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RFC 2326 Real Time Streaming Protocol April 1998| "proxy-revalidate"| "max-age" "=" delta-seconds| cache-extensioncache-extension = token [ "=" ( token | quoted-string ) ]no-cache:Indicates that the media stream MUST NOT be cached anywhere.This allows an origin server to prevent caching even by cachesthat have been configured to return stale responses to clientrequests.public:Indicates that the media stream is cacheable by any cache.private:Indicates that the media stream is intended for a single userand MUST NOT be cached by a shared cache. A private (nonshared)cache may cache the media stream.no-transform:An intermediate cache (proxy) may find it useful to convertthe media type of a certain stream. A proxy might, forexample, convert between video formats to save cache space orto reduce the amount of traffic on a slow link. Seriousoperational problems may occur, however, when thesetransformations have been applied to streams intended forcertain kinds of applications. For example, applications formedical imaging, scientific data analysis and those usingend-to-end authentication all depend on receiving a streamthat is bit-for-bit identical to the original entity-body.Therefore, if a response includes the no-transform directive,an intermediate cache or proxy MUST NOT change the encoding ofthe stream. Unlike HTTP, RTSP does not provide for partialtransformation at this point, e.g., allowing translation intoa different language.only-if-cached:In some cases, such as times of extremely poor networkconnectivity, a client may want a cache to return only thosemedia streams that it currently has stored, and not to receivethese from the origin server. To do this, the client mayinclude the only-if-cached directive in a request. If itreceives this directive, a cache SHOULD either respond using acached media stream that is consistent with the otherconstraints of the request, or respond with a 504 (GatewayTimeout) status. However, if a group of caches is beingoperated as a unified system with good internal connectivity,such a request MAY be forwarded within that group of caches.Schulzrinne, et. al. Standards Track [Page 48]
RFC 2326 Real Time Streaming Protocol April 1998max-stale:Indicates that the client is willing to accept a media streamthat has exceeded its expiration time. If max-stale isassigned a value, then the client is willing to accept aresponse that has exceeded its expiration time by no more thanthe specified number of seconds. If no value is assigned tomax-stale, then the client is willing to accept a staleresponse of any age.min-fresh:Indicates that the client is willing to accept a media streamwhose freshness lifetime is no less than its current age plusthe specified time in seconds. That is, the client wants aresponse that will still be fresh for at least the specifiednumber of seconds.must-revalidate:When the must-revalidate directive is present in a SETUPresponse received by a cache, that cache MUST NOT use theentry after it becomes stale to respond to a subsequentrequest without first revalidating it with the origin server.That is, the cache must do an end-to-end revalidation everytime, if, based solely on the origin server’s Expires, thecached response is stale.)12.9 ConferenceThis request header field establishes a logical connection between apre-established conference and an RTSP stream. The conference-id mustnot be changed for the same RTSP session.Conference = "Conference" ":" conference-id Example:Conference: 199702170042.SAA08642@obiwan.arl.wustl.edu%20StarrA response code of 452 (452 Conference Not Found) is returned if theconference-id is not valid.12.10 ConnectionSee [H14.10]12.11 Content-BaseSee [H14.11]12.12 Content-EncodingSee [H14.12]Schulzrinne, et. al. Standards Track [Page 49]
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