MIME The Multipurpose Internet Mail Extensions
While the message headers described in are satisfactory for sending ordinary ASCII text they are not sufficiently Reich for multimedia messages(for example messages with images audio and video) or for carrying non ASCII text formats ( for example characters used by language other then English ). To send content other then ASCII text the sending user agent must include additional headers in the message.
MIME defines five new message headers as show in table 8. These are described below one by one:
1.MIME version simply identifies the version of MIME.
2.The content description Header is an ASCII string telling what is in the message .
3.The content id heard identifies the content.
4.The content transfer encoding : Header alerts the receiving user agent that the message body has been ASCII encoded and indicates the type of encoding used. Thus when a user agent receives a message with these two header if first uses the value of the content transfer encoding heard to convert the message body to its original non ASCII form and then uses.
5.The content type header to determine what action it should take on the message body. Let take an example of MIME message.
From : heena@yahoo.
To : harish@rediff. Com
Subject : Picture of monalisa
MIME : Version : 1.0
Content transfer encoding : base 64
Content - Type image jpeg
Base 64 encoded date ................
.....................................................
............................ base 64 encoded data)
We observer form the above MIME message that heena user agent encoded the JPEG image using base 64 encoding. This is one of the several encoding techniques standardized in MIME for conversion to an acceptable 7 bit ASCII format.
When Harish reads his mail with his user agent his user agent operates on this game MIME message when Harish use agent observes the content transfer encoding base64 header line. It proceeds to decode the base 640 encoded message body.
The message also includes a content type image jpeg header line his indicates to Harish user agent that the message body should be JPEG decompressed. Finally the message includes the MIME version. Header which indicates the MIME version that is being used. In particular after the message header there is blank lien and then the message body.