Category: IMS

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.

IMS Centralized Services – Inter-Device Transfer

Looks like 3GPP members are thinking about extending IMS Centralized Services with a new feature, Inter-Device Transfers. Nomor's September 2008 3GPP news made me aware of SP-080507 which contains the work item description for gathering requirements for this feature to allow an ongoing media session to be moved from one device to another.

An interesting feature I can see many uses for. When coming home, I transfer an ongoing call from my mobile to a desktop phone with better hands-free support. Or, when I enter the car, I transfer the call from the mobile phone to the car's system, maybe dropping the video component that was part of the call in the proccess. After all, one should look at the road.

Maybe they were inspired a bit by the DAIDALOS project which has worked on such scenarios already a couple of years ago. Also, such Inter-Device transfers are interesting for converged fixed/mobile operators who could offer such services to the customer over their integrated network.

Remotely Connecting To Your Home Services

For those of you who have been following my blog entries on femtos, home services and DLNA in the past couple of days, here's a link to a previous blog entry on Ericsson's ideas on how one could connect back to home services while not being at home.

I wished that the currently defined set of home services could be extended to other things such as a centralized calendar, notes, address book, etc. as I am one of the few people who would like to have this data stored at home rather than in the cloud. But I guess the current DLNA initiative is more about multimedia content than personal information.

An IMS Wireshark Trace

Thanks to the guys at Fraunhofer FOKUS in Berlin, IMS has moved from theory to at least a bit of practice for me as I reported in THIS BLOG ENTRY. As a little souvenir, I got the (Wireshark) pcap trace for an IMS voice call from many different interfaces including interactions between the IMS core and the network layer. Traces a great, one can learn a great deal of how the system works by looking at who says what to whom. Since I got the permission to share the trace I thought I'd post it here since I am sure some of you would like to have a look, too.

Most packets will decode nicely with a standard Wireshark installation, only the router interaction to allow more bandwidth for the connection requires additional DIAMETER xml descriptions. These have to be put into the /wireshark/diameter directory and the dictionary.xml file in the same directory has to be extended as follows:

At the beginning of the file put the following xml descriptions into the already existing list:

<!ENTITY TGPPRx SYSTEM "TGPPRx.xml">
<!ENTITY TGPPGx SYSTEM "TGPPGx.xml">

Afterwards, put the following instructions at the end of the file to load them.

&TGPPRx;
&TGPPGx;
</dictionary>

Final step: Open Wireshark, go to 'edit, 'preferences', 'protocols', select DIAMETER and add ports 4868 and 5868 to the default port 3868.

Have fun!

Download BobcallsAliceandtoomuchBW.pcap

Download TGPPGx.xml

Download TGPPRx.xml

An IMS Morning at FOKUS in Berlin

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Some encounters are interesting, fun, inspiring and enlightening on top. The recent meeting I had with Dragos Vingarzan, Alberto Diez and Bogdan Harjoc of Fraunhofer FOKUS NGNI can certainly be counted among them. For those of you who have not come accross FOKUS before, they are a German research institute under the roof of the Fraunhofer Gesellschaft and their group is working on IMS related topics. Here's a short roundup of what I've seen and what we discussed, which might be interesting to those of you working on any kind of IMS topic:

Over the years they have put together an impressive IMS setup. Not only have they developed an extensible IMS client, an IMS core network for testing purposes comprising all elements from the various CSCF's, an HSS, presence server, etc., etc., but they have built lots of tools around it from application server toolkits to stress test utilities. Also, they've put their setup to good use and developed a number of stunning IMS application prototypes. On top, their lab and software is open for any company wishing to test their components, devices or IMS backend software in an end to end system. HP, Ericsson, Nokia, Tektronix and many others are making frequent use of it.

Want to play around with an IMS core at home and have a look at the code? No problem, they offer their open source IMS core as a Vmware package that is ready to run with a Vmware player right from your PC.

Not only did I see my first real IMS VoIP call including policy interactions between the IMS network and a core network router, for which I was kindly provided with the pcap trace for some follow up investigations, but I was also shown a stunning combined IMS VoIP/Instant Messaging/Sharing/Collaboration application and a utility called SIPNuke that can easily simulate 10.000 SIP messages a second on an off the shelf notebook to make that IMS core or application server sweat.

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If you want to see it for yourself you can do so on the 6th to the 7th November during the 4th International FOKUS IMS Workshop in Berlin. Here's the link for further information and registration. 

Thanks Dragos, Alberto and Bogdan, it has been an exciting visit! I'll put some more detailed thoughs on the demos I've seen in one of the next blog entries.

Connecting Back Home

For many years I’ve wished for some technology to allow me to check on things back home, to control devices and to stream content from wherever I am. Some applications have become available over the years such as the GSM module that is connected to my block heater in the car so I can remote control the heating in winter. The Slingbox is another good example which allows media streaming to notebooks and mobile phones outside the home network. But such applications are still the exception rather than the norm.

In the recent Ericsson Review, I found an interesting article that gives an overview of current activities in the industry and standardization bodies concerning this topic. Noteworthy standards, bodies and activities mentioned are the Digital Living Network Alliance (DLNA), UPnP, UPnP Remote Access. Ericsson says while this is a good start, the solution lacks good remote connectivity. While UPnP provides for an encrypted tunnel that can be established between a notebook or mobile devices in general to access resources in the home network from outside, it lacks Quality of Service (QoS) interaction with the outside network and requires devices to be authenticated in the home network of the user once before they can be taken outside.

Ericsson sees a solution for this in using the IMS (IP Multimedia Subsystem) as a secure way to authenticate external clients, to exchange ciphering parameters between the home network and the remote client and to ensure QoS of the transport network for media streams.

A good starting point to dig deeper into the topic!

Beyond 3G: The Manuscript is Ready

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Some of you might have noticed that recent blog entries haven grown in size again and speculated that I have a bit more time at hand again. Well you have guessed right. Over the past months, I spent most of my free time working on my next book, to be published by John Wiley and Sons by the end of the year. Finally, the manuscript is ready and the title will be

"Beyond 3G: Bringing Networks, Terminals and the Web Together"

For the moment, people at Wiley's are now working on the cover, they are proof-reading the manuscript, and typesetting is starting soon. After that, I'll have to work a bit on the index, on the glossary, etc., etc. But that's a bit later in the year. I always find it amazing how many steps are necessary from finalizing the manuscript to having the finished book finally being shipped to the bookstores.

It's a long process. However, I strongly feel that all of this work is necessary and justified to produce something outstanding that has something which is missing in day to day online publishing: Depth and broadness.

That doesn't mean that online sources are less valuable, they are just different. I very much like my blog for example, because it catches spontaneous thoughts, thoughts about a clearly defined single topics, ideas, it's great for posting the latest news, for responding to someone else publishing something, and it is thus a great complement to my offline writing activities. Together, online and offline are hard to beat!

So what exactly will the book be about? Here's the current version of the back cover text:

Giving a sound technical introduction to 3GPP LTE and SAE, this book explains the decisions taken during standardization while also examining the likely competition for LTE such as HSPA+ and WiMAX. As well as looking at next generation network technologies, Beyond 3G – Bringing Networks, Terminals and the Web Together describes the latest mobile device developments, voice and multimedia services and the mobile web 2.0. It considers not only how the systems, devices and software work but also the reasons behind why they are designed in this particular way. How these elements strongly influence each other is discussed as well as how network capabilities, available bandwidth, mobile device capabilities and new application concepts will shape the way we communicate in the future.

  • Examines current and next-generation network technologies such as UMTS, HSPA+, WiMAX, LTE and Wifi
  • Analyses and explains performance and capacity in practice as well as future capacity requirements and how they can be fulfilled.
  • Introduces the reader to the current cellular telephony architecture and to voice over IP architectures such as SIP, IMS and TISPAN
  • Looks at mobile device hardware and mobile operating system evolution
  • Encompasses all major global wireless standards for application development and the latest state of the mobile web 2.0

As I said above, it's going to take until the end of the year until the book is finally shipped. If you would like to be informed when it's available, please send an eMail to "gsmumts at gmx.de", I'll be happy to keep you informed.

IMS Centralized Services (ICS)

Interesting to see which 3GPP Release 8 work items around the IP Multimedia Subsystem (IMS) are bearing fruit these days. While in Release 7, the hot application specifications for IMS services were Multi Media Telephony (MMTel) and device centric Voice Call Continuity (VCC), work in Release 8 seems to have to have shifted towards IMS Centralized Services (ICS) and a network centric Voice Call Continuity.

As the name implies, ICS offers centralized services, which means an IMS Application Server for ICS manages sessions for a user in several respects:

Multiple Devices – Several devices can be associated to the same user account and can be active simultaneously. Incoming media sessions can then be forwarded to one, several or all of these devices. Devices can be switched during ongoing sessions.

Including GSM mobiles – ICS has been designed not only to work with IP/IMS devices but also with "legacy" GSM  phones without any special software on board. When mobiles are switched on the MSC server communicates with the ICS Application Server (the Service Centralization and Continuity Application Server SCC AS) on behalf of the mobile. This is done either directly, in case the MSC server has been enhanced to act as an IMS client for the mobile, or via an Intelligent Network (IN) node that communicates with the MSC Server via CAP (CAMEL Application Part). The later one is probably preferred by many suppliers since IN nodes and CAP are used today for many applications such as prepaid billing. This has the advantage that the MSC software does not have to be extended for ICS.

Managing Supplementary Services – The ICS offers a standardized way of implementing services such as call forwarding, barring, hold, resume, 3-way calling.

Combination of Different Types of Media– ICS is not limited to voice telephony. Video calling, picture sharing and other media streams can be added or removed from a session at any time. 

Handover to 2G – And finally, the 3GPP ICS working group has also thought about how to hand over the voice portion of a session to a circuit switched bearer when the mobile reaches the limit of the broadband wireless networks. Currently, handovers from LTE are supported to GSM and 1xCDMA (hello Verizon!). Unlike the previous Voice Call Continuity (VCC) specification which requires the handover decision to be made by the mobile, the ICS handover to a circuit switched channel is network initiated and controlled. The advantage of network control is that the device does not have to be attached to two different radio networks simultaneously. This is important since like GSM/UMTS mobiles today, future LTE mobiles will also not be able to connect to two cellular network technologies simultaneously. From my point of view this network centric Single Radio Voice Call Continuity (SR VCC) approach is a major step towards solving the LTE voice gap. I'll describe the details in a future post.

For further information, here are links to the three main ICS specifications:

And for some more general background reading, here are some more resources:

IMS Terminal Specifications

While 3GPP specs pretty much go on the bit layer to describe how the IMS should look like in the network, I was wondering lately how the IMS could be implemented from the handset point of view. Here are links to two interesting documents which give a rather interesting insight into how the industry thinks IMS should work on terminals:

IMS and the TISPAN secrets – Part 2

IMS and TISPAN, a bit of a mystery combination. In part one I’ve taken a look at what TISPAN is and how it uses IMS in it’s architecture. This part focuses on the PSTN/ISDN Emulation Sub-System and how the IMS can be used to simulate an analogue telephony switching center.

Besides the IMS subsystem the PSTN/ISDN (Public Switched Telephone
Network / Integrated Services Digital Network) Emulation Sub-System
(PES) is another important element of TISPAN. Its aim is to enable
legacy analog and ISDN telephones to be connected to an IP based next
generation network (NGN) via a media gateway which is either part of
the access modem or a standalone device. An IMS independent
implementation for PES is described in ETSI ES 282 002 while ETSI TS
182 012 defines how a PES can be implemented with IMS. Both standards documents are available via ETSI’s web site for free but one must register first.

As legacy devices can not be
modified a gateway has to be deployed on the user’s location. On the
one side of the gateway the analog or digital telephone is connected to
a legacy connector. In case of a standalone device the other side of
the device usually features an Ethernet connector with which the device
can be connected to the DSL or cable modem. The PES specification in
ETSI TS 182 012 knows two types of devices. Voice Gateways (VGWs)
emulate a SIP User Agent on the behalf of the legacy device and
communicate with SIP commands with the P-CSCF of the IMS. The second
approach is to deploy a media gateway (GW) which communicates via the
H.248 (Media Gateway Protocol, MEGACO) to the Access Gateway Control
Function (AGCF). In this approach the SIP User Agent functionality is
included in the AGCF, i.e. not on the customer device but in the
network itself.  Additionally, the AGCF includes the P-CSCF
functionality. During call establishment, the P-CSCF or the AGCF then
communicate with the RACS to reserve the required transport resources
to ensure the quality of service for a call. In addition, PES requires
an IMS Application Server (AS) to emulate the PSTN or ISDN service
logic when the PES User Agent sends SIP messages with embedded ISUP
messages.

And a final note: The TISPAN standard also aims to standardize non IMS
sub-systems. While out of scope of the current version of the
specification it is likely that TISPAN will specify a standardized IPTV
and Video on Demand (VoD) system in the next version.