Circuit Switched Fallback (CSFB): A Quick Primer

I have explained CSFB with basic signalling here and there is a very interesting Ericsson whitepaper explaining all Voice issues in LTE here.

The following CSFB details have been taken from NTT Docomo Technical Journal:

The basic concept of CS Fallback is shown in Figure 1. Given a mobile terminal camping on LTE, a mobile terminating voice call arrives at the terminal from the existing CS domain via EPC. On receiving a paging message, the mobile terminal recognises that the network is calling the mobile terminal for CS-based voice and therefore switches to 3G. The response confirming the acceptance of a call request is then sent from the mobile terminal to the 3G-CS system, and from that point on, all call control for the voice service is performed on the 3G side.

The CS Fallback consists of a function to notify a mobile terminal of a call request from the CS domain and combined mobility management functions between CS domain and EPC for that

purpose. The network architecture of CS Fallback is shown in Figure 2.

One of the remarkable characteristics of the EPC supporting CS Fallback is that it connects the Mobile Switching Center (MSC) and Visited Location Register (VLR) in the 3G CS domain

with the Mobility Management Entity (MME), which provides EPC mobility management functionality. The interface connecting MSC/VLR and MME is called an SGs reference point. This

interface is based on the concept of the Gs reference point that exchanges signalling with MSC, which connects to the Serving General Packet Radio Service Support Node (SGSN), a 3G

packet switch. The SGs provides nearly all the functions provided by the existing Gs.

The CS Fallback function uses this SGs reference point to transfer the mobile terminating call requests from the CS domain to LTE. It also provides combined mobility management

between the 3G CS domain and the EPC to enable this transfer to take place.

Combined Mobility Management between CS Domain and EPC Network:

A mobile communications network must always know where a mobile terminal is located to deliver mobile terminating service requests to the mobile user on the mobile terminating side. The procedure for determining terminal location is called “mobility management". As a basic function of mobile communications, 3G and LTE each provide a mobility management function.

To complete a call using the CS Fallback function, the CS domain needs to know which LTE location registration area the mobile terminal is currently camping on. To this end, the MME must correlate mobility management control of the CS domain with that of EPC and inform MSC/VLR that the mobile terminal is present in an LTE location registration area.

The 3G core network already incorporates a function for linking mobility management of the CS domain with that of the Packet Switched (PS) domain providing packet-switching functions. As described above, the CS domain and PS domain functions are provided via separate switches. Thus, if combined mobility management can be used, the mobility management procedure for the terminal only needs to be performed once, which has the effect of reducing signal traffic in the network. This concept of combined mobility management is appropriated by the CS Fallback function. Specifically, MSC/VLR uses the same logic for receiving a location registration request from SGSN as that for receiving a location registration request from MME. This achieves a more efficient combined mobility management between the CS domain and EPC while reducing the development impact on MSC.

As described above, a mobile terminal using LTE cannot use 3G at the same time. This implies that the MME, which contains the LTE location registration area (Tracking Area (TA)), is unable to identify which MSC/VLR it should send the mobility management messages to from the TA alone. To solve this problem, the mapping of TAs and 3G Location Areas (LA) within MME has been adopted. The concept behind TA/LA mapping is shown in Figure 3. Here, MME stores a database that manages the correspondence between physically overlapping TAs and LAs. This information is used to determine which MSC/VLR to target for location registration.

The combined TA/LA update procedure for CS fallback is shown in detail in Figure 4. First, the mobile terminal sends to the MME a Tracking Area Update (TAU) request message indicating a combined TAU and the current TA in which the mobile terminal is currently present (Fig. 4 (1)). The MME then performs a location update procedure towards Home Subscriber Server (HSS), which is a database used for managing subscriber profiles (Fig. 4 (2)). Next, the MME uses the TA/LA correspondence database to identify the corresponding LA and the MSC/VLR that is managing that area, and uses the SGs reference point to send a Location Area Update (LAU) request message to the MSC/VLR together with the LA so identified (Fig. 4 (3)). The MSC/VLR that receives the LAU request message stores the correspondence between the ID of the MME originating the request and an ID such as the International Mobile Subscriber Identity (IMSI) that identifies the subscriber (Fig. 4 (4)). This enables the MSC/VLR to know which MME the mobile terminal is currently connected to and that the mobile terminal is camping on LTE. Following this, the MSC/VLR performs a location registration procedure with the HSS (Fig. 4 (5)). Finally, the MSC/VLR informs the MME of temporary user identity (Temporary Mobile Subscriber Identity (TMSI)), which is used at the time of a mobile terminating call in the CS domain, and indicates that location registration has been completed. The MME then informs the mobile terminal of the TMSI and of the LA that the mobile terminal has been registered with thereby completing combined location registration (Fig. 4 (6) (7)).

CS Fallback Call Control Procedures - Mobile Originating Call:

To originate a voice call using the CS Fallback function, a mobile terminal in the LTE location registration area must first switch (fall back) to 3G. The mobile-originating voice call procedure is shown in Figure 5. To originate a call, the mobile terminal begins by sending a CS fallback service request message to the MME (Fig. 5 (1)). Since a packet-communications transmission path (bearer) must always exist in EPC for the purpose of providing an always-on connection, the bearer also has to be handed over to 3G. To accomplish this, the MME issues a handover command to the mobile terminal in LTE and initiates a handover procedure (Fig. 5 (2)). The mobile terminal changes its radio from LTE to 3G during this procedure (Fig. 5 (3)). On completion of handover, the mobile terminal issues an originating request for voice service to the MSC/VLR. A voice-call connection is then established using an existing calloriginating procedure on 3G and the CS Fallback procedure is completed (Fig. 5(4)).

CS Fallback Call Control Procedures - Mobile Terminating Call:

The mobile terminating voice call procedure using CS Fallback is shown in Figure 6. When the MSC/VLR receives a message indicating the occurrence of a mobile terminating call (Fig. 6 (1)), the MSC/VLR identifies the corresponding MME from the call information received (Fig. 6 (2)). Then, the MSC/VLR sends a paging message (Fig. 6 (3)) towards the MME. Next, the MME sends a paging message to the mobile terminal in LTE (Fig. 6 (4)). This paging message includes an indication that the call is a CS service, and on identifying the call as such, the mobile terminal sends a CS fallback service request signal to the MME (Fig. 6 (5)). Following this, a handover procedure to 3G as described above takes place (Fig. 6 (6), (7)). The mobile terminal that is now switched to 3G sends a paging response message to the MSC/VLR at which it is registered (Fig. 6 (8)). Finally, an existing mobile terminating call procedure on 3G is executed and the CS Fallback procedure is completed (Fig. 6 (9)).

Quick primer on Push-to-talk (PTT)

Push to Talk (PTT)

View more documents from Zahid Ghadialy.

MBMS in LTE Release-9

From NTT Docomo Technical Journal:

MBMS is a bearer service for broadcast/multicast transmission of data, to transmit the same information to all interested UEs in an area over a common bearer. Note that MBMS has been supported in UTRA since Release 6.

LTE Release 9 supports basic MBMS functionality not requiring complex control. One of the main features is support for MBMS Single Frequency Network (MBSFN) transmission. With MBSFN transmission eNBs in the MBSFN area transmit the same signal simultaneously using the same time-frequency resource. The UE receives the combined signals as a single, strong signal, improving coverage and signal quality without much additional complexity in the UE. By applying MBSFN transmission, a 3GPP study concluded that to provide 95% coverage with a packet error rate of 1%, a spectral efficiency of 3 bit/s/Hz or greater can be achieved.

The logical architecture for MBMS in LTE is shown in Figure 4. The MBMS gateway (GW) distributes data received from the Broadcast Multicast Service Center (BMSC) to the relevant eNBs by IP multicast. The Multi-Cell Multicast Coordination Entity (MCE) specifies the radio resources to be used by eNBs comprising the MBSFN and ensures that the content is synchronized. To support MBMS, logical channels, namely Multicast Traffic Channel (MTCH) and Multicast Control Channel (MCCH), and a transport channel, namely Multicast Channel (MCH), are defined (Figure 5).

Relation between 3GPP Release-8 and Release-9

Five quick videos from Mobile World Congress 2011 - 3

More on HTC Freestyle and Brew OS here.

More on Live translating service here.

Ps: I know there are 6 videos ;)

Five quick videos from Mobile World Congress 2011 - 2

Facebook onto a SIM using Class 2 SMS

I am sure you have already heard of Gemalto's (worlds largest SIM manufacturer and supplier) Facebook on the SIM announcement. The advantage of this approach is that 100% of the existing phones will be able to support facebook (if the operator supports the application on the SIM). This is a big step0 forward. The press release says:

Gemalto’s software development team has embedded the software application into the SIM. This ensures the Facebook application is compatible with 100% of SIM-compliant mobile phones.

The innovative solution provides mobile subscribers with simple and convenient access to core Facebook features such as friend requests, status updates, wall posts or messages. It also offers unique functions: people can sign up for this service and log in directly from the SIM application. Interactive Facebook messages pop-up on the phone’s screen so people can always share up-to-the-minute posts and events. One can also automatically search their SIM phonebook for other friends and send them requests.

Facebook for SIM is extremely easy to use and is available to everyone. No data contract or application download is needed, because the software is embedded in the SIM and it uses SMS technology. As a result, it works for prepaid as well as for pay-monthly customers. Following an initial limited free trial period, Facebook for SIM then operates on a subscription model via an unlimited pass for a given period of time.

“Facebook for SIM enables operators to leverage two of their main assets: the SMS to communicate with the web application and the SIM for application distribution to the masses,” added Philippe Vallée, Executive Vice President, Gemalto. “Over 200 million people already use Facebook on handsets and those are twice as active as non-mobile users . By providing anytime, anywhere availability to the social network, Gemalto delivers on the growing demand for mobile connectivity all over the world.”

An article on the Register had more details:

The SIM-based client isn't as pretty as its smartphone contemporaries – don't expect picture streams or sliding interfaces – but it was developed with the help of Facebook, and provides text-menu-based interaction with Facebook – including status updates, pokes and friend requests – to any GSM-compatible handset through the magic of the GSM SIM Toolkit and Class 2 SMS messages.

The SIM Toolkit is part of the GSM standard and thus supported on just about every GSM handset, from the dumbest PAYG talker to the latest iGear. It allows the SIM to present menu options to the user, collect responses, and pop up alerts when new data arrives, which is all that's necessary for a basic Facebook client.

Modern handsets also allow the SIM to make TCP/IP data connections, but Gemalto is eschewing that for Class 2 SMS to ensure compatibility with the most basic handsets, and networks.

Class 2 SMS messages are delivered direct to the SIM without the user being involved, so can update friends' status messages and deliver a poke or two. The application running on the SIM then prods the handset into alerting the user.

That user's own updates are sent over SMS too, following a status change or wall posting client pastes that into an SMS, which is sent silently on its way.

How, or if, the network operator charges for all those messages flying about isn't clear. Gemalto won't name operators yet but claims to be talking to one operator who reckons that Facebook is eating half its bandwidth, and another who's already working on SIM distribution strategies.

Not that a new SIM is necessarily required – SIMs are field upgradable, though few operators deploy them with sufficient empty space for an application like this and issuing replacement SIMs is probably easier from a marketing point of view.

You can also find some of these details here.

As I have been working on SMS for the last few weeks, I decided to dig a bit deep into what these Class 2 SMS are.

Classes identify the message's importance as well as the location where it should be stored. There are 4 message classes.

Class 0: Indicates that this message is to be displayed on the MS immediately and a message delivery report is to be sent back to the SC. The message does not have to be saved in the MS or on the SIM card (unless selected to do so by the mobile user).

Class 1: Indicates that this message is to be stored in the MS memory or the SIM card (depending on memory availability).

Class 2: This message class is Phase 2 specific and carries SIM card data. The SIM card data must be successfully transferred prior to sending acknowledgement to the SC. An error message will be sent to the SC if this transmission is not possible.

Class 3: Indicates that this message will be forwarded from the receiving entity to an external device. The delivery acknowledgement will be sent to the SC regardless of whether or not the message was forwarded to the external device.

You can also read this for more details on SMS message contents

Five quick videos from Mobile World Congress 2011

Follow the latest action in Mobile World Congress at Twitter here.

Non-Voice Emergency Services (NOVES)

Its been a while we talked about SMS for Emergency purposes and eCall. A new study item in 3GPP has looked at non-voice alternatives for Emergency purposes.

Picture Source: Dailymail

The following is from the recent 4G Americas report entitled: 4G Mobile Broadband Evolution: 3GPP Release-10 and Beyond:

Non-verbal communications such as text messaging and instant messaging via wireless devices has been very successful and continues to expand. Many of the consumers assume that they can utilize these types of non-verbal communications as mechanisms to communicate with emergency services whenever emergency assistance is required. Such mechanisms currently do not exist. The Emergency Services community has a desire to have multimedia emergency services supported with the same general characteristics as emergency voice calls.

Currently, service requirements for emergency calls (with or without the IP Multimedia Core Network) are limited to voice media. The Non-Voice Emergency Services (NOVES) is intended to be an end-to-end citizen to authority communications. NOVES could support the following examples of non-verbal communications to an emergency services network:

1. Text messages from citizen to emergency services

2. Session-based and session-less instant messaging type sessions with emergency services

3. Multimedia (e.g., pictures, video clips) transfer to emergency services either during or after other communications with emergency services.

4. Real-time video session with emergency services

In addition, to support the general public, this capability would facilitate emergency communications to emergency services by individuals with special needs (e.g., hearing impaired citizens).

The objectives of this study include the following questions for NOVES with media other than or in addition to voice:

1. What are the requirements for NOVES?

2. What are the security, reliability, and priority handling requirements for NOVES?

3. How is the appropriate recipient emergency services system (e.g., PSAP) determined?

4. What are the implications due to roaming?

5. Are there any implications to hand over between access networks?

6. Are there any implications due to the subscriber crossing a PSAP boundary during NOVES communications (e.g., subsequent text messages should go to the same PSAP)?

7. Do multiple communication streams (e.g., voice, text, video emergency services) need to be associated together?

8. What types of “call-back” capabilities are required?

9. What are the load impacts of NOVES in the case of a large scale emergency event or malicious use?

NOVES will be applicable to GPRS (GERAN, UTRAN) and to EPS (GERAN, UTRAN, E-UTRAN and non-3GPP). The content may be transmitted between the subscribers and the emergency services which might bring new security issues. Therefore, the security impacts need to be studied.

You can spend your weekend reading the 3GPP Study Item TR 22.871: Study on Non-Voice Emergency Services (Release 11).

A word of caution, the name NOVES may be changed in future as Emergency agencies in Europe have an objection to the name. See here and here.

Smarter Cars of the Future

We all know that cars are getting smarter. Back in Oct., Google unveiled the cars that can drive by themselves. I am sure they will make our life much better and we will be able to catch on the sleep at early morning commute.

Then there were quite a few futuristic cars at the CES 2011 last month. One such video is embedded below.

The following is a summary from the an IEEE article:

Cars have been getting smarter for years, studded with suites of sensors and supporting electronics aimed at keeping them from crashing. But entertainment and convenience have rapidly caught up to safety as the impetus for new in-car electronics development. Because automakers typically spend three years developing and producing new cars—and new gadget candy to go with them—they’ve found themselves constantly playing catch-up with consumer electronics and consumer expectations. So car companies have teamed up with the makers of smartphone software platforms to integrate a spectacular array of apps designed for handsets with cars’ digital dashboards, center consoles, and speaker systems.

Take for instance Ford’s new Focus all-electric vehicle, which made a big splash at the 2011 International Consumer Electronics Show in Las Vegas last month. It features a software application called MyFord Mobile.

The app, which runs on Ford’s proprietary Sync platform and is compatible with the BlackBerry, iPhone, and Android devices, links the car with the driver’s smartphone and home computer. The software lets the driver listen to a smartphone’s music library and lets passengers watch movies or TV shows. It delivers information such as when electricity prices are at their lowest (to allow for the cheapest battery recharging) and where the nearest charging stations are. And it allows a smartphone to function as a remote control, by means of a connection to cloud-based servers. This remote communication lets the handset keep tabs on the car’s location and the batteries’ state of charge. It will also let the driver start the Focus EV from indoors on a blustery January morning, then step into a car whose seats and steering wheel are already warm. The MyFord Mobile app lets the driver remotely start the car, turn on the heater or air conditioner, or unlock the doors from anywhere in the world (including beneath the bedcovers).

And because the system differentiates one driver’s key from another’s, it presents information on the reconfigurable 4-inch screens on either side of the speedometer in the current driver’s preferred color and style. The state of charge, for example, could be shown as a percentage of the full charge, as an estimate of the remaining miles before recharging, or as a simple bar that gets shorter as the batteries’ energy is consumed. This differentiation also works for utility and entertainment options; it automatically queues up driver A’s list of radio station presets, favorite mobile apps, and preferred display options for the 8-inch center console touch screen. Because MyFord Mobile links the Focus to the driver’s handset, it can also access his or her contact list for hands-free calling and read out e-mails and texts through the car’s speakers.

Ford is trying to position itself as a technological leader in the automotive industry with MyFord Mobile and Sync AppLink Voice Control, which puts the driver in control of all the Sync system’s capabilities via voice commands, but it has stiff competition from the likes of Mercedes-Benz, Continental, and Toyota. Launched by Mercedes-Benz in November 2009, the Mbrace system, designed and engineered by Hughes Telematics of Atlanta, was the first telematics service on the market to give smartphones the power to remotely lock, unlock, or locate a car. It didn’t signal a revolution in the way the average driver interacts with his or her vehicle because when the German luxury vehicle maker offers a new technology or set of features, there is usually a multiyear wait for them to trickle down to cars whose sticker prices aren’t stratospheric.

The second generation of Mbrace debuted last September. It introduced Mercedes-Benz Concierge, which not only opens the car to information from the outside but also makes some car-based information and entertainment options portable. The Mbrace Mobile Application 2.0 gives iPhone and Blackberry users single-phone-number access to recommendations for nearby entertainment and restaurant options, directions, traffic updates, and more, whether the person is in the car or not. The concierge then sends destination information to the smartphone or directly to the in-vehicle navigation system. With the Mbrace system’s latest wrinkle, the Drive2Friend service, the driver can dictate a friend’s mobile number and the app sends a text message reporting that the driver is trying to find the person. The friend has the option of allowing his or her location to be sent back to the car via cellular triangulation.

While Ford was showing off its wares at CES, Continental was also there showcasing the Android-based AutoLinQ system, which lets the driver connect to the car in three ways.

AutoLinQ’s Mobile View lets you to send text messages to your car; the smart vehicle can text you back with information such as its location. In this demo [Flash video], a smartphone user is shown making a remote inquiry about the status of his car. Mobile View reports that the sunroof is open and offers the option to close it or ignore the warning. When he taps Close on the handset’s touch screen, the sunroof’s glass panel glides shut. This type of call-and-response vehicle update also tells whether doors are closed and locked and whether the headlights or interior lights are on. Mobile View doesn’t wait for a query to alert the driver when the alarm is triggered, the battery is depleted, the air bag has been activated, or the internal temperature of the car is too high or low. And like MyFord Mobile, it turns the smartphone into a remote control for locking and unlocking the doors, starting the engine, flashing the lights, and more.

AutoLinQ’s Home View lets you download apps and configure vehicle settings from your home computer. Clickable tabs at the bottom of the Home View screen let the car owner move through screens showing a wealth of data on the car’s status, driver preferences, navigation information, and applications that can be downloaded or fine-tuned. The status menu tells whether the ignition is on and displays the fuel and motor oil levels, the pressure for each of the four tires, and much, much more.

Car View, in AutoLinQ, is for updating features from the driver’s seat. Car View provides the same information as Home View but lets the driver use the center console touch screen to download apps on the fly that provide better control of the car and the ability to remotely manipulate electronic devices back home. An app that sends an alert when a game or match in the driver’s favorite sport is about to appear on television also gives the option to activate a digital video recorder at home, pull up a Web site featuring periodic updates about the game, or listen to play-by-play on the radio.

Continental is also designing unique apps that will enhance vehicle performance. For instance, the Filling Assistant will detect underinflated tires and notify the driver. When the driver goes to inflate the tires, the Filling Assistant will report pressure information to the driver’s smartphone and honk the car’s horn or flash its lights to indicate when a tire has enough air.

Not to be left out, Toyota, the world’s leading automaker, debuted the QNX-based Entune at CES 2011. Entune is an upgradable suite of entertainment, navigation, and information functions. "Consumers have grown accustomed to having the world at their fingertips through their mobile phones," says Jon Bucci, vice president of Toyota’s advanced technology department, who notes that putting them in the car is a natural evolution.

After downloading the Toyota Entune app to a handset and syncing it with the Toyota vehicle, the driver can begin accessing content and services, including Bing for Web navigation and OpenTable, which can make reservations at any one of 15 000 restaurants, with directions sent seamlessly to the navigation system and information appearing on the center console. Entune also lets a driver get customizable real-time traffic updates, sports, weather, stocks, and information on prices at local fueling stations. The system doesn’t forget music, which has almost always been a part of the driving experience. Entune includes Iheartradio, which delivers roughly 750 local radio stations at the touch of a button.

The tide of apps extending handset capabilities to cars will only continue to rise. ABI Research, in Oyster Bay, N.Y., reports that the number of users of automotive apps will increase from 1.4 million in 2010 to more than 28 million by 2015. And according to Global Industry Analysts, the vehicle telematics market is expected to reach US $11.2 billion by 2015.

You can read the complete article here.

In other news, Robots in future will have their own Internet and content like Wikipedia, etc. Does anyone else remember 'The Terminator'?