Almost exactly a year ago I wrote a post about how much LTE capacity network operators in Germany have on air. One network operator had a total of 2x 50 MHz of LTE on air spread over 3 frequency bands. One year later, things have again improved.
Continue reading One German LTE Network Operator Now On-Air with 65 MHz
In the previous part of this series I gave a quick introduction to the difference between today’s handling model of a physical SIM that the user can insert in any device and embedded-SIMs to which subscription information can be downloaded. In part 2 I’ll now give a high level overview of how this download process works in practice and how the user remains in charge of when and how often he wants to change the subscription information in the eSIM.
Continue reading Embedded-SIM Intro – Part 2 – SIM vs. eSIM User Scenarios
I’m not and I never was never a great Apple fanboy. When I was a teenager in the second half of the 1980s, the Apple Macintosh still cost several thousand euros and was hence far beyond what I could afford. Like most, my computing world was that of Commodore, Atari and others who offered affordable computers for the likes of me. The PC with Windows followed my home computing phase which in turn was followed by Linux and Open Source. In other words, there was no space in my world for the always much more expensive Apple computers at any time. But obviously they played and are still playing an important role in the computing space so I decided to read up a bit on the history of the first Apple Macintosh.
One thing that has been surprisingly absent on this blog so far was a discussion on how embedded-SIM cards work. Call me a traditionalist, as for me, the SIM card in its current form has been the greatest invention since sliced bread and so I saw no reason to change the concept. This is because a removable SIM card allows me to use my mobile network subscription(s) with any device. I can move my subscription, i.e. the SIM card quickly from one device to another and, equally important, I can put in another SIM card in my main device, e.g. to use a local SIM card while traveling. The device belongs to me and there is no lock-in of a device to a specific network operator. Does this also work with eSIMs (or with eUICCs, to be exact), i.e. when the SIM card is soldered in place and thus no longer removable and subscriptions have to be downloaded?
Continue reading Embedded-SIM Intro – Part 1 – High Level Model
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.
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.
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
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.
Continue reading The Raspberry Pi as a SIP Client with PJSIP
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, …
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.