Category: Uncategorized

The Paris metro remains an interesting research location for me as especially during rush hour you can easily experience what congestion does to a network. Even with Opera Mini it's difficult to use the network at such times as you can almost see individual bits trickling in. Anyway, so I was wondering for a long time just how many cells they have in the metro to get an idea of the effort invested and the capacity available.

Recently I had the time and opportunity to dig a bit deeper. One line number 12 I've been looking, each metro station is covered by its own cell. By extending the coverage into the tunnels, handovers for voice calls and uninterrupted web browsing works most of the time. In other words, once cell has to absorb the load generated by all people currently waiting for a metro plus the traffic generated by the people in the metro trains currently in the stations or the tunnels.

That's an important first indication of the capacity deployed but a second parameter to come to a conclusion is more difficult to obtain: The number of carriers deployed. Unfortunately, that can't be seen with publicly available methods such as using AT commands that give you the current cell-id whenever it changes. So that part remains a mystery for the moment.

But capacity seems to be sufficient for voice calls, as all call attempts I made on the trip resulted in a connection. So no blocking here. The GPRS / EDGE side of the network is another story though. While speeds are good during non rush-hour times, the PS side is totally overloaded when people go and come from work. So either there are not enough timeslots available or some of them are taken for voice calls. Again, difficult to tell.

But one thing is good to know: With one base station per metro station, it is much easier for network operators to increase capacity if they wanted to compared to a situation in which a single cell was used for much longer parts of the underground network. But please don't bother adding a GSM TRX or two, just add 3G to the mix as other cities have already done to fix the issue for good.

I am just sitting in a café enjoying a late breakfast working on some stuff on my netbook. Instead of being connected over 3G I use the local Wi-Fi hotspot and a VPN for security. Not that I don't like using the 3G macro network but this way I don't have to plug in a 3G USB stick. But then, this comes at the expense of slower speeds as the Wi-Fi hotspot seems to be connected to a slow ADSL line with 'only' 2 MBit/s in the downlink direction and a couple of hundred kilobits in the uplink.

I just noticed this when sending an e-mail with a large file attachment as it took a couple of minutes for it to trickle through the line. I was tempted to stop the data transfer and use the 3G stick instead. With HSUPA and uplink speeds of 1.5 MBit/s it would have been much faster. But then, too much work to reorganize (…), so I just put the transmission into the background and continued working on other stuff in the meantime.

There we go, now hotspots aren't necessarily always faster anymore compared to the macro network.

Back in December 2007 I wrote a post on the term 'dumb pipe' that was starting to make the round and spreading negative emotions around the topic that in the Internet world, networks are transporting data while Internet based companies are actually getting the service revenue. I can understand where this twist came from but suggested that there is another way to look at it:

In an article by Chris Anderson, he pointed out that fact that most services on the net are pretty specialized and are hence on 'a long tail' and don't really make very much money at all for the service provider. However, for those enabling the services, i.e. the networks, it very well generates money. When applied to network operators, long tail services provide the incentive in the first place for people to go online and spend money for connectivity. At the time the term 'long tail enabler' started to emerge in my mind and I have used it ever since when somebody mentioned the 'dumb pipe' to offer an alternative way to look at it.

Obviously, the term 'long tail enabler' is a bit clunky to explain to someone who's not heard of the 'long tail' concept before. Now Dean Bubley over at Disruptive Wireless has come up with the term 'happy pipe' and part of what he means with this goes in my direction. I very much like the term as it contrasts a wording with a very negative spin with a wording that has a very positive spin.

I've rumbled before about the size of the 3GPP 3G Radio Resource Control Specification TS 25.331 here when I noticed the significant size difference to the much more lightweight brother specification for LTE. You can feel the whole weight of it when you try to open it and search for something specific. Without a mainframe computer it's impossible to browse it efficiently anymore and converting it to PDF to make it a bit more manageable is a night time task while you sleep. So hey, guys over there in RAN, how about splitting this document up in several parts!? It's been done before for other specs, ask the RAN4 people and have a look at the split test specs documents 🙂

I have just arrived in one of the few cities in this part of the world in which the metro (underground, tube, whatever you call it) is not covered by mobile networks. It's a sad state but maybe the mobile gaming industry is rejoicing as I noticed a lot of people this time using their mobile device, which has become utterly useless once they stepped into the underground for one of the few things that still work without the network: Offline gaming. But one could also turn the stick around and ask: As more people go online on their mobile devices, will mobile gaming revenues decrease due to people preferring to do things online rather than playing a game while commuting?

It's been a while since I last wrote a post on Bluetooth because the latest and greatest version that has been in use now for a number of years is still 2.1. Last year, however, the Bluetooth SIG finalized version 3 of the standard which includes the use of a Wi-Fi radio as a high speed option to transfer data. And just a couple of weeks ago, the Bluetooth SIG finalized version 4 of the standard for ultra low energy data transmission.

So are you aware of any Bluetooth v3 devices that will appear on the market anytime soon? I can imagine a couple of applications such as transmitting pictures quickly from the mobile phone to a Bluetooth / Wi-Fi enabled photo printer or to a PC but I haven't seen any announcements yet!?

And what about Bluetooth v4? What's the likelihood of devices using the low energy option in the next couple of years and which applications will be first?

I'll keep looking!

P.S.: For those with an appetite for the details, you can download all versions of the BT core specifications here.

One of the things that keep me from upgrading to an even more Internet connected device (or devices…) are the still very expensive roaming charges for Internet access. As I travel a lot I don't want to use my gadgets differently at home vs. when I travel abroad and there is sometimes just no time to buy a local prepaid SIM for Internet access.

However, I wonder if the trend to more connected devices will eventually bring a change here!? These days, smartphones of all shapes and forms are selling like hotcakes, mobile Internet use is growing strongly and new kinds of devices like tablets with built in 3G connectivity are also becoming popular.So I guess pressure from customers will rise once they discover how much it costs to use the devices they have integrated into their lives while on vacation or business abroad.

With voice and SMS, users can easily keep track of charges when abroad as the use of these service is charged by the minute or by the message. But with Internet connectivity, users have no idea how much data is transmitted by the e-mail client and other applications in the background. Widespread use only became popular once flatrates, potentially with a speed cap after a certain volume, where introduced. To me, it looks like the mobile Internet international roaming situation is at the same point as national use was a couple of years ago. Consequently, I hope international data roaming will also take a different direction than voice roaming did.

Maybe it will be seen as an incentive for some network operators to join forces and finally make data roaming affordable!? What do you think?

Some shameless self-advertising today: Intel has just included my book 'Beyond 3G – Bringing Networks, Devices and the Mobile Web Together' in the telecoms section on their recommended reading list. It's a great list which includes lots of books that I have in my bookshelf as well so I feel even more honored. If you'd like to take a look, here's the link.

In the standards, LTE has been specified for speeds up to around 350 km/h. The faster a user is moving the more tricky it gets to deal with fading, Doppler effects and handovers between cells. But that speed value from the standards is just a theoretical value, to be proven in practice.

It seems Huawei has just done that when they recently demonstrated their network's capabilities to journalists during a super high speed magnetic levitation train ride from Shanghai to Shanghai airport. At speeds of 430 km/h the connection was still maintained at high throughput as reported here by CNet news. Interesting pictures of the event are available here.

Via: Lightreading

Already since the very early days of 3G, there have been 5 air interface states in the specs: Cell-DCH, Cell-FACH, Cell-PCH, URA-PCH and Idle. In all networks I have so far encountered, only Cell-DCH, Cell-FACH and Idle have been used. I haven't seen the other two states yet, which can reduce the time it takes to return from a dormant to a fully active state, so I could only speculate on their effectiveness. Until today.

Here is a typical round trip delay (ping) behavior when returning from Idle to Cell-DCH:

PING 85.214.10.20 1000 (1028) bytes of data.
1008 bytes from 85.214.10.20: icmp_seq=1 ttl=47 time=2571 ms
1008 bytes from 85.214.10.20: icmp_seq=2 ttl=47 time=226 ms
1008 bytes from 85.214.10.20: icmp_seq=3 ttl=47 time=236 ms

Due to the state switching the answer to the first ping, the request takes over 2.5 seconds. Especially when web browsing this delay is quite noticeable.

And this is the round trip delay profile when returning from Cell- or URA-PCH to Cell-DCH:

PING 85.214.10.20 1000 (1028) bytes of data.
1008 bytes from 85.214.10.20: icmp_seq=1 ttl=47 time=987 ms
1008 bytes from 85.214.10.20: icmp_seq=2 ttl=47 time=236 ms
1008 bytes from 85.214.10.20: icmp_seq=3 ttl=47 time=236 ms

Instead of 2.5 seconds, the first answer is already received in less than a second, which significantly improves the overall user experience. Further, I observed that the network is configured with a fully active Cell-DCH state for 20 seconds after which the Cell- or URA-PCH state is entered pretty quickly without staying too long in Cell-FACH state.

Once in Cell- or URA-PCH state the network first goes to Cell-FACH and remains there if only small IP packets are are sent. This was the case for example with a standard ping which is why for the example above, a 1000 byte ping message was used to trigger an immediate state change to Cell-DCH. This is quite typical for web browsing as when clicking on a link, the HTTP request package has that kind of size if the page is on the same web server and hence no DNS lookup is required, the TCP link is already established and the request including cookies are sent straight away.

I also did some tests with my somewhat 'older' N95 8GB and with an old firmware version. Here the first packet took around 1500 ms to arrive. Quite a bit slower than the times above reached with a current Class-7 HSPA 3G USB stick but still much faster than returning from Idle state.

For further background reading on the state changes and procedures there's always my book on the topic for a more detailed introduction and 3GPP specs TS 25.331 for all the details.