Specification of the Null Service Type
Network Working Group Y. Bernet
Request for Comments: 2997 Microsoft
Category: Standards Track A. Smith
Specification of the Null Service Type
Status of this Memo
This document specifies an Internet standards track protocol for the
Internet community, and requests discussion and suggestions for
improvements. Please refer to the current edition of the "Internet
Official Protocol Standards" (STD 1) for the standardization state
and status of this protocol. Distribution of this memo is unlimited.
Copyright (C) The Internet Society (2000). All Rights Reserved.
In the typical Resource Reservation Protocol (RSVP)/Intserv model,
applications request a specific Intserv service type and quantify the
resources required for that service. For certain applications, the
determination of service parameters is best left to the discretion of
the network administrator. For example, ERP applications are often
mission critical and require some form of prioritized service, but
cannot readily specify their resource requirements. To serve such
applications, we introduce the notion of the 'Null Service'. The
Null Service allows applications to identify themselves to network
Quality of Service (QoS) policy agents, using RSVP signaling.
However, it does not require them to specify resource requirements.
QoS policy agents in the network respond by applying QoS policies
appropriate for the application (as determined by the network
administrator). This mode of RSVP usage is particularly applicable
to networks that combine differentiated service (diffserv) QoS
mechanisms with RSVP signaling [intdiff]. In this environment, QoS
policy agents may direct the signaled application's traffic to a
particular diffserv class of service.
Bernet, et al. Standards Track [Page 1]
RFC 2997 Specification of Null Service Type November 2000
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.
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