ADVANCED ISSUES

Email:

Email is a computer based method of sending messages from one computer user to another. These messages usually consist of individual pieces of text which you can send to another computer user even if the other user is not logged in (i.e. using the computer) at the time you send your message. The message can then be read at a later time. This procedure is analogous to sending and receiving a letter.

When mail is received on a computer system, it is usually stored in an electronic mailbox for the recipient to read later. Electronic mailboxes are usually special files on a computer which can be accessed using various commands. Each user normally has their individual mailbox.

Host-based mail systems

The original email systems allowed communication only between users who logged into the same host or "mainframe". This could be hundreds or even thousands of users within an organization.

By 1966 (or earlier, it is possible that the SAGE system had something similar some time before), such systems allowed email between different organizations, so long as they ran compatible operating systems.

Examples include BITNET, IBM PROFS, Digital Equipment Corporation ALL-IN-1 and the original Unix mail.

LAN-based mail systems

From the early 1980s, networked personal computers on LANs became increasingly important. Server-based systems similar to the earlier mainframe systems were developed. Again these systems initially allowed communication only between users logged into the same server infrastructure. Eventually these systems could also be linked between different organizations, as long as they ran the same email system and proprietary protocol.

Examples include cc:Mail, Lantastic, WordPerfect Office, Microsoft Mail, Banyan VINES and Lotus Notes - with various vendors supplying gateway software to link these incompatible systems.


Early interoperability among independent systems included:uucp was used as an open "glue" between differing mail systems, primarily over dialup telephones
• ARPANET which was the forerunner of today's Internet
• CSNet which used dial-up telephone access to link additional sites to the ARPANET and then Internet

Working with IIS:
IIS (Internet Information Server) is a group of Internet servers (including a Web or Hypertext Transfer Protocol server and a File Transfer Protocol server) with additional capabilities for Microsoft's Windows NT and Windows 2000 Server operating systems. IIS is Microsoft's entry to compete in the Internet server market that is also addressed by Apache, Sun Microsystems, O'Reilly, and others. With IIS, Microsoft includes a set of programs for building and administering Web sites, a search engine, and support for writing Web-based applications that access databases. Microsoft points out that IIS is tightly integrated with the Windows NT and 2000 Servers in a number of ways, resulting in faster Web page serving.
A typical company that buys IIS can create pages for Web sites using Microsoft's Front Page product (with its WYSIWYG user interface). Web developers can use Microsoft's Active Server Page (ASP)technology, which means that applications - including ActiveX controls - can be imbedded in Web pages that modify the content sent back to users. Developers can also write programs that filter requests and get the correct Web pages for different users by using Microsoft's Internet Server Application Program Interface (ISAPI) interface. ASPs and ISAPI programs run more efficiently than common gateway interface (CGI) and server-side include (SSI) programs, two current technologies. (However, there are comparable interfaces on other platforms.)
Microsoft includes special capabilities for server administrators designed to appeal to Internet service providers (ISPs). It includes a single window (or "console") from which all services and users can be administered. It's designed to be easy to add components as snap-ins that you didn't initially install. The administrative windows can be customized for access by individual customers.
Worker process isolation mode
Provides an easy way to insulate Web applications from each other, so that problems with one Web application don't impact the other Web applications on Microsoft Internet Information Services (IIS).
IIS 6.0 allows you to organize applications into application pools. Each application pool is a completely independent entity, served by one or more worker processes. Usually, a Windows administrator will create a separate application pool for each Web application that the server hosts -- but a single application pool can host multiple applications.
Of course, this raises the question of how application pools can isolate IIS Web applications from each other. True isolation is possible because Windows differentiates between code that is running in kernel mode vs. code that is running in user mode.
Windows runs core IIS components, such as HTTP.SYS and the WWW service, in kernel mode. Each application pool contains its own kernel-mode queue. This means that HTTP.SYS is able to route inbound requests directly to a queue that is dedicated to a specific application pool, all within kernel mode. Application pools are separated from each other by process boundaries.
Worker processes are dedicated to a specific application pool to actually service requests. If a failure occurs, it usually happens within a worker process. However, since worker processes are bound to particular application pools, a worker process failure will only affect the application in which it resides, but no others.
The really cool part is that IIS provides mechanisms for monitoring the health of a worker process. If a worker process fails, the process can be restarted without the end user even being aware of the failure.

Asp Page Directives

Asp.Net Page directives are something that is a part of every asp.net pages. Page directives are instructions, inserted at the top of an ASP.NET page, to control the behavior of the asp.net pages. So it is type of mixed settings related to how a page should render and processed.

Here’s an example of the page directive.
<%@ Page Language="C#" Auto Event Wire up="true" Code File="Sample.aspx.cs" Inherits="Sample" Title="Sample Page Title" %>

Totally there are 11 types of Pages directives in Asp.Net 2.0. Some directives are very important without which we cannot develop any web applications in Asp.Net. Some directives are used occasionally according to its necessity. When used, directives can be located anywhere in an .aspx or .ask file, though standard practice is to include them at the beginning of the file. Each directive can contain one or more attributes (paired with values) that are specific to that directive
Asp.Net web form page framework supports the following directives

1. @Page
2. @Master
3. @Control @Master Directive
4. @Register
5. @Reference
6. @Previous Page Type
7. @Output Cache
8. @Import
9. @Implements
10. @Assembly
11. @Master Type