How many voip calls can you squeeze through an access point?

While
checking out the eTel conference website to create a list for Debi (aka mobile
jones)
of sessions that I am interested in, I’ve stumbled over an interesting
article of Matthew Gast
analyzing just how many Voice over IP calls can be
squeezed through a Wireless Access Point. 22 to 23 is the answer 😉 In the
article, Matthew goes into the details of preambles, WLAN, IP, UDP and RTP
headers and shows how they influence the data rate and total number of
simultaneous calls. The article also
gives a brief overview of the voice codecs used by a number of voip systems
(including Skype!) and their required bandwidths.

The manuscript is ready!

To all people who have not given up calling me in the past twelve months to see if I am interested in joining them for a movie, party, or other quality time fun and always heard "sorry, working on the book": See the picture – it’s done, the manuscript is in the mail. 700 double spaced pages of wireless network knowledge. Might as well go out now again to see some sunlight (or a movie 😉

Now it’s the publishers turn to typeset the manuscript and make a real book out of it.   I am somewhat exhausted, but very happy and can hardly wait to see the final result.

See you at the movies 🙂

 

Series 60 and Audible Audio Books

I’ve subscribed to Audible a couple of months ago to download audio books instead of buying them from Amazon ,listening to them, and afterwards selling them on eBay. The only problem with their service is the DRM protection of the audio files. As there was no player available for Series 60 devices available that work with Audible, I had to burn the audio books on CD and  rip them from there into MP-3 format (I refuse to carry my 6680 and a MP-3 player!!!). Tiresome work, especially for 20 hour audio books which require 16 CDs. Nevertheless, I still prefer that to Amazon/eBay buying selling which also requires the MP3 ripping to put them on my mobile phone.

Now it seems Audible has recently launched ‘Audible Air‘ for Series 60 devices. Great application, it loads the audio books right over the network into the phone. However, you should have an unlimited data plan for this  (we are talking about 200 MB for a 20h audio book) whichi s unfortunately not yet offered for a reasonable price in Germany. So I was looking for a way to move the audio files from my PC to the phone and import it into the application as the link above mentions that this is possible. Zip, nada, nothing… The application just doesn’t want to recognize the files. On top, there is no manual for the application on Audible’s web site so I can’t even verify if I did something wrong.

So what’s the point in developing an S60 application that insists that it only wants to have the data over the air? It will be a nice feature in a year or two when unlimited data plans are a common thing… I am somewhat dissapointed.

The 1 kb/s 3G surfer

Every now and then a ‘brilliant’ analyst claims that UMTS is just too slow and only a couple of users would be enough to fully load a cell. However, they usually never reveal how they come to this conclusion. So let’s set something straight here:

Data Rate

Only a few years ago, a per user bandwidth of 384 kbit/s over the air interface almost seemed like magic. Compared to DSL speeds today, it seems to be rather slow as entry level DSL usually starts at 1000 kbit/s today. For web surfing, the main application of most people today, there is only little difference between page download times of UMTS and DSL. For file downloads, a data rate of 40 kbytes/s can also not be called slow. Here, DSL undoubtedly has an advantage. Voice over IP (over UMTS) software such as Skype also works quite well. And, not to forget, networks are about to be upgraded to HSDPA which increases peak data rates to  2-3 MBit/s per user. Not quite here yet, but coming soon.

Users per Cell

The next myth often spread by analysts is the low number of subscribers that can be served by a cell. It is certainly true that only three users can be assigned a 384 kbit/s bearer simultaneously in order preserve some bandwidth for voice telephony and slower data connections.  If all three users would transfer a file simultaneously or stream a video, the cell would be fully loaded. However, not all users of a cell download data at the same time. Apart from “power users”, most subscribers use their Internet connection for web browsing and only seldom for downloading files or streaming audio or video content. This will surely change in the next couple of years, but the network continues to evolve as well with HSDPA and other future enhancements.

Voice over IP systems, such as Skype, will surely be used by more and more people in the future. However, the data rate generated by such applications is around 3 kByte/s in both uplink and downlink direction. This is much less than the 40 kBytes/s offered by UMTS today. Intelligent Radio Resource scheduling in the UMTS network can detect streaming at a lower rate than what is offered by the current channel, and can automatically reduce the amount of bandwidth dedicated to the user on the air interface. Thus, more bandwidth is available for other subscribers of the cell.

Let’s make a real life example

If I am working away from the office, I generate about 40 megabytes of traffic in about 10 hours. This includes eMail, web browsing, company database access and Voice over IP via Skype. 40 megabytes seems to be a huge number at first. The average data over time however is only 40.000 kbytes/s / 10h / 60 mintues / 60 seconds = 1.1 kbytes/s.  Compared to the theoretical bandwidth of a cell of about 1500 kbytes/s this is not a lot and about 1000 other subscribers with the same amount of traffic could use the same cell simultaneously. However, to go shopping with such a high number just as wrong as the claims by analysts that a cell is fully loaded with only 3 subscribers. So let’s refine the calculation by taking some real life factors into account:

Resource Handling: Once the network detects that a subscriber wants to transfer data, it usually assigns more bandwidth then required. During web browsing for example, the channel is seldom fully used. After the web page has been transferred, the network releases the resources on the air interface again after some time of inactivity. The channel is not released immediately to ensure a fast reaction to new data packets. This also wastes some capacity on the air interface, but is necessary to reduce delays. Let’s assume that these effects reduce the efficiency of the air interface by 2/3. This reduces the number of simultaneous users per cell from 1000 to about 333.

Busy Hour: In most networks, there are certain hours of the day during which users are more active then during others. Let’s assume that during busy hour, usage is 5 times higher. This reduces the number of users per cell down to 66.

On the other side, a single base station site is usually comprised of 3 cells, each covering a 120 degrees sector. Thus, the number of high speed Internet users per base station increases to about 200.

All right, let’s talk about money. Let’s assume that a high speed Internet user would pay around 30 Euros a month for anytime, anywhere Internet access. 200 subscribers/cell * 30 Euros * 12 months = 72.000 Euros. Accumulated over the lifetime of a base station which I assume to be 10 years, that’s 720.000 Euros. I am sure the cost of the base station and operational costs are surely lower. In addition, the base station is also used for voice telephony and other low volume Internet applications such as MMS, which generate a lot of additional revenue for an operator.

The bottom line: There is really no reason for mobile network operators to complain and keep prices at the current level except for their margin. Furthermore, HSDPA is already on the horizon which increases efficiency of the base stations and subscriber speeds.

1 MMS in 20 contains a virus

Fortinet reports in it’s december summary that 1 out of 20 MMS messages is infected by the CommWarrior.A or B virus. They say they detected this after installing antivirus software on an operator’s MMS Gateway in Germany. CommWarrior is a virus for the Symbian Series 60 / S60 platform and uses Bluetooth and MMS messages to distribute itself.

The virus can’t tell if another phone is also a S60 phone but the sheer number is interesting.  The description of the CommWarror virus above does not say how often an MMS is sent once a phone is infected. This would be important to know together with the percentage of S60 phones used and the number of MMS messages sent per day to draw a conclusion of how many mobiles are infected.

Nevertheless, it looks like it’s about time for virus protection on MMS servers. I wonder if operators charge their customers for MMS messages they filter out…

At the moment, the virus is still harmless if you care to think for a mintue before installing an unknown .sis file. However, I dread the day somebody finds out how to trick a phone’s operating system to execute code embedded in an image. Not that it did not happen on other systems (WMF…) before…

First impressions of Yahoo! Go

This week,
Yahoo launched its Yahoo! Go service that brings the Y! Messenger and the Yahoo
web based desktop including eMail, calendar, address book and notes to (Nokia)
S60 mobile phones. The Yahoo website does not give a lot of details of how the
application works and what it does, so I’ll fill the gap with what I’ve found
out while playing around with it on two phones in the past days.

The application is quite big with its 2 MB installation file.
2 MB phone memory and 8 MB on the memory card are required. It looks like the 2
MB phone memory are just required to be able to download and install the
application. Afterwards, most of the application is stored on the external
memory card.

Even though
the application is quite big it uses the already installed calendar, address
book, notes, and web browser
. I like this approach very much as I don’t want
two calendars, etc. on my phone. I like the native phone applications
especially the calendar combined with the Active Desktop that shows upcoming
calendar entries of the day on the Idle screen of the phone. That’s a real
killer criteria for me so I am glad I can continue to use this!

When the
program is installed, all entries of the calendar, phone book, etc. are
synchronized to your Yahoo web based organizer. The application uses GPRS/UMTS
for this so make sure you know how much your operator charges you for data. The
amount of data transferred is very small (after the first synchronization just
a couple of kb per synch) so that should not be a problem.
Once
synchronized, all calendar entries, address book entries and notes are
available both on the phone and on the MyYahoo web page. The phone can be set
to synchronize automatically with Yahoo’s server via a GPRS/UMTS connection or
manually by the user. I’ve set it to manual as I often travel abroad were
packet calls are charged ridiculously high… Synchronization just takes a
couple of seconds.

First
installation is somewhat tricky. The mobile sends out an SMS to a
U.K. based phone number and waits for a
reply. The reply never came when I tried it the first time. When I tried the
next day, it worked but it took over 5 minutes for the response SMS to arrive.
This needs to change as most users (including me) are not comfortable waiting
so long and will abort and retry the process. For some like Debi Jones  in the U.S. it didn’t work at all despite Yahoo claiming support for both her
network and her mobile phone. Well, looks like this is the weak spot of the
application.

Multiple
Device Support
: Yahoo! Go supports multiple phones simultaneously! Changes made
on any device or on the web are synchronized to all other devices. The different phones can even be switched on at the same time.

There’s
lots more functionality in the package that still needs to be explored. The
Yahoo Messenger has to be mentioned in here, as Christian Lindhom has not promised too much when he said in his blog that the Messenger
Application is stunning. It just looks like the Yahoo Messenger on the desktop,
just smaller.
One can even send pictures from the Gallery to other people. The
application downsizes the picture so it can be sent quickly with a reasonable
picture quality. The messenger also offers the option to take a picture with
the internal camera. A great feature especially with UMTS were you can be on
the phone and send a picture simultaneously.

The first
version of the program is already very powerful and nicely integrated both with
phone applications and the Yahoo back office. People have already come up with
good suggestions for future versions like in comments to Russel Beattie’s blog. 

Martin

Telecoms back in 1996

The way we experience time and change is a strange thing. Sometimes I feel changes in telecoms are slow. A recent article in a German online magazine which looks back on how the telecoms world in Germany looked like 10 years ago made me change my view slightly. Back in January 1996, the German telecom monopoly started to fade away and Deutsche Telekom had to lower their prices for short and long distances call considerably. However, even after the first round of price reductions, a 10 minute nationwide call still cost €3.25! Ten years later, the same call is only about 17 cents… Calls between two voice over IP clients are virually free, apart fromt he monthly flat charge for the high speed Internet connection.

Speaking of high speed Internet at home. Back in 1996, 14.4 or 28.8 kbit/s was state of the art, ADSL and speeds of several megabits per second to the home not even conceivable.

Also, who used a mobile phone back in 1996? Almost no one, which included me. Today, 10 years later, everyone seems to have at least two. UMTS and HSDPA are a reality, the wireless Internet is a reality, even though just being in it’s infancy and not used by many today. But the wireless multimegabit connection to the Internet is already there so it is very likely that it will have become just as much of an everyday commodity in a couple of years from now as ADSL today.

Lower prices have not led to cheaper phone bills for most people. Instead, they just communicate more, communicate while on the move, and spend the money they’ve saved on other multimedia services such as Internet access, music and audio book downloads, blogs, online photo albums, etc.

There are interesting times ahead!

Wapedia – A great pocket encyclopedia

Wapedia

Every now and then, I find a digital marble which seems to make my PDA and mobile phone twice as useful as before. Wapedia, a service of Florian Amrhein, is my recent discovery. The website offers an interface to the Wikipedia database for (wireless) devices with small displays. The result of a query is reformatted for small screens and pictures are reduced in size for quicker download times and better viewing on a small device. Answers to questions such as "Where is Austerlitz?" or "What is a Home Agent?" at the breakfast table or while sitting in my favorite cafe in Paris or in a train are now only a couple of clicks away. Great, thanks very much, Florian!!!