16.2 Stateful Proxy

   When stateful, a proxy is purely a SIP transaction processing engine.
   Its behavior is modeled here in terms of the server and client
   transactions defined in Section 17.  A stateful proxy has a server
   transaction associated with one or more client transactions by a
   higher layer proxy processing component (see figure 3), known as a
   proxy core.  An incoming request is processed by a server
   transaction.  Requests from the server transaction are passed to a
   proxy core.  The proxy core determines where to route the request,
   choosing one or more next-hop locations.  An outgoing request for
   each next-hop location is processed by its own associated client
   transaction.  The proxy core collects the responses from the client
   transactions and uses them to send responses to the server
   transaction.

   A stateful proxy creates a new server transaction for each new
   request received.  Any retransmissions of the request will then be
   handled by that server transaction per Section 17.  The proxy core
   MUST behave as a UAS with respect to sending an immediate provisional
   on that server transaction (such as 100 Trying) as described in
   Section 8.2.6.  Thus, a stateful proxy SHOULD NOT generate 100
   (Trying) responses to non-INVITE requests.

   This is a model of proxy behavior, not of software.  An
   implementation is free to take any approach that replicates the
   external behavior this model defines.

   For all new requests, including any with unknown methods, an element
   intending to proxy the request MUST:

      1. Validate the request (Section 16.3)

      2. Preprocess routing information (Section 16.4)

      3. Determine target(s) for the request (Section 16.5)

            +--------------------+
            |                    | +---+
            |                    | | C |
            |                    | | T |
            |                    | +---+
      +---+ |       Proxy        | +---+   CT = Client Transaction
      | S | |  "Higher" Layer    | | C |
      | T | |                    | | T |   ST = Server Transaction
      +---+ |                    | +---+
            |                    | +---+
            |                    | | C |
            |                    | | T |
            |                    | +---+
            +--------------------+

               Figure 3: Stateful Proxy Model


      4. Forward the request to each target (Section 16.6)

      5. Process all responses (Section 16.7)

<< Prev - Next >>