The Cost Of Vacation Connectivity

You might have noticed that I am blogging a bit less at the moment than normal. Among other things it’s got something to do with that I am currently on vacation traveling through Europe. Staying connected has become much easier in recent years but still requires a fair amount of self organization, a bag full of SIM cards and willingness to spend a certain amount of money. So how much do I spend for Internet connectivity during my 3 weeks vacation?

Things are complicated since I spend my vacation in four countries: Austria, Italy, southern France and Spain. For Austria I’ve bought a prepaid SIM from ‘3’ for eMail and Web access via my Nokia N93. Works well and details will follow in a seperate blog entry. Cost: 20 Euros for the SIM card and credit which lasted me for the time I spent in Austria. During 3 days I required full Internet access so in addition I used two Vodafone Web Sessions for 15 Euros each. Total amount spent in Austria: 50 Euros.

Next stop Italy. Here, things are simple. I already have a TIM prepaid SIM and use it for notebook and phone web access. 20 Euros buy me 500 MB. That’s good enough for the 5 days I am staying in ‘Bella Italia’.

Next, the south of France is on my agenda for about 10 days. I’ll use Orange’s prepaid SIM for eMail and web access via the mobile phone. That’s 6 euros. In addition I will probably need full Internet access during 4 days. That’s four Vodafone Websessions that add up to 60 Euros.

Final Stop: Spain. Just a weekend but it’s unlikely that I want to spend them disconnected. Maybe I will find enough open Wifi Access Points in the street. An alternative is a Yoigo prepaid SIM with web access for a euro a day. The SIM will cost a couple of Euros, too. Well, we’ll see.

Altogether, that’s going to be around 150 Euros. Definitely not on the cheap side. I wished ‘3’ would be present in all countries I (live and) travel to since they don’t charge extra for data roaming in their networks.

For the details on the prepaid SIMs I use, take a look on the left side on the blog for the link to the Prepaid SIM Internet Access Wiki.

802.11 Options, Options, Options

Gone are the days when standards were pure and simple (well, probably never simple, but at least pure…). Today, it seems they are cluttered with options of which most are probably never going to be implemented. The Wireless LAN 802.11 standard seems to be no exception. Let me make two examples:

Packet Transmission:

  • Default: This is the good old "backoff period – send – ack" mechanism. Easy, works well but performance is not that great.
  • Frame Bursting: Packets are sent in the following manner: "packet – ack – packet – ack – packet – ack". Still easy, was  implemented as a proprietary enhancement in many 802.11g products and has been sort of legalized with 802.11e (WMM).
  • Block Acknowledgments: An addition to frame bursting which allows transmissions without ack’s. A whole set of frames are then acknowledged once they are all sent. To make things just a bit more complicated there’s immediate ACK and delayed ACK (which seems to have been defined for devices which can’t tell right away if all went fine).
  • Aggregation: And on top, 802.11n has now specified that several MAC frames can be put into a physical frame which can now have a size of up to 64kByte. Looks like this is mandatory so all 802.11 devices should support this.

The statistics on this one are not so bad. Even low end 802.11n devices should support the default method, frame bursting and aggregation. Haven’t seen block ack’s implemented in the devices that have come by me, however.

Power Saving:

I can see at least four possibilities here:

  • Standard Power Save (PS): This has been in the standards since the beginning. Devices tell the AP that they are going to sleep and the access point buffers incoming packets. When devices wake up and see that the access point has packets waiting for them they poll for each buffered frame.
  • U-APSD: Unscheduled Automated Power-Save Delivery: Introduced by 802.11e, optional in the WMM (Wireless Multimedia) specification. Similar to PS above but once a device sends a trigger frame, the access point forwards all frames of in the buffer that fit into the service period during which the device is active. Once the service period is over, the device automatically goes back to sleep.
  • S-APSD: Scheduled Automated Power-Save Delivery: No trigger frames. Instead, a schedule is agreed between the access point and wireless devices. The devices then wake up at predefined instants and packets are delivered automatically. This one is not included in the WMM specification, so this one probably has no chance of seeing the light of day.
  • PSMP: Power Save Multi Poll. Yet another power save scheme which was lately introduced with the 802.11n High Throughput specification. This one schedules uplink and downlink transmissions of end user devices. Outside the scheduled times, devices can enter sleep mode. It looks like this power save mode has been designed for devices and applications that have constant data streams with a static bandwidth requirement (e.g. VoIP, video streaming etc.). Nice but also optional.

Statistics on this one are bad. I haven’t seen an access point yet that supports more than the classic PS mode. Has anyone seen more than this implemented yet?

Incredible! France Telecom Has A Prepaid SIM 3G/GPRS Internet Access Offer

Sometimes I can’t believe the power of web 2.0. A couple of weeks ago I have set up a Wiki dedicated to information about prepaid SIM wireless Internet access. I’ve put all my information there which I have gathered over time on offers in different countries and invited the community to put their info into the Wiki as well. It has worked more than well for me as somebody has put information about a prepaid SIM Internet access offer in France.

Incredible, in the country that can certainly be found amongst the least competitive GSM/3G markets of all in Europe, France Telecom / Orange has silently started to offer transparent access to the Internet via their Mobicarte prepaid SIMs! 10 MB are to be had for 6 euros a month. The offer doesn’t mention what happens after the 10 MB are used up but the included data volume is enough for mobile eMail and limited mobile browsing. I wouldn’t, however, use it for connecting my PC to the Internet.

Also, one should be aware that all French operators have a minimum usage fee for prepaid cards per month. A €35.- top up card for example is valid for 3 months, i.e. the monthly minimum usage is €11,66. So be prepared to use the SIM for some phone calls as well.

So I rushed into the next Orange shop to get myself a prepaid SIM to test the offer myself. The SIM card cost 19.90 euros with a credit of 4.50 euros already on the SIM. To have more than 6 euros on the prepaid account I also bought and additional top up card for 10 euros. So my startup investment was 30 euros. All that is required to get the prepaid SIM card is a valid passport of any country and an address in France. I am sure a hotel address will do, they probably appreciate the incoming advertisement…

The card is activated by calling any number or sending an SMS. Afterwards I used my 10 euros credit to to up the prepaid account. Afterwards, I called the automatic service hotline to activate the 6 euro Internet access feature. A bit of French is required to navigate through the menu. Once confirmed the 6 euros are immediately taken from the balance and the option can be used.

Luckily, my N93 automatically created the configuration necessary when it detected the SIM card of Orange. I’ve set my mobile browser and my eMail application for manual access point selection and the list already contained an entry for Orange. Very well done, Nokia, congratulations!

So I’ve been using the option for a couple of days now and my balance has remained stable, i.e. the data traffic is taken from the option and not from the balance. Very nice. Suddenly I don’t feel completely disconnected anymore in France once I leave my Wifi cloud at home. Welcome, France, to the mobile connected world!

For the details on the offer and how to activate it take a look at this Prepaid Wireless Internet Access Wiki Page.

The Nokia N800, WiMAX And Embedded 802.16e Chips

Speculations are growing that Nokia is working on a version of the N800 Internet tablet with a WiMAX chip in addition to Bluetooth and Wifi. This report on Heise News, a reliable German tech website, links Nokia’s plans with the launch of Sprint’s WiMAX network in 2008.

They also link to an interesting data sheet of a WiMAX Module from SyChip, (which they say may or may not be related to the N800 WiMAX development) which contains quite interesting high level details of first generation embedded WiMAX chips. According to the data sheet the WiMAX module is 21.6 x 23.7 x 1.5mm in size and supports 802.16e. The block diagram shows two antenna connectors for MIMO in downlink direction and single stream transmission in uplink direction. Mobile devices communicate with the embedded module either via SDIO or USB.

One of the mysteries around WiMAX to me, still, is how users and devices will be authenticated since I haven’t seen any kind of SIM card specification for WiMAX yet. The data sheet, however, says that the following security mechanisms are supported: EAP-SIM, EAP-AKA, EAP-TLS. While EAP-TLS works with certificates, EAP-SIM was originally specified by 3GPP (UMTS standards body) for Wifi authentication using  the secret keys and subscriber ID contained on a GSM/UMTS SIM card. For details take a look here. Since EAP-SIM has been specified independently from the underlying network technology, it should integrate nicely into WiMAX as well.

This raises the question though what kind of equipment is used on the network side that supports EAP-SIM authentication!? If you have more information, please let me know!

Visual Mailbox – The MMS Killer Application?

Just read on Teltarif today that Vodafone Germany has launched a new product called "Visual Mailbox". Instead of saving voice mail messages on a central server the visual mailbox feature forwards voice mail messages via MMS to the subscriber. MMS is the multimedia cousin of the SMS message and can carry text, pictures and, quite useful for this service in particular, audio files. The advantage: The user does not have to call the voice mail system anymore but listen to voice messages by selecting an MMS message in the incoming messages folder of the mobile phone. Reminds me of the voice mail functionality of the iPhone.

Vodafone Germany offers the service for no additional charge. How nice 🙂

IEEE Wifi And Ethernet Standards Now Available For Free

Nortel and Cisco have decided to use some of their marketing budget for something really useful for engineers, namely to open up the IEEE standards 802 library for free public access. These include the famous Ethernet (802.1,2,3), Wifi (802.11) and WiMAX (802.16) standards. A great help for all doing research in this area. Little downside: Only approved documents are available which excludes hot documents such as the current 802.11n draft.

How Will Users Be Able To Differentiate 11n from 11n?

In the past, things were pretty much clear when it came to Wireless LAN performance. If the box in the shop said it’s an 802.11g device, users could pretty much assume the device would do 54 MBit/s on the physical layer and application layer speed would be around 20 MBit/s. Things are much less clear with the new Draft 802.11n standard, which contains a myriad of options a device may or may not implement.

The standard for example contains three different flavors of MIMO. The most popular one, MIMO spatial multiplexing will be implemented in many devices. But the standard gives devices the option to use 2, 3 or 4 transceivers/antennas. The more receivers, the higher the speed, if of course the receiver has at least as many. O.k. one might be able to sell this story in a fashion like "We do 4×4 MIMO compared to the competition which only does 2×2, so we are twice as fast".

The story doesn’t end there, however. There are two other MIMO modes, namely MIMO beamforming and MIMO STBC (Space Time Block Code) which can significantly enhance range and link stability. It just might turn out that these MIMO modes are just as important for applications such as video streaming to devices that are not close to the Wifi Access Point. Ruckus wireless for example is doing interesting things in this area.

And it certainly doesn’t end here. Draft 802.11n contains further options like multimedia power save (PSMP), shorter OFDM guard intervals, Antenna selection, Maximum Ratio combining, Modulation and Coding Scheme (MCS) feedback, etc. etc. In the end, marketing words on boxes in the electronics store are cheap. Let’s see, how about the Wifi Alliance coming up with something standardized about "enhanced 11n options"? Time will tell.

Will France Get A (Hopefuly More Agressive) Fourth 3G Operator?

Today I saw reports for example here and here that Illiad has brought forward the necessary papers to get the fourth and final batch of France’s 3G licenses in the 2.1GHz UMTS band before the deadline expired yesterday.

Illiad is the mother company of ADSL Internet provider "Free", certainly one of the most aggressive players in the French ADSL market. That gives me some hope that in case their bid is accepted and they are ready to go for it there might finally be reason for hope that competition could finally arrive in the French 3G market. Also, Free might have more of an Internet and IP angle than the local 3G incumbents so they might be more inclined to finally let customers use their network for Internet services for an attractive price rather than to let base stations sit around only producing hot air.

According to the report of Les Echos linked above the stock market was not quite happy to hear that Illiad has put their name in the hat. They see mobile as a risk rather than an opportunity. Short sighted bunch…

Need an 802.11n Beacon Frame?

Standards are well and good but usually contain a zillion options nobody ever implements. The 802.11 ‘draft-n’ standard is no exception. To find out which options different vendors have actually implemented, the best thing to do is to trace the beacon frames of ‘draft-n’ access points. A couple of months ago I described how to trace WLAN frames here.

If you are looking for beacon frames traced by other people to compare functionalities with your own ‘draft-n’ access point at home, take a look here. The beacon frame traced by ‘swordfish’ seems to be from a Linksys access point, judging from the first three bytes of the MAC address which identifies the manufacturer of the device. So here are the main ‘draft-n’ features this access point supports taken from the ‘HT Capability‘ (HT = high throughput) parameter (element ID 45):

  • 20 MHz and 40 MHz channel operation support
  • Greenfield mode support, i.e. protection mechanisms used to allow 802.11b and 11g devices to be part of the network can be switched off.
  • the access point has two independent transmitters and supports 2 spatial MIMO streams.
  • All of the other gazillion options such as short guard interval, STBC diversity, beamforming, MIMO power save, advanced coding, MCS feedback, antenna selection, etc. etc. are not supported.

The current mode of operation according to the ‘HT Information‘ parameter (element ID 61) erroneously called ‘Additional HT Capability’ in the trace):

  • The access point currently operates in 20 MHz mode only (either set by user or due to other networks using the same channel)
  • The access point runs in greenfield mode, i.e. only 11n devices have joined the network

Also interesting to see that the size of beacon frames has dramatically increased. Current 11g access points send beacon frames with a length of around 110 bytes. This ‘draft-n’ beacon frame has a length of 228 bytes!

Draft 802.11n Devices Must Implement 802.11e QoS

It’s good to see that both the IEEE 802.11n draft Standard and the Wifi-Alliance certification program require that future draft 802.11n Wifi devices also have to support the 802.11e QoS standard, sometimes also referred to as Wireless Multimedia (WMM).

WMM introduces Quality of Service for the Wifi Air Interface which means certain traffic flows can be prioritized over others. This is important for example when high bandwidth streaming and several phone calls are to be carried over the same wireless access point simultaneously.

By requiring QoS support from 802.11n devices I think this functionality has a real chance to become widespread in a relatively short amount of time which would probably not have happened otherwise.

Sources:

  • The 802.11n draft standard which confirms this in several paragraphs, like for example in a quite simple and not very easy to understand statement in chapter 5.2.8: "An HT STA is also a QoS STA"

For further information on WMM and how applications can use the functionality take a look at this previous blog entry.