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CASA CMTS Spectrum Rule - Modulation

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Endrit
CASA CMTS Spectrum Rule - Modulation

Hi,

I want to create a spectrum rule in which it can change the modulation of the upstream.
I know that i have to configure logical channel 1 in a different profile.
I have the configuration below but it doesn't seem to work. Can someone help me on this ?

#show spectrum rule
cable spectrum hop-period 30
cable spectrum monitor-period 30
cable spectrum cm-mode-monitor-period 45
cable spectrum back-hop-step
no cable spectrum trap
no cable spectrum syslog
no spectrum analysis full-spectrum

spectrum rule 10
action modulation
back-hop-limit 3 2
correctable-fec threshold 15
uncorrectable-fec threshold 2
profile 3 snr-threshold 300

Upstream Configuration :

spectrum-rule 10
frequency 58000000
channel-width 6400000
logical-channel 0 prov-attr-mask 0x0
logical-channel 0 channel-width 6400000
logical-channel 0 profile 3
logical-channel 0 minislot 2
logical-channel 0 data-backoff automatic
logical-channel 0 power-offset 0
logical-channel 0 ranging-priority 0x0
logical-channel 0 class-id 0x0
no logical-channel 0 shutdown
logical-channel 1 prov-attr-mask 0x0
logical-channel 1 channel-width 6400000
logical-channel 1 profile 10
logical-channel 1 minislot 2
logical-channel 1 data-backoff automatic
logical-channel 1 power-offset 0
logical-channel 1 ranging-priority 0x0
logical-channel 1 class-id 0x0
no logical-channel 1 shutdown
no shutdown

kwesibrunee
Casa's spectrum rules don't

Casa's spectrum rules don't work like that. Casa's spectrum rules move misbehaving (poor snr / correctables) modems to logical channel 1, rather than changing the upstream modulation/channel width of all the modems.

So when a modem is experiencing low SNR or too many correctable or uncorrectable errors, the CMTS would move that modem to logical channel 1 versus logical channel 0, which typically would have a narrower channel width and a lower modulation i.e. 16qam versus 64 qam and 1.6 mhz wide versus 6.4 mhz wide. Both logical channels share the same center frequency, and the CMTS uses time division multiplexing to allow both channels with different settings to use the same spectrum.

So now questions: What is profile 10 in your example? Profile 3 is a built in profile with 64qam, ideally you would either use profile 2 16qam or profile 1 qpsk on logical channel 1 so that modems with issues use modulations that are more tolerant of noise.

Does your modem with issues move to the other logical channel?

Have you added logical channel 1 to your service groups and docsis-macs?

Endrit
CASA CMTS Spectrum Rule - Modulation

Hello kwesibrunee,
Thank you for clearing things out for me.

Profile 10 is a profile which uses 16QAM in 6.4Mhz.
But for now i changed it to "logical-channel 1 profile 2"

I didn't add the Upstream under the MAC Domain. I thought logical channel 1 was like self-included.
Service group allows to add the RF Channel so i am guessing it includes both logical channels 0 & 1.
Does the Docsis-MAC interface sees logical channel 1 of an Upstream like any other upstreams in terms of reserving downstream bandwidth due to maps communications?

I will see if modem will switch to the logical channel in case of poor snr or errors.

Much appreciated ,
Endrit

wittmann
Other variants of Casa Spectrum Management desired?

Hi Endrit,

we don't use the logical-channel 1 in our Casa Spectrum Management. So the modulation will change for all CM on the particular upstream channel.

We use all steps from 64-QAM, 32-QAM, 16-QAM, 8-QAM and QPSK.

Are you interested on such config example?

Endrit
CASA CMTS Spectrum Rule - Modulation

Hello wittmann,

That was my inital request.
I did a test with another specteum rule just for the sake of a test in order to change the channel width of the upstream and i succeed but i fail doing same with the modulation.

In this case i am interested on your example.

Regards,
Endrit

wittmann
Here we go

Hello Endrit,

The whole setup is verified on Releases 6.5 and greater but I think I can remember that it was even running on Release 5.x

Disclaimer: Even with the best thoughts in mind I give no guarantee and propose that you check the config in your lab first before you run it in the field.

First we have to configure five different modulation profiles for
QPSK, 8-QAM, 16-QAM, 32-QAM and 64-QAM.


! === config begin ===
!
! Upstream Modulation Profiles
!
! Upstream Modulation Profile QPSK
modulation-profile 11
request atdma qpsk off 64 0 16 338 0 16 fixed on 1 1536 qpsk0
initial atdma qpsk off 640 5 34 338 0 48 fixed on 1 1536 qpsk0
station atdma qpsk off 384 5 34 338 0 48 fixed on 1 1536 qpsk0
a-short atdma qpsk off 104 12 75 338 6 16 shortened on 1 1536 qpsk1
a-long atdma qpsk off 104 16 220 338 0 16 shortened on 1 1536 qpsk1
!
! Upstream Modulation Profile 8-QAM
modulation-profile 12
request atdma qpsk off 64 0 16 338 0 16 fixed on 1 1536 qpsk0
initial atdma qpsk off 640 5 34 338 0 48 fixed on 1 1536 qpsk0
station atdma qpsk off 384 5 34 338 0 48 fixed on 1 1536 qpsk0
a-short atdma 8qam off 104 12 75 338 6 16 shortened on 1 1536 qpsk1
a-long atdma 8qam of
!
! Upstream Modulation Profile 16-QAM
modulation-profile 13
request atdma qpsk off 64 0 16 338 0 16 fixed on 1 1536 qpsk0
initial atdma qpsk off 640 5 34 338 0 48 fixed on 1 1536 qpsk0
station atdma qpsk off 384 5 34 338 0 48 fixed on 1 1536 qpsk0
a-short atdma 16qam off 104 12 75 338 6 16 shortened on 1 1536 qpsk1
a-long atdma 16qam off 104 16 220 338 0 16 shortened on 1 1536 qpsk1
!
! Upstream Modulation Profile 32-QAM
modulation-profile 14
request atdma qpsk off 64 0 16 338 0 16 fixed on 1 1536 qpsk0
initial atdma qpsk off 640 5 34 338 0 48 fixed on 1 1536 qpsk0
station atdma qpsk off 384 5 34 338 0 48 fixed on 1 1536 qpsk0
a-short atdma 32qam off 104 12 75 338 6 16 shortened on 1 1536 qpsk1
a-long atdma 32qam off 104 16 220 338 0 16 shortened on 1 1536 qpsk1
!
! Upstream Modulation Profile 64-QAM
modulation-profile 15
request atdma qpsk off 64 0 16 338 0 16 fixed on 1 1536 qpsk0
initial atdma qpsk off 640 5 34 338 0 48 fixed on 1 1536 qpsk0
station atdma qpsk off 384 5 34 338 0 48 fixed on 1 1536 qpsk0
a-short atdma 64qam off 104 12 75 338 6 16 shortened on 1 1536 qpsk1
a-long atdma 64qam off 104 16 220 338 0 16 shortened on 1 1536 qpsk1
!
! === config end ===

Now configure the spectrum rule for one upstream with the center frequency of 20 MHz.
For each upstream channel in the Service Group and different center frequency you need a new spectrum rule.

! === config begin ===
!
spectrum rule 1
frequency 20000000
action modulation
correctable-fec threshold 3
uncorrectable-fec threshold 1
profile 12 snr-threshold 160 190
profile 13 snr-threshold 190 220
profile 14 snr-threshold 220 250
profile 15 snr-threshold 250 280
!
! === config end ===

So the first snr-threshold value e.g. 160 is the Exit-Value of the profile 12 (8-QAM) and the modulation will drop to the next lower profile 11 (QPSK) from the configuration at the upstream interface (comes later). The second snr-threshold 190 is the Entry-Value for profile 12. This means, if your upstream channel is on QPSK (profile 11) because the SNR drops below of 16 dB in the past but the SNR has increased to > 19 dB the upstream will move to 8-QAM (profile 12). Or in other words: We have a hysteresis if 3 dB.
Also you have to notice that the spectrum rule has no line for profile 11 (QPSK) because it makes no sense. You can't configure a entry or exit threshold because QPSK is the lowest modulation already. The trick is that you have to configure the profile 11 in the upstream interface

cFEC is 3%
uFEC is 1%

Deconfigure cable spectrum back-hop-step if enabled
Default setting is disabled, so it will not displayed in the Running-Config
If it's disabled it will allow a modulation step from QPSK -> 64-QAM if SNR is good.
If it's enabled it will go due all configured profiles step by step even if the SNR is good enough for 64-QAM

! === config begin ===
!
no cable spectrum back-hop-step
!
! === config end ===

Now to the upstream interface configuration (Example with 13/0.0). Please notice that there is only the spectrum management related content:

! === config begin ===
!
interface upstream 13/0.0
spectrum-rule 1
frequency 20000000
logical-channel 0 profile 15 secondary-profile 14,13,12,11
!
! === config end ===

The first profile 15 (64-QAM) is the main modulation and all secondary profiles are in the order of the degradation steered by the spectrum rule. You'll notice that on the line you see the profile 11 (QPSK) which is missing in the spectrum rule. However, on the usptream interface configuration you have to congfigure this profile.

With the command

! === config begin ===
!
show spectrum hop-history upstream 13/0.0
!
! === config end ===

you can check the spectrum management history.

Modulation degradation:

Jump to lower modulation = (SNR < Exit-Value of the current profile) OR (cFEC >= 3%) OR (uFEC >= 1%)
Due the SNR value it's possible that 64-QAM will directly jump to QPSK. The cFEC or uFEC will degarde only to the next lower modulation.

Modulation improvement:

Jump to higher modulation = (SNR > Entry-Value of the highes possible profile in the upstream interface profile config) AND (cFEC < 3%) AND (uFEC < 1%)

Best regards,

Endrit
CASA CMTS Spectrum Rule - Modulation

Hello wittmann,

First of all thank you for dedicating your time not to just give me the example step by step but to explain it as well on how it works.
It really is a big help to me and anyone on this forum who struggle on this topic.

I have a question on your example of using 20Mhz.
Did you use 20Mhz for test purpose , cause the SNR dropped the moment i configured my upstream with 20Mhz.
I saw that my upstream changes the modulation now :

11/1.0/0 Wed Feb 6 21:28:11 2019 M 14 15 Back to Configuration
11/1.0/0 Wed Feb 6 21:28:11 2019 F 0 58000000 Configuration change
11/1.0/0 Wed Feb 6 21:26:24 2019 M 15 14 SNR 310 (250) cFEC 4 (3) uFEC 0 (1)
11/1.0/0 Wed Feb 6 21:23:53 2019 M 14 15 SNR 305 (280)
11/1.0/0 Wed Feb 6 21:22:53 2019 M 15 14 SNR 305 (250) cFEC 4 (3) uFEC 0 (1)
11/1.0/0 Wed Feb 6 21:18:53 2019 M 14 15 SNR 308 (280)
11/1.0/0 Wed Feb 6 21:17:53 2019 M 15 14 SNR 300 (250) cFEC 6 (3) uFEC 0 (1)
11/1.0/0 Wed Feb 6 21:17:22 2019 F 0 20000000 Configuration change

Typically we use 4 different frequencies on my upstreams.
Should i use on my spectrum rules the frequency i configure on the upstream itself or is there some other correlation ?

Also does the spectrum rule perform the same if i use "frequency band" option ?

Regards,
Endrit

wittmann
20 MHz just a example

The 20 MHz are just for this example.
With four upstream channels with different center frequencies you have to use different spectrum rule:

Example brakedown only to related commands:


! === config begin ===
!
spectrum rule 1
frequency 20000000
!
spectrum rule 2
frequency 28000000
!
spectrum rule 3
frequency 36000000
!
spectrum rule 4
frequency 44000000
!
interface upstream 13/0.0
spectrum-rule 1
frequency 20000000
!
interface upstream 13/0.1
spectrum-rule 2
frequency 28000000
!
interface upstream 13/0.2
spectrum-rule 3
frequency 36000000
!
interface upstream 13/0.3
spectrum-rule 4
frequency 44000000
!
! === config end ===

So the frequency of the spectrum rule should match with the frequency in the related upstream interface.

I have no experience with the frequency band option because our space is limited and I want to avoid the a upstream channel is hoping into a area were the return sweep points are located which cause trouble if it's inside moved upstream channel.

So only modulation hoping with fix center frequencies.

Best regards,

Endrit
CASA CMTS Spectrum Rule - Modulation

Thank you wittmann

Regards,
Endrit