A service provider supporting guaranteed service implements a queuing
algorithm which isolates the flow from the effects of other flows as much as possible,
and guarantees the flow the ability to propagate data at the TokenRate for the
duration of the connection. If the sender sends faster than that rate, the
network may delay or discard the excess traffic. If the sender does not exceed
TokenRate over time, then latency is also guaranteed. This service is designed for
applications which require a precisely known quality of service but would not
benefit from better service, such as real-time control systems.
A service provider supporting predictive service guarantees the flow the
ability to propagate data at the TokenRate for the duration of the connection. If
the sender sends faster than that rate, the network may delay or discard the
excess traffic. The delay limit is not guaranteed (occasional packets may take
longer than specified), but is generally highly reliable. This service is designed
for applications that can accommodate or adapt to some variation in service
quality, such as video service.
With this service, end-to-end behavior provided to an application by a series
of network elements tightly approximates the behavior visible to applications
receiving best-effort service "under unloaded conditions" from the same series
of network elements. Thus, applications using this service can assume that:
- A very high percentage of transmitted packets will be successfully delivered
by the network to the receiving end-nodes. (Packet loss rate will closely
approximate the basic packet error rate of the transmission medium).
- Transit delay experienced by a very high percentage of the delivered packets
will not greatly exceed the minimum transit delay experienced by any
successfully delivered packet at the speed of light.
This definition comes from the Internet Engineering Task Force (IETF).
A service provider supporting best effort service, at minimum, takes the flow
spec as a guideline and makes reasonable efforts to maintain the level of
service requested, however without making any guarantees whatsoever.
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