DOCSIS 3.0 and Multicast

Scott Helms khelms at
Fri Nov 29 14:58:30 UTC 2013

Keep in mind that in the cable world the node itself is a layer 1 device,
basically it converts between fiber and coax signaling, and so it doesn't
take part in any IP transactions.  Now, if your CMTS supports multicast and
the modems on the same node are on the same downstream AND multicast is
enabled on the CMTS then the devices behind the modem (which is a bridge)
can use the same stream.  A device behind the modem could actually be an
embedded device on the modem, but in the DOCSIS world the modem itself
(usually) has its own MAC address and each integrated device will have its
own so a home gateway product (video, MOCA, voice, router, and WIFI) will
often have 5+ MAC addresses, one for each of the devices and often each one
has its own configuration.

This tutorial may help some:

Scott Helms
Vice President of Technology
(678) 507-5000

On Fri, Nov 29, 2013 at 9:32 AM, mr. s <sigasecure at> wrote:

> To Those Who Do DOCSIS3.0,
> I can't seem to find a simple answer to this, possibly because it is self
> evident to those actually using Multicast over DOCSIS. Which we are not
> currently.
> Multicast over DOCSIS 3.0, to 3.0 CM, can the CM share the same media
> stream on their node?
> In example, 2 Cable Modems in the same node (no splitting, same US/DS
> channels/ports, CMTS..), each have a customer watching ESPN.
> Is there one or two media streams worth of content on the plant, channels,
> node?
> We now how this operates in other worlds, GPON, xDSL and AE. Just haven't
> seen it specifically mentioned out right in DOCSIS literature.
> Thanks for any direction you have.

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