Author: Martin

Teltarif recently published an interesting number on the use of Internet access over Wifi in the 250 high speed trains in Germany: 105 Terabytes per month (see here and here in German). An impressive number (at first). So what’s the average data throughput per train then?

Continue reading 105 TB in 250 Trains

I’m probably one of the few people on this planet who appreciates and uses IPv6 both over my DSL connection at home and also over my cellular connection. Unfortunately there is one thing missing on the mobile side: Unrestricted incoming IPv6 access.

Continue reading IoT Needs Bi-Directional IPv6 In Mobile Networks

In the previous blog post on VoLTE I discussed how speech codecs are negotiated during connection establishment. VoLTE uses the AMR and WB-AMR codecs that are adaptive and can encode the voice stream in several data rates and qualities. In the case of WB-AMR, voice streams can be sent with data rates between 6.6 and 23.65 kbit/s. In practice, many networks limit the codec rate to 12.65 kbit/s in the case of WB-AMR and to 12.2 kbit/s for the narrowband AMR codec. Let’s have a closer look how that is done in practice.

Continue reading VoLTE – Some Thoughts On Bandwidth Negotiation

When somebody asks me which book to read to really understand how a computer works I point him or her to the must read book on the topic ‘But How Do It Know‘. If after reading they come back and ask how such a computer actually ends up in chips here are my next suggestions for them:

Continue reading Gates, Transistors, Silicon

Quite high on my list of things to do and get into when I have a bit of time are quadcopters. Well, actually that topic is on my list for years now but there’s always something else to do. Anyway today I came across a Quadcopter project with LTE connectivity for control. Cool idea, have a look here.

Speaking of quadcopters, another project that is on that wishlist of mine is the Crazyflie. Everything is open in this project, so it has a special appeal to me. That quadcopter might be a bit too small for LTE connectivity, however.

In the good old fixed line SIP world, the originator of a speech call told the other side which speech codecs it supported. The other side then picked a suitable codec and informed the originator about the choice. That was it and things were ready to go. In VoLTE, you might have guessed, it’s not quite as simple. Today, codecs are rate adaptive and bandwidth for the data stream can be limited by the mobile network to a value that is lower than the highest data rate of a codec family.

Continue reading VoLTE – Some Thoughts On Codec Negotiation

I’m quite advanced in my IPv6 adventures but there has been one thing that has been holding me back so far: The DNS resolver in my DSL router at home refuses to properly return the IPv6 address of my local server. Instead it doesn’t respond at all to this request. As a consequence my web browser waits for 10 seconds before it gives up and then uses the IPv4 address of the server instead that was returned just fine. This had me baffled for a long time because all other DNS resolvers returned the IPv6 address just fine. Now it turned out that this is not a bug at all but a feature.

Continue reading My IPv6 DNS AAAA-Resolver Bug Is A Feature – With A Fix

Ubuntu visualizes current and previous power consumption and recharge behavior in a couple of nice graphs as shown in the screenshots above and below. When I have screen brightness quite high but not much else is going on, my notebook draws around 12-13 Watts of power and my battery lasts around 4 hours. Turning up brightness, running a virtual machine or two and streaming a video from Youtube and power consumption is obviously significantly higher. Sometimes it would be nice, however, to not only see a graph but to get a reading of how much power my notebook takes at any point in time. Fortunately there’s a command for that.

Continue reading Linux Command To Get The Notebook’s Current Power Consumption