Author: Martin

When I’m using the command line on Ubuntu it’s often for very repetitive tasks for which I would have typed in the same endless command a thousand times if it weren’t for the CTRL-R search function that let’s me execute commands from the history list quickly by typing a part of it. There is one tiny drawback, however. There are some commands which are a subset of others, such as logging into a server via ssh to get a shell or to automatically execute a job on the same serer. Here’s an example:

ssh martin@xyz.com 

ssh martin@xyz.com '/home/martin/xyz.sh'

Both commands are identical at the beginning so as a consequence I sometimes have to type in CTRL-R a number of times before I get to the shorter one. There must be a better way to do this! And indeed there is as a colleague of mine recently showed me.

Continue reading Linux: Adding Your Own Bash Shortcut Functions

Back in 2014 I had a post on how to cross compile tcpdump for Android to record all network traffic from cellular and Wifi into files for later analysis for Wireshark. I’ve known for a while that it’s also possible to use adb and tcpdump to pipe all network traffic from the smartphone over USB to Wireshark running on a PC for real time tracing. I didn’t really follow up on this since then because most dumping data into a file on the device and later transferring it to the PC was good enough for me. Recently, however, a more real time approach was required and I was actually quite surprised how easy it is to set this up once tcpdump is on the device.

Continue reading ADB and tcpdump on Android for Live Wireshark Tracing

Back in 2014 I came up with a solution to share a single hotel Wi-Fi connection to all devices I have with me and so so in a secure way with a built in VPN tunnel. Over the years the project has evolved a bit and I’m happy to report that with input from echaritos on Github the solution now also supports the Raspberry Pi 3 that has a built-in Wi-Fi interface.

Continue reading The Secure Hotel Wi-Fi Sharing Pi Solution Now Supports the Raspberry Pi 3

Earlier this week, the EU parliament reported that they have reached an agreement with the European council on the final piece of the puzzle for the abolishment of roaming charges in the EU by mid-June this year: Wholesale prices. This is good news and it’s interesting to take a closer look on the compromise that was reached.

Continue reading EU Roaming – The Final Word On Wholesale Caps?

One big advantage of ‘alternative’ voice solutions such as Skype and many others is the use of much better voice codecs that make a huge difference in practice. Many mobile network operator voice systems have been upgraded over the years to support Wideband-AMR. In practice I get a lot of WB-AMR calls while people use the same mobile network as I do. The rate of adaption is quite good as people quite frequently get themselves new devices that support the feature. The fun stops, however, as soon as I call someone on another network. For years, nobody thought it a priority to add gateways that support wideband codecs. A bit of a shame.

Many fixed line phone connections have also been converted to IP over the years and usually also support a wideband codec. The problem here is that in order to enjoy the speech quality of a wideband codec, not only the line but also the fixed line phone has to be upgraded.

Continue reading The Uptake of Wideband Speech Codecs in Fixed Line Networks Is… Glacial

Recently, I’ve been in Seoul again for a week. When I was there back in 2013 it was straight forward to buy a SIM card at the airport so I thought I’d do it again this time around. While selling prepaid SIM cards was something of a novelty then it seems to have become a lucrative business as there were a plethora of options this time. One has to be careful however, as not all SIM cards one can get at the airport can be used straight away.

Continue reading Getting a Prepaid SIM in Korea – Dos and Don’ts

In the previous post I’ve had a closer at, among other things, the spectrum use of ADSL vs. ADSL2+. The change in uplink and downlink throughput when the line was updated was quite significant. The main difference was made by using the lower spectrum that was previously used for voice telephony as additional spectrum for the DSL uplink and by doubling spectrum use from 1.1 to 2.2 MHz, i.e. from 256 tones (carriers) to 512. Let’s have a look at how ADSL2+ spectrum use compares with VDSL2, which I have at my home.

Continue reading VDSL2 Spectrum Use

A friend of mine lives in the countryside at the very fringe of DSL coverage. While a decade ago a 3 Mbit/s DSL line with a 450 kbit/s uplink could still be considered sufficient, things have changed quite a bit these days. Several computers and smartphones are now connected to his network which makes using voice over IP applications such as Skype difficult as especially the uplink is immediately affected when someone else uploads data. Don’t even think about video telephony with a reasonable video quality. Running Skype and desktop sharing simultaneously is also next to impossible, downloading software updates takes ages and streaming HD video has become impossible in many cases.

Recently, however, my friend’s DSL line with bundled analog telephony was migrated to all-IP, i.e. voice telephony now also runs over IP. The only benefit I could see when this was announced was that voice quality would be upgraded to Wideband-AMR so I made sure he had a compatible phone by the time of the switch. In addition, I noticed that at the same time, the telephone company switched the line from ADSL to ADSL2+ which brought a huge improvement to up- and downlink speeds. I’m glad I took a number of screenshots of the DSL connection information before and after the switch as they reveal some very interesting details.

Continue reading ASDL2+ More Than Doubles Speed At The Digital Fringe

In many countries around the world, network operators are sharing parts of their radio access networks. In many cases the country they operate in is split up into different parts and each network operator exclusively installs the network infrastructure for both. Obviously this reduces cost but also denies companies that are part of the agreement to differentiate themselves in the one thing that matters: Speed and capacity. Continue reading Network Sharing Pains In The UK