232 replies to this topic

[olo131]

I'm opening this topic after starting a conversation with System Tech Sr. If you have any questions about DOCSIS ask it here. If you want to share info please join in.

(DOCSIS) Data Over Cable Service Interface Specification

DOCSIS 1.1
DOCSIS 2.0
DOCSIS 3.0

My company is about to embark into the world of DOCSIS 3.0 and 16 QAM return. So I will be learning as well teaching as we go along. The return is about to get rough.

olo131

"The only dumb question is the one not asked"

Attached Files

•  DOCSIS_3_overview_rh.pdf   1.24MB   118 downloads

[Forbins]

We just had our meters upgraded to 3.0. We split all the busy nodes throughout the year and swapped our phone and data carriers around to get ready for 3.0. So now our internet is barely affected by ingress, but since we put the phone carriers in the low end, we're now getting static on the phone calls due to low end ingress. Which kind of sucks in a way, because since we launched phone like 10 years ago, we've never had any static problems aside from customer's internal wiring issues that only affected them. We started trailing that Arcom CPD hunter about a month ago, hopefully that helps.

[System Tech Senior]

I'm opening this topic after starting a conversation with Sr. System Tech If you have any questions about DOCSIS ask it here. If you want to share info please join in.

(DOCSIS) Data Over Cable Service Interface Specification

DOCSIS 1.1
DOCSIS 2.0
DOCSIS 3.0

My company is about to embark into the world of DOCSIS 3.0 and 16 QAM return. So I will be learning as well teaching as we go along. The return is about to get rough.

olo131

"The only dumb question is the one not asked"

Don't you mean 64 QAM upstream? That's what we're going to.

[System Tech Senior]

We just had our meters upgraded to 3.0. We split all the busy nodes throughout the year and swapped our phone and data carriers around to get ready for 3.0. So now our internet is barely affected by ingress, but since we put the phone carriers in the low end, we're now getting static on the phone calls due to low end ingress. Which kind of sucks in a way, because since we launched phone like 10 years ago, we've never had any static problems aside from customer's internal wiring issues that only affected them. We started trailing that Arcom CPD hunter about a month ago, hopefully that helps.

That's my problem with doing DOCSIS 3.0. I cannot understand why a company would put either the phones or modems down around 21 mhz... There is waaaay too much house garbage for a DOCSIS device to push through at that level. Return on set top boxes are around 11 mhz and they work fine, but they can plow through heavy trash. My company is putting both devices in the same 64 qam upstream haystack... They will put non 3.0 complient modems @ 21 mhz. you always have the customer who has their own modem, or has one of ours, but they don't want to switch it out. No matter how much you explain better service, they insist on keeping the one they have. So we reserved the 21-25 mhz range for non 3.0 complient docsis devices. Seems a lot of companies throw either the modem or phone modem down around 21 mhz and wonder why they have upstream snr issues with that service..

[System Tech Senior]

We just had our meters upgraded to 3.0. We split all the busy nodes throughout the year and swapped our phone and data carriers around to get ready for 3.0. So now our internet is barely affected by ingress, but since we put the phone carriers in the low end, we're now getting static on the phone calls due to low end ingress. Which kind of sucks in a way, because since we launched phone like 10 years ago, we've never had any static problems aside from customer's internal wiring issues that only affected them. We started trailing that Arcom CPD hunter about a month ago, hopefully that helps.

Here is a picture from our headend. You can see the wide 64 qam haystack (blue) and the slim 16 qam upstream in yellow. The phones and modems will be in the blue haystack, while the non docsis 3.0 complinet devices reside in the yellow. The numbers are a little hard to read, but the yellow haystack is about 19-22 mhz.. Blue is about 27-33 mhz, with the modems spiking about 31mhz.

Attached Files

•  qam.jpg   50.59K   129 downloads

[olo131]

My system is now DOCSIS 1.1 and 2.0 at 16 QAM

Scorce:
<a href="http://www.cable360....ech/24882.html" target="_blank">http://www.cable360..../24882.html</a>

DOCSIS 1.0 and 1.1 gave us downstream 64- or 256-QAM (quadrature amplitude modulation) in a 6 MHz bandwidth channel, and upstream quadrature phase shift keying (QPSK) and 16-QAM transmitted in a channel bandwidth up to 3.2 MHz. With DOCSIS 2.0, the ante was raised by adding support for 8-QAM, 32-QAM and 64-QAM capability, plus a wider channel that has been increased from 3.2 MHz to 6.4 MHz. DOCSIS 3.0 includes all of this in addition to the prospect of bonding multiple upstream channels.

Now, DOCSIS 3.0 opens the door for something known as channel bonding. Channel bonding means that data is transmitted to or from modems using multiple individual RF channels instead of just one channel. No, the channels aren't physically bonded into a gigantic digitally modulated signal. Rather, the bonding is logical. As DOCSIS 3.0 cable modems become available, forward path data throughput speeds won't be limited to the current per-channel max of about 38 Mbps. You have the potential to bond four or more channels, so do the math: 4 x 38 = 150+ Mbps throughput.

[olo131]

Remember everytime you change QAM to a larger QAM you loose attenuation by 3db in the return

[System Tech Senior]

Right on point! :)

[Forbins]

Remember everytime you change QAM to a larger QAM you loose attenuation by 3db in the return

I forgot about that. We still have 26 value taps everywhere, which is nuts in my opinion. I used to hate those back in the day when i was a field service tech going into homes. Nothing like running multiple drops to one customer just to desperately try to shave down that TX levels.

Do you guys use those taps where you work?

[System Tech Senior]

Remember everytime you change QAM to a larger QAM you loose attenuation by 3db in the return

I forgot about that. We still have 26 value taps everywhere, which is nuts in my opinion. I used to hate those back in the day when i was a field service tech going into homes. Nothing like running multiple drops to one customer just to desperately try to shave down that TX levels.

Do you guys use those taps where you work?

Lord no! LOL. We go 20 straight out an active. I normally go 20, 20, 17, 14, etc... Sometimes depending on cable spans and house size I can run 20,20,20,17,14, etc.. They sometimes put 23 starting out if it's new build, but we'll go back in and make it a 20.

[olo131]

See now I feel bad... We use 26's a lot and they know it is a problem and 27's in mdu's.

Someone shoot me please.

olo131

Here is a sample you count the 27's and 26's

Attached Files

•  Print.JPG   124.53K   101 downloads

[System Tech Senior]

See now I feel bad... We use 26's a lot and they know it is a problem and 27's in mdu's.

Someone shoot me please.

olo131

Here is a sample you count the 27's and 26's

WOW! 27's??? Never even seen a 27. We used 29's waaaaaay back in the day. Let's see here little math lol.. Let's say an LE in your cascade was running 38db on the return. A 27 value tap 27+18= (18 on the coax for reverse -20db test point) 45!!!! Good god.. That tap would have 45 on the reverse. (our range for modems is 35-50 on reverse. Let's go with a 100 ft RG-6 drop. I'll give it 1 more. 46 at the house box. 2 tv's, 1, mta, 1 modem. We would need a 4 way splitter. 46+7=53. 53 db leaving splitter. May hit the device at 53, probably 54... You need to chunk them thangs!!!

[theotherguy]

yea we are going to a full 64 right now we are at a mix. We are getting ready for faster upload speed's and impulse cable. Have any of you messed with impulse. When you go to 64 your plant has to be tight tight.

[olo131]

yea we are going to a full 64 right now we are at a mix. We are getting ready for faster upload speed's and impulse cable. Have any of you messed with impulse. When you go to 64 your plant has to be tight tight.

You stick around We may need you. Haven't heard Impulse in years we had Impulse PPV boxes no need for return Subs would call in to get PPV movies. Miss the good old days......NOT!!!!

[theotherguy]

yea we are going to a full 64 right now we are at a mix. We are getting ready for faster upload speed's and impulse cable. Have any of you messed with impulse. When you go to 64 your plant has to be tight tight.

You stick around We may need you. Haven't heard Impulse in years we had Impulse PPV boxes no need for return Subs would call in to get PPV movies. Miss the good old days......NOT!!!!

I may be wrong with the name but from what I have been told which is very little, is that when you go to an channel you would always have some type of memory there to rewind maybe 5 to 10 min like a DVR but on all channels. So if you miss the start of a show you would have the chance to rewind to watch it.

[System Tech Senior]

yea we are going to a full 64 right now we are at a mix. We are getting ready for faster upload speed's and impulse cable. Have any of you messed with impulse. When you go to 64 your plant has to be tight tight.

Is impuse the same as ip addressable? IE, when your set top box requests a channel it actually uses return to grab the channel out of the "pool" Once you switch channels it releases that channel back to the pool.. Indeed! noise must be waaaaaaaay down for 64!!

[System Tech Senior]

yea we are going to a full 64 right now we are at a mix. We are getting ready for faster upload speed's and impulse cable. Have any of you messed with impulse. When you go to 64 your plant has to be tight tight.

You stick around We may need you. Haven't heard Impulse in years we had Impulse PPV boxes no need for return Subs would call in to get PPV movies. Miss the good old days......NOT!!!!

He may be talking about ip addressable..

[theotherguy]

yea we are going to a full 64 right now we are at a mix. We are getting ready for faster upload speed's and impulse cable. Have any of you messed with impulse. When you go to 64 your plant has to be tight tight.

You stick around We may need you. Haven't heard Impulse in years we had Impulse PPV boxes no need for return Subs would call in to get PPV movies. Miss the good old days......NOT!!!!

He may be talking about ip addressable..

No that's IPTV did that when I was at Bell over twisted pair & HFC

[Dak]

Remember everytime you change QAM to a larger QAM you loose attenuation by 3db in the return

Attenuation does not change does it? I think that the S/N requirement changes.
S/N must be be 3 dB better for each higher order of modulation.

All versions of DOCSIS specify that 64-level or 256-level QAM (64-QAM or 256-QAM) be used for modulation of downstream data, and QPSK or 16-level QAM (16-QAM) be used for upstream modulation. DOCSIS 2.0 and 3.0 also specify 32-QAM, 64-QAM and 128-QAM also be available for upstream use. So if you are already doing 2.0, your 3.0 should work OK.

With Docsis 3.0, if you use upstream channel bonding, (which is really still under development for the upstream), well your reverse spectrum should be clean enough to eat off of.

It can be done, but only with a lot of work and constant vigilance. If your company does
not have a very good leakage program, along with good preventive maintenance,
then good luck to you.

As far as 29 and 26 taps are concerned, yeah, we don't use em anymore either.
When cable modems first came out (even before docsis) the outputs were only
40 dB. You couldn't get back through with 30, 29, 27, and 26 taps in line, or with
DC-12's or DC-16's in line. Now that cable modem outputs are 55 to 60 dB, we have
added DC-12's back in our design parameters, but still use them sparingly.

Keep your noise low and your upstream CPE levels in the high 40's to real low 50's.

Dak

[cypherstream]

yea we are going to a full 64 right now we are at a mix. We are getting ready for faster upload speed's and impulse cable. Have any of you messed with impulse. When you go to 64 your plant has to be tight tight.

You stick around We may need you. Haven't heard Impulse in years we had Impulse PPV boxes no need for return Subs would call in to get PPV movies. Miss the good old days......NOT!!!!

I may be wrong with the name but from what I have been told which is very little, is that when you go to an channel you would always have some type of memory there to rewind maybe 5 to 10 min like a DVR but on all channels. So if you miss the start of a show you would have the chance to rewind to watch it.

That's called Start Over. Time Warner and Brighthouse are big supporters of it. Mainly software and a rack full of content ingest servers caching stuff to disk. It works like VOD technology, except the content ingest servers are running pretty much live to a seperate storage area network for the feature.

There's also SDV (Switched Digital Video) which Time Warner and Brighthouse are big proponents of. I'm in a Comcast area and we don't believe in SDV. Instead were getting our bandwidth back from removing analog. SDV is a great idea where a set of frequencies are set aside for switched programming (like VOD). With newer edgeQAM's you can share channels for VOD and TV. The Session Resource Manager talks to the carosel server and it all talks to software in the set top to build or tear down a video session. Thing is if someone else in the node is watching that channel and you tune in, you visit that same stream, thanks to the SRM. So unlike VOD it's shared if more than one person is utilizing it. You'll see lesser viewed channels rarely 'switched in' on the plant, thus saving bandwidth. The upstream at the stb must be really clean in order for it's request messages to hit the headend. Comcast doesn't want to go this route since it breaks cablecards in one way TV's and Tivo's, unless there is a 'tuning resolver' (USB device that plugs into the cable line and the tivo).

We still use 26 value taps. The system was rebuilt in 1997-98 and they cut in SA 9" Stretch taps since it was a retro fit rebuild. The tap right out of an LE is always 26. Actually the tap that feeds me is a 26 value 4-way. Drop comes into my home and into an unbalanced 3-way. -3.5 leg goes to a 2-way and feeds a DCX3400 DVR and a TV's QAM tuner. Back at the 3-way the -7 leg goes to the bedroom (DCX700) and the other -7 goes to a Motorola SBV5220 eMTA. The eMTA reports downstream level of 0dB, 36 SNR, upstream is at 48. The return on the set tops are in the high 50's... I know not ideal but they have no issues, and I don't always trust the reading in the Motorola diagnostics, as opposed to an SLM. Plus the return on the STB's are at 8.096 MHz QPSK vs. the eMTA talks back in 16QAM at 24 MHz.

I'd rather the system not use 26 value taps. I think the migration to DOCSIS 3.0 would be helped with migrating those tap plates to 23 value or 20. Can't wait to see what 64QAM levels look like!