Virtual Um interface between OsmoBTS and OsmocomBB

During the last couple of days, I've been working on completing, cleaning up and merging a Virtual Um interface (i.e. virtual radio layer) between OsmoBTS and OsmocomBB. After I started with the implementation and left it in an early stage in January 2016, Sebastian Stumpf has been completing it around early 2017, with now some subsequent fixes and improvements by me. The combined result allows us to run a complete GSM network with 1-N BTSs and 1-M MSs without any actual radio hardware, which is of course excellent for all kinds of testing scenarios.

The Virtual Um layer is based on sending L2 frames (blocks) encapsulated via GSMTAP UDP multicast packets. There are two separate multicast groups, one for uplink and one for downlink. The multicast nature simulates the shared medium and enables any simulated phone to receive the signal from multiple BTSs via the downlink multicast group.

/images/osmocom-virtum.png

In OsmoBTS, this is implemented via the new osmo-bts-virtual BTS model.

In OsmocomBB, this is realized by adding virtphy virtual L1, which speaks the same L1CTL protocol that is used between the real OsmcoomBB Layer1 and the Layer2/3 programs such as mobile and the like.

Now many people would argue that GSM without the radio and actual handsets is no fun. I tend to agree, as I'm a hardware person at heart and I am not a big fan of simulation.

Nevertheless, this forms the basis of all kinds of possibilities for automatized (regression) testing in a way and for layers/interfaces that osmo-gsm-tester cannot cover as it uses a black-box proprietary mobile phone (modem). It is also pretty useful if you're traveling a lot and don't want to carry around a BTS and phones all the time, or get some development done in airplanes or other places where operating a radio transmitter is not really a (viable) option.

If you're curious and want to give it a shot, I've put together some setup instructions at the Virtual Um page of the Osmocom Wiki.

Ten years after first shipping Openmoko Neo1973

Exactly 10 years ago, on July 9th, 2007 we started to sell+ship the first Openmoko Neo1973. To be more precise, the webshop actually opened a few hours early, depending on your time zone. Sean announced the availability in this mailing list post

I don't really have to add much to my ten years [of starting to work on] Openmoko anniversary blog post a year ago, but still thought it's worth while to point out the tenth anniversary.

It was exciting times, and there was a lot of pioneering spirit: Building a Linux based smartphone with a 100% FOSS software stack on the application processor, including all drivers, userland, applications - at a time before Android was known or announced. As history shows, we'd been working in parallel with Apple on the iPhone, and Google on Android. Of course there's little chance that a small taiwanese company can compete with the endless resources of the big industry giants, and the many Neo1973 delays meant we had missed the window of opportunity to be the first on the market.

It's sad that Openmoko (or similar projects) have not survived even as a special-interest project for FOSS enthusiasts. Today, virtually all options of smartphones are encumbered with way more proprietary blobs than we could ever imagine back then.

In any case, the tenth anniversary of trying to change the amount of Free Softwware in the smartphone world is worth some celebration. I'm reaching out to old friends and colleagues, and I guess we'll have somewhat of a celebration party both in Germany and in Taiwan (where I'll be for my holidays from mid-September to mid-October).

How the Osmocom GSM stack is funded

As the topic has been raised on twitter, I thought I might share a bit of insight into the funding of the Osmocom Cellular Infrastructure Projects.

Keep in mind: Osmocom is a much larger umbrella project, and beyond the Networks-side cellular stack is home many different community-based projects around open source mobile communications. All of those have started more or less as just for fun projects, nothing serious, just a hobby [1]

The projects implementing the network-side protocol stacks and network elements of GSM/GPRS/EGPRS/UMTS cellular networks are somewhat the exception to that, as they have evolved to some extent professionalized. We call those projects collectively the Cellular Infrastructure projects inside Osmocom. This post is about that part of Osmocom only

History

From late 2008 through 2009, People like Holger and I were working on bs11-abis and later OpenBSC only in our spare time. The name Osmocom didn't even exist back then. There was a strong technical community with contributions from Sylvain Munaut, Andreas Eversberg, Daniel Willmann, Jan Luebbe and a few others. None of this would have been possible if it wasn't for all the help we got from Dieter Spaar with the BS-11 [2]. We all had our dayjob in other places, and OpenBSC work was really just a hobby. People were working on it, because it was where no FOSS hacker has gone before. It was cool. It was a big and pleasant challenge to enter the closed telecom space as pure autodidacts.

Holger and I were doing freelance contract development work on Open Source projects for many years before. I was mostly doing Linux related contracting, while Holger has been active in all kinds of areas throughout the FOSS software stack.

In 2010, Holger and I saw some first interest by companies into OpenBSC, including Netzing AG and On-Waves ehf. So we were able to spend at least some of our paid time on OpenBSC/Osmocom related contract work, and were thus able to do less other work. We also continued to spend tons of spare time in bringing Osmocom forward. Also, the amount of contract work we did was only a fraction of the many more hours of spare time.

In 2011, Holger and I decided to start the company sysmocom in order to generate more funding for the Osmocom GSM projects by means of financing software development by product sales. So rather than doing freelance work for companies who bought their BTS hardware from other places (and spent huge amounts of cash on that), we decided that we wanted to be a full solution supplier, who can offer a complete product based on all hardware and software required to run small GSM networks.

The only problem is: We still needed an actual BTS for that. Through some reverse engineering of existing products we figured out who one of the ODM suppliers for the hardware + PHY layer was, and decided to develop the OsmoBTS software to do so. We inherited some of the early code from work done by Andreas Eversberg on the jolly/bts branch of OsmocomBB (thanks), but much was missing at the time.

What follows was Holger and me working several years for free [3], without any salary, in order to complete the OsmoBTS software, build an embedded Linux distribution around it based on OE/poky, write documentation, etc. and complete the first sysmocom product: The sysmoBTS 1002

We did that not because we want to get rich, or because we want to run a business. We did it simply because we saw an opportunity to generate funding for the Osmocom projects and make them more sustainable and successful. And because we believe there is a big, gaping, huge vacuum in terms of absence of FOSS in the cellular telecom sphere.

Funding by means of sysmocom product sales

Once we started to sell the sysmoBTS products, we were able to fund Osmocom related development from the profits made on hardware / full-system product sales. Every single unit sold made a big contribution towards funding both the maintenance as well as the ongoing development on new features.

This source of funding continues to be an important factor today.

Funding by means of R&D contracts

The probably best and most welcome method of funding Osmocom related work is by means of R&D projects in which a customer funds our work to extend the Osmocom GSM stack in one particular area where he has a particular need that the existing code cannot fulfill yet.

This kind of project is the ideal match, as it shows where the true strength of FOSS is: Each of those customers did not have to fund the development of a GSM stack from scratch. Rather, they only had to fund those bits that were missing for their particular application.

Our reference for this is and has been On-Waves, who have been funding development of their required features (and bug fixing etc.) since 2010.

We've of course had many other projects from a variety of customers over over the years. Last, but not least, we had a customer who willingly co-funded (together with funds from NLnet foundation and lots of unpaid effort by sysmocom) the 3G/3.5G support in the Osmocom stack.

The problem here is:

  • we have not been able to secure anywhere nearly as many of those R&D projects within the cellular industry, despite believing we have a very good foundation upon which we can built. I've been writing many exciting technical project proposals
  • you almost exclusively get funding only for new features. But it's very hard to get funding for the core maintenance work. The bug-fixing, code review, code refactoring, testing, etc.

So as a result, the profit margin you have on selling R&D projects is basically used to (do a bad job of) fund those bits and pieces that nobody wants to pay for.

Funding by means of customer support

There is a way to generate funding for development by providing support services. We've had some success with this, but primarily alongside the actual hardware/system sales - not so much in terms of pure software-only support.

Also, providing support services from a R&D company means:

  • either you distract your developers by handling support inquiries. This means they will have less time to work on actual code, and likely get side tracked by too many issues that make it hard to focus
  • or you have to hire separate support staff. This of course means that the size of the support business has to be sufficiently large to not only cover the cots of hiring + training support staff, but also still generate funding for the actual software R&D.

We've tried shortly with the second option, but fallen back to the first for now. There's simply not sufficient user/admin type support business to rectify dedicated staff for that.

Funding by means of cross-subsizing from other business areas

sysmocom also started to do some non-Osmocom projects in order to generate revenue that we can feed again into Osmocom projects. I'm not at liberty to discuss them in detail, but basically we've been doing pretty much anything from

  • custom embedded Linux board designs
  • M2M devices with GSM modems
  • consulting gigs
  • public tendered research projects

Profits from all those areas went again into Osmocom development.

Last, but not least, we also operate the sysmocom webshop. The profit we make on those products also is again immediately re-invested into Osmocom development.

Funding by grants

We've had some success in securing funding from NLnet Foundation for specific features. While this is useful, the size of their projects grants of up to EUR 30k is not a good fit for the scale of the tasks we have at hand inside Osmocom. You may think that's a considerable amount of money? Well, that translates to 2-3 man-months of work at a bare cost-covering rate. At a team size of 6 developers, you would theoretically have churned through that in two weeks. Also, their focus is (understandably) on Internet and IT security, and not so much cellular communications.

There are of course other options for grants, such as government research grants and the like. However, they require long-term planning, they require you to match (i.e. pay yourself) a significant portion, and basically mandate that you hire one extra person for doing all the required paperwork and reporting. So all in all, not a particularly attractive option for a very small company consisting of die hard engineers.

Funding by more BTS ports

At sysmocom, we've been doing some ports of the OsmoBTS + OsmoPCU software to other hardware, and supporting those other BTS vendors with porting, R&D and support services.

If sysmocom was a classic BTS vendor, we would not help our "competition". However, we are not. sysmocom exists to help Osmocom, and we strongly believe in open systems and architectures, without a single point of failure, a single supplier for any component or any type of vendor lock-in.

So we happily help third parties to get Osmocom running on their hardware, either with a proprietary PHY or with OsmoTRX.

However, we expect that those BTS vendors also understand their responsibility to share the development and maintenance effort of the stack. Preferably by dedicating some of their own staff to work in the Osmocom community. Alternatively, sysmocom can perform that work as paid service. But that's a double-edged sword: We don't want to be a single point of failure.

Osmocom funding outside of sysmocom

Osmocom is of course more than sysmocom. Even for the cellular infrastructure projects inside Osmocom is true: They are true, community-based, open, collaborative development projects. Anyone can contribute.

Over the years, there have been code contributions by e.g. Fairwaves. They, too, build GSM base station hardware and use that as a means to not only recover the R&D on the hardware, but also to contribute to Osmocom. At some point a few years ago, there was a lot of work from them in the area of OsmoTRX, OsmoBTS and OsmoPCU. Unfortunately, in more recent years, they have not been able to keep up the level of contributions.

There are other companies engaged in activities with and around Osmcoom. There's Rhizomatica, an NGO helping indigenous communities to run their own cellular networks. They have been funding some of our efforts, but being an NGO helping rural regions in developing countries, they of course also don't have the deep pockets. Ideally, we'd want to be the ones contributing to them, not the other way around.

State of funding

We're making some progress in securing funding from players we cannot name [4] during recent years. We're also making occasional progress in convincing BTS suppliers to chip in their share. Unfortunately there are more who don't live up to their responsibility than those who do. I might start calling them out by name one day. The wider community and the public actually deserves to know who plays by FOSS rules and who doesn't. That's not shaming, it's just stating bare facts.

Which brings us to:

  • sysmocom is in an office that's actually too small for the team, equipment and stock. But we certainly cannot afford more space.
  • we cannot pay our employees what they could earn working at similar positions in other companies. So working at sysmocom requires dedication to the cause :)
  • Holger and I have invested way more time than we have ever paid us, even more so considering the opportunity cost of what we would have earned if we'd continued our freelance Open Source hacker path
  • we're [just barely] managing to pay for 6 developers dedicated to Osmocom development on our payroll based on the various funding sources indicated above

Nevertheless, I doubt that any such a small team has ever implemented an end-to-end GSM/GPRS/EGPRS network from RAN to Core at comparative feature set. My deepest respects to everyone involved. The big task now is to make it sustainable.

Summary

So as you can see, there's quite a bit of funding around. However, it always falls short of what's needed to implement all parts properly, and even not quite sufficient to keep maintaining the status quo in a proper and tested way. That can often be frustrating (mostly to us but sometimes also to users who run into regressions and oter bugs). There's so much more potential. So many things we wanted to add or clean up for a long time, but too little people interested in joining in, helping out - financially or by writing code.

On thing that is often a challenge when dealing with traditional customers: We are not developing a product and then selling a ready-made product. In fact, in FOSS this would be more or less suicidal: We'd have to invest man-years upfront, but then once it is finished, everyone can use it without having to partake in that investment.

So instead, the FOSS model requires the customers/users to chip in early during the R&D phase, in order to then subsequently harvest the fruits of that.

I think the lack of a FOSS mindset across the cellular / telecom industry is the biggest constraining factor here. I've seen that some 20-15 years ago in the Linux world. Trust me, it takes a lot of dedication to the cause to endure this lack of comprehension so many years later.

[1] just like Linux has started out.
[2] while you will not find a lot of commits from Dieter in the code, he has been playing a key role in doing a lot of prototyping, reverse engineering and debugging!
[3] sysmocom is 100% privately held by Holger and me, we intentionally have no external investors and are proud to never had to take a bank loan. So all we could invest was our own money and, most of all, time.
[4] contrary to the FOSS world, a lot of aspects are confidential in business, and we're not at liberty to disclose the identities of all our customers

FOSS misconceptions, still in 2017

The lack of basic FOSS understanding in Telecom

Given that the Free and Open Source movement has been around at least since the 1980ies, it puzzles me that people still seem to have such fundamental misconceptions about it.

Something that really triggered me was an article at LightReading [1] which quotes Ulf Ewaldsson, a leading Ericsson excecutive with

"I have yet to understand why we would open source something we think is really good software"

This completely misses the point. FOSS is not about making a charity donation of a finished product to the planet.

FOSS is about sharing the development costs among multiple players, and avoiding that everyone has to reimplement the wheel. Macro-Economically, it is complete and utter nonsense that each 3GPP specification gets implemented two dozens of times, by at least a dozen of different entities. As a result, products are way more expensive than needed.

If large Telco players (whether operators or equipment manufacturers) were to collaboratively develop code just as much as they collaboratively develop the protocol specifications, there would be no need for replicating all of this work.

As a result, everyone could produce cellular network elements at reduced cost, sharing the R&D expenses, and competing in key areas, such as who can come up with the most energy-efficient implementation, or can produce the most reliable hardware, the best receiver sensitivity, the best and most fair scheduling implementation, or whatever else. But some 80% of the code could probably be shared, as e.g. encoding and decoding messages according to a given publicly released 3GPP specification document is not where those equipment suppliers actually compete.

So my dear cellular operator executives: Next time you're cursing about the prohibitively expensive pricing that your equipment suppliers quote you: You only have to pay that much because everyone is reimplementing the wheel over and over again.

Equally, my dear cellular infrastructure suppliers: You are all dying one by one, as it's hard to develop everything from scratch. Over the years, many of you have died. One wonders, if we might still have more players left, if some of you had started to cooperate in developing FOSS at least in those areas where you're not competing. You could replicate what Linux is doing in the operating system market. There's no need in having a phalanx of different proprietary flavors of Unix-like OSs. It's way too expansive, and it's not an area in which most companies need to or want to compete anyway.

Management Summary

You don't first develop and entire product until it is finished and then release it as open source. This makes little economic sense in a lot of cases, as you've already invested into developing 100% of it. Instead, you actually develop a new product collaboratively as FOSS in order to not have to invest 100% but maybe only 30% or even less. You get a multitude of your R&D investment back, because you're not only getting your own code, but all the other code that other community members implemented. You of course also get other benefits, such as peer review of the code, more ideas (not all bright people work inside one given company), etc.

[1] that article is actually a heavily opinionated post by somebody who appears to be pushing his own anti-FOSS agenda for some time. The author is misinformed about the fact that the TIP has always included projects under both FRAND and FOSS terms. As a TIP member I can attest to that fact. I'm only referencing it here for the purpose of that that Ericsson quote.

Playing back GSM RTP streams, RTP-HR bugs

Chapter 0: Problem Statement

In an all-IP GSM network, where we use Abis, A and other interfaces within the cellular network over IP transport, the audio of voice calls is transported inside RTP frames. The codec payload in those RTP frames is the actual codec frame of the respective cellular voice codec. In GSM, there are four relevant codecs: FR, HR, EFR and AMR.

Every so often during the (meanwhile many years of ) development of Osmocom cellular infrastructure software it would have been useful to be able to quickly play back the audio for analysis of given issues.

However, until now we didn't have that capability. The reason is relatively simple: In Osmocom, we genally don't do transcoding but simply pass the voice codec frames from left to right. They're only transcoded inside the phones or inside some external media gateway (in case of larger networks).

Chapter 1: GSM Audio Pocket Knife

Back in 2010, when we were very actively working on OsmocomBB, the telephone-side GSM protocol stack implementation, Sylvain Munaut wrote the GSM Audio Pocket Knife (gapk) in order to be able to convert between different formats (representations) of codec frames. In cellular communcations, everyoe is coming up with their own representation for the codec frames: The way they look on E1 as a TRAU frame is completely different from how RTP payload looks like, or what the TI Calypso DSP uses internally, or what a GSM Tester like the Racal 61x3 uses. The differences are mostly about data types used, bit-endinanness as well as padding and headers. And of course those different formats exist for each of the four codecs :/

In 2013 I first added simplistic RTP support for FR-GSM to gapk, which was sufficient for my debugging needs back then. Still, you had to save the decoded PCM output to a file and play that back, or use a pipe into aplay.

Last week, I picked up this subject again and added a long series of patches to gapk:

  • support for variable-length codec frames (required for AMR support)
  • support for AMR codec encode/decode using libopencore-amrnb
  • support of all known RTP payload formats for all four codecs
  • support for direct live playback to a sound card via ALSA

All of the above can now be combined to make GAPK bind to a specified UDP port and play back the RTP codec frames that anyone sends to that port using a command like this:

$ gapk -I 0.0.0.0/30000 -f rtp-amr -A default -g rawpcm-s16le

I've also merged a chance to OsmoBSC/OsmoNITB which allows the administrator to re-direct the voice of any active voice channel towards a user-specified IP address and port. Using that you can simply disconnect the voice stream from its normal destination and play back the audio via your sound card.

Chapter 2: Bugs in OsmoBTS GSM-HR

While going through the exercise of implementing the above extension to gapk, I had lots of trouble to get it to work for GSM-HR.

After some more digging, it seems there are two conflicting specification on how to format the RTP payload for half-rate GSM:

In Osmocom, we claim to implement RFC5993, but it turned out that (at least) osmo-bts-sysmo (for sysmoBTS) was actually implementing the ETSI format instead.

And even worse, osmo-bts-sysmo gets event the ETSI format wrong. Each of the codec parameters (which are unaligned bit-fields) are in the wrong bit-endianness :(

Both the above were coincidentially also discovered by Sylvain Munaut during operating of the 32C3 GSM network in December 2015 and resulted the two following "work around" patches: * HACK for HR * HACK: Fix the bit order in HR frames

Those merely worked around those issues in the rtp_proxy of OsmoNITB, rather than addressing the real issue. That's ok, they were "quick" hacks to get something working at all during a four-day conference. I'm now working on "real" fixes in osmo-bts-sysmo. The devil is of course in the details, when people upgrade one BTS but not the other and want to inter-operate, ...

It yet remains to be investigated how osmo-bts-trx and other osmo-bts ports behave in this regard.

Chapter 3: Conclusions

Most definitely it is once again a very clear sign that more testing is required. It's tricky to see even wih osmo-gsm-tester, as GSM-HR works between two phones or even two instances of osmo-bts-sysmo, as both sides of the implementation have the same (wrong) understanding of the spec.

Given that we can only catch this kind of bug together with the hardware (the DSP runs the PHY code), pure unit tests wouldn't catch it. And the end-to-end test is also not very well suited to it. It seems to call for something in betewen. Something like an A-bis interface level test.

We need more (automatic) testing. I cannot say that often enough. The big challenge is how to convince contributors and customers that they should invest their time and money there, rather than yet-another (not automatically tested) feature?

Power-cycling a USB port should be simple, right?

Every so often I happen to be involved in designing electronics equipment that's supposed to run reliably remotely in inaccessible locations,without any ability for "remote hands" to perform things like power-cycling or the like. I'm talking about really remote locations, possible with no but limited back-haul, and a very high cost of ever sending somebody there for remote maintenance.

Given that a lot of computer peripherals (chips, modules, ...) use USB these days, this is often some kind of an embedded ARM (rarely x86) SoM or SBC, which is hooked up to a custom board that contains a USB hub chip as well as a line of peripherals.

One of the most important lectures I've learned from experience is: Never trust reset signals / lines, always include power-switching capability. There are many chips and electronics modules available on the market that have either no RESET, or even might claim to have a hardware RESET line which you later (painfully) discover just to be a GPIO polled by software which can get stuck, and hence no way to really hard-reset the given component.

In the case of a USB-attached device (even though the USB might only exist on a circuit board between two ICs), this is typically rather easy: The USB hub is generally capable of switching the power of its downstream ports. Many cheap USB hubs don't implement this at all, or implement only ganged switching, but if you carefully select your USB hub (or in the case of a custom PCB), you can make sure that the given USB hub supports individual port power switching.

Now the next step is how to actually use this from your (embedded) Linux system. It turns out to be harder than expected. After all, we're talking about a standard feature that's present in the USB specifications since USB 1.x in the late 1990ies. So the expectation is that it should be straight-forward to do with any decent operating system.

I don't know how it's on other operating systems, but on Linux I couldn't really find a proper way how to do this in a clean way. For more details, please read my post to the linux-usb mailing list.

Why am I running into this now? Is it such a strange idea? I mean, power-cycling a device should be the most simple and straight-forward thing to do in order to recover from any kind of "stuck state" or other related issue. Logical enabling/disabling of the port, resetting the USB device via USB protocol, etc. are all just "soft" forms of a reset which at best help with USB related issues, but not with any other part of a USB device.

And in the case of e.g. an USB-attached cellular modem, we're actually talking about a multi-processor system with multiple built-in micro-controllers, at least one DSP, an ARM core that might run another Linux itself (to implement the USB gadget), ... - certainly enough complex software that you would want to be able to power-cycle it...

I'm curious what the response of the Linux USB gurus is.

OsmoDevCon 2017 Review

After the public user-oriented OsmoCon 2017, we also recently had the 6th incarnation of our annual contributors-only Osmocom Developer Conference: The OsmoDevCon 2017.

This is a much smaller group, typically about 20 people, and is limited to actual developers who have a past record of contributing to any of the many Osmocom projects.

We had a large number of presentation and discussions. In fact, so large that the schedule of talks extended from 10am to midnight on some days. While this is great, it also means that there was definitely too little time for more informal conversations, chatting or even actual work on code.

We also have such a wide range of topics and scope inside Osmocom, that the traditional ad-hoch scheduling approach no longer seems to be working as it used to. Not everyone is interested in (or has time for) all the topics, so we should group them according to their topic/subject on a given day or half-day. This will enable people to attend only those days that are relevant to them, and spend the remaining day in an adjacent room hacking away on code.

It's sad that we only have OsmoDevCon once per year. Maybe that's actually also something to think about. Rather than having 4 days once per year, maybe have two weekends per year.

Always in motion the future is.

Overhyped Docker

Overhyped Docker missing the most basic features

I've always been extremely skeptical of suddenly emerging over-hyped technologies, particularly if they advertise to solve problems by adding yet another layer to systems that are already sufficiently complex themselves.

There are of course many issues with containers, ranging from replicated system libraries and the basic underlying statement that you're giving up on the system packet manager to properly deal with dependencies.

I'm also highly skeptical of FOSS projects that are primarily driven by one (VC funded?) company. Especially if their offering includes a so-called cloud service which they can stop to operate at any given point in time, or (more realistically) first get everybody to use and then start charging for.

But well, despite all the bad things I read about it over the years, on one day in May 2017 I finally thought let's give it a try. My problem to solve as a test balloon is fairly simple.

My basic use case

The plan is to start OsmoSTP, the m3ua-testtool and the sua-testtool, which both connect to OsmoSTP. By running this setup inside containers and inside an internal network, we could then execute the entire testsuite e.g. during jenkins test without having IP address or port number conflicts. It could even run multiple times in parallel on one buildhost, verifying different patches as part of the continuous integration setup.

This application is not so complex. All it needs is three containers, an internal network and some connections in between. Should be a piece of cake, right?

But enter the world of buzzword-fueled web-4000.0 software-defined virtualised and orchestrated container NFW + SDN vodoo: It turns out to be impossible, at least not with the preferred tools they advertise.

Dockerfiles

The part that worked relatively easily was writing a few Dockerfiles to build the actual containers. All based on debian:jessie from the library.

As m3ua-testsuite is written in guile, and needs to build some guile plugin/extension, I had to actually include guile-2.0-dev and other packages in the container, making it a bit bloated.

I couldn't immediately find a nice example Dockerfile recipe that would allow me to build stuff from source outside of the container, and then install the resulting binaries into the container. This seems to be a somewhat weak spot, where more support/infrastructure would be helpful. I guess the idea is that you simply install applications via package feeds and apt-get. But I digress.

So after some tinkering, I ended up with three docker containers:

  • one running OsmoSTP
  • one running m3ua-testtool
  • one running sua-testtool

I also managed to create an internal bridged network between the containers, so the containers could talk to one another.

However, I have to manually start each of the containers with ugly long command line arguments, such as docker run --network sigtran --ip 172.18.0.200 -it osmo-stp-master. This is of course sub-optimal, and what Docker Services + Stacks should resolve.

Services + Stacks

The idea seems good: A service defines how a given container is run, and a stack defines multiple containers and their relation to each other. So it should be simple to define a stack with three services, right?

Well, it turns out that it is not. Docker documents that you can configure a static ipv4_address [1] for each service/container, but it seems related configuration statements are simply silently ignored/discarded [2], [3], [4].

This seems to be related that for some strange reason stacks can (at least in later versions of docker) only use overlay type networks, rather than the much simpler bridge networks. And while bridge networks appear to support static IP address allocations, overlay apparently doesn't.

I still have a hard time grasping that something that considers itself a serious product for production use (by a company with estimated value over a billion USD, not by a few hobbyists) that has no support for running containers on static IP addresses. that. How many applications out there have I seen that require static IP address configuration? How much simpler do setups get, if you don't have to rely on things like dynamic DNS updates (or DNS availability at all)?

So I'm stuck with having to manually configure the network between my containers, and manually starting them by clumsy shell scripts, rather than having a proper abstraction for all of that. Well done :/

Exposing Ports

Unrelated to all of the above: If you run some software inside containers, you will pretty soon want to expose some network services from containers. This should also be the most basic task on the planet.

However, it seems that the creators of docker live in the early 1980ies, where only TCP and UDP transport protocols existed. They seem to have missed that by the late 1990ies to early 2000s, protocols like SCTP or DCCP were invented.

But yet, in 2017, Docker chooses to

Now some of the readers may think 'who uses SCTP anyway'. I will give you a straight answer: Everyone who has a mobile phone uses SCTP. This is due to the fact that pretty much all the connections inside cellular networks (at least for 3G/4G networks, and in reality also for many 2G networks) are using SCTP as underlying transport protocol, from the radio access network into the core network. So every time you switch your phone on, or do anything with it, you are using SCTP. Not on your phone itself, but by all the systems that form the network that you're using. And with the drive to C-RAN, NFV, SDN and all the other buzzwords also appearing in the Cellular Telecom field, people should actually worry about it, if they want to be a part of the software stack that is used in future cellular telecom systems.

Summary

After spending the better part of a day to do something that seemed like the most basic use case for running three networked containers using Docker, I'm back to step one: Most likely inventing some custom scripts based on unshare to run my three test programs in a separate network namespace for isolated execution of test suite execution as part of a Jenkins CI setup :/

It's also clear that Docker apparently don't care much about playing a role in the Cellular Telecom world, which is increasingly moving away from proprietary and hardware-based systems (like STPs) to virtualised, software-based systems.

[1] https://docs.docker.com/compose/compose-file/#ipv4address-ipv6address
[2] https://forums.docker.com/t/docker-swarm-1-13-static-ips-for-containers/28060
[3] https://github.com/moby/moby/issues/31860
[4] https://github.com/moby/moby/issues/24170

Book on Practical GPL Compliance

My former gpl-violations.org colleague Armijn Hemel and Shane Coughlan (former coordinator of the FSFE Legal Network) have written a book on practical GPL compliance issues.

I've read through it (in the bath tub of course, what better place to read technical literature), and I can agree wholeheartedly with its contents. For those who have been involved in GPL compliance engineering there shouldn't be much new - but for the vast majority of developers out there who have had little exposure to the bread-and-butter work of providing complete an corresponding source code, it makes an excellent introductory text.

The book focuses on compliance with GPLv2, which is probably not too surprising given that it's published by the Linux foundation, and Linux being GPLv2.

You can download an electronic copy of the book from https://www.linuxfoundation.org/news-media/research/practical-gpl-compliance

Given the subject matter is Free Software, and the book is written by long-time community members, I cannot help to notice a bit of a surprise about the fact that the book is released in classic copyright under All rights reserved with no freedom to the user.

Considering the sensitive legal topics touched, I can understand the possible motivation by the authors to not permit derivative works. But then, there still are licenses such as CC-BY-ND which prevent derivative works but still permit users to make and distribute copies of the work itself. I've made that recommendation / request to Shane, let's see if they can arrange for some more freedom for their readers.

OsmoCon 2017 Review

It's already one week past the event, so I really have to sit down and write some rewview on the first public Osmocom Conference ever: OsmoCon 2017.

The event was a huge success, by all accounts.

  • We've not only been sold out, but we also had to turn down some last minute registrations due to the venue being beyond capacity (60 seats). People traveled from Japan, India, the US, Mexico and many other places to attend.
  • We've had an amazing audience ranging from commercial operators to community cellular operators to professional developers doing work relate to osmocom, academia, IT security crowds and last but not least enthusiasts/hobbyists, with whom the project[s] started.
  • I've received exclusively positive feedback from many attendees
  • We've had a great programme. Some part of it was of introductory nature and probably not too interesting if you've been in Osmocom for a few years. However, the work on 3G as well as the current roadmap was probably not as widely known yet. Also, I really loved to see Roch's talk about Running a commercial cellular network with Osmocom software as well as the talk on Facebook's OpenCellular BTS hardware and the Community Cellular Manager.
  • We have very professional live streaming + video recordings courtesy of the C3VOC team. Thanks a lot for your support and for having the video recordings of all talks online already at the next day after the event.

We also received some requests for improvements, many of which we will hopefully consider before the next Osmocom Conference:

  • have a multiple day event. Particularly if you're traveling long-distance, it is a lot of overhead for a single-day event. We of course fully understand that. On the other hand, it was the first Osmocom Conference, and hence it was a test balloon where it was initially unclear if we'll be able to get a reasonable number of attendees interested at all, or not. And organizing an event with venue and talks for multiple days if in the end only 10 people attend would have been a lot of effort and financial risk. But now that we know there are interested folks, we can definitely think of a multiple day event next time
  • Signs indicating venue details on the last meters. I agree, this cold have been better. The address of the venue was published, but we could have had some signs/posters at the door pointing you to the right meeting room inside the venue. Sorry for that.
  • Better internet connectivity. This is a double-edged sword. Of course we want our audience to be primarily focused on the talks and not distracted :P I would hope that most people are able to survive a one day event without good connectivity, but for sure we will have to improve in case of a multiple-day event in the future

In terms of my requests to the attendees, I only have one

  • Participate in the discussions on the schedule/programme while it is still possible to influence it. When we started to put together the programme, I posted about it on the openbsc mailing list and invited feedback. Still, most people seem to have missed the time window during which talks could have been submitted and the schedule still influenced before finalizing it
  • Register in time. We have had almost no registrations until about two weeks ahead of the event (and I was considering to cancel it), and then suddenly were sold out in the week ahead of the event. We've had people who first booked their tickets, only to learn that the tickets were sold out. I guess we will introduce early bird pricing and add a very expensive last minute ticket option next year in order to increase motivation to register early and thus give us flexibility regarding venue planning.

Thanks again to everyone involved in OsmoCon 2017!

Ok, now, all of you who missed the event: Go to https://media.ccc.de/c/osmocon17 and check out the recordings. Have fun!

Things you find when using SCTP on Linux

Observations on SCTP and Linux

When I was still doing Linux kernel work with netfilter/iptables in the early 2000's, I was somebody who actually regularly had a look at the new RFCs that came out. So I saw the SCTP RFCs, SIGTRAN RFCs, SIP and RTP, etc. all released during those years. I was quite happy to see that for new protocols like SCTP and later DCCP, Linux quickly received a mainline implementation.

Now most people won't have used SCTP so far, but it is a protocol used as transport layer in a lot of telecom protocols for more than a decade now. Virtually all protocols that have traditionally been spoken over time-division multiplex E1/T1 links have been migrated over to SCTP based protocol stackings.

Working on various Open Source telecom related projects, i of course come into contact with SCTP every so often. Particularly some years back when implementing the Erlang SIGTAN code in erlang/osmo_ss7 and most recently now with the introduction of libosmo-sigtran with its OsmoSTP, both part of the libosmo-sccp repository.

I've also hard to work with various proprietary telecom equipment over the years. Whether that's some eNodeB hardware from a large brand telecom supplier, or whether it's a MSC of some other vendor. And they all had one thing in common: Nobody seemed to use the Linux kernel SCTP code. They all used proprietary implementations in userspace, using RAW sockets on the kernel interface.

I always found this quite odd, knowing that this is the route that you have to take on proprietary OSs without native SCTP support, such as Windows. But on Linux? Why? Based on rumors, people find the Linux SCTP implementation not mature enough, but hard evidence is hard to come by.

As much as it pains me to say this, the kind of Linux SCTP bugs I have seen within the scope of our work on Osmocom seem to hint that there is at least some truth to this (see e.g. https://bugzilla.redhat.com/show_bug.cgi?id=1308360 or https://bugzilla.redhat.com/show_bug.cgi?id=1308362).

Sure, software always has bugs and will have bugs. But we at Osmocom are 10-15 years "late" with our implementations of higher-layer protocols compared to what the mainstream telecom industry does. So if we find something, and we find it even already during R&D of some userspace code, not even under load or in production, then that seems a bit unsettling.

One would have expected, with all their market power and plenty of Linux-based devices in the telecom sphere, why did none of those large telecom suppliers invest in improving the mainline Linux SCTP code? I mean, they all use UDP and TCP of the kernel, so it works for most of the other network protocols in the kernel, but why not for SCTP? I guess it comes back to the fundamental lack of understanding how open source development works. That it is something that the given industry/user base must invest in jointly.

The leatest discovered bug

During the last months, I have been implementing SCCP, SUA, M3UA and OsmoSTP (A Signal Transfer Point). They were required for an effort to add 3GPP compliant A-over-IP to OsmoBSC and OsmoMSC.

For quite some time I was seeing some erratic behavior when at some point the STP would not receive/process a given message sent by one of the clients (ASPs) connected. I tried to ignore the problem initially until the code matured more and more, but the problems remained.

It became even more obvious when using Michael Tuexen's m3ua-testtool, where sometimes even the most basic test cases consisting of sending + receiving a single pair of messages like ASPUP -> ASPUP_ACK was failing. And when the test case was re-tried, the problem often disappeared.

Also, whenever I tried to observe what was happening by meas of strace, the problem would disappear completely and never re-appear until strace was detached.

Of course, given that I've written several thousands of lines of new code, it was clear to me that the bug must be in my code. Yesterday I was finally prepare to accept that it might actually be a Linux SCTP bug. Not being able to reproduce that problem on a FreeBSD VM also pointed clearly into this direction.

Now I could simply have collected some information and filed a bug report (which some kernel hackers at RedHat have thankfully invited me to do!), but I thought my use case was too complex. You would have to compile a dozen of different Osmocom libraries, configure the STP, run the scheme-language m3ua-testtool in guile, etc. - I guess nobody would have bothered to go that far.

So today I tried to implement a test case that reproduced the problem in plain C, without any external dependencies. And for many hours, I couldn't make the bug to show up. I tried to be as close as possible to what was happening in OsmoSTP: I used non-blocking mode on client and server, used the SCTP_NODELAY socket option, used the sctp_rcvmsg() library wrapper to receive events, but the bug was not reproducible.

Some hours later, it became clear that there was one setsockopt() in OsmoSTP (actually, libosmo-netif) which enabled all existing SCTP events. I did this at the time to make sure OsmoSTP has the maximum insight possible into what's happening on the SCTP transport layer, such as address fail-overs and the like.

As it turned out, adding that setsockopt for SCTP_FLAGS to my test code made the problem reproducible. After playing around which of the flags, it seems that enabling the SENDER_DRY_EVENT flag makes the bug appear.

You can find my detailed report about this issue in https://bugzilla.redhat.com/show_bug.cgi?id=1442784 and a program to reproduce the issue at http://people.osmocom.org/laforge/sctp-nonblock/sctp-dry-event.c

Inside the Osmocom world, luckily we can live without the SENDER_DRY_EVENT and a corresponding work-around has been submitted and merged as https://gerrit.osmocom.org/#/c/2386/

With that work-around in place, suddenly all the m3ua-testtool and sua-testtool test cases are reliably green (PASSED) and OsmoSTP works more smoothly, too.

What do we learn from this?

Free Software in the Telecom sphere is getting too little attention. This is true even those small portions of telecom relevant protocols that ended up in the kernel like SCTP or more recently the GTP module I co-authored. They are getting too little attention in development, even more lack of attention in maintenance, and people seem to focus more on not using it, rather than fixing and maintaining what is there.

It makes me really sad to see this. Telecoms is such a massive industry, with billions upon billions of revenue for the classic telecom equipment vendors. Surely, they would be able to co-invest in some basic infrastructure like proper and reliable testing / continuous integration for SCTP. More recently, we see millions and more millions of VC cash burned by buzzword-flinging companies doing "NFV" and "SDN". But then rather reimplement network stacks in userspace than to fix, complete and test those little telecom infrastructure components which we have so far, like the SCTP protocol :(

Where are the contributions to open source telecom parts from Ericsson, Nokia (former NSN), Huawei and the like? I'm not even dreaming about the actual applications / network elements, but merely the maintenance of something as basic as SCTP. To be fair, Motorola was involved early on in the Linux SCTP code, and Huawei contributed a long series of fixes in 2013/2014. But that's not the kind of long-term maintenance contribution that one would normally expect from the primary interest group in SCTP.

Finally, let me thank to the Linux SCTP maintainers. I'm not complaining about them! They're doing a great job, given the arcane code base and the fact that they are not working for a company that has SCTP based products as their core business. I'm sure the would love more support and contributions from the Telecom world, too.

SIGTRAN/SS7 stack in libosmo-sigtran merged to master

As I blogged in my blog post in Fabruary, I was working towards a more fully-featured SIGTRAN stack in the Osmocom (C-language) universe.

The trigger for this is the support of 3GPP compliant AoIP (with a BSSAP/SCCP/M3UA/SCTP protocol stacking), but it is of much more general nature.

The code has finally matured in my development branch(es) and is now ready for mainline inclusion. It's a series of about 77 (!) patches, some of which already are the squashed results of many more incremental development steps.

The result is as follows:

  • General SS7 core functions maintaining links, linksets and routes
  • xUA functionality for the various User Adaptations (currently SUA and M3UA supported)
    • MTP User SAP according to ITU-T Q.701 (using osmo_prim)
    • management of application servers (AS)
    • management of application server processes (ASP)
    • ASP-SM and ASP-TM state machine for ASP, AS-State Machine (using osmo_fsm)
    • server (SG) and client (ASP) side implementation
    • validated against ETSI TS 102 381 (by means of Michael Tuexen's m3ua-testtool)
    • support for dynamic registration via RKM (routing key management)
    • osmo-stp binary that can be used as Signal Transfer Point, with the usual "Cisco-style" command-line interface that all Osmocom telecom software has.
  • SCCP implementation, with strong focus on Connection Oriented SCCP (as that's what the A interface uses).
    • osmo_fsm based state machine for SCCP connection, both incoming and outgoing
    • SCCP User SAP according to ITU-T Q.711 (osmo_prim based)
    • Interfaces with underlying SS7 stack via MTP User SAP (osmo_prim based)
    • Support for SCCP Class 0 (unit data) and Class 2 (connection oriented)
    • All SCCP + SUA Address formats (Global Title, SSN, PC, IPv4 Address)
    • SCCP and SUA share one implementation, where SCCP messages are transcoded into SUA before processing, and re-encoded into SCCP after processing, as needed.

I have already done experimental OsmoMSC and OsmoHNB-GW over to libosmo-sigtran. They're now all just M3UA clients (ASPs) which connect to osmo-stp to exchange SCCP messages back and for the between them.

What's next on the agenda is to

  • finish my incomplete hacks to introduce IPA/SCCPlite as an alternative to SUA and M3UA (for backwards compatibility)
  • port over OsmoBSC to the SCCP User SAP of libosmo-sigtran
    • validate with SSCPlite lower layer against existing SCCPlite MSCs
  • implement BSSAP / A-interface procedures in OsmoMSC, on top of the SCCP-User SAP.

If those steps are complete, we will have a single OsmoMSC that can talk both IuCS to the HNB-GW (or RNCs) for 3G/3.5G as well as AoIP towards OsmoBSC. We will then have fully SIGTRAN-enabled the full Osmocom stack, and are all on track to bury the OsmoNITB that was devoid of such interfaces.

If any reader is interested in interoperability testing with other implementations, either on M3UA or on SCCP or even on A or Iu interface level, please contact me by e-mail.

OsmoCon 2017 Updates: Travel Grants and Schedule

/images/osmocon.png

April 21st is approaching fast, so here some updates. I'm particularly happy that we now have travel grants available. So if the travel expenses were preventing you from attending so far: This excuse is no longer valid!

Get your ticket now, before it is too late. There's a limited number of seats available.

OsmoCon 2017 Schedule

The list of talks for OsmoCon 2017 has been available for quite some weeks, but today we finally published the first actual schedule.

As you can see, the day is fully packed with talks about Osmocom cellular infrastructure projects. We had to cut some talk slots short (30min instead of 45min), but I'm confident that it is good to cover a wider range of topics, while at the same time avoiding fragmenting the audience with multiple tracks.

OsmoCon 2017 Travel Grants

We are happy to announce that we have received donations to permit for providing travel grants!

This means that any attendee who is otherwise not able to cover their travel to OsmoCon 2017 (e.g. because their interest in Osmocom is not related to their work, or because their employer doesn't pay the travel expenses) can now apply for such a travel grant.

For more details see OsmoCon 2017 Travel Grants and/or contact osmocon2017@sysmocom.de.

OsmoCon 2017 Social Event

Tech Talks are nice and fine, but what many people enjoy even more at conferences is the informal networking combined with good food. For this, we have the social event at night, which is open to all attendees.

See more details about it at OsmoCon 2017 Social Event.

Upcoming v3 of Open Hardware miniPCIe WWAN modem USB breakout board

Back in October 2016 I designed a small open hardware breakout board for WWAN modems in mPCIe form-factor. I was thinking some other people might be interested in this, and indeed, the first manufacturing batch is already sold out by now.

Instead of ordering more of the old (v2) design, I decided to do some improvements in the next version:

  • add mounting holes so the PCB can be mounted via M3 screws
  • add U.FL and SMA sockets, so the modems are connected via a short U.FL to U.FL cable, and external antennas or other RF components can be attached via SMA. This provides strain relief for the external antenna or cabling and avoids tearing off any of the current loose U.FL to SMA pigtails
  • flip the SIM slot to the top side of the PCB, so it can be accessed even after mounting the board to some base plate or enclosure via the mounting holes
  • more meaningful labeling of the silk screen, including the purpose of the jumpers and the input voltage.

A software rendering of the resulting v3 PCB design files that I just sent for production looks like this:

/images/mpcie-breakout-v3-pcb-rendering.png

Like before, the design of the board (including schematics and PCB layout design files) is available as open hardware under CC-BY-SA license terms. For more information see http://osmocom.org/projects/mpcie-breakout/wiki

It will take some expected three weeks until I'll see the first assembled boards.

I'm also planning to do a M.2 / NGFF version of it, but haven't found the time to get around doing it so far.

Osmocom - personal thoughts

As I just wrote in my post about TelcoSecDay, I sometimes worry about the choices I made with Osmocom, particularly when I see all the great stuff people doing in fields that I previously was working in, such as applied IT security as well as Linux Kernel development.

History

When people like Dieter, Holger and I started to play with what later became OpenBSC, it was just for fun. A challenge to master. A closed world to break open and which to attack with the tools, the mindset and the values that we brought with us.

Later, Holger and I started to do freelance development for commercial users of Osmocom (initially basically only OpenBSC, but then OsmoSGSN, OsmoBSC, OsmoBTS, OsmoPCU and all the other bits on the infrastructure side). This lead to the creation of sysmocom in 2011, and ever since we are trying to use revenue from hardware sales as well as development contracts to subsidize and grow the Osmocom projects. We're investing most of our earnings directly into more staff that in turn works on Osmocom related projects.

NOTE

It's important to draw the distinction betewen the Osmocom cellular infrastructure projects which are mostly driven by commercial users and sysmocom these days, and all the many other pure juts-for-fun community projects under the Osmocom umbrella, like OsmocomTETRA, OsmocomGMR, rtl-sdr, etc. I'm focussing only on the cellular infrastructure projects, as they are in the center of my life during the past 6+ years.

In order to do this, I basically gave up my previous career[s] in IT security and Linux kernel development (as well as put things like gpl-violations.org on hold). This is a big price to pay for crating more FOSS in the mobile communications world, and sometimes I'm a bit melancholic about the "old days" before.

Financial wealth is clearly not my primary motivation, but let me be honest: I could have easily earned a shitload of money continuing to do freelance Linux kernel development, IT security or related consulting. There's a lot of demand for related skills, particularly with some experience and reputation attached. But I decided against it, and worked several years without a salary (or almost none) on Osmocom related stuff [as did Holger].

But then, even with all the sacrifices made, and the amount of revenue we can direct from sysmocom into Osmocom development: The complexity of cellular infrastructure vs. the amount of funding and resources is always only a fraction of what one would normally want to have to do a proper implementation. So it's constant resource shortage, combined with lots of unpaid work on those areas that are on the immediate short-term feature list of customers, and that nobody else in the community feels like he wants to work on. And that can be a bit frustrating at times.

Is it worth it?

So after 7 years of OpenBSC, OsmocomBB and all the related projects, I'm sometimes asking myself whether it has been worth the effort, and whether it was the right choice.

It was right from the point that cellular technology is still an area that's obscure and unknown to many, and that has very little FOSS (though Improving!). At the same time, cellular networks are becoming more and more essential to many users and applications. So on an abstract level, I think that every step in the direction of FOSS for cellular is as urgently needed as before, and we have had quite some success in implementing many different protocols and network elements. Unfortunately, in most cases incompletely, as the amount of funding and/or resources were always extremely limited.

Satisfaction/Happiness

On the other hand, when it comes to metrics such as personal satisfaction or professional pride, I'm not very happy or satisfied. The community remains small, the commercial interest remains limited, and as opposed to the Linux world, most players have a complete lack of understanding that FOSS is not a one-way road, but that it is important for all stakeholders to contribute to the development in terms of development resources.

Project success?

I think a collaborative development project (which to me is what FOSS is about) is only then truly successful, if its success is not related to a single individual, a single small group of individuals or a single entity (company). And no matter how much I would like the above to be the case, it is not true for the Osmocom cellular infrastructure projects. Take away Holger and me, or take away sysmocom, and I think it would be pretty much dead. And I don't think I'm exaggerating here. This makes me sad, and after all these years, and after knowing quite a number of commercial players using our software, I would have hoped that the project rests on many more shoulders by now.

This is not to belittle the efforts of all the people contributing to it, whether the team of developers at sysmocom, whether those in the community that still work on it 'just for fun', or whether those commercial users that contract sysmocom for some of the work we do. Also, there are known and unknown donors/funders, like the NLnet foundation for some parts of the work. Thanks to all of you, and clearly we wouldn't be where we are now without all of that!

But I feel it's not sufficient for the overall scope, and it's not [yet] sustainable at this point. We need more support from all sides, particularly those not currently contributing. From vendors of BTSs and related equipment that use Osmocom components. From operators that use it. From individuals. From academia.

Yes, we're making progress. I'm happy about new developments like the Iu and Iuh support, the OsmoHLR/VLR split and 2G/3G authentication that Neels just blogged about. And there's progress on the SIMtrace2 firmware with card emulation and MITM, just as well as there's progress on libosmo-sigtran (with a more complete SUA, M3UA and connection-oriented SCCP stack), etc.

But there are too little people working on this, and those people are mostly coming from one particular corner, while most of the [commercial] users do not contribute the way you would expect them to contribute in collaborative FOSS projects. You can argue that most people in the Linux world also don't contribute, but then the large commercial beneficiaries (like the chipset and hardware makers) mostly do, as are the large commercial users.

All in all, I have the feeling that Osmocom is as important as it ever was, but it's not grown up yet to really walk on its own feet. It may be able to crawl, though ;)

So for now, don't panic. I'm not suffering from burn-out, mid-life crisis and I don't plan on any big changes of where I put my energy: It will continue to be Osmocom. But I also think we have to have a more open discussion with everyone on how to move beyond the current situation. There's no point in staying quiet about it, or to claim that everything is fine the way it is. We need more commitment. Not from the people already actively involved, but from those who are not [yet].

If that doesn't happen in the next let's say 1-2 years, I think it's fair that I might seriously re-consider in which field and in which way I'd like to dedicate my [I would think considerable] productive energy and focus.

Returning from TelcoSecDay 2017 / General Musings

I'm just on my way back from the Telecom Security Day 2017 <https://www.troopers.de/troopers17/telco-sec-day/>, which is an invitation-only event about telecom security issues hosted by ERNW back-to-back with their Troopers 2017 <https://www.troopers.de/troopers17/> conference.

I've been presenting at TelcoSecDay in previous years and hence was again invited to join (as attendee). The event has really gained quite some traction. Where early on you could find lots of IT security / hacker crowds, the number of participants from the operator (and to smaller extent also equipment maker) industry has been growing.

The quality of talks was great, and I enjoyed meeting various familiar faces. It's just a pity that it's only a single day - plus I had to head back to Berlin still today so I had to skip the dinner + social event.

When attending events like this, and seeing the interesting hacks that people are working on, it pains me a bit that I haven't really been doing much security work in recent years. netfilter/iptables was at least somewhat security related. My work on OpenPCD / librfid was clearly RFID security oriented, as was the work on airprobe, OsmocomTETRA, or even the EasyCard payment system hack

I have the same feeling when attending Linux kernel development related events. I have very fond memories of working in both fields, and it was a lot of fun. Also, to be honest, I believe that the work in Linux kernel land and the general IT security research was/is appreciated much more than the endless months and years I'm now spending my time with improving and extending the Osmocom cellular infrastructure stack.

Beyond the appreciation, it's also the fact that both the IT security and the Linux kernel communities are much larger. There are more people to learn from and learn with, to engage in discussions and ping-pong ideas. In Osmocom, the community is too small (and I have the feeling, it's actually shrinking), and in many areas it rather seems like I am the "ultimate resource" to ask, whether about 3GPP specs or about Osmocom code structure. What I'm missing is the feeling of being part of a bigger community. So in essence, my current role in the "Open Source Cellular" corner can be a very lonely one.

But hey, I don't want to sound more depressed than I am, this was supposed to be a post about TelcoSecDay. It just happens that attending IT Security and/or Linux Kernel events makes me somewhat gloomy for the above-mentioned reasons.

Meanwhile, if you have some interesting projcets/ideas at the border between cellular protocols/systems and security, I'd of course love to hear if there's some way to get my hands dirty in that area again :)

VMware becomes gold member of Linux Foundation: And what about the GPL?

As we can read in recent news, VMware has become a gold member of the Linux foundation. That causes - to say the least - very mixed feelings to me.

One thing to keep in mind: The Linux Foundation is an industry association, it exists to act in the joint interest of it's paying members. It is not a charity, and it does not act for the public good. I know and respect that, while some people sometimes appear to be confused about its function.

However, allowing an entity like VMware to join, despite their many years long disrespect for the most basic principles of the FOSS Community (such as: Following the GPL and its copyleft principle), really is hard to understand and accept.

I wouldn't have any issue if VMware would (prior to joining LF) have said: Ok, we had some bad policies in the past, but now we fully comply with the license of the Linux kernel, and we release all derivative/collective works in source code. This would be a positive spin: Acknowledge past issues, resolve the issues, become clean and then publicly underlining your support of Linux by (among other things) joining the Linux Foundation. I'm not one to hold grudges against people who accept their past mistakes, fix the presence and then move on. But no, they haven't fixed any issues.

They are having one of the worst track records in terms of intentional GPL compliance issues for many years, showing outright disrespect for Linux, the GPL and ultimately the rights of the Linux developers, not resolving those issues and at the same time joining the Linux Foundation? What kind of message sends that?

It sends the following messages:

  • you can abuse Linux, the GPL and copyleft while still being accepted amidst the Linux Foundation Members
  • it means the Linux Foundations has no ethical concerns whatsoever about accepting such entities without previously asking them to become clean
  • it also means that VMware has still not understood that Linux and FOSS is about your actions, particularly the kind of choices you make how to technically work with the community, and not against it.

So all in all, I think this move has seriously damaged the image of both entities involved. I wouldn't have expected different of VMware, but I would have hoped the Linux Foundation had some form of standards as to which entities they permit amongst their ranks. I guess I was being overly naive :(

It's a slap in the face of every developer who writes code not because he gets paid, but because it is rewarding to know that copyleft will continue to ensure the freedom of related code.

UPDATE (March 8, 2017):
  I was mistaken in my original post in that VMware didn't just join, but was a Linux Foundation member already before, it is "just" their upgrade from silver to gold that made the news recently. I stand corrected. Still doesn't make it any better that the are involved inside LF while engaging in stepping over the lines of license compliance.
UPDATE2 (March 8, 2017):
  As some people pointed out, there is no verdict against VMware. Yes, that's true. But the mere fact that they rather distribute derivative works of GPL licensed software and take this to court with an armada of lawyers (instead of simply complying with the license like everyone else) is sad enough. By the time there will be a final verdict, the product is EOL. That's probably their strategy to begin with :/

Gory details of USIM authentication sequence numbers

I always though I understood UMTS AKA (authentication and key agreement), including the re-synchronization procedure. It's been years since I wrote tools like osmo-sim-auth which you can use to perform UMTS AKA with a SIM card inserted into a PC reader, i.e. simulate what happens between the AUC (authentication center) in a network and the USIM card.

However, it is only now as the sysmocom team works on 3G support of the dedicated OsmoHLR (outside of OsmoNITB!), that I seem to understand all the nasty little details.

I always thought for re-synchronization it is sufficient to simply increment the SQN (sequence number). It turns out, it isn't as there is a MSB-portion called SEQ and a lower-bit portion called IND, used for some fancy array indexing scheme of buckets of highest-used-SEQ within that IND bucket.

If you're interested in all the dirty details and associated spec references (the always hide the important parts in some Annex) see the discussion between Neels and me in Osmocom redmine issue 1965.

GTA04 project halts GTA04A5 due to OMAP3 PoP soldering issues

For those of you who don't know what the tinkerphones/OpenPhoenux GTA04 is: It is a 'professional hobbyist' hardware project (with at least public schematics, even if not open hardware in the sense that editable schematics and PCB design files are published) creating updated mainboards that can be used to upgrade Openmoko phones. They fit into the same enclosure and can use the same display/speaker/microphone.

What the GTA04 guys have been doing for many years is close to a miracle anyway: Trying to build a modern-day smartphone in low quantities, using off-the-shelf components available in those low quantities, and without a large company with its associated financial backing.

Smartphones are complex because they are highly integrated devices. A seemingly unlimited amount of components is squeezed in the tiniest form-factors. This leads to complex circuit boards with many layers that take a lot of effort to design, and are expensive to build in low quantities. The fine-pitch components mandated by the integration density is another issue.

Building the original GTA01 (Neo1937) and GTA02 (FreeRunner) devices at Openmoko, Inc. must seem like a piece of cake compared to what the GTA04 guys are up to. We had a team of engineers that were familiar at last with feature phone design before, and we had the backing of a consumer electronics company with all its manufacturing resources and expertise.

Nevertheless, a small group of people around Dr. Nikolaus Schaller has been pushing the limits of what you can do in a small for fun project, and the have my utmost respect. Well done!

Unfortunately, there are bad news. Manufacturing of their latest generation of phones (GTA04A5) has been stopped due to massive soldering problems with the TI OMAP3 package-on-package (PoP). Those PoPs are basically "RAM chip soldered onto the CPU, and the stack of both soldered to the PCB". This is used to save PCB footprint and to avoid having to route tons of extra (sensitive, matched) traces between the SDRAM and the CPU.

According to the mailing list posts, it seems to be incredibly difficult to solder the PoP stack due to the way TI has designed the packaging of the DM3730. If you want more gory details, see this post and yet another post.

It is very sad to see that what appears to be bad design choices at TI are going to bring the GTA04 project to a halt. The financial hit by having only 33% yield is already more than the small community can take, let alone unused parts that are now in stock or even thinking about further experiments related to the manufacturability of those chips.

If there's anyone with hands-on manufacturing experience on the DM3730 (or similar) TI PoP reading this: Please reach out to the GTA04 guys and see if there's anything that can be done to help them.

UPDATE (March 8, 2017):
  In an earlier post I was asserting that the GTA04 is open hardware (which I actually believed up to that point) until some readers have pointed out to me that it isn't. It's sad it isn't, but still it has my sympathies.

Manual testing of Linux Kernel GTP module

In May 2016 we got the GTP-U tunnel encapsulation/decapsulation module developed by Pablo Neira, Andreas Schultz and myself merged into the 4.8.0 mainline kernel.

During the second half of 2016, the code basically stayed untouched. In early 2017, several patch series of (at least) three authors have been published on the netdev mailing list for review and merge.

This poses the very valid question on how do we test those (sometimes quite intrusive) changes. Setting up a complete cellular network with either GPRS/EGPRS or even UMTS/HSPA is possible using OsmoSGSN and related Osmocom components. But it's of course a luxury that not many Linux kernel networking hackers have, as it involves the availability of a supported GSM BTS or UMTS hNodeB. And even if that is available, there's still the issue of having a spectrum license, or a wired setup with coaxial cable.

So as part of the recent discussions on netdev, I tested and described a minimal test setup using libgtpnl, OpenGGSN and sgsnemu.

This setup will start a mobile station + SGSN emulator inside a Linux network namespace, which talks GTP-C to OpenGGSN on the host, as well as GTP-U to the Linux kernel GTP-U implementation.

In case you're interested, feel free to check the following wiki page: https://osmocom.org/projects/linux-kernel-gtp-u/wiki/Basic_Testing

This is of course just for manual testing, and for functional (not performance) testing only. It would be great if somebody would pick up on my recent mail containing some suggestions about an automatic regression testing setup for the kernel GTP-U code. I have way too many spare-time projects in desperate need of some attention to work on this myself. And unfortunately, none of the telecom operators (who are the ones benefiting most from a Free Software accelerated GTP-U implementation) seems to be interested in at least co-funding or otherwise contributing to this effort :/

Cellular re-broadcast over satellite

I've recently attended a seminar that (among other topics) also covered RF interference hunting. The speaker was talking about various real-world cases of RF interference and illustrating them in detail.

Of course everyone who has any interest in RF or cellular will know about fundamental issues of radio frequency interference. To the biggest part, you have

  • cells of the same operator interfering with each other due to too frequent frequency re-use, adjacent channel interference, etc.
  • cells of different operators interfering with each other due to intermodulation products and the like
  • cells interfering with cable TV, terrestrial TV
  • DECT interfering with cells
  • cells or microwave links interfering with SAT-TV reception
  • all types of general EMC problems

But what the speaker of this seminar covered was actually a cellular base-station being re-broadcast all over Europe via a commercial satellite (!).

It is a well-known fact that most satellites in the sky are basically just "bent pipes", i.e. they consist of a RF receiver on one frequency, a mixer to shift the frequency, and a power amplifier. So basically whatever is sent up on one frequency to the satellite gets re-transmitted back down to earth on another frequency. This is abused by "satellite hijacking" or "transponder hijacking" and has been covered for decades in various publications.

Ok, but how does cellular relate to this? Well, apparently some people are running VSAT terminals (bi-directional satellite terminals) with improperly shielded or broken cables/connectors. In that case, the RF emitted from a nearby cellular base station leaks into that cable, and will get amplified + up-converted by the block up-converter of that VSAT terminal.

The bent-pipe satellite subsequently picks this signal up and re-transmits it all over its coverage area!

I've tried to find some public documents about this, an there's surprisingly little public information about this phenomenon.

However, I could find a slide set from SES, presented at a Satellite Interference Reduction Group: Identifying Rebroadcast (GSM)

It describes a surprisingly manual and low-tech approach at hunting down the source of the interference by using an old nokia net-monitor phone to display the MCC/MNC/LAC/CID of the cell. Even in 2011 there were already open source projects such as airprobe that could have done the job based on sampled IF data. And I'm not even starting to consider proprietary tools.

It should be relatively simple to have a SDR that you can tune to a given satellite transponder, and which then would look for any GSM/UMTS/LTE carrier within its spectrum and dump their identities in a fully automatic way.

But then, maybe it really doesn't happen all that often after all to rectify such a development...

Towards a real SIGTRAN/SS7 stack in libosmo-sigtran

In the good old days ever since the late 1980ies - and a surprising amount even still today - telecom signaling traffic is still carried over circuit-switched SS7 with its TDM lines as physical layer, and not an IP/Ethernet based transport.

When Holger first created OsmoBSC, the BSC-only version of OpenBSC some 7-8 years ago, he needed to implement a minimal subset of SCCP wrapped in TCP called SCCP Lite. This was due to the simple fact that the MSC to which it should operate implemented this non-standard protocol stacking that was developed + deployed before the IETF SIGTRAN WG specified M3UA or SUA came around. But even after those were specified in 2004, the 3GPP didn't specify how to carry A over IP in a standard way until the end of 2008, when a first A interface over IP study was released.

As time passese, more modern MSCs of course still implement classic circuit-switched SS7, but appear to have dropped SCCPlite in favor of real AoIP as specified by 3GPP meanwhile. So it's time to add this to the osmocom universe and OsmoBSC.

A couple of years ago (2010-2013) implemented both classic SS7 (MTP2/MTP3/SCCP) as well as SIGTRAN stackings (M2PA/M2UA/M3UA/SUA in Erlang. The result has been used in some production deployments, but only with a relatively limited feature set. Unfortunately, this code has nto received any contributions in the time since, and I have to say that as an open source community project, it has failed. Also, while Erlang might be fine for core network equipment, running it on a BSC really is overkill. Keep in miond that we often run OpenBSC on really small ARM926EJS based embedded systems, much more resource constrained than any single smartphone during the late decade.

In the meantime (2015/2016) we also implemented some minimal SUA support for interfacing with UMTS femto/small cells via Iuh (see OsmoHNBGW).

So in order to proceed to implement the required SCCP-over-M3UA-over-SCTP stacking, I originally thought well, take Holgers old SCCP code, remove it from the IPA multiplex below, stack it on top of a new M3UA codebase that is copied partially from SUA.

However, this falls short of the goals in several ways:

  • The application shouldn't care whether it runs on top of SUA or SCCP, it should use a unified interface towards the SCCP Provider. OsmoHNBGW and the SUA code already introduce such an interface baed on the SCCP-User-SAP implemented using Osmocom primitives (osmo_prim). However, the old OsmoBSC/SCCPlite code doesn't have such abstraction.
  • The code should be modular and reusable for other SIGTRAN stackings as required in the future

So I found myself sketching out what needs to be done and I ended up pretty much with a re-implementation of large parts. Not quite fun, but definitely worth it.

The strategy is:

And then finally stack all those bits on top of each other, rendering a fairly clean and modern implementation that can be used with the IuCS of the virtually unmodified OsmmoHNBGW, OsmoCSCN and OsmoSGSN for testing.

Next steps in the direction of the AoIP are:

  • Implementation of the MTP-SAP based on the IPA transport
  • Binding the new SCCP code on top of that
  • Converting OsmoBSC code base to use the SCCP-User-SAP for its signaling connection

From that point onwards, OsmoBSC doesn't care anymore whether it transports the BSSAP/BSSMAP messages of the A interface over SCCP/IPA/TCP/IP (SCCPlite) SCCP/M3UA/SCTP/IP (3GPP AoIP), or even something like SUA/SCTP/IP.

However, the 3GPP AoIP specs (unlike SCCPlite) actually modify the BSSAP/BSSMAP payload. Rather than using Circuit Identifier Codes and then mapping the CICs to UDP ports based on some secret conventions, they actually encapsulate the IP address and UDP port information for the RTP streams. This is of course the cleaner and more flexible approach, but it means we'll have to do some further changes inside the actual BSC code to accommodate this.

Testing (not only) telecom protocols

When implementing any kind of communication protocol, one always dreams of some existing test suite that one can simply run against the implementation to check if it performs correct in at least those use cases that matter to the given application.

Of course in the real world, there rarely are protocols where this is true. If test specifications exist at all, they are often just very abstract texts for human consumption that you as the reader should implement yourself.

For some (by far not all) of the protocols found in cellular networks, every so often I have seen some formal/abstract machine-parseable test specifications. Sometimes it was TTCN-2, and sometimes TTCN-3.

If you haven't heard about TTCN-3, it is basically a way to create functional tests in an abstract description (textual + graphical), and then compile that into an actual executable tests suite that you can run against the implementation under test.

However, when I last did some research into this several years ago, I couldn't find any Free / Open Source tools to actually use those formally specified test suites. This is not a big surprise, as even much more fundamental tools for many telecom protocols are missing, such as good/complete ASN.1 compilers, or even CSN.1 compilers.

To my big surprise I now discovered that Ericsson had released their (formerly internal) TITAN TTCN3 Toolset as Free / Open Source Software under EPL 1.0. The project is even part of the Eclipse Foundation. Now I'm certainly not a friend of Java or Eclipse by all means, but well, for running tests I'd certainly not complain.

The project also doesn't seem like it was a one-time code-drop but seems very active with many repositories on gitub. For example for the core module, titan.core shows plenty of activity on an almost daily basis. Also, binary releases for a variety of distributions are made available. They even have a video showing the installation ;)

If you're curious about TTCN-3 and TITAN, Ericsson also have made available a great 200+ pages slide set about TTCN-3 and TITAN.

I haven't yet had time to play with it, but it definitely is rather high on my TODO list to try.

ETSI provides a couple of test suites in TTCN-3 for protocols like DIAMETER, GTP2-C, DMR, IPv6, S1AP, LTE-NAS, 6LoWPAN, SIP, and others at http://forge.etsi.org/websvn/ (It's also the first time I've seen that ETSI has a SVN server. Everyone else is using git these days, but yes, revision control systems rather than periodic ZIP files is definitely a big progress. They should do that for their reference codecs and ASN.1 files, too.

I'm not sure once I'll get around to it. Sadly, there is no TTCN-3 for SCCP, SUA, M3UA or any SIGTRAN related stuff, otherwise I would want to try it right away. But it definitely seems like a very interesting technology (and tool).

FOSDEM 2017

Last weekend I had the pleasure of attending FOSDEM 2017. For many years, it is probably the most exciting event exclusively on Free Software to attend every year.

My personal highlights (next to meeting plenty of old and new friends) in terms of the talks were:

I was attending but not so excited by Georg Greve's OpenPOWER talk. It was a great talk, and it is an important topic, but the engineer in me would have hoped for some actual beefy technical stuff. But well, I was just not the right audience. I had heard about OpenPOWER quite some time ago and have been following it from a distance.

The LoRaWAN talk couldn't have been any less technical, despite stating technical, political and cultural in the topic. But then, well, just recently 33C3 had the most exciting LoRa PHY Reverse Engineering Talk by Matt Knight.

Other talks whose recordings I still want to watch one of these days:

Osmocom Conference 2017 on April 21st

I'm very happy that in 2017, we will have the first ever technical conference on the Osmocom cellular infrastructure projects.

For many years, we have had a small, invitation only event by Osmocom developers for Osmocom developers called OsmoDevCon. This was fine for the early years of Osmocom, but during the last few years it became apparent that we also need a public event for our many users. Those range from commercial cellular operators to community based efforts like Rhizomatica, and of course include the many research/lab type users with whom we started.

So now we'll have the public OsmoCon on April 21st, back-to-back with the invitation-only OsmoDevcon from April 22nd through 23rd.

I'm hoping we can bring together a representative sample of our user base at OsmoCon 2017 in April. Looking forward to meet you all. I hope you're also curious to hear more from other users, and of course the development team.

Regards,
Harald