after which I’ll be an SAP certified consultant! It’s pretty much a 12+ week course crammed into a 4 week intensive.

The course is actually very very very interesting, but there is SOO much to learn/remember in a very short time period! I was hired for my Sales/Distribution experience at IKEA and what’s cool now is that I’m even putting to use things I learned back when I worked in a warehouse when I was 14!

I was glad when I saw it was a small class (only 6 of us) because I knew we would get really personalized attention. However, I got a little nervous when I found out that the other 5 students all have 5-10 years of SAP experience! As always, a potentially difficult situation has turned to my advantage: not only am I getting personalized attention from the instructor, but the other students are helping me a lot as well! For instance, when I ask a question and I get a response someone will say: “Hey, why don’t you show him xyz, it might make it clearer!”. Once again, it turns out I’m blessed! Wish me luck for the exam!!

Suppose you’re paying $30/month for your 3G mobile phone plan that includes 1,000 minutes of talk time and Internet access. Suppose your friends (possibly even in other countries) are doing the same. If you all have VoIP clients, why would any of you use your 1,000 minutes AND pay long distance charges? Once both parties are online on the packet switched network, the VoIP client will treat it as a free PC to PC call. Basically, by using VoIP you’ve got unlimited minutes as well as free long distance calling! This is obviously a problem for the operators because there isn’t much incremental income anymore! Mobile operators are much smarter than this, so of course they’ve come up with a solution to this dilemma. That solution is IMS.

IMS (IP Multimedia Subsystem)

In order to differentiate themselves, mobile operators can offer a variety of IMS services. IMS is essentially a ‘cloud’ of multimedia applications (voice, video, etc.) that can be offered (and managed) by the operator. Using IMS, the operator can now provide their OWN VoIP services and charge rates that they feel are suitable. You might be asking yourself “Well, what’s stopping me from using my own VoIP client and bypassing their IMS?” For one, mobile operators could have policies restricting VoIP such as T-Mobile UK’s ban on VoIP usage for their Super3G service. [1] Assuming they don’t have such policies, odds are that they will treat their own VoIP with higher priority than standard IP traffic; thus, you would get much higher quality calls using their proprietary VoIP clients/systems.

Besides VoIP there are many other services that IMS can provide. The beauty of IMS is that is in independent of the device (mobile phone, laptop, desktop PC, PDA, etc.) being used as long as it is used on a packet switched (IP) network. IMS opens up a whole new market of products and services. Many companies such as Ericsson are doing a lot of research into IMS because it is clear that this is where the money is (or will be). The last part of this report will look at a few services that will be possible with IMS.

Presence/Location Areas
In order to offer this service, the provider would have to be closely tied to the operator (or could be the operator itself). Since the mobile is constantly telling the base stations where it is, you could offer location based services to tell the user (or their friends) where they are; this can be combined with GPS systems to get directions to and from locations.

Opt-in Targeted Advertising
If you know the location of the person you can send them appropriate targeted advertising. For instance, if you’re walking downtown and you walk by a movie theatre you could automatically get notified if it’s playing movies that you like, give you the show times and even offer the ability to purchase the movie tickets via your phone.

Comfort Noise Selection
Comfort noise hasn’t been discussed in this report but in short: VoIP doesn’t transmit silence (because it wastes bandwidth). However, studies have shown that if a user hears silence they get worried and often think the connection is dead. Thus, white noise (also known as comfort noise) is generated on the receiving end if no voice/sound is coming in. As opposed to generating white noise, it might be interesting if you can select sounds as if the person is at the beach, or at the office, or any other place!

Language Translation
This is probably the most interesting one. Combining speech recognition, translation and text-to-speech software can give you a very powerful tool. Imagine this scenario: You speak English into a VoIP client; the codec takes your voice and turns it into text; the text is then translated into German and using text-to-speech the system outputs what you said in German to the listener. Pretty cool, huh? Skype is already offering live translation for $2.99USD/minute but the translation is still being done by humans; perhaps we will see this idea eventually! [2]

This report has shown how packet switching and VoIP have totally changed the business landscape of mobile telephone services. This is a constantly evolving market and it will be very fascinating to see how all this plays out as VoIP has implications in almost all areas of our lives (entertainment, legal, socioeconomic, etc.). VoIP has definitely shaken up the traditional phone companies and is proving to be a disturbance in the mobile phone arena as well. However, given that most mobile operators are “fresh blood” in the telecom industry they have, thus far, shown a willingness to change, adapt to and embrace IP technology. If you can’t beat ‘em, join ‘em…

References:
[1] T-Mobile Bans VoIP from Super-3G Service (ZDNet UK Article)
[2] Skype Language Line Personal Interpreter (Official Product Website)

Why are Handovers Smoother?

In a cellular environment, a subscriber’s phone is regularly telling the nearest base station where it is located. The mobile is also always aware of neighbouring stations and their signal strength. Due to this constant awareness of its environment, the mobile can handle handovers much more smoothly than an 802.11 device. Typically, 802.11 devices perform a scan only once the access point starts to become too weak and then it must perform a full network scan (i.e. it is not aware of the nearest access point).

What Makes 3G Special?

3G boasts much higher data transfer rates than its predecessors and offers “always on” connections to the Internet. One of the first sets of 3G protocols was UMTS under the W-CDMA umbrella which had speeds up to 38Kbps; the newer ones such as CDMA2000 1xEV can transfer data at rates as high as 300Kbps! [2] The so-called “killer app” for 3G was video phone calls. [1] Imagine not only hearing the person speaking but seeing them as well. The data transfer rates in 3G are high enough to make this a reality. Other interesting data intensive services include the ability to watch TV on your phone (this is already possible in Korea). [3]

The first 3G networks were rolled out in Japan and the United States as early as 2001 and 2002 respectively. [4][5] Although we don’t get data rates that are as fast as the IEEE 802 standards, 300Kbps is more than sufficient for basic Internet needs (e.g. email, IM, etc.) and VoIP.

3G is still a mix of circuit and packet switched networks whereas the future 4G networks will be completely packet based and thus, the entire underlying structures will all IP based. [6] Mobile operators clearly understand the benefits of packet switching and so they will be using it as well!

Now that we understand some of the key differences (and similarities) between VoWifi and cellular networks, let’s put them head to head. (Continued: Competition Between VoWifi and Cellular Networks)

References:
[1] 3G Wikipedia Article
[2] Comparing Data Transfer Rates of Digital Transmissions Around Us
[3] What You Can Do with 3G
[4] First 3G Mobiles Launched in Japan (BBC News Article)
[5] Verizon Launches First U.S. ’3G’ Network (CNN News Article)
[6] 4G Wikipedia Article

Number of Calls per Access Point

Microcellular base stations used in the mobile telephone network can typically handle 7 simultaneous phone calls. Larger base stations with more transmitters will handle more calls. Mobile operators will have hundreds of these placed in high usage areas to support all their users. [2]

Let us now compare how many phone calls a wireless access point can handle. In his article “How Many Voice Callers Fit on the Head of an Access Point?”, Matthew Gast at the O’Reilly network has examined the theoretical maximum number of phone calls an access point can handle. The reason it is a theoretical maximum is because the chances of you having setup the perfect wireless network and achieving those maximum data transfer speeds are very slim. Regardless of this, it’s clear that even if you don’t have the ‘perfect’ network, a simple access point can handle more calls than a microcellular base station.

The chart above shows the number of calls that can be handled by an access point when using the 3 different 802.11 protocols at their maximum data transfer speeds and 2 different codecs. It is important to note 2 key points: 1) the number of calls handled drops dramatically as the data transfer speed decreases as you get further away from the access point and 2) an unprotected (not backward compatible with 11b) 11g network can handle as many calls as 11a; if 11b support is needed then you lose anywhere from 1/4 to 1/3 of capacity.[3]

We’ve established that we can get greater voice quality via VoIP than on a cellular network. We’ve also established that an access point can handle more calls than a microcellular base station. Something I have not mentioned is that because so many wireless devices are manufactured and sold, the costs of the access points are much lower than a base station. Why isn’t everyone switching to VoWifi? There are a couple of major drawbacks.

Security and VoWifi

As mentioned earlier with Wifi, VoWifi faces the same security threats as any Wifi network. This is especially a concern in most free “open hotspots” because the network is often not protected and/or encrypted at all. VoWifi requires 3 levels of security: 1) for the voice transmission itself, 2) for the associated control signalling configuration and finally 3) for the WLAN channel being used. [1] Security issues are constantly being worked on and improved. In April 2006, Phil Zimmermann (who created PGP) released Zfone which is the best VoIP security/encryption software to date. [4] Since most home users are generally not THAT concerned with voice encryption, the main issue is not security.

Handovers and Reliability in VoWifi

The primary issue is handovers and roaming between access points. As opposed to the security issue where calls can still be made and maintained regardless of encryption, the issue with handovers and reliability is serious because it interrupts and/or stops the service entirely.

An interesting thesis paper about VoWifi roaming was written here at KTH by Syed Muhammad Ali. He first tested handover times using NetGear and LinkSys access points; sometimes the handover time took as long as 2 – 5 seconds! This is far too long in the VoIP world. He then tested programs that are normally used for online voice communications (MSN Messenger, Skype and X-Lite). He found that while on a voice call, most of the applications could not maintain the call when moving from one access point to the next. This of course is a very serious issue as it can get quite cumbersome and irritating to have to [manually] re-establish a phone call every time you move into the area of a new access point. [5].

As well, Wifi uses a very polite “contention based” system for transmitting data (each subscriber is competing for the access point’s attention). The subscriber station listens to see if anyone else is transmitting and then if not, it sends the packet. If someone else is transmitting, then it waits a random time interval and then listens again until no one is transmitting before resending the packet. Needless to say, this can go on and on in a congested network and thus Wifi doesn’t provide adequate QoS (Quality of Service) functions that are required for time-sensitive real time applications such as VoIP.

There is presently a standard being developed that begins to solve the handover and reliability issues with Wifi. This up and coming standard is called WiMax.

WiMax (Worldwide Interoperability for Microwave Access)

WiMax is the term used for the new IEEE 802.16 series of wireless MAN (metropolitan area network) protocols. WiMax is an improvement over Wifi by leaps and bounds. WiMax has a maximum data transfer rate of 70 Mbps whereas the highest data rate for 802.11 is 54 Mbps.

However, the best part is not the increased speed, but the immense improvement in coverage distance. The maximum distance of a Wifi connection is 175 feet; the maximum for WiMax is 50 kilometres! With this increased distance, the roaming area is MUCH bigger and the need for handovers is greatly reduced. 1 WiMax station could very well blanket a city’s financial district with wireless Internet access.

QoS is also greatly increased because as opposed to Wifi’s contention based system, WiMax uses a scheduling system whereby a subscriber is allocated a time slot (similar to mobile networks) by the base station. The time slot can enlarge or contract as needed, but now there is no more need to compete for a specific access point’s attention.[6]

At present there are still sceptics and despite backing by some large corporations (e.g. Intel) WiMax is still meeting a lot of resistance because it has the serious potential to disrupt mobile cellular technology. Billions of dollars were recently spent in Europe for the auctioned 3G frequencies and no company would like that to go down the drain because of WiMax! However, it appears
that WiMax is going to be one of the competing technologies in the 4G (fourth generation) packet switched networks.

A benefit of WiMax is the potential of interoperability. Mobile phone operators can install a WiMax base station on the same tower as a mobile network base station without fear of interference. Some cellular companies are considering WiMax as a method to increase bandwidth for more data intensive applications. [6]

Now that we’re starting to see the meeting of Wifi/WiMax with mobile cellular technologies, let’s have a quick look at the latest 3G (third generation) mobile networks. (Continued: 3G (Third Generation Cellular Networks))

References:
[1] VoIP and Wireless Networking
[2] Mobile Telephony and Health
[3] How Many Voice Callers Fit on the Head of an Access Point?
[4] A Pretty Good Way to Foil the NSA
[5] Wifi Roaming KTH Thesis Paper by Syed Muhammad Ali
[6] WiMax Wikipedia Article

802.11a
Released: 2001
Maximum Speed: 54 Mbps
Maximum Distance: 80 feet
Frequency Band: 5.8 Ghz

802.11g
Released: 2003
Maximum Speed: 54 Mbps
Maximum Distance: 175 feet
Frequency Band: 2.4 Ghz
[2]

Clearly 11g is the best standard because it allows for the highest transfer rate with the longest distance. In fact, today you will find very few devices using the 11a standard. 11g is backward compatible with 11b and most devices can easily accommodate b and g because they operate in the same frequency band.

One of the main reasons Wifi is so popular is because of its simplicity. Most devices are plug-and-play and wireless “hotspots” can be created on the fly wherever someone wants because these devices operate in an unlicensed frequency band. A disadvantage however is that many other devices (e.g. microwave ovens, cordless phones, Bluetooth devices, etc.) operate in the same frequency spectrum and can thus create interference when transmitting data.

At maximum distances, you will be getting very low bandwidth so in order to have a decent wireless network in place it is necessary to have wireless access points setup in key locations of the network. By using multiple access points a wireless network can span a few kilometres. While ‘roaming’ the network, if the signal becomes too weak the network card on the client computer will scan the network to see if there’s a closer access point with a better signal that it can connect to and if one is found it will switch over.

Unfortunately, one major concern most people have with WLANs is security. Given that the information floating through the airways many are often worried about unauthorized users tapping into their Wifi network. In 2001 a group of students from Berkeley presented a paper describing the flaws and vulnerabilities in the WEP (Wired Equivalent Privacy) security standard used by 802.11 networks. Today’s versions have increased security, but this is still a major concern for any WLAN user.

Given that Wifi is highly mobile and uses IP packet switching technology (like any other LAN) we can now throw VoIP into the mix! What do you get when you add VoIP and Wifi? VoWifi! (Continued: VoWifi (Voice Over Wireless Fidelity))

References:
[1] IEEE 802.11 Wikipedia Article
[2] Introduction to 802.11 Networks (PDF)