RFC 2997 (rfc2997) - Page 2 of 12
Specification of the Null Service Type
Alternative Format: Original Text Document
RFC 2997 Specification of Null Service Type November 2000
1. Motivation
Using standard RSVP/Intserv signaling, applications running on hosts
issue requests for network resources by communicating the following
information to network devices:
1. A requested service level (Guaranteed or Controlled Load).
2. The quantity of resources required at that service level.
3. Classification information by which the network can recognize
specific traffic (filterspec).
4. Policy/identity information indicating the user and/or the
application for which resources are required.
In response, standard RSVP aware network nodes choose to admit or
deny a resource request. The decision is based on the availability
of resources along the relevant path and on policies. Policies
define the resources that may be granted to specific users and/or
applications. When a resource request is admitted, network nodes
install classifiers that are used to recognize the admitted traffic
and policers that are used to assure that the traffic remains within
the limits of the resources requested.
The Guaranteed and Controlled Load Intserv services are not suitable
for certain applications that are unable to (or choose not to)specify
the resources they require from the network. Diffserv services are
better suited for this type of application. Nodes in a diffserv
network are typically provisioned to classify arriving packets to
some small number of behavior aggregates (BAs) [diffarch]. Traffic
is handled on a per-BA basis. This provisioning tends to be 'top-
down' with respect to end-user traffic flows in the sense that there
is no signaling between hosts and the network. Instead, the network
administrator uses a combination of heuristics, measurement and
experience to provision the network devices to handle aggregated
traffic, with no deterministic knowledge of the volume of traffic
that will arrive at any specific node.
In applying diffserv mechanisms to manage application traffic,
network administrators are faced with two challenges:
1. Provisioning - network administrators need to anticipate the
volume of traffic likely to arrive at each network node for each
diffserv BA. If the volume of traffic arriving is likely to
exceed the capacity available for the BA claimed, the network
administrator has the choice of increasing the capacity for the
BA, reducing the volume of traffic claiming the BA, or
compromising service to all traffic arriving for the BA.
Bernet, et al. Standards Track