Comments on: DOCSIS 3.0 Tutorial – Introduction http://volpefirm.com/docsis/docsis30-tutorial-introduction/ A Technical Communications Company Wed, 16 May 2012 06:51:01 +0000 hourly 1 http://wordpress.org/?v=3.3.2 By: Brady http://volpefirm.com/docsis/docsis30-tutorial-introduction/#comment-216 Brady Fri, 23 Dec 2011 15:01:55 +0000 http://bradyvolpe.com/?p=316#comment-216 Hi Justin, Unfortunately, buying a better modem is not going to get you faster speeds in your case. Since you already have a DOCSIS 3.0 cable modem that supports 4x downstream bonding, it can receive 4 x 42 Mbps = 168 Mbps in the downstream. The reason you are getting 50 Mbps is because the configuration file that your cable modem downloads during registration (boot-up) has a "maximum download rate cap" of 50 Mbps. So the cable modem throttles back download traffic once it hits the 50 Mbps limit. This is most likely the same service tier you are paying for. One other limiting factor on download speeds is the upstream. If you are familiar with TCP/IP, every downstream frame requires and upstream "ack" (acknowledgement) frame. A good rule of thumb is to make sure that your ratio of downstream to upstream is 10:1 to make sure that the upstream has enough "ack" capacity to make certain your upstream does not limit your downstream because the upstream unable to hand the capacity of "acks" for the downstream. So if you have a 50 Mbps downstream you should have at least a 5 Mbps upstream. Further, if your cable operator is only bonding four channels in the downstream, even if you have a cable modem that supports 8x downstream bonding, there won't be 8 channels for it to bond to, only the 4 channels that the cable operator has configured. -Brady Hi Justin,

Unfortunately, buying a better modem is not going to get you faster speeds in your case. Since you already have a DOCSIS 3.0 cable modem that supports 4x downstream bonding, it can receive 4 x 42 Mbps = 168 Mbps in the downstream. The reason you are getting 50 Mbps is because the configuration file that your cable modem downloads during registration (boot-up) has a “maximum download rate cap” of 50 Mbps. So the cable modem throttles back download traffic once it hits the 50 Mbps limit. This is most likely the same service tier you are paying for. One other limiting factor on download speeds is the upstream. If you are familiar with TCP/IP, every downstream frame requires and upstream “ack” (acknowledgement) frame. A good rule of thumb is to make sure that your ratio of downstream to upstream is 10:1 to make sure that the upstream has enough “ack” capacity to make certain your upstream does not limit your downstream because the upstream unable to hand the capacity of “acks” for the downstream. So if you have a 50 Mbps downstream you should have at least a 5 Mbps upstream.

Further, if your cable operator is only bonding four channels in the downstream, even if you have a cable modem that supports 8x downstream bonding, there won’t be 8 channels for it to bond to, only the 4 channels that the cable operator has configured.

-Brady

]]> By: Justin http://volpefirm.com/docsis/docsis30-tutorial-introduction/#comment-215 Justin Fri, 23 Dec 2011 00:09:36 +0000 http://bradyvolpe.com/?p=316#comment-215 I am receiving a 50mbps connection from insight cable in Louisville, KY. I currently have a cable modem that only does 4x channel bonding downstream. If I were to buy a newer modem that did 8x channel bonding downstream would I see a performance increase? In other words, is there a performance increase in adding more bonded channels even if your connection provider isn't currently maxing out the current 4x top speed spec? Something like allowing more parallel pipes? I am receiving a 50mbps connection from insight cable in Louisville, KY. I currently have a cable modem that only does 4x channel bonding downstream. If I were to buy a newer modem that did 8x channel bonding downstream would I see a performance increase? In other words, is there a performance increase in adding more bonded channels even if your connection provider isn’t currently maxing out the current 4x top speed spec? Something like allowing more parallel pipes?

]]> By: Brady http://volpefirm.com/docsis/docsis30-tutorial-introduction/#comment-214 Brady Mon, 21 Nov 2011 20:42:23 +0000 http://bradyvolpe.com/?p=316#comment-214 Hi Truls, Ron Hranac has by far written the most articles on micro-reflections and reading the tap values. Just google micro-reflections and Ron Hranac and I suspect you'll find what your looking for. If not, write back with the exact question of what your looking for and I can probably find someone in the industry who has a white paper for you. -Brady Hi Truls,

Ron Hranac has by far written the most articles on micro-reflections and reading the tap values. Just google micro-reflections and Ron Hranac and I suspect you’ll find what your looking for. If not, write back with the exact question of what your looking for and I can probably find someone in the industry who has a white paper for you.

-Brady

]]> By: Truls http://volpefirm.com/docsis/docsis30-tutorial-introduction/#comment-213 Truls Fri, 18 Nov 2011 10:50:49 +0000 http://bradyvolpe.com/?p=316#comment-213 Thanks for the great tutorials and the time you spend providing us with information regarding such a extensive subject as DOCSIS. But do you know of any good sources of information regarding microreflections and reading graphs of microreflections (technical repors, tutorials etc.)? Regards, Truls Thanks for the great tutorials and the time you spend providing us with information regarding such a extensive subject as DOCSIS. But do you know of any good sources of information regarding microreflections and reading graphs of microreflections (technical repors, tutorials etc.)?

Regards,
Truls

]]> By: Brady http://volpefirm.com/docsis/docsis30-tutorial-introduction/#comment-212 Brady Wed, 05 Jan 2011 12:15:18 +0000 http://bradyvolpe.com/?p=316#comment-212 Hi Maurizio, Currently the DOCSIS specification states that a minimum of four (4) upstream channels can be bonded. So the implication is that more than four can be bonded. I don't know of any system that is currently doing more than four, in fact few are actually truly doing four upstream bonded channels - its just getting traction now. -Brady Hi Maurizio,

Currently the DOCSIS specification states that a minimum of four (4) upstream channels can be bonded. So the implication is that more than four can be bonded. I don’t know of any system that is currently doing more than four, in fact few are actually truly doing four upstream bonded channels – its just getting traction now.

-Brady

]]> By: Maurizio http://volpefirm.com/docsis/docsis30-tutorial-introduction/#comment-211 Maurizio Fri, 10 Dec 2010 09:20:40 +0000 http://bradyvolpe.com/?p=316#comment-211 Brady as far as you know has CableLabs standardized more than 4 channels bonding in upstream? I mean, is there a new spec for Upstream channel Bonding? I agree with you downstream BW is never enough, and yes, laser clipping may be an issues. In general are more than 4 channels bonded in upsteream necessary? BR Maurizio Brady
as far as you know has CableLabs standardized more than 4 channels bonding in upstream? I mean, is there a new spec for Upstream channel Bonding? I agree with you downstream BW is never enough, and yes, laser clipping may be an issues. In general are more than 4 channels bonded in upsteream necessary?
BR
Maurizio

]]> By: Brady http://volpefirm.com/docsis/docsis30-tutorial-introduction/#comment-210 Brady Wed, 08 Dec 2010 13:06:05 +0000 http://bradyvolpe.com/?p=316#comment-210 Maurizio, You are correct, the new chipsets from Broadcom are supporting more advanced channel bonding. This is fantastic news for DOCSIS. There are no right or wrong answers for using more than 4x4 bonding. If your downstream has the bandwidth to support 12 bonded channels and your equipment (CMTS and Cable Modem) can support 12 bonded channels, then go for it. It allows faster data speeds and more simultaneous channel watching, tuning & recording at the set-top box. The same applies for the upstream. Just remember, in the upstream the more loading (RF Power), the greater chances you will run into laser clipping. -Brady Maurizio,

You are correct, the new chipsets from Broadcom are supporting more advanced channel bonding. This is fantastic news for DOCSIS. There are no right or wrong answers for using more than 4×4 bonding. If your downstream has the bandwidth to support 12 bonded channels and your equipment (CMTS and Cable Modem) can support 12 bonded channels, then go for it. It allows faster data speeds and more simultaneous channel watching, tuning & recording at the set-top box. The same applies for the upstream. Just remember, in the upstream the more loading (RF Power), the greater chances you will run into laser clipping.

-Brady

]]> By: Maurizio http://volpefirm.com/docsis/docsis30-tutorial-introduction/#comment-209 Maurizio Wed, 01 Dec 2010 16:26:47 +0000 http://bradyvolpe.com/?p=316#comment-209 Brady In your Docsis primer is clearly reported that the upstream channel bonding for Docsis 3.0 is 4 channels. Downstream it was max 8, but recently I have seen that it is possible to increase the downstream Docsis 3.0 band bonding up to 16 channels. The downstream band is wide enough to make this possible. I have recently seen vendors offering up to 16 channels bonding in upstream. How is this possible, as long as there is not enough spectrum to allocate 16x6MHz in upstream? Does it make sense to use smaller channels? BR Maurizio Brady
In your Docsis primer is clearly reported that the upstream channel bonding for Docsis 3.0 is 4 channels. Downstream it was max 8, but recently I have seen that it is possible to increase the downstream Docsis 3.0 band bonding up to 16 channels. The downstream band is wide enough to make this possible.
I have recently seen vendors offering up to 16 channels bonding in upstream. How is this possible, as long as there is not enough spectrum to allocate 16x6MHz in upstream? Does it make sense to use smaller channels?

BR
Maurizio

]]> By: Maurizio http://volpefirm.com/docsis/docsis30-tutorial-introduction/#comment-208 Maurizio Fri, 26 Nov 2010 13:31:46 +0000 http://bradyvolpe.com/?p=316#comment-208 Hello Brady, thanks for confirming my suspects. Just for everybody to know at the end it was the MSO that didn't commission the mac addresses range of the meters we were using. I have another question for you. Cable Labs have standardized a spectrum measurement at the CMTS. Essentially via SNMP a meter can ask the CMTS to provide RF measurements of the upstream band. As far as you know has this feature been implemented by most CMTS manufacturer or only few can do it? Regards Maurizio Hello Brady, thanks for confirming my suspects. Just for everybody to know at the end it was the MSO that didn’t commission the mac addresses range of the meters we were using. I have another question for you. Cable Labs have standardized a spectrum measurement at the CMTS. Essentially via SNMP a meter can ask the CMTS to provide RF measurements of the upstream band. As far as you know has this feature been implemented by most CMTS manufacturer or only few can do it?

Regards
Maurizio

]]> By: Brady http://volpefirm.com/docsis/docsis30-tutorial-introduction/#comment-207 Brady Fri, 08 Oct 2010 19:26:01 +0000 http://bradyvolpe.com/?p=316#comment-207 Maurizio, When you have: NetworkAccess 0; MaxCPE 0; set in the config file, two things are going to happen. 1) No devices attached to the cable modem (CPEs or Customer Premise Equipment) will be able to get an IP address, because MaxCPE = 0. You should define this at least as 1 or more. 2) You will receive not be able to get TCP/IP network access from the CPEs be Network Access is disabled since Network Access = 0, or "False". This should be a "1" for "True" in order to get access to the IP network. This is why you are getting the “FORWARDING_DISABLED” error message. Regards, -Brady Maurizio,

When you have:
NetworkAccess 0;
MaxCPE 0;
set in the config file, two things are going to happen. 1) No devices attached to the cable modem (CPEs or Customer Premise Equipment) will be able to get an IP address, because MaxCPE = 0. You should define this at least as 1 or more. 2) You will receive not be able to get TCP/IP network access from the CPEs be Network Access is disabled since Network Access = 0, or “False”. This should be a “1″ for “True” in order to get access to the IP network. This is why you are getting the “FORWARDING_DISABLED” error message.

Regards,
-Brady

]]>