Optimus Launches IMS with PC Offer

Here's an interesting link to Optimus Portugal's IMS offer for their customers, translated into English thanks to the help of Google. Looks like the offer is based on an IMS core of Ericsson and a IMS client of Movial. Since it is the first IMS offer I have seen being deployed in a real network for real customers I took a closer look to see exactly what is offered and how it works:

First, there is no software being deployed on mobile devices, they keep functioning as before. Instead, Optimus uses a PC based IMS client, so their subscribers can make and receive calls from both their mobile phone and their PC. So far, the offer takes the simplest approach: Calls are either received on the mobile device or on the PC, the user has to choose.

While the user is connected to the network with the IMS PC client, other users also online via the PC client can be called for free. This involves presence, i.e. the PC clients can see each other. Also, instant messaging and video calling are free between PC clients.

SMS is interesting, too. While the PC client is active, SMS message are routed to the client and not to the mobile phone. However, this only applies to SMS messages being sent by other Optimus users. SMS message coming from other networks are still delivered to the mobile device. That's probably got something to do with SMS message routing, as SMS Service Centers in other networks can deliver the messages directly to the mobile device without going to an Optimus SMSC first. A bit of a catch.

Another plus they are advertising is that calls from abroad via the PC client are charged at the standard rate as if you were in Portugal. Incoming calls to the PC client would be free, no matter how far you are away from your home country.

It looks like the IMS PC client and the mobile device are still strictly separated and all IMS parts of the system are only used for the PC client. A good way to start working with IMS, especially for mobile operators with fixed line (DSL) assets.

I wonder, however, if this is a bit of a dangerous path for a mobile operator to walk as some fixed line operators could start wondering why interconnection charges are higher even if a call is not delivered via the cellular network but via a fixed line PC client.

Would I be compelled to use the service? Once I am at home I wonder if for free voice and video calls, Skype with its superior voice and video quality would be better for me. SMS might be more convenient to use on the PC as typing is easier but I would still have to keep an eye on the mobile device in order not to miss incoming messages from people using other networks. And for instant messaging, I have a program already in place as well.

So I guess I would try it, with the Optimus IMS client being one more application running in the background, which I hopefully do not forget to switch off before I leave the house or I would not receive incoming calls. A good place to start from, I hope they keep expanding the functionality.

There Are Many Places in the Network For Services

So far there are three places where services and applications run/hosted/placed in the network:

  • In the core network of the mobile operator, think voice calls and IMS
  • On the Internet, think web based applications like Google Reader, Yahoo maps, etc, etc.
  • On the device itself, think Microsoft applications on PCs, Java and native applications on mobile devices.

When services and applications are connected, they usually interact with some other part of the network. A web browser for example is only useful because there are web servers on the Internet providing content. Some services and applications are also hybrid. Take Opera Mini for example. The browser is split between a light-weight Java application on the mobile device and a compression proxy somewhere on the net.

And now a fourth place for applications and services is emerging, on femtocells and home gateways. Services under development are automatic multimedia file transfers from/to mobile devices when they enter the femto area, forwarding of messages left by friends on Facebook and elsewhere for when the user returns home, automatic notification of parents when kids have returned home, etc.

Ip.Access is pretty outspoken on the topic and has announced a Femtocell Applications Live Event in London on June 23rd over at ForumOxford.

The Paradox of Open

Yesterday, Ajit Jaokar over at Open Gardens published a thought piece he called "The Paradox of Open: What we can learn on Open from Apple and Microsoft". He argues that despite Apple and Microsoft having closed mobile operating systems they are successful. The conclusion he reached was the following:

"I believe that: A 'closed platform' works provided you have an 'Open ecosystem' BUT an Open platform (open source and / or open standards) without an ecosystem (open or closed) does not work."

An interesting statement I agree with and would like to extend a bit to show further influences:

A couple of days ago I met with a friend who's had an iPod touch for some time now and is a glowing part-time developer. When I asked him why he picked up programming for the iPhone / iPod touch and what he thought about the development environment, he said that:

  • he picked it up because Apple is doing great things
  • because he likes the UI and how easy it makes things for users.
  • the development environment for the iPhone is not so nice with the license you have to get and all the restrictions that are put in place with developer codes, distribution, etc.
  • he only works on it because the product on which the application will run is so great. Otherwise he would not bother.

So I think in the end it doesn't really matter if an OS is open or closed. If it is not liked by users for whatever reason and is not easy to use and there is a better alternative available, then nothing will come of it.

Speaking of ecosystems: I think for a free and open source OS it is much simpler to get an ecosystem in place because the community can help vs. a closed source OS where the burden of fostering an ecosystem lies in the hands of the company that owns it.

A good example is Nokia's Memo platform for their tablet devices. It's for the most part free and open source and yet, only few users have bought one. In my opinion the handling and UI is just nowhere near the iPhone or similar touch devices yet.

In other words: Part of the ecosystem, a part that one can't touch, is the success of the product, its ease of use and in turn how many people use it. So Open alone is not warranting success on its own. In that respect I am not sure if there is a paradox with Open? As always, comments are welcome.

LTE TDD in China and Europe?

Even though LTE is a global standard there are two different air interface flavors: The first one is FDD and pretty much destined to be used around the world. And then there is TDD, for the moment mostly foreseen to be used in China. However, many European operators have acquired TDD spectrum in the 2.1 GHz band during the 3G auctions back in 2000. So while I haven't heard anyone talking about this so far, I wonder if LTE TDD might be something of interest to European carriers!? In that regard, does anyone know if the TDD band in China is anywhere near the TDD region that was auctioned in Europe? Might be a great push for dual mode FDD and TDD devices.

How to Explain the Thoughts Behind BICN

Bicn-stack There are lots of things in this world that don’t make a lot of sense unless you know how they have evolved to their current state. One of those things is the migration of circuit switched telephony to the IP world with the Bearer Independent Core Network concept specified in ITU Q.1901 and introduced in GSM and UMTS starting with 3GPP Release 4.

Here’s my take at it:

With BICN, the circuit matrix of the MSC (Mobile Switching Center) that creates a physical voice circuit between two subscribers is replaced by a media gateway. The media gateway maps the concept of a circuit connection to an IP stream between two parties. The stream is then transmitted together with many other streams over a shared packet switched link, which is for example based on Ethernet.

The Signaling System Number 7 (SS-7) used in the circuit switched world is still used in this architecture but has been changed to some degree. The protocols of this family are used for the following tasks:

  • For the establishment of voice calls
  • For the interaction between different network nodes (e.g. between the switching center and the subscriber database node)
  • For communication between the switching center, the radio network and the mobile device

The main difference with SS-7 over IP is that the lower layer MTP protocols have been replaced by IP, SCTP and M3UA, so the messages can be transported over IP instead of a circuit switched timeslot. The figure on the left shows the MTP based SS-7 protocol stack in comparison to the IP based SS-7 protocol stack.

Above the MTP layers, the ISUP protocol that is used for establishing voice circuits has been replaced by BICC (Bearer Independent Call Control). BICC is very similar to ISUP. Message names are the same and only some parameters have been changed as the messages are now used to control media streams instead of circuit connections.

Protocols for the interaction between different network nodes (e.g. between the voice switch and the subscriber database) such as SCCP, TCAP and MAP have not been altered at all. DTAP (Direct Transfer Application Part), the protocol used for interaction between a mobile device and the switching center for purposes such as authentication, location updates, etc., has also remained unaltered. In other words, applications that use these protocols are not aware if the messages are transported over signaling timeslots of a circuit switched network or over an IP link.

To enable IP based SS-7 nodes to communicate with MTP based nodes in the network, Signaling Gateways are used to translate MTP into IP / SCTP / M3UA. This way, a traditional circuit switched MSC is able to communicate with a subscriber database node that is connected to the network over an IP connection.

And finally, from a mobile point of view, the air interface between the base station and the mobile device also remains unchanged. This means that GSM and UMTS mobiles have no visibility what kind of access or core network technology is used.

Today, both traditional circuit switching and BICN can be found in live networks so knowing only one of them won’t do, at least for the moment. So I’ve decided to coin two terms:

  • “Traditional circuit switching”, i.e. the origins of circuit switching with voice calls transported over physical circuits and SS-7 messages being transported over circuit timeslots.
  • “Virtual circuit switching over IP”, i.e. a voice channel is transported over an IP stream and the SS-7 protocol is used in a modified form in the IP world.


Traditional circuit switching vs. virtual circuit switching over IP. Do the terms make sense to you?

GPRS Detached, Attached and a PDP Context

Over at Boy Genius Report there's been a post yesterday about how to keep a data connection alive on S60 devices over some time of inactivity. Unfortunately, the conclusions drawn there are technically not quite correct. So, as there is probably some interest in the community of how always-on connections work over GPRS and UMTS from a lower layer point of view, I've put together a summary to show what is really going on.

GPRS Detached

When you power up an S60 mobile for the first time, it is usually configured to only establish what is referred to as a "packet data connection" when needed. The term "packet data connection" however, is grossly misleading. When set this way, the mobile will only attach to the voice part of the network but will not make itself known to the GPRS packet switched side of the network. An S60 device shows this state, referred to as GPRS detached, by showing a little antenna symbol below the signal strength bars at the top left of the screen.

GPRS Attached

Screenshot0055 When the "packet data connection" option is set to "when available", the mobile performs a GPRS attach procedure as soon as it is switched on. This means that the mobile in addition to becoming known to the voice part of the network also becomes known to the GPRS part of the network. An S60 device shows this state to the user by showing two little dashed horizontal arrows below the signal strength bars. If the network supports EDGE, a little E is shown in addition above the arrows. This is shown in the picture on the left. If UMTS is supported, 3G is displayed above the arrows. In this state, and this is the crucial point here, the mobile device is NOT connected to the Internet, i.e. it has no IP address. Hence, the user is not charged and it has nothing to do with always-on connectivity.

So what's the use of this state? Not a lot actually. In the past, it was envisaged that applications from the Internet could trigger an IP connection being established to the mobile device when packets for it are received. However, to the best of my knowledge, no operator has ever made use of this functionality as it is pretty much obsolete due to the real always-on connectivity described just below. It's only real benefits are that the user sees on the display if EDGE is available or not, and that Internet connections are established faster in a subsequent step because the mobile is already registered.

In terms of power consumption, being GPRS attached should not require any more power than if one only attaches to GPRS when establishing an Internet connection if the network operator has configured the network accordingly. In practice, many network operators these days use an interface between the circuit and packet switched part of the network (the Gs interface between the MSC and the SGSN) so the mobile registers only once to the network when it is powered on and not to each part of the network individually. Also, periodic location update timers are set to the same value for the circuit and packet switched part so there is no additional signaling involved for being GPRS attached.

PDP Context Activated

Once an application wants to access the Internet for the first time, an IP address is requested from the network. This procedure is referred to as "PDP (Packet Data Protocol) context activation". Once an IP address has been acquired, the horizontal arrows at the top left of the screen changes from dashed to solid. The IP connection stays in place until one of two things happen. When the user closes an application that has requested an IP connection and no other applications are still running that use the connection as well, the IP address is released and the two arrows go back to their dashed state (GPRS Attached). But until this happens, the IP address remains assigned even if the application doesn't transfer any data. There is no technical limit of how long an IP address can stay assigned without exchanging data, it can persist for days, weeks or years. In practice, however, some (but not all) operators reset all IP connections once every 24h or after some time of inactivity. There are also operators who don't have their network properly configured so it can also happen that the IP connection is dropped when moving through the network and neighbor relationships are not properly set or if a core network component (SGSN or GGSN) malfunctions and is rebooted. However, those are exceptions.

A little Mystery

In the picture on the left there is a second option in that GPRS Attached/Detached configuration menu which is called "Access Point". I am a little bit puzzled what this option could be good for as it doesn't change the behavior of my N95 no matter whether it is set to "none" per default, to an APN or to a profile name.

Summary

The summary of this somewhat long text is that the description in the Boy Genius post is not accurate. The post suggest that by changing these options, the mobile will be switched to an always-on state and that the data connection will be kept. The only thing these options do is toggle between GPRS Detached and GPRS Attached state. The assignment of an IP address (PDP context activation) is a separate procedure, completely independent of these settings.

As a consequence, the "Packet Data Connection" option does not make anything better or worse if one has an unlimited data plan, or if one is billed per kilobyte or by the minute. Since it only speeds up getting an IP address when the first application that uses a connection requests data for the very first time, the setting should be the same for all kinds of data plans: "when available".

For more details, great places to look are the GPRS service description stage 2 (3GPP TS 23.060) or the GPRS introduction Chapter 2 in my book on mobile networks.

The Current LTE Spectrum Situation

I was recently asked by a friend how I see the current LTE spectrum assignments. I would have liked to give a simple answer but it is actually not quite straight forward. This is how I see it at the moment:

Europe:

  • 2.1 GHz band, used for 3G today but still a lot of unused capacity: Most likely the first band where 5 MHz LTE carriers will be deployed. No limitations from regulators, LTE can be deployed straight away.
  • 2.5 GHz spectrum auctions still outstanding in most countries. Good for going beyond 5 MHz carriers
  • 900 MHz band: Maybe some deployments of 5 MHz carriers or less. Good for in-house coverage but the band is heavily used for GSM today so it's difficult to clean up enough space for a meaningful LTE deployment without running into congestion issues. It might get better as more people get 3G phones and some of voice and data traffic currently running over GSM in the 900 MHz band will start flowing over 3G in the 2.1 GHz band. That reduces the load, hence, it might be possible for carriers to clear some spectrum for LTE, if they haven't opted for UMTS 900 deployment, which is available today.
  • 800 MHz band (Digital Dividend): Strong push in Europe at the moment to free the same bandwidth in all member countries. First trials have started to bring high speed Internet to rural areas with HSPA and LTE.

North America:

  • Verizon will deploy LTE in the 700 MHz band and has a single 10 MHz carrier available. That's not much. The spectrum has been assigned, so it can be deployed straight away.

Japan:

  • According to the presentation of NTT DoCoMo at the Mobile World Congress in Barcelona this year, they will also deploy LTE in the 2.1 GHz band, replacing one of their UMTS carriers with LTE at the beginning.

China:

  • Not sure

Unfortunately, it does not end here, 3GPP has lots of additional frequency bands defined for LTE. So fracturization is likely to increase. As always, comments, additions, etc. are very welcome!

Operator QoS for Skype & Co.

Recently, Nokia has announced that they will integrate Skype into the Nokia N97. Reactions, obviously, have been mixed. But I think the trend is difficult to stop, if not on this device it will be on another or in another way entirely. Some network operators have responded by announcing that they are thinking about introducing special tariffs which would include VoIP. But there is one thing over the top VoIP (i.e. non-operator circuit switched voice) doesn't have today, and that is the possibility to ensure the quality of service (i.e. latency, delay and jitter) especially over the air interface.

However, with a bit of imagination it wouldn't be too difficult to set this up. Here's one example of how it could work: In tariffs that take VoIP into account, the network could establish a secondary PDP context (UMTS) or a dedicated bearer (LTE) when it detects IP traffic of VoIP applications. This prioritizes the voice IP packets over other IP packets in the data stream of the user and also over IP packets of other users. Most mobile network operators already have deep packet inspection devices in their networks for all sorts of things and these could easily do the job.

I think it's an interesting technical possibility, let's see if somebody picks it up and puts it into commercial reality.

LTE – The First Global Cellular Standard – But Does it Matter?

Indeed on first thought, LTE will be the first global cellular standard in the future to which GSM, UMTS/HSPA, CDMA and potentially other cellular wireless technologies are likely to converge on. But does it really change anything?

Being a global standard does not necessarily mean all LTE capable devices can communicate with all networks around the globe. There are two main issues:

1) FDD and TDD Mode

While in most parts of the world, FDD (Frequency Division Duplex) will be the dominant air interface technology, TDD (Time Division Duplex) is pushed especially by China as an upgrade path for TD-SCDMA. So an FDD LTE device will not be able to use a TDD network and vice versa. With some luck, we might see devices that can do both FDD and TDD but nobody's really commenting on how feasible this really is. Only time will tell.

2) Two Dozen Different Frequency Bands

What's worse is the number of frequency bands are foreseen for LTE. In practice, this will mean that devices will be built for some but not all of those frequency bands. So it's nice to have a global standard but it's unlikely the mobile devices themselves will be usable on a global scale. The single 4G device working everywhere will remain a nice dream.

A Little Light At The End Of The Tunnel For Vendors

LTE being a global standard is a good thing for network equipment vendors. Most of the equipment will be the same including the base stations where only a few parts or modules are different to work on a different frequency band or operating mode (TDD/FDD).

Benefits For Network Operators

An economy of scale is created for networks operating on the
main LTE frequency bands (e.g. 900, 1800, 2100 and 2600 MHz). Most other frequency bands are only used by a few network operators so it's unlikely these will get the same prices from network vendors as their colleagues who use the mainstream bands. Also, the number of devices working outside the standard LTE bands are likely to be as limited as for UMTS/HSPA today. Just have a look of how many 3G devices are available for HSPA network in the U.S. compared to Europe.

Benefits For Users

For the users, I don't see a big change from the situation with HSPA today. Where the mainstream frequencies are used, there is a big choice of devices and this is likely to be the same with LTE. And network operators using less used frequency ranges will probably receive as few devices as those operating 3G network in such bands today.

What We Really Need

So what we really need is not only a global standard but also global frequency bands so everyone benefits the same. But, unfortunately, that's a dream that is very unlikely to come true anytime soon.

Voice – Bearer Aware, Bearer Adaptive or Bearer Agnostic?

It seems I am not the only one thinking quite positivity about Voice over LTE via Generic Access Network (VOLGA). Recently, Ajit Jaokar posted an interesting article in which he mentions that with VOLGA, the traditional circuit switched voice service becomes a bearer aware application, as it can choose between a 2G circuit bearer, a 3G circuit bearer and an IP based bearer over LTE. All seamlessly with handovers during the call with all bells and whistles attached!

An interesting way to look at it even more so as the bearer awareness does not come into play on the mobile device but actually in the network. This is because the controlling entity for the voice call, the mobile switching center (MSC), sits in the network and is informed by the network that a different bearer should be selected. It can then decide to go along, arrange for the network to prepare the handover and then instructs the device to make the jump.

So maybe VOLGA makes voice even more than bearer aware!? So far the term 'bearer aware' has mostly been used for applications being aware what kind of networks are available at a time and then make a choice as to which IP network to use or to stay put in case a network is available but the cost attached to it is too high to make the application feasible.

In the case of voice, however, the service can ensure continuity by jumping from one bearer to another. So terms like 'bearer adaptive' or maybe even 'bearer agnostic'  come to my mind, because that voice call will just work over any kind of network the device supports.

It could even work over the Wi-Fi you have at home if you extend the idea of VOLGA. Not for the moment, as the standard currently focuses on LTE, but in the future, who knows?