An introduction to DOCSIS (in 2 parts)

[Lew]

Interesting article from Ars Technica. It's a bit geeky in places but still an interesting read.

Meet DOCSIS, Part 1: the unsung hero of high-speed cable Internet access (http://arstechnica.com/business/news/2011/05/docsis-the-unsung-hero-of-high-speed-cable-internet-access.ars)

Meet DOCSIS, Part 2: the jump from 2.0 to 3.0 (http://arstechnica.com/business/news/2011/05/meet-docsis-part-2-the-jump-from-20-to-30.ars/)

[craigj2k12]

good info....no doubt ignition will find some errors in the article :D

[PGPGPG]

great artical

[Maggy]

Interesting article from Ars Technica. It's a bit geeky in places but still an interesting read.

Meet DOCSIS, Part 1: the unsung hero of high-speed cable Internet access (http://arstechnica.com/business/news/2011/05/docsis-the-unsung-hero-of-high-speed-cable-internet-access.ars)

A bit geeky!! What an understatement that is..:D

[Pbryanw]

Hi,

Just thought I'd post this article about DOCSIS I found on Ars Technica. It's not all that technical (so even I could understand it) and it may be of interest to those who want to learn a bit more about DOCSIS, and how it works (without going into great detail).

http://arstechnica.com/business/news/2011/05/docsis-the-unsung-hero-of-high-speed-cable-internet-access.ars

It's aimed towards an American audience, but I assume the same system is used here on the Vigin Media Cable Network. (If any details differ, hopefully someone can point them out).

I'll post the link to part 2, when it comes out.

[Chrysalis]

thanks, I wonder if VM have this enabled on docsis2 channels.

And there's a completely new way for multiple modems to share the upstream bandwidth: S-CDMA (Synchronous Code Division Multiple Access). S-CDMA allows multiple cable modems to transmit at the same time, and it’s also more resistant to the noise that is present on channels below 20MHz. Let's look at both the bits-per-symbol and S-CDMA issues in more detail.

[pip08456]

VM use ATDMA

"Advanced Time Division Multiplex Access (ATDMA) and Synchronous Code Division Multiple Access (SCDMA). CableLabs has mandated that, for a cable product to be fully DOCSIS 2.0 compliant, it must support both competing protocols. There have been several discussions about migration to DOCSIS 2.0 and about which protocol (ATDMA or SCDMA) is the best fit for any one particular business model. Based on recent surveys, some providers are still very unsure about the migration to DOCSIS 2.0."

Scource (http://www.cisco.com/en/US/tech/tk86/tk168/technologies_q_and_a_item09186a00802de427.shtml)

[craigj2k12]

already being discussed

http://www.cableforum.co.uk/board/26/33677413-how-cable-internet-works.html

[Chrysalis]

wow only a day apart, I await the merge :)

[Pbryanw]

wow only a day apart, I await the merge :)
Hehe, I swear I looked for a thread on this article before I posted :blush: :)
already being discussed

http://www.cableforum.co.uk/board/26/33677413-how-cable-internet-works.html

Sorry, didn't look in that particular forum before posting :(

[pip08456]

Hehe, I swear I looked for a thread on this article before I posted :blush: :)

Don't worry, it'll gives the mods something to do.

[Chrysalis]

seems SCDMA is not used on VM according to this post.

http://www.cableforum.co.uk/board/35231921-post51.html

continuing that discussion here as this topic is relevant to it.

[pip08456]

seems SCDMA is not used on VM according to this post.

http://www.cableforum.co.uk/board/35231921-post51.html

continuing that discussion here as this topic is relevant to it.

Actually Chrys it was mentioned in post 3 here, but I assumed you didn't want to discuss it.:D

[DABhand]

@Igni if he comes here

I didn't say SCDMA uses 128QAM all the time, I said it can use it. But that is not the only plus, I listed the others in the "telfordmania" thread.

[pip08456]

@Igni if he comes here

I didn't say SCDMA uses 128QAM all the time, I said it can use it. But that is not the only plus, I listed the others in the "telfordmania" thread.

Yeh, keep going on about the plus side and forget about the negative side (as usual).

As Igni posted.

SCDMA is less efficient than ATDMA. 128QAM requires an insane upstream SNR, 64QAM is a challenge for operators to push to let alone another 3dB to cater to 128QAM and after overheads it doesn't actually provide anything more than 64QAM ATDMA.

SCDMA does indeed have a purpose, it is more resilient in the presence of burst noise that ATDMA, however horses for courses. If it were so evidently superior everyone would be doing it. They aren't.

[Chrysalis]

yeah I am neutral again on this now following ignitions input, I will just stick to I wish that they be using QAM64 :)

[pip08456]

When they can, they will.

[Pbryanw]

For those interested, part 2 of this series on Ars Technica is now up:

Meet DOCSIS, Part 2: the jump from 2.0 to 3.0 (http://arstechnica.com/business/news/2011/05/meet-docsis-part-2-the-jump-from-20-to-30.ars/)

[Chrysalis]

interesting that interleaving on cable only adds small latency unlike adsl where it can go crazy high.

[Brian Hertz]

Now if only they would turn interesting stuff like this into a TV series, presented by someone like Neil Morrissey or Kate Humble. :D

[Ignitionnet]

interesting that interleaving on cable only adds small latency unlike adsl where it can go crazy high.

Cable lives in a system that is supposed to be closed, insulated and shielded. ADSL runs on unbalanced and unshielded twisted pair and in some cases requires extreme interleave to mitigate noise spikes.

[Chrysalis]

Cable lives in a system that is supposed to be closed, insulated and shielded. ADSL runs on unbalanced and unshielded twisted pair and in some cases requires extreme interleave to mitigate noise spikes.

heh indeed.