* it tries to stay as close to POSIX and other Unix APIs as possible
* you can actually have executable programs in the file system
* it contains a small interactive shell
* the changelog is verbose and releases are frequent
* there's a test suite
* there are already ports to other ARM7TDMI microcontrollers
* there is a small UI framework and the notion of drivers for SPI-
attached LCDs (with 1/2/4 bpp)
* it has tasks and threads, pre-emptive and with priorities
* it has posix message queues, which we could use for passing around
primitives between elements in the stack
* it can be used on Unix-like and Windows/Cygwin host OS
* it has its own scripts to generate toolchains, which means we
could possibly standardize on one of those toolchains
Of course, not everything is perfect
* there seems to be no writeable FS we can put in NOR flash
* it has no scripting language integration (like lua) yet
* i didn't find any memory allocator optimized for pools of objects
of the same size (like 'struct msgb' or the like). Something with
an API [not implementation!] of the SLAB/SLUB in Linux would probably
be a good start.
I've done some example compile runs for arm7, including the shell and
the graphics support (nx example). I end up with an object code size of
something like 70 kilobytes, which is pretty good!
So unless anyone raises major objections, I think we should move ahead
with Nuttx. Who is interested in working on the calypso port?
Let's use this list for coordinating the effort.
As for where to put the code: I already have a git-svn clone of Nuttx,
and will push that to a soon-to-be-created nuttx.git repository on
git.osmocom.org. The core calypso support (irq, uart, spi, etc.) should
all go in that tree. Meanwhile we will figure out how it would be
possibel to keep the gsm related 'application' code out-of-tree from
the nuttx code base.
Regards,
Harald
--
- Harald Welte <laforge(a)gnumonks.org> http://laforge.gnumonks.org/
============================================================================
"Privacy in residential applications is a desirable marketing option."
(ETSI EN 300 175-7 Ch. A6)
Sure, it would be a nice addition, but it's not something that I consider
extremely important. With regard to 'near future': I would say that in
something like six months the osmo-bts (BTS-side A-bis) code will have matured,
and is ready for an relaatively painless integration with OpenBTS.
I personally think the USRP hardware cost is still way too high, and I would
rather want to work on something that puts the financial entrance barrier to
private BTS ownership much lower.
Most of the people using OpenBSC today either use it commercially (and can
afford the nanoBTS units), or they use it private and either with a very
cheap second hand nanoBTS, or with a inexpensive BS-11. The recent work
on supporting the RBS2308 that can be found for < 1000 USD goes into the
same direction.
I think whatever hardware will be affordable to hackers will see OpenBSC
support - just as well as any hardware where we have a commercial customer
will get OpenBSC support.
> > This is where I don't get you. All that needs to be removed is the L3-to-SIP
> > bridge. It doesn't make the vast majority of OpenBTS code disappear,
> > and it does not render that latter part useless. A full-blown GSM network with
> > all its components brings a lot of complexity. The stand-alone OpenBTS is
> > much more simple. And why would you want all the complexity if you don't
> > need to interoperate with legacy GSM?
>
> Well, because the the osmocom-integrated version will be, before or
> later, more full-featured than OpenBTS standalone.
>
> Features such as multi-arfcn, handover, maybe GPRS/EDGE will be usable
> only jointly with Osmocom integration but not by the opensource OpenBTS
> standalone version.
If you use the USRP hardware (or any other SDR hardware), you cannot use
GPRS/EDGE whether you use Osmocom + OpenBTS or OpenBTS standalone. As for
hand-over, you may be right, but I don't know the OpenBTS plans here.
Multi-ARFCN: This is an aspect of the radio-modem. So again, on the same
hardware any OpenBTS/OpenBSC integration will not change this.
> Obviously the community will then use the OpenBTS/OpenBSC integration
> that would reach more features than just OpenBTS in the opensource edition.
well, but you loose the important 'simplicity' feature. Right now I doubt
there are that many people in our community who understand OpenBSC and the
GSM/GPRS network architecture enough to deploy a network (like the burning man
or CCC event networks) with it. We have close to zero documentation, and
unless you know GSM protocol details, you are lost. VoIP is much better
understood in the FOSS and Internet community!
> So the integrated code will grow while the "OpenBTS commercial code"
> will leave behind with less features and more buggy code (because less
> used).
you are making assumptions here. Do you have evidence or at least some
other indication that bug fixes are not being propagated from the commercial
to the free version?
> Osmocom and it's possible future changes to the market of GSM
> technologies could be defined as "the WikiLeaks of the GSM Industry" :-)
I think this is a very bad comparison. We do not leak any proprietary/secret
information. We just break the ignorance of the Free Software community to
ever implement any of those openly-specified protocols. Not different from
Free Software entering any other area of technology.
And while we're doing that, we of course also like to challenge the ridiculous
claims of hundred-man-year efforts that allegedly went into some proprietary
GSM protocol stack implementations, which are often claimed by the existing
carrier equipment industry.
Regards,
Harald
--
- Harald Welte <laforge(a)gnumonks.org> http://laforge.gnumonks.org/
============================================================================
"Privacy in residential applications is a desirable marketing option."
(ETSI EN 300 175-7 Ch. A6)
> Meanwhile, Andreas Eversberg has been working on a BTS-side A-bis implementation
> for the OsmocomBB-BTS (idea: using 2 heavily modified phones to run a
> simplistic BTS), and I have started to split that code out into a separate
> repository at http://cgit.osmocom.org/cgit/osmo-bts/
>
> This code should eventually be used with the OpenBTS, and potentially other
> BTS types, too.
That's cool!!!!
>
>> With that approach the 'GSM-um' interface would be a very simplified
>> module of the overall system and osmocom would completely replace
>> OpenBTS all-in-one project.
>
> This is where I don't get you. All that needs to be removed is the L3-to-SIP
> bridge. It doesn't make the vast majority of OpenBTS code disappear,
> and it does not render that latter part useless. A full-blown GSM network with
> all its components brings a lot of complexity. The stand-alone OpenBTS is
> much more simple. And why would you want all the complexity if you don't
> need to interoperate with legacy GSM?
Well, because the the osmocom-integrated version will be, before or
later, more full-featured than OpenBTS standalone.
Features such as multi-arfcn, handover, maybe GPRS/EDGE will be usable
only jointly with Osmocom integration but not by the opensource OpenBTS
standalone version.
Obviously the community will then use the OpenBTS/OpenBSC integration
that would reach more features than just OpenBTS in the opensource edition.
That means that in few times only the "integrated code" will works
better, because it will attract more user and will start getting used in
"production environment".
So the integrated code will grow while the "OpenBTS commercial code"
will leave behind with less features and more buggy code (because less
used).
That's why i just think that the destinity of OpenBTS is to integrate
(directly or just some piece) with OpenBSC, but doing that it will loose
several important value of the "OpenBTS commercial edition" and people
will start using what can be used for free instead of paying.
That's what usually happen within the opensource environment, before or
later.
It could reasonably happen also with that opensource gsm environment.
My comments was just consideration on this to stimulate the
considerations on this by the various project players.
I am just an opensource advocacy troll that like telephony stuff and
perceive very valuable the achievement of the hacking community in
opening a closed technology like GSM.
Osmocom and it's possible future changes to the market of GSM
technologies could be defined as "the WikiLeaks of the GSM Industry" :-)
-naif
p.s. i have no commercial interests of any kind in that stuff
all the powerfull eye-candy apps. But that takes processing power. So
SoC provider would separate processing on two cores, puting stack on
the other core. Since this other core do not demand any application
except PS, you would like to run some nice lightweight OS like eCos,
or similar that have good RT performances to assure timing
requirements for L1 and inter-CPU communication.
If there would be satisfying performance on one core, there would
certanly be interest to save money by rejecting the other. And to
figure out how to separate closed source, how to keep legacy RTOS and
RT apps, etc... And since more powerful cores are appearing, L4 comes
into play on big doors (not to mention that it's the worlds first
formally verified kernel).
BR,
Drasko
main_simtrace.bin, using dfu-util from http://dfu-util.gnumonks.org
--
- Harald Welte <laforge(a)gnumonks.org> http://laforge.gnumonks.org/
============================================================================
"Privacy in residential applications is a desirable marketing option."
(ETSI EN 300 175-7 Ch. A6)
patience" is a really good guess.
Let me explain how this works: In Shenzhen there is a huge electronics
area. Thousands of shops and companies, hundreds of thousands of people
working and trading there.
I have a small collection of pictures so you get the idea...
http://en.qi-hardware.com/wiki/Shenzhen_markets
(this stretches over an area of at least 1x1 km, with dozens of 8+ level
buildings, some higher like the 70-floor office tower :-))
Basically you can walk up to any PCB shop (there are at least 50 I would
say). I went to one I used before with 2 Sciphone Dream G2 boards,
and they accepted the job for 600 RMB (=ca. 90 USD). I got the pictures
4 days later. I got them as .bmp files, then I did some post-processing
to make nice horizontally aligned, contrast-enriched PNGs out of them,
and a big PDF too to easily flip through the layers (PDF readers tend
to be quite powerful and efficient in scaling and flipping, so this
seems to work well).
I am not an electronics guy, so I need feedback to do this kind of
work better in the future. For example, I don't know the exact names
of the layers. Can someone who knows what they are add subtitles
to the wiki? Copper layer, ground layer, via, whatever? (I just don't
know...) Or reply here and I'll annotate the wiki.
Anything else I should do to make this better next time?
This is all background info I have, one day I will convince them to
let me take some pictures of the actual work :-)
Wolfgang
\subsection{How to synchronize the GSM TDMA multiplex}
As part of the BCCH, the BTS not only sends the FCCH but also the
Synchronization CHannel (SCH). The Synchronization channel indicates the
current GSM time / frame number (skipping the 3 least significant bits).
By using this received GSM time and incrementing it every time the GSM bit-clock
timer wraps at the beginning of a new TDMA frame, the GSM time is synchronized.
Understanding the multiple layers of time multiplex such as the 26/51
multiframe, superframe and hyperframe, the L1 can multiplex and demultiplex all
the logical channels of GSM.
\section{Miscellaneous Topics}
\subsection{GPRS}
GPRS was the first packet switched extension to GSM. In fact, it is much more
its entirely own mobile network, independent of GSM. The only parts shared are
the GSM modulation scheme (GMSK) and time multiplex, in order to ensure peaceful
coexistence between them.
The L1 and L2 protocols are very different (and much more complex) than GSM.
So while the phone baseband hardware did not need any modifications for a basic
GPRS enabled phone, the software needed to be extended quite a lot.
\subsection{EDGE}
EDGE is a very small incremental step to GPRS. It reuses all of the time
multiplex and protocol stack, but introduces a new modulation: Offset
8-PSK instead of GMSK to increase the bandwidth that can be transmitted.
Offset 8-PSK is used (as opposed to simple 8-PSK) to avoid
zero-crossings in the modulator output.
So while the software modifications from GPRS to EDGE are minimal, the 8PSK
modulation scheme has a significant impact on the DSP, ABB and even RF
PA design.
\subsection{UMTS}
UMTS (sometimes called WCDMA) is an entirely separate cellular network
technology. Its physical layer, modulation schemes, encoding, frequency
bands, channel spacing are entirely different, as is the Layer1.
UMTS Layer2 has some resemblance to the GPRS Layer2.
UMTS Layer3 for Mobility Management and Call Control are very similar to GSM.
Given the vast physical layer and L1 differences, a UMTS phone hardware design
significantly differs from what has been described in this document.
Notwithstanding, all known commercial UMTS phone chipsets as of today still
include a full GSM modem in hardware and software to remain
backwards-compatible.
\subsection{Dual-SIM and Triple-SIM phones}
In recent years, a large number of so-called {\em Dual-SIM} or even {\em
Triple-SIM} phones have entered the market, particularly in China and other
parts of East Asia.
Those phones come in various flavours. Some of them simply have a multiplexer
that allows electrical switching between multiple SIM card slots. This is
similar to replacing the SIM card in a phone, just without the manual process
of mechanically removing/inserting the card. As a result, you can only use one
of the two SIMs at any time.
The more sophisticated Dual-SIM phones have two complete phones in one case. Yes,
that's right! They contain two full GSM phone chipsets, i.e. 2 antennas, 2 rf
frontends, 2 analog basebands, 2 digital basebands, ...
However, they use the same trick as smartphones: One of the two basebands does
not have keypad or display and is simply a GSM modem connected via serial line
to the other baseband processor.
So if a smartphone (as defined in this document) is a GSM modem connected to a
PDA in one case, a Dual-SIM phone is a GSM modem connected to a feature phone
in one case.
Triple-SIM phones often combine the two approaches, i.e. they contain two
complete GSM baseband chips, but three SIM slots that can be switched among
the base bands. Only two SIMs can be active at the same time.
\subsection{Powerful feature phones}
Feature phones are becoming more and more powerful. However, their
comparatively lower market price cannot afford a full-blown smartphone design
with its two independent processors and the associated design complexity.
Thus, more and more hardware peripherals are added to the only processor left
in the phone: The baseband processor. Such peripherals include sophisticated
camera interfaces, high-resolution color display controllers, TV output,
touchscreen controllers, audio and video codecs and even interfaces for mobile
TV reception.
However, all of those features are still implemented on a fairly weak ARM7 or
ARM9 CPU core (compared to ARM11 and Cortex-A8 in the smartphone market). They
also lack a real operating system and still run on top of a real-time
microkernel intended for much less complex systems. They almost always lack
any form of memory protection or multiple address spaces. This makes them
more prone to security issues as there is no privilege separation between
the GSM protocol stack and the applications, or between the applications
themselves.
\subsection{Security features}
There are several (sometimes conflicting) security requirements that
apply to mobile phones. Interestingly, the security features are
typically used to protect some industry interest against the interest of
the customer. There are very few security features in a phone that are
meant to protect the user or his interests.
\subsubsection{IMEI - The hardware serial number}
The International Mobile Equipment Identifier (IMEI) uniquely identifies
a GSM phone. It is a globally unique serial number which is programmed
into the phone non-volatile memory (Flash or EEPROM) during the
production process. There are no particular security features used to
store the IMEI. Once you are able to write to flash and have found it,
it can be changed.
\subsubsection{The SIM Card}
The SIM card is a cryptographic smart card that stores the secret key
used for authenticating the user to the GSM network (Ki). The Ki is
never released by the card, and as such copying (cloning) of the SIM
is prevented.
Furthermore, the SIM stores the International Mobile Subscriber Identity
(ISMI). The IMSI is not encrypted or protected in some way.
There is no security channel on the connection between the SIM card and
the baseband MCU. Furthermore, there is no way how the MCU can securely
identify/authenticate the SIM itself. Physical access to the SIM card
slot allows sniffing and/or modification of the communication between
MCU and SIM.
\subsubsection{SIM or Operator Locking}
GSM is an international standard. This ensures interoperability, i.e.
any phone can be used on any network.
However, in some cases, the vendors of a GSM phone want to restrict this
interoperability and lock a phone to one specific network, or even lock
it to a particular SIM.
Those locks are implemented by software only, i.e. the MCU software will
instruct the GSM protocol stack not to register with a network unless
its network operator code is a certain factory-programmed network number.
As such, techniques for circumventing those locks have become
commonplace. It's somewhat of an ongoing race between the phone makers
and the phone-unlockers. The industry invents ever more complex methods
of obfuscating their locks in the software, while the phone-unlockers
reverse engineer those bits for each and every phone model after some
time.
\subsubsection{DBB firmware signatures}
In order to protect the operator and phone manufacturers peculiar
business models based on SIM or operator locking, some vendors
extended their baseband software with cryptographic signatures. Only
if the correct signature is present in a software update, the bootloader
program will accept the new software.
However, there are more or less invasive hardware-related approaches in
circumventing those signature checks, such as hardware debugging
interfaces like JTAG, or replacing the external flash memory components.
More recently, GSM chipset vendors introduced features such as
hardware-assisted software signature checks. In this case a master key
hash might be present in DBB-internal fuses, together with a
signature-verifying boot loader in DBB-internal mask ROM. As the root
of the chain of trust is moving deeper into the hardware, it becomes
more difficult for anyone to make software modifications to the DBB.
Especially with tighter integration, where RAM and FLASH are no longer
present as discrete components but part of a multi-chip-package, the
number of options are becoming more limited.
On the other hand, an ever more complex baseband software stack is
opening up many more options for exploiting software vulnerabilities.
Given the lack of a proper/modern operating system with privilege
separation and virtual memory, such exploits immediately give away
full access to all aspects of the respective DBB.
\section{Personal rant on the closedness of the GSM industry}
The GSM industry is one of the most closed areas of computing that I've
encountered so far. It is very hard to get any hard technical
information out of them. All they like to spread is high-level
marketing information, but they're very reluctant when it comes down to
hard technical facts on their products.
If you want to build a phone, you need to buy a GSM chipset for your
product. There are only very few companies that offer such chipsets.
The classic suppliers are Infineon, Texas Instruments, ST/Ericsson, ADI
(now MediaTek) and Freescale.
The GSM handset products they sell are not generally available and
distributed like other electronic component they manufacture. If you
need a Microcontroller/SoC, a power management IC, a Wifi or Bluetooth
chip, RFID reader ASIC, you simply approach the respective distributors
and order them. You get your samples directly from Digikey.
This is impossible for GSM (or other cellphone) chipsets. For some
reason those chips are sold only to hand-picked manufacturers. If you
want to qualify, you have to subscribe to at least six-digit annual
purchasing quantities. And in order for them to believe you, you have
to cough up a significant NRE (non-refundable engineering fee). This
has been reported as high as a seven-digit US\$ amount and is to make
sure that even if you end up buying less chips than you indicate, the
chipset maker will still have your upfront NRE money and keep it.
And if you buy your way into that select club of cellphone makers, what
you get from the chipset maker is typically not all too impressive
either. The documentation you get is incomplete, i.e. it alone would
not enable you as a cellphone maker to make any use of the hardware,
unless you license the software (drivers, GSM protocol stack, ...) from
the chipset maker, too.
On the software side, most of the technologically interesting bits (like
the protocol stack) are provided as binary-only libraries, you only get
source code to some parts of the systems, i.e. some hardware drivers
that might need modification for your particular phone electrical
design.
That GSM protocol stack was not written by the chipset maker either.
They simply license a stack from one of the estimated 4 or 5
organizations who have ever implemented a commercial GSM protocol stack.
It is not like the GSM protocols were some kind of military secret.
They are a published international standard, freely accessible for
anyone. So why does everybody in that industry think that there is
a need to be so secretive?
Having spent a significant part of the last 6 years with reverse
engineering of various aspects of mobile phones in order to understand
them better and do write software tools for security analysis, I still
don't understand this secrecy.
All the various vendors do more or less the same. The fundamental
architecture of a GSM baseband chip is the same, whether you buy it from
TI, Infineon or from MediaTek. {\em They all cook with water}, like we
Germans tend to say. The details like the particular DSP vendor or
whether you use a traditional IF, zero-IF or low-IF analog baseband
differ. But from whom do they want to hide it? If people like myself
with a personal interest in the technical aspects of mobile phones can
figure it out in a relatively short time, then I'm sure the competiton
of those chipset makers can, too. In much less time, if they actually
care.
This closedness of the cellular industry is one of the reasons why there
has been very little innovation in the baseband firmware throughout the
last decades. Innovation can only happen by very few players. Source
code bugs can only be found and fixed by very few developers at even
fewer large corporations. No chance for a small start-up to innovate,
like they can in the sphere of the internet.
It is fundamentally also the reason why the traditional phone makers
have been losing market share to newcomers to the mobile sphere like
Apple with its iPhone or Google with its Android platform.
Those innovations really only happened on the application processor on
high-end smartphones. The closed GSM baseband processor had to be
accompanied by an independent application processor running a real
operating system, with real processes, memory management, shared
libraries, memory protection, virtual memory spaces, user-installable
applications, etc.
They still don't happen on the baseband processor, which is as closed as
it was 15 years ago.
\end{document}
--3V7upXqbjpZ4EhLz--
