Working of Routing Algorithms

How Routing Algorithms Work

Think you know how routers work? These devices use intricate formulas to figure out exactly where to send a packet and how to get it there.

If you have read the article How Routers Work, then you know that a router is used to manage network traffic and find the best route for sending packets. But have you ever thought about how routers do this? Routers need to have some information about network status in order to make decisions regarding how and where to send packets. But how do they gather this information?


In this article, we'll find out precisely what information is used by routers in determining where to send a packet.

The Basics

Routers use routing algorithms to find the best route to a destination. When we say "best route," we consider parameters like the number of hops (the trip a packet takes from one router or intermediate point to another in the network), time delay and communication cost of packet transmission.




Based on how routers gather information about the structure of a network and their analysis of information to specify the best route, we have two major routing algorithms: global routing algorithms and decentralized routing algorithms. In decentralized routing algorithms, each router has information about the routers it is directly connected to -- it doesn't know about every router in the network. These algorithms are also known as DV (distance vector) algorithms. In global routing algorithms, every router has complete information about all other routers in the network and the traffic status of the network. These algorithms are also known as LS (link state) algorithms. We'll discuss LS algorithms in the next .

LS Algorithms

In LS algorithms, every router has to follow these steps:

1. Identify the routers that are physically connected to them and get their IP addresses
   When a router starts working, it first sends a "HELLO" packet over network. Each router that receives this packet replies with a message that contains its IP address.
   


2. Measure the delay time (or any other important parameters of the network, such as average traffic) for neighbor routers
   In order to do that, routers send echo packets over the network. Every router that receives these packets replies with an echo reply packet. By dividing round trip time by 2, routers can count the delay time. (Round trip time is a measure of the current delay on a network, found by timing a packet bounced off some remote host.) Note that this time includes both transmission and processing times -- the time it takes the packets to reach the destination and the time it takes the receiver to process it and reply.
   


3. Broadcast its information over the network for other routers and receive the other routers' information
   In this step, all routers share their knowledge and broadcast their information to each other. In this way, every router can know the structure and status of the network.
   


4. Using an appropriate algorithm, identify the best route between two nodes of the network
   In this step, routers choose the best route to every node. They do this using an algorithm, such as the Dijkstra shortest path algorithm. In this algorithm, a router, based on information that has been collected from other routers, builds a graph of the network. This graph shows the location of routers in the network and their links to each other. Every link is labeled with a number called the weight or cost. This number is a function of delay time, average traffic, and sometimes simply the number of hops between nodes. For example, if there are two links between a node and a destination, the router chooses the link with the lowest weight.

The Dijkstra algorithm goes through these steps:

1. The router builds a graph of the network and identifies source and destination nodes, as V1 and V2 for example. Then it builds a matrix, called the "adjacency matrix." In this matrix, a coordinate indicates weight. For example, [i, j] is the weight of a link between Vi and Vj. If there is no direct link between Vi and Vj, this weight is identified as "infinity."
   


2. The router builds a status record set for every node on the network. The record contains three fields:
   
   
   • Predecessor field - The first field shows the previous node.
   
   
   • Length field - The second field shows the sum of the weights from the source to that node.
   
   
   • Label field - The last field shows the status of node. Each node can have one status mode: "permanent" or "tentative."
   
   
   
   
   
   


3. The router initializes the parameters of the status record set (for all nodes) and sets their length to "infinity" and their label to "tentative."
   


4. The router sets a T-node. For example, if V1 is to be the source T-node, the router changes V1's label to "permanent." When a label changes to "permanent," it never changes again. A T-node is an agent and nothing more.
   


5. The router updates the status record set for all tentative nodes that are directly linked to the source T-node.
   


6. The router looks at all of the tentative nodes and chooses the one whose weight to V1 is lowest. That node is then the destination T-node.
   


7. If this node is not V2 (the intended destination), the router goes back to step 5.
   


8. If this node is V2, the router extracts its previous node from the status record set and does this until it arrives at V1. This list of nodes shows the best route from V1 to V2.

These steps are shown below as a flowchart.



We will use this algorithm as an example on the next .

Example: Dijkstra Algorithm

Here we want to find the best route between A and E (see below). You can see that there are six possible routes between A and E (ABE, ACE, ABDE, ACDE, ABDCE, ACDBE), and it's obvious that ABDE is the best route because its weight is the lowest. But life is not always so easy, and there are some complicated cases in which we have to use algorithms to find the best route.

1. As you see in the image below, the source node (A) has been chosen as T-node, and so its label is permanent (we show permanent nodes with filled circles and T-nodes with the --> symbol).
   
   
   
   
   
   
   
   


2. In this step, you see that the status record set of tentative nodes directly linked to T-node (B, C) has been changed. Also, since B has less weight, it has been chosen as T-node and its label has changed to permanent (see below).
   
   
   
   
   
   
   


3. In this step, like in step 2, the status record set of tentative nodes that have a direct link to T-node (D, E), has been changed. Also, since D has less weight, it has been chosen as T-node and its label has changed to permanent (see below).
   
   
   
   
   
   
   


4. In this step, we don't have any tentative nodes, so we just identify the next T-node. Since E has the least weight, it has been chosen as T-node.
   
   
   
   
   
   
   
   


5. E is the destination, so we stop here.

We are at end! Now we have to identify the route. The previous node of E is D, and the previous node of D is B, and B's previous node is A. So the best route is ABDE. In this case, the total weigh is 4 (1+2+1).
Although this algorithm works well, it's so complicated that it may take a long time for routers to process it, and the efficiency of the network fails. Also, if a router gives the wrong information to other routers, all routing decisions will be ineffective. To understand this algorithm better, here is the source of program written by C:

#define MAX_NODES 1024 /* maximum number of nodes */ #define INFINITY 1000000000 /* a number larger than every maximum path */ int n,dist[MAX_NODES][MAX_NODES]; /*dist[I][j] is the distance from i to j */ void shortest_path(int s,int t,int path[ ]) {struct state { /* the path being worked on */ int predecessor ; /*previous node */ int length /*length from source to this node*/ enum {permanent, tentative} label /*label state*/ }state[MAX_NODES]; int I, k, min; struct state * p; for (p=&state[0];p < &state[n];p++){ /*initialize state*/ p->predecessor=-1 p->length=INFINITY p->label=tentative; } state[t].length=0; state[t].label=permanent ; k=t ; /*k is the initial working node */ do{ /* is the better path from k? */ for I=0; I < n; I++) /*this graph has n nodes */ if (dist[k][I] !=0 && state[I].label==tentative){ if (state[k].length+dist[k][I] < state[I].length){ state[I].predecessor=k; state[I].length=state[k].length + dist[k][I] } } /* Find the tentatively labeled node with the smallest label. */ k=0;min=INFINITY; for (I=0;I < n;I++) if(state[I].label==tentative && state[I].length < min)=state[I].length; k=I; } state[k].label=permanent }while (k!=s); /*Copy the path into output array*/ I=0;k=0 Do{path[I++]=k;k=state[k].predecessor;} while (k > =0); }

 

DV Algorithms

DV algorithms are also known as Bellman-Ford routing algorithms and Ford-Fulkerson routing algorithms. In these algorithms, every router has a routing table that shows it the best route for any destination. A typical graph and routing table for router J is shown below.

Destination	Weight	Line
A	8	A
B	20	A
C	28	I
D	20	H
E	17	I
F	30	I
G	18	H
H	12	H
I	10	I
J	0	---
K	6	K
L	15	K

A typical network graph and routing table for router J
As the table shows, if router J wants to get packets to router D, it should send them to router H. When packets arrive at router H, it checks its own table and decides how to send the packets to D.
In DV algorithms, each router has to follow these steps:

1. It counts the weight of the links directly connected to it and saves the information to its table.


2. In a specific period of time, it send its table to its neighbor routers (not to all routers) and receive the routing table of each of its neighbors.


3. Based on the information in its neighbors' routing tables, it updates its own.

One of the most important problems with DV algorithms is called "count to infinity." Let's examine this problem with an example: Imagine a network with a graph as shown below. As you see in this graph, there is only one link between A and the other parts of the network. Here you can see the graph and routing table of all nodes:

	A	B	C	D
A	0,-	1,A	2,B	3,C
B	1,B	0,-	2,C	3,D
C	2,B	1,C	0,-	1,C
D	3,B	2,C	1,D	0,-

Network graph and routing tables
Now imagine that the link between A and B is cut. At this time, B corrects its table. After a specific amount of time, routers exchange their tables, and so B receives C's routing table. Since C doesn't know what has happened to the link between A and B, it says that it has a link to A with the weight of 2 (1 for C to B, and 1 for B to A -- it doesn't know B has no link to A). B receives this table and thinks there is a separate link between C and A, so it corrects its table and changes infinity to 3 (1 for B to C, and 2 for C to A, as C said). Once again, routers exchange their tables. When C receives B's routing table, it sees that B has changed the weight of its link to A from 1 to 3, so C updates its table and changes the weight of the link to A to 4 (1 for C to B, and 3 for B to A, as B said).
This process loops until all nodes find out that the weight of link to A is infinity. This situation is shown in the table below. In this way, experts say DV algorithms have a slow convergence rate.

	B	C	D
Sum of weight to A after link cut	,A	2,B	3,C
Sum of weight to B after 1st updating	3,C	2,B	3,C
Sum of weight to A after 2nd updating	3,C	4,B	3,C
Sum of weight to A after 3rd updating	5,C	4,B	5,C
Sum of weight to A after 4th updating	5,C	6,B	5,C
Sum of weight to A after 5th updating	7,C	6,B	7,C
Sum of weight to A after nth updating	...	...	...

The "count to infinity" problem One way to solve this problem is for routers to send information only to the neighbors that are not exclusive links to the destination. For example, in this case, C shouldn't send any information to B about A, because B is the only way to A.

Hierarchical Routing

As you see, in both LS and DV algorithms, every router has to save some information about other routers. When the network size grows, the number of routers in the network increases. Consequently, the size of routing tables increases, as well, and routers can't handle network traffic as efficiently. We use hierarchical routing to overcome this problem. Let's examine this subject with an example:
We use DV algorithms to find best routes between nodes. In the situation depicted below, every node of the network has to save a routing table with 17 records. Here is a typical graph and routing table for A:

Destination	Line	Weight
A	---	---
B	B	1
C	C	1
D	B	2
E	B	3
F	B	3
G	B	4
H	B	5
I	C	5
J	C	6
K	C	5
L	C	4
M	C	4
N	C	3
O	C	4
P	C	2
Q	C	3

Network graph and A's routing table In hierarchical routing, routers are classified in groups known as regions. Each router has only the information about the routers in its own region and has no information about routers in other regions. So routers just save one record in their table for every other region. In this example, we have classified our network into five regions (see below).

Destination	Line	Weight
A	---	---
B	B	1
C	C	1
Region 2	B	2
Region 3	C	2
Region 4	C	3
Region 5	C	4

Hierarchical routing If A wants to send packets to any router in region 2 (D, E, F or G), it sends them to B, and so on. As you can see, in this type of routing, the tables can be summarized, so network efficiency improves. The above example shows two-level hierarchical routing. We can also use three- or four-level hierarchical routing.
In three-level hierarchical routing, the network is classified into a number of clusters. Each cluster is made up of a number of regions, and each region contains a number or routers. Hierarchical routing is widely used in Internet routing and makes use of several routing protocols.

Working of Firefox

How Firefox Works

Firefox is an alternative browser to Opera, Safari, Internet Explorer and other Web browsers.

­A Web browser is sort of like the tires on your car. You don't really give them much daily thought, but without them, you're not going anywhere. The second something goes wrong, you definitely notice.

Chances are, you're reading this article on a version of Microsoft's Internet Explorer. It's the browser that comes already installed on computers with Windows operating systems; most people use Windows, and many Windows users don't give a second thought to which browser they're using. In fact, some people aren't aware that they have an option at all.

Options are out there, however, and one of them has been steadily chipping away at Internet Explorer's dominance. It's called Firefox. From its origins as an offshoot of the once-popular Netscape browser, Firefox is building a growing legion of dedicated users who spread their enthusiasm by word of mouth

For a while, it seemed like Microsoft's Internet Explorer was going to dominate the browser market indefinitely. Its competitors included Netscape Navigator and the AOL Browser -- and it soundly beat both of them. When Firefox debuted, it faced an uphill battle to claim space in the market. But Firefox's popularity has grown since its debut, particularly among Web administrators and developers.

­The word is spreading quickly. On June 17, 2008, Firefox held an event called Download Day as it unveiled the final build of Firefox 3. The goal for the event was to encourage people to download the new browser and establish a record for the most downloads of a single application within a 24-hour period. The event was a success -- Firefox 3 is now in the Guinness Book of World Records for the application receiving the most downloads in a single day: 8,002,530 to be exact [source: Spread Firefox].

In this article, we'll find out what makes Firefox different, what it can do and what effect an open-source browser might have on the Internet landscape.

Firefox History

Popularity Contest According to W3Schools, an educational site focusing on Web tutorials, more than 47 percent of its visitors use the Firefox Web browser [source: W3 Schools]. Internet Explorer has dropped to second place with 39.3 percent split between IE 6, IE 7 and IE 8.

The origins of Firefox can be traced directly to Netscape, a compan­y whose Web browser, Netscape Navigator, was the dominant browser before Microsoft developed Internet Explorer. The internal company name for the browser was Mozilla. Eventually, Netscape released the source code for Navigator under an open source license, meaning anyone could see and use the code. A non-profit group was set up to direct the development of browsers using this code. This group became the Mozilla Foundation in 2003.

However, Firefox is not the browser the Mozilla group would have released if everything had gone as planned. Like Netscape Navigator before it, the Mozilla software was becoming bigger and bigger as more features were added in -- a problem in software development known as "feature creep" or "bloat." Enter Blake Ross, a computer enthusiast who first started helping out the Mozilla project as a hobby when he was 14. Instead of accepting feature creep, Ross decided to start developing his own Mozilla-based browser, focusing on a streamlined and simple version. Software developer Dave Hyatt also played a major role. Ross was joined by Ben Goodger in 2003, and development progressed rapidly from that point.

At first, the browser that would be known as Firefox was known as Phoenix. There were trademark problems, however, so the name was changed to Firebird. Another software company had a project known as Firebird, so the name changed again. Firefox was chosen because it was distinctive, and no one else was using it (although it turned out a European company did own the trademark to the word Firefox, and a deal was reached).

When Firefox was still in the beta stage (when a program hasn't been publicly released, but people can download and use it to help find and fix problems), it was already generating a healthy buzz among tech-savvy Web surfers. In just four months after the official release on Nov. 9, 2004, an estimated 23 million people downloaded Firefox. Web tracker OneStat.com reported on Nov. 22, 2004, that Internet Explorer's share of Web browser use had dropped five percent since May of that year. Firefox had a user percentage of 4.5 percent. Current estimates (as of September 2009) have Firefox's market share at nearly 20 percent [source: Net Applications].

Next, learn about the basics of Firefox and how to download it.

Firefox Basics

The easiest way to learn about Firefox is to go ahead and download it (it's free). You can find it at the official site: http://www.getfirefox.com. There you'll find the latest version of Firefox: Firefox 3.5. If you're hesitant to install and learn to use a new program, rest assured that Firefox looks and acts very similar to Internet Explorer and most other Web browsers. There's even a feature for IE users that lists the expressions with which you're familiar and tells you the corresponding Firefox names for those functions.

Firefox is an alternative browser to Internet Explorer and other web browsers.

At the top of the screen, you'll find the Awesome Bar (a space for typing in Web addresses), a small search panel and a row of buttons -- the typical tools for common Web-surfing activities. Forward, back, home, reload and stop can all be found in this basic setup. These buttons, like just about everything else in Firefox, are fully customizable. You can rearrange them, get rid of some of them or add new ones.

The Awesome Bar isn't just a place to type in Web site URLs. It's linked to your browsing library. If you visit a site containing information of firefox regularly, Firefox's Awesome Bar will learn and anticipate your browsing habits. As soon as you begin typing "how," the browser will pull up a list of sites you've visited that it thinks you want. You can just pick from the list in the drop-down menu and the browser will take you there directly. The Awesome Bar doesn't just track URLs, either. It also picks terms found in the sites you visit. So if you're looking for a site with a particular name, just start typing the name in the Awesome Bar, and there's a good chance that Firefox can help you track the site down.

Now, if Firefox is so similar to Internet Explorer, why bother switching? There are quite a few reasons, but the most important for many users is security.

Now That's Advertising In December 2004, a two-page ad ran in The New York Times promoting Firefox. The main text read: Are you fed up with your Web browser? You're not alone. We want you to know that there is an alternative. The sponsors of the ad were more than 10,000 Firefox fans who donated money to promote their favorite indie browser. The ad was intended to coincide with the release of Firefox 1.0 in November 2004, but publication was delayed -- it took until December to figure out how to squeeze the names of more than 10,000 underwriters into the spread.

There is much debate over the security of Web browsers, stemming mainly from Internet Explorer's vulnerability as a common target for hackers and virus writers. Microsoft regularly releases patches and updates to fix security holes in Internet Explorer that might allow someone to install malicious software or steal information from a computer. Early on, Firefox was considered safer than IE, but every program has its flaws. In fact, just five hours after Firefox 3 was released, a vulnerability was discovered in the browser's code [source: Gohring]. Internet Explorer is sitll a bigger target for hackers because more people use it, but as Firefox becomes more popular among Web browsers, that may change. See the Firefox Security section on the next page to learn more.

Now let's take a closer look at Firefox's features and see how they can be expanded.

Firefox Features

Firefox comes with a few useful features that set it apart from earlier versions of Internet Explorer -- so useful, in fact, that virtually every other browser, including Internet Explorer, Opera, Safari and Google Chrome, has also adopted them. One of the most noticeable is tabbed browsing. If you're browsing in Internet Explorer 6, and you want to visit a new Web site while keeping your current one open, you have to open a completely new browser window. Intensive Web surfing can result in browser windows cluttering up your taskbar and dragging on system resources. Firefox solves that by allowing sites to open in separate tabs within the same browser window. Instead of switching between browser windows, a user can change between two or more different sites by clicking on the tabs that appear just below the toolbar in Firefox.

Firefox features "tabbed browsing."

You can open a new, blank tab from a menu or by clicking on the "New Tab" button that you can add to the toolbar.

Firefox also has a built-in pop-up blocker. This prevents annoying ads from popping up in front of the browser window. You can configure it to let you know when pop-ups are blocked and to allow certain pop-ups from certain sites. This lets you enable pop-ups that are useful windows as opposed to unwanted ads.

One feature of Firefox that's vital to some users is that it is a cross-platform application. That means that Firefox works under several different operating systems, not just Windows. For now, all versions of Windows after Windows 98 are supported, along with recent versions of Mac OS X and Linux.

Firefox 3.5, released in 2009, added some other new features that, again, are becoming standard on multiple browsers. One of these is called Private Browsing. This feature allows you to use the browser without it recording any of your search history or other identifiable information about your session. Or if you prefer, you can use the Forget this Site option instead to eliminate all traces of that one source.

There's another notable Firefox feature that might be the coolest. It's like when someone asks you what you'd wish for if you could only have one wish, and you say, "I'd wish for unlimited wishes." Firefox extensions mean the browser has an almost unlimited number of features, with new ones being created every day. Still, the program remains fairly small, because users only add the extensions they want to use.

Firefox features include tabbed browsing, a built-in pop-up blocker, cross-platform capabilities and security advantages.

Junior high school students probably don't need stock market tickers, while people doing serious research don't necessarily need an MP3 player built into their browsers. If there's a feature from another browser that you really like, chances are someone has made an extension so that it can be included in Firefox.

Where do all these extensions come from? They're a product of Firefox's open source nature Not only is the code to Firefox available for examination and use, but Firefox provides developer tools for free to anyone who wants to create an extension.

Up next, we'll check out a sampling of extensions available for Firefox.

Firefox Extensions

Firefox extensions range from the indispensable (ad blocking) t­o the utterly silly (an extension that changes the Options menu's definition of "Cookies" from a technical explanation to "Cookies are delicious delicacies"). Here are a few of the more notable extensions.

• Themes -- Themes are technically a separate category from extensions, but they all do the same thing -- they change how Firefox looks. There are several dozen themes to choose from on the official Firefox site. If you want your browser to look like it's made out of wood or have big, brightly colored icons or look sleek and futuristic, there's a theme for you. You can change it every day if you want to.

• Gestures -- Mouse gesturing is a feature taken from another browser, Opera. When this extension is installed, users can execute various common Web surfing commands by holding down the right mouse button and "gesturing" in a certain direction with the mouse. A gesture to the left takes you back one page, while a gesture to the right takes you one page forward. You can customize the gestures and combine them (a down-then-left gesture minimizes the browser window, for example).

• FoxyTunes -- This extension places a small control panel on the Firefox toolbar, allowing users to control any media player software from within the browser.

Firefox extensions range from indispensable to silly. Explore Firefox extensions like mouse gesturing, FoxyTunes, Ad Block, ForecastFox and RadialContext.

• ForecastFox -- This popular extension puts a short-range weather forecast in your toolbar. You can select your location (or several different ones), how many days you want in the forecast and whether you want only daytime forecasts or both days and nights.

• RadialContext -- Most browsers give you a drop-down menu of options when you right-click on a Web site. The RadialContext extension livens this up by giving you a small dial of graphical options (sort of like the controls on your car stereo) instead of that plain text menu.

RadialContext

• Adblock Plus -- There are several different ad-blocking extensions available in addition to the pop-up blocking Firefox has built-in. These extensions allow users to block some or all banner ads and other advertisements that appear on Web pages. Some use a list of known ad servers or block images from servers with the words "banner" or "adserver" in the domain name. Others display ads normally, but if a user finds a particular ad exceptionally annoying or obtrusive, he or she can right-click on it and choose to remove it in the resulting drop-down menu.

Before and after using the remove-ad feature

Up next we learn about Firefox security.

Firefox Security

Firefox simply handles security differently from Internet Explorer. Where Internet Explorer uses security zones, which can sometimes be confused by malicious software, Firefox does not rely on zones. Also, Firefox doesn't use digital signatures, which are verifications programmers can purchase. If you try to install software on your computer, Internet Explorer checks to see if the digital signature matches the actual vendor of the program. Peter Torr, a program manager at Microsoft, pointed this out as a serious flaw in Firefox's security. However, a digital signature doesn't guarantee safe software, either. It just means that someone paid for the signature, and there have been cases of fraudulent signatures being issued.

ActiveX controls present another security issue. ActiveX is built into Internet Explorer and allows certain Web sites to automatically download scripts or execute small applications. While the absence of ActiveX in Firefox does mean that some sites will not be viewable, it also closes many security holes; in this case, Firefox chooses security over functionality.

Firefox 3.5 offers several other security enhancements. Clicking on the favicon -- that small image at the left of its URL in the Awesome Bar -- will tell you if that site's identity can be verified. In addition, Firefox now offers anti-phishing and anti-malware protection. If you visit a site that may attempt to install spyware, a Trojan horse or worm on your computer, Firefox will give you a warning and even provide you with a reason why it's not safe to visit that site.

Firefox 3.5 offers several other security enhancements. Clicking on the favicon -- that small image at the left of its URL in the Awesome Bar -- will tell you if that site's identity can be verified. In addition, Firefox now offers anti-phishing and anti-malware protection. If you visit a site that may attempt to install spyware, a Trojan horse or worm on your computer, Firefox will give you a warning and even provide you with a reason why it's not safe to visit that site.

Another aspect of Firefox versus Internet Explorer security is the fact that Firefox is an open source program. This means that anyone can access the code in which the program is written. That might sound like a bad idea, because you're giving potential hackers access to the code; but in fact, the opposite is true. There are far more people who want to close security holes than there are hackers who want to exploit them. Having thousands of people looking over your code and helping to spot problems means that most security flaws will get fixed very quickly. In fact, the developers of Firefox even offered a "bounty" of $500 and a t-shirt to anyone who successfully spotted a bug in the program.

In 2009, a new version of the Firefox browser appeared.

Firefox 3.5: What's New?

Misapplication One of the criticisms some users have for new versions of Firefox is that it doesn't support all the extensions you could add to earlier generations of the browser. But if a particular extension was really popular in the previous version, there's a good chance a developer is working on a new version.

Firefox 3.5 includes some new features, functions and a few fixes thrown in to boot. Between its June 2009 release and September of that same year, more than 220 million copies of the new browser were downloaded worldwide [source: Mozilla]. In the first 24 hours of its release, Firefox 3.5 was being downloaded at a rate of 100 copies per second [source: Siegler].

The current generation of Firefox is built on the Gecko 1.9.1 rendering engine [source: Mozilla Developer Center]. A rendering engine is a program that interprets code and markup languages (such as HTML or XSL) and generates the image of the Web page you see in your Web browser. The Gecko 1.9.1 engine is faster than previous versions but it comes with a price. As Mozilla began to upgrade its engine, starting with Firefox 3 the browser isn't compatible with Windows 98 or earlier versions. It also won't work on versions of Mac OS X before version 10.3.

With earlier versions of Firefox, some people noticed their computers acting sluggish as they used the browser. It seemed that Firefox consumed more memory resources the longer it remained active, particularly if the user opened multiple tabs while browsing. Firefox had a memory leak.

Memory leaks aren't necessarily a serious problem -- most of the time, a simple reboot takes care of the issue. But having to reboot your computer multiple times whenever you sit down for an extended Web browsing break is pretty annoying. If you have a lot of applications running at the same time, your computer's processing speed might slow to a crawl. Patching the memory leaks became a top priority for Mozilla with Firefox 3.

The Firefox development team has several tools that help them measure and patch memory leaks. These tools have names like BloatView, Leaky and Trace Malloc. The developers used these tools to diagnose the problems in earlier Firefox builds [source: Mozilla]. In addition, the XPCOM cycle collector tool in Firefox 3.5 looks for unused memory to feed back to the computer [source: Mozilla].

Mozilla designed the browser to integrate as seamlessly as possible with different operating systems. Each version -- Windows, Mac and Linux -- has a look and style that complements the native operating system.

Next, we'll look at possible problems with Firefox.

Firefox Problems and Concerns

Does Firefox mean anything more than another option for users fed up with what they perceive as slow development and rampant security problems with Internet Explorer? It might. As Firefox grows in popularity, Microsoft feels more pressure to compete with added features of its own. In a move that industry analysts attribute to Firefox's success (but Microsoft attributes to IE6 security risks), Microsoft released Internet Explorer 7 and Internet Explorer 8 separately from its Windows operating system.

Now that Firefox has a healthy share of the browser market, it will start getting a lot more attention, and not all of it welcome. The efforts of hackers focusing on the upstart browser could cause security problems. The result might be an ongoing, ever-escalating arms race as programmers race to patch security holes and hackers find new ones -- much like the current situation with Internet Explorer. Higher usage rates will also remove one of the benefits of using Firefox that appeals to many users -- it's something different.

The fact that Firefox is based on open source code also has implications. Not only is the program free to download and use, but the code is also freely available -- to look at, develop independently and release in an altered form. It's likely that some developers will grow dissatisfied with the direction of Firefox and splinter off to form their own version. Already, there are alternate builds of Firefox available, though they lack the stability of the official release.

Another possible problem with Firefox is its ability to block advertisements on Web sites. Although some ads are obtrusive and annoying, they also pay for the huge amount of information available on many sites (like this one). If people can quickly and easily avoid seeing those ads, Web sites will have to find a new business model for providing content while turning a profit.

One survey indicates that Firefox users are less likely to click on Web ads than users of other browsers, but this seems to be more an indication of greater Internet savvy than of ad-blocking [source: Marson]. One solution to the problem: Advertisers need to create better ads, ones that aren't malicious or deceptive. Ads that mimic Windows error messages or system dialogue boxes are universally hated, while flashing, blinking and scrolling ads are distracting for almost everyone.

The problem may not be as serious as some think. Removing all banner ads on Web pages doesn't come built into Firefox -- users have to install an extension. If Firefox's market share grows, it will reach more users who are less technically inclined -- users who are less likely to seek out and install extensions.

­

What's next for Firefox

With the rapid pace of development going on at Mozilla, it won't be long before there's another new version of the popular browser in the works. So what's going to be in the next version of Firefox? Starting with the current generation, there's plenty of room to grow. Firefox 3.5 includes support for a host of next-generation Web technologies, including HTML 5, Ogg Vorbis, Ogg Theora, microformats and animated portable network graphics (APNG). These formats are likely to change Web page functionality once they're adopted more fully.

Support for computers with multitouch functionality is under development at Mozilla. Multitouch refers to computer interfaces such as touchscreens on cell phones and trackpads on portable computers that can detect the touch of more than one finger at a time and support special multifinger commands. When it becomes available, the Firefox multitouch application programming interface (API) will allow Web developers to include new features in Web sites that provide more functionality for users. The first version of Firefox to support multitouch may come as soon as version 3.6 [source: Gilbertson].

Though Firefox 3.5 was released in June 2009, there were already screenshots of Firefox 3.7 floating around the following July. Of course, specifications for beta software are always in question, but Firefox 3.7 may feature a new see-through, glassy interface. Mozilla's product roadmap has releases planned for versions 3.6 and 3.7, and it already details some of the specifications for Firefox 4.0. As of this writing, it's due out in October or November 2010. Multitouch and interface changes are on the list, but so are other improvements, such as faster JavaScript, better page loading capability and synchronization of bookmarks, which can be handled now with the help of third-party plug-ins. In addition, Firefox may be borrowing features from the newcomer to the browser wars, Google Chrome: Tabs may have their own processing threads, which means that if one Web site open in your browser is having trouble, it's less likely to force you to restart your entire session [source: Brandick].

Working of Internet Explorer 8

What's new with Internet Explorer 8?

Users who downloaded the beta version of Internet Explorer received a thank you from Microsoft upon launching the new browser.

The World Wide Web is constantly evolving. The earliest Web pages were static sites that featured a few images, some text and the occasional unwelcome MIDI file. Today, Web sites may incorporate sophisticated elements such as Flash animation, video and customized markup languages. But you can't experience innovative features on the Web without a browser designed to handle everything the Web can offer.

That's why Microsoft released a beta version of Internet Explorer 8 (IE 8) in 2008. Beta versions are unfinished builds of programs. The purpose of a beta version is to allow people to test a product before its final build. This gives developers an opportunity to see which features become popular, which ones are ignored and which ones may need some tweaking before the final release. It also lets the developers test the stability of their program before launch. In January 2009, Microsoft offered consumers a release candidate version of the browser -- one step closer to the final official build of Internet Explorer 8.

It took five years for Internet Explorer 7 to hit the Web after the introduction of Internet Explorer 6. But the beta for Internet Explorer 8 appeared only two years after its predecessor. As the Internet and Web evolve, browser developers have to push to stay ahead -- or even keep up. That's just one reason IE 8 appeared so quickly on the heels of IE 7.

Another reason is that Microsoft is preparing Windows 7, the next version of the Windows operating system, for the market. Internet Explorer 7 harnessed the capabilities of the previous operating system: Windows Vista. But Vista suffered from bad press. It turns out the operating system had some problems when it went to market. Many journalists pointed out those problems and before long, people associated Vista with security issues and stability problems. Even though Microsoft released patches to address these early problems, the stigma remained.

Microsoft has designed Internet Explorer 8 to take advantage of some of the capabilities in Windows 7, much as IE 7 worked with Vista. But IE 8 will work on other operating systems as well. Let's take a closer look at the new browser.

New Features in Internet Explorer 8

You can choose to add and remove Accelerators applications to Internet Explorer 8 with a couple of mouse clicks.

Dean Hachamovitch is Microsoft's General Manager of Internet Explorer. He says that the Web is becoming more central to our lives and is almost synonymous with computing. Arguably, the Web browser is one of the most important computer applications in the world of software. To make Internet Explorer 8 an improvement over earlier versions, he and his team concentrated on making the browser faster, easier and safer to use.

To compete with browsers like Mozilla Firefox and Google Chrome, the Internet Explorer team configured IE 8 so that it loads Web pages faster than earlier builds of the browser. They paid particular attention to Web pages based on languages like JavaScript or AJAX.

The team wanted to avoid compatibility problems, so one feature they incorporated into IE 8 was the Compatibility View. This gives you the option of viewing Web pages as if you were using Internet Explorer 7. A related feature allows you to designate Web sites as either IE 8 or IE 7 sites. After categorizing a site, you'll view it using the optimal version of IE every time you visit it.

One thing the team noticed as it researched the best way to build IE 8 was that most people open several tabs while browsing the Web. That's why the team spent time trying to create a simple way to organize and manage multiple tabs. They developed tab groups. Whenever you open a new tab from a Web page, Internet Explorer 8 places the new tab next to the original Web site. It also color-codes all tab groups. You can also remove a tab from a group, close an individual tab or close an entire tab group with a right-click of the mouse.

Another feature of Internet Explorer 8 is a new address bar that functions in a way similar to Firefox's "Awesome Bar" or Google Chrome's "Omnibar." As you type in a term, Internet Explorer 8 searches your browsing history, bookmarks and Rss subscriptions to find a match. It displays matches in a drop-down menu. Clicking on an entry in this menu takes you to the corresponding page.

Safety First with Internet Explorer 8

Hachamovitch points out that browsing the Web isn't just informative and entertaining -- it can also be risky. Many sites on the Web host malware. Malware includes applications that can harm your computer or make it vulnerable to attacks from hackers. The best way to avoid malware is to use safe browsing habits. But sometimes it's hard to tell if a site is safe or not. The Internet Explorer team tried to make it easier for users to recognize safe sites with some special features included in IE 8.

Private Filters Internet Explorer 8 lets you tweak privacy settings to avoid being tracked by third-party entities. Some Web sites feature content from other sources -- advertising is a good example. Even if the primary Web site may be trustworthy, you can still encounter malware from third-party sources.

The key feature in the team's safety strategy is the SmartScreen Filter. The filter is an opt-in feature, which means users can choose whether or not to turn it on. It builds upon the phishping filter Microsoft designed for Internet Explorer 7. The SmartScreen Filter refers to a database of sites known to host malware. When you try to visit such a site, a warning screen pops up alerting you to the risks associated with that page.

Another safety feature is the new InPrivate feature. Similar to Google Chrome's "Incognito" mode, the InPrivate setting allows users to browse Web sites without retaining cookies or browsing history. This makes it more difficult for outside parties to track your browsing habits. While some people refer to this feature as "porn mode," there are plenty of reasons you may want to avoid leaving a trail. For example, if you are using someone else's computer to research private health information, you may not want to leave evidence behind.

Microsoft also built in an automatic crash recovery system to help prevent users from losing work due to a browser crash. This system isolates browser extensions for each tab -- Microsoft says that extensions cause 70 percent of all browser crashes. By isolating the extensions to each tab, IE 8 helps contain crashes. It also stores information so that you can return to your browsing once you reopen a tab or browser.

Internet Explorer 8 Extra Features

If a Web site looks weird in IE 8, you can use Compatibility View to look at it as if you were using IE 7.

Internet Explorer 8 includes some new functions designed to make browsing easier and more intuitive. These include features Microsoft calls Accelerators, Suggested Sites and Web Slices.

Accelerators are features that allow you to make better use of information from the text on a Web site. Microsoft designed these features to eliminate the necessity of copying text from one page and pasting it into another. Let's say you read an article and want to blog about it using a Windows Live Spaces account. Using IE 8, you could highlight the section that interests you, click your mouse's right button and select Blog with Windows Live Spaces from the menu. Internet Explorer 8 will take you to your blog and automatically insert the highlighted text into your edit field. You can also use Accelerators to find directions to a location, search for an item on eBay and define a term using Microsoft's Encarta encyclopedia.

Suggested Sites is another opt-in feature. If you choose to activate it, Internet Explorer 8 will examine your browsing history and suggest Web sites similar to the ones you visit regularly. It doesn't pull information from any sites you've deleted from your browser history or visited while using the InPrivate mode.

Web Slices let you subscribe to specific blocks of content on Web pages. You can use Web Slices to keep you informed of new e-mail messages, weather reports, eBay auctions and news services. Webmasters have the option to build out Web Slices on their pages by adding some code on the back end. In a way, this turns the IE 8 browser into a portal -- you can pull information from multiple Web sites into a unified view.

If you use Web Slices to subscribe to a page, the information from that page becomes available in a toolbar Microsoft calls the Favorites bar. The Favorites bar helps you organize your favorite sites -- it's essentially a bookmarks manager. But the Favorites bar can also keep track of documents you create in Microsoft Office products like Word and Excel, turning your browser into a more general organization application.

These are just some of the updates you can expect from the new Internet Explorer. Microsoft may incorporate more changes before releasing the final build.

Working of Yahoo Messenger

How Yahoo Messenger Works

Without instant messaging through Yahoo Messenger and other services, teens would lose a vital social communications tool, and the rest of us wouldn't have an easy way to send and receive messages quickly from our computers or mobile phones.

Yahoo messenger allows friends to chat online.

While Yahoo Inc. wan't the first Internet service provider to offer free instant messaging, it is one of the Web's most popular IM services. Launched in 1999, Yahoo Messenger has more than an estimated 94 million users who use to exchange instant messages with other Yahoo, Microsoft Windows Live Messenger or Lotus Sametime users [sources: Time Warner and PC World].

Once you download Yahoo Messenger software and complete the Yahoo Messenger sign in, you'll find the service also does a lot more. You can, for example, access contacts and messages anywhere from any Web browser, communicate in any of 40 languages and share photos and large-file Web video.

Before we delve further into Yahoo Messenger, let's take a quick look at instant messaging. What exactly is it? Instant messaging allows you to carry on a conversation with someone else via your personal computer. You type in a message, which then travels in digital form over the Internet from your computer through the provider's server to the other person's computer. Within a few seconds, the message appears in an IM window on the recipient's computer screen. That person reads the message and types back a response. Small, separate IM windows on the screen allow you to carry on conversations with several different people at a time. For more information about instant messaging, check out How Instant Messaging Works.

When e-mail contact isn't fast or convenient enough, Internet users turn to IM. Many teens use IM daily to talk to five or six friends at a time while simultaneously listening to music, doing homework and talking on their cell phone.

Teens aren't the only group found IM handy. This communications tool also works for business colleagues checking details with sales reps on the road, friends trying to find a time to talk at length and mobile phone users who need to check in with the office or contact each other. The number of IM users worldwide was estimated at 461 million in 2007 and is expected to reach 711 million by 2011, according to the Radicati Group, a market research firm specializing in messaging and collaboration technologies.

Next, let's see how easy it's to get started with Yahoo Messenger.

Yahoo Messenger Basics

Yahoo Messenger basics start with a visit to the Yahoo Web site. You'll need to download Yahoo Messenger software and complete the Yahoo Messenger sign up before you can use the free instant messaging service to IM your friends or colleagues, and you'll need to set up a messenger list. Here's how to set it up:

1. Go to Yahoo Messenger, and click on "download now" to download the Yahoo Messenger software.


2. Install the software on your computer, following specific directions for your operating system (Windows XP, Windows Vista, Mac or Unix).


3. If you don't already have a Yahoo account, sign up for a Yahoo ID. You'll be asked for your name, gender, country, ZIP code and e-mail address. You'll also need to provide your birthday, since Yahoo Messenger isn't available to anyone age 12 or under.

   After that, you select an ID -- a name to use when you IM -- and a password. You'll also be asked to select and answer a security question (like your first car model or pet's name) that can be used for identification if you forget your password. Click acceptance of the terms of service and privacy policy, and your account will be set up.

4. Now, you're ready to sign in. Go to http://www.yahoo.com, and click on the smiling yellow Yahoo Messenger button near the upper right corner of the screen. You'll see a sign-in screen next. Just enter your Yahoo ID name and password, hit the "sign in" button and you'll be signed in.

   Lists allow users to see which friends are on and off line.

   If you've forgotten your ID or password, click on the statement below the "sign in" button. After you answer some questions to verify your identity, you'll be sent your ID by e-mail or given the option of selecting a new password.

   To sign out when you're done, just click on the words "sign out" near the upper right of the screen page.

5. While you're signed in, you'll see your messenger list at the left of the screen. This is where you can list up to 300 friends, relatives, co-workers and others that you want to IM with. To add a name, click "Add" at the bottom of the messenger list, and then click "Yahoo Contact" or "Windows Live Contact." Type or paste the person's Yahoo or Windows Live ID in the box that opens at the top of your messenger list. To finish, type "Enter." Contacts receive an invitation with your request to add them to your list. If they say no, their names won't appear on your list.

   You can create groups within your messenger list by clicking on the Contacts menu, selecting "Organize Messenger Group" and then "Create New Group." Then just drop and drag contacts' names into the group.

6. To tell whether your contacts are available to talk, check the icon that appears in front of their names on the list. A yellow circle shows they're online and available to talk, while a blank circle means they're not available.
   
7. You can indicate your own availability by changing the icon near your ID at the top of the messenger list. Beyond clicking "available," you have choices like "busy," "stepped out" or "on the phone" -- or the option of writing your own message. By choosing "invisible," you can talk or work online while appearing to be offline.

Now that you're signed up, signed in and have some contacts in your messenger list, let's look at how you can send and retrieve instant messages.

Using Yahoo Messenger

Using Yahoo Messenger to send or receive messages is easy to learn. Yahoo offers a straightforward process and even has online help to provide tips on message formatting, sending files and other parts of the IM process. Let's go through the basics related to messages themselves.

Many Yahoo users rely on Yahoo Messenger to chat online with friends.

Sending an instant message
To send a message to someone on your messenger list, start by clicking on their name in the list or typing a few letters of their ID in "Find Contacts." Click their name from the list that appears, type your message in the space below the conversation window and click on "Send" or hit the Enter key.

For someone not on your list, type the ID in the "Find Contacts" box, press "Enter" and type your message the same as before. However, you won't be able to exchange messages if the person doesn't have Yahoo or Windows Live.

To send the same message to more than one person, hold down the Control key while clicking on names in your messenger list that you want to receive the message. Then click on the Actions menu, select "Send an Instant Message" and type and send your message as usual.

If you send an IM to someone who is offline, the message will pop up as soon as they sign back in.

Formatting a message
Why just send straight text when you can be more creative? Yahoo Messenger offers you options like sending messages in different fonts and colors. Pull-down menus below the conversation window let you format the text and message for the look you want.

You also can add emoticons for emphasis in the text. These are faces made of type that can express emotions ranging from happy to sad to puzzled. Just place the cursor where you want the emoticon in the text and then click on any of the 25 options from the pull-down menu.

Receiving a message and responding
You'll hear an alert sound when someone sends a message. Type your response as before and click on "Send" or hit "Enter." You can mute the alert by clicking on the speaker icon above the conversation window.

Sending a file or photo
To send a document or a photo, just drop and drag the document into the conversation window. This works even if the person is offline. The person receiving the file will be asked to save or decline it. Another option during a conversation is to click the Actions menu and then choose "Send a File." You can send a file as big as 1GB (or 2GB with Yahoo Messenger 9.0).

For up to 300 photos, you can use photo sharing. Yahoo Messenger will ask if you want to start a session and invite the other person to join in. If the other person accepts the files, the images will appear in a side panel for both of you to see.

Message archiving
Yahoo Messenger allows you to save, store and search your instant messages. The encrypted archives you create can only be viewed with your Yahoo ID on your computer. To set up a message archive:

• Click on the Messenger menu, select "Preferences" and click on "Archive."
• Choose one of the options for archiving messages.
• Click the "OK" button.

To view the messages later, choose the "Contacts" menu and select "Message Archive." Once the message archive for your ID appears, pick the folder you want to view.

Yahoo Messenger Features

With Yahoo Messenger features, Yahoo gives you options beyond the basics of instant messaging. You can set Yahoo Messenger to alert you of incoming messages or e-mail. You can protect your privacy, personalize with IMVironments and avatars or add webcam features. Here's more about each of these features.

Alerts
Alerts let you know when you receive an IM, when someone on your messenger list comes on or goes offline, when you receive e-mail, or when your calendar shows an upcoming event. To set an alert:

• Go to the Messenger menu, select "Preferences," click "Alerts" and select "Enable Alert Sounds."
• Pick when you want an alert, using the Event menu.
• Choose the type of alert you want for each event. This can be a sound from the menu or one you add yourself.
• Close the window to finish.

Privacy
By using stealth settings and ignoring unwanted contacts, you can help ensure your privacy and security. Stealth settings allow you to appear offline to some contacts and online to others. To set this, start by right-clicking on the group name or contact. Select "Stealth Settings," and choose online, offline or permanently offline. Click "OK" to finish. You'll know you appear offline to a certain contact or group if their name is in italics in your messenger list.

You can block messages from a single contact or up to 100 by ignoring them. You'll always appear to be offline to them. First, though, you have to delete the contact from your messenger list. Here's how you can block, or ignore, someone.

• Click on the Messenger menu, select "Preferences" and then "Ignore List." Choose "Ignore only the people below."
• Click on "Add" and enter the Yahoo ID of the person you want to ignore.
• To finish, click "Ignore" and "OK."
• To later stop ignoring the person, enter the contact's ID and click "Remove."

Personalizing
Avatars, audibles and IMVironments (themed IM window backgrounds) let you make Yahoo Messenger your own. An avatar is a character that you can personalize by changing its physical appearance, clothes, accessories and backgrounds and then show as your personal icon on Yahoo Messenger.

Yahoo Messenger extras like imvironments allow users to customize the appearance of their messenger screens.

To create and customize your avatar, go to http://avatars.yahoo.com/. To display the avatar in IMs and the messenger list, follow these steps:

Go to the Messenger menu, select "Preferences" and click on "Display Image." Click the Avatar box to show your avatar, and select "Enable display images everywhere" to see pictures and avatars from your contacts.

Audibles are talking animated characters you can send in an IM to comment or make a joke. Click the lips icon below the conversation window to access the audibles. Click the Send button above the one you want to send. Click "More Audibles" to see them all.

An IMVironment (IMV) is a themed conversation window that you select. You and your contacts can see your IMV every time you IM. Your messages print over IMVs like Fishtank, which is animated with swimming fish. The Doodle IMV lets you and your contact draw in color on the same canvas, while other IMVs let you play interactive games together.

Webcams
Webcam capabilities let you view a contact's webcam video or send your own. Viewing someone else's webcam is easy. Just click "Contact" in the IM window and select "Contact Options" and "View Webcam." Sending your own is more complicated. For specific requirements, see Yahoo Messenger's Webcam Help section.

Yahoo Messenger also offers tools to simplify instant messaging -- and make it more fun.

Convenient Tools for Yahoo Messenger

Convenient tools for Yahoo Messenger make instant messenging even faster and easier. Yahoo Messenger offers keyboard shortcuts, voice chat, parental controls and more. Keep reading to learn about each of these.

Keyboard Shortcuts
Typing key commands can make Yahoo Messenger faster to use. You can, for example, type "Control + F" to find contacts in the messenger list. The drop-down menus show keyboard shortcuts for commands.

Flickr for Photos
Available in Yahoo Messenger 9.0, Flickr lets you share photos in a side panel during IM. All of the images are shown in a thumbnail strip below the photo being displayed. A slider lets you change from one displayed image to another. Click the arrow left of the slider, and you can turn the photos into a slide show to view with your contact.

Yahoo Messenger users can chat with video capabilities.

Video and Map Preview
If you have the Web address of a video or map, you can watch it with a friend in the conversation window of Yahoo Messenger 9.0. Copy the URL of the video or map into the window where you type messages, and it will open in the conversation window. To watch a video with your friend, click "Watch with Me."

Yahoo Chat and Voice Chat
You can type or talk with voice chat in Yahoo Messenger chat rooms. To join a chat room, click on "Messenger," "Yahoo Chat" and "Join a Room." Select an alias to use for the chat, check out the rooms available and double-click on one you want to enter. Chat room visitors must be at least 18 years old.

For voice chat, you'll need a Windows operating system with Internet Explorer, plus a microphone, sound card and speakers. To use voice chat, click the voice icon after you enter a chat room. Hold down the green "Talk" button to start talking. When you're done talking, release the button.

Plug-Ins
Plug-ins are mini-programs that plug into Yahoo Messenger. Conversation plug-ins let you share activities -- like shopping, playing games or checking a flight schedule -- during IM conversations. Tab plug-ins give instant information, for example about important activities on your calendar or the status of an online auction bid.

You'll find tab plug-ins below the messenger list and can click "Add Plug-ins" for a list. Conversation plug-ins are above the conversation window. Click the Plug-ins button to see the list.

Parental Controls
Yahoo parental controls let you restrict the places your children go online and the people with whom they communicate. You also can receive weekly report cards showing Web sites visited, e-mails sent and received, and IMs completed with Yahoo Messenger.

The Web filter can block types of Web sites or specific sites. You can limit e-mail pals to those you approve, and you can limit when and how long your child stays online. You also can access your child's account to view and change inaccurate personal information.

To activate parental controls, you have to set up a Yahoo family account with sub accounts for all family members. You'll also need to install a program on every computer your family uses. Once you have a Yahoo account for yourself, go to the Member Center and look for information under "Sub Accounts."

Yahoo recommends that youths represent themselves with an avatar rather than a photo, use an alias, set their online status as invisible and archive all IM conversations.

Next, let's look at how you can use Yahoo Messenger anywhere, including from smartphones or PDAs.

New Innovations for Yahoo Messenger

Innovations for Yahoo Messenger reach beyond your own computer to allow you access to IM services wherever you are. For example, Yahoo Messenger for the Web provides instant messaging from any browser when you're away from home. Yahoo Messenger also provides free PC to PC phone service and IM services for your mobile device.

Yahoo Messenger for the Web
Log into Yahoo Messenger for the Web to IM from any browser -- with access to your contacts and message archives. You can add contacts, change your online status and save and search messages. You also can show your avatar and use your block list and stealth settings. But you won't be able to change any of these until you're home. And you won't be able to transfer files or use features like chat, voice, IMvironments, plug-ins or audibles.

To use Yahoo Messenger for the Web, go to Yahoo Messenger for the Web and sign in with your Yahoo ID and password. Once you're signed in, you'll see the usual screen display with your message list at the left. You can send and receive messages as you would at home.

PC to PC Phone Calls
Using your computer to call someone else on theirs is simple, easy -- and free. Yahoo Messenger's call feature uses voice over Internet protocol (VoIP) technology for worldwide computer-to-computer calling. You and the person you're calling will need Yahoo Messenger with Voice, a Windows operating system and sound card, a microphone and speakers or a headset.

Before you make a call, you can make sure your microphone and speakers are set up right by clicking on "Actions" and then "Call Setup." To call someone on your messenger list with a phone number listed, click first on that person's name, then the phone icon and finally "Call (Person's) computer." You'll hear a ring, they'll answer and the call starts. When you're done, click "End Call."

To call someone while the two of you are IMing, just click the phone icon above the conversation window. To call someone who's not on your messenger list, type the computer phone number in the "Type a Yahoo ID" bar above the messenger list.

Yahoo Mobile Messenger
You can sign into Yahoo Messenger from your mobile device when you're away from your computer and receive your IMs as text messages. You also can access your messenger list and change your online status from your cell phone, smartphone or PDA.

Yahoo Messenger users can even chat using their mobile devices.

Start by registering your mobile phone number. Click "Forward" above your messenger window. Then click "Add a phone number" next to "Forward offline IMs to" and register your number. After that, IMs will automatically be forwarded to your mobile device when you sign out of Yahoo Messenger on your computer. A phone icon in front of your name on your contacts' messenger lists will show you're mobile.

To send a text message from your mobile phone with Yahoo Messenger, click the Actions menu and then "Send an SMS Message." Enter your contact's mobile phone number, type your message and click "Send." You also can start by clicking the text message icon in the address book, or clicking on the contact name in the messenger list and then selecting "Send an SMS Message."

While we've tried to give an overview here of Yahoo Messenger, there's plenty more. For lots more information about Yahoo Messenger and instant messaging, go to the links on the next page.