Author: Martin

Devicescape Makes Use of Wifi Hotspots Easier With Mobile Devices

Jukka over at the Nokia Web Server blog made me aware of an interesting new service from Devicescape which will be bundled with Nokia Nseries and Eseries phones that makes using Wifi hotspots easier in the future.

You probably know the hassle. You sit down at the airport but before you can use the local Wifi network a user name and password has to be entered on a web page to get access to the Internet. While inconvenient with a notebook it’s still manageable since you have a keyboard available. With a mobile device however, typing in user names and passwords on a web page becomes a real pain.

Devicescape has an elegant solution for this. A little program, that has to be installed on the phone, checks all Wifi networks and automatically logs into those it knows. Usernames and passwords are stored on a centralized server so the user never has to type them in on the mobile device. When accessing the network from a Wifi hotspot they are downloaded automatically and entered into the web page by the program.

I was a bit puzzled at first. How can they store passwords remotely? Usually, access to the Internet is only possible once one the username and password have been entered on the web page. Devicescape uses an interesting trick to circumvent this. They piggyback their server interaction on DNS (Domain Name Server) queries which are required to resolve a URL (e.g. http://mobilesociety.typepad.com) into a numeric IP address. This works even before full access to the Internet is granted. The DNS server system has a treelike structure so a DNS query to a Devicescape URL will end up on the central Devicescape server. The server then checks the request and returns the username and password in the answer.

Pretty sleek!

IMS Applications

In my previous IMS post I’ve taken a look at the difference between SIP telephony networks and the IP Multimedia Subsystem (IMS). With that list it is quite obvious that the IMS is a centralized session management system that gives lots of control to the network operator and makes it quite difficult for third parties to integrate their services on a global scale. So while in theory the IMS is capable to be a platform for many web 2.0 services I think that in practice it will manly be used in the future for voice and instant messaging based services. Here’s a list of services which I think we will see in the IMS in the mid-term. If you have other examples, please leave a comment!

  • Voice telephony as the main application. This includes handing over voice calls between networks as the user roams out of coverage of a network. Furthermore, advanced IMS solutions will enable handovers of voice calls to a 2G network if no high speed B3G network is available anymore.
    The IMS enables video calls with the advantage over current 3G circuit switched mobile video calls that the video stream can be added or dropped at any time during the session.
    Presence and instant messaging.
  • Voice and video session conferencing with three or more parties
    Push message & video services such as sending subscribers messages when their favorite football team has scored a goal, when something exciting has happened during a Formula-1 race, and so on.
  • Calendar synchronization among all IMS devices.
  • Notification of important events (birthdays, etc.).
  • Wakeup service with auto answer and the users preferred music or news.
  • Live audio and videocasts of events. The difference to current solutions is the integrated adaptation to the capabilities of the device.
  • Peer to peer document push.
  • Unified voice and video mail because all devices used by a person are subscribed to the same IMS account.
  • One identity / telephone number for all devices of a user. A session is delivered to all or some devices based on their capability. A video call would only be delivered to registered devices of the user capable of receiving video. Sessions can also be automatically modified if devices do not support video.
  • A session can be moved from one device to another while it is ongoing. A video call for example might be accepted on a mobile device but transferred to the home entertainment system when the user arrives at home. Transferring the session also implies a modification of the session parameters. While a low resolution video stream is used for a mobile device the resolution can be increased for the big screen of the home entertainment system if this is supported by the device at the other end.
  • Use of several user identities per device. This allows only using a single device or a single set of devices to be reached friends and business partners alike. With user profiles in the network incoming session requests can be managed on a per user identity basis. This way, business calls could be automatically redirected to the voice mail system at certain times, to an announcement or to a colleague while the user is on vacation while private session requests are still connected.

Linksys Offers Dual Band Draft-N Wifi Router

Glenn Fleishman over at Wifi Networking News has posted a review on the Linksys WRT600N. What makes this device special is the support of both the 2.4 GHz and 5 GHz band simultaneously. Other products either only support the 2.4 GHz, which is too crowded in most cases to take full advantage of the 802.11n ‘double channel’ feature, or they support the 2.4 GHz and the 5 GHz band but only one at a time. Good to see these products appearing on the market!

P.S. Hopefully there is an OpenWRT or DD-WRT OS version for that device soon 🙂

IMS vs. Naked SIP

Everyday we get a bit closer to all IP wireless networks in which operators are hard pressed to present a voice over IP solution. Today two approaches are on the horizon: ‘Naked SIP’, already implemented in some 3G phones such as Nokia N-Series and E-Series S60 phones. And then there is the IP Multimedia Subsystem (IMS), based on SIP but with lots of additional specification put around it. So what does IMS do that SIP doesn’t? I came up with the following list of things which are laking in naked SIP today which are dealt with in IMS:

  • General SIP implementations are network agnostic and can not signal their quality of service requirements to a wireless access network. Thus, voice over IP data packets can not be preferred by the system in times of congestion.
  • Handling of transmission errors on the air interface can not be optimized for SIP calls. While web browsing and similar applications benefit from automatic retransmissions in case of transmission errors, VoIP connections would prefer erroneous packets to be dropped rather than be repeated at a later time since such packets are likely to come too late.
  • SIP VoIP calls can not be handed over to the 2G network in case the user roams out of the coverage area of B3G networks.
  • SIP does not work in 2G networks.
  • Most SIP implementations today use the 64 kbit/s PCM codec for VoIP calls. Compared to optimized GSM and UMTS codecs, which only require about 12 kbit/s, this significantly decreases the number of VoIP calls that can be delivered via a base station. Furthermore, mobile network optimized voice codecs have built in functionality to deal with missing or erroneous data packets. While this is not required for fixed networks due to the lower error rates it is very beneficial for connections over wireless networks.
  • Emergency Calls (112, 911) can not be routed to the correct emergency center since the subscriber could be anywhere in the world.
  • No billing flexibility. Since SIP implementations are mostly used for voice sessions, billing is usually built into the SIP proxy and no standardized interfaces exist to collect billing data for online and offline charging.
  • Additional applications such video calls, presence, instant messaging, etc. are usually not integrated in SIP clients and networks.
  • It is difficult to add new features and applications since no standardized interfaces exist to add these to a SIP implementation. Thus, adding new features to User Agents and the SIP network such as a video mailbox, picture sharing, adding a video session to an ongoing voice session, push to talk functionality, transferring a session to another device with different properties, etc. is proprietary on both the terminal and the network components. This is costly and the use of these functionalities between subscribers of different SIP networks is not assured.
  • Insufficient security: Voice data is usually sent unencrypted from end to end which makes it easy to eavesdrop on a connection. Signaling can be intercepted since it is not encrypted. Man in the middle attacks are possible. No standards exist of how to securely and confidentially store user data (e.g. username/password) on a mobile device.
  • Scalability: Mobile networks today can easily have 50 million subscribers or more. This is very challenging in terms of scalability since a single SIP proxy in a network can not handle such a high number of subscribers. A SIP network handling such a high number of subscribers must be distributed over many SIP proxies/registrars.
  • There is no standardized way to store user profiles in the network today. Also, no standardized means exist to distribute user data over several databases which is required in large networks (see scalability above).

The list is quite long I have to admit. But there is one thing the list does not say: While naked SIP is available today I have yet to see an IMS capable terminal in the wild. I wonder how long it will still take?

As always, comments are welcome.

What next for mobile telephony?

… asks Moray Rumney, Lead Technologist over at Agilent in the latest edition of the Agilent Measurement Journal (3/2007). In his article, Moray takes a look at which factors contribute to the ever increasing wireless transmission speeds and explains where the limits are and why the 300+ MBit/s promised by LTE and other technologies in a 20MHz channel will remain a theoretical promise rather then becoming a practical reality. He then goes on to describe what is possible with the given physical limits and presents his thoughts about how to address capacity issues in the future. An absolute must read!

The journal is available here and the article can be found on page 32.

International MMS: A Case Study of Failure

It’s a strange situation: Most mobile operators today would like to retain control over the application layer and rollout new services themselves instead of letting Internet economics do the job. In practice however, they do not spend a lot of effort to making even the few advanced services they have universally usable. MMS is a prime example as I had to discover recently.

Situation 1: I am in France, I have a French SIM card and wanted to send an MMS to a prepaid subscriber of another French operator, Bouygues. Instead of receiving the MMS, only a text message arrives at the other end with a web link. The reason is that the other end did not have a GPRS subscription. 5 years after the introduction of MMS!? It leaves me puzzled.

Situation 2: O.k. so I can’t send my French friend an MMS but maybe I can send one to a friend in Germany. Message sent, I’ve been charged for it but the MMS never arrived. How nice.

Situation 3: Some days later I was in Spain and repeated the international MMS scenario with a Spanish SIM card. Again, the MMS to a German SIM card was not delivered.

To me it looks like even 5 years after the introduction of MMS, there are still no international agreements in place to forward MMS between operators. Could you imagine eMail not being delivered because the recipient lives in another country? No, probably not. That’s because no international agreements for applications have to be in place to forward eMail. And if there had to be, just imagine how the Internet would look like today and how many people would use it.

Some might say, the difficutlies stem from the fact that telephone numbers are used instead of eMail addresses for MMS messages. True, but international SMS messages which also use telephone numbers work just fine these days. But maybe 5 years is too short a time to make it work? One should not think so.

Light Reading Webinar on Mobile Backhaul Evolution

With mobile networks getting faster and faster a growing pain for network operators is the backhaul connection between the base station sites and the next element in the network. Today, T-1 or E-1 connections are used with a line rate of 1.5 and 2 MBit/s. With HSDPA being put in place today,  backhaul capacity requirements of 3G base stations now reach 10 MBit/s or more. This means putting additional T-1 or E-1 lines in place. While this might still work today for HSDPA speeds despite the associated rising costs it certainly won’t work tomorrow for WiMAX, LTE and other Beyond 3G technologies that require backhaul capacities of 60 MBit/s per base station and more.

So the big question is what comes after T-1/E-1 connections over copper, fiber or microwave!? The common answer these days seems to be:

IP over Ethernet with the capability to carry legacy GSM (TDM) and UMTS/HSDPA (ATM) links in IP pseudo-wires alongside native IP traffic generated by native WiMAX and LTE base stations.

But how do you connect the base station sites to Carrier Ethernet Networks? Can the last mile be done over copper, is fiber required or is next generation microwave an alternative? Questions over Questions 🙂

I found some answers in a recent one hour Light Reading Webinar on the topic which is available for free at this link. If you are interested in the topic take a look.

Testing a Cat-7 HSDPA Card In a Live Network

Tpunkt_fdh I recently got an invitation from T-Mobile’s press center to check out T-Mobile’s HSDPA network in Friedrichshafen, which has become Deutsche Telecoms open air test bed  ‘T-City’. There, the invitation said the HSDPA network was upgraded for maximum performance with category 7 HSDPA cards. In theory (no interference, no neighboring cells, single user, close to the antenna), such HSDPA cards are capable of speeds up to 7.2 MBit/s. Interesting stuff, so I went there to check it out.

In the local Telecom shop they let me check things out first hand with a notebook and an Option Globetrotter GT max HSDPA card which they said they had updated with the latest software. You won’t see a big difference when web browsing once speeds are higher than about 1 MBit/s so I decided to download a large file from a high capacity server on the Internet. The average download speed was around 4.2 MBit/s. Quite impressive even when compared to my already fast category 6 Motorola V3xx HSDPA mobile with which I have reached 2.5 MBit/s in the past.

For more on HSDPA on my blog take a look here.

Jumping from EDGE to EDGE on the Train with SFR

I had an interesting wireless experience recently when I took the TGV from Stuttgart to Paris. There isn’t a lot of 3G network coverage along the railway track so while in France I used SFR’s network with a Vodafone Websession from Strasbourg to Paris. So far I thought that  SFR did not have EDGE in its network. Looks like that assumption was not quite correct.

No_edge_lgv_est_sfr_3
Every now and then one of the cells along the railway track was EDGE activated and data rates suddenly jumped from a meager 60 kbit/s (typical GPRS) up to 200 kbit/s, even at 300 km/h. The bad thing is just that EDGE was only available in few places so it’s not really worthwhile to go online and download eMails and do some web browsing. I can only speculate that SFR tries to cover some towns along the railway track but they certainly don’t try to do anything in terms of higher rate data for the railway track in particular. What a shame…

Edge_lgv_est_sfr_2
At first I thought it might be a mobile device problem. So I tried with a second mobile which has an engineering mode which confirmed that EDGE is only sporadically activated. The pictures on the left shows the throughput of a file download in a standard GPRS cell and with EDGE when it was available.

Have to try with Orange next time.