Thursday, August 27, 2009

Huawei E220 HSDPA modem in GNUNTU

E220 works perfectly with wvdial on ubuntu Hardy Haron.

  • Plug in the modem and run - sudo wvdialconf

  • Then edit the wvdial.conf file… - sudo vim /etc/wvdial.conf - Uncomment Username and Password lines in wvdial.conf and add the following to the end of the file "stupid mode = yes"

  • Save the wvdial.conf

  • Run wvdial to get connected :)

If you are using ubuntu 8.10 then the Graphical Network Manager recognizes the modem and connects you within seconds.

Saturday, August 15, 2009

Saving us from forged DNS data: an update on DNSSEC



Like so many of the Internet protocols invented decades ago, the Domain Name System has some serious security issues. Earlier this week in Stockholm, the Internet Society (ISOC), the Internet Engineering Task Force, and DNS experts provided a status update on DNSSEC, the secure DNS protocol designed to close a security hole in the bowels of the Internet that has been the target of exploits.

iPhone/GSM phones vulnerable to SMS hacks



As promised, iPhone security expert Charlie Miller, along with colleague Collin Mulliner, demonstrated a vulnerability in the SMS messaging system which can ultimately lead to hacking of an iPhone. Miller and his cohorts identified similar flaws in the Android and Windows Mobile operating systems, though no complete exploits were demonstrated. However, security researchers Zane Lackey and Luis Miras also demonstrated that the vulnerability can affect any GSM phone, though exactly how each phone reacts to the vulnerability differs.

The problem stems from the SMS system. Phones have to accept SMS messages, and these security experts have found that carefully crafted messages can be interpreted as binary instructions instead of text. Some phones may see a scrambled message—the iPhone, for instance, will show a text with just a square—or may see nothing at all. Lackey and Miras showed an exploit for a Sony Ericsson phone that simply showed the message, "New settings received. Install?" The user might easily assume the data is from a legitimate source.

Russia - Skype as a security threat



VoIP services like Skype and Vonage radically changed the US communication landscape years ago and ignited a telecom race to catch up. The most powerful business lobbying group in Russia, partnering with Prime Minister Vladimir Putin's political party, is hoping to avoid the same fate with "legal safeguards" for home turf competition. Lobbyists also cite national security concerns, hinting that Russia should join China by spying on conversations over Skype and similar services.

Called the Russian Union of Industrialists and Entrepreneurs (RUIE), the 1,000-member strong business lobby organization recently announced that it wants government restrictions on IP telephony services from foreign countries like Skype and ICQ. RUIE believes that the VoIP market is now growing faster than traditional telecoms, estimating that by 2012, 40 percent of Russia’s voice conversations will travel through Internet tubes. Unsurprisingly, the group—composed of telecom executives and other members of private and state-run businesses—wants to "protect domestic producers in [the telecom market]," reads a loose Google translation of RUIE’s official statement.

Minorities embrace internet via handheld devices



A new report released by the Pew Internet and American Life Project will surely spill over into arguments about broadband penetration in the United States, not to mention other debates. It says that African-Americans access the Internet via handheld devices more often than whites, for whom an online connection is more likely to come from an ISP-connected computer. "This means the digital divide between African Americans and white Americans diminishes when mobile use is taken into account," Pew says. Expect arguments about audience ratings systems and exclusive handset deals to be influenced by the report as well

Apple claims jailbreaking could crash cell towers



Apple has filed responses to specific questions from the Copyright Office considering a proposed DMCA exemption for jailbreaking its phones. Aside from the usual issues concerning copyrights, which Apple naturally asserts do not warrant a DMCA exemption, the response also details possible harm to a cell network that jailbreaking could cause, including facilitation of drug dealers and crashing cell towers.

As part of the triennial review of requests for DMCA exemptions, the EFF filed a request that jailbreaking iPhones be considered for an exemption. While Apple hasn't brought any lawsuits against jailbreaking or those who create jailbreaking tools, the EFF filed an exemption request to stave off any possible DMCA violation that might arise from what the EFF characterizes as consumers exercising their rights to use a device as they see fit.

Apple naturally opposed the request, suggesting that the DRM on the iPhone was intrinsic to both Apple's business model and the safety of the iPhone in general.

Google Voice and you



With so much news lately about Google Voice, those who haven't kept up on every tiny development have found themselves lost. What exactly is Google Voice? Is it a phone redirecting service? VoIP? Voicemail? All of the above? None of the above? Even some of our staff members are confused about what Google Voice offers and why people would want to use it, so we thought it would be helpful to offer a guide to Google Voice for those just tuning in.

Google Voice originated as GrandCentral, an independent company that hit the scene in 2005. GrandCentral allowed users to register a new phone number and direct it to ring multiple phones; it could also collect messages and act as your personal switchboard operator. This sounds boring on the surface, but it provided a number of cool features, such as the ability to listen in on voicemail messages as they were being left or to tell a specific number that your phone number is no longer connected (great for stalkers and crazed PR people, who are kind of like stalkers). Google acquired GrandCentral in 2007, and promptly sat on the project for nearly two years before it relaunched the service as Google Voice in March of 2009.

Google didn't just take GrandCentral and slap a colorful logo on it, though. The search giant made a number of improvements on the already nifty service, and it has become a must-have for the handful of early adopters who were lucky enough to get in either as a grandfathered GrandCentral user or through an invite. Let's look at what you can get out of the (currently) free service.

AT&T to enable MMS on iPhone?



Two class action lawsuits have been filed recently against Apple and AT&T for the lack of support for multimedia messaging (MMS) in the US. While support is baked in to iPhone OS 3.0 that was released this past June, the feature has yet to be enabled for US customers by AT&T.

When Apple announced that iPhone OS 3.0 was coming, it said that it would support MMS on the iPhone 3G and the upcoming iPhone 3GS. Unfortunately—to a chorus of boos during the keynote—Apple SVP Scott Forstall said that support from AT&T wouldn't be ready at launch. At the time, AT&T said that support would be coming in "late summer." Summer's not over quite yet, so we presume that AT&T is still completing "some system upgrades that will ensure our customers have the best experience with MMS."

iPhone video sharing app Qik now available



Mobile streaming video company Qik has, after more than a year of waiting, finally gotten an iPhone version of its eponymous app approved for distribution via the App Store. It comes with a number of compromises, however, that depart from the promise of mobile live video streaming directly from the iPhone.

Qik is a website where users can store, view, and stream videos. It's also a mobile phone app that lets users record, stream, and upload videos directly from their phones. Naturally, Qik announced that it was making an iPhone app early on in the App Store process, but ran into a few problems: the video stream from the iPhone's camera wasn't available from a public API and AT&T's terms of service don't permit streaming video from "Web camera posts or broadcasts." (Such limitations were also problematic for SlingPlayer Mobile, but oddly, not for YouTube or MLB.com.) That essentially forced Qik to go underground with its iPhone client, and the company released a version that worked with jailbroken iPhones.

Snow Leopard & Outlook for Mac

Snow Leopard may be arriving far sooner than most of us expected, and Microsoft is dropping Entourage in order to replace it with a version of Outlook for the Mac. If that's not exciting enough for this week, other top Apple news involved antiglare screens coming back to the MacBook Pro, more rumors about the Apple tablet, and possible Blu-ray support coming to iTunes. Read on for the roundup:

Snow Leopard cometh soon, brings installation tricks galore: The latest build seeded to developers has gone golden master and could be set for retail release any day now. The latest information suggests that installing Snow Leopard should be a breeze, too.

Office for Mac to get actual version of Outlook in 2010: Hell has frozen over: Microsoft's Mac Business Unit says that the next version of Office for Mac will arrive in 2010 with a genuine Outlook client and better Exchange support.

Wednesday, August 12, 2009

Intel & Facebook


Intel introduces distributed computing to Facebook

Intel has announced a new partnership designed to increase the prominence of volunteer grid computing. Its new Progress Through Processors program will see the chipmaker partner with Facebook and GridRepublic to promote several of the projects that are run through BOINC, a distributed computing client that runs during idle time on volunteers' machines. Although there are a whole host of projects that can be run through the BOINC interface, Intel has chosen to focus on three: Rosetta@home, Climateprediction.net, and Africa@home.

The technology behind the endeavor is fairly well established. BOINC, run out of the University of California, Berkeley and supported by the National Science Foundation, was developed in response to the success of several early distributed computing projects, most notably SETI@home. It's designed to provide a single piece of client software that runs while a user's machine is idle. Different projects can provide computational engines that are loaded and run by the BOINC client. The single client infrastructure is intended to make it easier for individual projects to roll out updated software and for users to divide their machine's time among multiple worthy projects.

Microsoft & Nokia

Microsoft and Nokia bringing Office to Symbian next year

The world's largest software maker and the world's largest smartphone manufacturer are going to join forces in an attempt to bring some desktop productivity applications to the mobile space. As expected, and despite their long-standing competition, Microsoft and Nokia have agreed to an alliance that will bring Microsoft Office and related software on the Symbian mobile operating system.

Up until today's announcement, native versions of mobile Office have been limited to Windows Mobile, making this is the first time that Microsoft is developing Office software for another company's platform for handheld devices. Microsoft Business Division President Stephen Elop and Nokia's Executive Vice President for Devices Kai Öistämö made the announcement via a teleconference call in which they emphasized that both companies are still looking into more ways to collaborate.

IPTV

Television is changing
Over the last decade, the growth of satellite service, the rise of digital cable, and the birth of HDTV have all left their mark on the television landscape. Now, a new delivery method threatens to shake things up even more powerfully. Internet Protocol Television (IPTV) has arrived, and backed by the deep pockets of the telecommunications industry, it's poised to offer more interactivity and bring a hefty dose of competition to the business of selling TV.

IPTV describes a system capable of receiving and displaying a video stream encoded as a series of Internet Protocol packets. If you've ever watched a video clip on your computer, you've used an IPTV system in its broadest sense. When most people discuss IPTV, though, they're talking about watching traditional channels on your television, where people demand a smooth, high-resolution, lag-free picture, and it's the telcos that are jumping headfirst into this market. Once known only as phone companies, the telcos now want to turn a "triple play" of voice, data, and video that will retire the side and put them securely in the batter's box.

In this primer, we'll explain how IPTV works and what the future holds for the technology. Though IP can (and will) be used to deliver video over all sorts of networks, including cable systems, we'll focus in this article on the telcos, which are the most aggressive players in the game. They're pumping billions into new fiber rollouts and backend infrastructure (AT&T alone inked a US$400 million deal for Microsoft's IPTV Edition software last year, for instance, and a US$1.7 billion deal with hardware maker Alcatel). Why the sudden enthusiasm for the TV business? Because the telcos see that the stakes are far higher than just some television: companies that offer the triple play want to become your household's sole communications link, and IPTV is a major part of that strategy.

How it works
First things first: the venerable set-top box, on its way out in the cable world, will make a resurgence in IPTV systems. The box will connect to the home DSL line and is responsible for reassembling the packets into a coherent video stream and then decoding the contents. Your computer could do the same job, but most people still don't have an always-on PC sitting beside the TV, so the box will make a comeback. Where will the box pull its picture from? To answer that question, let's start at the source.

Most video enters the system at the telco's national headend, where network feeds are pulled from satellites and encoded if necessary (often in MPEG-2, though H.264 and Windows Media are also possibilities). The video stream is broken up into IP packets and dumped into the telco's core network, which is a massive IP network that handles all sorts of other traffic (data, voice, etc.) in addition to the video. Here the advantages of owning the entire network from stem to stern (as the telcos do) really come into play, since quality of service (QoS) tools can prioritize the video traffic to prevent delay or fragmentation of the signal. Without control of the network, this would be dicey, since QoS requests are not often recognized between operators. With end-to-end control, the telcos can guarantee enough bandwidth for their signal at all times, which is key to providing the "just works" reliability consumers have come to expect from their television sets.

The video streams are received by a local office, which has the job of getting them out to the folks on the couch. This office is the place that local content (such as TV stations, advertising, and video on demand) is added to the mix, but it's also the spot where the IPTV middleware is housed. This software stack handles user authentication, channel change requests, billing, VoD requests, etc.—basically, all of the boring but necessary infrastructure.

All the channels in the lineup are multicast from the national headend to local offices at the same time, but at the local office, a bottleneck becomes apparent. That bottleneck is the local DSL loop, which has nowhere near the capacity to stream all of the channels at once. Cable systems can do this, since their bandwidth can be in the neighborhood of 4.5Gbps, but even the newest ADSL2+ technology tops out at around 25Mbps (and this speed drops quickly as distance from the DSLAM [DSL Access Multiplier] grows).

So how do you send hundreds of channels out to an IPTV subscriber with a DSL line? Simple: you only send a few at a time. When a user changes the channel on their set-top box, the box does not "tune" a channel like a cable system. (There is in fact no such thing as "tuning" anymore—the box is simply an IP receiver.) What happens instead is that the box switches channels by using the IP Group Membership Protocol (IGMP) v2 to join a new multicast group. When the local office receives this request, it checks to make sure that the user is authorized to view the new channel, then directs the routers in the local office to add that particular user to the channel's distribution list. In this way, only signals that are currently being watched are actually being sent from the local office to the DSLAM and on to the user.

No matter how well-designed a network may be or how rigorous its QoS controls are, there is always the possibility of errors creeping into the video stream. For unicast streams, this is less of an issue; the set-top box can simply request that the server resend lost or corrupted packets. With multicast streams, it is much more important to ensure that the network is well-engineered from beginning to end, as the user's set-top box only subscribes to the stream—it can make no requests for additional information. To overcome this problem, multicast streams incorporate a variety of error correction measures such as forward error correction (FEC), in which redundant packets are transmitted as part of the stream. Again, this is a case where owning the entire network is important since it allows a company to do everything in its power to guarantee the safe delivery of streams from one end of the network to the other without relying on third parties or the public Internet.

Though multicast technology provides the answer to the problem of pumping the same content out to millions of subscribers at the same time, it does not help with features such as video on demand, which require a unique stream to the user's home. To support VoD and other services, the local office can also generate a unicast stream that targets a particular home and draws from the content on the local VoD server. This stream is typically controlled by the Real Time Streaming Protocol (RTSP), which enables DVD-style control over a multimedia stream and allows users to play, pause, and stop the program they are watching.

The actual number of simultaneous video streams sent from the local office to the consumer varies by network, but is rarely more than four. The reason is bandwidth. A Windows Media-encoded stream, for instance, takes up 1.0 to 1.5Mbps for SDTV, which is no problem; ten channels could be sent at once with bandwidth left over for voice and data. But when HDTV enters the picture, it's a different story, and the 20-25Mbps capacity of the line gets eaten up fast. At 1080i, HDTV bit rates using Windows Media are in the 7 to 8 Mbps range (rates for H.264 are similar). A quick calculation tells you that a couple of channels are all that can be supported.

The bandwidth situation is even worse when you consider MPEG-2, which has lower compression ratios. MPEG-2 streams will require almost twice the space (3.5 Mbps for SDTV, 18-20 Mbps for HDTV), and the increased compression found in the newer codecs is one reason that AT&T will not use MPEG-2 in the rollout of its IPTV service dubbed "U-verse."

Simultaneous delivery of channels is necessary to keep IPTV competitive with cable. Obviously, multiple streams are needed to support picture-in-picture, but they're also needed by DVRs, which can record one show while a user is watching another. For IPTV to become a viable whole-house solution, it will also need to support enough simultaneous channels to allow televisions in different rooms to display different content, and juggling resulting bandwidth issues is one of the trickiest parts of implementing an IPTV network that will be attractive to consumers.

iPhone SIM Lock




The majority of iPhones are sold with a SIM lock, which restricts the use of the phone with one particular carrier, a common practice with subsidized GSM phones. Unlike most GSM phones however, the phone cannot be officially unlocked via inputting a code. The locked/unlocked state is maintained on Apple's servers per IMEI and is set when the iPhone is activated.

While the iPhone was initially sold on the AT&T network only with a SIM lock in place, various hackers have found methods to "unlock" the phone from a specific network. Although AT&T is the only authorized iPhone carrier in the United States, unlocked iPhones can be used with an unauthorized carrier after unlocking. More than a quarter of the original iPhones sold in the United States were not registered with AT&T. Apple speculates that they were likely shipped overseas and unlocked, a lucrative market prior to the iPhone 3G's worldwide release. Unlocking iPhones in the U.S. is done because many would-be users dislike switching carriers or consider AT&T's monthly fees too expensive.

On November 21, 2007, T-Mobile in Germany announced it would sell the phone unlocked and without a T-Mobile contract, caused by a preliminary injunction against T-Mobile put in place by their competitor, Vodafone. On December 4, 2007, a German court decided to grant T-Mobile exclusive rights to sell the iPhone with SIM lock, overturning the temporary injunction. In addition, T-Mobile will voluntarily offer to unlock customers' iPhone after the contract expires.

AT&T has stated that the "iPhone cannot be unlocked, even if you are out of contract". On March 26, 2009 AT&T in the United States began selling the iPhone without a contract, though still SIM-locked to their network. Such iPhone units are often twice as expensive as those with contracts, because Apple and AT&T lose the deferred income. Vendors in Hong Kong, Italy, New Zealand, and Russia (among others) sell iPhones not locked to any carrier. In Australia, four major carriers (Three, Optus, Telstra, and Vodafone) sell locked phones, but will unlock upon request, in addition to Apple selling unlocked iPhones directly.

Tuesday, August 11, 2009

VOIP

VoIP is nothing but Voice over Internet Protocol, which has taken the world by storm. VoIP is both the cause and consequence of a shrinking world. Now one does not need to spend huge amount of money on making international calls. Simply with the help of Internet, one can make calls in any part of the world without having to burn a whole in the pocket.

VoIP, also known as IP Telephony or Broadband telephony, is basically routing the voice messages over the Internet or through any other kind of IP based network services. There are dedicated service providers which are basically companies that provide such VoIP services to common people on an individual basis or in a group, however VoIP services are mostly used by corporate houses. These service providers use protocols to carry out voice signals over the IP network and they are commonly known as Voice over IP or VoIP protocols.

VoIP is increasingly replacing the POST or Plain Old Telephone System. Now more and more organisations are switching over to the latest mode of communication. This has become a necessity as companies are extending their client base abroad and till far away from their country. Now you can speak to your client sitting in Middle East or China or USA or just about anywhere where Internet has touched the human life. VoIP ha s decreased the requirement and therefore the cost of traveling tremendously and therefore it is reaching out to more number of people in more number of countries.

Suppliers of VoIP

VoIP has spread its wings far and wide. And the spread has become possible due to increasing number of VoIP service providers. These suppliers provide the VoIP services on the basis of plans. One can choose services as per the requirements or the frequency at which one needs to make international calls. You can also choose to take the help of leading suppliers of traditional telephones or cordless phones, who are providing VoIP services.

Frequency Hopping

Major Advantages of using frequency hopping

* FREQUECY RESUSE AND TO AVOID CO-CHANNEL INTERFERENCE
* INCREASES THE CHANNEL CAPACITY OF LIMITED GSM CHANNELS
* DECREASES MULTIPATH INTERFERENCE OF RADIO SIGNAL.



" Frequency Hopping rule is simple, that our conversation must remain on the same physical channel and time slot for the entire time we are on a particular site. If the network were able to move us from slot to slot, and from frequency to frequency, then we could randomize the effects of interference "

Here below i would discuss how Frequecy hopping fights all the three major disadvantage specifed above.

As we know GSM uses physical channels, but each of those channels is divided into 8 time slots. One user consumes one slot, thus allowing 8 users to be on a GSM channel simultaneously. Each GSM channel is 200 kHz wide, thus giving a 30 MHz license-holder a grand total of 75 physicals channels within their spectrum allotment.

Obviously 75 channels isn’t enough to spread evenly among the 200 some odd cell sites around the GTA, each of which has 3 independent sectors. A sector is an area covering 120 degrees around the site. That’s a grand total of 600 sectors and only 75 channels. Obviously the idea is to reuse channels in multiple sites, and to keep those co-channels far enough apart that they don’t interfere with one another.

Next The most common type of interference suffered by a dense GSM network is therefore co-channel inference. This means that your phone call is interfered with by another site operating on the same physical channel and time slot. Unlike analog, where co-channel interference would often result in you actually hearing the other conversation, that never happens in GSM.

Another problem facing narrowband radio systems is multipath. This happens when large objects such as buildings reflect your desired signal. The reflection can sometimes be just as strong as the direct signal, and the two can interfere with one another.

Consider co-channel interference. Not all of the slots are in use on all of the physical channels on each site where they are reused, so although slot 4 on channel 522 might be clobbered by another conversation, slot 7 on channel 530 probably isn’t. So, if we can take each caller on a particular sector and jump them from slot to slot, and from frequency to frequency, then each user runs a far lower risk of suffering from co-channel interference. And when such interference does occur, chances are good that the error correction algorithms can take care of it.

You know that the number of frequencies for GSM is 124 and it is not much. The range is divided for some operators. What happen when the sites configuration is high? They do not have enough frequencies. One way, they expand their range to use CDS 1800. So, they have to spend more money.

There are two types of frequency hopping: Baseband and Syntherizer.

The main technique for frequency hopping is that 1 carrier atleast uses more than one predefined frequecy to serve their purpose.

In Baseband hopping, the transmitter will change its frequency on frame basis.

All TRX can hop, but the list of frequencies is limited to the number of TRX in the cell. For instance, if you have 4 TRX, the amount of frequencies will be 4. It uses a round robin mechanism, for each TDMA frame, one of those four frequencies are used in round robin pattern.

In syntherizer hopping, the transmitter will change its frequency on time slot basis. That is why they also said it is fast hopping.

All TRX except BCCH TRX will hop over a list of frequencies (= frequency hopping sequence). You can put as many frequencies as you want in the list (up to more than 30 usually).
Only the BCCH TRX requires a fixed frequency (bcch frequency that shouldn't be included in the FHS !).


The frequency hopping sequences are orthogonal inside one cell (i.e. no collisions occur between communications of the same cell), and independent from one cell to an homologue cell (i.e. using the same set of RF channels, or cell allocation).

The hopping sequence is derived by the mobile from parameters broadcast at the channel assignment, namely,

The mobile allocation (set of frequencies on which to hop),

MA: Mobile allocation of radio frequency channels, defines the set of radio frequency channels to be used in the mobiles hopping sequence.

The index offset (to distinguish the different mobiles of the cell using the same mobile allocation).


MAIO: Mobile allocation index offset.(0 to N 1, 6 bits).

MAIO is applied to same timeslot of different TRX (belonging to a same cell). For instance, each timeslot #3 will have a different MAIO, because they're using the same HSN.

The hopping sequence number of the cell (which allows different sequences on homologue cells)

HSN: Hopping sequence (generator) number (0 to 63, 6 bits).
HSN =0, means cyclic hopping (no hopping, generally BCCH carrier)

NOTE:
Only the 1st timeslot of the BCCH TRX cannot hop.
There is no real need for The broadcast channel (BCCH) to hop(Bcoz no tarffic is carried on this channel so no error or interference).
Remaining 7 full rate channels or 14 half rate channels may use frequency hopping.
Everytime a timeslot uses the BCCH frequency, it cannot use downlink power control.

Transcoder - BSS

The transcoder is responsible for transcoding the voice channel coding between the coding used in the mobile network, and the coding used by the world's terrestrial circuit-switched network, the Public Switched Telephone Network. Specifically, GSM uses a regular pulse excited-long term prediction (RPE-LPC) coder for voice data between the mobile device and the BSS, but pulse code modulation (A-law or μ-law standardized in ITU G.711) upstream of the BSS. RPE-LPC coding results in a data rate for voice of 13 kbit/s where standard PCM coding results in 64 kbit/s. Because of this change in data rate for the same voice call, the transcoder also has a buffering function so that PCM 8-bit words can be recoded to construct GSM 20 ms traffic blocks.

Although transcoding (compressing/decompressing) functionality is defined as a base station function by the relevant standards, there are several vendors which have implemented the solution outside of the BSC. Some vendors have implemented it in a stand-alone rack using a proprietary interface. In Siemens' and Nokia's architecture, the transcoder is an identifiable separate sub-system which will normally be co-located with the MSC. In some of Ericsson's systems it is integrated to the MSC rather than the BSC. The reason for these designs is that if the compression of voice channels is done at the site of the MSC, the number of fixed transmission links between the BSS and MSC can be reduced, decreasing network infrastructure costs.

This subsystem is also referred to as the transcoder and rate adaptation unit (TRAU). Some networks use 32 kbit/s [ADPCM] on the terrestrial side of the network instead of 64 kbit/s PCM and the TRAU converts accordingly. When the traffic is not voice but data such as fax or email, the TRAU enables its rate adaptation unit function to give compatibility between the BSS and MSC data rates.

Base Station Controller

The base station controller (BSC) provides, classically, the intelligence behind the BTSs. Typically a BSC has tens or even hundreds of BTSs under its control. The BSC handles allocation of radio channels, receives measurements from the mobile phones, controls handovers from BTS to BTS (except in the case of an inter-BSC handover in which case control is in part the responsibility of the anchor MSC). A key function of the BSC is to act as a concentrator where many different low capacity connections to BTSs (with relatively low utilisation) become reduced to a smaller number of connections towards the mobile switching center (MSC) (with a high level of utilisation). Overall, this means that networks are often structured to have many BSCs distributed into regions near their BTSs which are then connected to large centralised MSC sites.

The BSC is undoubtedly the most robust element in the BSS as it is not only a BTS controller but, for some vendors, a full switching center, as well as an SS7 node with connections to the MSC and serving GPRS support node (SGSN) (when using GPRS). It also provides all the required data to the operation support subsystem (OSS) as well as to the performance measuring centers.

A BSC is often based on a distributed computing architecture, with redundancy applied to critical functional units to ensure availability in the event of fault conditions. Redundancy often extends beyond the BSC equipment itself and is commonly used in the power supplies and in the transmission equipment providing the A-ter interface to PCU.

The databases for all the sites, including information such as carrier frequencies, frequency hopping lists, power reduction levels, receiving levels for cell border calculation, are stored in the BSC. This data is obtained directly from radio planning engineering which involves modelling of the signal propagation as well as traffic projections.

Location Area Identity Format

A Location Area Identity (LAI) code identifies the location area in a PLMN. The LAI code has three components:

· Mobile Country Code (MCC)
The MCC is a 3-digit code that uniquely identifies the country of domicile of the mobile subscriber (for example, Sri Lanka 413). It is assigned by the ITU-T.

· Mobile Network Code (MNC)
The MNC is a 2-digit code that identifies the home GSM PLMN of the mobile subscriber. If more than one GSM PLMN exist in a country, a unique MNC is assigned to each of them. The government of each country assigns it. Mobitel - 01

· Location Area Code (LAC)
The LAC component identifies a location area within a PLMN; it has a fixed length of 2 octets and can be coded using hexadecimal representation. An operator assigns it.

CRBT - Color Ring Back Tone

A Ring-back Tone (RBT) is the audible ringing that is heard on the telephone line by the calling party after dialing and prior to the call being answered at the receiving end. This tone assures the calling party that a ringing signal is being sent on the called party's line, although the ring-back tone may be out of sync with the ringing signal. RBT is also known as Color Ringback Tone

Implementing CRBT in Mobile Network

Scenario 1 — ISUP Call Control Implementation
Scenario 2 — Through IN Signaling
Scenario 3 — CRBT with IN Call Party Handling

IMEI

The International Mobile Equipment Identity or IMEI is a number unique to every GSM and UMTS mobile phone.
The IMEI number is used by the GSM network to identify valid devices and therefore can be used to stop a stolen phone from accessing the network. For example, if a mobile phone is stolen, the owner can call network provider and instruct them to block the phone using its IMEI number. This renders the phone useless, regardless of whether the phone's SIM is changed.
Unlike the Electronic Serial Number or MEID of CDMA and other wireless networks, the IMEI is only used to identify the device, and has no permanent or semi-permanent relation to the subscriber. Instead, the subscriber is identified by transmission of an IMSI number, which is stored on a SIM card.
Example of the IMEI code 37-209900-176148-1
TAC: 372099 so it was issued by the BABT and has the allocation number 2099
FAC: 00 so it was numbered during the transition phase from the old format to the new format (described below)
SNR: 176148 - uniquely identifying a unit of this model
CD: 1 so it is a GSM Phase 2 or higher
SVN: 23 - The 'software version number' identifying the revision of the software installed on the phone. 99 is reserved
Final Assembly Code (FAC) For different vendor

01,02 AEG
07 , 40 Motorola
10, 20 Nokia
30 Ericsson
40, 41, 44 Siemens
47 Option International
50 Bosch
51 Sony
51 Siemens
51 Ericsson
60 Alcatel
70 Sagem
75 Dancall
80 Philips
85 Panasonic

Retrieving IMEI information from a GSM device
On many devices the IMEI number can be retrieved by entering *#06#. The IMEI number of a GSM device can be retrieved by sending the command AT+CGSN through data cable.
The IMEI information can be retrieved from most Nokia mobile phones by pressing *#92702689# (*#WAR0ANTY#), this opens the warranty menu in which the first item is the serial number (the IMEI). The warranty menu also shows other information such as the date the phone was made and the life timer of the phone.The IMEI can frequently be displayed through phone menus, under a section titled 'System Information', 'Device', 'Phone Info' or similar.
Computation of the Check Digit
The last number of the IMEI is called the Check Digit and is defined using a formula called "Luhn formula", thus sometimes the last digit is called the Luhn Check Digit and does not necessarily always set to 0.
According to the IMEI Allocation and Approval Guidelines,
The Check Digit is calculated according to Luhn formula (ISO/IEC 7812). The Check Digit shall not be transmitted to the network. The Check Digit is a function of all other digits in the IMEI. The Software Version Number (SVN) of a mobile is not included in the calculation. The purpose of the Check Digit is to help guard against the possibility of incorrect entries to the CEIR and EIR equipment.The check digit shall always be transmitted to the network as "0".
This check digit is computed in three steps as shown in the following example.
Given 14 most significant digits of the IMEISV without the SVN which are the 6-digit TAC, 2-digit FAC, and 6-digit SNR and are labelled as follows:
TAC = D14 D13 ... D9 (with D9 the least significant digit of TAC);
FAC = D8 D7 (with D7 the least significant digit of FAC); and
SNR = D6 D5 ... D1 (with D1 the least significant digit of SNR).
Example IMEI: 49015420323751? (ignore the last digit)
TAC: 490154
D14:4
D13:9
D12:0
D11:1
D10:5
D09:4
FAC: 20
D08:2
D07:0
SNR: 323751
D06:3
D05:2
D04:3
D03:7
D02:5
D01:1
Computation of its check number / CHK for the IMEI proceeds as follows:
Step 1: Double the values of the odd labelled digits D1, D3, D5 ... D13 of the IMEI.
.D14:4=4
D13:9x2=18
.D12:0=0
D11:1x2=2
.D10:5=5
D09:4x2=8
.D08:2=2
D07:0x2=0
.D06:3=3
D05:2x2=4
.D04:3=3
D03:7x2=14
.D02:5=5
D01:1x2=2

Step 2: Add together the individual digits of all the seven numbers obtained in Step 1,
1+8 + 2 + 8 + 0 + 4 + 1+4 + 2 = 30
and then add this sum to the sum of all the even labelled digits D2, D4, D6 ... D14 of the IMEI.
4 + 0 + 5 + 2 + 3 + 3 + 5 = 22
The result is:
30 + 22 = 52 or 4 + 1+8 + 0 + 2 + 5 + 8 + 2 + 0 + 3 + 4 + 3 + 1+4 + 5 + 2 = 52
Step 3: If the number obtained in Step 2 ends in 0, then set CHK to be 0. If the number obtained in Step 2 does not end in 0, then set CHK to be that number subtracted from the next higher number which does end in 0.
Since 52 ends in "2", CHK can't be set to "0". The next higher number that does end in "0" after 52 is 60, so we set: CHK = 60 - 52 = 8
So the IMEI number is: 490154203237518 and it ends in 8.d it ends in 8.