Author: Martin

Ever since I discovered the use of a TV in hotel rooms for streaming videos or its use as a second screen almost a decade ago, I’m always taking a DVI/HDMI cable along when I travel. These days, however, TVs in hotel rooms are getting larger and larger. While this is great news for video streaming from the PC, they become less and less useful as a second screen for work. But recently I’ve found a great alternative: Portable USB screens.

Continue reading Ubuntu And A USB Attached Screen While Traveling

There are a number of devices and network operators out in the wild now which do not only support Voice over LTE (VoLTE) but also Voice over Wifi (VoWifi) and can even hand-over ongoing calls between the two radio access networks. But there is one thing: Which RAN should be preferred if both LTE and Wifi are available? The answer is not as simple as it looks at first.

Continue reading Voice over Wifi – Which RAN to Prefer?

I’ve been in Sweden for a couple of days recently, around 30 km outside of Göteborg in a pretty rural area. Obviously I did not only enjoy the beautiful landscape but also had a closer look at what is on air in this region. I was quite surprised about what I found as GSM is definitely on the way out here.

Continue reading LTE in Sweden – Bye Bye GSM (Almost)

When GSM was designed, the network and the voice service running over it were inseparable. That’s because the GSM network was designed in the 1980s as a mobile voice network. Fast forward 20 years and the picture had changed significantly with LTE having been designed as a wireless network that only transports IP packets. Agreed, it took another 10 years before Voice over LTE (VoLTE) was ready to replace the CS-fallback (to GSM and UMTS) mechanism for voice telephony. Now Voice over Wifi that is deployed by first network operators shows that VoLTE really is network independent. Continue reading VoLTE and VoWifi – Wireless Telephony Has Truly Become Network Independent

When I recently wanted to find out which network operators have which and how much spectrum assigned in a country I found an incredibly cool website that has up to date information on this topic. Have a look over at spectrummonitoring.com! Not included in the charts is the US, probably because in this part of the world spectrum assignments vary quite significantly even between cities. But for Europe, Asia and the Americas a huge number of countries are present on the site.

Even if you have a VoLTE capable phone and use it in a VoLTE capable home network, chances are that when push comes to shove and you have to make an emergency call, it’s not done over VoLTE. Instead, CS-Fallback is used to establish the emergency call in GSM or UMTS. But at some point, network operators will likely retrofit their VoLTE installations to be also able to handle emergency calls. I recently wanted to have a closer look and found an interesting resource on the web that saved me a lot of time.

Continue reading VoLTE – Some Thoughts On Emergency Calls

Ten years ago, Bluetooth tethering was a big thing and the only option to wirelessly tether a notebook via a phone to the Internet. How things have changed since then…

Continue reading USB-2 Is Not Fast Enough for LTE 3-CA

If your uplink bandwidth at home is limited and you use Skype or other Internet based voice services you’ve probably experienced more than once that when someone else in your household starts uploading cat videos, your Skype call goes south. That’s because the voice packets are treated like all other packets and start queuing up behind those fat IP packets with parts of the cat video inside. This is not a theoretical scenario, it happens in practice. So how does VoLTE on LTE cope with this?

Continue reading VoLTE and Quality of Service – The Ultimate Test

In LTE, data is transferred over the air interface over ‘Default Bearers’ and ‘Dedicated Bearers’. The terms are a bit confusing but actually the concepts behind them can easily be explained: Virtual Network Interfaces and Traffic Shaping Rules.

Continue reading LTE Bearers Are Like Virtual Network Interfaces

Recently I noticed, much to my dismay, that when using OpenVPN over network interfaces for which IPv4 and IPv6 is configured, Ubuntu 16.04 doesn’t configure DNS lookups correctly. As a result, DNS requests that should only be sent inside the OpenVPN tunnel are sent on the outside network interface thus massively compromising security and privacy. Read on for the details and a temporary fix.

Continue reading Ubuntu 16.04 Leaks DNS Requests With OpenVPN Tunnels and IPv6