How Fixed Mobile Convergence Works

Cell Phone Image Gallery Wouldn't it be nice if you could simply have one phone that worked everywhere, no matter where you are? See more cell phone pictures.
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You're running late for work, but the phone starts ringing. You answer the call with a distracted, "Hello." It's your old college roommate. You haven't talked to him in ages, but there's just no time to talk right now. You ask if you can call him back that night. Unfortunately, he's calling from the airport on his way to a photo assignment and he'll be out of pocket for a few weeks. You have so much to catch up on -- including your recent engagement. So before you hang up, you quickly tell him to call you back on your cell phone, figuring you can at least chat a few minutes while you're catching the train and he's sitting at the airport. As you're shutting the front door, you realize he doesn't have your new cell phone number. You run back inside to check the caller ID only to find there's nothing listed for the last call. You simply can't be late for work again, so there's no time to wait to see if he calls back. If only you could have taken that call to go like you did with your homemade mocha latte …

With fixed mobile convergence, you just might be able to.

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Fixed mobile convergence (FMC) is an industry term that has been making the rounds in the past few years as a possible next big thing in communications. In a nutshell, it refers to the ability to use one phone, moving between your house or office and everywhere else, but in practice, it's a little more difficult than it seems.

For starters, the "fixed" part, which refers to existing wired systems like the telephone lines coming into your house, also includes things like WiFi Internet that come in through the same wires. And "mobile" is the system used by cellular phones. The two systems have grown up independently of each other and they work in completely different ways. But before we get into that, let's take a closer look at the convenience FMC could offer.

 

The Convenience of FMC

With FMC, your phone could switch from cell service to WiFi seamlessly; you could go from home to work to the coffee shop, all the while saving money on cell charges and still being able to share that funny video while you wait in line for a latte.
With FMC, your phone could switch from cell service to WiFi seamlessly; you could go from home to work to the coffee shop, all the while saving money on cell charges and still being able to share that funny video while you wait in line for a latte.
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Proponents of fixed mobile convergence (FMC) tout convenience as a big factor: One phone number reaches you wherever you are. You'd be able to start a call in the house, then hike off to wherever there's cell service without hanging up or switching phones (Voice Call Continuity, in industry-speak). It would also let you take advantage of VoIP (Voice over Internet Protocol) services like Skype, when an Internet connection is available, saving expensive cell phone minutes. The ability to use WiFi would also effectively expand coverage for your cell phone, particularly inside buildings, where it can be difficult to get cell service. In a converged world, you could make a call through your office WiFi network, head outside and connect to the cellular system, then connect back up to the WiFi at the coffee shop, all without losing the call or, really, doing anything at all. Just don't keep talking when you're in line for coffee. Everybody hates that.

For the communications industry, FMC offers a way to reverse another trend -- Fixed Mobile Substitution, where customers get rid of their home phones in favor of a cell phone. In the United States, the National Center for Health Statistics reports that one in six homes had abandoned their wired phone for wireless by the end of 2008, and studies in other countries have shown similar trends [Source: Blumberg].

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With the growing popularity of Internet capable phones like Apple's iPhone, switching to WiFi when it's available also reduces load on the cellular network, and customers can still Twitter about being in line for a coffee, or perhaps pass the time by watching amusing videos of cats.

Of course, transmitting videos of cats was not what Alexander Graham Bell had in mind when he invented the telephone. This was not shortsightedness on his part-- it would, in fact, take many decades to reach this stage.

Leading up to FMC

Skipping over the invention of the telephone and how it works, let's just assume that by the time you're reading this, hard-wired telephones still exist somewhere.

Because of the way the telephone companies grew up, they operated more or less like railroads -- the phone company owned the equipment, including the phones and the wires connecting them. In the U.S., that was one phone company, AT&T, who had a monopoly until the Justice Department broke the company up in 1982, creating smaller, regional companies and opening the field to competitors like MCI and Sprint. Because telephone lines ran into most American houses, it was a natural choice when people began linking computers together. On the fixed telephone system, all the parts worked together.

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It was Bell Labs, a division of AT&T, who came up with the cell phone system, based on towers transmitting and receiving signals, forming "cells" of coverage that united to form a network. The cellular network, unlike the old hardwired lines, needed to have the ability to hand off calls as the recipient traveled between cells -- different antennas would take over, but as long as you were in a coverage area, you wouldn't lose the call.

When computers began to be connected over the telephone lines, they used a different method of exchanging information (see the sidebar on circuit and packet switching). For proponents of fixed mobile convergence, the challenge is to get these different systems, each requiring different hardware, to work together. But to do that, they all need to speak the same language.

FMC: Speaking the Right Language

If you have several different companies working on doing the same thing, they'll find different ways of doing it. This isn't necessarily a big deal for some things, like say a house. Having multiple contractors in one neighborhood works because the houses don't have to interact with each other. Your phone, on the other hand, is only useful to you if you can use it to communicate with other people, even if they're using a phone made by a different company. The same is true of the Internet -- if you want to access the whole thing, your computer needs to understand the language.

For WiFi networks, the Institute of Electrical and Electronics Engineers (IEEE) sets the standards. The IEEE's 802.11 rules set the framework that allows the wireless antenna in your computer to communicate with the wireless antenna in your router, which in turn sends the signal out of your house through a telephone or cable line. It doesn't make any difference what kind of information you're sending and receiving, as long as your computer speaks the same language as the server.

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Networks of computers have become commonplace, and they're getting bigger -- from Local Area Networks (LANs) in your home or business, to Campus and Metropolitan Area Networks (CANs and MANs, respectively) as universities and cities have gotten into the act. The network by itself can be as simple as connecting two computers together, or accessing information from the university computers, but more often, they connect to the larger Internet, and wireless networks that allow computers to connect anywhere in range have become the norm.

Cell phone standards, however, evolved differently.

FMC and Cell Phone Standards

Based on the old telephone models, cell phones were designed to transmit voices. The first generation of cell phones were basically radios, transmitting an analogue signal through the air to a cell tower. With the second generation of cell phones, voices were digitized, but still sent the same way, via a circuit-switched network that established a connection between two phones, keeping it open for as long as your conversation lasted.

The most popular standard for the second generation cell phones is GSM, or Global System for Mobile Communications, which was developed in Europe, and it is based on a model called Time Division Multiple Access (TDMA) but it isn't the only one [source: GSM Association]. The CDMA (Code Division Multiple Access) system was developed in the United States by Qualcomm [source: CDMA Development Group]. The two systems differ in how they allow multiple users to transmit information over the same airwaves. Each standard has its adherents. T-Mobile, for instance, uses the GSM standard, while AT&T uses CDMA -- and each standard has its own governing body. You can still call a GSM phone from a CDMA phone, and vice versa, but you can't use one type of phone to connect to the other type of network, so a GSM phone needs GSM coverage to get a signal.

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The allure of being able to connect to the Internet wherever you are has led to an increase in data plans offered by cell phone companies, bringing us into the third generation of cell phones (AT&T actually calls its network 3G, but there are others, such as the EDGE network offered by T-Mobile, among others). Third generation networks allow larger chunks of data than just voice, but they still transmit data through the cellular phone system, with the same limitations as second generation phones. As different companies with different network standards head toward uniting the fixed and mobile networks, they've taken a number of different paths, and we'll take a look at some of those next.

FMC Solutions

So we've got two systems -- WiFi and cellular, and we need to get them to talk to each other. One solution seems pretty easy -- put two radios in each phone, one using the 802.11 standards, one using the cellular system. If you've ever had a dropped call, though, you know how annoying it is to lose your connection, so something in the telephone has to keep track of which network you're on, which networks are available, and seamlessly make the switch between them. Companies like California's Divitas Network offer software to do this with compatible phones, and some carriers offer so-called Universal Mobile Access service to switch between networks, like T-Mobile's Hotspots.

Another option relies on small cellular transmitters, called femtocells, to extend the range of the cellular 3G networks. Femtocells connect to a broadband line, like a cable Internet connection, but use the cellular system rather than WiFi, eliminating the need for two radios inside one phone.

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Femtocells work by extending the cellular network indoors, but the other option is extending the WiFi network outside. WiMax is an attempt to do that. Essentially, it's an upgraded wireless network that allows broadband wireless access over large distances. A WiMax network could replace GSM and CDMA networks, allowing phones, computers, or other devices to connect anywhere within range, using the 802.11 standard's relative 802.16.

IEEE's 802.21 standard attempts to solve the problem of switching between different types of networks via a process called Media Independent Handover (MIH). A seamless handoff between the two (without losing data or dropping the call) would bridge a gap for fixed mobile convergence. The IEEE has a group working on the 802.21 standard, which is still evolving. For something like downloading a Web page, which takes little time, switching between networks isn't usually a problem. But something longer, like making a phone call or watching a movie, requires a few steps: the phone needs to notice that it's losing a signal, detect a new network (possibly among many), and connect to the right one, without skipping a beat. InterDigital of Pennsylvania recently demonstrated an MIH system using software capable of switching between cellular and wireless systems for VoIP and streaming video while transferring from 3G to WiFi [source: InterDigital].

The cellular network hasn't given up the fight. LTE, or Long Term Evolution, is a protocol based on the third generation systems and a stepping-stone to the so-called Long Term Evolution Advanced standard, which would provide broadband wireless access through a cellular network.

Although some providers already advertise fourth generation networks, complete convergence of voice and data services at the speeds specified by the next set of protocols, are still under development [source: Goldman]. Fourth generation wireless standards have a theoretical maximum speed of up to one gigabyte per second. In fact, there are two organizations developing them, the 3GPP with LGE Advanced (based on existing LTE), and the IEEE's version of 4G, based on WiMax and the 802.16 standards [source: 3GAmericas]. Other suggestions include using both LTE and WiMax, and at least one chip manufacturer has announced that it will use both technologies at once [source: Beceem Communications].

For more information on current communications technologies, visit the links on the following page.

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