WirelessMoves – Page 27 – My Thoughts on the Evolution of Wireless, FOSS and the Past, Present and Future of Computing

18 Hours With 600 Grams of Battery

I like being able to work from anywhere and the only limiting factor is how long the battery of the notebook will last when I’m away from a power outlet. When I bought a new notebook August 2021, I made sure it came with USB-C Power Delivery (PD) so I could take as many spare batteries with me as I wanted to increase my time away from the desk. So one of the first things I bought once I had the new notebook was a third party battery that can charge just about any USB device, including notebooks with USB-C power delivery function. But how long would the internal and external battery power my notebook in practice? The answer: It depends.

Downloading an eSIM – in Practice – Part 3

After the positive experience I had with my first eSIM download (see part 1 and part 2 of this series), I wanted to explore the topic a bit more, and decided to purchase yet another eSIM via the Airalo web portal and download it to my device. I did this because I wanted to see if more than one eSIM could be installed on the eSIM chip in the device, and if I could go back and forth between several eSIMs. Also, I wanted to see if I could perform the download over Wi-Fi instead of over an existing cellular connection.

Downloading an eSIM – in Practice – Part 2

In part 1 of this series, I’ve taken a look at the process of purchasing an eSIM online for roaming purposes and then downloading it to a smartphone. In this part, I’ll have a look at some technical details such as the home network operator of the eSIM, location of the Internet connectivity, performance and other tidbits.

Downloading an eSIM – in Practice – Part 1

Back in 2017, I wrote quite a number of blog entries about an upcoming technology: Virtual SIMs, also referred to as eSIMs. As with many network technologies, it took a number of years before things end up in the mass market. But it has finally happened, and an interesting ecosystem has grown around downloadable SIM cards. One use case that has become popular are downloadable SIM cards which replace physical SIM cards when a subscriber of a network operator buys a new eSIM enabled device. A second use case is the convenient distribution of (temporary) prepaid roaming eSIMs, which are available these days for little money. Due to their low price, they are ideal to experiment with in practice.

An Extra Gigabyte per Minute with a Tinfoil

When I’m not in the lab and out in the field, I use tinfoil and shielded bags to reduce the signal strength, to force devices to and from lower frequency bands, to see the impact on data rates, or to increase their power output for testing. But tinfoil does not only block RF signals, it also reflects them. So I recently wondered, if I could use tinfoil to increase the datarate of my Wi-Fi link at home.

Compiling Wireshark on Ubuntu

I’m running Ubuntu 20.04 on my notebook, which by now is around 2 years old. This means that some programs are of the same age, as newer versions are not included in the repository. For most programs, that is just fine for me. Some programs are evolving quickly, however, and when it comes to Wireshark, it might be good to have the latest version. As I wanted to have a closer look at http3 and also at some 5G core network related interactions (the two topics are independent), I decided to get the latest Wireshark version to see if the dissectors of the latest version would show me more than those in the two year old version of Wireshark.

When it comes to Linux, there are no binaries of the latest version available, one has to compile from source. Sounds more complicated than it actually is.

Compacting A Virtual Machine Image to Reclaim 120 GB

It’s interesting how virtual machine images grow over time and how much space can be freed up by compacting them every now and then. When I recently compacted a VM that I use quite heavily, I could free up 120 GB on my SSD in one go. That’s an incredible amount of storage and here is how things came together:

HTTP/3 and QUIC

A while ago, I had a closer look at HTTP/2 (from a 5G core network point of view), and how a client could detect during connection establishment if it can use this flavor of the protocol or not. The short answer to the question is that the client and the server use an extension parameter of the TLS protocol during the authentication and ciphering exchange. In the meantime, the world has moved on, and HTTP/3 has made it out of the starting gate and is already used in practice. Unlike previous versions of the HTTP protocol that use TCP, HTTP/3 is based on UDP and the new QUIC protocol, which implements TCP like flow control and a number of other improvements to speed up the simultaneous transfer of many different files that usually comprise a web page these days. And so I had the same question again: How does the browser detect that it can use HTTP/3, and, as a consequence UDP/QUIC, for a web page instead of TCP?

Wireshark: Tracing Encrypted HTTP/2 Traffic

After optimizing Firefox HTTP/1.1 settings for slow wireless connections 17 years ago (!) , I pretty much forgot all about it again, because networks became faster and default browser settings and features were adapted for the cellular world. Only recently did I have another look at HTTP, when I noticed that HTTP/2 is now widely used in practice, and also plays a big role in the 5G core networks. From a security point of view, the great thing about HTTP/2 is that browsers only support TLS encrypted HTTPS connections. This has the downside, of course, that tracing and analyzing HTTP/2 connections with Wireshark is not possible out of the box any more. But there’s a fix for this!

The 2 Hour Kernel Compile

Recently, Ubuntu 20.04 LTS bumped the Linux kernel version they use from 5.11 to 5.13. While that is generally welcome to support newer hardware, it unfortunately also broke the suspend/resume functionality of my notebook with an AMD Ryzen 7 4750U CPU. Bummer!

This seems to be a known problem in the 5.13 kernel line, and was subsequently fixed somewhere down the road. It’s definitely ok again in the current Linux 5.15 long term support kernel. More good news: Ubuntu 20.04 is likely to switch to 5.15 in a few months from now, and I could of course just stay with the last 5.11 kernel until that time. However, I’m not really happy with that, because security issues are no longer fixed in in 5.11, which potentially exposes me to security vulnerabilities in the next couple of months.

Long story short: To be on the save side, I started looking for ways to use a 5.15 kernel with Ubuntu 20.04 until Canonical moves to that kernel line on their own. Fortunately, there are options: