When it comes to SIP, getting things to work is usually not straight forward. The more I was surprised when I recently wanted to connect a SIP software client running on Linux to my fixed line network operator’s IMS system.
Reading stock exchange IPO prospectuses is probably not the first thing that comes to your mind when you want to learn something about computing history. This article by Hansen Hsu recently published on the blog of the Computer History Museum will convince you otherwise! In his article, Hansen discusses how NeXT, the company founded by Steve Jobs after he was ousted from Apple in the mid-1980s helped to shape the transition from a static to a dynamic web. His research is based on a draft S-1 filing for a potential NeXT IPO which was recently donated to the museum.
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 email@example.com ssh firstname.lastname@example.org '/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.
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.
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.
I have several Raspberry Pi servers at home all running on Raspbian / Debian Jessie. All of them have IPv6 enabled by default but I was quite surprised that they behave a bit differently when it comes to IPv6 address generation.
While those running a somewhat older Jessie images configure themselves with a static IPv6 interface identifier, I noticed that others running on somewhat newer Jessie images configure random interface IDs that change over time. While this is a cool feature for client devices, referred to as IPv6 privacy extensions, it’s quite undesirable when using a Raspberry Pi as a server and making it accessible over the Internet over IPv6.
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.
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.
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.
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.