Symmetric VDSL

Good night/day everyone.

First of all, things may be confusing here, since Wikipedia does not have much information about symmetric DSL, and vendor information regarding certain products (such as regarding the Planet VC-231G) seems to conflict with it.

I was wondering whether OpenWrt supports symmetrical VDSL connections (which is supported by the aforementioned VC-231G, as well as some other business-grade devices), as well as what is the theoretical limit of symmetric VDSL (the aforementioned VC-231G is claimed to support up to 150/150, however it also claims to support up to profile 30a (which is up to 230/100) but slightly manages to surpass it in asymmetrical VDSL2 with G.INP in upload speeds, at 197/101 at 200 meters according to Planet's testing, and one of our community members found out that it has a a VRX518 SoC with support for up to profile 35b).

Also, what is preventing CO mode with VDSL2? After all, there are reports of contributors managing to get it working with certain models (such as the aforementioned VC-231G). If we could get it working, it could allow situations where fiber is provided up to the premise, but not up to the house, and something like the VC-231GF to reuse existing wiring as a temporary measure, or for a similar purpose as WISPs, just for situations where proper Ethernet cannot be used, only 2-wire CAT3 cabling.

There isn't really anything special about a VDSL2 connection with symmetric data rates. The allocation of the spectrum between upstream and downstream is just a matter of choosing the right band plan, and there are some symmetric ones (although it looks like the VC-231G uses a non-standard band plan).

That doesn't mean that every DSL modem (in CPE mode) can necessarily achieve the maximum data rate which is theoretically possible. For example for profile 30a, the specification (ITU-T G.993.2) only requires devices to support at least 200 Mbit/s for downstream and upstream combined. The data rate may also be limited by the available memory for interleaving/retransmission buffers.

The Planet VC-231G actually contains a modem from Metanoia, and it doesn't support profile 35b.

What has been mentioned in the VRX518 thread is the possibility to establish a connection to a VC-231G that is running in CO mode. However, that only works properly if G.INP is disabled (there appears to be a compatibility issue specific to the VC-231G in combination with Lantiq modems, because it works with others). The upstream data rate also seems to be limited to a maximum of 105 Mbit/s.

For the DSL modems currently supported by OpenWrt, the drivers just don't include CO support. And the DSL firmware probably also only supports CPE mode.

Realistically, the only option for CO mode is to get a device that already supports it. There are also devices using (e.g. ALL-BM310), which should allow much higher data rates than VDSL2 (although that means that OpenWrt is no longer an option even for the CPE device).

Thanks for the detailed response, that really helps me.

I'm surprised though that 200Mbps combined is the highest theoretical speed for profile 30a, as I would expect it to be 330Mbps (230+100).

Also, I am also quite surprised regarding the VC-231G, I must have misread, thank you for the correction.

Yeah, it's a shame that this is the situation, as currently it means getting a device with CO support is just unfeasible for most people. I hope that someone manages to get the FALCON devices properly working with FOSS drivers on the main OpenWrt versions eventually, however that is currently unrelated.

I guess that the best I can currently do, in that case, is try looking at Lantiq DSL firmwares to try finding any mention of CO support, unlikely as it is.

This gets me thinking, I wonder if ALLNET's SFP DSL unit supports CO mode, that could be an interesting situation (but realistically, due to pricing and attainability, it would mean that any hardware with CO support, VDSL2 or G.Fast, would be impractical for me, even if possible, unless Cisco's old VDSL2 (profile 30a) routers (Broadcom SoC and DSL modem, unfortunately) may include support for it (however, I am still learning how to set one up via serial).

The big(gest) problems about that will be
a) finding the correct (~best) firmware blobs
b) testing of driver and the system as a whole

expect a considerable potential for issues all over the stack.

It isn't the highest theoretical data rate. The 200 Mbit/s are just the minimum that every modem is required to support.

It is not going to help for VRX518, but the firmware of some Fritzboxes (those using a VRX618/619 modem) contains DSL firmware files for both CPE and CO mode. However, the functionality is not exposed, and it is not clear if it would even work with the available hardware. The intended purpose is probably the Fritzbox 5550, which was announced with CO support (but it was never actually released).

Sometimes these devices are available for reasonable prices on the used market. Setting up notifications for the model numbers helps to find them.

True, which is why I am not expecting anything at this point.


Regarding 2nd hand, yeah, I am aware of that (I purchase 2nd hand more often than 1st hand, as well as dumpster dive, so I was speaking about this market as well when I mentioned pricing and attainability), currently the cheapest options with support for profile 35b or G.Fast and CO support I have found that actually ship to my country (nothing locally), cost almost as much as a new VC-231G (which is available locally, but for roughly the equivalent of nearly $200USD), with many far exceeding it.

Anything cheaper is being sold by people who are not shipping to my country (which is a common occurrence with business/enterprise networking equipment here, the cheapest SFP G.PON transceivers on the main G.PON network's whitelist that are available to us, are new units from said network's owners, since while second hand units that are being sold elsewhere can be obtained for cheap, none of them ship to here, and those who do, charge more than that network's owners do for 1st hand units).

When purchasing BCM5719 cards, I had to work hard to find anything below $40 (nothing local, and shipping drove up the prices), and for a BCM57810S, while I did eventually find something local, it was not via local channels, and I payed close to the equivalent of nearly $80USD, which was the cheapest option available to me.

In the UK, symmetric VDSL is called EoFTTC, it guarantees 20/20 only, so 20 down and 20 up.

Yeah, that is pretty much the limit of what Wikipedia has about this subject as well (it's actually slightly above 20, but not by much).

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