Chapter 2: Managing Content Policy Language
Table 2.1: When Policy is Evaluated (Continued)
Windows Media HTTP streaming transactions
Before the authentication challenge.
After the authentication challenge, but before the requested object is fetched.
Before making an upstream connection, if necessary. (Up to this point it is similar to an HTTP transaction.)
What happens at this stage depends on negotiations with the origin server:
•After the origin server is contacted, if the User Agent header denotes the
Windows Media player and the server supports Microsoft streaming HTTP extensions, it finishes like an MMS transaction: Object information is available at this stage but streaming has not begun.
•If the
Some conditions cannot be evaluated during the first stage; for example, the user and group information will not be known until stage two. Likewise, the response headers and MIME type are unavailable for testing until stage three. For conditions, this is known as the earliest available time.
Policy decisions can have similar timing considerations, but this is known as the latest commit time. In this example, the requirement to authenticate must be known at stage one, and a forwarding host or gateway must be determined by stage three.
Cache Transactions
Cache transactions are initiated by the ProxySG in order to load or maintain content in the local object store during adaptive refresh or pipelining, or as a result of a content distribute CLI command. These may be HTTP, FTP, or streaming media transactions. Since no specific user is associated with these transactions, content related policy is evaluated for cache transactions, but user related policy is not evaluated.
A cache transaction evaluates policy in <Cache> and <Forward> layers. The <Forward> layers are only evaluated if an origin server must be contacted to complete the transaction.
The following is a list of cache transactions:
•A content distribute transaction that is initiated by the content distribute CLI command. A content distribute transaction may use one of the following protocols: HTTP, HTTPS, Real Media, or Windows Media. This type of transaction may be preceded by a separate Administrator transaction, since the administrator must be authenticated and authorized to use the command.
•Pipeline transactions (HTTP only).
•Advertisement transactions (HTTP only).
•
•Refresh transactions (HTTP only).
•ICP transactions.
Cache transactions have no client identity since they are generated internally by the ProxySG, and they do not support authentication or authorization. Therefore, they do not support conditions such as client.address= and group=, or the authenticate() property.
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