Tuesday, December 8, 2009

What is CDMA?

Definition: CDMA, or Code Division Multiple Access, is a competing cell phone service technology to GSM, which is the world’s most widely used cell phone standard. CDMA uses a “spread-spectrum” technique whereby electromagnetic energy is spread to allow for a signal with a wider bandwidth. This allows multiple people on multiple cell phones to be “multiplexed” over the same channel to share a bandwidth of frequencies. With CDMA technology, data and voice packets are separated using codes and then transmitted using a wide frequency range. Since more space is often allocated for data with CDMA, this standard became attractive for 3G high-speed mobile Internet use. The CDMA standard was originally designed by Qualcomm in the U.S. and is primarily used in the U.S. and portions of Asia by other carriers. Sprint, Virgin Mobile and Verizon Wireless use CDMA while T-Mobile and AT&T use GSM. While CDMA and GSM compete head on in terms of higher bandwidth speed (i.e. for surfing the mobile Web), GSM has more complete global coverage due to roaming and international roaming contracts. GSM technology tends to cover rural areas in the U.S. more completely than CDMA. Over time, CDMA won out over less advanced TDMA technology, which was incorporated into more advanced GSM.

What is EDGE?

Definition: EDGE takes GSM even further. GSM, which stands for Global System forMobile communications, reigns as the world’s most widely used cell phone technology. EDGE, which stands for Enhanced Data rates for GSM Evolution, is a faster version of GSM. EDGE is a high-speed 3G technology that was built upon the GSM standard. EDGE networks are designed to deliver multimedia applications such as streaming television, audio and video to mobile phones at speeds up to 384 Kbps. Such speeds still pale in comparison, though, to standard DSL and high-speed cable access today. EDGE delivers a boost of more than three times the capacity and performance over GSM. The EDGE standard was first launched in the United States in 2003 by Cingular, which is now AT&T, on top of the GSM standard. AT&T, T-Mobile and Rogers Wireless in Canada all use EDGE networks.

What is GSM?

Definition: GSM, which stands for Global System for Mobile communications, reigns as the world’s most widely used cell phone technology. Cell phones use a cell phone service carrier’s GSM network by searching for cell phone towers in the nearby area. The origins of GSM can be traced back to 1982 when the Groupe Spécial Mobile (GSM) was created by the European Conference of Postal and Telecommunications Administrations (CEPT) for the purpose of designing a pan-European mobile technology. It is approximated that 80 percent of the world uses GSM technology when placing wireless calls, according to the GSM Association (GSMA), which represents the interests of the worldwide mobile communications industry. This amounts to nearly 3 billion global people. Cell phone carriers T-Mobile and AT&T use GSM for their cell phone networks. Sprint, Virgin Mobile and Verizon Wireless use the competing CDMA standard. For practical and everyday purposes, GSM offers users wider international roaming capabilities than other U.S. network technologies and can enable a cell phone to be a “world phone”. More advanced GSM incorporates the earlier TDMA standard. GSM carriers have roaming contracts with other GSM carriers and typically cover rural areas more completely than competing CDMA carriers (and often without roaming charges, too). GSM also has the advantage of using SIM (Subscriber Identity Module)cards in the U.S. The SIM card, which acts as your digital identity, is tied to your cell phone service carrier’s network rather than to the handset itself. This allows for easy exchange from one phone to another without new cell phone service activation. GSM uses digital technology and is a second-generation (2G) cell phone system. GSM, which predates CDMA, is especially strong in Europe. EDGE is faster than GSM and was built upon GSM.

Saturday, February 21, 2009

Ten ways to speed up the download time of your web pages

Ten ways to speed up the download time of your web pages

Why is download speed so important?

Do you like to wait for pages to download? Neither do your site users. Read on...

1. Lay out your pages with CSS, not tables

CSS downloads faster than tables because:

  • Browsers read through tables twice before displaying their contents, once to work out their structure and once to determine their content

  • Tables appear on the screen all in one go - no part of the table will appear until the entire table is downloaded and rendered

  • Tables encourage the use of spacer images to aid with positioning

  • CSS generally requires less code than cumbersome tables

  • All code to do with the layout can be placed in an external CSS document, which will be called up just once and then cached (stored) on the user's computer; table layout, stored in each HTML document, must be loaded up each time a new page downloads

  • With CSS you can control the order items download on to the screen - make the content appear before slow-loading images and your site users will definitely appreciate it

To learn more about CSS and the amazing things it can do for your website, check out the excellent tutorials both here at DNzone or at places like HTML Dog.

2. Don't use images to display text

It's our old friend CSS to the rescue again. There's no need to use images to display text as so much can be accomplished through CSS. Have a look at this code:

a:link.example, a:visited.example, a:active.example
{
color:#fff;
background:#f90;
font-size:1.2em;
font-weight:bold;
text-decoration:none;
padding:0.2em;
border:4px #00f outset
}

a:hover.example
}
color:#fff;
background:#fa1;
font-size:1.2em;
font-weight:bold;
text-decoration:none;
padding:0.2em;
border:4px #00f inset
}

This will give you a really simple button that appears to be pushed down when you mouseover it - See it in action here if you like.

3. Call up decorative images through CSS

It's possible to present images as part of the background, called up through CSS. If you've got an image that's 200px by 100px you can use the following HTML code:

<div class="pretty-image"></div>

And this CSS:

.pretty-image
{
background: url(filename.gif);
width: 200px;
height: 100px
}

This may at first seem a little pointless but this technique could really improve the download time of your pages. Browsers basically download background images after everything else. By using this technique, your text will load instantaneously and your site users can freely roam about the page while your 50kb fancy image downloads.

This technique disables the ALT attribute though so if you really want to have one then replace the above HTML code with this:

<image src="spacer.gif" class="pretty-image" alt="description" />

Spacer.gif is a 1px x 1px transparent image. Now you have a 50 byte transparent image and the main content loading first, and your great big decorative image, complete with ALT text, loading second. Perfect.

Please note that this technique is only good for decorative images and not informational ones. Any user who has CSS disabled will not be able to see your CSS-embedded images (or their alternative text).

4. Use contextual selectors

This is inefficient:

<p class="text">This is a sentence</p>
<p class="text">This is another sentence</p>
<p class="text">This is yet another sentence</p>
<p class="text">This is one more sentence</p>

.text
{
color: #03c;
font-size: 2em
}

Instead of assigning a value to each individual paragraph, we can nest them within a <div> tag and assign a value to this tag:

<div class="text">
<p>This is a sentence</p>
<p>This is another sentence</p>
<p>This is yet another sentence</p>
<p>This is one more sentence</p>
</div>

.text p
{
color: #03c;
font-size:2em
}

This second CSS example basically says that every paragraph within class="text" should be assigned a colour value of #03c and a font size of 2em.

At first glance this doesn't look too important, but if you can apply this properly throughout your document you can easily knock off 20% of the file size.

You may have noticed the colour values are shorter than normal. #03c is a shortened version of #0033cc - you can assign this abbreviated value to any colour value like this.

5. Use shorthand CSS properties

Font

Use:

font: 1em/1.5em bold italic serif

...instead of:

font-size: 1em;
line-height: 1.5em;
font-weight: bold;
font-style: italic;
font-family: serif

Border

Use:

border: 1px black solid

...instead of

border-width: 1px;
border-color: black;
border-style: solid

Background

Use:

background: #fff url(image.gif) no-repeat top left

...instead of:

background-color: #fff;
background-image: url(image.gif);
background-repeat: no-repeat;
background-position: top left;

Margin, padding, border

Use:

margin: 2px 1px 3px 4px (top, right, bottom, left)

...instead of:

margin-top: 2px;
margin-right: 1px;
margin-bottom: 3px;
margin-right: 4px

Use:

margin: 5em 1em 3em (top, left and right, bottom)

...instead of:

margin-top: 5em;
margin-bottom: 1em;
margin-right: 1em;
margin-right: 4em

Use:

margin: 5% 1% (top and bottom, left and right)

...instead of:

margin-top: 5%;
margin-bottom: 5%;
margin-right: 1%;
margin-right: 1%

These rules can be applied to margin, border and padding.

6. Minimise white space, line returns and comment tags

Every single letter or space in your HTML code takes up one byte. It doesn't sound like much but it all adds up. We've found that by working through your page source and eliminating unnecessary white space and comments, you can shave off up to, or even over (if your HTML is really inefficient) 10% of its file size.

7. Use relative call-ups

Try to avoid absolute call ups as they take up more space. An example of an absolute call up is: <a href="http://www.URL.com/filename.htm">.

Much better would be <a href="filename.htm">. But what if some files are in different folders to other ones? Use these shorthand properties:

8. Remove unnecessary META tags and META content

Most META tags are pretty much unnecessary and don't achieve very much. If you're interested, you can see a list of META tags that are available. The most important tags for search engine optimisation are the keywords and description tags, although due to mass abuse they've lost a lot of importance in recent times.

When using these META tags try to keep the content for each under 200 characters - anything more increases the size of your pages. Lengthy META tags are not good for search engines anyway because they dilute your keywords.

9. Put CSS and JavaScript into external documents

To place CSS in an external document use:

<link type="text/css" rel="stylesheet" href="filename.css" />

To place JavaScript in an external document use:

<script language="JavaScript" src="filename.js" type="text/javascript"></script>

Any external file is called up just once and then cached (stored) on the user's computer. Instead of repeating JavaScript or CSS over and over again in HTML files, just write it out once in an external document.

And don't forget, there's no limit to the number of these external documents that you can use! For example, instead of making one huge CSS document, have one main one and some others that are specific to certain areas of your site.

 

10. Use / at the end of directory links

Don't do this: <a href="http://www.URL.com/directoryname">

Do this instead: <a href="http://www.URL.com/directoryname/">

Why? If there's no slash at the end of the URL the server doesn't know if the link is pointing to a file or to a directory. By including the slash the server instantly knows that the URL is pointing to a directory and doesn't need to spend any time trying to work it out.