Vodafone Cable Internet shenanigans - Part 2: Third party modems

Posted Oct 11, 2024 Updated Oct 11, 2024

By Robin W. Hunter

16 min read

Motivation

In the last article of this series, we learned how to activate Bridge Mode on Vodafone’s (in Germany) standard issued “Vodafone Station”. As a reminder, once this mode is activated, the Vodafone Station acts as a simple modem, relegating routing functionalities to whichever router is connected downstream from it. With this configuration, I was able to delegate the routing and wireless network management responsibilities to other devices on my network, thus circumventing the limitations of the hardware and software of the Vodafone Station. However, I was still annoyed by the Vodafone Station. Particularly, I found it to be very bulky, and unnecessarily big. Additionally, it seems the Station was not designed to be laid on its side: Annoyingly enough, the bottom of the device has this extruding cylindrical part which is wider than the rest of its body, and makes it impossible to lay it on its side (See Figure 1). Finally, the parallelepipedic shape of the Station (I had to google the name) is probably one of the worst picks for a network appliance, as it makes it very hard to put in a rack.

Figure 1: Close-up of the Vodafone Station’s bottom side

For all the reasons above, I started looking into alternative modems to the Vodafone Station. In the following I will be covering what I learned while looking for such an alternative.

DOCSIS

The main requirement of any replacement modem is support of the communication protocol used for communication between my modem and my ISP’s upstream equipment (commonly referred to as the Cable Modem Termination System, or CMTS) over the coaxial-cable infrastructure. Vodafone Germany, makes use of the Data Over Cable Service Interface Specification or DOCSIS for short, which is the predominant standard for data transfer over coaxial TV cables. Development of this specification is led by CableLabs, which is a non-profit corporation based in the US. As new versions of the DOCSIS specification are released by CableLabs, they are submitted to the International Telecommunication Union (ITU-T) for standardization. The first version of this standard (DOCSIS 1.0) was first published in 1997, and supported speeds up to 40Mbps (Down) and 10Mbps (Up). The latest version (DOCSIS 4.0) was introduced in 2019 and supports speeds up to 10Gbps (Down)and 6Gbps (Up)¹

Vodafone Germany has recently undergone a big effort to upgrade all its Cable Internet customer lines to DOCSIS 3.1, and as of 2023 only few holdouts still only support DOCSIS 3.0². Up until 2020, Vodafone still had plans to support DOCSIS 4.0³, with plans for some field tests to take place in 2021/2022⁴. However, as revealed in February 2024, it seems Vodafone had changed course, and was no longer interested in deploying DOCSIS 4.0 any time soon, opting instead to focus more on the expansion of their optic-fiber network⁵⁶.

In summary, any replacement modem for the Vodafone Station will need to support DOCSIS 3.1. As of this writing, Vodafone offers Cable Internet contracts with speeds going from 50Mbps up to 1000Mbps. For speeds up to 500Mbps it seems one can make use of a DOCSIS 3.0 modem⁷. However, for 1Gbps contracts, DOCSIS 3.1 is a hard requirement. The good news is that DOCSIS 3.1 is backward compatible, meaning, even if you don’t have a Gigabit line, you could use a DOCSIS 3.1 modem. That might even be the better choice, considering how older modems supporting only DOCSIS 3.0 are harder to come-by. Additionally, using a DOCSIS 3.1 modem would mean you will be all set in case Vodafone ever gets around to upgrading your line from DOCSIS 3.0 to 3.1. In my case, as I have a Gigabit contract, I will need a DOCSIS 3.1 device.

EuroDOCSIS

There is one very important nuance when it comes to DOCSIS, namely that there exists two versions of the specification: One for North America, and another for Europe. The latter is commonly referred to as EuroDOCSIS. Without getting too much into the details of it, this is due to the difference in the standards previously used for analog television broadcasting systems:

The European Phase Alternating Line (PAL) system used 8MHz channels.
The North American National Television System Committee (NTSC) used 6MHz channels.

These standards are for the most part no longer in use, as digital television has overtaken its analog predecessor. However, the digital standards which overtook television broadcasting (DVB-C for Cable TV in Europe and ATSC in North America) kept the same frequency channels previously used by their analog predecessors. The DOCSIS standard was developed to carry Internet traffic over the coaxial cable lines initially used for carrying these TV signals. As such, the North American DOCSIS specification makes use of 6MHz channels, whereas EuroDOCSIS uses 8MHz channels.

So, what does this all practically mean? It means that when looking for a replacement modem, it is not enough to check for the DOCSIS version supported, but also for the support of the correct variant. Meaning in my case, I now needed a DOCSIS 3.1 modem, with support for the EuroDOCSIS channels.

Security considerations

Newer versions of the DOCSIS specification have not only allowed for higher speeds, but have also brought more management and security features. Specifically, DOCSIS 3.1 implements a new security specification: Base Line Privacy Plus (PBL+)⁸ This specification expands on the original Base Line Privacy (BPL) specification, supported on previous versions of DOCSIS, and specifies two security features:

An encapsulation protocol for encrypting the traffic between the customer’s Cable Modem and the ISP’s Cable Modem Termination System. Thus guaranteeing data privacy and preventing cable customers from eavesdropping on each other’s traffic.
A key management protocol the ISP can use to securely distribute encryption keys to customers’ modems to be used for traffic encryption. Additionally, it also allows the ISP to restrict access to their network, to only authorized devices.

This second feature is what is of importance to us. Again, without getting too much into the details, DOCSIS 3.1 devices are all delivered with an Asymmetric cryptographic key pair. The public key, needs to have been previously signed by one of the DOCSIS certification authorities. This takes place during the DOCSIS 3.1 certification process. The certification authority in North America is CableLabs itself (remember that is the non-profit in charge of issuing DOCSIS specifications). The European certification authority is the Belgian Excentis (previously tComLabs). When put in operation, one of the first things a compliant device will do when connected to an ISP’s network, is send an Authorization Request to the ISP’s CMTS. This authorization request contains:

Identifying information of the modem: namely its serial number and MAC Address.
The modem’s public key.
A certificate, which is signed by one of the trusted certification authorities, and which binds the modem’s identifying information to its public key.

When the CMTS receives this request, it can check the validity of the certificate, authenticate its signature, and verify that it was issued by a trusted authority. Additionally, the CMTS verifies that the MAC of the modem matches the one included in the request, and mentioned in the certificate. Finally, the ISP can check if the modem in question has been authorized to connect to the ISP’s network (e.g. by checking that its identity has been whitelisted beforehand). Once these checks have passed, the connection with the modem is further established, and its public key can be used to establish an encrypted session to securely transfer Internet traffic.

The reason I have included the explanation above is twofold: Because only certified equipment will be allowed to connect to the network, one needs to make sure their third party equipment has been certified by one of the above-mentioned certification authorities. Additionally, the ISP will need to know the identification information of the modem before it attempts to connect to the network (in order to whitelist it). As such, it is required to communicate the MAC and serial number of the modem to the ISP, before one can connect their third party modem to the ISP’s coax infrastructure. In the case of Vodafone, this can be done through the support Hotline. When calling to switch to your own modem, you will be asked for the serial number and MAC address of the device⁷⁹.

Available alternatives

Below is the not-so-long list of devices I found which fulfill the above-mentioned requirements:

FRITZ!Boxes (6660, 6670 or 6690): These are very popular in Germany, and I have covered a FRITZ!Box DSL router/modem combo device previously. You can buy one of these from many consumer electronics stores. Alternatively, if you are a Vodafone customer you can (as of the writing of this article) upgrade your Vodafone Station to either a FRITZ!Box 6670 or 6690 by booking the Homebox options (at an additional monthly cost)¹⁰. FRITZ!Boxes are all-in-one devices, taking over the three roles of modem/router/wireless access point. All three devices support DOCSIS 3.1. Their hardware is usually much better than the Vodafone Station, and their software offers much more features, and receives updates more frequently. So switching to one of these devices from a Vodafone Station is still worth it for most people. However, if you were to use one of these devices as a simple Cable modem (by switching them to bridge mode), you would be leaving a lot the performance you would have paid for on the table.

Figure 2: The Technicolor TC4400 EU modem¹¹

Technicolor TC4400 EU (The tried and true): Throughout my research, this device kept showing up as a very popular choice among people who made the switch to a third party device⁹¹². It supports DOCSIS 3.1, and as the name hints at, supports the EuroDOCSIS frequencies. There also exists a non-EU variant, so if you were to purchase this device, make sure you are getting the right variant.
The device’s dimensions are much more conservative than the Vodafone Station, and it comes in a very traditional cuboid shape (also had to google that one). Additionally, the device has two Gigabit Ethernet ports. However, I am still unsure if one can make use of both ports simultaneously, thus obtaining two different IP addresses from the ISP. One major inconvenience with this device is that it seems to be out of stock everywhere, which leads me to believe that it is a phased-out product. The only way to get one of these seems to be through ebay auctions at relatively high prices (200€ and up).

Figure 3: The ARRIS CM3500 B CE modem¹³

ARRIS CM3500 B CE (The new kid on the block?) I have only learned about the existence of this modem as I was doing additional research for this article. This device supports DOCSIS 3.1, and even has a 2.5G Ethernet port. It is important to note that, the highest Cable Internet speed currently offered by Vodafone is 1Gbps, so you will not be able to fully make use of the 2.5G Ethernet interface. However, as covered previously, DOCSIS 3.1 is theoretically capable of achieving 10Gbps, meaning if Vodafone ever decides to upgrade its infrastructure to support higher speeds, you would be better prepared for it, if you opt for this device. ARRIS, the device’s manufacturer are also the manufacturer of the Vodafone Station (officially the ARRIS TG3442DE). Finally, multiple people seem to have already used the device for Vodafone Cable Internet without issue¹³.

My experience switching to my own modem

You might have guessed from the previous section, but for my own replacement I opted for the Technicolor TC4400 EU, which I managed to get used off an auction on Ebay. In order to switch from my Vodafone Station which I was using in Bridge Mode to my own modem, all I had to do was call the Vodafone Hotline, and ask to switch to my own modem. As a reminder, I had already previously switched to Dual Stack instead of Dual-Stack Lite (which is the default for Vodafone customers in Germany). I believe that this has spared me additional complications when it came time to switch to my own modem.

In order to allow me to switch to my own modem, I was asked for the device’s serial number and MAC (both were printed on a sticker on the device). After giving this information, I was told that my modem would be activated within a few minutes. After plugin my modem in, the few minutes turned into an hour, and the “Link” LED on my modem was still only blinking, instead of showing a solid color, which was an indicator that my modem was not able to establish an upstream connection. I called the Hotline again, and was informed (by a different person) that it could take up to two hours for the new modem to be activated. So I hang up, and decided to give the modem the whole night to get through the “activation process”.

The next morning, my modem’s LED was still only blinking, and I was still left without Internet at home. I was getting desperate, particularly because I was working from home, and needed Internet access for the day. Calling the hotline again was not very helpful, I was asked to verify both the serial number and MAC address of the device again (both were correct), and was only told that the “activation process” can (sometimes) take up to 48 hours (?!). At this point, I asked if it were possible to simply reconnect my Vodafone Station for the time being, and perhaps attempt to connect my own modem some other day (e.g. on a weekend) where I could make do without Internet access. I was then informed that by asking for the switch to my own device, my old Vodafone was no longer bound to my customer account, and that if I wanted to switch back to a Vodafone Station, a new one would need to be issued to me, and sent by post to my address. I opted to keep my device, and asked for a technician to come-by and help diagnose the issue. The closest possible technician appointment was in three days… To Vodafone’s credit, they offered to give me a 15GB mobile data credit for the three days I would remain without Internet access.

I had spent two days without Internet access, saving my 15GB for the strictest necessary needs (meaning mainly work). On the morning of the third day, and as I was getting ready to start work, I noticed that the “Link” LED on my modem was no longer blinking and was showing a solid green color. After making sure I wasn’t hallucinating, I connected to my home network’s Wi-Fi only to realize I had Internet access, not believing myself, I connected to my router’s web UI only to find it had a public IP address and was successfully connected to the Internet. I spent the rest of the day at work as usual, now connected to my home network, and after making sure that my home Internet was stable, I called off the technician’s appointment.

Important Note

After switching to my own modem, I received an email with instruction for returning the Vodafone Station. I initially had intended to keep the Station to use as backup in case my new modem had issues. As mentioned above, such a switch is not really possible, and if I ever needed to revert to the Vodafone Station, I would need a new one be sent to me from Vodafone. Still, I thought I would keep the old Station, seeing as I was not paying rental fees on it. As it turns out, that too was not as straight forward as I had hoped, and my Internet bill of the following month included an additional fee of 29€ for not returning the Vodafone Station. I have not been billed any additional fees since then, so I believe that it was a one time fee and that it does not reflect the price of the device (which is supposedly amortized through the minimum contract duration). Still, this is something you might want to know in case you plan on keeping your old equipment.

Conclusion

This whole experience has been a great learning opportunity for me. Learning the protocol that my modem was using to speak to the upstream ISP equipment has allowed me to adopt a new perspective on the inner-workings of my Internet access. Having to spend multiple days without Internet access was not a low price to pay. However, the freedom I now enjoy, having completely decoupled from my ISP’s standard-issued hardware is unrivaled.

In the previous article in this series, I explained how one of the disadvantages of the Vodafone Station, is the fact that it takes over three different roles at once. In this article, I have shown how one can use a third party modem, which is a special piece of hardware specifically constructed to assume one of these roles (modulation & demodulation). One thing I have not yet covered in this series is how to replace and delegate the other responsibilities previously assumed by the Vodafone Station (routing and wireless network management) to other devices. That will be the subject of the next article in this series. If that sounds like something you’d be interested in, then stay tuned!

References

Network organization

networks docsis modem vodafone isp cable

This post is licensed under CC BY 4.0 by the author.