Author: Martin

Recently, Dean Bubbley has written an interesting blog post about how most industrial nations are beyond “peak telephony”, i.e. the number of voice minutes in fixed line and mobile networks combined is decreasing. When the German regulator published its report for 2014 a couple of days ago I had a closer look here as well to see what the situation is in Germany. And indeed, we are clearly past peak telephony as well.

And here are the numbers:

In 2014, fixed line networks saw 154 billion outgoing minutes in Germany which is 9 billion minutes less than last year. On the mobile side they've been observing an increase of 1 billion minutes. In total that's 8 billion minutes less than the previous year, which is about -3%. The trend has been going on for quite a while now. In 2010, combined fixed and mobile outgoing voice minutes were at 295 billion compared to 265 minutes in 2014. That's 11% less over that time frame.

A question the numbers can't answer is where those voice minutes have gone. Have they been replaced by the ever growing traffic of instant messaging apps such as Whatsapp or have the been replaced by Internet based IP voice and video telephony such as Skype? I'd speculate that it's probably both to a similar degree.

Despite my fears last year that Skype that is owned by Microsoft these days might cease to support PC Linux at some point and leave me stranded, it hasn't happen yet. Last year I speculated that should this happen I would probably just move Skype to an Android tablet and be done with it. As I remarked at the time this would have the additional benefit that I would reduce exposure of my private data to non-open source programs as an added benefit. Between then and now I went ahead and tried out using Skype on a tablet and a smartphone despite its ongoing support for Linux on PCs and found that it's even nicer to use on these platforms than on the PC. During video calls I can even walk around now without cutting multiple cords first. And I have the added benefit that there's no exposure to my private information anymore by a non-open source program as I otherwise only use that tablet for ebook reading. I'm glad tablets have become so cheap that one can have several of them each dedicated to a few sepcific purposes. That ties in well with my thoughts on the Macbook 2015 becoming the link between Mobiles and Notebooks.

Since I know how a gigabit GPON fiber link feels and performs and that it's deployed significantly in some countries I can't but wonder when telecom operators in other countries stop praising DSL vectoring with 100 Mbit/s downlink and a few Mbit/s in the uplink as the future technology and become serious about fixed line optical network development!? Having said that I recently noticed that the Gigabit Passive Optical Network (GPON) I have in Paris with a line rate of 1 Gbit/s is actually quite out of date already.

10G-PON, already specified since 2010, is the successor technology and, as the abbreviation suggests, offers a line rate of 10 Gbit/s. According to the Wikipedia article that line rate can be shared by up to 128 users. And thankfully, PON networks are upgradable to 10G-PON as the fiber cable is reused by changing the ONT. Backwards compatibility is ensured as 10G-PON uses a different wavelength compared to GPON so both can coexist on the same fiber strand thus allowing a gradual update of subscribers by first changing the optical equipment in the distribution cabinet and subsequently the fiber devices in people's homes.

But that's not all as standardization of the successor to the successor is already full swing. NG-PON2 is the new kid on the block and will offer 40 Gbit/s downlink speeds on several wavelengths over a single fiber cable and 10 Gbit/s in the uplink direction. For details have a look at the ITU G.989.1 document that contains the requirements specification and G.989.2 for the physical layer specification.

So who's still talking about a measly 100 Mbit/s in the downlink?

Being a bit of a history buff (e.g. see my article on 'C64 Vintage and Virtual Hardware For Exploring The Past') I stumbled over a recent podcast the Amp Hour did with Chuck Peddle. If the name doesn't sound familiar it could be because main stream media often portrays the 1980s and 1990s as an epic struggle between Apple, Microsoft and IBM. This is perhaps because all three companies still exist today but the story is a lot bigger than that as companies such as Commodore and Atari and home computers like the C64 play a big part in that revolution as well. In the Amp Hour interview with Chuck Peddle, the leader of the team that designed the 6502 processor that would make home computing in the 1980s affordable for the masses, goes back to the times before and after the C64 and tells history from his point of view.

Peddle says that while Apple built in style and IBM for business, Commodore built for the masses. I more than agree with this statement as the C64 was the only home computer my parents could afford to buy me as a kid. Both Apple and IBM played in a totally different league from a pricing point of view. So if you want to spend a good time hearing about history, lean back and enjoy that podcast. And if you want to learn more, Brian Bagnall's 'Commodore – A Company On The Edge' is a great source for additional details and stories about the 1980s and 90s in computing.

The 2015 Macbook is certainly not a product that could replace my productivity notebook. With only a single connector for power and connectivity it utterly disqualifies for my usage scenario where 3 USB ports, a single external screen connector and a single Ethernet port I have on my current notebook is often not enough. But while that is so that device is a first of its kind because it's a product that bridges the gap between smartphones/tablets on the one side and notebooks/PCs on the other.

Have a look at the iFixit tear down and you see what I mean. The motherboard is only slightly bigger than what you find in a tablet today and certainly doesn't look like a traditional notebook motherboard anymore. But the whole setup is strong enough to run a "full" operating system and not a stripped down version such as Android or iOS. If the screen was touch sensitive that device would actually be a tablet with a built in keyboard with a full desktop operating system rather than a notebook.

So what began in the mobile space when the Linux/BSD kernel replaced operating systems that were developed far away from the desktop world in 2007/2008 with the first Android and iOS devices has now extended to the overall operating system itself.

Apart from mobile, I like to explore other computer topics every now and then as there are often surprising ideas springing up from this that also impact my work in mobile. Android programming, Raspberry Pi's, Owncloud and my dive into PHP web programming and databases last year immediately filtered back to the work that earns the daily bread. Earlier this year I started having a closer look (again) at the Linux kernel.

The great thing about the Linux kernel is that it's open source and you can have a look yourself. The problem is, however, that it's a monumental piece of code and without any prior kernel knowledge, diving into the material seems daunting. I'm a hands-on person so just going through the code for the fun of it is not my piece of cake. So I was looking for some insight with practical things to be done along the way. That's not easy to come by as books on the topic with hands-on tutorials are rather dated. One of the best books on the topic is perhaps the "Linux Device Drivers" book as it explains many things about the kernel from a device driver perspective. The good thing about this approach is that it offers hand-on experience with a couple of sample drivers one can compile, modify and run. 

Unfortunately the current 3rd edition of the book is from 2005. Ancient history… I would have never bought it in print at first. Fortunately, it is available online free of charge and so I decided to start reading it in electronic form first and see if the sample code would still run. The source code would of course not compile anymore, too many changes were made to the kernel since. But a number of people have updated the source over time and there's a working version available that compiles with current kernels on Github by duxing2007.

Together with the working source the book suddenly made a lot more sense and even though some of the book's content is clearly dated (e.g. using the parallel port for some of the sample code or discussing the ISA bus) the majority of the content still gives a good introduction to the kernel with lots of things to try out via the driver examples that one can compile, run and modify. At some point I decided it was worth to buy the print version of the book as sometimes information in print still beats the electronic version. In other words, despite the book being 10 years old now, I still found it a worthwhile read!

While not necessary to compile and run the examples in the book, having the kernel source to explore is great. As it turns out it's quite simple to download and even compile it. If you are running Ubuntu, have a look here for how to do that. On my notebook in a virtual machine running an Ubuntu guest, it takes around 2.5 hours to compile the kernel. Installing the compiled kernel to boot from is a simple command. I wouldn't have dared that on my notebook but in a virtual machine there's nothing you can break in the process that couldn't be restored with the click of a button that restores a previous snapshot of the guest OS.

With all these things in place it's never been easier to explore the kernel! Have fun!

LTE deployments are making steady progress and with good network coverage, network operators are keen to make sure devices are on LTE as much as possible instead of lingering around in 2G or 3G for too long. There are actually quite a number of mechanisms I've seen in various networks in the past so I thought I'd sum them up in a single post. Note that there are more mechanisms than described below but those are the one's I've seen in different networks while traveling.

Autonomous Reselection: This one's the easiest as the network only needs to signal LTE availability in 2G or 3G System Information messages (2G SIB 2quater and 3G SIB19). Mobile devices in idle state that have ended up in 2G or 3G for various reasons then periodically scan for LTE coverage in spectrum locations indicated in the SIBs and autonomously change back.

Release With Redirection: Instead of switching a mobile from active to a more power conserving state (e.g. from Cell-DCH to Cell-PCH), the network releases the connection with an RRC Connection Release message that contains redirect information to LTE. The mobile device then has a look if LTE is available straight away and leaves for greener pastures if LTE is found. For this to work the network operator must be reasonably sure that LTE coverage is actually present in the area where a release is made instead instructing the mobile device to use an active but less power hungry 3G state. Otherwise the mobile ends up in 3G idle state from which it takes more than one and a half seconds before data can flow again (for details see this post).

CSFB Release With Redirection: That's almost the same as above but part of a CS-Fallback procedure for voice calls. After the voice call ends the network releases all bearers and also includes redirect information. This is even done when a PS bearer is still established at the end of the call and IP packets are flowing.

GPRS to LTE Reselection During Data Transfer: This is a relatively new feature and allows the mobile to interrupt an ongoing 2G data transfer and switch back to LTE. Have a look here for the details.

UMTS to LTE Handover During Data Transfer: This functionality is unfortunately not yet widely deployed in networks, I haven't come across a single network that supported it. But from my point of view it's a very important piece of the puzzle as often I use a notebook and VPN that constantly keeps data flowing and once I end up in 3G due to running out of LTE coverage I'm stuck there until I run out of 3G coverage. At this point anything can happen, depending on how the network looks like once coverage is regained. I already wrote a post about this back in November 2014 so have a look in this post for the details.

While aggregating two LTE carriers in Europe exists but is still not very widespread due to the availability of 20 MHz single carriers there is talk in the industry about aggregating 3 carriers. There is still some room in the specs for the moment as the maximum number of aggregated carriers that can be accommodated so far is 5. But eventually, carriers might want to go beyond that as well so 3GPP is gearing up to work on a solution to eventually combine up to 32 carriers.

The work item description can be found in document RP-142286 presented not long ago in TSG RAN#66 in December 2014. At first I thought extending CA beyond 5 carriers might be straight forward by introducing a couple of additional information elements and extensions. But that's a bit too short sighted as the current solution puts all uplink transmissions including channel feedback on the primary cell (i.e. the primary carrier). So as more and more devices become carrier aggregation capable there's more and more uplink traffic in the PCell which increases as more and more carriers are aggregated. Therefore the model does not scale well and uplink traffic and feedback at some point needs to be distributed over several carriers if more and more of them are combined.

From an overall conceptual point if find an aggregation of up to 32 carriers quite interesting. Before the aggregation of 2 carriers made it into chipsets many people were saying that this is going to be difficult as it would increase complexity and hardware cost significantly. Fast forward to 2015 and the aggregation of 2 carriers is in the wild and built into many devices. Obviously the aggregation 32 carriers is yet again another beast. And then again who would have predicted just two years ago that we would see mass market devices that support 20 LTE bands?

One of the features I was dearly missing when I finally switched my main device from a Symbian phone to an Android device was that I had to give up the feature to put the device into silent mode but still make it ring for selected contacts. This was and still is an important feature for me, especially when traveling to other timezones and people being unaware that they are calling while it's night in my current time zone and I'm sleeping. So for the last two years I fixed this with a kludge, i.e. taking an extra phone and SIM only known to few contacts. Now I discovered that the feature was introduced on Android and the iPhone at some point between then and now.

On my Android 4.4.4 based CyanogenMod Samsung Galaxy S4 which I've been using for more than half a year now, the sound menu now contains a menu item called "Quiet Hours". When selecting the item it's not only possible to set the quiet hours but also further things such as which events shall not be indicated to the user and the "Phone Ringer" menu item which can be set to "Ring for Favorite Contacts" (only). Works like a charm!

O.k. so this is a pretty much stock Android OS, how about customized variants? I had a quick look on a current high end Samsung device with Android L and while it looks slightly different the option is there as well. Also I could find a similar option on the iPhone.

Great stuff and nobody told me… 😉 Must have been in the software for quite some time now.