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