A Proposed Flow Specification
RFC 1363

Document Type RFC - Informational (September 1992; No errata)
Author Craig Partridge 
Last updated 2013-03-02
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Network Working Group                                     C. Partridge
Request for Comments: 1363                                         BBN
                                                        September 1992

                     A Proposed Flow Specification

Status of this Memo

   This memo provides information for the Internet community.  It does
   not specify an Internet standard.  Distribution of this memo is


   A flow specification (or "flow spec") is a data structure used by
   internetwork hosts to request special services of the internetwork,
   often guarantees about how the internetwork will handle some of the
   hosts' traffic.  In the future, hosts are expected to have to request
   such services on behalf of distributed applications such as
   multimedia conferencing.

   The flow specification defined in this memo is intended for
   information and possible experimentation (i.e., experimental use by
   consenting routers and applications only).  This RFC is a product of
   the Internet Research Task Force (IRTF).


   The Internet research community is currently studying the problems of
   supporting a new suite of distributed applications over
   internetworks.  These applications, which include multimedia
   conferencing, data fusion, visualization, and virtual reality, have
   the property that they require the distributed system (the collection
   of hosts that support the applications along with the internetwork to
   which they are attached) be able to provide guarantees about the
   quality of communication between applications.  For example, a video
   conference may require a certain minimum bandwidth to be sure that
   the video images are delivered in a timely way to all recipients.

   One way for the distributed system to provide guarantees is for hosts
   to negotiate with the internetwork for rights to use a certain part
   of the internetwork's resources.  (An alternative is to have the
   internetwork infer the hosts' needs from information embedded in the
   data traffic each host injects into the network.  Currently, it is
   not clear how to make this scheme work except for a rather limited
   set of traffic classes.)

Partridge                                                       [Page 1]
RFC 1363             A Proposed Flow Specification        September 1992

   There are a number of ways to effect a negotiation.  For example a
   negotiation can be done in-band or out-of-band.  It can also be done
   in advance of sending data (possibly days in advance), as the first
   part of a connection setup, or concurrently with sending (i.e., a
   host starts sending data and starts a negotiation to try to ensure
   that it will allowed to continue sending).  Insofar as is possible,
   this memo is agnostic with regard to the variety of negotiation that
   is to be done.

   The purpose of this memo is to define a data structure, called a flow
   specification or flow spec, that can be used as part of the
   negotiation to describe the type of service that the hosts need from
   the internetwork.  This memo defines the format of the fields of the
   data structure and their interpretation.  It also briefly describes
   what purpose the different fields fill, and discusses why this set of
   fields is thought to be both necessary and sufficient.

   It is important to note that the goal of this flow spec is to able to
   describe *any* flow requirement, both for guaranteed flows and for
   applications that simply want to give hints to the internetwork about
   their requirements.

Format of the Flow Spec

       0                   1                   2                   3
       0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
      |              Version          |    Maximum Transmission Unit  |
      |      Token Bucket Rate        |        Token Bucket Size      |
      |  Maximum Transmission Rate    |     Minimum Delay Noticed     |
      |     Maximum Delay Variation   |        Loss Sensitivity       |
      |     Burst Loss Sensitivity    |          Loss Interval        |
      |    Quality of Guarantee       |

Discussion of the Flow Spec

   The flow spec indicates service requirements for a single direction.
   Multidirectional flows will need to request services in both
   directions (using two flow specs).

   To characterize a unidirectional flow, the flow spec needs to do four

Partridge                                                       [Page 2]
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