Author: Martin

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

One reason for referring to 3GPP Release 13 as ‘LTE-Advanced Pro” is that this version of the specification finally has everything in place for Mission Critical Communication, the LTE based successor to 2G TETRA networks designed in the 1990’s and used by public safety organizations in many countries today. One of the first countries that will use LTE-Advanced Pro’s Mission Critical Communication is the UK and a contract has already been awarded to Everything Everywhere. Time to have a look at the specs for Mission Critical Push to Talk (MCPTT), the central feature for public safety organizations.

Continue reading The Specs Behind LTE-Advanced Pro’s Mission Critical Communication

I like going on vacation to Austria. One of the reasons is that I have a SIM card from local operator “Drei” (Hutchison Three) that gives me unlimited Internet access over 3G (sadly not LTE) for 18 Euros per month. In other countries, I had to be bit more careful with my daily data usage while traveling. But at least for Europe things have changed to the better in the past months once again.

Continue reading I Don’t Even Bother With Hotel Wifi Anymore (in Europe)

While I got my first mobile phone at the end of the 1990’s, mobile devices and networks have been around for a bit longer than that. In their book ‘30 Years of Mobile Phones in the UK‘, Nigel Linge and Andy Sutton take a look at the developments over the past 30 years. An interesting title and I obviously couldn’t resist to pick up a copy.

Continue reading Book Review – 30 Years of Mobile Phones in the UK

Most trains these days come with specially coated windows to keep the heat out. Unfortunately these windows also block the RF waves of wireless networks. While most high speed trains in Germany these days compensate for the loss with RF repeaters many regional and inter-city trains don’t come with the luxury. Thus, without really strong network coverage outside, passengers are pretty much sitting in a moving coverage hole. But there seems to be a fix for this now.

Continue reading New Train Windows Against Moving Coverage Holes

3GPP Release 13 finally brings all bits and pieces together for Mission Critical Push To Talk (MCPTT) services, i.e. the cornerstone for Public Safety Communication. I’m going through 3GPP TS 23.179 which contains Stage 2 of the functional architecture description of the service. MCPTT services can be implemented over traditional IP unicast, i.e. a copy of the speech data is sent to each subscriber of a push to talk group call or via eMBMS, i.e. over a single IP multicast transmission to all group participants in a cell. But is eMBMS really needed?

Continue reading MCPTT: Is eMBMS Really Needed For Public Safety Communication?

Just a quick note today about this video over at the Raspberry Pi blog in which Eben Upton talks about the history of the Raspberry Pi. Yes, we are at this stage with the Raspberry Pi now, it’s iconic and it has a story for the history books.

An amazing project and I have stopped counting how many Pis I’m using myself (8 when I stopped counting in 2014), have configured for other people or given away as a present to get others hooked on computing.

It’s a bit sad but unfortunately still true, in some places there is still better GSM coverage than LTE. Network operators using VoLTE thus need to be able to hand-over an ongoing VoLTE call to a GSM circuit switched channel when the user leaves the LTE coverage area. The method to do this is referred to as Single Radio Voice Call Continuity (SR-VCC) and the basic flavor of it has probably been deployed by all VoLTE operators that have a legacy radio network out there. When taking a closer look one notices that there is a surprising variety of states a voice call can be in and the basic flavor can’t handle all of them. Let’s have a closer look.

Continue reading VoLTE – Some Thoughts on SR-VCC