[c-nsp] Ubr Docsis 2.0 Question

[Anton Kapela]

I sense a wrong conclusion here:

> Thank you for the response... I didn't see this being 
> possible but somewhere someone had told me you could run it 
> that way.... only way I could see is 3.2Mhz width with Docsis 
> 2.0 being backwards compatible ... thanks again for the 
> confirmation...

Based on a small exclusion here:

> No, of course not. Your DOCSIS 1.x (TDMA) modems will only 
> support channel-widths up to 3.2 MHz. If you want use the 
> benefits of a 6.4 MHz channel-width you need to use DOCSIS 
> 2.0 modems (ATDMA).

It is correct that a DOCSIS 1.0 or 1.1 modem will not support US channel
widths/modulations over 3.2 MHz @ qam16 (without considering
vendor-proprietary hacks). However, this does *not* have to exclude
DOCSIS 2.0 modems from using 6.4 MHz channels at qam32/64 and sharing
the same downstream. 

You can indeed run multiple upstream profiles on several different
frequencies to support TDMA 1.x modems with old-school US channel widths
and at the same time support the newer-school A-TDMA 2.0 channel widths.

Since Cisco doesn't support the S-CDMA mode, we'll avoid getting into
coexisting with it here. It's probably better (given some of if timing
related issues) that they don't support S-CDMA, imho. It also
complicates matters when configuring MAP-related fetaures on the
downstream, given the symbol rates and FEC codeword differences create
an 'alternate reality' for S-CDMA speakers relative to TDMA speakers.

Back to the original question:

> > My question is in regards to Docsis1.1 modems - if we change the 
> > channel size to 6.4 is there a way to support modems that only work 
> > with 3.2 channel width (therefore Docsis 1.x)??

Yes, the two can coexist and still provide benefits to the A-TDMA
modems. 

The following URL's should prove instructive:

http://tinyurl.com/3x4m74

http://tinyurl.com/34zzk9

Also read about a-tdma profile configs here:

http://tinyurl.com/2vqttj

..and then specific line-card support issues for upstream profiles:

http://tinyurl.com/2sgg37

I would recommend you start with, as the documents suggest, the default
profiles for mixed tdma/atdma.

To see example configs for this, see:

http://tinyurl.com/2tjvnx

I also want to point out several important caveats with Cisco's DOCSIS
2.0 support which may, or may not be important depending on the
type/featureset of the linecards you have (from the following URL):

"Restrictions for DOCSIS 2.0 A-TDMA Services

-Advanced hardware-based spectrum management is not supported for DOCSIS
2.0 mixed-mode and A-TDMA upstreams. Advanced spectrum management
features (such as guided frequency hopping, dynamic upstream modulation,
and proactive CNR-based frequency hopping and channel width changes) can
be configured only on DOCSIS and EuroDOCSIS 1.X upstreams. You cannot
use these features on channels configured for mixed mode or DOCSIS 2.0
A-TDMA mode. Advanced hardware-based spectrum management for A-TDMA
operations is scheduled to be supported in a future release of the Cisco
IOS software.

-DOCSIS 2.0 A-TDMA cable modems will not register on a TDMA upstream if
an A-TDMA or mixed upstream exists in the same MAC domain, unless the
CMTS explicitly switches the cable modem to another upstream using an
Upstream Channel Change (UCC) message. DOCSIS 1.0 and DOCSIS 1.1 cable
modems cannot register on an A-TDMA-only upstream."

Best of luck,

-Tk