / Password: password

Thomson DCM425___________ Need Info.
Thomson DHG535 (IMS/NCS)__ Need Info.
Thomson DHG536 (IMS/NCS)__ »192.168.100.1/ ___ No Username or Password required

Ubee DDM3503____________ »192.168.0.1/ _____ Username: user / Password: user or »192.168.100.1/ ___ Username: admin / Password:cableroot
Ubee DDM3513____________ »192.168.0.1/ _____ Username: user / Password: user or »192.168.100.1/ ___ Username: admin / Password:cableroot
Ubee DVM3203B (IMS/NCS)__ »192.168.100.1/ ___ Username: admin / Password:cableroot
Ubee U10C018____________ »192.168.100.1/ ___ Username: admin / Password:cableroot
Ubee U10C035____________ »192.168.100.1/ ___ Username: user / Password: user

Zoom Telephonics 5241_______ »192.168.100.1/ ___ Username: admin / Password: cable
Zoom Telephonics 5341(G/H)__ »192.168.100.1/ ___ No Username or Password required / Additional Login: »192.168.100.1/rf_index.asp
Zoom Telephonics 5341J______ »192.168.100.1/ ___ Username: admin / Password: password Additional Login: »192.168.100.1/RgEventLog.asp
Zoom Telephonics 5350_______ »192.168.0.1/ _____ Username: admin / Password: admin
Zoom Telephonics 5352_______ »192.168.0.1/ _____ Username: admin / Password: admin
Zoom Telephonics 5363_______ Need Info.

ZyXEL BRG-35503___________ »192.168.100.1/ __ No Username or Password required


•Thanks to all the posters in this thread who helped with updating this FAQ: »I need your help updating a FAQ !!


• 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:

1) Set the IP of your ethernet connection to 192.168.100.254

2) Set the Subnet Mask of your ethernet connection to 255.255.255.0

3) Leave the Default Gateway and DNS Servers blank.

4) Reboot your PC.

5) Repeat step "1" as necessary.


• 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.



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





by Kylemaul See Profile edited by Johkal See Profile
last modified: 2014-12-15 08:23:28

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 Comcast or any of its affiliates.

Feedback received on this FAQ entry:
  • Great information here. Made troubleshooting my internet connection nearly painless. Thank you!

    2014-06-20 23:24:50



by Kip patterson See Profile edited by Johkal See Profile
last modified: 2012-08-16 13:37:42

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 Comcast or any of its affiliates.



by Johkal See Profile
last modified: 2014-02-18 05:36:14

While there is no clear-cut answer to this question, and the purpose of these FAQs is not to endorse products, multiple threads & polls have been created on this topic that should provide some information into what most BBR users own or lease & which they endorse.


Comcast's current Approved Modem List

August 2012: Heads Up, Time to Replace Your DOCSIS 1.1 Modem


Polls:

2014 Xfinity/Comcast Modem Poll

2013 Comcast Modem Poll

2012 Comcast Modem Poll

2011 Comcast DOCSIS 3.0 Modem Poll

2010 Comcast Modem Poll

2007 Comcast Modem Poll

2006 Comcast Modem Poll

2004 Comcast Modem Poll

2004 Comcast Additional "Which Modem is Best" Poll


Topics:
»Want to use my own modem - which one and where to buy?
»[Speed] Which modem/firmware gets the best throughput 4 BLAST sp
»Best modem?
»Best Linksys Cable Modem for Comcast HSI
»Which modem should I buy and why?
»Need a new cable modem
»[Connectivity] What router and modem ?
»[Connectivity] Motorola 5100 vs. 5120
»Got New Modem- It the New LINKSYS MODEM VERSION!!



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




by Nerdtalker See Profile edited by Johkal See Profile
last modified: 2014-04-26 15:06:23

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.

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

by Nerdtalker See Profile edited by Johkal See Profile
last modified: 2008-11-01 14:52:25

Many cable modems have an LED labeled Cable or Data. Often, this LED flashes or blinks even when your PC is idle or turned off. Legitimate network data (most often DHCP and ARP traffic) is generated by Comcast, causing this behavior. This traffic should not be cause for worry, and should not affect your bandwidth.

To add, any given make / model number of a modem's particular firmware load can and could be coded to make that indicator light blink continuously regardless of the presence of or the absence of any traffic.

thanks to oldTDNickell5 See Profile

Definitions of terms: DHCP & ARP

DHCP: Dynamic Host Configuration Protocol. A protocol for assigning dynamic IP addresses to devices on a network.

ARP: Address Resolution Protocol. Its a protocol that allows the OS to associate an ip address (layer 3) with an ethernet MAC address (layer 2).

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

by Big_D See Profile edited by EG See Profile
last modified: 2013-04-18 14:17:38