Here you can find assorted information regarding DOCSIS cable modems and their ISP specific settings and values (mainly for Europe).
General DOCSIS information
Downstream (RX) power levels
- Specification: -15 dBmV to 15 dBmV
- Recommended: -6 dBmV to 12 dBmV
SNR (signal to noise ratio) levels
- QPSK: 12 dB minimum. 15 dB or higher recommended
- 16 QAM: 18 dB minimum. 21 dB or higher recommended
- 64 QAM: 24 dB minimum. 27 dB or higher recommended
- 256 QAM: 30 dB minimum. 33 dB or higher recommended
Usually maxes out at 40 dB.
Upstream (TX) power levels
- Specification: 8 dBmV to 54 dBmV
- Recommended: 35 dBmV to 52 dBmV
Usually located in your basement. Amplifies the signal by given amount. Can be fine-tuned.
There are two types of cable installations:
- Line: All amps are independent of each other houses amps.
- Cascade: All amps are dependent of the one before in the casade termination. Usually these are not safe to touch. You are risking to get sued by your ISP and your neighbours. You have been warned.
- You don’t know what type of connection mode you have
- You don’t exactly know what you are doing, i.e. know what the terms ‘slope’, ‘pad’, ’equalizer’, ‘interstage’ and the likes are without looking them up
You may damage your and/or your neighbors hardware!
If you are having issues with packet and/or signal loss but checked your hardware for issues and couldn’t find any, then most probably the problem is not your hard- and software. Unitymedia/Vodafone has notoriously bad line quality. Their customer nodes are totally overbooked for several years now and are dropping packets heavily, especially in the evening peak times. With the acquisition of Unitymedia by Vodafone things got severely worse. The telephone support is not able to help you a bit. The online support ignores you. The only thing that (temporarily) helps is complaining publicly via social media. To sum that up: Vodafone doesn’t give a crap about you!
So the general recommendation is: TERMINATE YOUR CONTRACT NOW and switch to an ISP with better line quality. A 100MBit (or even 250MBit) stable connection (e.g. Telekom DE, at least currently) is faster than a proclaimed gigabit connection provisioned as 500-700MBit with a packet loss of >70%.
- Downstream power level: -4 dBmV to 9 dBmV (-6 dBmV to 13 dBmV tolerable)
- Downstream SNR: 34 dB or higher
- Upstream power level: 40.5 dBmV to 49 dBmV
Old but gold.
Unitymedia doesn’t hand out these devices anymore. If you have one: HOLD ONTO IT! Don’t let anyone tell you that you need a new device. Unitymedia is lying. It is perfectly fine for speeds up to 400 Mbit and is one of the most stable and all around best modems out there. Furthermore you have a little bit of control over it and is not a black box.
Its single drawback is its limited channel count and thus requires a stable signal in crowded areas.
If your power brick dies, you can urge Unitymedia to get you a new power brick for it. They usually have a few spare ones lying around in their warehouses. Again, stay persistent and you’ll eventually get a spare one for free.
- Type: Modem only
- DOCSIS: 3.0
- Downstram channels: 8
- Upstream channels: 4
- Maximum downstream speed: 440 Mbit (360 - 380 Mbit effectively)
- Maximum upstream speed: 120 Mbit (100 Mbit w/o overhead)
- Management interface (consumer side): 192.168.100.1 (http)
- Management login: User: admin, password: atlanta
Seriously, they are dumpster fires. Stay away at all costs! You should contact Unitymedia and demand a new device. These ones tend to deliver abysmal performance and have questionable firmware security.
“Unitymedia ConnectBox” (Compal CH7465LG)
These devices are notoriously out of your hands. You can almost control nothing relevant and Unitymedia will configure random things remotely without your consent (e.g. enable guest wifi). Randomly locks up and needs a reboot (a reboot often takes more than 4 minutes).