How ClientServer Architecture Works


How Client/Server Architecture Works

The PC-based browser software controls the client end of the Web application. Using TCP/IP, the browser issues HTTP requests to the host server. The browser can request a specific web page, or it can ask the host server to perform a database query. In either instance, the request is broken into HTTP packets that are sent across the Internet's TCP/IP communications infrastructure to the host computer.



 


Chapter 5. How Internet Addresses and Domains Work

The heart of how the Internet works is the Domain Name System (DNS), the way in which computers can contact each other and do things such as exchange email or display web pages. When someone on the Internet wants to contact a locationfor example, to visit a websitehe types in an address, such as www.metahouse.com. (A specific location on the Internet is also referred to as a uniform resource locator, or URL.) The DNS translates the plain English address, www.metahouse.com, into a series of numbers called an IP (for Internet Protocol) address. An IP address, such as 123.23.43.121, marks the location of a computer on the Internet similar to the way a house number and street mark the location of where you live.

In this example, metahouse.com is called a domain. To work most efficiently, the Internet has been organized into a number of major domains. Major domains refer to the letters at the end of a plain English address, such as .com. A number of common domains are .com (commercial), .edu (education), .gov (government), .mil (military), .net (Internet service providers and networkscompanies and groups concerned with the organization of the Internet), and .org (organization).

Domains are organized in a hierarchical manner, so that beneath major domains are many minor domains. As an example of how the DNS and domains work, look at NASA's SPACElink Internet address: spacelink.nasa.gov. The top domain is .gov, which stands for government. The domain just below that is .nasa, which is the NASA domain. Then, spacelink identifies the NASA computer that runs the SPACElink program. SPACElink's numeric IP address has changed through the years, but its Internet address has stayed the same.

Computers called name servers are responsible for keeping track of such changes and translating them between IP addresses and domain addresses. The Internet can't understand alphanumeric Internet addresses, such as ziffdavis.com, so name servers translate those addresses into their proper numeric IP addresses, such as 163.52.128.72. Name servers contain tables that match alphanumeric Internet addresses to numeric IP addresses.

When you connect your computer to the Internet, your computer needs to have an IP address assigned to it to do common things, such as browsing the Web. Depending on how your computer is set up and how your service provider operates, you might have a static address or a dynamic address. A static IP address never changes, so if you have one, you will have the same IP address every time you connect to the Internet. However, because the Internet has only a limited number of IP addresses, many ISPs use dynamic addresses. With a dynamic IP address, you are given an IP address from a limited block of IP addresses every time you connect. In this way, ISPs don't have to have an individual address for every subscriber. Instead, they can share their pool of addresses among all subscribers.