The Cache-Control header and the max-age directive

Most of this is of little importance right now (although some of it is interesting), except for that one line that reads Cache-Control: max-age=18000. The M-Business Sync Server uses this line to determine how old that Web page is allowed to be before we have to search for a fresh version. The time listed there is in seconds, so these headers are telling the M-Business Sync Server that in 18000/3600 = 5 hours, we should consider the associated Web page out of date.

Note

As you will see, there are other ways to control caching, such as setting up an Expires: header, but we prefer using Cache-Control instead.

Suppose that the M-Business Sync Server is grabbing a page from your channel with the above headers. It would notice the Cache-Control header, and keep the document on its hard drive. It would also note the current time and the document's Last-Modified date.

Note

Technically, we add on a few seconds depending on how long it took us to retrieve the document, but this is close enough for the purposes of instruction.

M-Business Sync Server stores information about cached pages

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