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Downstream Bonding Groups question

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Downstream Bonding Groups question

Hello all,

I'm having issues with a couple of different CMTS's. The first one we started with is a Pico mini-CMTS. We got it up and working great in our lab using it for distributing IPTV, internet and MTA. As soon as we moved it to a production site we started to have issues with multicast traffic. Very bad pixelation and freezing which sees likely to be dropped packets. We noticed that any time our channel utilization was near 100 percent on any one or more downstream rf channel most video channels would pretty much become unwatchable. It seems that the downstreams causing issues are not overflowing properly onto un-utilized channels. We would have one maybe two channels peaked out at 97-98% and many others would sit around 3% pretty much not being used at all. All CMs at this site are 8 channel downstream Arris's or Zoom's. We have tried only arris's and only zoom's on the cable plant. Both behave the same way. They are all locked on the same 8 downstream channels (the only ones on the plant) and have great signal levels down and up. I have contacted pico and they have been literally no help for months. They eventually send us a docsis configuration file every couple of weeks to load and it never works/fixes our issue. We email them daily reports of what we are seeing and then get maybe one email a week back. We have pretty much done everything possible in the web/cli and none of it addresses this issue. It does seem pretty locked down as far as the software goes. I initially suspected load balancing problems, but after doing some research I'm not sure load balancing is what we need here. It seems that our systems are not using these 8 downstream channels as a Downstream Bonded Group or channel and thus when they exceed one D/S's bandwidth we are losing packets. We need it to overflow onto the other D/S channels or even equally distribute the load as the channels are filling up. Is this something that needs to be set in the CMTS or is it possible we can set this up through our provisioning server(tlv or mib)? I would like to set these 8 D/S's to either two 4 channel groups or one 8 channel group. We have an Incognito Broadband Command Center that we use for modem provisioning.

The other CMTS we have is a Versa 7900I. It exhibits the same symptoms when installed, but seems much less locked down and is more accepting of Cisco type CMTS commands.

Thanks in advance.

Sounds like the DS bonding

Sounds like the DS bonding groups are not working. If they were, the traffic would automatically be shared across all the DS.

Not sure how to troubleshoot your CMTS though. I am only familiar with Cisco, sorry.

Thanks for the response. That's what I was thinking as well...

However, if you were to begin troubleshooting in a Cisco environment do you believe this issue lies totally on the CMTS? Is it possible we are missing something in the modem configuration files(tlv or mibs)? All equipment (CM's and CMTS) are Docsis 3.0 capable... Channel bonding is one of the fundamental features of Docsis 3 correct? Is this something that just works when the CMTS is functioning properly or does something need to be done with CM provisioning as well?

I really want to let these vendors have it about this issue, but want to make sure it isn't something that I have missed on the modem configs beforehand.


try posting your cm config

try posting your cm config and then we can answer that question. But usually all the config for downstream bonding is on the CMTS, what controls whether bonding can occur is the cmts. What does your modems status page show? does it show it locked to all (how ever many channels your doing) or does it show it locked to only one channel?

Docsis config

Here's the CM config file. Let me know what you think.

We have about 75 modems online right now. All 75 are connected on the same 8 D/S channels. Our CMTS has 16D/S capability, but the CM's only have 8 D/S. We initially had 16 downstreams enabled and the CM's were all locked on mostly 1-8 or 9-16. We decided to disable 9-16 in an attempt to get the CM's all on 1-8 hoping that they would bond correctly. We are running mpeg-4 multicast streams in this setup. The streams average 5mbps or so, and we are able to see they have about 10-15 multicast streams active at a given time. The 8 D/S's are 256qam so there should be PLENTY of bandwidth for these streams, it seems that the CMTS is just not distributing them properly and overloading one or two D/S's instead of moving them to un-utilized channels.

I don't see anything game

I don't see anything game changing, in the config at first glance.

But if the modems are using bonded channels it should see them all as 1 large channel i.e. the cmts should distribute the packets evenly across all downstreams, it won't move them to another channel there is only one channel the wideband channel.

I think one of a few things are happening:
1) least likely -- the cmts is not using a wideband interface properly and is not distributing packets across all downstreams

2) more likely -- the cmts is sending traffic across the wideband interface and the individual downstreams and your looking only at the individual downstreams (which has narrowband and ranging traffic only) you have to look at the individual downstreams and the wideband interface to get a view of what bandwidth its using. i.e.

so your mac domain could be saturated but if your only looking at the individual bandwidth per DS you will never see it.

On a CMTS there are two separate interfaces to look at bandwidth usage to get an overall picture of how much bandwidth is being used.

you have to add the interfaces together to see actual usage. You have to get the individual channels and the wideband channel(s) and add all their bandwidth together and that will show you your actual usage.

3) Most likely-- there are different rules for Multicast traffic on Downstream interfaces, cisco CMTSes have a crap ton of config to make it work right i.e.

perhaps your manufacturer has similar settings or needs to add the similar settings. There also may be some docs on CableLabs about Multicast traffic on Downstreams be sure to check there.

Any suggestions?

I had to link the cfg on drive, but it should be shared openly to anyone with that link. Let me know if you have problems with the download.

Any suggestions on improving the config? Incognito helped us setup the initial config so I would think it's ok. But If there is anything that directly relates to multicast, igmp, or channel bonding specifically then they were unaware when helping us. This cfg is for an Arris TG862 if that helps.

Thanks in advance.

my response was queued for admn approval because it was so long

But yes it likely has to do with Multicast, and is likely on the CMTS rather than the config/ or a combo of both. I am most familiar with Cisco CMTSes and they have a lot of settings for multicast traffic

perhaps some of them will help you with your cmts.

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