RFC 2211 (rfc2211) - Page 2 of 19

Specification of the Controlled-Load Network Element Service

RFC 2211                Controlled-Load Network           September 1997


2. End-to-End Behavior

   The end-to-end behavior provided to an application by a series of
   network elements providing controlled-load service tightly
   approximates the behavior visible to applications receiving best-
   effort service *under unloaded conditions* from the same series of
   network elements.  Assuming the network is functioning correctly,
   these applications may assume that:

     - A very high percentage of transmitted packets will be
     successfully delivered by the network to the receiving end-nodes.
     (The percentage of packets not successfully delivered must closely
     approximate the basic packet error rate of the transmission
     medium).

     - The transit delay experienced by a very high percentage of the
     delivered packets will not greatly exceed the minimum transmit
     delay experienced by any successfully delivered packet. (This
     minimum transit delay includes speed-of-light delay plus the fixed
     processing time in routers and other communications devices along
     the path.)

   To ensure that these conditions are met, clients requesting
   controlled-load service provide the intermediate network elements
   with a estimation of the data traffic they will generate; the TSpec.
   In return, the service ensures that network element resources
   adequate to process traffic falling within this descriptive envelope
   will be available to the client. Should the client's traffic
   generation properties fall outside of the region described by the
   TSpec parameters, the QoS provided to the client may exhibit
   characteristics indicative of overload, including large numbers of
   delayed or dropped packets. The service definition does not require
   that the precise characteristics of this overload behavior match
   those which would be received by a best-effort data flow traversing
   the same path under overloaded conditions.

      NOTE: In this memo, the term "unloaded" is used in the sense of
      "not heavily loaded or congested" rather than in the sense of "no
      other network traffic whatsoever".

3. Motivation

   The controlled load service is intended to support a broad class of
   applications which have been developed for use in today's Internet,
   but are highly sensitive to overloaded conditions.  Important members
   of this class are the "adaptive real-time applications" currently





Wroclawski                 Standards Track