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Versions: 00 01 02 rfc2215                                              
Internet Engineering Task Force                   Integrated Services WG
INTERNET-DRAFT                                             Scott Shenker
draft-ietf-intserv-charac-00.txt                              XEROX PARC
                                                        14 November 1995
                                                         Expires: ?/?/96



          Specification of General Characterization Parameters


Status of this Memo


   This document is an Internet-Draft.  Internet-Drafts are working
   documents of the Internet Engineering Task Force (IETF), its areas,
   and its working groups.  Note that other groups may also distribute
   working documents as Internet-Drafts.

   Internet-Drafts are draft documents valid for a maximum of six months
   and may be updated, replaced, or obsoleted by other documents at any
   time.  It is inappropriate to use Internet-Drafts as reference
   material or to cite them other than as ``work in progress.''

   To learn the current status of any Internet-Draft, please check the
   ``1id-abstracts.txt'' listing contained in the Internet-Drafts Shadow
   Directories on ftp.is.co.za (Africa), nic.nordu.net (Europe),
   munnari.oz.au (Pacific Rim), ds.internic.net (US East Coast), or
   ftp.isi.edu (US West Coast).

   This document is a product of the Integrated Services working group
   of the Internet Engineering Task Force.  Comments are solicited and
   should be addressed to the working group's mailing list at int-
   serv@isi.edu and/or the author(s).


Abstract


      This memo defines general characterization parameters for network
      elements supporting enhanced qualities of service.  General
      characterization parameters are those that are not specific to a
      particular quality of service.








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Introduction


   This memo defines general, or service-independent, characterization
   parameters for network elements.  General characterization parameters
   are those that are not specific to a particular quality of service.
   A discussion of how these parameters fit into an integrated services
   architecture can be found in [1].  Please refer to that document for
   definitions and additional information about the specification of
   qualities of service within the IP protocol family.

   The specifications of the various qualities of service ([2-4])
   describe the associated characterization parameters that must be
   exported.  However, there are some quantities of interest that are
   not specific to a particular quality of service.  These "general"
   characterizations are described in this document.

   Characterization parameters associated with a particular service are
   attached to a service_name.  The service-name associated with general
   characterizations is 0.  We describe these general characterization
   parameters below.


Number of IS Hops

   IS stands for "integrated services aware".  An integrated services
   aware network element is one that conforms to the various
   requirements described in this document and the documents [1-4] (it
   need not offer those services, but if it does it supports and
   characterizes the services in conformance with the relevant
   specification).  The composition rule is to increment the counter by
   one.  This quantity, when composed end-to-end, informs the endpoint
   of the number of Integrated-Services aware network elements
   traversed along the path from sender to receiver.  The parameter_name
   for this field is 1.  The characterization parameter may be
   represented as a single 16-bit unsigned integer in network byte
   order.



Number of IP Hops

   The local parameter is the number of IP hops between the last (i.e.,
   upstream) IS network element and this one.  Observe that since the
   network element may not be aware of its neighbor on the the upstream
   path, *the local parameter must be provided to the network element by
   the setup protocol* (possibly by tracking the TTL value).




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   The composition rule is additive.  This quantity, when composed end-
   to-end, informs the endpoint of the number of IP network elements
   ("hops") traversed along the path from sender to receiver.  The
   parameter_name for local parameter is 2.  The parameter_name for the
   composed quantity is 3.  These characterization parameters may be
   represented as 16-bit unsigned integers in network byte order.

   Comparison of the end-to-end composition of the two previous
   characterization values will yield the number of non-IS network
   elements  along the path.

Bandwidth

   The local parameter is the bandwidth of the network element. For
   links, this value would be the bandwidth of the link.  The
   composition rule is to take the minimum of the network element's
   value and the previously composed value.  This quantity, when
   composed end-to-end, informs the endpoint of the minimal bandwidth
   link along the path from sender to receiver.  The parameter_name for
   the bandwidth of the network element's link is 4.  The parameter_name
   for the composed minimal bandwidth along the path is 5.

   These values are measured in bytes per second, and can range from 1
   byte per second to as large as 40 terabytes per second (or about what
   is believed to be the maximum theoretical bandwidth of a single
   strand of fiber).  Clearly, particularly for large bandwidths, only
   the first few digits are significant and so the use of floating point
   representations, accurate to at least 0.1% is encouraged.  These
   characterizations of bandwidth can be represented by floating point
   numbers in single-precision IEEE floating point format.

      NOTE: If the number of IS hops is less than the number of IP hops,
      end systems should treat this value as a hint rather than a
      reliable value.


Latency

   The local parameter is the latency of the link associated with the
   network element, where the latency is defined to be the minimal
   possible packet delay along the path taken by the flow.  This delay
   may result from "speed-of-light" propagation delay, or from packet
   processing limitations, or both.  The composition rule is additive.
   This quantity, when composed end-to-end, informs the endpoint of the
   minimal packet delay along the path from sender to receiver.  The
   parameter_name for the latency of the network element's link is 6.
   The parameter_name for the cumulative latency along the path is 7.




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   The delays are measured in units of one microsecond.  An individual
   element can advertise a delay value between 1 and 2**28 (somewhat
   over two minutes) and the total delay added across all elements can
   range as high as (2**32)-1.  Should the sum of the different elements
   delay exceed (2**32)-1, the end-to-end advertised delay should be
   (2**32)-1.

   Note that while the granularity of measurement is microseconds, a
   conforming element is free to measure delays more loosely.  The
   minimum requirement is that the element estimate its delay accurately
   to the nearest 100 microsecond granularity.  Elements that can
   measure more accurately are, of course, encouraged to do so.

      NOTE: If the number of IS hops is less than the number of IP hops,
      end systems should treat this value as a hint rather than a
      promised value.

      NOTE: Measuring in milliseconds is not acceptable, because if the
      minimum delay value is a millisecond, a path with several hops
      will lead to a composed delay of at least several milliseconds,
      which is likely to be misleading.

   The characterization parameters may be represented as 32-bit unsigned
   integers in network byte order.

      NOTE: There are some subnet technologies where determining this
      minimal delay is difficult.  For instance, the speed-of-light
      delays on an ethernet bridged via satellite with another ethernet
      vary by several orders of magnitude.  The exported values should
      be conservative estimates of the delays.  Any additional delays
      (that is, delays larger than this minimal amount) must be
      considered part of the variable delays which are described by
      characterizations specific to the individual services.  For
      example, in predictive service the maximal delay experienced going
      from one network element to the next should be the delay bound
      plus the latency.



MTU

   The local characterization parameter is the MTU, where the MTU of a
   network element is defined to be the maximum transmission unit the
   network element can accommodate without fragmentation.  The
   composition rule is to take the minimum of the network element's MTU
   and the previously composed value. This quantity, when composed end-
   to-end, informs the endpoint of the maximum transmission unit that
   can traverse the path from sender to receiver without fragmentation.



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   The parameter_name for the MTU of the network element's link is 8.
   The parameter_name for the composed MTU along the path is 9.

      NOTE: If the number of IS hops is less than the number of IP hops,
      end systems should treat this value as a hint rather than a
      promised value.


Service Availability

   The INT SERV working group is still developing proposals for handling
   heterogeneity. When that work is complete, a set of requirement
   parameters will be defined.


Security Considerations

   Security considerations are not discussed in this memo.

References


   [1] S. Shenker and J. Wroclawski. "Network Element Service
   Specification Template", Internet Draft, June 1995, <draft-ietf-
   intserv-svc-template-01.txt>

   [2] S. Shenker, C. Partridge, and J. Wroclawski. "Specification of
   Controlled Delay Quality of Service", Internet Draft, ?? 1995,
   <draft-ietf-intserv-control-del-svc-02.txt>

   [3] S. Shenker and C. Partridge. Specification of Guaranteed Quality
   of Service", Internet Draft, ?? 1995, <draft-ietf-intserv-
   guaranteed-svc-03.txt>

   [4] S. Shenker, C. Partridge, B. Davie, and L. Breslau.
   "Specification of Predictive Quality of Service", Internet Draft, ??
   1995, <draft-ietf-intserv-predictive-svc-01.txt>



Author's Address:


   Scott Shenker
   Xerox PARC
   3333 Coyote Hill Road
   Palo Alto, CA  94304-1314
   shenker@parc.xerox.com



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