Category: Uncategorized

It almost time for the 32C3 now and I'm on my way to attend in person this year. One thing the organizers have kept pointing out over the last few years is that due to the very limited spectrum available in the 2.4 GHz band, the network experience will be rather mediocre in this band. To get much better throughput, participants are advised to use the 5 GHz band instead. That's all nice and well but my notebook, and I guess the notebooks of many others, does not support the 5 GHz band with the built-in Wi-Fi PCI card. But there's an elegant solution!

These days even medium-priced smartphones come with 2.4 + 5 GHz Wi-Fi built in. What many people don't know is that the smartphones Internet connectivity, no matter whether it is over cellular or over Wi-Fi can be shared with a PC over USB. It's called USB tethering and can be activated in the tethering menu as shown on the left.

To make sure Wi-Fi is used as the backhaul, go to flight mode and only enable Wi-Fi on the smartphone. On the PC, disable Wi-Fi connectivity. Once the smartphone is connected to the Wi-Fi network, connect it to the PC and activate USB tethering if not already done. And that's it, your smartphone is now acting as a USB Wi-Fi dongle for your PC.

Note: I'm not sure if Windows requires a driver for this to work but on Ubuntu this works out of the box. But who uses Windows at the 32C3 anyway…

In Ocotober 2015, NTT Docomo was the first network operator who has started VoLTE Roaming based on a pre-standard implementation of the S8 Home Routing (S8HR) concept. I wrote about it at the time and speculated how they might have implemented the service as there was little official technical documentation available. In the meantime, 3GPP has continued their investigation of what is necessary to fully standardize the S8-HR concept and the details can be found in Technical Report (which is not a specification, it's just a report) TR 23.749 for 3GPP Release 14 (!). In December 2015, version 1.0.0. of the document was published that contains a number of interesting insights into what is already available and what is still missing in the specifications depending on which features an operator wants to use for VoLTE S8HR Roaming.

Dedicated Bearers for voice packets possible: At the time I wrote that if a network operator wants to play things purely on his own, VoLTE Roaming can be deployed without any interaction with the visited network operator except for the need, of course, to have a general LTE roaming requirement in place. If some more cooperation between home and visited network is put in place it is even possible to assign a dedicated bearer for voice packets by the IMS system in the home network to prefer voice packets in the network and especially on the air interface.

As shown in TR 23.749 in figure 4-2.1 this works without any additional specification work as the PCRF (Packet Control Resource Function) in the home network is told by the VoLTE IMS system in the home network to establish a dedicated bearer. The PCRF then talks to the Packet Gateway (P-GW) in the home network which in turn forwards the request to the Serving Gateway (S-GW) in the visited network. From there it goes to the LTE base station (eNodeB) and from there to the mobile device. In principle it is the same message flow as in a non-roaming scenario but the roaming interconnect has to let such configuration messages pass between P-GW and S-GW. The big advantage of the approach is that the VoLTE client on the mobile device does not have to behave differently when roaming abroad, i.e. there is no need for it to decide whether it has to wait for a dedicated bearer for the voice packets or not before proceeding the call.

Single Radio Voice Call Continuity: One of the main drawbacks off S8-HR VoLTE roaming that it is more difficult to put a mechanism in place to switched over from an IP-based LTE bearer to a circuit switched 2G or 3G channel at the edge of LTE coverage. TR. 23.749 points out that from an architectural point of view, no additional specifications are necessary for SR-VCC to work across borders in a Release 8 SR-VCC configuration. I presume, however, that quite a number of network operators have already gone to a post-Release 8 SR-VCC implementation in the network which has a number of additional components to speed up the process. For this setup, SR-VCC across borders is not possible with the current specification. Interestingly enough the 3GPP technical report excludes discussions of potential solutions from the document. In other words, it seems to be complicated enough to be put into a separate TR. It would be interesting to know of Docomo has actually implemented SR-VCC for their S8HR VoLTE roaming with Korea or if they just went ahead without it as LTE coverage is said to be pretty much deployed everywhere in Korea in the meantime anyway so there's no need for it in the first place.

There are two other topics discussed in the technical report, how emergency calls could be made properly and how to best signal to the VoLTE IMS system that the device is not at home but roaming in another country. Falling back to 2G or 3G cellular for emergency calls is a quick and working solution but the report also gives some details of how it could be done over VoLTE. If you are interested have a look at the document.

While the document had a few positive surprises for me it by and large confirms that S8HR VoLTE roaming should not be too difficult to implement and I wonder how long it will take for other network operators to follow Docomo's lead!?

Tip of the day: Sometimes simple things can massively improve productivity! Recently I saw a friend resizing two windows on a Mac with a key combination so they each occupied exactly half of the screen. That's very helpful in many situations I thought and immediately wondered if and how that would work on Ubuntu as well. And indeed there are key combinations for resizing windows this way as well:

To set a window occupying the left half of the screen use this shortcut:

Ctrl + Super + ←

And for the right half:

Ctrl + Super + →

(Super = the W*ndows key…)

USB Wi-Fi dongles are super cheap these days but not very durable it seems. Recently the cap on one of mine broke off and revealed the antenna that is connected to the tiny PCB board which is part of the USB connector. Click on the picture to get an enlarged version that shows the meandering antenna in detail. Amazing technology! 

I'm a bit nostalgic today because my ISDN telephony days are over. A few days ago, I was “upgraded” to an all-IP line at home because my network operator of choice wants to decommission its ISDN public telephone network, offer VDSL vectoring (instead of fiber connectivity, yeah, right…) and migrate everyone to Voice Over IP. For me an era comes to an end.

Back in the days at the end of the 1990's when 52 kbit/s modems for analog lines where the hype of the day I switched to an ISDN line at home so I could make phone calls and be connected to the Internet at the same time. Another plus was being able to bundle the two 64 kbit/s ISDN channels for a blazing Internet speed of 128 kbit/s. Back in the day that was not only considered ultra-fast but it actually also felt like it as web pages and stuff to download were tiny compared to the multi-megabyte downloads when accessing a single web page these days with all the adds included (if you don't have an add-blocker installed). Even when I switched from ISDN to DSL for Internet access I kept my ISDN line to benefit from several phone numbers, immediate call forwarding to other destinations on some of them and other 'digital' features that were not so easy to get on analog lines.

Now after almost 20 years, ISDN has gone. The picture on the left shows my decommissioned ISDN equipment: ISDN base phone with a DECT unit, a DECT cordless phone, DSL/ISDN splitter and an NTBA (ISDN network terminator). But to sweeten things up I got four very worthwhile things as part of the “upgrade”.

First, in anticipation of the switch, I bought a new fixed line cordless DECT (or CAT-iq as it's called today) phone a few months ago that can be connected to both ISDN and a VoIP core network which is HD-Voice capable. Not only will I have a much better voice quality to other VoIP fixed line phones in the country, but there's also an HD-Voice gateway between the VoIP fixed line network and my mobile network operator of choice's GSM and UMTS network that converts the 12.2 kbit/s WB-AMR codec used in mobile networks (G.722.2) into the 64 kbit/s wideband codec used in fixed line networks (G.722). Works great and the audio quality is much improved.

Second, my VDSL line was upgraded from 25 Mbit/s in the downlink direction and 5 Mbit/s in the uplink direction to 50 down and 10 up. I fail to be really impressed by that as my fiber line in Paris gives me 264 Mbit/s in the downlink and 48 Mbit/s in the uplink. But every bit/s counts and I did notice the increased speed immediately when I downloaded a Linux image the other day. Also, my VPN server and Owncloud server that I host at home very much benefit from the 10 Mbit/s in the uplink direction.

Third, my VDSL line is now IPv6 enabled so I will finally be able to connect to my servers over IPv6 while out and about, at least while I'm in my home country, as my mobile network operator of choice has introduced IPv4v6 connectivity this summer. Also, it will help me to better understand the IPv6 firewall features of the mobile network and my VDSL router at home. More about that in a future post.

And finally, the overall package now only costs about half of what I paid before. I'm the conservative type when it comes to connectivity so I hadn't changed my fixed line subscription in 6 years. Never change a running system…

Three and a half years ago I had a closer look at how a dual-SIM 3G mobile worked in practice and how both SIM cards can be used simultaneously, or not. Up to today, the two articles (see here and here) remain one of the most viewed ones so I'm not alone with my interest. These days, there are also dual-SIM LTE phones available, not only in the mid- and low-range market but also in the high-end sector. Time to have a look how these work in practice and if two networks can be used simultaneously.

By and large, the behavior of the dual-SIM LTE phone I had is pretty much identical to the Dual-SIM 3G phone from three and a half years back. The phone can receive (i.e. listen) to two networks simultaneously but can only be active (i.e. transmit and receive) in one at at a time. One can, for example, browse the Internet via one network (used with the first SIM card) while the device keeps listening for incoming voice calls and SMS messages on the other network (with the second SIM card). When a voice call comes in on the second SIM card, the mobile interrupts the communication with the first network during the phone call. In other words, it's not possible to access the Internet via one network and have a phone call over the other network at the same time. That means that, like three and a half years ago, it's still a dual-standby approach.

Also, like the device three and a half years ago, one transceiver chain is limited to GSM while the other chain is capable of GSM, UMTS and LTE. SIM cards can by assigned to one of those chains via the menu so its possible to switch SIM cards to and from the LTE chain for data transfers when necessary. This is useful, for example, when using one SIM card for Internet access in the home country and another SIM card for Internet access when traveling abroad. To get an idea of how that looks like in practice click on the links above. The user interface looks a bit different now but the steps to switch and select SIM cards are still the same.

When I was a teenager it took me two years to convince my parents to buy me a computer. I would have taken anything, big small, TV output, LCD display, whatever, just programmable please. I finally got one but it took too long, mostly because even home computers were expensive at the time. Well, times have really changed, haven't they!?

Yesterday, Eben Upton, one of the creators of the Raspberry Pi, announced the $5 Raspberry Pi Zero. It's much smaller than a "normal" Raspberry Pi, has fewer connectors but is more powerful than the first Raspbery Pi and can act as a fully functional as a desktop computer as it has an HDMI (mini) out and old fashioned TV interface (for which a connector has to be soldered onto the board). Even better, to get one, just go around the corner to a newsstand (at least in the UK) and pick up the latest edition of the Magpi magazine for 6 pounds in which the Raspberry Pi Zero is included as a supplement. Wow, I just imagine myself as a boy having done that instead of having had to preach to my parents for years about the need for having a computer.

I wasn't quite sure when I started writing this article but while writing it, I found this video in which Eben confirms that the Pi Zero is the first "real" computer ever shipped as a magazine supplement! True, an SD card is needed as a mass storage device in addition to an HDMI cable to connect it to a TV as well as a mouse and keyboard which easily exceed the price of the Pi itself, but hey, compared to two years preaching that's a hurdle that can be overcome easily as all of these things are available in abundance and can probably be gotten second hand for next to nothing.

A "real" computer as a supplement in a computer magazine that can be bought at a news stand! I'm sure the late Steve J. would agree, this is insanely great!

When I was recently in China a number of my fellow travelers asked me if I could access the Google Play store. Over a Wi-Fi connection without a VPN I couldn't. I wasn't really all that much surprised, most Google services, Facebook, etc., etc, and most VPN services with servers outside of China are blocked as well, so why should the Play Store be accessible?

Well, for one thing I thought at first, because there are said to be 700 million Android based smartphones and tablets in China. As we are all taught how important it is to download software only from a carefully controlled App store these days, how are those 700 million devices getting software and updates? So I asked one of my local friends with a Chinese Android device if Chinese Android devices can access the Google Play store. As expected I got the answer that the Play store does not work in China and that people just search for Apps on Baidu (the local Google search equivalent) and install it right from a web page. Baidu offers and app store for Android as well but direct installation from web pages seems to be quite popular as well. So much for security screened apps and automatic updates.

Perhaps 700 million Android devices without access to the official store is one of the reasons why Android still makes it easy to download apps from, what is called, "unknown sources" in the user interface and allows to use alternative App stores (of which there seem to be quite many in China). If I were a cynic I would probably be thankful for the censorship so I have more freedom.

Which makes me wonder what kind of concessions Apple had to make as their app store can be accessed in China…

Incredible, I made my first video call only or already a decade ago, depending on how you look at it. At the time I was convinced it would become a mass market phenomenon once more people had 3G phones. It didn't really work out like that, however, and I have to admit that the service never really became popular, perhaps because most network operators massively overpriced the service and failed to continuously innovate and evolve the service.

Today, 3G video calling is still in the same state as it was 10 years ago. For today's devices the resolution and frame rate of the video is far too low and picture quality on the large screens of today's devices is far from what people expect. In the meantime some network operators have even given up on the service entirely and have begun blocking the service for new subscriptions.

But I'm glad that others haven't given up and have continued to innovate. Facetime on mobile has reached some popularity, e.g. see my post from New York from back in 2011. Personally, I use Skype for smartphone and tablet video telephony. Over LTE and even 3G, the video resolution and frame rates are fantastic. These days, I'm seeing more and more people engaged in video calling, especially at airports. Still a niche when compared to the billions of voice minutes generated every day, I agree, but nevertheless quite mature and useful today.