How Client Pull and Server Push Animation Work

How Client Pull and Server Push Animation Work

Client Pull

Client pull is executed by the Refresh command. A refresh command is written into an HTML document using the <META> tag. The contents of the <META> tag are added to the header's meta-information that the server sends along with the HTTP response. During a client pull sequence, the browser reads this header information that instructs it to use your PC's internal clock to keep track of the time elapsed between pages retrieved. When the time has elapsed, the browser requests and displays the next page.

Each page in a client pull sequence can be located anywhere on the Web. The URL following the Refresh command might lead the browser to any active server. Page E is located on a different server than pages AD, but is still requested automatically after five seconds.


A client pull sequence might continue for as many or as few pages as the site designer wants. The last page will simply not have a Refresh command in the header. A user can stop the process manually by clicking the browser's Stop button.

Server Push

Server push is more complicated than client pull, but it enables inline animation that does not require an entire web page to load each animation frame.

The HTML source code for a server push animation is deceptively simple. The <IMG> (image) tag references the animation just like a static picture or icon.


The server and client make one connection that is open for as long as the CGI script runs. You can manually end a server push animation by clicking the browser's Stop button.

How Shockwave Works

The first step in a Shockwave animation happens in a multimediaauthoring program such as Director or Authorware. An animation designer must gather the raw materials, such as still images, music, and sound effects, necessary for a short and compelling animation.


How Flash Works

Flash is an animation program that enables designers to add animation, sound, and interactivity to web pages. Flash uses vector graphics instead of bit-mapped graphics. Vector graphics are mathematical descriptions of a shape, while a bit-mappedimage is an actual pixel-by-pixel representation of the image. Not only are vector graphics smaller and more suitable to the Web because of reduced download time than bit-mapped images, but, unlike bit-mapped graphics, they can also be zoomed in on without any degradation in quality.


Part 8: Shopping and Doing Business on the Internet


The Internet has its roots in the military and in academia, but it has become intimately tied to the way we live and work, and it will become more so with each passing year. At work, for entertainment, to get information, and to shopthe Internet has become a vital part of our daily lives.

The Internet's dramatic growth has been fueled in large part by business and consumers. It has become one of the primary places in which businesses operate, and where billions of dollars in goods and services are bought and sold every year.

Thousands of businesses use the Internet to market and sell their products, and many people buy things from home and from their places of business through the Internet instead of at retail stores. You can use the Internet to browse through catalogs and make purchases online; to buy and sell stock, mortgages, and insurance; and even to participate in online auctions. Companies are figuring out ways not only to sell online, but also to hook those online transactions into their internal computer and billing systems.

This part of the book looks at the various ways the Internet is used for business and shopping online. It covers how the Internet is being used by businesses as their primary corporate networks and how business and commerce are being conducted on the Internet every day.

Chapter 42, "How Intranets Work," covers intranets. Intranets are private networks set up by companies for their employees, using Internet technology. They're used for many purposes, including email, group brainstorming, group scheduling, and access to corporate databases and documents, among others.

Although intranets use TCP/IP networks and technologies, the network and its resources are used only by the businesses and are not available to people outside the company. Intranets are separated from the Internet by firewalls that don't allow unauthorized access to the intranet. People who work in the company can access the intranet and use its resources, but intruders are kept out by the firewalls.

This chapter also looks at one of the most important parts of an intranetworkgroup software. This type of software ties together everyone in a corporation and enables them to work together better. Among other things, it enables people to share files and information; to cooperate more easily on projects; and in general, to work together in ways never before possible. It allows people to go beyond simply communicating and enables them to work together on shared documents.

This chapter examines a variety of workgroup software. It covers messaging software that enables people to publicly participate in group discussions. It also looks at whiteboard software, which enables people to see what is on other people's computers and work together on documents. Several people could look at a spreadsheet together, for example, and one person could mark up the spreadsheet while everyone else sees what is being done.

The chapter also explains how Virtual Private Networks (VPNs) work. VPNs allow people to securely access corporate networks remotely, from home or when they are traveling, and can be big corporate productivity boosters.

Chapter 43, "Shopping on the Internet," covers what has become one of the most popular parts of the Internetshopping online. Today, shopping on the Internet accounts for billions of dollars a year in revenue, and every year many more billions are spent. In fact, you can't turn on your television set or open a newspaper or magazine without being confronted by advertising for a variety of online shopping sites. Although many of the original shopping sites have gone out of business, they've been replaced by the very businesses they expected to supplantexisting retailers. So, today you'll find stores such as the Gap and Wal-Martso called brick-and-mortar stores, or bricks-and-clickswith big online shopping sites.

This chapter shows you what's going on behind the scenes when you shop online. It shows you how online shopping carts worka technology that lets you gather together goods you're thinking of buying into a virtual shopping cart and then go through a checkout with them and pay by credit card. Finally, this chapter covers one of the most popular ways to shop onlinebuying at online auctions. Every day, millions of people buy and sell millions of items through auction sites, particularly the popular eBay. You'll see, in this chapter, how technology enables eBay to work.


Chapter 42: How Intranets Work


Chapter 43: Shopping on the Internet