[VFKD] RWS in 83416 Bahnhofstr. | 4QAM Upstream

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Flole
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Re: [VFKD] RWS in 83416 Bahnhofstr. | 4QAM Upstream

Beitrag von Flole »

There's a difference between logical upstream channels and switching the modulation on a per-modem-basis though. And logical upstream channels don't mean, that you can just send whatever you want and the CMTS will interpret and demodulate it correctly. You still need to follow the CMTSs instructions on how to modulate, when to send and so on.
denunge
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Re: [VFKD] RWS in 83416 Bahnhofstr. | 4QAM Upstream

Beitrag von denunge »

Yes, the modem must follow the rules, but the logical channels mean that it is possible for modem 1 to use 64-QAM while modem 2 only uses 16-QAM. The CMTS knows what profile each modem uses to transmit with.
Flole
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Re: [VFKD] RWS in 83416 Bahnhofstr. | 4QAM Upstream

Beitrag von Flole »

Yes and no, you need to setup logical channels for that case then, and the CMTS needs to support all that. It's kinda like with the "perfect OFDMA profile" that should (according to the specification and the design philosophy) provide the optimum channel for each modem, but in reality that's just not working that way (yet). Casa is kinda limited when it comes to logical channels anyways, plus the operator needs to set it up, which Vodafone hasn't done, so all Modems will switch modulation, as I said.
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RcRaCk2k
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Re: [VFKD] RWS in 83416 Bahnhofstr. | 4QAM Upstream

Beitrag von RcRaCk2k »

On the cisco cli there are options to handle voip-traffic (directly generated on FXS ports on the modem) to use 16QAM on Upstream Channel and use up to 64QAM for data.

I think that the demodulation for upstream is done in software. or it is done in hardware.

I believe in dynamic upstream modulation for each modem for its own.

The CMTS have to measure the MER, is the MER to high, tell the modem it should send data at lower QAM to get better signal.

As you said, a normal TV set to QAM256 on a QAM64 channel will see "no signal". But the CMTS and the Modem knows what is going on on the upstream-channel, so the modem can modulate the correct signal on given time and the cmts can demodulate.

If you are right, all the modems on the same C-Line should do the same wired things (hopping from 64QAM to QPSK and 16QAM) synchronously.
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Re: [VFKD] RWS in 83416 Bahnhofstr. | 4QAM Upstream

Beitrag von Flole »

RcRaCk2k hat geschrieben: 17.09.2023, 23:03 On the cisco cli there are options to handle voip-traffic (directly generated on FXS ports on the modem) to use 16QAM on Upstream Channel and use up to 64QAM for data.
Yes, that's a logical channel.
RcRaCk2k hat geschrieben: 17.09.2023, 23:03 I think that the demodulation for upstream is done in software. or it is done in hardware.
It is done in hardware. Or kinda both in a Casa CMTS with it's FPGA.
RcRaCk2k hat geschrieben: 17.09.2023, 23:03 I believe in dynamic upstream modulation for each modem for its own.
That's not how it's done on SC-QAM channels though. It's not even specified, the closest you can get are logical channels, but they work in a different way.
RcRaCk2k hat geschrieben: 17.09.2023, 23:03 The CMTS have to measure the MER, is the MER to high, tell the modem it should send data at lower QAM to get better signal.
Doesn't work that way on SC-QAM channels. The UCD is sent as a broadcast.
RcRaCk2k hat geschrieben: 17.09.2023, 23:03 As you said, a normal TV set to QAM256 on a QAM64 channel will see "no signal". But the CMTS and the Modem knows what is going on on the upstream-channel, so the modem can modulate the correct signal on given time and the cmts can demodulate.
The CMTS doesn't do that though. There's no point in saying "it could", it's simply not done.
RcRaCk2k hat geschrieben: 17.09.2023, 23:03 If you are right, all the modems on the same C-Line should do the same wired things (hopping from 64QAM to QPSK and 16QAM) synchronously.
Correct, that's what's happening. You can use a DVB-C receiver to look at the UCD if you want, then you will see what's going on.