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cablegeek01

join:2003-05-13
USA
kudos:1

1 recommendation

Small CMTS installs

Click for full size
4 Cisco 7246 chassis with wavecom upconverters
Click for full size
anoterh 7246 vxr with wavecom HD4000
Click for full size
more cabling
Some smaller CMTS installations

voxframe

join:2010-08-02

1 recommendation

This is how ignorant I am on the cable side of things...

Each coax coming out of the unit handles how many actual client modems?

I am more familiar with the DSL 1:1 sync style more than anything cable. Is it the same in cable world or does each coax carry more than one subscriber signal?

Also what about fiber nodes? How do they and CMTS fit into the scope of things? I'm assuming it's the same as CO based DSLAMs and remote DSLAMS?



cablegeek01

join:2003-05-13
USA
kudos:1

That all depends on who you ask I think right now Cisco is leaning towards 100-200 subscribers per upstream port (the red/orange cables in the pictures).
In the CATV world, it's like a tree where all the branches lead back to the CMTS ports for the return path (or flow from the CMTS in the downstream direction). Each Upstream port will generally have a node or two attached to it (A node feeds a neighborhood)
A fiber node is technically the point where the Coaxial network in the neighborhood is converted to fiber and runs back to the cable company. In the CMTS world, it's a description of the MAC domain that defines what nodes are tied to what up and downstream ports so the CMTS "knows" where modems are located.

(node diagram)
»www.cablefax.com/images/articles···9394.gif

(cable fiber node best practice)
»www.cisco.com/en/US/tech/tk86/tk···fd.shtml

These are small DOCSIS 2.0 installations. Larger installations utilizing the ARRIS C4 platforms and Cisco UBR10012 chassis (with edge QAMs) can include hundreds of upstream ports and serve tens of thousands of customers per chassis.
I have some pictures of installs like that around here somewhere...I'll try and find them

Here's an older document that outlines the combining network and goes over some of the underlying technology (it's a little outdated, but the principles are the same)

»www.cisco.com/en/US/tech/tk86/tk···69.shtml



cablegeek01

join:2003-05-13
USA
kudos:1

I should also add that on a CMTS the upstream and downstream are separate ports. On the orange/black cmts cabling , the DS is black, and on the red/yellow, the DS is yellow.
You configure the UP/Downstream combining in software on the CMTS, as well as with RF splitters and combiners (and diplexers if you want to get specific) to combine multiple HFC nodes onto a single set of cables heading towards the CMTS.


voxframe

join:2010-08-02
reply to cablegeek01

Bang on!

Thanks for the info! This will help me wrap my head around it a little better. I come from the DSL/WISP/Telco side of things so cable is my weak point and it handles a little differently.



jmich
Premium
join:2001-08-28
Toms River, NJ
reply to cablegeek01

Great pics, thanks for sharing.



TomS_
Git-r-done
Premium,MVM
join:2002-07-19
London, UK
kudos:5
reply to cablegeek01

I have to say this is interesting stuff. I only finally bothered to look up what all those ports on the line cards in the Cisco are.

Originally I thought it was something like

Video "headend" -> (1 or 2 ports on right of linecard) -> left ports fan out to multiple nodes somewhere around the neighborhood

But it seems that the left hand ports are to handle upstream data from users, and the right hand ports are to handle downstream data to users?

Interesting scheme...

Each port has its own frequency Im guessing?


voxframe

join:2010-08-02
reply to cablegeek01

I've just always thought it was a hard process converting all that RF to fiber to RF etc. Or it would just be horribly lossy etc.



Killa200
Premium
join:2005-12-02
Southeast TN
Reviews:
·Charter
reply to TomS_

said by TomS_:

I have to say this is interesting stuff. I only finally bothered to look up what all those ports on the line cards in the Cisco are.

Originally I thought it was something like

Video "headend" -> (1 or 2 ports on right of linecard) -> left ports fan out to multiple nodes somewhere around the neighborhood

But it seems that the left hand ports are to handle upstream data from users, and the right hand ports are to handle downstream data to users?

Interesting scheme...

Each port has its own frequency Im guessing?

On the cards in that system each upstream port has a selectable frequency range so you can work around noise, and then the downstream pets come out in a low frequency and run through an up convertor, where you set your downstream frequency


TomS_
Git-r-done
Premium,MVM
join:2002-07-19
London, UK
kudos:5

So the DS frequency output from those linecards is always the same, and you use a box to shift it to a new frequency to slot into your network?



Killa200
Premium
join:2005-12-02
Southeast TN
Reviews:
·Charter
reply to cablegeek01

On those particular cards (look like uBR-MC28X), and some of cisco's other linecards (uBR-MC16 series) yes. The cards output in the IF band, and you use an external up convertor to place the downstream on the frequency desired.

Cisco does however make a card in that form factor for that chassis (uBR-MC28U) that has a built in up convertor that you would specify the frequency to drive at in the CLI.


voxframe

join:2010-08-02
reply to cablegeek01

*Is bubbling with nerd giddyness*

Totally awesome info! For once I'm putting the puzzle pieces together and can see into some of the cable world!

Keep going! LOL



cablegeek01

join:2003-05-13
USA
kudos:1

1 recommendation

Click for full size
basic DOCSIS 1.0/1.1/2.0 combining
Here's a good diagram that shows some basic combining for a system like this.


cablegeek01

join:2003-05-13
USA
kudos:1

1 recommendation

reply to voxframe

If you really want to geek out, here's a presentation that explains at the packet level how the modem and CMTS interact.

»shannon.cm.nctu.edu.tw/netexp/catv03.pdf

/If you couldn't tell already, I have a passion for DOCSIS :-D



cablegeek01

join:2003-05-13
USA
kudos:1
reply to TomS_

As Killa200 said, on those particular cards, yes. And to go a bit further, the CMTS tells the CM(cable modem) what frequency to transmit back on by sending out packets in the downstream called UCDs or upstream channel descriptors. The CMTS then listens for modems on that frequency.



TomS_
Git-r-done
Premium,MVM
join:2002-07-19
London, UK
kudos:5

Cool stuff. Thanks for the info.

Sounds a bit like split system microwave radios. The modem cards in the IDU are tuned to fixed transmit/receive frequencies, but the ODU is an up/down converter, and shifts frequencies to or from the transmission frequency you configure/according to your licence.

Makes me want to get into this stuff.


voxframe

join:2010-08-02
reply to cablegeek01

Lemmme get this straight...

Between Blue and Green clouds is Coax (What we see in the pics)

From the Green cloud to the nodes is fiber...

From the Nodes is back out to Coax to the taps/etc.

What kind of method is both the TV/Data streamed with over the fiber so that it is easily converted to coax?

Maybe this is a limitation of my knowledge, but I'm still imagining 1 channel per freq etc. Is there really X number of transmitters in a node converting everything from the fiber to each individual freq?

This may also be a limitation that I'm thinking back to the analog channel days. Being digital for most everything I may be completely out of whack.


Hahausuck
Premium
join:2003-12-14
kudos:2
reply to cablegeek01

Looks good, but you guys use too many zip ties.....



Killa200
Premium
join:2005-12-02
Southeast TN
Reviews:
·Charter
reply to voxframe

said by voxframe:

Lemmme get this straight...

Between Blue and Green clouds is Coax (What we see in the pics)

From the Green cloud to the nodes is fiber...

From the Nodes is back out to Coax to the taps/etc.

What kind of method is both the TV/Data streamed with over the fiber so that it is easily converted to coax?

Maybe this is a limitation of my knowledge, but I'm still imagining 1 channel per freq etc. Is there really X number of transmitters in a node converting everything from the fiber to each individual freq?

This may also be a limitation that I'm thinking back to the analog channel days. Being digital for most everything I may be completely out of whack.

Only thing your off on in the layout is that out of the green cloud is still coax. It breaks out into fiber at the transmitters / receivers and travels there to the nodes.

The nodes receive signal in one frequency, and transmit in another. Each frequency of light carries the entire cable band for that respective direction of transit. The amount of information on those light channels depends on what the node and transmitters / receivers are capable of handling, but it is all happening over 1 light frequency in each direction. Some nodes can take multiple transmitters and receivers.

cablegeek01 I'd love to pick your brain sometime when your not busy. I have some issues on our plant I'd like to figure out, lol.


cablegeek01

join:2003-05-13
USA
kudos:1
reply to Hahausuck

said by Hahausuck:

Looks good, but you guys use too many zip ties.....

Lol tell me about it. The project manager wouldn't allow wax string for some odd reason.


jeffmoss26

join:2002-07-22
Beachwood, OH

No waxed string? Weird!


JoeHemi

join:2011-05-06
united state
reply to cablegeek01

At first I thought these were pics from inside a Comcast HE. You've got all the SEMs, old style NSGs and 8 pack cabling. Then you said no wax tie allowed lol so I knew it couldn't be that. Looks good though, at least the DC guys used string



tubbynet
reminds me of the danse russe
Premium,MVM
join:2008-01-16
Chandler, AZ
kudos:1
reply to cablegeek01

for what its worth -- your c7609 chassis looks like a c6509 chassis in this drawing.
more appropriate to use a 6509v-e chassis for accuracy's sake.



q.
--
"...if I in my north room dance naked, grotesquely before my mirror waving my shirt round my head and singing softly to myself..."



cablegeek01

join:2003-05-13
USA
kudos:1

Funny you mention that. IIRC we were using 6509s with the SUP720 (in effect making them 7609 routers). I cant remember if they were VE chassis or not though...I'll have to dig into my photo album and see if I can find some pics of it. That diagram is 7-10 years old.



tubbynet
reminds me of the danse russe
Premium,MVM
join:2008-01-16
Chandler, AZ
kudos:1

said by cablegeek01:

Funny you mention that. IIRC we were using 6509s with the SUP720 (in effect making them 7609 routers).

nope.
big difference between a c6509 and a c7609. while you can run a sup720 inside of a c7600 -- there are a lot of stupid caveats that go with it. more people run the 'rsp720' in the c7600 -- which has a lot more features and better performance as a 'router' -- instead of a campus switch with routing features.

both are used extensively in service provider networks, but the two are not the same.

q.
--
"...if I in my north room dance naked, grotesquely before my mirror waving my shirt round my head and singing softly to myself..."


DarkLogix
Texan and Proud
Premium
join:2008-10-23
Baytown, TX
kudos:3
reply to cablegeek01

Cool
can you go into the bonding on D3?
is it still upconverted later or does D3 require the combo cards that can self upconvert? if its up/down converted later do the channels that will be bonded have to be programed in as to port 1, 3, ect or does it use them as a port group or something?



cablegeek01

join:2003-05-13
USA
kudos:1

I haven't done any D3 installs on the Cisco UBR7246 chassis, but from what I understand, the only card that supports D3 is the MC88V. It has built in upconversion, and outputs 4 QAMs per DS port.
Any of D3 CMTSs that I've worked with (Cisco 10K, Arris C4, CASA) all had "Upconverted" RF outputs where you selected the Downstream frequencies and QAM(64/256) on the box (or on the EQAM in the case of the cisco 10K when using linecards like the 3g60 and manual depi sessions).



Killa200
Premium
join:2005-12-02
Southeast TN
Reviews:
·Charter

said by cablegeek01:

I haven't done any D3 installs on the Cisco UBR7246 chassis, but from what I understand, the only card that supports D3 is the MC88V.

And it has a mighty pretty price attached to it too, lol. Cheapest i have seen is 25k a card. At 100k for 4 cards, and then reserve cards to boot, that is what is keeping us from upgrading to d3.


tubbynet
reminds me of the danse russe
Premium,MVM
join:2008-01-16
Chandler, AZ
kudos:1

$25k/card is not a bad price -- all things considered.
most of the d/c work that i do requires n7k-m132 cards -- list of about $45k/card. and you have to buy two chassis if you want all of the neat features.

i'm sure that if you get in touch with your friendly cisco se -- they can work something out with you.

q.
--
"...if I in my north room dance naked, grotesquely before my mirror waving my shirt round my head and singing softly to myself..."



Killa200
Premium
join:2005-12-02
Southeast TN
Reviews:
·Charter

said by tubbynet:

$25k/card is not a bad price -- all things considered.
most of the d/c work that i do requires n7k-m132 cards -- list of about $45k/card. and you have to buy two chassis if you want all of the neat features.

i'm sure that if you get in touch with your friendly cisco se -- they can work something out with you.

q.

As small of a system as we are, at 25k a card it would far surpass a return doing the retro... but i could always dream