Wirelessinternet

2008-02-13T19:18:00.000-08:00

How IP Telephony Works
If you regularly make long-distance phone calls, chances are you've already used IP telephony without even knowing it. IP telephony, known in the industry as Voice-over IP (VoIP), is the transmission of telephone calls over a data network like one of the many networks that make up the Internet. While you probably have heard of VoIP, what you may not know is that many traditional telephone companies are already using it in the connections between their regional offices.
This person is using a computer to talk to a friend in another state.
Now, you'll learn about VoIP and the technology that makes it possible. We'll talk about VoIP's major protocols, about the various services provided and the low-cost, often free software that allows you to take advantage of them.
But first, let's discuss the fundamental problem with existing telephone networks -- namely, their reliance on circuit switching.

2008-02-13T18:51:00.000-08:00

Circuit Switching

Circuit switching is a very basic concept that has been used by telephone networks for over 100 years. What happens is that when a call is made between two parties, the connection is maintained for the entire duration of the call. Because you are connecting two points in both directions, the connection is called a circuit. This is the foundation of the Public Switched Telephone Network (PSTN).
Here's how a typical telephone call works:
You pick up the receiver and listen for a dial tone. This lets you know that you have a connection to the local office of your telephone carrier. You dial the number of the party you wish to talk to. The call is routed through the switch at your local carrier to the party you are calling. A connection is made between your telephone and the other party's line, opening the circuit. You talk for a period of time and then hang up the receiver. When you hang up, the circuit is closed, freeing your line. Let's say that you talk for 10 minutes. During this time, the circuit is continuously open between the two phones. Telephone conversations over the traditional PSTN are transmitted at a fixed rate of about 64 kilobits per second (Kbps), or 1,024 bits per second (bps), in each direction, for a total transmission rate of 128 Kbps. Since there are 8 kilobits (Kb) in a kilobyte (KB), this translates to a transmission of 16 KB each second the circuit is open, and 960 KB every minute it's open. So in a 10-minute conversation, the total transmission is 9600 KB, which is roughly equal to 9.4 megabytes (MB).
If you look at a typical phone conversation, much of this transmitted data is wasted. While you are talking, the other party is listening, which means that only half of the connection is in use at any given time. Based on that, we can surmise that we could cut the file in half, down to about 4.7 MB. Plus, a significant amount of the time in most conversations is dead air -- for seconds at a time, neither party is talking. If we could remove these silent intervals, the file would be even smaller.
Data networks do not use circuit switching. Your Internet connection would be a lot slower if it maintained a constant connection to the Web page you were looking at. Instead of simply sending and retrieving data as you need it, the two computers involved in the connection would pass data back and forth the whole time, whether the data was useful or not. That's no way to set up an efficient data network. Instead, data networks use a method called packet switching.

2008-02-13T18:43:00.000-08:00

Packet Switching

While circuit switching keeps the connection open and constant, packet switching opens the connection just long enough to send a small chunk of data, called a packet, from one system to another. What happens is this: The sending computer chops data into these small packets, with an address on each one telling the network where to send them. When the receiving computer gets the packets, it reassembles them into the original data. Packet switching is very efficient. It minimizes the time that a connection is maintained between two systems, which reduces the load on the network. It also frees up the two computers communicating with each other so that they can accept information from other computers as well. Click "Play" to see how packet switching works.VoIP technology uses this packet-switching method to provide several advantages over circuit switching. For example, packet switching allows several telephone calls to occupy the amount of space occupied by only one in a circuit-switched network. Using PSTN, that 10-minute phone call consumed 10 full minutes of transmission time at a cost of 128 Kbps. With VoIP, that same call may have occupied only 3.5 minutes of transmission time at a cost of 64 Kbps, leaving another 64 Kbps free for that 3.5 minutes, plus an additional 128 Kbps for the remaining 6.5 minutes. Based on this simple estimate, another three or four calls could easily fit into the space used by a single call under the conventional system. And this example doesn't even factor in the use of data compression, which further reduces the size of each call. Let's say that your company had equipment installed and a contract set up so that you can use VoIP. You have installed about a dozen telephones and a digital private branch exchange (PBX) in your office. A PBX is essentially a switch used to connect a number of phones (extensions) to each other and to one or more outside phone lines. In our example, the PBX is also a gateway. Gateways are used to connect devices on two different types of networks so that they can communicate with each other. Our PBX is a gateway because it converts the standard circuit-switched signal from each phone into digital data that can be sent over a packet-switched, IP-based network. IP stands for "Internet protocol," the language used by most data networks. Let's take another look at that typical telephone call, but this time using VoIP over a packet-switched network:

1. You pick up the receiver, which sends a signal to the PBX.

2. The PBX receives the signal and sends a dial tone. This lets you know that you have a connection to the PBX.

3. You dial the number of the party you wish to talk to. This number is then temporarily stored by the PBX.

4. Once you have entered the number, the PBX checks it to ensure that it is in a valid format. 5. The PBX determines whom to map the number to. In mapping, the number is attached to the IP address of another device called the IP host. The IP host is typically another digital PBX that is connected directly to the phone system of the number you dialed. In some cases, particularly if the party you are calling is using a computer-based VoIP client, the IP host is the system you wish to connect with.

6. A session is established between your company's PBX and the other party's IP host. This means that each system knows to expect packets of data from the other system. Each system must use the same protocol to communicate. The systems will implement two channels, one for each direction, as part of the session.

7. You talk for a period of time. During the conversation, your company's PBX and the other party's IP host transmit packets back and forth when there is data to be sent. The PBX at your end keeps the circuit open between itself and your phone extension while it forwards packets to and from the IP host at the other end.

8. You finish talking and hang up the receiver.

9. When you hang up, the circuit is closed between your phone and the PBX, freeing your line. 10. The PBX sends a signal to the IP host of the party you called that it is terminating the session. The IP host terminates the session at its end, too.

11. Once the session is terminated, the PBX removes the number-to-IP-host mapping from memory. Probably one of the most compelling advantages of packet switching is that data networks already understand the technology. By migrating to this technology, telephone networks immediately gain the ability to communicate the way computers do. Of course, having the ability to communicate and understanding the methods of communication are two very different things. For telephones to communicate with each other and with other devices, such as computers, over a data network, they need to speak a common language called a protocol.

2008-02-13T18:40:00.000-08:00

Protocol

There are two major protocols being used for VoIP. Both protocols define ways for devices to connect to each other using VoIP. Also, they include specifications for audio codecs. A codec, which stands for coder-decoder, converts an audio signal into a compressed digital form for transmission and back into an uncompressed audio signal for replay. The first protocol is H.323, a standard created by the International Telecommunications Union (ITU). H.323 is a comprehensive and very complex protocol. It provides specifications for real-time, interactive videoconferencing, data sharing and audio applications such as IP telephony. Actually a suite of protocols, H.323 incorporates many individual protocols that have been developed for specific applications.H.323 Protocol SuiteVideo Audio Data TransportH.261H.263 G.711G.722G.723.1G.728G.729 T.122T.124T.125T.126T.127 H.225H.235H.245H.450.1H.450.2 H.450.3RTPX.224.0As you can see, full implementation of H.323 requires a lot of overhead. This page provides detailed information about the entire H.323 suite of protocols and how they relate to the OSI Reference Model. An alternative to H.323 emerged with the development of Session Initiation Protocol (SIP) under the auspices of the Internet Engineering Task Force (IETF). SIP is a much more streamlined protocol, developed specifically for IP telephony. Smaller and more efficient than H.323, SIP takes advantage of existing protocols to handle certain parts of the process. For example, Media Gateway Control Protocol (MGCP) is used by SIP to establish a gateway connecting to the PSTN system. You can learn more about the architecture of SIP on this page.

2008-02-13T18:37:00.000-08:00

Calling

There are four ways that you might talk to someone using VoIP. If you've got a computer or a telephone, you can use at least one of these methods without buying any new equipment:
Computer-to-computer - This is certainly the easiest way to use VoIP. You don't even have to pay for long-distance calls. There are several companies offering free or very low-cost software that you can use for this type of VoIP. All you need is the software, a microphone, speakers, a sound card and an Internet connection, preferably a fast one like you would get through a cable or DSL modem. Except for your normal monthly ISP fee, there is usually no charge for computer-to-computer calls, no matter the distance. A good example of this software is MSN Explorer.
The Net2Phone software client is easy to set up and use.
Computer-to-telephone - This method allows you to call anyone (who has a phone) from your computer. Like computer-to-computer calling, it requires a software client. The software is typically free, but the calls may have a small per-minute charge. For example, Net2Phone offers free calls to anywhere in the United States for the first five minutes. If the call is over five minutes, a rate of 3.9 cents per minute kicks in. Net2Phone's international rates vary widely, ranging from 3.9 cents to $7.52 per minute, depending on where you call.
Telephone-to-computer - A few companies are providing special numbers or calling cards that allow a standard telephone user to initiate a call to a computer user. The caveat is that the computer user must have the vendor's software installed and running on his or her computer. The good news is that the cost of the call is normally much cheaper than a traditional long-distance call.
Telephone-to-telephone - Through the use of gateways, you can connect directly with any other standard telephone in the world. To use the discounted services offered by several companies, you must call in to one of their gateways. Then, you enter the number you wish to call, and they connect you through their IP-based network. The downside is that you have to call a special number first. The upside is that the rates are typically much lower than standard long distance. Although it will take some time to happen, you can be sure that, eventually, all of the circuit-switched networks will be replaced with packet-switching technology. IP telephony just makes sense, in terms of both economics and infrastructure requirements. More and more businesses are installing VoIP systems, and the technology will continue to grow in popularity as it makes its way into our homes

2008-02-13T18:09:00.000-08:00

BLUETOOTH TECHNOLOGY TO HARNESS THE SPEED OF 802.11

Wireless transfer of large format entertainment data – music, video, and photos – between devices at short range is imminent. The Bluetooth Special Interest Group (SIG) today announced a new way it will provide for consumers’ growing need for speed.
The Bluetooth SIG is developing an innovative method of radio substitution. It will allow the well known Bluetooth protocols, profiles, security and pairing to be used in consumer devices while achieving faster throughput with momentary use of a secondary radio already present in the device. This architecture, called ‘Alternate MAC/PHY’ by Bluetooth SIG members working on the specification, is taking on a two-phased approach as SIG member companies drive the specification forward.
“This is the wireless technology equivalent of ‘low hanging fruit,’” said Michael Foley, Ph.D., executive director, the Bluetooth SIG. “What we’re doing is taking classic Bluetooth connections – using Bluetooth protocols, profiles, security and other architectural elements – and allowing it to jump on top of the already present 802.11 radio, when necessary, to send bulky entertainment data, faster. When the speed of 802.11 is overkill, the connection returns to normal operation on a Bluetooth radio for optimal power management and performance.”
In 2006, the Bluetooth SIG announced the selection of the WiMedia Alliance brand of ultra wideband technology as a high speed channel for Bluetooth technology. This development work continues between the two organizations in advance of widespread ultra wideband technology adoption – expected to be co-located in many Bluetooth devices. In the meantime, however, the SIG will make use of IEEE 802.11, a technology already present in many of the devices demanding greater speeds.
This two-phased roadmap for higher speeds will allow for a steady evolution in Bluetooth devices utilizing the presence of 802.11 today while continuing preparations for the presence of ultra wideband in the near future. “We’re committed to speedy wireless personal area network connections and we’ll always be looking for the best near term and long term way to accomplish that,” adds Foley. “The greatness of a generic alternate radio architecture being developed is that it’s adaptable.”
With the availability of high speed Bluetooth technology, device users can expect to move their entertainment data between their own devices and the trusted devices of friends, without the need for cables and wires. Some applications consumers will experience include:
Wirelessly bulk synchronize music libraries between PC and MP3 player Bulk download photos to a printer or PC Send video files from camera or phone to computer or televisionMeanwhile, Bluetooth devices will continue to offer the well known, low power and secure connections that make up the nearly 2 billion products already on the market. The core specification enabling the Alternate MAC/PHY is expected to be published to members in mid-2009 with work already well underway.
“The Bluetooth SIG is taking a logical step by applying Bluetooth protocols over an existing 802.11 radio to achieve efficient transfers of high data throughput applications," said Flint Pulskamp, wireless and mobile analyst at IDC. "Since Bluetooth and 802.11 already have significant traction in mobile devices, this coupled solution could prove to be an efficient interim solution, as the Bluetooth SIG continues to develop UWB for the future."

2008-02-13T18:03:00.000-08:00

Bluetooth Basics

Bluetooth is a standard developed by a group of electronics manufacturers that allows any sort of electronic equipment -- from computers and cell phones to keyboards and headphones -- to make its own connections, without wires, cables or any direct action from a user. Bluetooth is intended to be a standard that works at two levels:

• It provides agreement at the physical level -- Bluetooth is a radio-frequency standard.

• It also provides agreement at the next level up, where products have to agree on when bits are sent, how many will be sent at a time and how the parties in a conversation can be sure that the message received is the same as the message sent. The companies belonging to the Bluetooth Special Interest Group, and there are more than 1,000 of them, want to let Bluetooth's radio communications take the place of wires for connecting peripherals, telephones and computers. There are already a couple of ways to get around using wires. One is to carry information between components via beams of light in the infrared spectrum. Infrared refers to light waves of a lower frequency than human eyes can receive and interpret. Infrared is used in most television remote control systems, and with a standard called IrDA (Infrared Data Association) it's used to connect some computers with peripheral devices. For most of these computer and entertainment purposes, infrared is used in a digital mode -- the signal is pulsed on and off very quickly to send data from one point to another. Infrared communications are fairly reliable and don't cost very much to build into a device, but there are a couple of drawbacks. First, infrared is a "line of sight" technology. For example, you have to point the remote control at the television or DVD player to make things happen. The second drawback is that infrared is almost always a "one to one" technology. You can send data between your desktop computer and your laptop computer, but not your laptop computer and your PDA at the same time. These two qualities of infrared are actually advantageous in some regards. Because infrared transmitters and receivers have to be lined up with each other, interference between devices is uncommon. The one-to-one nature of infrared communications is useful in that you can make sure a message goes only to the intended recipient, even in a room full of infrared receivers. The second alternative to wires, cable synchronizing, is a little more troublesome than infrared. If you have a Palm Pilot, a Windows CE device or a Pocket PC, you know about synchronizing data. In synchronizing, you attach the PDA to your computer (usually with a cable), press a button and make sure that the data on the PDA and the data on the computer match. It's a technique that makes the PDA a valuable tool for many people, but synchronizing the PDA with the computer and making sure you have the correct cable or cradle to connect the two can be a real hassle.

2008-02-13T18:00:00.000-08:00

Bluetooth

Bluetooth is intended to get around the problems that come with both infrared and cable synchronizing systems. The hardware vendors, which include Siemens, Intel, Toshiba, Motorola and Ericsson, have developed a specification for a very small radio module to be built into computer, telephone and entertainment equipment. From the user's point of view, there are three important features to Bluetooth:

• It's wireless. When you travel, you don't have to worry about keeping track of a briefcase full of cables to attach all of your components, and you can design your office without wondering where all the wires will go.

• It's inexpensive.

• You don't have to think about it. Bluetooth doesn't require you to do anything special to make it work. The devices find one another and strike up a conversation without any user input at all. Bluetooth communicates on a frequency of 2.45 gigahertz, which has been set aside by international agreement for the use of industrial, scientific and medical devices (ISM). A number of devices that you may already use take advantage of this same radio-frequency band. Baby monitors, garage-door openers and the newest generation of cordless phones all make use of frequencies in the ISM band. Making sure that Bluetooth and these other devices don't interfere with one another has been a crucial part of the design process.

2008-02-13T17:54:00.000-08:00

Avoiding

InterferenceOne of the ways Bluetooth devices avoid interfering with other systems is by sending out very weak signals of 1 milliwatt. By comparison, the most powerful cell phones can transmit a signal of 3 watts. The low power limits the range of a Bluetooth device to about 10 meters, cutting the chances of interference between your computer system and your portable telephone or television. Even with the low power, the walls in your house won't stop a Bluetooth signal, making the standard useful for controlling several devices in different rooms. With many different Bluetooth devices in a room, you might think they'd interfere with one another, but it's unlikely that several devices will be on the same frequency at the same time, because Bluetooth uses a technique called spread-spectrum frequency hopping. In this technique, a device will use 79 individual, randomly chosen frequencies within a designated range, changing from one to another on a regular basis. In the case of Bluetooth, the transmitters change frequencies 1,600 times every second, meaning that more devices can make full use of a limited slice of the radio spectrum. Since every Bluetooth transmitter uses spread-spectrum transmitting automatically, it’s unlikely that two transmitters will be on the same frequency at the same time. This same technique minimizes the risk that portable phones or baby monitors will disrupt Bluetooth devices, since any interference on a particular frequency will last only a tiny fraction of a second. When Bluetooth-capable devices come within range of one another, an electronic conversation takes place to determine whether they have data to share or whether one needs to control the other. The user doesn't have to press a button or give a command -- the electronic conversation happens automatically. Once the conversation has occurred, the devices -- whether they're part of a computer system or a stereo -- form a network. Bluetooth systems create a personal-area network (PAN), or piconet, that may fill a room or may encompass no more distance than that between the cell phone on a belt-clip and the headset on your head. Once a piconet is established, the members randomly hop frequencies in unison so they stay in touch with one another and avoid other piconets that may be operating in the same room.

2008-02-13T17:52:00.000-08:00

An Example

Let’s take a look at how the Bluetooth frequency hopping and personal-area network keep systems from becoming confused. Let’s say you’ve got a typical modern living room with the typical modern stuff inside. There’s an entertainment system with a stereo, a DVD player, a satellite TV receiver and a television; there's a cordless telephone and a personal computer. Each of these systems uses Bluetooth, and each forms its own piconet to talk between main unit and peripheral. The cordless telephone has one Bluetooth transmitter in the base and another in the handset. The manufacturer has programmed each unit with an address that falls into a range of addresses it has established for a particular type of device. When the base is first turned on, it sends radio signals asking for a response from any units with an address in a particular range. Since the handset has an address in the range, it responds, and a tiny network is formed. Now, even if one of these devices should receive a signal from another system, it will ignore it since it’s not from within the network. The computer and entertainment system go through similar routines, establishing networks among addresses in ranges established by manufacturers. Once the networks are established, the systems begin talking among themselves. Each piconet hops randomly through the available frequencies, so all of the piconets are completely separated from one another. Now the living room has three separate networks established, each one made up of devices that know the address of transmitters it should listen to and the address of receivers it should talk to. Since each network is changing the frequency of its operation thousands of times a second, it’s unlikely that any two networks will be on the same frequency at the same time. If it turns out that they are, then the resulting confusion will only cover a tiny fraction of a second, and software designed to correct for such errors weeds out the confusing information and gets on with the network’s business. Most of the time, a network or communications method either works in one direction at a time, called half-duplex communication, or in both directions simultaneously, called full-duplex communication. A speakerphone that lets you either listen or talk, but not both, is an example of half-duplex communication, while a regular telephone handset is a full-duplex device. Because Bluetooth is designed to work in a number of different circumstances, it can be either half-duplex or full-duplex. The cordless telephone is an example of a use that will call for a full-duplex (two-way) link, and Bluetooth can send data at more than 64,000 bits per second in a full-duplex link -- a rate high enough to support several human voice conversations. If a particular use calls for a half-duplex link -- connecting to a computer printer, for example -- Bluetooth can transmit up to 721 kilobits per second (Kbps) in one direction, with 57.6 Kbps in the other. If the use calls for the same speed in both directions, a link with 432.6-Kbps capacity in each direction can be made.

2008-02-13T17:47:00.000-08:00

Specs

Here are some specification details from the Bluetooth Web site

• The devices in a piconet share a common communication data channel. The channel has a total capacity of 1 megabit per second (Mbps). Headers and handshaking information consume about 20 percent of this capacity.

In the United States and Europe, the frequency range is 2,400 to 2,483.5 MHz, with 79 1-MHz radio frequency (RF) channels. In practice, the range is 2,402 MHz to 2,480 MHz. In Japan, the frequency range is 2,472 to 2,497 MHz with 23 1-MHz RF channels.

• A data channel hops randomly 1,600 times per second between the 79 (or 23) RF channels. • Each channel is divided into time slots 625 microseconds long.

• A piconet has a master and up to seven slaves. The master transmits in even time slots, slaves in odd time slots.

• Packets can be up to five time slots wide.

• Data in a packet can be up to 2,745 bits in length.

• There are currently two types of data transfer between devices: SCO (synchronous connection oriented) and ACL (asynchronous connectionless).

• In a piconet, there can be up to three SCO links of 64,000 bits per second each. To avoid timing and collision problems, the SCO links use reserved slots set up by the master.

• Masters can support up to three SCO links with one, two or three slaves.

• Slots not reserved for SCO links can be used for ACL links.

• One master and slave can have a single ACL link.

• ACL is either point-to-point (master to one slave) or broadcast to all the slaves.

• ACL slaves can only transmit when requested by the master

How the Internet Works

2008-01-05T03:14:00.000-08:00

How the Internet Works

So what is "The Internet"? The Internet is a gigantic collection of millions of computers, all linked together on a computer network. The network allows all of the computers to communicate with one another. A home computer is usually linked to the Internet using a normal phone line and a modem that talks to an Internet Service Provider (ISP). A computer in a business or university has a Network Interface Card (NIC) that directly connects it to a Local Area Network (LAN) inside the business. The business then connects its LAN to an ISP using a high speed phone line like a T1 line. A T1 line can handle approximately 1.5 million bits per second, while a normal phone line using a modem can usually handle 30,000 to 50,000 bits per second.

ISPs then connect to larger ISPs, and the largest ISPs maintain fiber-optic "backbones" for an entire nation or region. Backbones around the world are connected through fiber-optic lines, undersea cables or satellite links (see this page for a nice backbone and connection diagram). In this way, every computer on the Internet is connected to every other computer on the Internet.

2008-01-05T03:00:00.000-08:00

Clients and Servers

In general, all of the machines on the Internet can be categorized as two types: servers and clients. Those machines that provide services (like Web servers or FTP servers) to other machines are servers. And the machines that are used to connect to those services are clients. When you connect to Yahoo at www.yahoo.com to read a page, Yahoo is providing a machine (probably a cluster of very large machines), for use on the Internet, to service your request. Yahoo is providing a server. Your machine, on the other hand, is probably providing no services to anyone else on the Internet. Therefore it is a user machine, also known as a client. It is possible and common for a machine to be both a server and a client, but for our purposes here you can think of most machines as one or the other.

A server machine may provide one or more services on the Internet. For example, a server machine might have software running on it that allows it to act as a Web server, an e-mail server and an FTP server. Clients that come to a server machine do so with a specific intent, so clients direct their requests to a specific software server running on the overall server machine. For example, if you are running a Web browser on your machine, it will most likely want to talk to the Web server on the server machine. Your telnet application will want to talk to the telnet server, your e-mail application will talk to the e-mail server, and so on...

How IP Addresses Work

2008-01-05T02:58:00.000-08:00

How IP Addresses Work

To keep all of these machines straight, each machine on the Internet is assigned a unique address called an IP Address. IP stands for Internet protocol, and these addresses are 32-bit numbers, normally expressed as 4 "octets" in a "dotted decimal number." A typical IP address looks like this:

216.27.61.137

The four numbers in an IP address are called octets, because they can have values between 0 and 255, which is 28 possibilities per octet.

Every machine on the Internet has a unique IP address. A server has a static IP address that does not change very often. A home machine that is dialing up through a modem often has an IP address that is assigned by the ISP when you dial in. That IP address is unique for your session -- it may be different the next time you dial in. This way, an ISP only needs one IP address for each modem it supports, rather than for each customer.

If you are working on a Windows machine, you can view a lot of the Internet information for your machine, including your current IP address and hostname, with the command IPCONFIG/ALL. On a UNIX machine, type nslookup at the command prompt, along with a machine name, like stuff.dewsoftoverseas.com -- e.g. "nslookup stuff.dewsoftoverseas.com" -- to display the IP address of the machine, and you can use the command hostname to learn the name of your machine. [For more information on IP addresses see IANA]

As far as the Internet's machines are concerned, an IP address is all you need to talk to a server. For example, in your browser you can type the URL http://216.27.61.137 and you will arrive at the machine that contains the Web server for Stuff.dewsoftoverseas.com. On some servers, the IP address alone is not sufficient, but on most large servers it is

How Name Servers Work

2008-01-05T02:53:00.000-08:00

How Name Servers Work

Because most people have trouble remembering the strings of numbers that make up IP addresses, and because IP addresses sometimes need to change, all servers on the Internet also have human-readable names, called domain names. For example, is a permanent, human-readable name. It is easier for most of us to remember than it is to remember 216.27.61.137.

The name stuff.dewsoftoverseas.com actually has 3 parts:

1. The host name ("www")
2. The domain name ("howstuffworks")
3. The top-level domain name ("com")

Domain names are managed by a company called Network Solutions. Network Solutions' primary job is to create the top-level domain names, and to guarantee that all names within a top-level domain are unique. Network Solutions also maintains contact information for each site and runs the "whois" database. The host name is created by the company hosting the domain. "www" is a very common host name, but many places now either omit it or replace it with a different host name that indicates a specific area of the site. For example, in encarta.msn.com, the domain name for Microsoft's Encarta encyclopedia, "encarta" is designated as the host name instead of "www."

The whois Command
On a UNIX machine, you can use the whois command to look up information about a domain name. You can do the same thing using the whois form at Network Solutions. If you type in a domain name, like "howstuffworks.com", it will return to you the registration information for that domain, including its IP address.
A set of servers called Domain Name Servers (DNS) maps the human-readable names to the IP addresses. These servers are simple databases that map names to IP addresses, and they are distributed all over the Internet. Most individual companies, ISPs and universities maintain small name servers to map host names to IP addresses. There are also central name servers that use data supplied by Network Solutions to map domain names to IP addresses.

If you type the URL http://stuff.dewsoftoverseas.com/web-server.htm into your browser, your browser extracts the name "stuff.dewsoftoverseas.com", passes it to a Domain Name Server, and the Domain Name Server returns the correct IP address for stuff.dewsoftoverseas.com. A number of name servers may be involved to get the right IP address. For example, in the case of stuff.dewsoftoverseas.com, the name server for the "com" top-level domain will know the IP address for the name server that knows host names, and a separate query to that name server, operated by HSW's ISP, may deliver the actual IP address for HSW's server machine.

On a UNIX machine you can access the same service using the nslookup command. Simply type a name like "stuff.dewsoftoverseas.com" into the command, and the command will query the name servers and deliver the corresponding IP address to you.

So here it is: The Internet is made up of millions of machines, each with a unique IP address. Many of these machines are server machines meaning that they provide services to other machines on the Internet. You have heard of many of these servers: e-mail servers, Web servers, FTP servers, Gopher servers and telnet servers, to name a few. All of these are provided by server machines.

How Ports Work

2008-01-05T02:51:00.000-08:00

How Ports Work

Any server machine makes its services available to the Internet using numbered ports, one for each service that is available on the server. For example, if a server machine is running a Web server and an FTP server, the Web server would typically be available on port 80, and the FTP server would be available on port 21. Clients connect to a service at a specific IP address and on a specific port number.

Each of the most well-known services is available at a "well-known port number." Here are some common port numbers:

* echo 7
* daytime 13
* qotd 17 (Quote of the Day)
* ftp 21
* telnet 23
* smtp 25 (Simple Mail Transfer, meaning email)
* time 37
* nameserver 42
* nicname 43 (Who Is)
* gopher 70
* finger 79
* WWW 80

If the server machine accepts connections on a port from the outside world, and if a firewall is not protecting the port, you can connect to the port from anywhere on the Internet and use the service. Note that there is nothing that forces, for example, a Web server to be on port 80. If you were to set up your own machine and load Web server software on it, you could put the Web server on port 918, or any other unused port, if you wanted to. Then, if your machine were known as xxx.yyy.com, someone on the Internet could connect to your server with the URL http://xxx.yyy.com:918. The ":918" explicitly specifies the port number, and would have to be included for someone to reach your server. When no port is specified, the browser simply assumes that the server is using the well-known port 80.

How Protocols Work

2008-01-05T02:48:00.000-08:00

How Protocols Work

Once a client has connected to a service on a particular port, it accesses the service using a specific protocol. The protocol is the pre-defined way that someone who wants to use a service talks with that service. The "someone" could be a person, but more often it is a computer program like a Web browser. Protocols are often text, and simply describe how the client and server will have their conversation. Perhaps the simplest protocol is the daytime protocol. If you connect to port 13 on a machine that supports a daytime server, the server will send you its impression of the current date and time and then close the connection. The protocol is, "If you connect to me, I will send you the date and time and then disconnect." Most UNIX machines support this server. If you would like to try it out, you can connect to one with the telnet application. In UNIX the session would look like this:

On a Windows machine, you can access this server by typing "telnet web67.ntx.net 13" at the MSDOS prompt.
In this example, web67.ntx.net is the server's UNIX machine, and 13 is the port number for the daytime service. The telnet application connects to port 13 (telnet naturally connects to port 23, but you can direct it to connect to any port), then the server sends the date and time and disconnects. Most versions of telnet allow you to specify a port number, so you can try this using whatever version of telnet you have available on your machine.
Most protocols are more involved than daytime and are specified in Request for Comment (RFC) documents that are publicly available (for a nice archive of all RFCs). Every Web server on the Internet conforms to the HTTP protocol, summarized nicely in this article. The most basic form of the protocol understood by an HTTP server involves just one command: GET. If you connect to a server that understands the HTTP protocol and tell it to "GET filename", the server will respond by sending you the contents of the named file and then disconnecting. Here's a typical session:
In the original HTTP protocol, all you would have sent was the actual filename like "/" or "/web-server.htm". The protocol was later modified to handle the sending of the complete URL. This has allowed companies that host virtual domains, where many domains live on a single machine, to use one IP address for all of the domains they host. It turns out that hundreds of domains are hosted on 216.27.61.137 -- HSW's IP address.

Putting It All Together

2008-01-05T02:37:00.000-08:00

Putting It All Together

Now you know a tremendous amount about the Internet. You know that when you type a URL into a browser, the following steps occur:

* The browser breaks the URL into 3 parts:
1. The protocol ("http")
2. The server name ("stuff.dewsoftoverseas.com")
3. The file name ("web-server.htm")
* The browser communicates with a name server to translate the server name, "stuff.dewsoftoverseas.com", into an IP Address, which it uses to connect to that server machine.
* The browser then forms a connection to the Web server at that IP address on port 80.
* Following the HTTP protocol, the browser sends a GET request to the server, asking for the file "http://stuff.dewsoftoverseas.com/web-server.htm". [Note that cookies may be sent from browser to server with the GET request -- see How Cookies Work for details.]
* The server sends the HTML text for the Web page to the browser. [Note that cookies may also be sent from server to browser, in the header for the page -- see How Cookies Work for details.]
* The browser reads the HTML tags, and formats the page onto your screen.

How a Web Server Works

2008-01-05T02:35:00.000-08:00

How a Web Server Works

You can see from this description that a Web server can be a pretty simple piece of software. It takes the file name sent in with the GET command, retrieves that file and sends it down the wire to the browser. Even if you take into account all of the code to handle the ports and port connections, you could easily create a C program that implements a simple Web server in less than 500 lines of code. Obviously, a full-blown enterprise-level Web server is more involved, but the basics are very simple.

Most servers add some level of security to the serving process. For example, if you have ever gone to a Web page and had the browser pop up a dialog box asking for your name and password, you have encountered a password-protected page. The server lets the owner of the page maintain a list of names and passwords for those people who are allowed to access the page; the server lets only those people who know the proper password to see the page. More advanced servers add further security to allow an encrypted connection between server and browser, so that sensitive information like credit card numbers can be sent on the Internet.

That's really all there is to a Web server that delivers standard "static" pages. "Static" pages are those that do not change unless the creator edits the page.

But what about the web pages that are "dynamic"? For example:

* Any guest book allows you to enter a message in an HTML form, and the next time the guest book is viewed, the page will contain the new entry.
* The whois form at Network Solutions allows you to enter a domain name on a form, and the page returned is different depending on the domain name entered.
* Any search engine lets you enter keywords on an HTML form, and then it dynamically creates a page based on the keywords you enter.

In all of these cases, the Web server is not simply "looking up a file." It is actually processing information and generating a page based on the specifics of the query. In almost all cases, the Web server is using something called CGI scripts to accomplish this feat. CGI scripts are a topic unto themselves, and are described in the HSW article titled How CGI Scripts Work.

History

2007-12-04T19:42:00.000-08:00

History

Wi-Fi uses both single carrier direct-sequence spread spectrum radio technology (part of the larger family of spread spectrum systems) and multi-carrier OFDM (Orthogonal Frequency Division Multiplexing) radio technology. These regulations then enabled the development of Wi-Fi, its onetime competitor HomeRF, and Bluetooth.
Unlicensed spread spectrum was first made available by the Federal Communications Commission in 1985 and these FCC regulations were later copied with some changes in many other countries enabling use of this technology in all major countries.[11] The FCC action was proposed by Michael Marcus of the FCC staff in 1980 and the subsequent regulatory action took 5 more years. It was part of a broader proposal to allow civil use of spread spectrum technology and was opposed at the time by main stream equipment manufacturers and many radio system operators.
The precursor to Wi-Fi was invented in 1991 by NCR Corporation/AT&T (later Lucent & Agere Systems) in Nieuwegein, the Netherlands. It was initially intended for cashier systems; the first wireless products were brought on the market under the name WaveLAN with speeds of 1 Mbit/s to 2 Mbit/s. Vic Hayes, who held the chair of IEEE 802.11 for 10 years and has been named the 'father of Wi-Fi,' was involved in designing standards such as IEEE 802.11b, and 802.11a.

WI-FI

2007-12-04T19:41:00.000-08:00

WI-FI

Wi-Fi (pronounced wye-fye, IPA: /ˈwaɪfaɪ/) is a wireless technology brand owned by the Wi-Fi Alliance intended to improve the interoperability of wireless local area network products based on the IEEE 802.11 standards. Common applications for Wi-Fi include Internet and VoIP phone access, gaming, and network connectivity for consumer electronics such as televisions, DVD players, and digital cameras.
The Wi-Fi Alliance is a consortium of separate and independent companies agreeing to a set of common interoperable products based on the family of IEEE 802.11 standards.[1]
The Wi-Fi Alliance certifies products via a set of established test procedures to establish interoperability. Those manufacturers that are members of Wi-Fi Alliance whose products pass these interoperability tests can mark their products and product packaging with the Wi-Fi logo.[2]
Wi-Fi technologies have gone through several generations since their inception in 1997. Wi-Fi is supported to different extents under Microsoft Windows, Apple Macintosh and open source Unix and Linux operating systems.

Uses

2007-12-04T19:40:00.001-08:00

Uses

A Wi-Fi enabled device such as a PC, game console, cell phone, MP3 player or PDA can connect to the Internet when within range of a wireless network connected to the Internet. The area covered by one or more interconnected access points is called a hotspot. Hotspots can cover as little as a single room with wireless-opaque walls or as much as many square miles covered by overlapping access points. Wi-Fi has been used to create a mesh networks, for example, in the City of London.[3] Both architectures are used in community networks.[citation needed]
Wi-Fi also allows connectivity in peer-to-peer (wireless ad-hoc network) mode, which enables devices to connect directly with each other. This connectivity mode is useful in consumer electronics and gaming applications.
When the technology was first commercialized there were many problems because consumers could not be sure that products from different vendors would work together. The Wi-Fi Alliance began as a community to solve this issue so as to address the needs of the end user and allow the technology to mature. The Alliance created the branding Wi-Fi CERTIFIED to show consumers that products are interoperable with other products displaying the same branding.
Many consumer devices use Wi-Fi. Amongst others, personal computers can network to each other and connect to the Internet, mobile computers can connect to the Internet from any Wi-Fi hotspot, and digital cameras can transfer images wirelessly.
Routers which incorporate a DSL or cable modem and a Wi-Fi access point are often used in homes and other premises, and provide Internet access and internetworking to all devices connected wirelessly or by cable into them. Devices supporting Wi-Fi can also be connected in ad-hoc mode for client-to-client connections without a router.
Business and industrial Wi-Fi is widespread as of 2007. In business environments, increasing the number of Wi-Fi access points provides redundancy, support for fast roaming and increased overall network capacity by using more channels or creating smaller cells. Wi-Fi enables wireless voice applications (VoWLAN or WVOIP). Over the years, Wi-Fi implementations have moved toward 'thin' access points, with more of the network intelligence housed in a centralized network appliance, relegating individual Access Points to be simply 'dumb' radios. Outdoor applications may utilize true mesh topologies. As of 2007 Wi-Fi installations can provide a secure computer networking gateway, firewall, DHCP server, intrusion detection system, and other functions.
In addition to restricted use in homes and offices, Wi-Fi is publicly available at Wi-Fi hotspots provided either free of charge or to subscribers to various providers. Free hotspots are often provided by businesses such as hotels, restaurants, and airports who offer the service to attract or assist clients. Sometimes free Wi-Fi is provided by enthusiasts, or by organizations or authorities who wish to promote business in their area. Metropolitan-wide WiFi (Mu-Fi) already has more than 300 projects in process.[4]

Advantages of Wi-Fi

2007-12-04T19:38:00.000-08:00

Advantages of Wi-Fi

Wi-Fi allows LANs to be deployed without cabling for client devices, typically reducing the costs of network deployment and expansion. Spaces where cables cannot be run, such as outdoor areas and historical buildings, can host wireless LANs.
As of 2007 wireless network adapters are built into most modern laptops. The price of chipsets for Wi-Fi continues to drop, making it an economical networking option included in ever more devices. Wi-Fi has become widespread in corporate infrastructures, which also helps with the deployment of RFID technology that can piggyback on Wi-Fi.[5]
Different competitive brands of access points and client network interfaces are inter-operable at a basic level of service. Products designated as "Wi-Fi Certified" by the Wi-Fi Alliance are backwards inter-operable. Wi-Fi is a global set of standards. Unlike mobile telephones, any standard Wi-Fi device will work anywhere in the world.
Wi-Fi is widely available in more than 250,000 public hotspots and tens of millions of homes and corporate and university campuses worldwide. WPA is not easily cracked if strong passwords are used and WPA2 encryption has no known weaknesses. New protocols for Quality of Service (WMM) make Wi-Fi more suitable for latency-sensitive applications (such as voice and video), and power saving mechanisms (WMM Power Save) improve battery operation.

Ramon Magasaysay Award for 2007, has made us Nepalis proud

2007-11-05T20:52:00.000-08:00

Ramon Magasaysay Award for 2007, has made us Nepalis proud

Mahabir Pun, the recipient of the prestigious Ramon Magasaysay Award for 2007, has made us Nepalis proud. I salute him. I also look forward to the day when there will be a thousand more Mahabir Puns who will come up with such exemplary deeds.

I had the good fortune of interacting with Pun last year when we were in a workshop making midterm review presentations on various projects funded under the World Bank assisted Poverty Alleviation Program. Pun was there to make a presentation on his wireless internet system, and I was there to make a presentation on Solar Tuki.

While talking with him at that time, it became clear that the wireless internet system and network he was setting up in the villages in Myagdi was actually against the telecom laws in Nepal at that time. The parabolic antennas and other hardware needed for the wireless internet system had entered Nepal as accompanied luggage items of Pun's numerous Nepali and foreign well-wishers and volunteers. These items could not have entered Nepal legally as Pun did not have the license to either import the wireless hardware, or install and operate the wireless internet system. Unlike in other developed countries, the frequency for operating the wireless network was neither free for use nor available in the public domain. So Pun had to use the wireless network without proper authorisation.

Pun, the brave visionary, was so highly motivated and driven to improve the lives of his village folks in Myagdi that he worked selflessly and tirelessly to establish internet access to the villages even though he knew that he was breaking the law. He got away without being punished probably because the arm of the law enforcement agency was either too short or did not feel it worth the trouble to reach out for him in Myagdi. If Pun had waited for the "proper" procedures to be set in place and for the full cooperation of the government and its agencies, he probably would still be waiting endlessly, and the villages in Myagdi would still be as isolated from the worldwide web and the global village.

HISTORY

2007-11-05T20:26:00.000-08:00

History
The term "wireless" came into public use to refer to a radio receiver or transceiver (a dual purpose receiver and transmitter device), establishing its usage in the field of wireless telegraphy early on; now the term is used to describe modern wireless connections such as in cellular networks and wireless broadband Internet. It is also used in a general sense to refer to any type of operation that is implemented without the use of wires, such as "wireless remote control", "wireless energy transfer", etc. regardless of the specific technology (e.g., radio, infrared, ultrasonic, etc.) that is used to accomplish the operation.
Early wireless work
David E. Hughes, eight years before Hertz's experiments, induced electromagnetic waves in a signalling system. Hughes transmitted Morse code by an induction apparatus. In 1878, Hughes's induction transmission method utilized a "clockwork transmitter" to transmit signals. In 1885, T. A. Edison uses a vibrator magnet for induction transmission. In 1888, Edison deploys a system of signalling on the Lehigh Valley Railroad. In 1891, Edison attains the wireless patent for this method using inductance (U.S. Patent 465,971 ).
In the history of wireless technology, the demonstration of the theory of electromagnetic waves by Heinrich Rudolf Hertz in 1888 was important.[3][4] The theory of electromagnetic waves were predicted from the research of James Clerk Maxwell and Michael Faraday. Hertz demonstrated that electromagnetic waves could be transmitted and caused to travel through space at straight lines and that they were able to be received by an experimental apparatus.[3][4] The experiments were not followed up by Hertz and the practical applications of the wireless communication and remote control technology would be implemented by Nikola Tesla.
The electromagnetic spectrum
Light, colors, AM and FM radio, and many popular electronic devices all work on the electromagnetic spectrum. In the US the frequencies that are available for use for communication are treated as a public resource and are regulated by the Federal Communications Commission (FCC). This determines which frequency ranges can be used for what purpose and by whom. In the absence of such control, chaos might result if, for example, airlines didn't have specific frequencies to work under and a ham radio operator was interfering with the pilot's ability to land an airplane. Wireless communication spans the spectrum from 9 kHz to 300 GHz.

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Applications of wireless technology

2007-11-05T20:12:00.000-08:00

Applications of wireless technology

Security systems
Wireless technology may supplement or replace hard wired implementations in security systems for homes or office buildings. The operations that are required (e.g., detecting whether a door or window is open or closed) may be implemented with the use of hard wired sensors or they may be implemented with the use of wireless sensors which are also equipped with a wireless transmitter (e.g., infrared, radio frequency, etc.) to transmit the information concerning the current state of the door or window.
Television remote control
Some televisions were previously manufactured with hard wired remote controls which plugged in to a receptacle or jack in the television whereas more modern televisions use wireless (generally infrared) remote control units.
Cellular telephones
Perhaps the best known example of wireless technology is the cellular telephone. These instruments use radio waves to enable the operator to make phone calls from many locations world-wide. They can be used anywhere that there is a cellular telephone site to house the equipment that is required to transmit and receive the signal that is used to transfer both voice and data to and from these instruments. (For more information see mobile phones).
Wireless communication
Wireless is a term used to describe telecommunications in which electromagnetic waves (rather than some form of wire) carry the signal over part or the entire communication path. Common examples of wireless equipment in use today include:
• Cellular phones and pagers: provide connectivity for portable and mobile applications, both personal and business.
• Global Positioning System (GPS): allows drivers of cars and trucks, captains of boats and ships, and pilots of aircraft to ascertain their location anywhere on earth.
• Cordless computer peripherals: the cordless mouse is a common example; keyboards and printers can also be linked to a computer via wireless.
• Cordless telephone sets: these are limited-range devices, not to be confused with cell phones.
• Satellite television: allows viewers in almost any location to select from hundreds of channels.
Wireless networking is used to meet a variety of needs. Perhaps the most common use is to connect laptop users who travel from location to location. Another common use is for mobile networks that connect via satellite. A wireless transmission method is a logical choice to network a LAN segment that must frequently change locations. The following situations justify the use of wireless technology:
• To span a distance beyond the capabilities of typical cabling,
• To avoid obstacles such as physical structures, EMI, or RFI,
• To provide a backup communications link in case of normal network failure,
• To link portable or temporary workstations,
• To overcome situations where normal cabling is difficult or financially impractical, or
• To remotely connect mobile users or networks

2007-05-25T08:59:00.000-07:00

Wireless Internet
The wireless Internet is defined by access to the Internet on any wireless or mobile device. The wireless Internet encapsulates a variety of wireless Internet access alternatives including wide-area networks (WANs), wireless local area networks (WLANs), and wireless personal area networks (PANs).
Wide area networks - WANs
Wide-area networks (WANs) are essentially the cellular networks maintained by major carriers, including in the U.S. Verizon Wireless, Sprint PCS, and Cingular Wireless. Wireless internet access over wide-area networks is still slow and is conducted mostly through what are currently known as 2G or 2.5G wireless networks. Data speeds are slow (averages run between 20 and 60 Kbps), but coverage is nearly ubiquitous. 3G, the next generation of wireless wide-area networks, promise greater data speeds (up to 384 Kbps) with the same level of nearly ubiquitous coverage as current wireless networks.
Wireless local area networks - WLANs
Wireless local area networks (WLANs) are smaller-scale wireless networks with a typical radius of several hundred feet. The most prevalent form of Wireless Local Area Network technology is called WiFi, which includes a host of standards including 802.11a, 802.11b, and 802.11g. Wireless Internet via WiFi offers blazing fast data speeds (11Mbps at the low end with 802.11b and 54 Mbps at the high end for 802.11a and 802.11g). While WiFi technology does not offer the degree of ubiquity as wide area networks, the WLAN's data speeds and relatively cheap costs have spurred it ahead in the popular market as a wireless internet solution.

2007-05-25T08:54:00.000-07:00

The Cellular Explosion
Probably the most important factor in the birth of wireless Internet has been the proliferation of digital cell phones in the last few years. The expanding network of digital cellular and personal communication services (PCS) has created a solid foundation for wireless Internet services. It is estimated that there are more than 50 million Web-enabled cell phones in use. In 1997, Nokia, Motorola, Ericsson and Phone.com came together to create the WAP because they believed that a universal standard is critical to the successful implementation of wireless Internet. Since then, more than 350 companies have joined them in the WAP Forum.

Making a Web site accessible through a wireless device is quite a challenge. So far, only a small portion of the more than a billion Web sites, about 1.5 million, provide any wireless Internet content. As the use of WAP-enabled devices grows, you can expect that many more Web sites will be interested in creating wireless content.
WAP is designed to work on any of the existing wireless services, using standards such as:
Short Message Service (SMS)
Circuit Switched Data (CSD)
General Packet Radio Service (GPRS)
Unstructured Supplementary Services Data (USSD) For more information on these services, check out this page

2007-05-25T08:52:00.000-07:00

Wireless Markup Language
WAP uses Wireless Markup Language (WML), which includes the Handheld Device Markup Language (HDML) developed by Phone.com. WML can also trace its roots to eXtensible Markup Language (XML). A markup language is a way of adding information to your content that tells the device receiving the content what to do with it. The best known markup language is Hyper Text Markup Language (HTML). Unlike HTML, WML is considered a meta language. Basically, this means that in addition to providing predefined tags, WML lets you design your own markup language components. WAP also allows the use of standard Internet protocols such as UDP, IP and XML.
There are three main reasons why wireless Internet needs a different protocol:
Transfer speed
Size and readability
Navigation
Most cell phones and Web-enabled PDAs have data transfer rates of 14.4 Kbps or less. Compare this to a typical 56 Kbps modem, a cable modem or a DSL connection. Most Web pages today are full of graphics that would take an unbearably long time to download at 14.4 Kbps. Wireless Internet content is typically text-based in order to solve this problem.

2007-05-25T08:50:00.000-07:00

Wireless Application Protocol
Here's what happens when you access a Web site using a WAP-enabled device:
You turn on the device and open the minibrowser.
The device sends out a radio signal searching for service.
A connection is made with your service provider.
You select a Web site that you wish to view.
A request is sent to a Gateway Server using WAP.
The Gateway Server retrieves the information via HTTP from the Web site.
The Gateway Server encodes the HTTP data as WML.
The WML-encoded data is sent to your device.
You see the wireless Internet version of the Web page you selected.
To create wireless Internet content, a Web site creates special text-only or low-graphics versions of the site. The data is sent in HTTP form by a Web server to a WAP gateway. This system includes the WAP encoder, script compiler and protocol adapters to convert the HTTP information to WML. The gateway then sends the converted data to the WAP client on your wireless device.
What happens between the gateway and the client relies on features of different parts of the WAP protocol stack. Let's take a look at each part of the stack:

2007-05-25T08:47:00.000-07:00

WAP protocol stack
WAE - The Wireless Application Environment holds the tools that wireless Internet content developers use. These include WML and WMLScript, which is a scripting language used in conjunction with WML. It functions much like Javascript.
WSP - The Wireless Session Protocol determines whether a session between the device and the network will be connection-oriented or connectionless. What this is basically talking about is whether or not the device needs to talk back and forth with the network during a session. A connection-oriented session means that data will be passed both ways between the device and the network. WSP would then send the packet to the Wireless Transaction Protocol layer. If the session is connectionless, commonly used when information is being broadcast or streamed from the network to the device, then WSP redirects the packet to the Wireless Datagram Protocol layer.
WTP - The Wireless Transaction Protocol acts like a traffic cop, keeping the data flowing in a logical and smooth manner. It also determines how to classify each transaction request:
Reliable two-way
Reliable one-way
Unreliable one-way
The WSP and WTP layers correspond to HyperText Transfer Protocol (HTTP) in the TCP/IP protocol suite.
WTLS - Wireless Transport Layer Security provides many of the same security features found in the Transport Layer Security (TLS) part of TCP/IP. It checks data integrity, provides encryption and performs client and server authentication.
WDP - The Wireless Datagram Protocol works in conjunction with the network carrier layer. WDP makes it easy to adapt WAP to a variety of bearers because all that needs to change is the information maintained at this level.
Network carriers - Also called bearers, these can be any of the existing technologies that wireless providers use, as long as information is provided at the WDP level to interface WAP with the bearer.
Once the information is received by the WAP client, it is passed to the minibrowser. This is a tiny application built into the wireless device that provides the interface between the user and the wireless Internet. Here's a look at the start page of a typical minibrowser:

2007-05-25T08:29:00.000-07:00

The minibrowser offers streamlined functionality

The minibrowser does not offer anything more than basic navigation. Wireless Internet is still a long way from being a true alternative to the normal Internet. It is really positioned right now for people who need the ability to connect no matter where they are. The WAP Forum is continually working on the specifications of the WAP standard to ensure that it evolves in a timely and useful manner. For more information on wireless Internet and related topics, check out the links on the next page