WirelessMoves

While VoIP and video streaming in the home network might have been exotic applications just a year or two ago, they are more and more moving into the main stream segment. Quite a number of VoIP phones are on the market now such as the Linksys Skype phone, the UTStarcom F1000G SIP phone or the Nokia E-series 3G/Wifi phones. While network load on the wireless link is low, speech quality is usually rather good. Things start to deteriorate, however, once the network starts to get loaded, e.g. due to a high bandwidth file transfer.

To improve things, the IEEE standards body has created the 802.11e standard which defines a number of Quality of Service measures for 802.11b/g/n Wifi networks. All are backwards compatible so 802.11e compatible Wifi access points can handle new and old devices simultaneously. In addition, the Wifi Alliance has created the WMM (Wireless Multimedia) certification program to ensure that devices are interoperable with each other and implement the most important options of the 802.11e standard, priorities and prioritized scheduling (EDCA, Enhanced DCF Channel Access).

While researching the topic, I was wondering how applications running on a PC or notebook for example can take advantage of WMM. After all, not all packets originating from a single device should be treated alike by the wireless card. While packets of a VoIP SIP client running on a machine should be treated with the highest priority, packets of a simultaneously ongoing download or web session should be treated with less priority in order for the VoIP packets to flow smoothly. It took quite some reading to find the answer to the puzzle:

• The WMM certification requires that an application shall control the setting of the QoS field in the 802.11 header by setting the DSCP (Differentiated Services Code Point) field in IP (layer 3) packets according to the priority needs of the application. I gave it a try with a SIP soft-phone client and indeed the DSCP field is set to "Expedited Forwarding" instead of "default" as is the case in other packets (see picture above).

• This and this blog entry by Gabe Frost explain how an application can set the DSCP field when opening a socket connection in Windows Vista and how a WMM compatible wifi network driver then makes use of this information to add a QoS header to the 802.11 MAC (layer 2) frame. In addition, wireless devices will only get the "Designed for Windows Vista" sticker if they implement WMM. Good thing!

Once the frame is maked with a QoS header it is delivered to the wifi card. The wifi card then uses the layer 2 QoS header field to put the frame into the correct priority queue. The following parameters, which are broadcast by the wifi access point, are then used by the network card to decide how long to wait before attempting to send a packet once the air interface is not used by another device:

• The number of slots to wait before starting the random backoff procedure. This value is called the AIFSN (Arbitrary Inter-Frame Space Number). The highest priority queue has to wait for the fewest number of slots before the random backoff procedure is started.

• The random backoff procedure is used to prevent several network clients to start transmitting at the same time. The backoff window size for a frame also depends on the priority queue it is currently waiting in. High priority queues have lower maximum backoff window sizes then lower priority queues. This allows other wireless clients to send their high priority frames before low priority frames of other clients.

• The maximum time before the client has to cease transmitting (TXOP). High priority frames are usually very short (e.g. 74 bytes of a VoIP RTP packet compared to 1500 bytes of data contained in a frame which transports part of a web page). A low TXOP time for high priority queues prevents applications mis-using a high priority for large data transfers and they are also not able to interfere with high priority frames from other local and remote applications.

So if access point vendors, network card manufacturers and operating system designers do their homework VoIP calls and video streaming over wifi should be smooth in the future, no matter what other users are doing in the network simultaneously.

P.S.: QoS issues do not end at the Wifi access point of course. Other measures have to be taken to let the VoIP packets flow in the DSL up- and downlink just as nicely. But that’s another story for another day 🙂

In lots of places 1 MBit/s ADSL connections are almost a thing of the past already and telcos are starting to offer fast ADSL2+ connections with speeds up to 24 MBit/s. These speeds are quite challenging for todays home networks for two reasons. First of all, the TCP parameters of PCs and notebooks in the network have to be tweaked. Otherwise, a single connection to a server on the Internet will level out at 5 MBit/s with the standard TCP window settings of Windows XP. More about TCP windows and how to adapt them can be found in this blog entry. Secondly, Wifi access points and Wifi adapters in PCs and notebooks used to connect to the ADSL line are also not always capable of transferring data at such high speeds.

If you still use either 802.11b access points or wireless network adapters in the PC/notebook, think about replacing this kit when getting a faster ADSL line. The maximum speed that can be reached in a 802.11b network is around 5 to 6 MBit/s. This is far too slow for an ADSL2+ connection.

Most people these days probably have an 802.11g wifi access point which in many cases has a built in ADSL or ADSL2+ DSL modem. But even here, with theoretical speeds of 54 MBit/s, the air gets "virtually" thin. Due to the way data is sent and received in a Wifi networks, actual data rates in 11g networks are much less than the advertised 54 MBit/s.

To see how well the combination of my wifi access points and devices in work together I used iperf to generate traffic on my wireless network. Iperf is a free program and can be found here. To simulate a download from the Internet one of the computers used in the tests was connected to the wifi access point via a 100 MBit/s Ethernet cable. Like when receiving data from the internet, packets are thus only sent once over the wireless link. Here are my results:

Netgear DG834GB access point and Intel Centrino notebook with 802.11g chipset: This is the fastest possible setup as both access point and client device are 11g compatible. No other devices were present in the network for the test. With packet bursting activated, the maximum transmission speed was 20.7 MBit/s. Not bad for a wireless link but not enough if you should be lucky enough to get the best possible ADSL2+ speed of 24 MBit/s.

Same setup as above with an additional Intel Centrino notebook with 802.11b chipset: As soon as 11g devices detect a device which still uses the older 11b standard, additional safeguards are automatically activated for peaceful coexistence of 11b and 11g devices in the same network. For details on how this co-existence works, take a look at the book on the left (sorry, shameless self advertisement). In this mode, the maximum data rate I got on the 802.11g notebook was 12 MBit/s. This is already far from the 24 MBit/s of a good ADSL2+ line. Also beware of neighbors using old 11b access points or devices on the same frequency band used by your network as the effect will be the same.

Shame on the Siemens SE515DSL

I repeated the same tests using my Siemens SE515DSL access point with the latest router firmware. No matter what I tried I was never able to get more than 12 MBit/s out of this router. Even switching to 11g only mode on the router and the notebook brought no improvements. Quite a frustrating experience.

802.11n

802.11g reaches its limits quickly with new ADSL 2+ lines. Should you be one of the happy few to get the full 24 MBit/s out of your ADSL2+ line, you might want to think about other wireless network alternatives. Unfortunately, the long awaited 802.11n standard, which promises speeds of 100 MBit/s and more, is still not finalized. This blog entry describes the situation back in October 2006. Pre-N devices with Mimo (Multiple Input Multiple Output) technology are already on the market for quite some time now, but might not be to everybody’s taste due to a lack of compatibility between different products and bulky PC cards sticking out of notebooks.

The next generation of even faster Internet connections at home and office like for example VDSL with 50+ MBit/s per second and fiber are already on the horizon. Also, video streaming at home over wifi which requires high bandwidths is also getting more and more main-stream. Let’s hope 802.11n will be finished soon in order to leave notebook manufacturers, chipset vendors and the market enough time to put inter-operable devices into the homes and offices before wireless home networks become the bottleneck.

I’ve recently come across an interesting article by Jürgen Schmidt on Heise Security describing how Skype establishes a direct call between two subscribers behind NAT (Network Address Translation) firewalls. NAT firewalls only allow the initiation of a connection from the inside and reject packets which are not a response to a previously sent packet. In addition, some NAT firewalls also map internal TCP and UDP port numbers to new values which are used externally. This in theory prevents establishment of a connection between two computers behind two NAT firewalls which is required for a Skype connection. Skype clients, however, are quite clever and use a number of different schemes to find the right port in the firewall of the other party. In case the right port can not be found, Skype clients use a fallback mechanism and communicate via a super node in the network which bridges their media flows. For details, see this article.

So what does this have to do with wireless? Well, Skype can be used over a 3G connection as well and many operators use NAT and a private IP address space for their 3G subscribers.

In addition: As with firewalls, Skype seems to be quite flexible in regard to the Internet connection available and adapts to a UMTS bearer nicely as shown in this presentation of Tobias Hoßfeld called "Skype over UMTS".

Today I came across this interesting video which shows the vision of the Daidalos project for pervasive communication in the future. There is lots of talk in the industry lately on voice call continuity, i.e. switching a voice call between circuit and packet switched networks. The vision of the Daidalos project goes one step beyond and shows how a call could be switched between different networks and devices and how additional information such as video streams and textual information are automatically included in the call when the current device allows and the situation requires. The roots of this concept are also known as "rich call".

So far, I’ve been somewhat reluctant to see a benefit in voice call continuity (VCC). Since watching the video however, I can quite clearly see the benefits of VCC and its evolution. An interesting example made in the video is two people discussing a trip to the airport. The person at the other of the connection end gives his conversational partner further information about whom he is to meet at the airport and when. The call continues when he goes to his car and the on-board computer automatically extracts the location information given by the other party to calculate a route to the airport and to reserve a parking place.

Diadalos stands for "Designing Advanced network Interfaces for the Delivery and Administration of Location independent, Optimised personal Services" and is a project funded as an EU Framework Programme 6 Integrated Project.

Here’s a
statement made by Anssi Vanjoki at the recent Nokia World Conference: “Broadband Internet is not a socket in the
wall, it is all around us”.

He draws
and interesting picture and I think he is right. Today, many people already use
Wifi access points to create their personal broadband Internet cloud. Thus, the
broadband Internet IS virtually all around them. In the future people will not
only use this cloud with desktop computers and notebooks but also with smaller
devices such as mobile phones with built in Wifi capabilities (like Nokia
N-series phones for example) or physical widgets .
Smaller devices will also change the way we perceive the Internet cloud. No
longer do you have to sit down at a specific place, e.g. in front of a
computer, in order to communicate (VoIP, eMail, IM), to get information, or to
publish information to the web yourself (pictures, blog entries, videos, etc.).
Even today you don’t need to be in your personal Internet cloud anymore to
perform these activities. When you leave your personal broadband cloud, 3G and
3.5G networks and WiMAX in the future are a natural extension. Instead of using Wifi, mobile Internet
devices then switch over to the cellular network. As we move into the future
the cloud will extend into areas not covered today, available bandwidth will
increase and moving between the personal Internet cloud at home and the larger external
cloud will become ever more seamless.

An
interesting scenario for handset manufacturers like Nokia and others developing
3G/Wifi integrated multimedia handsets, for innovators of cool mobile services
and for network operators such as Vodafone, O2 and Orange who have decided to include DSL lines
into their portfolio to offer a home cloud in addition to the larger network
coverage. It’s time to start the integration of handset, personal cloud and
external cloud and mobile services into a homogeneous experience.

"Well, you know I like the fireworks" said Rudy De Waele to me today after announcing that the MobileMonday Global Peer Awards Ceremony 2007 is to be held during the 3GSMWorldCongress week in Barcelona next February. And indeed, a firework of ideas, conversations and fun this is going to be. I haven’t been to the  Espacio Movistar where the event will take place yet but the pictures on the Mobile Monday Barcelona blog look impressive. So if you are at the 3GSMWC in February, this is the event you definitely don’t want to miss. So, no time to waste, head over to the MoMo Barcelona blog to get more info and reserve your ticket. 

Heidelberg is the first city I’ve seen that has started to offer local Wifi coverage in combination with a mobile optimized city portal for tourists. Supported mobile devices are Windows Mobile, Palm, the Nokia 770 Internet tablet and Safari / Nokia S60 phones. In addition to pictures and textual information the web site offers localization and audio guides:

Localization

The Heidelberg-mobile site can be accessed from anywhere via the Internet or a wireless 2G or 3G network or via one of the hotspots in town. If accessed via the local Wifi hotspots (hello people with  N-Series Wifi enable Nokia phones!) your position is analyzed by the web server and maps of the city will be centered around your current location. Very helpful if you don’t know your way around.

Audio Guides

I like audio guides in museums. Heidelberg-mobile goes a step beyond and offers audio guides for sights all around the city. Once you are at one of the attractions covered by the audio guide you can listen to it on your phone. The audio data is transfered over the Wifi network or in case you "only" have a 2G or 3G phone via an IP connection over UMTS or GPRS. This is a great idea, so I gave it a try on my N93 via my Wifi network at home. The audio files can be played by following the link to the audio guide section on the web site and selecting one of the links which lead to a specific story (sorry, all in German for the moment). After a few seconds the files are downloaded and are then played back in the media player.

I still vividly remember standing in front of a big audience for the first time in 2001 speaking about wireless network evolution. At the time, GPRS was still in it’s infancy, GPRS enabled phones were not yet available and the 384 kbit/s promised by UMTS sounded miraculous to me. Today, five years later, UMTS is a reality and networks have already far surpassed the outlook from five years ago. Mobile Web 2.0 is in everybody’s ears these days and here’s my take on it from the network point of view:

Rudy de Waele recently posted a very good summary of his thoughts on Mobile Web 2.0. From the network point of view Mobile Web 2.0 social applications such as Flickr Mobile, mobile blogs, mobile podcasting, web and AJAX applications, mobile eMail, Widgets, location based services, etc. require one thing: Bandwidth, bandwidth and once again bandwidth. It’s one thing to download a tiny mobile optimized web page and quite another to upload large pictures and podcasts. In the fixed line world, DSL and cable modems have been the enablers on the network side for Web 2.0. For the Mobile Web 2.0 here are today’s and tomorrow’s enabling technologies from the wireless network side:

Today’s Enablers

EDGE: While GPRS was way too slow for most Web 2..0 applications, things got a lot better with the introduction of EDGE about one and a half years ago. EDGE improves GPRS downlink speeds to about 220 kbit/s and uplink speeds to about 100 kbit/s.

UMTS: Here, things are getting really exciting. First networks started operation about two and a half years ago and a data rate of 384 kbit/s in downlink and 64 to 128 kbit/s in uplink direction make the mobile Internet almost feel like over a fixed line connection.

HSDPA and HSUPA: This is the step about which only five years ago I did not even dream about. Only five years after GPRS downlink speeds reached about 35 kbit/s, HSDPA today offers data rates of 3.6 MBit/s. That’s almost 100 times faster than networks were five years ago! With HSUPA, uplink data rates will also get a big push and will exceed 800 kbit/s in favourable conditions. Again, 100 times more than the status quo five years ago.

Future Enablers

Again, I am at a point where I look into the future to get an idea what kind of mobile networks we are going to see in five years from now. HSDPA will keep evolving for some time to come and data rates of over 7 Mbit/s in downlink direction will be introduced in networks in the next year or two.

To increase speeds yet again by a factor of ten will be though. On the other hand, going from GPRS to UMTS was no child’s play either. Current plans for the UMTS successor called LTE (Long Term Evolution) and WiMAX foresee data rates of about 100 MBit/s in downlink and well over 30 MBit/s in uplink. First WiMAX networks are already in the deployment phase, LTE networks will follow in about three to four years.

WiMAX operators will have a crucial role in the development of the wireless web in general depending on whether they will offer their services in an open hotspot fashion or decide to go for a closed 3G like approach. More on this can be found here.

Private and public Wifi hotspots and networks (aka Muni Wifi) will also be an important ingredient for the mobile eco-system in the future. High end mobile devices already include both 3G and Wifi interfaces today. This both off-loads traffic from cellular 2G and 3G networks and offers additional possibilities to Web 2.0 applications today and in the future. It might very well be that in five years from now, 3G access will have become so cheap that most people download podcasts and upload pictures to Flickr wherever they are. In another scenario many people might still prefer up- and downloads multimedia content over their Wifi/DSL connection to and from their mobile device while at home and choose to keep their 3G bill as small as possible. Combined 3G/DSL operators as discussed here are in an ideal position to benefit both ways.

Impact on the Evolution of Mobile Web 2.0

The anytime anywhere Internet has already been promised to us five years ago with GPRS. The limitations financially as well as from a bandwidth point of view, however, were reason enough to prevent widespread adoption. Starting with UMTS and especially with HSDPA, the limitations of the mobile web are more and more dwindling away. Smartphones such as Nokia N or E-series devices, Sony Ericsson’s UIQ devices and Windows Mobile PDAs today have processors, memory and graphics capabilities surpassing those of PCs from 10 years ago. This trend will hardly stop either and in combination with ever faster and farther reaching mobile networks, Web 2.0 and the Mobile Web 2.0 will merge into a single social eco-sphere where people can truly access content and contribute anytime anywhere.

More on the technical side of the evolution of wireless can be found here.

It’s done, it’s over and it looks like it has been a great week for the wireless Internet in Germany. After a four day auction, three companies have each received a nationwide license to deploy Broadband Wireless Access (BWA) networks in the 2.5 3.5 GHz band. The three companies are DBD (Deutsche Breitband Dienste GmbH), Clearwire (WiMAX operator already active in the U.S.) and Inquam (partly owned by NextWave Wireless) and all have indicated that they will use their licenses to build WiMAX networks.

Total price of the licenses is 56 million euros which includes some regional licenses acquired by local companies. All three companies who are now likely to rush to beat the competition to the market already have WiMAX deployment experience. DBD already operates small WiMAX islands in Germany while Clearwire and Nextwave have already deployed WiMAX or pre-Wimax networks in the U.S.

From the end users point of view it’s good to see three companies now poised to compete with each other. There’s a lot of pressure now to roll out networks as quickly as possible as the first one is likely to get the major share of customers in areas without DSL or other fast Internet connectivity. Competition will also ensure that prices will be competitive, again good news for users. And finally, three additional nationwide wireless high speed Internet companies will also put some pressure on the four incumbent UMTS operators.

56 million euros in licenses sound like a lot at first. However, these companies "only" need to get 5-10% of people in Germany to sign up to their services in order to drop the impacting of the fees on end user prices to the order of a few of cents per user per month. For details on this, the background of the auction, frequency bands, bandwidths, etc., take a look here and here.

My WiMAX Expectations In Germany For The Next Few Years

I wonder if three nationwide networks will be able to successfully compete next to the four UMTS operators and DSL. I would not be surprised to see some mergers down the road. It also seems certain to me that all three companies will start deploying their networks in undeserved DSL regions first and then work their way towards DSL covered areas to compete head on with DSL and 3G/3.5G in addition to offering their existing WiMAX subscribers national roaming possibilities.

In contrast to 3G networks which were designed for handheld devices and seamless handovers of calls from cars and trains, WiMAX network roll outs are likely to have a different focus. I expect that these networks will mainly target users with notebooks at first who use the Internet in a nomadic rather than a truly mobile fashion. This helps to save costs as fewer base stations are required. Once demand picks up and truly mobile WiMAX devices like smart phones become available, the networks might even be densified to allow a more mobile experience for the user.

Interesting times are ahead. I’ll keep you posted!

Despite being promised by the local incumbent telco, a friend for mine has now been waiting for months to get a DSL connection at his home in the countryside. Doesn’t look to good for him. He’s finally fed up of waiting and has started to experiment with Wifi as about a kilometer away people are connected to the DSL network. His first experiments are quite promising. With the kit shown below in the images (click on the pictures to enlarge), he was able to get a stable wifi connection between the access point and the strange looking antenna and a notebook with built in wifi antenna over a distance of 1 kilometer. Now he’s found someone who’s willing to share his DSL line with him about a kilometer away, line of sight in between them. Two "Yagi" antennas and a second access point are on the way and the end of Internet-less days are hopefully over for him soon. To be continued…