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best way to go adding capacity.. and other issues

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best way to go adding capacity.. and other issues

I currently have a ubr7246vxr with 4x MC28U line cards. I'm currently running two sets of 4 downstreams, one to each laser. I'm getting a second cmts as we have outgrown this one alone. we are running up to 95-98% utilization on downstream ports and seeing some issues from that. I'm seeing a lot of t3 timeouts and modem reboots during peak traffic with no other explanation. returns are clean, SNR > 30db on all ports. I'm running 16 qam 3.2 mhz wide on upstreams currently, I've tried dropping a node back to qpsk to make sure there isnt some underlying rf issue in the return that i'm not catching...same result. 6 nodes, 4 return channels per node currently. Load balancing on downstreams currently.. I have one channel in each node in each mac domain so the downstreams can balance. wired like this:

3/0,3/1,4/0,4/1 DS combined to one laser, node 1 returns are 3/0 u0, 3/1u0, 4/0 u0, 4/1 u0. All are on proper channels, working fine until we get busy in the evenings. No upstream combining, one node per set of ports on CMTS. I'm prepping now to go to 4 lasers, I'm preparing for the change in light level with the change in light levels at the nodes and adjusting for that.

A little background:

small cable system - around 1300 video subs, 500 data subs, passes 2200 serviceable addresses, 6 nodes, working on expanding that to 8 nodes, splitting the two busiest areas as far as data traffic.

Working on a shoestring budget through all the outside plant repairs, we've had the system since november, this is my first cable system, learning something new every day.

Every modem reset I've been able to trace back to a spike in the traffic on a downstream port.

Is there a way to manage the utilization of the downstream ports, even if that meant slowing down the heaviest users at peak time? Guarantee timeslots to maintenance/ranging responses?

Thanks for any help anyone can offer.

switching to a 10k is

switching to a 10k is probably your best bet you can get a 10k and a 20x20 card on the used market for about $10k ish that gives you a lot more flexibility

or if you want to stay on the 7246 platform acouple of mc88v cards and a G2 but that will likely be more than the 10k and only get 16 downstreams ...

keep in mind the 10k uses 220v or dc only so if your AC you will need new circuits and UPSes

I'm planning to go to a 10k

I'm planning to go to a 10k next year sometime when we go docsis 3.0.... for now I'm constrained by budget to grabbing another 7246.. 220v is not a problem, headend is on a large dual conversion UPS already. And you're right on the mc88v and npe-g2.. mc88v seem to be going for around $10k each, not counting the npe-g2 and the fan module that needs to be replaced. Only reason I'm ok with going the 2nd CMTS route is its cheap and I have the ipv4 address space to allocate a block to the 2nd cmts without worrying...I have a /21 that I'll probably never utilize all of.

The next best option then if

The next best option then if your going to add a second 7246 is smaller nodes/trunks so you can manage the traffic by recombining.

Also note adding a second cmts will cause all of the customers who move to it to have new IPs, and customers who are on your old cmts may get new ips too depending on your subneting, not much of a problem if you are all dhcp but if you have static customers their statics won't move to the other cmts unless they have their own subnet i.e. /29 or /30 or /31 something to think about.

even if you switched to a 10k now with older style blades you would be better off, less than $5k but less ip management hassle.

as someone who once had 4 7246vxr chassis in one headend I would highly reccommend not going to multiple cmtses it is a crap ton of headache

Subscriber Traffic Management

> Is there a way to manage the utilization of the downstream ports, even if that meant slowing down
> the heaviest users at peak time?

You could have a look at the Subscriber Traffic Management feature :

I would think about looking

I would think about looking at a DOCSIS 2.0 10K setup, with upgrade path to D3. You can get a basic UBR10K D2 system (with 10DS and 40US) for only slightly more than it would cost for the additional 7246VXR. Then, in a year from now, when you want to upgrade to DOCSIS 3.0, you simply have to add the 20X20 cards to the existing 10K system. If you get the 7246VXR now as a stopgap, that cost will essentially be sunk when you want to upgrade to a 10K. Also, in a year from now, the cost of the 20X20 cards for DOCSIS 3.0 will likely have come down, saving you money in both short term and long term.

Mike Baker
RocNet Supply

Adding Capacity

Try DS load balancing in MC285Us or you can try C-DOCSIS.
Huawei,Sumavision and Cisco have products.For Cisco solution you require uBR 10k.

re:best way to go adding capacity.. Try C-Docsis

You can think of DS load balance in MC28U or across MC28Us if your plant topology permits

Or C-Cmts

This is zen thing.In my previous employment we have used few hundred boxes. Mainly Huawei and Sumavision.Cisco is having similar thing but different approach,you still need uBr10k in it.

we are currently doing

we are currently doing balancing on the downstream. We are at a point where we are equally utilizing all 8 ports. Additional CMTS going in this week, already have everything worked out to get us by until we make the move to DOCSIS 3.0 next year.

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