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ProxySG Content Policy Language Guide
34
Each of the protocol-specific proxy transactions has specific information that can be 
tested—information that may not be available from or relevant to other protocols. HTTP Headers and 
Instant Messaging buddy names are two examples of protocol-specific information.
Other key differentiators among the proxy transaction subtypes are the order in which information 
becomes available and when specific actions must be taken, as dictated by the individual protocols. 
Variation inherent in the individual protocols determines timing, or the sequence of evaluations that 
occurs as the transaction is processed.
The following table summarizes the policy evaluation order for each of the protocol-specific proxy 
transactions. 
Table 2.1:  When Policy is Evaluated
Transaction Type
Policy is Evaluated....
Tunneled TCP transactions
before the connection is established to the origin server.
HTTP proxy transactions
Before the authentication challenge.
After the authentication challenge, but before the requested object is fetched.
Before making an upstream connection, if necessary.
After the object is fetched
FTP over HTTP transactions:
Before the authentication challenge.
After the authentication challenge, but before the required FTP commands are 
executed.
Before making an upstream connection, if necessary.
After the object is fetched.
Transparent FTP transactions
Policy is examined before the requested object is fetched.
Real Media streaming 
transactions
Before the authentication challenge.
After the authentication challenge, but before getting object information.
Before making an upstream connection, if necessary.
After the object information is available, but before streaming begins.
After streaming begins (this evaluation can be done multiple times, for example 
after playback is paused and restarted).
Windows Media MMS 
streaming transactions
Before the authentication challenge.
Before making an upstream connection, if necessary.
After the authentication challenge but before getting object information.
After the object information is available, but before streaming begins.
After streaming begins (this evaluation can be done multiple times, for example 
after playback is paused and restarted).