RFC 2210 (rfc2210) - Page 3 of 33

The Use of RSVP with IETF Integrated Services

RFC 2210                   RSVP with INTSERV              September 1997


      - Information generated at each sender describing the data traffic
      generated by that sender (the Sender TSpec). This information is
      carried from the sender to intermediate network elements and the
      receiver(s) by RSVP, but is never modified by intermediate
      elements within the network. This information is carried in RSVP
      SENDER_TSPEC objects.

      - Information generated or modified within the network and used at
      the receivers to make reservation decisions.  This information
      might include available services, delay and bandwidth estimates,
      and operating parameters used by specific QoS control services.
      this information is collected from network elements and carried
      towards receivers in RSVP ADSPEC objects.  Rather than carrying
      information from each intermediate node separately to the
      receivers, the information in the ADSPEC represents a summary,
      computed as the ADSPEC passes each hop.  The size of this summary
      remains (roughly) constant as the ADSPEC flows through the
      network, giving good scaling properties.

   From the point of view of RSVP objects, the breakdown is as follows:

      - The RSVP SENDER_TSPEC object carries the traffic specification
      (sender TSpec) generated by each data source within an RSVP
      session.  It is transported unchanged through the network, and
      delivered to both intermediate nodes and receiving applications.

      - The RSVP ADSPEC object carries information which is generated at
      either data sources or intermediate network elements, is flowing
      downstream towards receivers, and may be used and updated inside
      the network before being delivered to receiving applications.
      This information includes both parameters describing the
      properties of the data path, including the availability of
      specific QoS control services, and parameters required by specific
      QoS control services to operate correctly.

      - The RSVP FLOWSPEC object carries reservation request
      (Receiver_TSpec and RSpec) information generated by data
      receivers.  The information in the FLOWSPEC flows upstream towards
      data sources.  It may be used or updated at intermediate network
      elements before arriving at the sending application.

        NOTE: The existence of both SENDER_TSPEC and ADSPEC RSVP objects
        is somewhat historical. Using the message format described in
        this note it would be possible to place all of the service
        control information carried "downstream" by RSVP in the same
        object. However, the distinction between data which is not
        updated within the network (in the SENDER_TSPEC object) and data
        which is updated within the network (in the ADSPEC object) may



Wroclawski                  Standards Track