You are here

Operating multiple CMTS on same coax

5 posts / 0 new
Last post
Operating multiple CMTS on same coax

I apologize beforehand for the naive question but I am unfamilar with the details of how DOCSIS works.

I am interested to find out if it would be theoretically possible to have 2 different operators share the same outside plant by operating separate CMTS on it. Could they operate their networks independently by deciding on the allocation of some fixed amount of spectrum on the upstream and downstream to each?


Multi cmts's on same plant.

About a decade ago we used to run 2 cmts's on our systems, one for data and one for voip. Our voice provider was nervous about having public internet close to the phone equipment, so that was our solution. Once we were able to convince them that security wasn't an issue, we got rid of the 2 cmts thing.
However, we used the same dhcp server, and by using downstream frequencies in the modem config files, it was possible to steer devices to the proper cmts. In your case, that would take serious cooperation between providers, but it could be done.
Thank goodness those days are over!
Lack of upstream spectrum was a big problem, as we were at the time limited from about 20mhz to 34mhz. Even at 64qam

Yes, it can be done, and is

Yes, it can be done, and is being done.

Eg in Australia you have Telstra (internet) and NBN (internet) and Foxtel (paytv) sharing one HFC.

Each company gets allocated their own channels. Telstra and NBN have their own CMTSes.

There are different methods available to steer modems to the correct CMTS (eg settings in the CM config files, or modified modem firmwares)

Sharing downstream probably isn't too bad, but I reckon NBN is going to have some problems in the upstream.

NBN sell packages with high upload speeds like 100/40, and penetration rate is expected to be almost 100%

So even after doing 4 way node split, it wont take much for the US capacity of this shared network to be exhausted.

Eventually all the Telstra customers are to be migrated to NBN, and then NBN will take over Telstra's spectrum. But during the co-habitation period I think they might have some pain.

Thanks a lot for your answers

Thanks a lot for your answers and the concrete examples.

One more question: with DOCSIS 3.1, OFDM modulation is introduced. Based on what I understand of it (, channels are no longer separated by a guard band and the same demodulator also demodulates the other carriers. In those circumstances how could separate CTMS manage adjacent channels?


The thought of this is a nightmare. Especially as we are reducing the number of customers per node. Better off having either a single provider or one provider managing the cmts while the others just manage modem macs and pay allocation based on number of users or a per month fee. No clean way to separate the bandwidth without complex VRF's and for what?