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4 Things You Never Knew Your Mobile Phone Could Do

4 Things You Never Knew Your Mobile Phone Could Do

There are a few things that can be done in times of grave emergencies. Your mobile phone can actually be a life saver or an emergency tool for survival. Check out the things that you can do with it:

1. Emergency

The Emergency Number worldwide for Mobile is 112. If you find yourself out of the coverage area of your mobile; network and there is an emergency, dial 112 and the mobile will search any existing network to establish the emergency number for you, and interestingly this number 112 can be dialed even if the keypad is locked. Try it out.

Also in Australia , the Australian emergency number 000 can be dialled whilst your mobile phone keyboard is locked. This is another reason why 000 receives so many false emergency calls!

2. Have you locked your keys in the car?

Does your car have remote keyless entry? This may come in handy someday. Good reason to own a cell phone: If you lock your keys in the car and the spare keys are at home, call someone at home on their mobile phone from your cell phone.

Hold your cell phone about a foot from your car door and have the person at your home press the unlock button, holding it near the mobile phone on their end. Your car will unlock. Saves someone from having to drive your keys to you. Distance is no object. You could be hundreds of miles away, and if you can reach someone who has the other "remote" for your car, you can unlock the doors (or the trunk).

Editors Note: It works fine! We tried it out and it unlocked our car over a mobile phone!"

3. Hidden Battery Power

Imagine your mobile battery is very low. To activate, press the keys *3370# Your mobile will restart with this reserve and the instrument will show a 50% increase in battery. This reserve will get charged when you charge your mobile next time.

4. How to disable a STOLEN mobile phone?

To check your Mobile phone's serial number, key in the following digits on your phone!:

star-hash-zero-six-hash

* # 0 6 #

A 15 digit code will appear on the screen. This number is unique to your handset. Write it down and keep it somewhere safe. When your phone get stolen, you can phone your service provider and give them this code. They will then be able to block your handset so even if the thief changes the SIM card, your phone will be totally useless. You probably won't get your phone back, but at least you know that whoever stole it can't use/sell it either. If everybody does this, there would be no point in people stealing mobile phones.

Not only the above, but also in Australia your stolen phone is added to a "Stolen Mobile Phone" database, so if your phone is found later on it can be returned to you.

Giz Explains: What AT&T's 7.2Mbps Network Really Means(Copy from gizmodo.com)

AT&T's contribution to the improved overall speed of the iPhone 3GS—their upgraded 7.2Mbps network—is nearly as important as Apple's. But 7.2 is just a number, and AT&T's network is just one of many. Here's where it actually stands.


First, a direct translation: AT&T's upgraded (or more accurately, upgrading) 3G network claims data download rates of 7.2 megabits per second. Though that's the lingo used to describe bandwidth, it's important to remember that those are not megabytes. AT&T's impressive-sounding 7.2 megabits would yield somewhere closer to .9 megabytes (900 kilobytes) per second, and that's only if you're getting peak performance, which you never will because...

That 7.2Mbps is theoretical, and due to technical overhead, network business, device speed and overzealous marketing, real world speeds are significantly lower. UPDATEDEven looking at the old hardware on the current 3G network—the networking guts in your iPhone 3G is technically capable of reaching the 3.6Mbps downstream that AT&T's network is technically capable of pushing. There are lots of reasons you don't ever see that. For one, it's limited to 1.4Mbps to preserve battery life—the faster you download, the faster you burn that battery. Another is congestion—all the a-holes watching YouTubes around you—and backhaul—the amount of pipe running to a tower, or more English-y still, the total bandwidth the tower has available. Another is proximity—the closer to the tower you are, the faster your phone is gonna fly. So for top speeds, you should sit under a deserted tower with plenty of backhaul.

As you can see on our chart above, our tested speeds for everything from EV-DO Rev. A to WiMax ran at anywhere from one half to one sixth their potential speed. Accordingly, Jason found AT&T's network to run at about 1.6Mbps with the iPhone 3G S—about a third faster than with the 3G, though he was probably still connecting at 3.6Mbps rates—the 7.2 rollout won't be complete until 2011, according to AT&T.

AT&T-style HSDPA is expected to reach out to an eventual theoretical speed of 14Mbps, which will undoubtedly make the current 3G networks feel slow, but won't necessarily blow them out of the water. That's the thing: the iPhone, and indeed just about all high-end handsets on the market today, operate at speeds that are reasonably close to the limits of 3G technology. In a funny sort of way, the iPhone 3GS is already a bit out of date.

So what's next? And what the hell are those really long green bars up there? Those are the so-called 4G (fourth generation) wireless technologies. Americans can ignore HSPA+ and EV-DO Rev B. for the most part, and given that they're the slowest of the next-gen bunch, shouldn't feel too bad. And anyway, as Matt explained, WiMax and LTE are what's next for us.

Both Verizon and AT&T are within a couple of years of deploying LTE in their networks, and WiMax is already out there in some cities. Our own WiMax tests on Clearwire's network peaked at an astounding 12Mbps—nearly eight times faster than the iPhone 3GS on AT&T. And even if WiMax is shaping up to be more of a general broadband protocol than a cellular one, this is the kind of thing that'll be in your phones in a few years, and the promises are mind-boggling: earlier this year, Verizon's LTE were breaking 60Mbps.

So in short, your brand-new, "S"-for-speed iPhone is pretty speedy—as long as you only look to the past.

(this article is copy from gizmodo.com to see the original post go to gizmodo.com)

Giz Explains: Why WiMax and LTE Wireless 4G Data Will Blow Your Mind(copy from gizmodo.com)

3G sucks. Yeah I said it. Try watching YouTube video or hell, loading Giz. Real wireless, ubiquitous broadband for slurping up crazy data anywhere, anytime is coming. Soon. In the form of WiMax and LTE.

We're going to try to keep this pretty simple, as usual, but there are going to be some acronyms and a bit of jargon involved—our previous explainer on mobile terms might be a good place to start, actually, if you're walking into this totally oblivious to mobile tech.


Quickly, though, the current state of mobile networks is that we use 2.5G and 3G networks—mid-second-gen and newer third-gen data protocols. On the Verizon and Sprint side, known as CDMA, 2.5G is referred to as 1XRTT, or just 1X. On the AT&T and T-Mobile side, GSM, the 2.5G flavor is EDGE. Verizon and Sprint's 3G is EVDO, while AT&T and T-Mobile have HSDPA (you might not know that one, since they usually just say "3G").


Second gen wireless was basically just the leap to a digital network, and third gen is a closer attempt at true mobile broadband—kind of. Right now, with their 3G networks, they can all get you typical speeds of around 1 Megabit per second downstream, give or take (though the specs are rated for peak speeds of 3Mbps down on EVDO Rev. A, and 3.6 on HSDPA). 3G has a bit of breathing room left in it—EVDO Rev. B is capable of downstream speeds of 14.7Mbps , while the current HSDPA spec will go up to 14.4Mbps downstream with the right equipment, and depending on how far down the HSPA spec sheet you wanna go, maybe even faster.


But the fourth generation is already on its way. Technically, no wireless technology is officially 4G. But that's what everybody's calling WiMax and Long-Term Evolution, because they both promise crazyfast mobile internet speeds that leave the current 3G in the dirt. In the US, the main WiMax player is Clearwire, which Sprint owns 51 percent of after they combined their operations into one company and actually gave WiMax a chance to live. LTE is championed by AT&T (which makes sense because it was developed initially by companies who mainly build GSM networks like AT&T and T-Mobile's). Verizon also selected LTE, which blew everyone away at first because Verizon isn't in the GSM camp, but it makes sense because Verizon's parent company, Vodafone, is gung-ho for LTE in Europe, where everyone's on GSM.


So here's the crazy thing about WiMax and LTE, which you might not realize from all the smack talk coming out of Verizon and AT&T. I'm probably going to blow your mind right now: "They both use the same fundamental technology," says Barry West, Clearwire's President and Chief Architect. They both use orthogonal frequency-division multiplexing access and they're both IP (internet protocol) based. More simply, you can kind of think of the difference between WiMax and LTE as a software, not a hardware thing (kind of like Macs and PCs using the same Intel chip). Alcatel-Lucent, who makes the 4G wireless hardware, is actually "building hardware that is on a common platform," Paul Mankiewich A-L's Wireless CTO told us. In fact, West told us, at "some point in the future it's possible to harmonize" LTE and WiMax, it just "requires people to be willing to do that."


Here's what the fundamental difference is: Time division duplexing versus frequency division duplexing. Sounds complicated! But it's not. AT&T Labs VP of Architecture Hank Kafka explained it like this: "TDD is like CB radios or walkie-talkies—when one person is talking, the other person can't talk." The same channel is used for downstream and upstream, so the transmission is divided up over very tiny increments of time. Clearwire's West says they currently use a 2/3 downstream and 1/3 upstream split, so 2/3 of the time, you're swallowing data, and 1/3 of the time, you're spitting it. With LTE, Kafka says "it's more like a modem or phone conversation." It separates the available bandwidth into two parts—one operating downstream full time, and one operating upstream—so "you both can talk back and forth at the same time."


Great. But what's so special about WiMax and LTE? And how fast can they really get? Very simply, West told us, "The magic is the channel width." LTE and WiMax use really fat wireless channels, so they can move a lot of data at once. For example, AT&T's Kafka told us that "peak speed for LTE in 10MHz is about 140Mbps and peak speed in 20MHz is about 300Mbps." The thing about them being OFDM is that it makes them more flexible than 3G, since they can use a wide range of spectrum—LTE can use anything from the 1.4MHz channel up through 20MHz—whereas current 3G always uses 5MHz.


Did you see that? 300Mbps? Over the air? Whoooa. Well, don't let your panties get blown away yet. Yes, 4G will be way faster than 3G. But don't expect Asian city internet speeds wirelessly in the next couple of years. Clearwire's Barry West throws a bit of cold water on the ridiculously scorching speeds you might see hyped for LTE: To get to that 170Mbps, "that's like 8.5 bits per hertz and I've never seen a system achieve more than 5 bits per hertz." Huh? Basically, it doesn't take a whole lot of interference to slow your connection down, because it and WiMax use a complicated modulation scheme that you can't have constantly cranked to 11. So real world speeds will be slower.


WiMax is no slouch either, technically capable of up to 72Mbps.


Another thing about those superfat channels is that they don't reach as far out from the tower, and your response drops (obviously) as you get farther away. Which, Alcatel-Lucent's Mankiewich said, is one of the major infrastructure things with 4G: They're going to need to build more cell sites. That's why building out 4G is very pricey. (Not to mention all the money everyone had to spend on the right kind of airwaves to use for 4G.) If you thought 3G rollout was slow, 4G might be slower.


Here's what the real-soon-future looks like: Verizon isn't dicking around, and is doing commercial rollouts of LTE in 2010, while AT&T is following up with their commercial trials in 2011. (AT&T says Verizon "is in a big rush to move to LTE because their 3G technology gives them no room" to increase bandwidth and that red is a stupid color, nyah nyah nyah.) Clearwire has rolled out WiMax to a few cities already, and plans to have 120 million covered by the end of 2010. Verizon says they're getting about 60Mbps in testing, but expect it to be more like cable modem speeds when it launches—like Clearwire has now. For the reasons we mentioned above, and also because there won't be devices that can handle that kind of ridiculous speed—as you probably guessed, battery life being a major reason.

Will one standard eventually beat the other into submission, slinking away into the night, arm and arm with Betamax and HD DVD? Well, LTE does have a lot of momentum—the two biggest carriers in the US are rolling with it, and as part of the GSM family, you can bet all of the GSM carriers all over the world will be on board. But Alcatel-Lucent's Mankiewich says, "there's no real technological reason to pick one over the other." In fact, he thinks no one will "win," and just like now where "multiple technologies exist for economic reasons," it'll be the same thing with WiMax and LTE. So our only real hope for a single, happy standard is that they get together and make sweet, sweet love with some Marvin Gaye crooning in the background. It could happen.

(this article is copy from gizmodo.com to see the original post go to gizmodo.com)

Introduction to How WiFi Works

If you've been in an airport, coffee shop, library or hotel recently, chances are you've been right in the middle of a wireless network. Many people also use wireless networking, also called WiFi or 802.11 networking, to connect their computers at home, and some cities are trying to use the technology to provide free or low-cost Internet access to residents. In the near future, wireless networking may become so widespread that you can access the Internet just about anywhere at any time, without using wires.




One wireless router can allow multiple devices to connect to the Internet.

WiFi has a lot of advantages. Wireless networks are easy to set up and inexpensive. They're also unobtrusive -- unless you're on the lookout for a place to use your laptop, you may not even notice when you're in a hotspot. In this article, we'll look at the technology that allows information to travel over the air. We'll also review what it takes to create a wireless network in your home.
First, let's go over a few WiFi basics.

What Is WiFi?

What's in a name?

You may be wondering why people refer to WiFi as 802.11 networking. The 802.11 designation comes from the IEEE. The IEEE sets standards for a range of technological protocols, and it uses a numbering system to classify these standards.


A wireless network uses radio waves, just like cell phones, televisions and radios do. In fact, communication across a wireless network is a lot like two-way radio communication. Here's what happens:
A computer's wireless adapter translates data into a radio signal and transmits it using an antenna.
A wireless router receives the signal and decodes it. The router sends the information to the Internet using a physical, wired Ethernet connection.
The process also works in reverse, with the router receiving information from the Internet, translating it into a radio signal and sending it to the computer's wireless adapter. The radios used for WiFi communication are very similar to the radios used for walkie-talkies, cell phones and other devices. They can transmit and receive radio waves, and they can convert 1s and 0s into radio waves and convert the radio waves back into 1s and 0s. But WiFi radios have a few notable differences from other radios:
They transmit at frequencies of 2.4 GHz or 5 GHz. This frequency is considerably higher than the frequencies used for cell phones, walkie-talkies and televisions. The higher frequency allows the signal to carry more data.
They use 802.11 networking standards, which come in several flavors:
802.11a transmits at 5 GHz and can move up to 54 megabits of data per second. It also uses orthogonal frequency-division multiplexing (OFDM), a more efficient coding technique that splits that radio signal into several sub-signals before they reach a receiver. This greatly reduces interference.
802.11b is the slowest and least expensive standard. For a while, its cost made it popular, but now it's becoming less common as faster standards become less expensive. 802.11b transmits in the 2.4 GHz frequency band of the radio spectrum. It can handle up to 11 megabits of data per second, and it uses complementary code keying (CCK) modulation to improve speeds.
802.11g transmits at 2.4 GHz like 802.11b, but it's a lot faster -- it can handle up to 54 megabits of data per second. 802.11g is faster because it uses the same OFDM coding as 802.11a.
802.11n is the newest standard that is widely available. This standard significantly improves speed and range. For instance, although 802.11g theoretically moves 54 megabits of data per second, it only achieves real-world speeds of about 24 megabits of data per second because of network congestion. 802.11n, however, reportedly can achieve speeds as high as 140 megabits per second. The standard is currently in draft form -- the Institute of Electrical and Electronics Engineers (IEEE) plans to formally ratify 802.11n by the end of 2009.
Other 802.11 standards focus on specific applications of wireless networks, like wide area networks (WANs) inside vehicles or technology that lets you move from one wireless network to another seamlessly.
WiFi radios can transmit on any of three frequency bands. Or, they can "frequency hop" rapidly between the different bands. Frequency hopping helps reduce interference and lets multiple devices use the same wireless connection simultaneously.
Other Wireless Networking Standards

Another wireless standard with a slightly different number, 802.15, is used for Wireless Personal Area Networks (WPANs). It covers a very short range and is used for Bluetooth technology. WiMax, also known as 802.16, looks to combine the benefits of broadband and wireless. WiMax will provide high-speed wireless Internet over very long distances and will most likely provide access to large areas such as cities.


­As long as they all have wireless adapters, several devices can use one router to connect to the Internet. This connection is convenient, virtually invisible and fairly reliable; however, if the router fails or if too many people try to use high-bandwidth applications at the same time, users can experience interference or lose their connections.
Next, we'll look at how to connect to the Internet from a WiFi hotspot.

Making calls with Mobile phone via VOIP Save money on local, long distance & roaming

Making calls with Mobile phone via VOIP Save money on local, long distance, inter-national & roaming


While the emergence of VoIP, or voice-over-Internet protocol, technology has already helped push down the cost of making a phone call, now it’s starting to have a deflationary impact on the world of mobile, where call charges remain stubbornly high.
In the meantime, the ongoing adoption of 3G broadband and the inclusion of Wi-Fi in many high-end phones is drawing a growing amount of attention to mobile VoIP services. Indeed, research firm Disruptive Analysis predicts that the number of VoIP-over-3G users will top 250 million by the end of 2012 — from virtually zero in 2007.
We at GigaOM are constantly tinkering with these mobile services, so we’ve put together a list of seven mobile VoIP apps that we think you’ll find handy.
Skype Options

Service: Skype Mobile
Platform/Network: Java-based application that works on 50 popular phones from Nokia, Sony Ericsson, Motorola and Samsung. Can be used on numerous cellular data networks.
Cost: Free
Features: Chatting (including with a group), presence settings (offline, online, do not disturb), and Skype-to-Skype calls (including SkypeIn).
Our Opinion: If your phone is supported, Skype Mobile is a great way to add Skype chatting and calls to it. Though it would be nice if the Skype application weren’t written in Java, as these applications are often sluggish and unstable.

Service: 3 Skypephone
Platform/Network: Uses a specialized handset. Currently available in the UK, Italy, Austria, Hong Kong, Australia, Ireland, Denmark and Sweden.
Cost: The phone costs £49.99 (about $98) and can be used on a pre-paid basis. Calls cost nothing if they’re made from Skype.
Features: Free Skype-to-Skype mobile calls and the ability to conduct Skype IM conversations, all without touching your computer.
Our Opinion: The 3 Skypephone is best suited for those who need a few monthly mobile minutes and wish to talk/IM to their Skype friends along the way. The pre-paid feature makes it an attractive and inexpensive option for Skype chatters in the geographies it serves.

Service: iSkoot
Platform/Network: Mobile handsets such as BlackBerry, Nokia, Windows Mobile and Palm OS models. Also works on GSM networks.
Cost: Modest to expensive, based on usage. Because iSkoot is a hybrid VoIP/GSM service, it uses SMS and mobile minutes when making and receiving calls or Skype IM messages.
Features: SkypeIn and Skype-to-Skype calls, Skype IM messages.
Our Opinion: iSkoot is a good option for keeping in touch with your Skype contacts. However, I would look at other software applications that just use data to send Skype SMS and Skype voice traffic.
Mobile VoIP Players

Service: Truphone
Platform/Network: Nokia handsets
Cost: Incoming free calls while on the Truphone network, low per-minute rates while on a GSM network. Outgoing calls are billed at very low per minute rates.
Features: Truphone offers free calls, SMS and voice mail while logged into the Truphone network via Wi-Fi. Otherwise, Truphone forwards calls to your mobile handset and you pay a low per-minute charge.
Our Opinion: With its smart forwarding options, Truphone is particularly useful for international travelers. Whether you’re on Wi-Fi or just your normal GSM network, you can be reached via your Truphone number no matter where you are (charges apply in certain cases, see their site for details). For times when Wi-Fi is not available, Truphone just released Truphone Anywhere, which utilizes local gateways for outgoing calls at low per-minute charges. I have trialed the service by forwarding calls from my Truphone number to my cell phone and the call quality was fantastic; voices were indistinguishable from any other cell phone call. A Truphone-to-Truphone VoIP call yielded even higher voice quality.

Service: Fring
Platform/Network: Nokia/Symbian handsets, Widows Mobile, iPhone (pre-release beta)
Cost: Free
Features: Allows you to make VoIP calls on any SIP network, Skype or to other Fring users. Additionally, Fring is a multi-protocol IM client that will allow you to chat with your buddies on Skype, MSN, ICQ, Google Talk, Twitter, AIM and Yahoo.
Our Opinion: I have used Fring to make SIP and Skype voice calls, and over EDGE the call is choppy and hard to understand. However, Wi-Fi provides enough bandwidth to make Fring calls clear and understandable. I wouldn’t say the quality is fantastic, but it is very comparable to a normal cell phone call.

Service: Talkonaut
Platform/Network: Available for Java-based phones, Symbian and Windows Mobile
Cost: Free
Features: Talkonaut offers free VoIP and IM chatting. For instant messaging, the application supports Google Talk, ICQ, AIM, and Yahoo. Talkonaut can also use SIP for VoIP calling.
Our Opinion: Talkonaut is a Russian offering and is still very new. The application was quite unstable on my Nokia N82 handset. With iffy performance and a very rusty user interface, I would recommend looking at other applications for this functionality, namely Fring.

Service: Nimbuzz
Platform/Network: Java program, Symbian; an iPhone version is coming soon.
Cost: Free
Features: Allows you to engage in IM conversations and conduct VoIP calls, as well as to share media such as photos and video. Nimbuzz also allows for client-to-client calls and has widgets enabling calls to originate from Facebok and MySpace. Compatible with Skype, Google Talk, AOL Instant Messenger, Windows Live Messenger, Yahoo, MySpace, Facebook and Jabber IM networks.
Our Opinion: The Symbian application is very responsive and easy to use. A VoIP call originating from my Facebook page to Nimbuzz over a Wi-Fi connection sounded good — just as good as any call over a GSM network.

Service: Gizmo5 (formerly Gizmo Project)
Platform/Network: Nokia Symbian handsets, BlackBerry, Windows Mobile, Nokia Tablets
Cost: Free for VoIP calls, low per-minute charge to call landlines and to SMS to mobiles.
Features: Gizmo5 allows you to conduct voice calls to other Gizmo5 users and grants IM conversations with friends on Gizmo5, MSN, AIM, Yahoo and Jabber.
Our Opinion: Gizmo5 is a great competitor to Skype, just not as established or well-known. They have wisely developed their client software for many platforms including numerous mobile phones, and on both Mac and PC. VoIP call quality is stellar when calling between clients, as well as to landline/mobile phones

How the Cellular System Works

How the Cellular System Works:
Every cellular system digital or analog is comprised of four parts.

1 ) Cells and cell sites ( base stations )

2 ) Switching station ( mobile telephone switching office or MTSO )

3 ) System operator and its local office

4 ) Cellular telephones



The heart of the system is made up of individual radio coverage areas called " cells. " Each cell is a self-contained calling area. Within the cell, a cell site is strategically positioned as a base station for receiving, sending and routing the radio signals of cellular phone calls. Because the cellular system is a radio system, no exact boundary can be drawn on a map. In most cases calls can be place and received throughout the service area, except for certain enclosed areas such as underground parking garages. The No Svc ( No Service ) indicator will illuminate on the cellular phone when in one of those areas or is outside of the service area. The cell site's transmitter is low powered and does not reach much beyond that cell's boundaries. That makes it possible to reuse channels ( frequencies ) - a given channel can be used at the same time in different cells, as long as the cells do not border one another, without causing signal interference. This is particularly valuable in urban areas where lots of cellular phones are in use at the same time. All cell sites are connected to the Mobile Telephone Switching Office ( MTSO ), which provides connection into the Public Switched Telephone network ( PSTN ) - the local telephone company. The MTSO also provides other central functions, including call processing, traffic management, and transferring calls as a phone moves between cell sites.

Making a Call
When a cellular user makes a call from a cellular phone, radio signals are transmitted to the cell site. The cell site alerts the Mobile Telephone Switching Office ( MTSO ) switching station. The MTSO, in turn, provides an open channel ( frequency ) and connects the call to the Public Switched Telephone Network ( PSTN ). The PSTN put the call through to the number to be reached. This process takes the same amount of time that it takes to make a call from a land line phone.

Receiving a Call
These are the steps that occur when you receive a call on a cellular phone. A call placed to a cellular phone may come from either a land line phone or another cellular phone. Whichever the source, the MTSO is notified that a call has been placed to a specific cellular telephone number. At this point, the MTSO searches for the correct cellular phone by sending out data over the radio waves. Cellular phones that are in standby mode ( i.e., turned on but not being used in a call ) continuously scan the radio waves being transmitted by the MSTO. If a phone " hears " its telephone number, it sends back a signal that informs the closest cell site of its Electronic Serial Number ( ESN ) and its telephone number ( Mobile Identification Number or MIN ). The cell site passes this information to the MTSO, where the ESN and MIN are verified and a channel ( frequency ) is assigned for the call. The cellular phone receives the message directing it to tune to the correct voice channel. The cell site makes the voice channel available, and the call is completed.

Hand-off
Hand-off is the transfer of a call from one cell site to another as the cellular phone moves through the service coverage area. The cell site warns the MSTO that the mobile's signal strength is falling below a predetermined level. The MTSO then alerts all cell sites bordering on the first one. They measure the mobile's transmitting signal and report back to the MTSO. The MTSO, which is programmed to select the site receiving the strongest signal, then switches the call from the weak cell to the strongest cell without interrupting the call. The whole process takes a fraction of a second, and the caller usually is unaware of it. Such hand-offs may occur several times during a single conversation as the caller moves through the coverage area.

(Copy from gsmreport.dot5hosting.com)

What is VoIP?

What is VoIP?
VoIP (voice over IP) is an IP telephony term for a set of facilities used to manage the delivery of voice information over the Internet.VoIP involves sending voice information in digital form in discrete packets rather than by using the traditional circuit-committed protocols of the public switched telephone network (PSTN). A major advantage of VoIP and Internet telephony is that it avoids the tolls charged by ordinary telephone service.

VoIP derives from the VoIP Forum, an effort by major equipment providers, including Cisco, VocalTec, 3Com, and Netspeak to promote the use of ITU-T H.323, the standard for sending voice (audio) and video using IP on the public Internet and within an intranet. The Forum also promotes the user of directory service standards so that users can locate other users and the use of touch-tone signals for automatic call distribution and voice mail.

In addition to IP, VoIP uses the real-time protocol (RTP) to help ensure that packets get delivered in a timely way. Using public networks, it is currently difficult to guarantee Quality of Service (QoS). Better service is possible with private networks managed by an enterprise or by an Internet telephony service provider (ITSP).

A technique used by at least one equipment manufacturer, Adir Technologies (formerly Netspeak), to help ensure faster packet delivery is to use ping to contact all possible network gateway computers that have access to the public network and choose the fastest path before establishing a Transmission Control Protocol (TCP) sockets connection with the other end.

Using VoIP, an enterprise positions a "VoIP device" at a gateway. The gateway receives packetized voice transmissions from users within the company and then routes them to other parts of its intranet (local area or wide area network) or, using a T-carrier system or E-carrier interface, sends them over the public switched telephone network.

Companies providing VoIP service are commonly referred to as providers, and protocols which are used to carry voice signals over the IP network are commonly referred to as Voice over IP or VoIP protocols. They may be viewed as commercial realizations of the experimental Network Voice Protocol (1973) invented for the ARPANET providers. Some cost savings are due to utilizing a single network - see attached image - to carry voice and data, especially where users have existing underutilized network capacity that can carry VoIP at no additional cost. VoIP to VoIP phone calls are sometimes free, while VoIP to PSTN may have a cost that's borne by the VoIP user.

There are two types of PSTN to VoIP services: DID (Direct Inward Dialing) and access numbers. DID will connect the caller directly to the VoIP user while access numbers require the caller to input the extension number of the VoIP user. Access numbers are usually charged as a local call to the caller and free to the VoIP user while DID usually has a monthly fee.[1] There are also DIDs that are free to the VoIP user but chargeable to the caller.

A major development starting in 2004 has been the introduction of mass-market VoIP services over broadband Internet access services, in which subscribers make and receive calls as they would over the PSTN. Full phone service VoIP phone companies provide inbound and outbound calling with Direct Inbound Dialing. Many offer unlimited calling to the U.S., and some to Canada or selected countries in Europe or Asia as well, for a flat monthly fee.

These services take a wide variety of forms which can be more or less similar to traditional POTS. At one extreme, an analog telephone adapter (ATA) may be connected to the broadband Internet connection and an existing telephone jack in order to provide service nearly indistinguishable from POTS on all the other jacks in the residence. This type of service, which is fixed to one location, is generally offered by broadband Internet providers such as cable companies and telephone companies as a cheaper flat-rate traditional phone service. Often the phrase "VoIP" is not used in selling these services, but instead the industry has marketed the phrase "Internet Phone" or "Digital Phone" which is aimed at typical phone users who are not necessarily tech-savvy. Typically, the provider touts the advantage of being able to keep one's existing phone number.

At the other extreme are services like Gizmo Project and Skype which rely on a software client on the computer in order to place a call over the network, where one user ID can be used on many different computers or in different locations on a laptop. In the middle lie services which also provide a telephone adapter for connecting to the broadband connection similar to the services offered by broadband providers (and in some cases also allow direct connections of SIP phones) but which are aimed at a more tech-savvy user and allow portability from location to location. One advantage of these two types of services is the ability to make and receive calls as one would at home, anywhere in the world, at no extra cost. No additional charges are incurred, as call diversion via the PSTN would, and the called party does not have to pay for the call. For example, if a subscriber with a home phone number in a U.S. area code calls someone else in his home area code, it will be treated as a local call regardless of where that person is in the world. Often the user may elect to use someone else's area code as his own to minimize phone costs to a frequently called long-distance number.

For some users, the broadband phone complements, rather than replaces, a PSTN line, due to a number of inconveniences compared to traditional services. VoIP requires a broadband Internet connection and, if a telephone adapter is used, a power adapter is usually needed. In the case of a power failure, VoIP services will generally not function. Additionally, a call to the U.S. emergency services number 9-1-1 may not automatically be routed to the nearest local emergency dispatch center, and would be of no use for subscribers outside the U.S. This is potentially true for users who select a number with an area code outside their area. Some VoIP providers offer users the ability to register their address so that 9-1-1 services work as expected.

Another challenge for these services is the proper handling of outgoing calls from fax machines, TiVo/ReplayTV boxes, satellite television receivers, alarm systems, conventional modems or FAXmodems, and other similar devices that depend on access to a voice-grade telephone line for some or all of their functionality. At present, these types of calls sometimes go through without any problems, but in other cases they will not go through at all. And in some cases, this equipment can be made to work over a VoIP connection if the sending speed can be changed to a lower bits per second rate. If VoIP and cellular substitution becomes very popular, some ancillary equipment makers may be forced to redesign equipment, because it would no longer be possible to assume a conventional voice-grade telephone line would be available in almost all homes in North America and Western-Europe. The TestYourVoIP website offers a free service to test the quality of or diagnose an Internet connection by placing simulated VoIP calls from any Java-enabled Web browser, or from any phone or VoIP device capable of calling the PSTN network.

Although few office environments and even fewer homes use a pure VoIP infrastructure, telecommunications providers routinely use IP telephony, often over a dedicated IP network, to connect switching stations, converting voice signals to IP packets and back. The result is a data-abstracted digital network which the provider can easily upgrade and use for multiple purposes.

Corporate customer telephone support often use IP telephony exclusively to take advantage of the data abstraction. The benefit of using this technology is the need for only one class of circuit connection and better bandwidth use. Companies can acquire their own gateways to eliminate third-party costs, which is worthwhile in some situations.

VoIP is widely employed by carriers, especially for international telephone calls. It is commonly used to route traffic starting and ending at conventional PSTN telephones. Many telecommunications companies are looking at the IP Multimedia Subsystem (IMS) which will merge Internet technologies with the mobile world, using a pure VoIP infrastructure. It will enable them to upgrade their existing systems while embracing Internet technologies such as the Web, email, instant messaging, presence, and video conferencing. It will also allow existing VoIP systems to interface with the conventional PSTN and mobile phones.