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ARRIS Group, Inc > 
Item#: 9SIA5T23742439

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  • Overview
  • Specifications
  • Warranty & Returns
  • Reviews


SB6121 SURFboard Cable Modem RJ-45

Building upon the success of the SB6120, The ARRIS SURFboard SB6121 delivers your complete personal media experience, at lightning-fast broadband speed. It harnesses the power of DOCSIS 3.0 technology to bond up to four downstream channels and four upstream channels - providing you advanced multimedia services with data rates of more than 100Mbps in each direction. That makes gaming, shopping, downloading, working, high-quality voice and video conferencing, and peer-to-peer networking applications far more efficient than ever before.



SB6121 Easy to Set Up and Use
  • Plug-and-play installation
  • Front panel LEDs indicate status and simplify troubleshooting
  • Multi-language user guides
  • Supports standard internet software
  • User-friendly online diagnostics

  • Stylish and space-saving enclosure
  • Offers innovative, high-bandwidth data and multimedia services to customers
  • Backward-compatible to DOCSIS / EuroDOCSIS 1.x and 2.0

Advanced Services Ready
  • DOCSIS 3.0-certified (EuroDOCSIS 3.0-based)
  • Channel bonding of up to four downstream and four upstream channels
  • 1GHz capable tuners
  • Supports IPv4 and IPv6 to expand network addressing capabilities
Versatile and Convenient
  • Compatible with Windows, Macintosh, and UNIX computers.
  • Gigabit Ethernet (RJ-45) data port enable flexible, high-speed connectivity with Auto Negotiate and Auto MDIX

Reliable and Secure
  • Enhanced security: supports Advanced Encryption Services (AES) traffic encryption
  • Remotely configurable and monitorable using SNMP and TFTP

As part of the ARRIS DOCSIS 3.0 Ultra-Broadband family of products, the SB6121 includes an enhanced tuner that supports up to a 1GHz downstream input, which allows operators to increase the frequency spectrum for deployment of new high-value service - such as bandwidth on-demand, commercial services, interactive gaming, and IPTV. The SB6121 features a 10/100/1000 Base-T Ethernet (RJ-45) port, as well as intuitive, easy-to-read front-panel operational status LEDs.

What Is DOCSIS 3.0?

With the DOCSIS 3.0 specification, cable Internet providers can take advantage of the extra capacity provided by channel-bonding technology in order to offer ultra-fast broadband services. Channel bonding allows parallel data pipes to act as a single broadband conduit. With each channel capable of providing around 40Mbps of data, the ARRIS SURFboard SB6121's four downstream channels can provide a theoretical maximum of 160Mbps of throughput.

Currently, cable providers max out at around 50Mbps of downstream data throughput, but DOCSIS 3.0 will enable cable Internet providers to continue to improve the speed of their networks.

System Requirements
The SB6121 is compatible with the following operating systems:
  • Windows 7
  • Windows Vista, Service Pack 1 or later
  • Windows XP, Service Pack 2 or later
  • Mac 10.4 or later (Ethernet connection only)
  • UNIX (Ethernet connection only)
  • Linux (Ethernet connection only)

What's in the Box

ARRIS SURFboard SB6121, Ethernet cable, Installation sheet


Learn more about the ARRIS Group, Inc SB6121




Cable Modem
1 x RJ-45, Gigabit Ethernet
Cable Interface
75ohm F-connector
DOCSIS 3.0, 2.0 and 1.1, Euro-DOCSIS 3.0
Max Transmission Rate
Up To 172 Mbps Down and 131 Mbps Up


Data Protocol: TCP/IP

Power: 9W (nominal)

Input Power: 105 to 125 VAC, 60 Hz

-Modulation: 64 or 256 QAM

-Capture Bandwidth: 100 MHz (edge to edge)

-Maximum Theoretical Data Rate:
DOCSIS: 171.537 Mbps (4 channels) / 42.884 (single channel)@ 256 QAM at 5.36 Msym/s
EuroDOCSIS: 222.464 Mbps (4 channels) / 55.616 (single channel)@ 256 QAM at 6.952 Msym/s.

DOCSIS: = 24 MHz
EuroDOCSIS: = 32 MHz.

-Symbol Rate:
DOCSIS: 64 QAM 5.057 Msym/s; 256 QAM 5.361 Msym/s

EuroDOCSIS: 64 QAM 6.952 Msym/s; 256 QAM 6.952 Msym/s.

-Operating Level Range: –15 to 15 dBmV

-Security: DOCSIS 3.0 Security (BPI+, EAE, SSD)

-Network Management: SNMP v2 & v3

-Provisioning Supports: IP addressing using IPv4 and/or IPv6 (dual stack).

-Modulation: QPSK and 8, 16, 32, 64, 128 QAM

-Maximum Channel Rate
DOCSIS 131.072 Mbps (4 channels) / 32.768 Mbps (single channel): @ 128 QAM at 6.4 MHz
EuroDOCSIS 131.072 Mbps (4 channels) / 32.768 Mbps (single channel): @ 128 QAM at 6.4 MHz.

-Channel Width 200 kHz, 400 kHz, 800 kHz, 1.6 MHz, 3.2 MHz, 6.4 MHz

-Symbol Rates: 160, 320, 640, 1280, 2560, 5120 ksym/s

-Frequency Range: DOCSIS 5-42 MHz (edge to edge), EuroDOCSIS and optional DOCSIS 5 to 65 MHz (edge to edge)

Compatibility PC: 90496, Pentium, or later; Windows Vista, 2000, XP or 7 or Linux with Ethernet connection (older versions of Windows, although not specifically supported, will work with this cable modem).
Macintosh: Power PC or later; OS 9 or higher, Ethernet connection.
UNIX: Ethernet connection.
Home Networking: Ethernet router or wireless access point.


Package Contents
Ethernet Cable
Power Supply
Software License & Regulatory Card
Product Guide (Install Sheet)
Warranty, Returns, And Additional Information
  • Warranty
  • Limited Warranty period (parts): 2 years
  • Limited Warranty period (labor): 2 years
  • Read full details

Customer Reviews of the ARRIS Group, Inc SB6121

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  • Greg M.
  • 10/16/2015 9:10:17 AM
  • Tech Level: Somewhat High
  • Ownership: 1 day to 1 week
  • Verified Owner

1 out of 5 eggsDidn't work...

Pros: N/A

Cons: Comcast couldn't recognize the device

Other Thoughts: I received the Motorola Arris SB6121 modem yesterday. I contacted Comcast to activate the modem this morning. Unfortunately, Comcast could not recognize the device. The modem kept showing offline on their end. We reset, unplugged, and tried reactivating the device several times but it still refused to work. To say that I'm frustrated and disappointed is an understatement. What a pain in the...

0 out of 1 people found this review helpful. Did you? Yes No

  • Archie R.
  • 9/27/2015 7:43:36 AM
  • Tech Level: High
  • Ownership: 1 month to 1 year
  • Verified Owner

1 out of 5 eggsDied within 90 days

Pros: Started solid,good speed.

Cons: Over time dropped net with greater frequency then would not connect at all. Buying a modem online means a 1-3 week turn around for replacement.

Other Thoughts: Arris tech support was helpful and friendly but they bounced me back and forth with the cable provider when they knew on the first call the modem would not talk to the computer.
I bought a different brand and will put the Arris replacement on the shelf as a backup.

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  • Walter S.
  • 9/22/2015 9:03:44 AM
  • Tech Level: High
  • Ownership: more than 1 year

5 out of 5 eggsGood Product

Pros: I have had this Modem for 3 years now, and knock on wood not a single issue.
I did not purchase from new egg.

Cons: Dealing with Time Warner

Other Thoughts: I have recommended and installed this Modem for a number of friends.

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  • Tianjian W.
  • 8/29/2015 1:03:54 PM
  • Tech Level: High
  • Ownership: more than 1 year
  • Verified Owner

5 out of 5 eggsSB6121 modem

Pros: Very useful and money saving for Time Warner Cable.

Cons: mac address not automatically placed in a new router setting.

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  • Rachel S.
  • 8/26/2015 8:40:05 AM
  • Tech Level: Somewhat High
  • Ownership: 1 day to 1 week
  • Verified Owner

5 out of 5 eggsWorks great, Comcast still sucks

Pros: Just as fast as the rental modem
Doesn't cost $10/month

Cons: Had to call to have it set up

Other Thoughts: Bought this because we were tired of paying the $10/month for a modem rental through Comcast - especially since the wireless modem they sent us liked to drop the wireless signal at random intervals, which required disabling and enabling wireless on our devices in order to reconnect.

When I set it up, though, I couldn't access the Comcast activation page - or any pages - and wound up having to spend over an hour on the phone with them to get it taken care of.

It was worth it, though - I'm downloading at 90Mbps, when we're paying for 75. (Even with an older, cheap router.) Very happy with this purchase. Not so much with the ISP.

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  • David E.
  • 8/24/2015 8:31:47 PM
  • Tech Level: High
  • Ownership: 1 month to 1 year

5 out of 5 eggsChicken or Egg

Pros: This is probably the closest thing to the defacto standard for cable modems there is out there. It just works as advertised and was simple to set up and configure and for the first 10 months I think it rebooted once when we lost power.

Cons: None at the moment. By the way this runs quite warm, borderline hot might be a closer description, and the sides and top are a wide open mesh that gives good passive ventilation as there is no fan.

Other Thoughts: Here's where the chicken and egg thing comes in. Lately my network has been slowing down or hanging connections. If I try just rebooting my router alone it often doesn't make much difference, however if I also reboot the modem and the router then things will return to normal for some indeterminate time.

The problem is I no longer have a spare router to toss in there to see if the problem is with the router or the modem. Since the router is an older dual band I may just go ahead and upgrade that, though it may still not solve anything if my real problem is with the modem.

I also run an Ooma phone over IP on this and it breaks up from time to time and I'll have to hang up and reestablish a new connection. The Ooma and the modem were bought 10 months ago. I have a 50Mbs connection through Cox which was a brand new install so all cabling is new from the box to the house and its the latest spec. They also would like to sell me their version of phone over IP so who knows if they are doing anything to cause interference. Hard to trust any corporation these days.

Regardless, I don't have an extra router or modem so I am left flipping a coin as to which one may the culpret and I am leaning toward my older dual band being on the way out. Wish new equipment like routers were built like my old WRT54 which never failed in 6 years, but just got old technologically. It also doesn't seem to hold true that if you buy an expensive feature laden router that it will last any longer. If you get 1 - 2 years that seems to be about it for a lot of the routers built today in China but with a brand name on the outside.

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  • Arnold H.
  • 8/22/2015 8:54:48 PM
  • Tech Level: Average
  • Ownership: more than 1 year

5 out of 5 eggsvery happy with modem

Pros: Purchased 3/14 when TW introduced modem rental fee. Setup with TW was simple, and modem has run for over a year without issues. Had recent speed upgrade from ISP, and modem provides steady 55/5 speeds. Had I known these speed upgrades were coming I might have purchased a faster modem, but currently I'm very happy with the SB6121. Also think it looks nice, and the LED lights really don't bother us since the unit sits behind our monitor.

Cons: None.

Other Thoughts: Unless you have a really fast service plan (over 100Mbs), this is a great choice.

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  • JAMES T.
  • 8/21/2015 3:29:30 PM
  • Tech Level: Somewhat High
  • Ownership: less than 1 day
  • Verified Owner

1 out of 5 eggsComcast/Xfinity

Pros: Cannot determine. See cons.

Cons: This modem may very well be okay but if you are considering becoming a Comcast customer, please think again if you have any choice.

Other Thoughts: Comcast spent two hours on the phone with me. Set up an appointment for a technician and no one called or showed up. When I called them, they denied everything. Completely unacceptable. Just don't do it..

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  • Brad S.
  • 8/21/2015 6:48:06 AM
  • Tech Level: Somewhat High
  • Ownership: more than 1 year
  • Verified Owner

4 out of 5 eggsLast 30 months - not bad

Pros: I spent $80 to buy this modem, it worked for 30 months, so I saved approximately $160 by buying instead of renting

Cons: It died after 30 months

Other Thoughts: Buying a zoom this time

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  • Matt D.
  • 8/20/2015 8:34:45 AM
  • Tech Level: High
  • Ownership: 1 month to 1 year
  • Verified Owner

5 out of 5 eggsSolid

Pros: Consistent with ISP advertised speeds. The modem does not drop connection and I have not reboot it since I first installed it over 6 months ago.

Cons: None

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Wired Networking > 
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ARRIS Group, Inc > 
Item#: 9SIA5T23742439
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