Application Layer

2166
User-Server Interaction: Cookies
User-Server Interaction: Cookies

We cited above that an HTTP server is stateless. This makes server design simpler and has allowed engineers to develop high-performance Web servers that can manage thousands of simultaneous TCP connections. Nevertheless, it is frequently desirable for a Web site to identify

Tags cookies, end system, back-end database,
2172
Web Caching
Web Caching

A Web cache - also called a proxy server - is a network entity that satisfies HTTP requests on the behalf of an origin Web server. The Web cache has its own disk storage and keeps copies of recently requested objects in this storage. As shown in Figure 1, a user's browser can be

Tags web cache, proxy server, network entity, router, internet delay
1764
The Conditional GET
The Conditional GET

Though caching can decrease user-perceived response times, it initiates a new problem - the copy of an object residing in the cache may be stale. In other words, the object housed in the Web server may have been modified since the copy was cached at the client. Fortunately,

Tags web server, conditional get, proxy cache, internet protocol, http protocol
1652
File Transfer: FTP
File Transfer: FTP

In a normal FTP session, the user is sitting in front of one host (the local host) and wants to transfer files to or from a remote host. In order for the user to access the remote account, the user must provide a user identification and a password. After providing this authorization

Tags remote host, file system, control connection, data connection, ftp, http, tcp
1168
FTP Commands and Replies
FTP Commands and Replies

We finish this section with a brief discussion of some of the more common FTP commands and replies. The commands, from client to server, and replies, from server to client, are sent across the control connection in 7-bit ASCII format. Therefore, like HTTP commands, FTP

Tags ftp commands, tcp connection, remote host, http commands, server
1935
Electronic Mail in the Internet
Electronic Mail in the Internet

Electronic mail has been around since the beginning of the Internet. It was the most popular application when the Internet was in its infancy [Segaller 1998], and has become more and more complicated and powerful over the years. It remains one of the Internet's most important

Tags user agent, mail server, mailbox, message queue, electronic mail
2229
SMTP
SMTP

SMTP, defined in RFC 5321, is at the heart of Internet electronic mail. As mentioned above, SMTP transfers messages from senders mail servers to the recipients mail servers. SMTP is much older than HTTP. (The original SMTP RFC dates back to 1982, and SMTP was around long

Tags smtp, http, tcp connection, mail server
1174
Comparison with HTTP / MaiI Message Formats
Comparison with HTTP / MaiI Message Formats

Let's now compare SMTP with HTTP in brief. Both protocols are used to transfer files from one host to another: HTTP transfers files (also called objects) from a Web server to a Web client (typically a browser); SMTP transfers files (that is, e-mail messages) from one mail server

Tags pull protocol, push protocol, peripheral information, http, smtp, mail server
2162
Mail Access Protocols
Mail Access Protocols

Once SMTP delivers the message from Alice's mail server to Bob's mail server, the message is placed in Bob's mailbox. Throughout this discussion we have tacitly assumed that Bob reads his mail by logging onto the server host and then executing a mail reader that runs on

Tags mail server, smtp, http protocol, imap protocol
1421
DNS -The Internets Directory Service
DNS -The Internets Directory Service

We human beings can be recognized in many ways. For instance, we can be recognized by the names that appear on our birth certificates. We can be recognized by our social security numbers. We can be recognized by our driver's license numbers. Though each of these identifiers

Tags canonical hostname, hierarchical structure, dns servers, routers, internet applications, end system
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