RFC 2210 (rfc2210) - Page 3 of 33
The Use of RSVP with IETF Integrated Services
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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
