Author: Martin

When I still had a prepaid SIM in my mobile phone and had to pay for mobile data use by the megabyte I was quite heavily using my phones Wi-Fi at home so my e-mail, web browsing, podcast downloads, etc. would run over my “free” network while being at home. Great money saver. These days, I’ve switched to a contract that includes 1GB of data a month. It’s interesting to notice that, probably unsurprisingly, I only use Wi-Fi for exceptional things like download a couple of hundred megabytes of podcasts every now and then. The rest is all 2G/3G now.

I guess it has to do with convenience as it is still a bit of a hassle to switch applications from 3G to Wi-Fi at home. Symbian makes it quite easy by having connection profiles and priorities so applications always connect to the network with the highest priority. However, the application doesn’t change the bearer once it is connected so a manual restart of applications is still required with this scheme. If you pay by the megabyte, there is an incentive to do that, but if you have a huge bucket of data available at least I’ve stopped caring.

So why do I post about it? Well, I’m thinking ahead a bit and about Wi-Fi offload scenarios. I can see network operator Wi-Fi hotspot networks and Wi-Fi networks at home as interesting offload infrastructure that is already available today. But to make it work, the switchover has to be fully automatic and fully seamless. On the usability layer that means that the phone automatically switches the bearer without the applications knowing it. On the protocol layer it means that the IP address assigned to the device must not change so the switch is transparent to the application. In other words, a form of mobile-IP is required. And there is more than one option to choose from.

When home Wi-Fi networks are part of the equation, things have to get a bit more intelligent still, as a mobile device should then also be able to access devices in the home network. Once could do that with an additional local IP address that comes and goes when the home Wi-Fi is in range or a tunnel back to the home network. This would have the additional benefit that the user could access devices and data at home even while he is not under the umbrella of his own home Wi-Fi.

I think this should be standardized to bring together manufacturers and network operators. If every operator comes up with its own solutions and manufacturers to the same thing it’ll be ugly. And since connectivity is the bread and butter service of network operators, it’s them who should take this up and get it working. In the end it has two benefits for them, macro network offload and integrating services running in the home network.

Finally, it has become more apparent than ever now that this is also a good opportunity to make sure that communication over public Wi-Fi hotspots is secure, no matter whether a notebook or mobile device is used. For details see my recent post on FireSheep. And don’t think you are secure just because you access that popular social network side from a mobile phone with an app instead of via the browser on the notebook. Are you sure the app encrypts the data before it is sent?

In some countries there's fierce competition between network operators, and the media is anually reporting about the performance of the networks. To come up with meaningful values, they perform yearly drive tests on their own in cooperation with field test companies. Reported values are then for example call setup success rates, call setup times, call drop rates, average and hotspot data throughput in the networks, etc. When recently analyzing the results of such a test in more detail, it occured to me that it's likely to be a challenge to match call setup success rates that are today beyond 98% and call setup times of less than 7 seconds (mobilt to mobile) once there is one method or the other deployed for Voice over LTE.

The challenge will be to match all of those values, be it call setup success rates, call setup times and also the drop rate when the call is handed over (or not) to a 2G or 3G network at the LTE coverage border area. CS fallback for example is unlikely to match any of those values as it is undisputed that the fallback mechanism adds 2-3 seconds to the call establishment time on each side. Also, making the fallback a success in at least 97% of the cases is a challenge as the procedure either requires the UE to blindly drop to the 2G/3G network or a well configured LTE network with perfect neighbor relationships. In addition, good interworking configuration between the 2G/3G CS core network and the LTE core for the signaling exchange of incoming calls is required. Quite a challenge. VoLTE and VoLGA would probably do a bit better in this regard but I won't go into the details in this post, no need for a fight between the two sides today.

Think about it, what will happen if a network operator deployes a Voice over LTE solution and the values do not match those of the 2G/3G network today. It's going to be a bloodbath in the press. I can already imagine the headlines…

Over at Light Reading, Michelle Donegan reports that TeliaSonera over in Sweden who were early in starting their LTE network about a year ago have now gotten competition from Telenor, who has built an LTE network together with Tele2. From a consumer point of view it's great to see a second LTE network being fired up. I haven't heard of any other country in which two overlapping LTE networks are running and open to the public yet, so that's another first.

Personally, I am a bit sceptical about the network sharing part of the announcement because that reduces competition between network operators which in the long term might not only have positive consequences for the consumer. I've done some background reading and Sweden seems to be one of those countries where this is already done for 3G as well. Interestingly, the constelation is a bit different here. While Tele2 shares the LTE network with Telenor, it's 3G network is a shared operation with TeliaSonera (click on Sweden for details). Interesting triangle. 

And on top, Telenor seems to share it's 3G network with Hutch 3G according to Wikipedia. Is your head spinning? Mine is, so here's a summary:

• TeliaSonera — LTE
• Tele2 + Telenor — LTE
• Tele2 + TeliaSonera — 3G
• Telenor + H3G — 3G

Pretty much everyone with everyone, except for Hutch 3G who doesn't yet seem to have ties with TeliaSonera.

 

Yes, app stores is where most people get their applications for their smartphones today. While this is convenient, simple and offers a way to earn money I'd argue it's not the 'natural' state of things. I'd never buy a PC, notebook, netbook or any other device where I can only download programs from a single store that is controled by a single entity with its own agenda. So why should I limit myself to that for a mobile device (think smartphone, tablet, etc.)?

This became quite apparent from a technial point of view to me when I recently tried to download something from an app store and couldn't due to some strange error that persisted for quiet a while. Well, at least I could download my most favorite apps (web browser and email client) from the web pages of the developers and thus bypass the store and the problem. A single point of failure, always a bad thing.

Recently I was in a hotel that had dedicated indoor cellular 3G coverage on the lower floors. Dedicated in this case meant that one mobile network operator installed indoor coverage with antennas distributed throughout the hotel. So I would say that most foreign visitors sooner or later landed on just that network as the other networks had only weak or no coverage at all. And despite roaming prices having come down in recent years I think calls from foreigners are still highly lucrative. So I wonder who paid whom for the indoor coverage? Did the hotel pay the network operator so guests have reception in all places where outdoor coverage is weak or is the mobile network operator paying the hotel for the opportunity to get (more or less) exclusive access to foreign visitors? I'd speculate that it's the later but that's just a guess on my side. In any case, good cooperation from both sides to make the customer happy.

One of the biggest assets mobile network operators have is the ability to handover voice calls seamlessly between different radio access technologies. If the calls starts in a UMTS network and the user leaves the coverage area of the 3G network, the call is handed over to the GSM network without the user noticing it. The reverse direction from 2G to 3G is also standardized but I have yet to observe any network actually doing it during an ongoing call. It could actually be quite useful so background data transfers such as email reception, facebook updates, etc. can continue during a voice call, something that is usually not possible unless the network supports GSM DTM (Dual Transfer Mode).

Anyway, things get a bit complicated in the LTE domain. First, there is no single Voice over LTE solution clearly dominating today, probably due to the lack of networks and devices. But let's say, for arguments sake, that we'll get there one day. How do you hand over a Voice over IP call to GSM once the user runs out of the LTE coverage area. The solution is Single Radio Voice Call Continuity, or SR-VCC for short, which has been specified some time ago in 3GPP TS 23.216. The procedure is voice technology agnostic so it can be used by IMS, VoLTE (an IMS implementation) and also VoLGA.

But once you are there, how do you get back to LTE or UTMS during the call? Well, not at all so far. However, there's a study item currently worked on in 3GPP Release 10 in TR 23.885 that gives a number of options of how reverse SR-VCC could be implemented. How interesting! I'm tempted to read it but I guess I'll just hold off until I see the first (forward) SR-VCC implementation used in a real the network. Have fun putting it into a TS until then 🙂

Have you ever tried the following: While sitting in a train, talk to someone standing outside through the window over a mobile phone.

It's interesting to experience the voice delay which isn't very big, I would say in the order of 250 milliseconds, but quite 'visible' as the lip movement of the person outside and the speech path are not quite synchronous anymore. In a mobile phone call where you don't see the other party this delay usually goes fully unnoticed unless you call someone on the other side of the planet and the delay becomes so long that there are odd silence periods and people start talking simultaneously.

The second interesting effect that can be observed is noise supression. As you know exactly how the background noise sounds outside, its interesting to hear if and how well the mobile outside surpresses the background noise and what effect that has to the talker's voice.

I haven't tethered my mobile phone with my netbook for Internet access for quite some time now for a number of reasons. One of them is that in the countries I usually stay, cheap prepaid options for a couple of hundred megabytes or gigabytes per month are available in the 10 to 20 euro price range. As a result I usually buy a SIM card that I then only use with a 3G dongle. With roaming prices capped in Europe I then mostly use my home SIM card for telephony and small screen web browsing.

But leaving that scenario asside, tethering is still worth at least 120 euros a year (based on 10 euros a month) if you can use the data contract with your phone/smartphone SIM instead of buying a separate 3G dongle and prepaid/contract SIM with it. I'm sure that still appeals to many people.

One of my 'must haves' from a mobile device in this regard is Linux/Ubuntu support for tethering. To my delight, even the latest Nokia models such as the N8 are still detected as 'modems' in Ubuntu (10.04 Lucid in my case) without any need for additional drivers. Very good!

I have noticed that espeically Android phones are used under windows as "virtual network card" but I never tried them under Ubuntu. Has anybody tried that and can leave some feedback here as to if/how that works?

Back in April I wrote a post on the dangers of NOT using a VPN over public Wi-Fi hotspots. As data is not encrypted, anyone in range using a network tracing tool on a notebook or other devcie can tap into the data traffic of the hotspot and filter out email passwords from non-encrypted POP and SMTP connections and session cookies e.g. from social networking sites (think Facebook, Twitter, …) that are only using non-encrypted http connections. While email passwords are straight forward to be used, things are a bit more tricky with the session cookies. But nothing a willy hacker with a bit of background knowledge couldn't overcome. Agreed, it takes a bit of effort which has so far probably prevented this sort of identity stealing from taking off so far.

But now cookie stealing in unencrypted public Wi-Fi hotspot seems to have become almost trivial with a Firefox plugin called FireSheep. It requires the Winpcap network driver to be installed, the same that is also used by programs such as Wireshark for network tracing. This way FireSheep can intercept all data traffic in a public hotspot and with some processing of the intercepted data, all computers used in the hotspot are shown to the user. As soon as someone with that computer accesses a service only using http, cookies are extracted and the computer running FireSheep can now be used to impersonate the other user with a single click on an icon in the browser. This is really scarry as it doesn't take a lot of effort or knowledge to install FireSheep and Winpcap. When I checked, the software was already downloaded 600 000 times! So I wonder when the first victim stories will appear. How far this will spread probably depends on the precentage of Wi-Fi adapters FireSheep can set into promiscuous mode so all packets are delivered to higher layers of the protocol stack.

Let's be clear, FireSheep does not exploit weaknesses in the browser or the OS that could be fixed. No, FireSheep exploits the intended design of public hotspots, i.e. to send data without any protection. But there's an easy fix: Use secure SMTP and POP (available from most email providers today) and make sure to only use web based services that offer https (still not done by many web sites today). If and when victim stories pop up I wonder how long it will take popular sites to switch over to https!?

On a further note, have a look at Dean Bubley's blog, he's got some interesting thoughts how this "click and shoot" hacking method might influence future 3G offload technology. Especially in that area, automatically established VPN tunnels as part of a Wi-Fi offloading solution would fix the issue for good. For the ordinary use of public Wi-Fi's, however, most users will probably still not care, know, be willing or capable of using a VPN solution. So for that scenario, https is likely to be the best defense.

Back in summer this year I ran a post on UMTS state switching and Fast Dormancy evolution to highlight the challenge current mobile devices have with battery consumption due to applications running in the background that access the Internet periodically. A major part of the current solution to the issue is a functionality referred to as "Fast Dormancy" which saves battery capacity by setting the radio link into Idle state quickly. This comes at the expense of a longer delay once data has to be exchanged again with the network and an increased signaling load in the network.

The fix for both downsides comes with the introduction of a new parameter in the Signaling Connection Release Indication message in 3GPP Release 8. With this parameter, the radio connection is not put into the Idle state but instead in the Cell-PCH state which is similar but doesn't have the afore mentioned downsides. Have a look at this post for a more detailed explanation. Usually, standards changes take years before they end up in real networks. This one, however, is quite simple to implement and there is real demand for it today. Now there are first indications from NSN, a vendor for 3G infrastructure, that they have implemented it and have run some first tests in a lab together with Qualcomm, one of the companies producing 3G radio chips.

Good stuff, let's see how quickly this is pushed out to real networks and real devices.