VoIP over Wifi – A Field Report

I think I am renowned for being open to try out new things, especially if they’ve got anything to do with wireless. This time I have even had a practical application in mind. The scenario: Multi tenant flat in Paris, only one phone line, constant search for the phone because somebody has put it where it doesn’t belong, always ending up with the wrong person first when I call in, nightmare each time the phone bill comes in to figure out who made which call, exorbitant prices of the local incumbent, etc. I guess you get the idea. The solution is simple, or so I thought: Wifi VoIP phones have been around for a year or so now. So I figured they would be stable enough by now to be usable over the local DSL line and Wifi Access point as well as fool proof so even a non technical person can just use it like an ordinary phone. Well, so I thought and happily set out to get a Wifi SIP VoIP phone. Reality was somewhat disillusioning.

The Phone and my "Out of the Box" Experience

The market for VoIP phones is still fairly small and there are only a couple of options. As a wireless enthusiast I opted for the UTStarcom F1000G, as its predecessor has been around for quite a while now so it should be fairly stable. The F1000G is a true Wifi phone with an 802.11g chip inside and an embedded web server so the phone is easy to configure once it’s connected to a Wireless LAN access point. I ordered the phone from Sipgate which offers a local number and a prepaid account for free together with the phone. The phone itself is not subsidized and available at Sipgate and other companies for around 130 euros. The phone came pre-configured with only the Wireless LAN encryption key to be configured by the user. Sounds simple, no? Well, it would be if the online description or the printed manual would have given a hint on the password to be typed in to be able to enter the menu via the phone’s screen. Nothing, nada, zip… O.k., well, after trying a dozen standard passwords like 0000, 1234, 12345, etc., I decided to deactivate encryption on my Wireless LAN for a minute to be able to get to the built in Web Server from my PC. Access to the configuration pages, however, is also password protected. Again, the online description and the manual mention nothing about it… But, there’s Google and a quick search revealed the standard password for the administrator account: "psw". This trick worked and I was finally able to set the WPA encryption password and the phone’s password so I can access the security features directly from the phone. Not bad for 45 minutes, except that the whole process should have taken 2 minutes…


A Wifi phone without a WLAN access point and a high speed Internet connection is like a plain old phone without a phone socket to plug it in. The difference between a phone socket and a WLAN access point is the small little fact that one of them has been around for decades and pretty much every phone (country specific…) fits into pretty much every phone socket. I had to find out that the same is not true with Wifi phones. For some reason beyond my understanding, my F1000G phone and Netgear Wireles LAN Access point with built in DSL modem (DG844GB) do not really like each other very much. Voice quality was lousy and every now and then I even lost the speech path completely, especially when going into another room. Not even a software update of the phone and access point resolved the problem. I just don’t get it. Two components, mass produced, millions of them sold and they just don’t want to work together!? I really don’t get it. In the meantime, I’ve tried the Netgear AP with another VoIP product with pretty much the same result. So the phone is not to blame for this one. Anyway, help was near as for occasions like this I have a second WLAN access point with built in DSL modem, a Siemens Gigaset SE515 DSL. So I switched off the Netgear AP and put this on in place. Incredible, the voice quality suddenly became much better and no speech path losses in the next room. Eureka! … and shame on Netgear!!!

Over the Long Run

Telephony over IP is a tough business. Not only do packets have to be sent and received at precise intervals, the equipment and software must be rock solid and not stop working over night. After all, that’s just how ordinary phones act. Unfortunately, not the F1000G with the Siemens Access point. Once a day (or night) or so, the phone suddenly looses contact with the network and refuses to do anything about it. There’s no problem with the Access Point in most cases as the notebook just works fine over the wireless connection. Sometimes the access point dies, too and the whole setup has to be rebooted. Totally unacceptable!

Voice Quality

Voice quality even during long phone calls of 20 minutes was consistently o.k. but far away from the voice quality of a standard phone. Also, other activities on the DSL line while on a call have a negative impact on voice quality. Uploads of eMails with large attachments have a very negative impact on the voice quality in the uplink, while downloading of large files pretty much destroys the experience in downlink direction. Traffic shaping is the magic word, but both of my AP’s do not support this. Simple Web surfing over my 1 MBit/s DSL line on the other hand while being on the call had no audible effects as far as I could tell.


Well, that phone goes back into it’s box and to the shop. It’s good to see SIP working in a true Wifi phone, it’s good as a proof of concept. For everyday use, however, it is much too instable and until UTStarcom has figured out a way to keep the phone communicating with the network permanently and how to improve the voice quality, it’s a no go for me.

So in the end, I am still stuck with my phone problem in Paris. But I am adventurous, so I gave the Siemens Gigaset C450 IP a try, a DECT phone with a SIP adapter box. SIP terminates in the box instead of the phone which from a technical point of view is inferior to a true Wifi SIP phone. But maybe it’s more stable. But that’s for another blog entry. To be continued…

How long will EDGE be good enough?

Walking through the countryside today I reflected on current EDGE and UMTS deployments and what to expect in the future if you are living outside of towns or cities. While UMTS just made a big jump from 384 kbit/s to 1.8 or 3.6 MBit/s with HSDPA, EDGE is pretty much the last push GSM/GPRS networks will see in terms bandwidth. Sure, standardization work is ongoing for multicarrier EDGE which might once again one day increase througput in old GPRS/EDGE/EDGE+(?) networks. But the increase will be quite modest compared to HSDPA and future 4G technology. It will come to late.

On the other hand it’s quite clear that bandwidth requirements even of "ordinary" users is increasing quickly. EDGE’s 200 kbit/s is still quite o.k. today for many things but I wonder if this will still be the case in, say, 3 or 4 years from now. Probably not with websites increasing their graphics and video content from month to month. It would be nice to see UMTS/HSDPA deployed even in remote areas by then but I wouldn’t count on it. WiMAX might be deployed in such regions but the big question is of whether travellers will be able to use such networks which will be potentially local in nature for a fair price?

But then, maybe I shouldn’t give up on nationwide 3G coverage as GSM licenses will run out in 2012 in many countires. That’s only 6 years away from now. By then, most mobiles will be 2G/3G dual mode. So maybe we’ll see some GSM network replacement with UMTS for the simple reason that there is no price difference for replacing and aging GSM BTS with a new GSM BTS or a new UMTS BTS. UMTS in the 900 MHz band would surely help in rural areas. Let’s hope regulators and operators in Europe and elsewhere get the idea.

Video of the Nokia Open Studio New York 2006

For all of you who were not able to attend the Nokia Open Studio last month in New York here is a link (via N80 geek) to the video that was recorded of the event. A must see for all mobile enthusiasts to get behind the scenes and find out more about what Nokia’s thinking about mobility, mobile phones (aka multimedia computers), convergence, multimedia and the future. And besides, it was a cool show.

Do cheap 3G licenses push coverage?

So far I always thought that high 3G license costs like the 50 billion euros that were spent in Germany would inhibit growth, deployment and use of 3G networks and services. I am not so sure anymore as according to the ITU, 3G licenses were given out for free in Finland with only a modest administration fee of 1000 euros per 25 kHz (per year I assume according to this article).

Even if you consider the difference in population (roughly 80 million Germans vs. roughly 4.3 million Finns), 0.2 million euros for 5 MHz a year is still next to nothing. While Germany has a widespread deployment of 3G networks in 2006, Finland seems to be far behind with only a few major cities covered (take a look here at the GSMA coverage maps). Also, there doesn’t seem to be a big difference in 3G pricing. Only recently, Finish carriers seem to have introduced interesting data tariffs which let you surf the web for 20 euros a month with a bandwidth limited to 128 kbit/s. Full speed access is available for 40 euros a month. Similar offers are available in other countries as well these days where operators have paid a lot more for the licenses.

So to me it looks almost the other way around from what I have initially thought if you only look at these two examples. The more expensive the licenses, the more eager companies seem to be to deploy the technology. After all, if you have spent more money for the licenses then what is necessary for buying and deploying a network it doesn’t seem to hurt that much anymore.

Two more examples to make the confusion perfect:

  • Japan: 3G licenses were given out for free as well according to this Gartner article. But contrary to Finland, 3G is a major hit in Japan these days.
  • France: Only two companies have deployed a UMTS network, with a third operator slowly starting in 2006. Cost for the licenses were 4.5 billion euros per operator. 3G coverage, however, is still limited to major cities in France (see the link to the map above again). Cities below 100.000 inhabitants usually don’t have UMTS coverage by the end of 2006. So in this country, 3G coverage is quite limited despite very high licensing costs.

Strange, though, that end user prices seem to be pretty much on the same level, no matter how much operators had to spend on licenses. Anyone’s got an explanation for this?

Summary: I think it’s pretty obvious that licensing fees do not have the same impact in each country as far as coverage and end user pricing is concerned. There seem to be other factors which are different in each country which have a much more profound impact.

Podcast: Wireless Operator Landscape in Finland

This is the third podcast in my series about how wireless operators in different countries around the world offer the wireless Internet to their users. This time I am focusing on Finland, or Nokialand as some people call it, with Nicolas Fogelhom, whom I guess many of you know from his blog about-nokia.com.

From the podcast:

  • The N70 radio is his number one application
  • Camera and mobile phone browsers as driver for the mobile Internet
  • Mobile network operators in Finland: TeliaSonera, DNA and Elisa
  • Unlimited volume data plans, limited bandwidth from Elisa. For those of you speaking Finish, take a look here for further information.
  • Competition on the Finish wireless market.
  • GSM/UMTS coverage in Finland. Also take a look here for GSMA coverage maps.
  • Percentage of UMTS phones and current phone subsidies.

The Podcast, 20min, MP3, 14MB

The previous podcasts in this series:

T-Mobile US: 3 Billion Euros for Licenses, 2 Billion for the Network

Recently, T-Mobile USA has acquired the necessary frequencies to deploy their 3G UMTS/HSDPA network in the U.S. The cost for the licenses amounts to about 3.3 BILLION euros. Compare this to the costs for hardware and network deployment of about 2 billion euros. While thousands of engineers in companies have worked to build the hardware and software for the networks, less money goes to them than to the government which hasn’t really done a lot to earn that money. Or has it!? Please enlighten me… I know, it was an auction, but I just find that imbalance somewhat strange. Seen from a different point of view, over half of the money they will charge for network access and services later on do not go to the people who’ve worked on the technology but to a third party.

P.S.: I know the imbalance is much bigger in other countries, like for example in Germany where UMTS licenses have been bought for 12 BILLION euros per operator at the time…

My N95 GPS Killer Application

O.k., o.k., so the hype around the Nokia Open Studio in New York last week has calmed down a bit. However, I still keep thinking about all those new possibilites with the Nokia N95’s built in GPS receiver module and navigation software will have. So here’s my killer application for it:

Regularly, just like two days ago again, I am talking five minutes on the phone to tell people where I am at the moment and where they can find me. Sometimes it’s complicated because I don’t really know where I am exactly and sometimes the other person does not know his/her way around in the city. Three calls and half an hour later we usually meet. No more with the N95! To tell somebody where you are, you just need to enter the navigation application and send your current location via SMS to the other party who hopefully also has an N95 in his/her hand. The SMS is usually received instantly and the navigation application can take my coordinates right out of the SMS. Two or three clicks later and the software calculates the shortest way to me. It’s already in the package. Take a look at this video which shows the mapping software on the N95.

There’s one thing that is critical for the scenario above and I hope they’ve done it right:

  • The startup time of the GPS module should be less than 20 seconds to the first fix.

Other potential killer applications which I would wish for:

  • Put location data into taken images
  • Plan a trip on the PC, download trip info to the N95 and then navigate with it
  • Take a picture, geodate it, upload to Flickr or another site for others to see in their N95 mapping application.
  • … much more once I get such a phone into my hands to try it out for myself.

WiMAX details from Intel

While doing some research on which frequency bands mobile WiMAX will be specified for I found this interesting website from Intel in which they give some information about the upcoming Rosedale 2 chip. They say that Centrino notebooks with the chipset will support both Wifi and WiMAX.

Supported WiMAX Frequency Bands

A link to this .pdf document gives further info on the bands supported by the chip. Looks like it will cover the most important band for the U.S., which is 2.5 GHz and also the 3.5 GHz band which will be used in Europe and Latin America. Good preconditions for mobile roaming. I wonder which bands will be used in Asia!? Also, the pdf document gives a good introduction to the WiMAX network architecture and how Intel plans to integrate WiMAX into notebooks.

Multiple Wireless Technologies with one SIM card

Also, take a closer look at the figures at the end of the document. Looks like Intel would like to see interfaces for authentication and billing into 3GPP2 networks (i.e. current EVDO networks). This would make quite a lot of sense for carriers like Sprint who will deploy WiMAX networks along their already existing EVDO networks. Such an interface would be required for what Intel calls "smart card re-use […] for support of seamless authentication while roaming across technologies" which Intel says "is under investigation". The wording suggests that they are not sure about this detail yet.

TCP settings for HSDPA and ADSL

HSDPA, the 3.5G speed booster for UMTS networks is up and running in many neworks these days and data cards have been available for some time. Now, HSDPA phones have entered the market with Samsung’s SGH-ZV50 and Nokia in close pursuit with the N95. As an article in the latest C’T, a german computer magazine, points out, some tweaks are required for the TCP/IP stack of the notebook to achieve full performance.

The tweak mainly consists in increasing the "TCP Receive Window" to 128480 bytes. The window is used to throttle a data transfer by using receiver acknowledgements which advance the receive window. This prevents receiver buffer overflows in the routers between source and destination which would appear if the sender has a faster connection to the to the network than the receiver. As HSDPA has a delay time of about 150ms, which is about three times higher than an equally fast DSL connection, three times more unacklnowledged data can be in transit. An appropriate window size should be much higher than the bandwidth delay product (BDP) of the connection. Take a look here for further explanations. For a 1800 kbit/s HSDPA link and a round trip delay time of 150 ms plus let’s say an additional 80 ms delay in the Internet, the BDP is about 52 kBytes.

Other values Vodafone suggests to change is to increase the "Maximum MTU size" (packet size) to 1500 and to set the "Maximal TCP connect request retransmissions" parameter to 5.

The Test Run

To see if changing the values has a positive effect, I gave it a try myself. I don’t have an HSDPA mobile yet (it’s all in Nokia’s hand…) so
instead I tried the settings on my fast ADSL2+ Internet connection.
While the round trip times of the ADSL line are quicker than HSDPA, the total bandwidth of 7 MBit/s (7000 kbit/s) I get on the line is much higher than HSDPA. Thus, changing the TCP window size should have an impact as well. To compare, I went to a web site that does not throttle transmissions on its end and downloaded a file. I achieved a download speed of about 3.5 MBit/s. With
the new TCP window setting the speed went up to an amazing 7.000 kbit/s, i.e. the line was fully utilized. So if you
have an ADSL or ADSL2+ connection with a speed exceeding 3.5 MBit/s the
tweak is not only helpful for HSDPA but also for your ADSL connection
at home.

How to Change the TCP Window Size

The TCP Window Size for Windows XP can be optimized with programs like Tweakmaster or TCPOptimizer. While Tweakmaster is easier to handle, their registration process for the free version is somewhat dubious. TCPOptimizer is really free but only seems to be able to change the settings for all network cards at once instead of individually.

It’s also possible to change the parameters manually in the Windows registry. For network cards, the TCP receive window can be changed on a per adapter basis in the following registry key: HKEY_LOCAL_MACHINESYSTEMCurrentControlSetServicesTcpipParametersInterfacec{Interface ID}.  If not already present, create a new DWORD called TcpWindowSize  and assign it a value of 64240 (decimal). I also tried to set it to 128480 but for some reason the value is not accepted and the standard window size of 17520 bytes is still used after a restart.

For dial up connections things seem to be handled differently by the operating system. Here, global values which are valid for all network connections have to be changed. These can be found in the following registry key: HKEY_LOCAL_MACHINESYSTEMCurrentControlSetServicesTcpipParameters. If not already present, create the following DWORDs and assign them a value of 128480 (decimal): TcpWindowSize and MaxTcpWindowSize.

To activate network card specific changes the adapter has to be deactivated and activated again. For global values to take effect a reboot is required. If HSDPA is not always available it might be a good idea to remove these values before using a slower connection. This might proove to be somewhat impractical to do on a day to day basis due to the required restart.

To simplyfiy the process I’ve created to short scripts which add or remove the TcpWindowSize parameter from the list of global TCP parameters. Still, a reboot is required. You can find the two scripts at the end of this blog entry. The script to add the parameters is a .reg file so it can be executed by double clicking on the icon. The script to remove the parameters again is a .inf file which has to be executed by right clicking on the icon and selecting "execute" from the menu.

Bluetooth and HSDPA

A word to HSDPA mobile phone manufacturers: Make sure you put Bluetooth 2.0 into your phones as version 1.2’s top speed of 723 kbit/s is far too slow for HSDPA. I don’t want to be stuck with a cable again!

Download add_128k_tcp_window.REG

Download remove_128k_tcp_window.inf