Author: Martin

IMS and the TISPAN secrets

No this is not a Harry P. sequel but just about as mysterious. For a long time I was aware that besides IMS there is a group called TISPAN that deals with Next Generation Networks (NGNs) in the fixed line world. Lots of articles note that TISPAN is based on IMS but give no further details. Recently I did some research in this area and here is my summary of how TISPAN and IMS are related. A word of caution, though: For the text below I assume that you are familiar in general with how IMS works, i.e. what is a P-CSCF, S-CSCF, etc.

As the IMS mainly addresses the requirements of wireless operators, the European Standards Institute (ETSI) has decided to define a broader NGN architecture in their TISPAN (Telecommunications and Internet converged Services and Protocols for Advanced Networking) standards project. In the meantime 3GPP and TISPAN are working in close co-operation and it is expected that Release 8 of the 3GPP standard will contain a common architecture. In its core, a TISPAN Next Generation Network (NGN) consists of the following entities:

  • A subset of the IP Multimedia Subsystem (IMS) as defined by 3GPP;
  • A PSTN / ISDN Emulation Subsystem (PES);
  • Other non-SIP subsystems for IPTV, Video on Demand and other services.

As can be seen in the list the IMS is only one of several core subsystems of TISPAN. The reason for this is the fact that many services today are not based on SIP and sessions such as IPTV or Video on Demand (VoD). Many different approaches exist on the market today to deliver such services to the user. TISPAN aims to standardize the way such services are delivered, controlled and billed and how such applications can interact with the transport network to request a certain quality of service level for their data packets.

While the IMS has been defined to be access network agnostic, the 3GPP standards still make a number of assumptions on the kind of access network and subscriber databases to be used. To make IMS usable for DSL and cable operators it is required to fully generalize interaction with the access network and to have a generalized user database in the network. The figure on the left shows a simplified model of how the IMS is enhanced by TISPAN for this purpose as defined in ETSI ES 282 001 and ETSI ES TS 182 006 (available at the ETSI website for free but you have to register).

A main difference between fixed line and wireless networks is how devices connect to the network. In case of fixed line access networks, a DSL or cable modem at the customer’s premises is usually the gateway device that establishes the connection to the network. One or more devices behind this gateway device will then use the established connection to register with the IMS service. This is quite different compared to 3GPP where each device connects both to the transport network (PDP context activation) and to the IMS service (SIP register).

A number of different ways exist today how a DSL or cable modem can attach to the network.  TISPAN has made the step to standardize the functionality required in the network for user management at the network layer with the Network Attachment Subsystem (NASS). When a DSL or cable modem is powered on it first communicates with the NASS to authenticate and to obtain an IP address. Protocols used for this purpose are for example PPPoE (Point to Point Tunneling Protocol over Ethernet) and PPP over ATM.
The NASS is reached during the attachment process via the Resource Control Enforcement Function (RCEF) / Border Gateway Function (BGF) which sits between the access network and the core network of the operator. Their tasks are among others to route IP traffic between an external network and subscribers and to ensure that quality of service requests coming from the IMS or other core systems listed above are enforced on the transport layer.

The TISPAN Resource and Admission Control Subsystem (RACS) performs a similar task as the IMS Policy Decision Function (PDF). When an IMS session is established by a TISPAN device the P-CSCF contacts the RACS subsystem to reserve the required resources for the session and to allow IP packets to flow between the participants of the session. The RACS then communicates with the RCEF/BGF to see if enough resources are available for the session and configures them accordingly.

While in the 3GPP IMS model resources are reserved by the mobile devices and the P-CSCF once codecs have been agreed on, the TISPAN P-CSCF already contacts the RACS for the first time when receiving the INVITE message from the originator. If bandwidth requirements change during the session setup because a different codec has been selected by the devices the P-CSCF contacts the RACS again to modify the policy. This means that unlike a 3GPP IMS mobile device, which requests a certain bandwidth and QoS with a secondary PDP context activation, TISPAN IMS devices are not involved in QoS processes at all since the P-CSCF takes care of the whole process. This is necessary as TISPAN devices, unlike 3GPP mobile devices, are pure IP devices and thus can not influence the quality of service settings of the network themselves.

So much for this blog entry. Stay tuned for part two in which I will discuss the PSTN/ISDN Emulation Sub-System (PES).

As always, comments are welcome!

Viviane Redding Continues Her Mobile Struggle

Viviane Redding, EU Media Commissioner continues to put outrageous 2G/3G data roaming prices in the EU on the table. Heise online quotes her saying that "[data roaming] prices are too high and hamper international communication" at a conference in Budapest.

Good that this topics keeps being discussed as I would like to give up my dozened SIM cards for Internet access rather sooner than later for a single one I can use in all countries I travel to!

Carnival of the Mobilists #101

It is said that all good things are three and I feel greatly honored to host the Carnival of the Mobilists for the third time now. The mobile ecosphere is moving at an astounding pace and it becomes quite obvious when I look back to when I first hosted the Carnival early 2006: The first usable 3G phones slowly coming to market, Nseries in it’s infancy, no iPhone, not a lot of talk then about mobile web 2.0 applications. Today, all of this is in full swing and this week’s Carnival of the Mobilists is the proof:

Kindle: Starting off with Michael Mace’s analysis of Amazon’s Kindle eBook reader. I like Michael’s drill down approach of looking at new products and services including their impact on the industry. He always goes far beyond ordinary device reviews. He writes to the point: "Kindle makes the wireless network do what it should do: Disappear". True words of what should happen, not only for the Kindle. Vero over at Taptu has also taken a look at Kindle and shares her thoughts whether this will be the future device for book reading.

Education: Judy Breck over at the Golden Swamp writes about the "The Million" program which is an initiative considered in New York to give mobile phones to school students with on board learning software. Students get rewarded when using the software by additional voice minutes, SMS messages, etc. Great stuff!

More Education: Judy is not the only one writing about education this week. Mark van ‘t Hooft has attended Handheld learning 2007 in London and gives us his impression from the exhibition/conference.

Mobile News From China: To most non-Chinese the Chinese mobile market is a big mystery especially due to the total absence of 3G because no licenses have been given out yet. Paul Ruppert gives some insight in his post on Mobile Point View about a Chineese future of Vodafone.

Mobile and Africa: I think Tomi Ahonen and his Communities Dominate Brands blog needs no further introduction here. This
week, Tomi has written about short wave transmissions of SW Radio
Africa being blocked by the Zimbabwean government and what the radio
station does about it: To bring uncensored news to the people in
Zimbabwe, they have started using SMS messages. 8000 people have
already signed up with 100 additions daily. A great service and let’s
hope that those who have figured out how to block radio waves don’t
also figure out how to stop SMS messages.

The Real Web on the Mobile: Dennis Bournique over at Wap review has written a pretty extensive article on the “real” web on phones and what it means for designers. A very difficult topic and I am still waiting for a one approach does it all as everything he mentions in his article has happened to me in the past.

Missing Local Wifi Apps: Dean Bubley over at Disruptive Wireless is also somebody to whom you should listen closely when he’s got something to say. This week he joins the Carnival with an analysis of why Wifi now built into many cellular mobile devices have not yet started a revolution in the local network.

More Android: Andreas Constantinou of the VisionMobile forum has written a great piece about the significance of Google’s Android – A long, analytical thought piece on why Android is different to every other OS out there. Definitely worth to be checked out!

Battery Life: Staying in the mobile device area for another moment, Amir has analyzed battery capacity enhancements in Nokia’s N95 evolution to see what effect the larger batteries and new hardware have on the latest N95 versions.

IMS and fixed/wireless convergence: And finally, here’s my contribution to this week’s Carnival: I guess there’s not a lot that can be found on YouTube today. So I am not sure why I was a bit surprised to see Telecom vendors such as Ericsson, Nortel, Nokia-Siemens-Networks and Alcatel-Lucent spreading the word there, too. The mobile world from the vendors perspective!

Next week, the Carnival goes to to Symbiano-Tek in Egypt. I wished I could go there fore a little vacation, too 🙂

Nokia ships first UTMS/HSPA 900 Phone

Recently, Finland’s Elisa has started the operation of one of the first UMTS/HSPA networks in the 900 MHz frequency band. While I heard this news some time ago I never quite figured out which mobile devices they had for the product launch. Most mobile devices shipped in Europe only support UMTS/HSPA on the 2100 MHz band. One of the few exceptions is Sony-Ericsson with their K850i, which also support U.S. frequency bands. But even this model does not support the 900 MHz band. Now Wikipedia reveals the secret: Elisa offers the Nokia 6121 classic for use in their network. As confirmed by this page on the Nokia web site it supports 3.5G on both the 2100 MHz and 900 MHz band. An encouraging first step! Keep going Nokia!

Carnival of the Mobilists #100

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The Carnvial of the Mobilists celebrates its 100th edition today over at Abhishek Tiwari’s blog today. As always great insight from this planet’s top bloggers on wireless. BTW: Did you know Android applications will be written in Java? It was quite a surprise for me. For more, head over and discover.

Next week it will be my pleasure to host the carnival on mobilesociety. So keep these entries coming!

Will Fixed/Wireless Convergence Push IMS?

Despite its multimedia capabilities the IP Multimedia Subsystem (IMS) hasn’t yet gotten a lot of opportunities to show its capabilities in wireless networks. One of the reasons for this is that current circuit switched mobile voice telephony works well and meets user expectations. Things, however, are improving for IMS.

With the introduction of the iPhone, more and more people are getting aware of multimedia and Internet capabilities of mobile devices. Thus, it might well be possible that multimedia enriched voice calls might also soon appear on the radar screen of users. On the network side many operators are upgrading their current 3G networks to 3.5G and with the first WiMAX networks rolled out now and LTE on the horizon there is sufficient bandwidth for such services. Additionally, WiMAX and LTE networks no longer have a circuit switched part and operators need a solution such as the IMS to be able to offer conversational services over their next generation networks. It thus seems inevitable, that the IMS will have a bright future.

In practice, however, things will be a bit more difficult since third party VoIP service providers such as Skype, Vonage and others could try to take a piece of the wireless market in a similar way as in fixed line networks today. After all, the application layer does not care whether IP packets traverse a DSL line or the air interface of a wireless network as long as there is enough bandwidth. From my own experience, SIP and proprietary VoIP services such as Skype work well over 3.5G wireless networks and even Skype video calls have excellent video quality in both directions.

Network operator based IMS systems, however, have a number of advantages over voice services provided by third parties if the play their cards right:

Network operators today sell both a mobile device and voice service. This means that the service works out of the box, no configuration required by the user. With pre-installed and pre-configured IMS applications such as voice, video calling, presence, etc. they have a head start over third party services for which applications have to be installed on mobile devices.

The IMS is also able to request a certain bandwidth for a session from the transport layer. In case there is congestion anywhere in the network, it will be made sure that multimedia sessions are not impacted.

The third advantage, which I think is a major one, is that IMS gives network operators with both fixed line (think DSL, cable) and wireless assets (think HSPA, WiMAX and LTE) the opportunity to converge their voice + multimedia service offerings both in the network and from the users point of view.

In the fixed line world the transition from analog telephony to VoIP over DSL or cable is already in full swing. The incentive for the user to switch to VoIP is usually a lower price for a combined voice service and Internet access over DSL or cable. When combined with mobile voice + Internet access, network operators can offer their clients Internet access + voice (and multimedia) telephony both at home, in the office or while roaming outside with a single device and a single telephone number.

The IMS also allows to have many devices registered to the same telephone number. This is great since at home it might be more convenient to use a dedicated phone, a notebook or even an IMS capable and connected television set to make a voice or video call.

With Voice Call Continuity (VCC) there is even the possibility that a mobile device automatically switches to Wifi when the user returns home or to his office thus reducing the load on the cellular network. Switching to Wifi at home also solves the issue of 3G/4G in-house coverage which in many regions of the world is inferior to 2G coverage due to the use of higher frequency bands.

And finally, the IMS has the capabilities to transfer a voice call from one device to the other. This is quite interesting in scenarios in which the user returns home and then transfers an ongoing voice call from his mobile phone to a television set and adding a live video stream to the call in the process.

It’s clear that getting all of this right is not a trivial task. But if network operators want to retain their role as a service provider they have to go beyond what third party service providers could offer over a bit pipe.

As always, thoughts and comments are welcome!

Prepaid Mobile Internet Access in Switzerland

Switzerland has had some pretty good tariffs for mobile Internet access via mobile networks for a while now but only for postpaid customers. Looks like times are slowly changing there, too. Sunrise and Aldi Switzerland (using the Sunrise network) now at least offer data tariffs with prices that should allow mobile eMail and web surfing via the mobile phone browser.

Sunrise and Aldi Switzerland ask for 0.10 Swiss Francs per 20 kb block which is 5 Swiss Francs per MB or about 2.90 Euros. Well, way to go, but it’s a start. But I definitely would not use it with a notebook.

When roaming the price per 20kb block is 0.30 Swiss Francs per 20 kb block for all roaming countries according to the price list of Sunrise. That’s 15 Swiss Francs per MB or about 8.90 Euros. Not really on the cheap side but still cheaper than many other roaming alternatives for countries for which you don’t have a SIM and don’t want to spend a full 15 Euros for a 24 hour Vodafone Germany Websession.

I had a look on the Aldi Switzerland homepage for the details. To get a SIM card a registration form has to be downloaded, filled out and taken to one of the Aldi supermarkets when buying a SIM card together with your passport. Activation of the SIM card then takes around 24 hours. I wonder if things work quicker when going to a Sunrise shop!?

One more note: Orangeclick also offers mobile Internet access but prices are not competitive unless you subscribe to a 5 Swiss Francs add on which is deducted from the prepaid account once a month. This gives you 2MB worth of data and a price of 2.5 euros per megabyte afterwards.

More information on prepaid wireless Internet access via cellular networks for many countries can be found here.

I-WLAN for IMS access over Wifi

I’ve taken a look at IMS lately and ways to access the IMS from non 3GPP networks such as Wifi hotspots and Wifi at home. Looks like 3GPP TS 23.234 and TS 33.234 contains everything required for the purpose. The first major building block of I-WLAN (Wireless Local Area Network interworking) is how the subscriber database of a 2G/3G network can be used to authenticate Wifi users that have a device with built in GSM/UMTS SIM card. For this purpose EAP/AKA or EAP/SIM is used. For EAP-SIM I’ve written a blog entry some time ago. The standard also foresees methods for the access point to deliver billing information to the 3GPP network.

What I didn’t realize at that time was that the second building block in those two documents is a method to establish an IPSec encryption tunnel between a mobile device and a gateway between an external network (e.g. the Internet) and the 3GPP core network which hosts an IMS. This gateway is called the Packet Data Gateway (PDG). The standard even says that the IPsec tunnel setup can be used without the above mentioned EAP-SIM authentication step. That’s good news as the EAP-SIM authentication requires support of the Wifi Access point while the tunnel establishment is transparent to the Wifi access point.

So let’s see maybe we’ll see 3G+/Wifi IMS devices with the ability to establish an IPSec tunnel over Wifi to the IMS of their wireless operator. Great stuff for mobile operators with DSL assets.