RFC 2211 (rfc2211) - Page 2 of 19
Specification of the Controlled-Load Network Element Service
Alternative Format: Original Text Document
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