1. Overview of HTTP

- Because HTTP uses reliable data-transmission protocols, it guarantees that your data will not be damaged or scrambled in transit, even when it comes from the other side of the globe.

 

- The simplest kind of web resource is a static file on the web server's filesystem

 

- In summary, a resource is any kind of content source.

 

- HTTP carefully tags each object being transported through the Web with a data format label called a MIME type. MIME(Multipurpose Internet Mail Extensions) was orginally designed to solve problems encountered in moving messages between different electronic mail systems.

 

- MIME worked so well for email that HTTP adopted it to describe and label its own multimedia content.

 

- When a web browser gets an object back from a server, it looks at the associated MIME type to see if it knows how to handle the object. Most browsers can handle hundreds of popular object types: displaying image files, parsing and formatting HTML files, playing audio files through the computer's speakers,

 

- Each web server resource has a name, so clients can point out what resources they are interested in. The server resource name is called a uniform resource identifier, or URI. ~ uniquely identifying and locating information resources around the world.

 

- The uniform resource locator is the most common form of resource identifier. URLs describe the specific location of a resource on a particular server. They tell you exactly how to fetch a resource from a precise, fixed location.

 

- A URN serves as a uniquue name for a particular piece of content, independent of where the resource currently resides. These location independent URNs allow resources to move from place to place.

 

- HTTP supprots several different request commands, called HTTP methods.(fetch a web page, run a gateway program, delete a file etc)

 

- A web browser issues a cascade of HTTP transactions to fetch and display a graphic-rich web page.

 

- TCP provides:

1. Error-free data transportation

2. In-order delivery (data will always arrive in the order in which it was sent)

3. Unsegmennted data stream ( can dribble out data in any size at any time)

 

- Once a TCP connection is establihshed, messages exchanged between the client and server computers will never be lost, damaged, or received out of order.

 

- Before an HTTP client can send a message to a server, it needs to establish a TCP/IP connection between the client and server using Internet protocol (IP) addresses and port numbers.

 

- The hostname is just a human-friendly alias for an IP address.

 

- When the port number is missing from an HTTP URL, you can assume the default value of port 80.

 

- The Telnet utility connects your keyboard to a destination TCP port and connects the TCP port output back to your display screen. Telnet is commonly used for remote terminal sessions, but it can generally connect to any TCP server, including HTTP servers.

 

- Telnet lets you open a TCP connection to a port on a machine and type characters directly into the port.

 

proxies : HTTP intermediaries that sit between clients and servers

caches : HTTP storehouses that keep copies of popular web pages close to clients

gateways : special web servers that connect to other applications

tunnels : special proxies that blindly forward HTTP communications

agents : semi-intelligent web clients that make automated HTTP requests.

 

- Gateways are special servers that act as intermediaries for other servers. They are often used to convert HTTP traffic to another protocol. A gateway always receives requests as if it was the origin server for the resource. The client may not be aware it is communicating with a gateway.