B.1. An HTTP interaction

A simple example of an HTTP interaction might go as follows:

1. A browser makes a TCP/IP connection over the Internet to a server's TCP/IP Port 80 and transmits an HTTP request message containing:

• An HTTP request method is a command sent to the HTTP server, such as GET MainPage.vxml HTTP/1.0. (See Table B-3 for a list of all HTTP request methods.)

• An optional HTTP request header contains information about the browser so the server can customize its response.

• An optional HTTP entity body contains information collected by the browser to be posted up to the server. This information is typically consumed by a Web application.

2. The server reads this message, then transmits an HTTP response containing:

• A status line indicates the HTTP version, a status code (see Table B-1 for a list of HTTP status codes), and a short status description.

• An HTTP response header provides information about the HTTP server and about the document that the server is responding with, including the document type specified as a MIME type (see Table B-2 for a list of MIME types often used in VoiceXML) and the length of the document.

• The HTTP entity body is the actual payload of the HTTP response. This typically contains the document requested by the browser.

Using VoiceXML's catch element, you can catch each different HTTP response status code and handle it differently. For example, if you want to have a particular behavior for a 500 - Internal Server Error status code, you could catch this event with the following catch element:

<catch event="error.badfetch.http.500">
...
</catch>

MIME types are a standardized way of describing resource types such as images, audio clips, HTML documents, Microsoft Word documents, etc. Since a VoiceXML interpreter cannot interpret many of the formats popular in the browser-based WWW, the MIME types pertinent to VoiceXML are limited to text formats and audio formats. A brief summary of these MIME types is in Table B-2.