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Name: Harald Welte
Member since: 2000-08-20 17:12:09
Last Login: 2016-06-25 11:24:42

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Going to attend Electromagnetic Field 2016

Based on some encouragement from friends as well as my desire to find more time again to hang out at community events, I decided to attend Electromagnetic Field 2016 held in Guildford, UK from August 5th through 7th.

As I typically don't like just attending an event without contributing to it in some form, I submitted a couple of talks / workshops, all of which were accepted:

  • An overview talk about the Osmocom project
  • A Workshop on running your own cellular network using OpenBSC and related Osmocom software
  • A Workshop on tracing (U)SIM card communication using Osmocom SIMtrace

I believe the detailed schedule is still in the works, as I haven't yet been able to find any on the event website.

Looking forward to having a great time at EMF 2016. After attending Dutch and German hacker camps for almost 20 years, let's see how the Brits go about it!

Syndicated 2016-07-23 14:00:00 from LaForge's home page

EC-GSM-IoT: Enhanced Coverage GSM for IoT

In private conversation, Holger mentioned EC-GSM-IoT to me, and I had to dig a bit into it. It was introduced in Release 13, but if you do a web search for it, you find surprisingly little information beyond press releases with absolutely zero information content and no "further reading".

The primary reason for this seems to be that the feature was called EC-EGPRS until the very late stages, when it was renamed for - believe it or not - marketing reasons.

So when searching for the right term, you actually find specification references and change requests in the 3GPP document archives.

I tried to get a very brief overview, and from what I could find, it is centered around GERAN extension in the following ways:

  • EC-EGPRS goal: Improve coverage by 20dB
    • New single-burst coding schemes
    • Blind Physical Layer Repetitions where bursts are repeated up to 28 times without feedback from remote end
      • transmitter maintains phase coherency
      • receiver uses processing gain (like incremental redundancy?)
    • New logical channel types (EC-BCCH, EC-PCH, EC-AGC, EC-RACH, ...)
    • New RLC/MAC layer messages for the EC-PDCH communication
  • Power Efficient Operation (PEO)
    • Introduction of eDRX (extended DRX) to allow for PCH listening intervals from minutes up to a hour
    • Relaxed Idle Mode: Important to camp on a cell, not best cell. Reduces neighbor cell monitoring requirements

In terms of required modifications to an existing GSM/EDGE implementation, there will be (at least):

  • changes to the PHY layer regarding new coding schemes, logical channels and burst scheduling / re-transmissions
  • changes to the RLC/MAC layer in the PCU to implement the new EC specific message types and procedures
  • changes to the BTS and BSC in terms of paging in eDRX

In case you're interested in more pointers on technical details, check out the links provided at https://osmocom.org/issues/1780

It remains to be seen how widely this will be adopted. Rolling this cange out on moderm base station hardware seems technicalyl simple - but it remains to be seen how many equipment makers implement it, and at what cost to the operators. But I think the key issue is whether or not the baseband chipset makers (Intel, Qualcomm, Mediatek, ...) will implement it anytime soon on the device side.

There are no plans on implementing any of this in the Osmocom stack as of now,but in case anyone was interested in working on this, feel free to contact us on the osmocom-net-gprs@lists.osmocom.org mailing list.

Syndicated 2016-07-23 10:00:00 from LaForge's home page

Deeper ventures into Ericsson (Packet) Abis

Some topics keep coming back, even a number of years after first having worked on them. And then you start to search online using your favorite search engine - and find your old posts on that subject are the most comprehensive publicly available information on the subject ;)

Back in 2011, I was working on some very basic support for Ericsson RBS2xxx GSM BTSs in OpenBSC. The major part of this was to find out the weird dynamic detection of the signalling timeslot, as well as the fully non-standard OM2000 protocol for OML. Once it reached the state of a 'proof-of-concept', work at this ceased and remained in a state where still lots of manual steps were involved in BTS bring-up.

I've recently picked this topic up again, resulting in some work-in-progress code in http://git.osmocom.org/openbsc/log/?h=laforge/om2000-fsm

Beyond classic E1 based A-bis support, I've also been looking (again) at Ericsson Packet Abis. Packet Abis is their understanding of Abis over IP. However, it is - again - much further from the 3GPP specifications than what we're used to in the Osmocom universe. Abis/IP as we know consists of:

  • RSL and OML over TCP (inside an IPA multiplex)
  • RTP streams for the user plane (voice)
  • Gb over IP (NS over UDP/IP), as te PCU is in the BTS.

In the Ericsson world, they decided to taka a much lower-layer approach and decided to

  • start with L2TP over IP (not the L2TP over UDP that many people know from VPNs)
  • use the IETF-standardized Pseudowire type for HDLC but use a frame format in violation of the IETF RFCs
  • Talk LAPD over L2TP for RSL and OML
  • Invent a new frame format for voice codec frames called TFP and feed that over L2TP
  • Invent a new frame format for the PCU-CCU communication called P-GSL and feed that over L2TP

I'm not yet sure if we want to fully support that protocol stack from OpenBSC and related projects, but in any case I've extende wireshark to decode such protocol traces properly by

  • Extending the L2TP dissector with Ericsson specific AVPs
  • Improving my earlier pakcet-ehdlc.c with better understanding of the protocol
  • Implementing a new TFP dissector from scratch
  • Implementing a new P-GSL dissector from scratch

The resulting work can be found at http://git.osmocom.org/wireshark/log/?h=laforge/ericsson-packet-abis in case anyone is interested. I've mostly been working with protocol traces from RBS2409 so far, and they are decoded quite nicely for RSL, OML, Voice and Packet data. As far as I know, the format of the STN / SIU of other BTS models is identical.

Is anyone out there in possession of Ericsson RBS2xxx RBSs interested in collboration on either a Packet Abis implementation, or an inteface of the E1 or packet based CCU-PCU interface to OsmoPCU?

Syndicated 2016-07-16 10:00:00 from LaForge's home page

Recent public allegations against Jacob Appelbaum

In recent days, various public allegations have been brought forward against Jacob Appelbaum. The allegations rank from plagiarism to sexual assault and rape.

I find it deeply disturbing that the alleged victims are putting up the effort of a quite slick online campaign to defame Jakes's name, using a domain name consisting of only his name and virtually any picture you can find online of him from the last decade, and - to a large extent - hide in anonymity.

I'm upset about this not because I happen to know Jake personally for many years, but because I think it is fundamentally wrong to bring up those accusations in such a form.

I have no clue what is the truth or what is not the truth. Nor does anyone else who has not experienced or witnessed the alleged events first hand. I'd hope more people would think about that before commenting on this topic one way or another on Twitter, in their blogs, on mailing lists, etc. It doesn't matter what we believe, hypothesize or project based on a personal like or dislike of either the person accused or of the accusers.

We don't live in the middle ages, and we have given up on the pillory for a long time (and the pillory was used after a judgement, not before). If there was illegal/criminal behavior, then our societies have a well-established and respected procedure to deal with such: It is based on laws, legal procedure and courts.

So if somebody has a claim, they can and should seek legal support and bring those claims forward to the competent authorities, rather than starting what very easily looks like a smear campaign (whether it is one or not).

Please don't get me wrong: I have the deepest respect and sympathies for victims of sexual assault or abuse - but I also have a deep respect for the legal foundation our societies have built over hundreds of years, and it's principles including the human right "presumption of innocence".

No matter who has committed which type of crime, everyone deserve to receive a fair trial, and they are innocent until proven guilty.

I believe nobody deserves such a public defamation campaign, nor does anyone have the authority to sentence such a verdict, not even a court of law. The Pillory was abandoned for good reasons.

Syndicated 2016-06-06 10:00:00 from LaForge's home page

Nuand abusing the term "Open Source" for non-free Software

Back in late April, the well-known high-quality SDR hardware company Nuand published a blog post about an Open Source Release of a VHDL ADS-B receiver.

I was quite happy at that time about this, and bookmarked it for further investigation at some later point.

Today I actually looked at the source code, and more by coincidence noticed that the LICENSE file contains a license that is anything but Open Source: The license is a "free for evaluation only" license, and it is only valid if you run the code on an actual Nuand board.

Both of the above are clearly not compatible with any of the well-known and respected definitions of Open Source, particularly not the official Open Source Definition of the Open Source Initiative.

I cannot even start how much this makes me upset. This is once again openwashing, where something that clearly is not Free or Open Source Software is labelled and marketed as such.

I don't mind if an author chooses to license his work under a proprietary license. It is his choice to do so under the law, and it generally makes such software utterly unattractive to me. If others still want to use it, it is their decision. However, if somebody produces or releases non-free or proprietary software, then they should make that very clear and not mis-represent it as something that it clearly isn't!

Open-washing only confuses everyone, and it tries to market the respective company or product in a light that it doesn't deserve. I believe the proper English proverb is to adorn oneself with borrowed plumes.

I strongly believe the community must stand up against such practise and clearly voice that this is not something generally acceptable or tolerated within the Free and Open Source software world. It's sad that this is happening more frequently, like recently with OpenAirInterface (see related blog post).

I will definitely write an e-mail to Nuand management requesting to correct this mis-representation. If you agree with my posting, I'd appreciate if you would contact them, too.

Syndicated 2016-06-01 10:00:00 from LaForge's home page

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