3G FACH capacity

With the rising number of push eMail devices in 3G networks and mobile applications such as instant messengers and voice over IP clients the number of small IP packets to keep the connections of such applications alive through network address translation routers is rising. For the network this means of lot of radio layer signaling and waste of bandwidth. For the mobile device, keep alive messaging means significantly increased battery consumption.

3G UMTS networks are thus putting devices that only send little data on the Forward Access Channel (FACH) which requires much less radio channel signaling overhead than if the device is instructed to remain or use the High Speed Downlink/Uplink channels for such kind of traffic. As more always-on devices are used in the networks, this will quickly become an issue since the total capacity of the FACH of a cell is limited to 32 kbit/s today. With the bandwidth so small I think most operators will be very thankful for the enhanced-FACH extension which reserves some capacity on the high speed downlink channels for FACH operation. Despite using the high speed channels, no additional radio layer signaling will be used so overhead and battery consumption remains limited at the expense of spectral efficiency. While networks and mobile devices do not support this feature today I expect that this is definitely a feature that will be implemented in the future.

For more on radio interface optimization for future devices and services have a look at my previous entries on continuous packet connectivity (here, here and here), some more background on enhanced FACH (here) and some thoughts on upcoming capacity issues due to keep alive messaging (here).

It seems there is now also an initiative in Release 8 of the 3GPP standards to improve the uplink behavior of the system while a device in in Cell_FACH state. More about that once I have taken a look at the details.

RIM’s European Advertisment Campain for the Young and Cool

It's interesting to see how RIM attempts to push their Blackberrys beyond their core market, email business users, and how it advertises the new models. It's funny when you come across the same poster in different countries in different languages, it's almost like a deja vu. Below are two examples of the same poster, one from the U.K. and the other from Italy.

While Michael Mace says RIM is not in the same market as Apple except for some overlap, it seems to me that this overlap is not that small anymore. With their campaign they are definitely trying to increase the overlap, just as Apple tries to add functionality to appeal to business users to increase the overlap in their favor.

I think even before this advertising campaign, RIM has already moved beyond the typical business user anyway. When I was in the US recently, I saw lots of definitely "non-business" people carrying a Blackberry. Maybe that's because there is not a lot of choice. In operator stores, there was the iPhone, a couple of Blackberry variants and a couple of very low end phones. Nothing much in between.

Bb-uk
Bb-italy

Why Are We Still Using Narrow Band Codecs for SIP to SIP Calls?

I really like the SIP Voice over IP implementation of the Wifi enabled Nokia Nseries phones such as the N95 and the N82. After all, they save me a lot of money these days as SIP to SIP calls for example even between different operators are free. On first thought, voice quality seems to be excellent, I can't tell the difference between a VoIP call and a traditional circuit switched call over a cellular network. But put into a different perspetive, that's a bit short sighted. For direct SIP to SIP calls that do not cross a circuit switched interface, why do the two SIP clients still use the backwards compatible G.711 narrow band voice codec released in 1972 or the narrowband AMR (Adaptive Multi Rate) codecs? Today, much better codecs such as Wideband AMR (AMR-WB) are available that have a similar audio quality as Skype to Skype calls. So why are we still stuck with a narrow band encoding? It can't be computing power, especially in the case of high end Nseries phones. Maybe license or patent issues? Ideas, anyone?

SIP providers miss a great opportunity to go beyond the limitations of circuit switched networks and offer subscribers a superior experience for direct VoIP to VoIP calls. And I think it would be a good selling argument once suddenly for some connections you have a much better audio quality than to someone still stuck in the circuit switched world (or in a SIP network that is not interconnected and thus has to use a circuit bridge). I can very well imagine that at some point conversations would start with "oh, you are still on an old phone line" 🙂

P.S.: Some details: The N95 SIP client supports AMR, G.711 a- and my-law, iLBC and G.729. All narrowband…

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

Manuscript-sm
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.

Opera Mini on Entry Level Devices

Today, a friend showed me Opera Mini on his new 'Nokia 3110 Evolve', an entry level phone with supposedly a slow processor (compared to Nseries phones) and a screen resolution of 'only' 128×160 pixels. Since he's using OperaMini it was a good opportunity for me to find out how practicable web browsing is on this phone compared to higher end phones. After upgrading from the default OperaMini 2 to OperaMini 4, the browing behavior is the same as on my N95 including the overview mode and zoom in functionality. Concerning browsing speed and scrolling through the page I didn't notice any uncomfortable delay after pressing a button. Even scrolling quickly through a long page is very quick as well. I didn't quite expect such a smooth behavior. Great stuff, kudos to both Nokia and OperaMini!

The Nokia 6300i and VoIP over Wifi

Back in April this year, Nokia announced the 6300i that comes with Wifi and VoIP (but no 3G support). At the time, it was not quite certain from the press release what kind of VoIP the phone would offer. Now that the mobile is available, the user guide gives further details on page 30. The word SIP is never used but based on the configuration information, it certainly looks like SIP like on the Nseries phones and not like UMA. For UMA, the 6300i seems to have a brother, the 6301. Together with Firmware Over the Air (FOTA) update capability, and Opera Mini coming pre-installed, it looks like Nokia has started an interesting test balloon in the sub 200 euro category (Amazon Germany has it for 179 euros, taxes and shipping included!). I'd really like to try the VoIP implementation. I wonder if it is as good as that of the N95? Or maybe even better?

LTE Air Interface Primer

It's good to see whitepapers coming out from different companies taking a closer look at LTE. Lots of interesting material can be found at Agilent's LTE Network Testing web page. I especially like the LTE (Air Interface) introduction webcast and the LTE System Overview whitepaper.

Although I am already aware of many things discussed in the paper, its always good to read about things from an author that looks at the topic from a different perspective. Here are a few of the things I found outstanding (for me personally) in the whitepaper:

Good Air Interface Graphics: The paper has some awesome graphics on how the physical channels map onto the different sub-carriers (or more precisely resource blocks). It's interesting to note that the control channels can take up to 30% of the cell capacity in case lots of devices require to be scheduled (e.g. Figure 23). That's quite a lot of capacity wasted for signaling. I guess we have to wait and see if in practice that much signaling capacity is really required.

Fractional Frequency Re-use: To improve cell edge performance the paper mentions the use of only a fraction of the sub-carriers to be broadcast at higher power levels. I've written about this quite some time ago and it's good to finally see some papers who are going into this direction as well.

BCCH: Broadcast once every 10ms (one frame) around the center frequency.

HARQ ACK/NACK: Contains intereresting details on where, when and how the acknowledgments are sent in uplink and downlink direction.

Nokia N79 and N85 UMTS Band Options

It’s good to see Nokia presenting two new Nseries models yesterday. While I leave it to others to report on all the multimedia details, I was intrigued that both devices support several UMTS frequency bands, a first for Nseries devices.

The N85 has the most wide ranging UMTS band support. According to the datasheet, there will be two versions: The first one supports UMTS in the 900/1900/2100 MHz and is thus clearly targeted at Europe and the starting deployments of UMTS in the 900 MHz band in addition to the 2100 MHz band. The 1900 MHz band is at least partly usable in the US, where AT&T has deployed UMTS in some cities. The second version supports 850/1900/2100 and is probably mainly targeted at the US since AT&T uses both frequencies. Too bad it doesn’t support all four bands, it would make a great world band phone that way.

But despite the support of three UMTS bands there are some combinations which don’t work so well: For Australia, both models are needed since Telstra uses the 850 MHz band for 3G and Optus deploys 3G in the 900 and 2100 MHz bands. So should both operators sell the phone in the future they will each sell a different version.

Some people in Europe might actaully prefer the US version of the phone as there are only few places where 3G is deployed in the 900 MHz band yet and they might thus benefit more from the 850 MHz band when roaming in the US (e.g. with an AT&T prepaid card for Internet access). Bizare… Also interesting is that T-Mobile US won’t be able to sell the phone since it doesn’t support the AWS 1700/2100 MHz band.

The N79 seems to support 900/2100 MHz for now, so clearly targeted at Euope and potentially Optus in Australia. I wouldn’t be surprised though to see a 850/2100 MHz version soon.

Well done, Nokia, it was really time to add multi band 3G suport to Nseries, especially for roamers like me!

CS Voice (And Other Services) over LTE

I've been speculating recently how voice calls could work in next generation 3GPP LTE networks. The politically and technically foreseen way is IMS, the IP Multimedia Subsystem, and a service platform running on top of IMS such as the IMS Centralized Services (ICS). ICS is quite promising as it includes a solution to bring GSM only handsets without any IMS extensions into an overall voice solution and can hand-over voice calls from LTE to GSM when leaving the coverage area. The major drawback of ICS is its complexity and its anyone's guess when we will see this in mobile devices for the general public.

In the meantime, there has been some support in 3GPP to investigate a different solution: How to extend the current circuit switched voice service of GSM to LTE. In 3GPP a number of companies started writing some proposals, which were gathered in 3GPP TR 23.879. In this paper, the main proposal is to connect the Media Gateway part of the Circuit Switched Mobile Switching Center (MSC) to the packet core and give the the MSC Server direct access to the Mobility Management (MME) Entity of the Access Gateway to the LTE Radio network.

This approach completely circumvents the IMS and reuses all upper signaling protocols already known from GSM. Only the lower protocol layers are replaced by TCP/IP. For the voice call itself, all higher layers of the voice transmission protocol are foreseen in the technical report to be kept, while the lower layers would be replaced by TCP/UDP/RTP between the mobile device and the MSC's media gateway.

Handovers would be supported via the interface between the LTE Access Gateway and the evolved MSC (eMSC). When the base station signals that a handover to a 2G GSM cell is required, the Access Gateway informs the evolved MSC via this interface of the handover and the intended target cell. The eMSC can then prepare a circuit switched channel in the 2G or 3G network and respond to the LTE Access Gateway with the necessary details which are then given to the mobile device by the base station in the handover command.

From a development point of view such an approach is much simpler than installing a full IMS system and put ICS on top. Also, all services available today, including SMS, are instantly available, without any further development.

Here are the main developments that I think would be required for such a solution:

  • Mobile device: The stack for voice telephony must be enhanced to put the signaling and voice data a packet switched connection while the device is attached to LTE. Also, the handover code must be enhance to not only support 2G to 2G, 3G to 2G, 2G to 3G handovers but also 4G to 2G or 3G and vice versa.
  • LTE Base station: The software needs a small enhancement to transparently forward the CS handover information it receives from the Access Gateway to the mobile device.
  • LTE Access Gateway: The MME in the Access Gateway needs to be enhanced to report a handover to the eMSC and to wait with the handover until the eMSC gives the go-ahead. Also, it would have to forward a transparent data container with information about the resources allocated in the circuit switched network to the mobile device.
  • MSC: Would have to be enhanced to communicate via DTAP over IP (instead of ATM, IuCS, BSSMAP and BSSAP) and to perform handovers from 4G to 3G or 2G and vice versa. Further, instead of assigning circuit switched traffic channels it would have to interact with the packet core to assign the correct QoS attributes which will ensure a smooth call and sets the scene for the MME to signal a 2G handover to the eMSC.

For further details, including how to deal with roaming subscribers, have a look at the technical report.

All in all, I would say that the enhancements required for 4G handovers are far less complicated than those required at the time to implement 3G to 2G handovers when UMTS was specified. 

From a technical point of view, this architecture has the drawback that voice calls to mobile clients would continue to use a protocol other than SIP, which is the dominant protocol in the fixed line VoIP world. The MSC and the Media Gateway would in effect act as a signaling protocol converter and, in case the call is handed over to a circuit switched 2G connection, as a voice codec transcoding function. Considering the comparatively small enhancements required in the handset and the newtork compared to a full IMS/ICS solution, this architectural imperfection could well be worth it.

From an IMS/ICS point of view the proposed solution looks of course "stone age". It would only support voice calls, i.e. no multimedia sessions, would not support several devices per account, no sessions, no instant messaging, you name it, just pure and simple voice and SMS (but with all the supplementary services that have been developed over the past 30 years!).

BUT: Due to its handover capabilities to 2G GSM and and seamless use over 2G, 3G and 4G networks, it might be the killer VoIP solution for operators to beat Internet based VoIP services (think Skype, etc) which are also pushing into wireless networks and devices today.

Strangely enough, the current work plan lists the technical report as "moved to Release 9" (look for "FS on CS Domain Services over evolved PS access"). I am not sure what that means but it sounds like it didn't meet the love of enough companies represented in 3GPP.