VoLTE – GBA Authentication For XCAP

Recently I wanted to have a closer look at how authentication works for the XCAP protocol that is used in VoLTE by mobile devices to control things such as call forwarding settings. At first I thought that the topic is so far off the beaten path that I need to have a look in the specifications right away. But I gave Google a chance and was quite positively surprised that there’s a ton of information out there that is much easier to digest than going to the specs right away.

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Port 22 Anecdotes

Recently my firewall at home had a bit of a hick-up and decided to change the rule to forward a high external TCP port number to port 22 of one of my servers into a 1:1 mapping of that port instead. As I was about to go into a long meeting I couldn’t immediately react and fix things so for a couple of hours the SSH server of that machine was accessible from the Internet via its native port – with interesting results.

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Multihop SSH

I’m running a number of servers at home and of course I want to access them over the Internet. As per good practice I have one gateway to which I can connect to with SSH from my Linux notebook. Once logged in I can then SSH to other machines in my network. This has worked well for me over many years but has three disadvantages: Despite using certificates, the process of first logging into the gateway and then logging into another machine is a bit more of an effort than it should be. Secondly, I can’t use SFTP via the file manager to exchange files with my machines at home this way. And finally this setup is not ideal from a security point of view because the internal machines have to trust the SSH key from the gateway machine. If the gateway is ever compromised, all machines inside are compromised as well. Recently, I found a cool way of how to fix all three things: Multihop-SSH! Continue reading Multihop SSH

The Raspberry Pi as a SIP Client with PJSIP

I know, most people have no need to call a phone line to endlessly listen to an announcement or, even better, music. However, in my line of work I sometimes do. Over the years I’ve helped myself out with calling the time service that repeats giving me the current time endlessly. But it’s a kludge and I always wanted to have my own system. Finally, I had some time to fill the gap and the result is a Raspberry Pi connected via SIP to the telephone system that endlessly plays music when I call its phone number.

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Why I Might Just Buy A Nokia 3310 (2017)

Smartphones must have become a really boring thing as a big hype was made at this year’s Mobile World Congress around the Nokia 3310 feature phone. It’s GSM dual band only (GSM is being phased-out in the US so why bother to include these frequencies) and its main purpose is to make phone calls and for SMS messaging. While most people wonder who would possibly buy such a phone who is in his or her right mind, …

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Backup Doubts? Use Checksums and Rsync

I recently got a bit of a scare when I noticed that some large files of several gigabytes that I copied from an SD card to a hard drive and vice versa were corrupted afterwards. Corrupted as in the last gigabyte of the file missing on the target device. Up to today I have no idea how this happened, I’m usually diligent enough to eject media and wait for the pop-up to notify me that it is save to remove the drive. One thing that was even worse was that I started wondering if my regular backups were affected as well. It’s a strange feeling when you suddenly don’t trust your backups anymore so I invested some time to find out if things were all right or not. Turns out it is not so difficult.

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EU-Roaming – The Lowest End Cuts the Cord

In a few months, the next state of EU roaming regulation will come into effect and network operators must charge the same prices in the EU as at home. Already last year, however, I was wondering if some network operators will respond by simply not offering international roaming anymore. And indeed, I’ve noticed the first German MVNO doing so now for some of his tariffs.

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EVS Speech Codec Experience In The Wild – Forget AMR-WB…

When I heard about the Enhanced Voice Service (EVS) codec for the first time a couple of years ago I was a bit skeptical. After all, the AMR-Wideband Codec just went live in a number of networks back then and its sound quality compared to the traditional AMR-Narrowband was just stunning. So I thought that EVS could not raise the bar by much. In the meantime a number of network operators have launched EVS in their VoLTE networks and when I recently made my first EVS end-to-end call I was stunned at how much better it was even compared to a good AMR-Wideband call.

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Volumio Re-Connects my Hifi to the Internet

Back in 2013 I discovered SqueezePlug and used a Raspberry Pi to stream music from an online service to my 25 year old Hifi. It worked great at the time on a Pi-1 for a long time until the SD card gave out. Unfortunately time had moved on and I couldn’t get the latest software version run smoothly on a Pi-1. Yes, I could have replaced it for a faster model. However there were other things that needed more attention so I never got around to it. Fast forward a year to the present and I was still stuck with no audio streaming to the Hifi when a friend told me about Volumio by Michelangelo Guarise and how well it ran on his Raspberry Pi 1 connected to his Wifi. Easy to install and easy to use, just flash the image to an SD card, he said, and you are good to go. Could it really be that easy?

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