Deep Inside the Network: T-Mobile starts using GPRS NOM-1

Quite recently T-Mobile has started to make use of the GPRS Network Mode of Operation (NMO) 1 feature in southern Germany. I haven’t seen any other operator using NMO-1 in Germany so far and only few in other countries so this came as quite a surprise. In this network operation mode, the circuit switched part of the network used for voice calls and SMS and the packet switched part of the network used for GPRS and EDGE data transmissions are connected via a signaling interface. This interface, referred to as the Gs interface, has a number of subtle but important advantages:

  • During an ongoing GPRS / EDGE data transfer (TBF established), mobiles can’t detect incoming voice calls and SMS messages as they are focused on receiving packets and thus can not observe the paging channel. In NMO-1 (sometimes also abbreviated as NOM-1), the circuit switched part of the network forwards the paging message to the packet switched side of the network which then forwards the paging message between the user data blocks while a data transfer is ongoing. Mobiles can thus receive the paging message despite the ongoing data transfer, interrupt the session and accept the voice call or SMS.
  • Location/Routing area updates when moving to a cell in a different location/routing area are performed much faster as the mobile only communicates with the packet switched part of the network. The packet switched network (the SGSN) then forwards the location update to the circuit switched part of the network (to the MSC) which spares the mobile from doing it itself. This is especially important for ongoing data transfers as these are interrupted for a shorter period of time.
  • Cell reselections from UMTS to GPRS can be executed much faster due to the same effect as described in the previous bullet. Whithout NOM-1 an Inter RAT (Radio Access Technology) cell reselection with Location and Routing Area update requires around 10 to 12 seconds. With NOM-1 the time is reduced to around 5 to 6 seconds. An important difference as this reduces the chance to miss an incoming call during the change of the radio network. Also, ongoing data transfers are interrupted for a shorter time,an additional benefit that should not be underestimated.

Talkline Launches Try And Buy Offer for Mobile Internet Access

Recently, a number of German MVNOs have slashed prices for prepaid mobile Internet access. Now, mobile network reseller Talkline has launched a 60 day try and buy offer for mobile Internet connectivity for people with a usage that makes a contract more attractive than prepaid. During this time the two year contract can be canceled at any time.

Other offers by the competition, except for the prepaid data mentioned above, always bind customers two a two year contract without the possibility to cancel the contract for reasons such as lacking coverage at the places of use.

Included in the offer is a free PCMCIA or USB 1.8 MBit/s HSDPA modem. A 27 Euro activation fee is charged when signing up (which is probably not refundable) and a monthly basic charge of 8 Euros applies for the duration of the contract. The first six months, however, are free. On top of the basic charge, users can select a data offer either based on volume or time:

  • 200MB: €20.-
  • 400MB: €35.-
  • 5GB: €50.-

The SIM card can also be used to make voice calls, but prices are not attractive with 39 cents a minute to the national fixed line network and 69 cents to other national mobile phone networks.

My First UMA Phone In the Wild

Timuma
TIM (Telecom Italia Mobile) seems to have entered into the UMA (Unlicensed Mobile Access) VoIP domain back last year. Today I saw their UMA offer in a TIM shop in Roma which includes the UMA Wifi capable Samsung SGH-P200 GSM/EDGE phone and a Wifi Access Point together with an ADSL subscription (see picture). It’s the first time I hear of this and an Internet search has also not uncovered a lot of evidence of a major breakthrough of the service so far. Anyone from Italy got an opinion on this? For more on UMA take a look at this blog entry.

Ericsson And Telstra Experiement With 200 km UMTS Cell Range

In this press release Ericsson and Telstra (Australia) report that they have successfully tested a range update of Telstra’s W-CDMA UMTS/HSDPA network operating in the 850 MHz band to support cell ranges of up to 200 km. The press release says that downlink speeds of 2.3 MBit/s were achieved over this distance.

It would have been nice if the press release would have gone a bit more into the details of how this was achieved as that sort of range and speed can not be achieved with the typical cell site on a rooftop transmitting at 10 watts and a standard mobile phone in the hands of a user. It is more likely that a base station with high transmit power on an elevated position like a hill was used in combination with a stationary handset, power amplifier and directional antenna.

It would also have been interesting to hear some details from Telstra on where they plan to deploy this. Australia is a big country so I guess there is quite an opportunity this way to bring high speed internet to people living far away from cities where broadband Internet is available either by conventional UMTS coverage, DSL or cable. Also, this offers interesting opportunities to cover ship routes along costs.

The technical background: Looks like this is the result of Ericsson’s recent Release 7 work item in 3GPP on "Extended WCDMA Cell Range up to 200km" which was reported to completed in December 2006 in TSG#34. According to the work item, a Node-B (base station) so far was only able to report propagation delays on the random access channel in the order of 768 chips, or a range of about 60 km. The work item description further says that changing this parameter in the radio network has no impact on currently deployed terminals, hence, the measure is backwards compatible.

Note that for conventional network deployment scenarios, being able to report propagation delays for the random access channel of up to 60 km is more than enough given the fact that due to capacity reasons and propagation in urban environments, UMTS cells are usually spaced just 2 km or even less apart.

Cryptophone: End to End Encryption for Voice Calls

Cryptophone
I’ve known for some time that there are special mobile and fixed line phones out there which can encrypt calls from end to end. I recently met Dr. Björn Rupp, CEO of GSMK, a company developing such phones. While probably not of much interest for the average person, there are a lot of people out there from politicians, police, top level managers, etc. who want to be sure their call is not intercepted. Not by the government, not by a secret service, not by tech savvy reporters or nosy mobile phone company employees. All these people can get access to normal mobile calls as the only interface over which the call is encrypted is between the mobile phone and the base station (GSM) or the radio network controller (UMTS). Over all other interfaces, the call is sent without any encryption and core networks even contain standardized interfaces for law enforcement agencies to tap into calls.

The phones developed by GSMK encrypt calls end to end by establishing a data connection between the two ends instead of a normal voice call and then use a strong encryption algorithm to ensure eavesdroppers have no chance. Dr. Rupp’s business card is also the first one I’ve ever seen which contains his PGP key ID and fingerprint. Also, they’ve published the source code of their encryption algorithm on their website, so no security through obscurity. Cool stuff, I am impressed!

3G Licensens Of T-Mobile U.S. Are Incompatible With The Rest Of The World Today

UMTS is operated on the 2.1 GHz band (or UMTS operating band I) pretty much everywhere around the globe. The U.S., however, is a special case. There, the band is already occupied for other uses. Thus, operators are using the 1900 MHz band both for 2G and 3G wireless (UMTS operating band II) and in addition the 850 MHz band (operating band V), again both for 2G and 3G. It looks like T-Mobile ran a bit out of luck when it came to 3G as they had to resort to a frequency band which is not used by anyone else so far.

During FCC frequency auctions last year, T-Mobile received frequencies in the what seems to be the new 1700/2100 MHz band (UMTS operating band IV). Here’s a report from Unstrung that describes this detail. The 1700 MHz part is used for the uplink while the 2100 MHz part of the spectrum is used for the downlink (network to mobile). I guess this is a bit confusing because speculations have been going on if T-Mobile will be compatible with UMTS devices sold in the rest of the world in the areas where they deploy 2100 MHz. Well no, they are not because the 2100 MHz part is just the downlink part of their spectrum. The uplink is on 1700 MHz and not on 1920-1980 MHz as for UMTS operating band I devices.

3gfrequencybands_2
Here’s the table of UMTS operating bands from the standards (3GPP TS 25.101). Take a look on line 4. The frequency ranges match with those in the Unstrung report about the auction I linked to above.

Therefore be careful! Some people are saying that T-Mobile U.S. uses 2100 MHz but it is slightly off the European band. Well, that’s not accurate. The 2100 MHz portion is inside the frequency range used in the rest of the world. The uplink however, is totally off mark.

I am not sure if T-Mobile U.S. will be happy with these frequencies both long and short term. Not even the latest and greatest data cards supporting multiple UMTS bands like the Globtrotter from Option supports band IV today. Also, I wonder if the band will be used in other regions of the world in the future. If not, T-Mobile might have a big problem with 3G handset vendors as the market for band IV devices will be quite small. Also, the use of yet another frequency range for 3G in the U.S. will fracture the market even more.

MEX 2007 – The Different Mobile User Experience Conference

Mex
The 3GSM Congress 2007 is over but the year continues to provide interesting meeting and discussion opportunities in real life for people working in the mobile industry. London is not only attractive for it’s monthly Mobile Monday gatherings but also for Symbian’s Smartphone Show and the Mobile User Experience Conference (MEX) which will take place on the 2nd and 3rd of May at the Wallacespace near Covent Garden.

It seems this conference is different for a number of reasons. Firstly, the conference has a 10 point ‘manifesto’ which deals with the current state of the mobile user experience and how the organizers around Marek Pawlowski think it can be improved. No beating around the bush, they come right to the point. The manifesto was then given out to potential speakers of the conference for them to choose one of these topics to kick off discussion from their point of view during the conference.

The speaker lineup is very interesting indeed as well. Christian Lindholm for example, one of my favorite ‘mobile’ personalities, formerly director at Nokia and serving as a VP at the mobile division of Yahoo for some time will lead a session on how mobiles and applications should adapt to changing physical environments of the mobile user. Among others, the speaker lineup also includes Cliff Crosbie, Director of Retail Marketing at Nokia, Al Russell, head of Mobile Internet & Content services at Vodafone, Mathew Menz, Head of Interaction Design of Motorola and Antti Ohrling, co-founder of Bylk.

The venue itself is also quite interesting. Instead of a standard conference place, the organizers have selected Wallacespace, which, judging from the pictures on their web space, is quite comfortable and very much different from normal conference places. I am quite thrilled about the whole lineup so if my daytime job allows, I’ll attend.