Cisco Computer Networking

Asking Someone Else to Look Up the Phone Number (IP Address) for You How Names Should Be Formatted For the DNS processes to work well, DNS defines some rules for how hosts are named. This section covers the structure and meaning of ... [full story]

Chapter 8. Shipping Goods over a (Network) Roadway What You Will Learn After reading this chapter, you should be able to Explain how e-mail uses multiple servers Describe the two parts of an e-mail address Name the two most popular e-mail protocols and describe when ... [full story]

Warehouse Lingo and Procedures FTP shares many of the same general concepts with applications like e-mail. Here are some of the similarities: Like e-mail, FTP uses client software on the end user computer. Like e-mail, the FTP client software has both user interface ... [full story]

Figure 8-11. Stocking the FTP Warehouse The following list describes what happens with each of the four messages Keith sends in the figure: 1. Keith first sends the server his username, using the FTP USER command. This command allows Keith's FTP ... [full story]

Figure 8-12. Copying Inventory (Files) from the FTP Warehouse Conner repeats the same basic steps as Keith had in Figure 8-11. However, instead of issuing a PUT command, Conner issues a GET command. In FTP lingo, PUT means to copy ... [full story]

Rules, Schmools for FTP Many standards exist for file transfer. However, the one I've been writing about here, called FTP, has one core RFC that defines the details: RFC 959. The FTP RFC defines the messages that FTP uses to send ... [full story]

Browsing Around the Internet Shopping Mall: The World Wide Web Back in Chapter 2, "A Network's Reason for Existence," you had a brief look at how the World Wide Web works. In many ways, the web works a lot like the ... [full story]

Figure 8-13. Building and Stocking the New Retail Store, AKA New Website [View full size image] The following list describes what happens with each of the four messages that Conner sends in the figure: Web server software must be installed on ... [full story]

Rules, Schmools for Web Retailing To start, let's consider how to load a default web page, often called a home page. From the users' perspective, they must identify the website. They can do that in many ways. For now, let's assume ... [full story]

Figure 8-14. Connecting to the Fredsco Home Page [View full size image] Notice the string of characters that starts with HTTP (http://www.fredsco.com). The whole string is called a uniform resource locator (URL). The URL identifies the protocol in use, as ... [full story]

Buy One, Get a Bunch for Free Have you ever tried to load a web page and noticed that some parts show up right away while the rest of the page fills in slowly? In this section, you'll learn what causes ... [full story]

Figure 8-15. Transferring All the Files That Make Up a Web Page [View full size image] Conner's browser gets the original home page, reads it, and processes it. The home page HTML file told Conner to get two other objects: ... [full story]

Chapter 9. Choosing Shipping Options When Transporting the Goods over the (Network) Roadway What You Will Learn After reading this chapter, you should be able to List the main features of TCP Explain the TCP error recovery process Describe why a computer needs to use ... [full story]

"Hello, I'm at Your Service" "Hello, this is Fred at Fred's Shipping Company. How can I help you today?" Yep, Fred, the owner, is answering the phones at his small shipping company. He's waiting for the phone to ring so that ... [full story]

Figure 9-1. Application Program and Application Layer Asking the Transport Layer for Help [View full size image] As shown in Figure 8-4 in the previous chapter, the application program includes the user interface and the application layer protocols. In Figure ... [full story]

Full-Service Shipping Just like a company can create its own shipping department, an application layer protocol could avoid using a transport layer protocol, but it almost never happens. Why? Well, the transport layer protocols already exist. They provide great services that ... [full story]

Shipping Basics: Controlling Shipments Using Shipping Labels When you decide to ship a package using any well-known shipping company, you fill out a shipping label, attach it to the package, and leave the package where the shipper will find it when ... [full story]

Figure 9-2. Adding Shipping Information to Data by Encapsulating in a TCP Header [View full size image] Keith's TCP software, which is typically just a part of the OS, is in charge of delivering the data to the web server. ... [full story]

Figure 8-10. FTP Process for Transferring Files With FTP, everyone puts files on the server, as Keith did at Step 1 in the figure. Later, users can connect to the FTP server and get the files, as Conner did in ... [full story]

Figure 8-9. Warehousing Process for Transferring Stuff At Step 1, Keith fills the warehouse with widgets that his company has manufactured. Later, at step 2, Conner goes to get a widget so that he can deliver it to a customer. Now, ... [full story]

Building a Centralized Warehouse: File Transfer As you saw in the previous section, e-mail has some obvious comparison points with snail mail. The next application, file transfer, does not compare directly with a noncomputing example, but it does work a little ... [full story]

Neither Rain, Nor Sleet, Nor Dark of Night: E-Mail The United States Postal Service (USPS) promises to consistently deliver mail, no matter what's going on with the weather. Although e-mail services make no such promise, they have become equally as important. ... [full story]

Dropping Off and Getting Your (e)Mail If you live in a house or apartment, a postal worker typically comes by your place every working day. He leaves your mail in your mailbox. He also picks up any outgoing mail that you ... [full story]

Postal Worker Picking Up and Dropping Off the Mail [View full size image] After the postal worker has picked up your mail, he brings it back to the local post office. Eventually, your letter gets to the post office near your ... [full story]

Sending E-Mail Using E-Mail Servers [View full size image] Although not exactly like the postal service, the same general ideas apply. Each company has one (or more) e-mail servers, acting as local post offices. Also, Internet service providers (ISPs) have one ... [full story]

Postal Address Versus E-Mail Address To send snail mail, you need to put the recipient's name and address on the front of the letter. The postal service then delivers the letter to the correct address. Similarly, to send an e-mail, you ... [full story]

shows why a two-part e-mail address is useful. Both Keith and Conner send an e-mail to different people inside Fredsco. The text following the figure explains how the e-mail address helps in delivering the e-mail. Figure 8-3. How a Two-Part E-Mail ... [full story]

Rules, Schmools: Even More Rules? Now that you have the general idea of how e-mail works, you should know about a few of the protocols and standards for e-mail. First, Table 8-1 lists the standards. Afterward, I'll explain a little about ... [full story]

TCP/IP E-Mail Standards Standard RFC Description Internet Message Format 2822 Defines the headers used to encapsulate the e-mail text, including the sender and receiver e-mail addresses Simple Mail Transport Protocol (SMTP) 2821 Defines protocols for transmitting and receiving e-mails Post Office Protocol Version 3 (POP3) 1939 Defines protocols for a client to ... [full story]

The protocols shown in Table 8-1 happen to be application layer protocols according to the TCP/IP model. Interestingly, there is an important distinction here between the application itself and the application layer protocol. Figure 8-4 provides a good backdrop to ... [full story]

Protocols for Addressing the Envelope Correctly: Internet Message Formats When an e-mail client sends an e-mail and the e-mail servers forward it, they not only send the text of the e-mail message, but also a header. The header contains several fields, ... [full story]

The KISS Principle and SMTP The KISS principle refers to a wise adage to Keep It Simple, Stupid. Much of what you do every day might be better done if you make it uncomplicated. One of the most popular e-mail protocols ... [full story]