Prepaid Mobile Internet Access In Austria

I am in Austria for a couple of days again and finally had the chance to get hold of a 3 Prepaid SIM card for Internet access. The price 3 charges per megabyte is 80 cents. It’s a bit too expensive to be used with a notebook but o.k. to check eMails and surf the web via the mobile phone.

The SIM card is €19,90 with an already included balance of 5 euros. When buying the SIM card make sure packet data services are activated for the SIM card in the shop. The access point name (APN) for web, eMail (POP3, SMTP), etc. is "". For easy access and bookmarking I’ve put the information on the Prepaid SIM Internet Access Wiki as well.

Happy surfing!

P.S.: For Internet access with a notebook while roaming in Austria, Vodafone Germany’s Websession offer is still the best choice.

How To Top-Up A Vodafone Prepaid SIM for Websessions

A final piece of information for users of Vodafone Germany Prepaid SIMs for Websessions has so far been missing: How to top-up without scratch cards that can only be bought in Germany!?

Here’s a link to an online service here that allows to top-up German prepaid SIM cards. The pages itself are in German but pretty easy to figure out for non natives as well. To top-up a Vodafone SIM card, select "Vodafone CallNow", create an account by typing in your eMail address, specifiy the SIM card’s phone number, select the amount to top-up and enter your credit card details. After a minute the selected amount is on the SIM card and can then be used for WebSessions. All quite straight forward and works well.

HSDPA On A High Speed Train – Part 2

In the previous blog entry (here) I have started to report my experiences while using Vodafone Germany’s 3G HSDPA network on board of a high speed train from Saarbrücken to Frankfurt. On this line the 3G network experience is quite positive and for the general remarks see my first entry. In this second entry I’ll now show some information retrieved from Wireshark traces I took during the ride. They reveal stuff that is very difficult to simulate in the lab without special equipment. In short, a treasure chest for the TCP researcher.

All figures shown in this blog entry were made at a train speed of about 200 km/h and come from a trace of a 6MB file download. Figure one on the left shows the throughput during the file download. Total transmission for the file was about 75 seconds, top throughput about 1.5 MBit/s and average throughput about 800 kbit/s. During the file download three transmission outages can be seen at 25s, 43s and 64s. Each of them lasted about about 2.3 seconds. These timeouts where either caused by a handover or by very bad network coverage at these times.

The trace behind the graph reveals that despite the outage no TCP packets where lost so obviously the RLC layer of the radio network recovered all packets. On the TCP layer, however, such prolonged outage times without acknowledgments provoked a TCP timeout resulting in the automatic retransmission of about 15 kBytes of data (11 packets). This is shown in figure 2 on the left. Packet 2796 marked in black is the last packet received before the outage at 23.52s. Communication resumes at 25.76 seconds and it can be seen that no packet is missing by looking at the ACK numbers. The green packets that follow must thus have been saved by the RNC in the radio network. Starting with packet 2809 the sender suddenly retransmits packets (the black block in figure 2) that have already been received and ACK’d after the outage. However, the ACK’s were not received by the sender of the data in time which provoked the TCP timeout and the automatic retransmission.

Figure 3 on the left shows the packet interspacing diagram for the file download which tells a lot about HSDPA HARQ (Hybrid Automatic Retransmission Requests) operation on layer 2 of the air interface between the Node-B and the mobile. I was quite surprised to see that even at such high user speeds most packets where delivered without retransmission, and only about 20 – 30% going through one retransmission. This is quite similar to the traces I made when not moving as shown for example in this blog entry.


The trace discussed above shows impressively that high speed Internet access on board high speed trains without any on board equipment is possible. The radio network used for the test was certainly not optimized to give the best coverage along the railway. Nevertheless, overall throughput and recovery behavior on the TCP layer are impressive.

3G and HSDPA Internet Access On A High Speed Train

So far I’ve tested HSDPA all across Europe and have enthusiastically reported the great results on this blog (see here). Usually, I use HSDPA in a nomadic fashion, i.e. while being at home, in hotel rooms, on customer sites, etc. This is simple for the network, not much mobility management, no handover, stable radio environments, thus not much of a challenge. But how does HSDPA perform on a high speed train? I didn’t know until recently when I took a German ICE high speed train on the brand new LGV Est Européenne (Ligne à Grande Vitesse) from Paris to Frankfurt.

From a radio point of view the line is kind of black and white. On the French side, UMTS / HSDPA radio coverage is almost non existent. Even while still in Paris, my mobile frequently lost the 3G network once we got out of the train station. Once on the German part of the track, however, I had HSDPA coverage about 70% of the time during the 2h trip between Saarbrücken and Frankfurt. During the rest of the time, my connection fell back to the 2G network and there were only very few places without any network coverage at all.

The Network Under Test: Vodafone Germany’s 3.5G network

The Test Equipment: No fancy stuff, just a notebook and a Motorola V3xx HSDPA category 6 mobile phone, bought back in Rome a couple of weeks ago.

The Result:

During the 2 hours I ran a lot of throughput tests and downloaded around 75 MB of data. The Train speed during most of the tests ranged between 150 and 200 km/h. Very surprisingly, speed did not seem to have a great impact on the data rates. No matter how fast the train was going I always got peak data rates of about 1.5 MBit/s while radio coverage was good.

As there was no dedicated 3G radio coverage for the track there were of course also periods during which radio coverage was poor. Here, data rates dropped but were still at a respectable level of around 250 – 500 kbit/s.

I was also very positively surprised of the handover performance. Shortly before a handover occurred, radio conditions usually got quite bad so the file downloads slowed considerably. Then there’s a gap of around 1 or 2 seconds before the situation improves and the transfer speeds recovered within a few seconds. Downloads of 6 MByte files had an average throughput according to Wireshark statistics of 850 kbit/s with peak data rates of around 1.5 MBit/s. Not a single download failed!

To get a better feeling for the handover behavior I checked the link stability during handovers by sending pings to the network. Packet loss was minimal and seldom were two ping responses lost in a row which would have pointed to a prolonged network outage. To see how many packets are lost during handover I set the ping timeout to 500 ms. Here, single packet loss started to increase which points to a connection interruption during handovers or multiple failed RLC retransmissions during bad radio conditions. Most packets that were reported as lost due to the reduced timeout where nevertheless delivered, just a bit too late to be counted as a valid response. A Wireshark trace revealed that almost all ping responses eventually made it back to the notebook. This test indicates therefore, that HSDPA handovers take between 0.5 and 1 seconds. Sounds almost too good to be true. When analyzing some of the Wireshark traces in which I recorded the throughput tests, however, I could see that at some points the radio connection was lost for about 2.5 seconds (more about this in the next episode). Whether this was due to handovers or simply very bad radio conditions is difficult to say. But even if this can be attributed to handovers only it’s not too bad for a start. It’s probably also important to point out that it’s still early days for HSDPA and optimal handover performance was surely not very high on the R&D agenda so far.

File downloads and ping experiments are not the typical network usage so I also tested sending and receiving eMails and web browsing. I have to say I felt little to no difference in page download times compared while moving at high speed in a train compared to sitting at my desk at home.

Also worth mentioning is the software stability of the Motorola V3xx mobile. While most other mobiles I used in the past have sooner or later become confused by the many handovers and 2G/3G network changes with an active Internet connection, the V3xx was rock stable. Not a single reboot was required during the whole trip and the mobile even performed 2G to 3G network reselections during file transfers.

Apart from the good HSDPA performance, Vodafone has made a good job engineering their network between Saarbrücken and Frankfurt. During the two hours the Internet connection did not drop once  (e.g. due to missing datafill on the SGSNs for intersystem handovers). This is rather exceptional as on other lines, like for example between Munich and Stuttgart, my Internet connection usually drops a couple of times. So whoever did the network verification along that track, please Vodafone, send him to optimize the Munich – Stuttgart line as well. And while you are at it, install additional 3G base stations along the line, I’d really appreciate the same performance as between Saarbrücken and Frankfurt.


Before doing the tests I was a bit skeptical about the outcome. The good results, however, speak for themselves and certainly answered a lot of questions concerning high speed Internet access on high speed trains. The results also indicate that dedicated 3G train line coverage would fill the gaps observed and result in a very smooth user experience independent of train speed and also without any on board equipment such as 3G/Wifi bridges.

Stay tuned for the technical deep dive once I have analyzed the Wireshark trace I took in more detail.

Vodafone WebSessions Tested in A1’s 3G Network in Austria

As a frequent traveler I often use Vodafone Germany’s Websession offer which lets me connect wirelessly to the Internet in most countries in Europe and also in some countries overseas using 3G UMTS or 3.5G HSDPA. I’ve first reported about the details of the offer here and also posted reports of how well it performs in Italy, France and Switzerland in the meantime. This blog entry takes a look at how the offer performs in Austria:

A1’s 3G network (Mobilikom) coverage area throughout Austria is excellent and even in areas without 3G coverage, EDGE capable GSM base stations deliver throughput good enough for work and play. While in 3.5G HSDPA coverage, I reached top speeds of about 2 MBit/s when downloading three files simultaneously.

Single file download top speeds where at about 800 kbit/s. As in previous cases I am still a bit puzzled to why that happens as round trip delay time for the file download was around 230 ms. Together with a TCP window size of 65k, the throughput of a single TCP session should be 2.2 MBit/s. Note: For background information on the effect of the TCP window size and round trip delay times on throughput see here.

Nevertheless, 800 kbit/s per file is more than what I observed in Italy and France where bandwidth is throttled to around 500 kbit/s overall, independently of how many files are downloaded at the same time. Looks like Vodafone A1 does something differently with Vodafone Germany then the roaming partners in Italy (Vodafone Italy) and France (SFR).

So all things taken together the Websession performance in Austria is quite convincing, too.

Wireless Internet Access: Consumer Theory and Reality

Due to my recent reports on high speed wireless Internet access via prepaid SIMs in Italy (like here, here and here) I recently got an eMail from somebody who will go there for some time asking for my advice. At first, I wanted to write a short and crisp reply saying “no problem”. Once I started typing, however, I realized there are actually more than just a few things to consider. So here’s my response:


The Theory

You know I’d really like to give you the following answer: Yes, no problem, go ahead, buy the HSDPA card, go to Rome, pick up a prepaid SIM and you are all set. Or even better, just take your notebook to Rome, visit a TIM shop and they’ll sell you a prepaid SIM, a data card for a reasonable price, and install it on your notebook while you are in the shop. Reality, however, is a bit more complex. Not because it has to be but because of a less than ideal way of how things are handled by the parties involved.

The Reality

Buying a Mobile Phone or PC Card

Buying an HSDPA Express card in the US and bringing it to Italy should work. Before you buy however, make sure of two things: For once, the card must not be locked to a specific network it must be open to all. Therefore, buying an HSDPA card from a network operator will not work as they are usually locked. […] Second, you should make sure the card supports the European UMTS band, which is 2100 MHz. The US uses different frequency bands so if the card is limited to them it won’t work in Europe. Third, you should also make sure you can get software updates via the web page of the manufacturer. It’s not uncommon that cards get pushed out the door with an unstable software version at the beginning so being able to update it is important.

Getting a SIM and Activating Mobile Internet Access

So let’s say you have a card and you’ve arrived in Italy. TIM definitely has the best HSDPA network for your purpose so I advise you to go for one of their prepaid SIM cards. Try to find a TIM shop with a helpful and friendly shop assistant and buy a prepaid SIM. Once you’ve got it, put it into a normal GSM phone and make a phone call which gets connected. This way the card is activated and only after that is it possible to put some more money on the account in order to enable the data option. Note: Just calling another party which does not pick up does not work, the call needs to be connected. Don’t ask me why. To top up, buy a top up card and be prepared to read the Italian instructions. In the TIM network you can top up your prepaid SIM by buying a scratch card and sending the secret digits via SMS to the network. Some shops also offer top ups by giving them the telephone number of the line. Works nice as well. Once there is enough money on the prepaid SIM you can activate the data offer. I think the offer is called WEB FACILE 500 MB so ask the shop attendant in the TIM store how to activate this option. Afterwards, happy surfing.

House Keeping

I don’t think TIM warns you when you are close to having used up the 500 MB or when the 4 weeks for which it is valid expire. God only knows why. So you have to check every now and then how much is left on your card by calling the TIM voice server and go to menu 3. If you are close to your limit, put some more money on the SIM card and extend the option. I am not sure how to do this as I tried as described and it didn’t work. An Italian friend of mine then called the TIM hotline and after 20 minutes of heated discussion in Italian they did it manually.

Another option is to buy a prepaid SIM card of WIND. They also seem to have an HSDPA network in Rome now. Their network performance is not as good as TIM’s when I was there but it probably also will do the job. However, you’ll get more bits for your buck  🙂  Their offer is called WIND MEGA NO LIMIT 15000.

In Building Coverage

As long as you have a window in the room and are not underground it should be all right. It’s still a bit of a gamble but you should be fine, Rome is well covered.

Misc Stuff

Other options: In case you can’t find an unlocked HSDPA card to buy in the US you can buy an HSDPA capable card or phone in Italy. If you buy a card it’s probably locked to the operator. USB adapters are another interesting alternative because you can place them in a good spot without moving the notebook if coverage is less than ideal. Phones can be bought unlocked, you might have seen that I choose to do this when I was there and bought a Motorola V3xx with a branding from TIM. As it turned out it worked fine in all networks except for TIM’s. Again, completely beyond me.

So I hope I haven’t discouraged you from going ahead with your plan. It can be done and if you have an Italian friend who knows a thing or two about computers and maybe also something about how to connect wirelessly to the Internet you should get it working without too much trouble.

Looking at it from the bright side I think one could say that there is lots of room for improvement. All it takes is the will and a bit of work from network operators…

Hope this helps,

So to me, how things could be (an not unrealistically so) sounds a lot nicer than how things actually are. As I said, there’s a lot of room for improvement…

Interesting Data On Rural 3G Deployments

Here’s a link to another fascinating article published in an Ericsson’s "Review" periodical. This one deals with the technology and business case to cover rural areas with 3G WCDMA HSPA for mobile telephony as well as for fixed and mobile broadband Internet access. I was quite surprised to see Ericsson disclosing and discussing a number of very interesting numbers in a public paper.

One part of the document deals with the technical background information on the WCDMA 850 MHz network deployment by Telstra in Australia. The paper describes how different factors such as antenna types and configuration of base stations, indoor and outdoor directional antennas at customer sites influence both the coverage area of a base station and throughput per user at the cell edge. Ericsson says in the paper that the typical rural 3G cell in the Australian outback has a cell radius of 60 km.  Indirectly, they also mention in that for this scenario the land needs to be flat, the radio tower needs to be very high and directional outdoor antennas are required at the subscriber’s home. Note: Telstra’s got a coverage map online here, type in 6450 as postal code to get started)

Another part of the document deals with a business case for a 3G network generally and for rural deployment specifically. They base their calculation on a network with an average rural cell radius of 12 km and 15 inhabitants per square kilometer. Some noteworthy figures:

  • CAPEX for upgrade of an existing GSM site to 3G: € 240.000. I assume this is the price of the base station plus site preparation, installation, etc.
  • For their calculation they use a voice telephony ARPU (average revenue per user) of €15.- a month, €3.- a month per subscriber for mobile data and €1.- a month per subscriber for mobile TV. In addition 40% of the subscribers use the network for broadband Internet access as ADSL is not available.

With those numbers, Ericsson calculates that the cell generates €212.184 a year in voice, mobile handset data and mobile TV revenues. Broadband internet adds another €132.000 to that. A clear statement that data revenues are strong but the main revenue is still made with mobile handset voice and data applications. With a 6 year deprecation and annual OPEX costs of €40.000 of the cell, Ericsson estimates the cost of the cell to be around €80.000 a year which translates into a gross margin of the site to 75%.

And finally it’s also quite interesting to see that the paper clearly pushes 3G’s advantage over WiMAX, i.e. combined broadband Internet and voice telephony service with one infrastructure and lays out it’s arguments accordingly. A similar paper from the WiMAX industry laying out their arguments so one could compare would be nice. If you have seen one, please let me know.

HSDPA Performance Of Vodafone’s 3G Network in Italy Has Me Puzzled

Back I am in Italy for a while. I’ve grown quite accustomed to the great performance of the TIM HSDPA network, which I’ve described in a number of previous posts. This time around, I set out to test the Vodafone HSDPA network in Rome and to compare it with the results achieved in TIM’s (Telecom Italia Mobile) network. The results were quite a surprise.

I had two SIM cards to test the network. For the first tests, I used my German Vodafone SIM card and a Roamer WebSession, described in more detail here, to establish an Internet connection. As already experienced in the SFR network in France, file download speeds were capped at around 45 kBytes/s. While already quite good it falls far short of 160 kBytes/s that are reachable with my category 12 Sierra Wireless 850 HSDPA card in the TIM network.

In France I was quite uncertain if and where the speed was throttled down. With the help of the Vodafone Italy network, I can now add a further piece to the puzzle which unfortunately raises more questions then it answers. To find out more, I bought a local Vodafone prepaid SIM card for direct access to the Internet and not via the GGSN of Vodafone in Germany used by the German Vodafone SIM card. To my great surprise the download speed of the file was almost the same as with the German SIM card. In the IP packet inter-spacing diagram (for an introduction of how to interpret the diagram see here), however, the download of the same file with the two different SIM cards in the same network looks completely different. As can be seen in the first graph on the right side, the file download via the German Web Session in the Italian Vodafone network shows IP packet inter-spacing mostly around the 30 ms line. A clear but not yet conclusive indication for throttling. With the Italien SIM card however, most packets of the same file are transmitted with a packet inter-spacing time of 10 ms as can be seen on the left side of the graph. So the transmission would be much faster if it were not for the randomly distributed packet inter-spacing of quite a lot of packets between 50 ms and 200 ms. To be honest, I have no idea why some packets take such a long time to arrive. I don’t think it can be RLC retransmissions as the automatic retransmission of packets discarded by the Node-B’s HARQ process usually takes around 80 to 100 milliseconds. Also these inter-spacings were not caused by IP layer retransmissions.

More clues

I then went on to do a direct comparison of the performance of the TIM network and the Italian Vodafone network by downloading two files from different servers to exclude the possibility that the Vodafone network has a problem with the connection to one file server. The result is shown in the second graph. On the left, the download speed for file 1 and file 2 are shown for the Vodafone network. Note the constantly changing top speeds. Afterwards I replaced the Vodafone SIM card with the TIM SIM card in the wireless card and performed the same downloads in the TIM network. The result is shown on the right side of the graph. The throughput is fairly constant and much higher than in the Vodafone network. When looking into the Wireshark trace the Vodafone throughput suffers from two things. First, the random packet inter-spacing times described above. Second, I have observed IP layer retransmissions every couple of seconds which also greatly reduce the download speed. The TIM network does not suffer from any of those.


As I repeated the tests over several days and at different times of the day a temporary error or network overload can be excluded as the reason. There are two likely causes for the problems observed in the Vodafone network. The most probable one is that there is an incompatibility between my Sierra Wireless 850 HSDPA card and Vodafone’s HSDPA network. It’s still early days for HSDPA so I would not be surprised if this were the case. Another possible cause could be that Vodafone has a big IP routing problem somewhere in the network. A good way to verify this would be to repeat the tests with a different HSDPA card or mobile phone. If the situation improves it’s an interoperability issue. If not, well, then it could still be both.

Vodafone Websessions with SFR in France

Spring is one of the best times of the year to be at the Côte d’Azur in France. While the weather and landscape is great, France is really missing attractive prices for Internet access over 3G. Not really affordable for post-paid customers, nothing is available for pre-paid customers at all. A good opportunity to use my Vodafone Germany prepaid SIM card for Internet access via the WebSessions roaming offer.

Downlink Speeds

Vodafone’s partner network in France is SFR and according to their web page, they’ve got HSDPA deployed in some parts of the network. Accordingly my speed expectations where high. And indeed, when I activated the 3G connection my data card showed that HSDPA is available in the network. Speed tests performed over several days revealed however, that the downlink speed is artificially limited to around 45 kBytes/s. The limitation is certainly not the air interface as the signal strength was good and speeds I measured in Germany and Italy were much higher.

It’s hard to tell from a users point of view exactly where the bottleneck is. It could be that Voda’s Home Location Register (HLR) in Germany and SFRs SGSN in France can not exchange the QoS profile correctly which subsequently leads to the throttling of my connection. It could also be that there is a limitation on the IP link used for forwarding my packets between the SFR network and the Vodafone Germany network. It’s also possible that the SFR SGSN or the Vodafone GGSN is unilaterally limiting my speed. In practice this means that HSDPA does not give me a great advantage in the SFR network over a 3G UMTS device as the speeds are the same. Due to this I was not sure if the connection was HSDPA at all. Subsequent tests described below showed, however, that the data card really got an HSDPA and not UMTS bearer.

Uplink Speeds

After getting a 384 kbit/s uplink bearer in Italy and Germany I was also disappointed about the ‘meager’ uplink speed of only 128 kbit/s in the SFR network. It’s likely that this is no interoperability or throttling problem but a general network limitation of the SFR radio network. Either they haven’t activated the higher bearer option or it’s not yet available in the current software version of their radio network. Whichever it is they should consider upgrading or switching on the option as the difference is remarkable.

Round Trip Delay Times

One of the indicators that the data card got an HSDPA bearer and not a UMTS bearers were the round trip delay times. With the data card I got a round trip time of about 170 ms. HSDPA usually delivers a round trip time to an external host of around 120 ms (100 ms to the first hop). The additional delay is most likely due to international roaming which means that my data is tunneled from SFR into Vodafone Germany’s network before entering the Internet via Vodafone’s GGSN. With a Nokia N93 3G ‘only’ terminal I got round trip times of around 380 ms. I am not quite sure why there are an additional 200 ms of dealy as UMTS is usually only around 50 ms slower.

Radio Ressource Management

On the positive side I noted that the HSDPA radio resource management was more advanced than what I experienced in the TIM network in Italy and the Vodafone network in Germany. While the HSDPA bearer is active, the above mentioned round trip times to an external host of about 170 ms can be observed. In Cell_FACH state, which TIM and Voda’s network in Germany might not support yet, round trip delay time s were around 360 ms. This reduced activity state was only entered after around 45 seconds. After about 60 seconds the connection is put into Idle, Cell_PCH or URA_PCH state from which it takes around 800 ms to get back into active state. This is a lot quicker then the 2 seconds observed in Vodafone’s network in Germany and TIM’s network in Italy.

Skype, VoIP and IPSec

I tried Skype and my companies VoIP client over both HSDPA and UMTS and got crystal clear connections. Also, my IPSec tunnel worked fine between the notebook and my company. Very well!

Wifi competition

Except for the artificially throttled speed, my experiences in the SFR network with the HSDPA card were very positive. I should also note, however, that some Wifi operators such as Orange have moved forward a bit as well and are now offering 10 hours online for 15 euros. The 10 hours can be distributed over 30 days. For 15 euros, one can stay online for several days if the connection is only used for a couple of hours a day. For me a Vodafone 24h WebSession for 15 Euros is still better because I am online for more than 10 hours a day. Also, I need access at different locations throughout the day which is difficult with Wifi hotspots. People with less online time and stationary use, however, might find a 10h over 30 days for the same price more attractive. Also, they are not limited to 50MB of traffic per WebSession Vodafone intends to introduce in September.

P.S. For more articles on this topic, click on the HSDPA link next to the date below

Are Virtual COM Ports Fast Enough for HSDPA, WIMAX And Other Wireless Broadband Technologies?

I’ve been having a lot of fun lately with my Sierra Wireless HSDPA data card for my notebook which reaches speeds I still have difficulties to believe that they are possible over a wireless network. While many people probably prefer data cards for wireless Internet access I’d rather like to use my mobile phone to connect the notebook to the Internet. This is because I use connected applications both on the mobile phone and the notebook and don’t want to have two subscriptions for mobile data access. While the data card acts like a network adapter and thus has no speed limitation on the interface between the data card and the notebook, mobile phones simulate a modem over a serial port, also called a COM port. The question I thus had was if those virtual COM ports have the same speed limitations as their real counterparts. If so, this could be a problem for mobile phones that support HSDPA, WiMAX and other future wireless broadband technologies which can deliver higher data rates than real COM ports can transport.

The maximum data rate that can be set for a real or a virtual COM port is 921.600 bits/s. This is far too slow for modern HSDPA mobiles that support downlink speeds of up to 3.6 MBit/s. For real serial ports this limit is real as the speed setting in the modem dialog translate into commands to a UART chip to send bits over a serial wire at exactly this speed. Most if not all high end phones today, however, have no serial connector anymore. Instead they use USB for communicating with a PC. In order not to modify the dial up networking software of operating systems, serial port emulations over USB are used. To the dial up network softwae it looks like the ‘modem’ in the mobile phone is connected via a serial port. The question now is whether the same speed limitations apply to these virtual COM ports over USB as well. At least in the dial up networking menus, the maximum speed that can be set for them is also 921.600 bits/s. USB is much faster than HSDPA or any other wireless wide area network. Even USB 1.1 can already handle a speed of up to 12 MBit/s, so physically no limitation exists.

As I don’t have an HSDPA capable mobile phone yet I did the next best thing and used a Nokia 6680 UMTS mobile. Instead of setting the COM port speed to 921.600 bit/s, which is twice as high as what UMTS can deliver, I set it to 19.200 bit/s which equals a maximum transfer rate of 2.4 kBytes/s. This is much less than what a UMTS connection can deliver, about 40 kBytes/s. Then, I established a UMTS connection, started a download of a big file and monitored the throughput. As can be seen in the picture on the left, the COM port speed is set to 19.2 kbit/s = 2.4 kBytes/s. The download rate, however is 40 kByte/s.

This proves that the speed setting for a virtual COM port has no influence on the actual speed of the data transfer over the virtual connection. Thus, if both the driver on the PC and the mobile phone support higher speeds over the virtual COM port, HSDPA and WiMAX speeds will be supported without a need for modifying the dial up networking software of the operating system. Very well, so I am looking forward to testing things with a real HSDPA mobile phone!