rfc3134.txt

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Network Working Group                                            J. Dunn
Request for Comments: 3134                                     C. Martin
Category: Informational                                        ANC, Inc.
                                                               June 2001


                  Terminology for ATM ABR Benchmarking

Status of this Memo

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

Copyright Notice

   Copyright (C) The Internet Society (2001).  All Rights Reserved.

Abstract

   This memo discusses and defines terms associated with performance
   benchmarking tests and the results of these tests in the context of
   Asynchronous Transfer Mode (ATM) based switching devices supporting
   ABR (Available Bit Rate).  The terms defined in this memo will be
   used in addition to terms defined in RFCs 1242, 2285, and 2544 and
   2761.  This memo is a product of the Benchmarking Methodology Working
   Group (BMWG) of the Internet Engineering Task Force (IETF).

1. Introduction

   This document provides terminology for benchmarking ATM based
   switching devices supporting ABR.  It extends terminology already
   defined for benchmarking network interconnect devices in RFC's 1242,
   2285, and 2544 and 2761.  Although some of the definitions in this
   memo may be applicable to a broader group of network interconnect
   devices, the primary focus of the terminology in this memo is on ATM
   ABR.

   This memo contains two major sections: Background and Definitions.
   The background section provides the reader with an overview of the
   technology and IETF formalisms.  The definitions section is split
   into two sub-sections.  The formal definitions sub-section is
   provided as a courtesy to the reader.  The measurement definitions
   sub-section contains performance metrics with inherent units.

   This document assumes that necessary services are available and
   active.  For example, IP connectivity requires SSCOP connectivity
   between signaling entities.  Further, it is assumed that the SUT has



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   the ability to configure ATM addresses (via hard coded addresses,
   ILMI or PNNI neighbor discovery), has the ability to run SSCOP, and
   has the ability to perform signaled call setups (via UNI or PNNI
   signaling).  Finally, this document presents only the terminology
   associated with benchmarking IP performance over ATM; therefore, it
   does not represent a total compilation of ATM test terminology.

   The BMWG produces two major classes of documents: Benchmarking
   Terminology documents and Benchmarking Methodology documents.  The
   Terminology documents present the benchmarks and other related terms.
   The Methodology documents define the procedures required to collect
   the benchmarks cited in the corresponding Terminology documents.

2. Existing Definitions.

   RFC 1242, "Benchmarking Terminology for Network Interconnect
   Devices", should be consulted before attempting to make use of this
   document.  RFC 2544, "Benchmarking Methodology for Network
   Interconnect Devices", contains discussions of a number of terms
   relevant to the benchmarking of switching devices and should be
   consulted.  RFC 2285, "Benchmarking Terminology for LAN Switching
   Devices", contains a number of terms pertaining to traffic
   distributions and datagram interarrival.  RFC 2761, "Terminology for
   ATM Benchmarking", contains a number terms pertaining to traffic
   management [TM4.0, TM4.1].  Many of the metrics defined in RFC 2761
   (e.g., CDV, CER, CLR, CMR, and CTD) also apply to ABR performance
   benchmarking.  These metrics will not be redefined in this document.
   For the sake of clarity and continuity, this RFC adopts the template
   for definitions set out in Section 2 of RFC 1242.

II. Definitions

   The definitions presented in this section have been divided into two
   groups.  The first group is formal definitions, which are required in
   the definitions of the performance metrics but are not themselves
   strictly metrics.  These definitions are subsumed from other work
   done in other working groups both inside and outside the IETF.  They
   are provided as a courtesy to the reader.

1. Formal Definitions

1.1. Definition Format (from RFC 1242)

   Term to be defined.

   Definition: The specific definition for the term.





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   Discussion: A brief discussion of the term, its application and any
   restrictions on measurement procedures.

   Specification: The working group and document in which the terms are
   specified and are listed in the references section.

1.2. Related Definitions.

1.2.1. Allowed Cell Rate (ACR)

   Definition: An ABR service parameter, ACR is the current rate
   (cells/second) at which a source is allowed to send.

   Discussion: For ABR traffic, ACR constitutes the actual data
   throughput for a particular VC.  The time change of this value
   effects TCP round trip time calculations, which in turn effects TCP
   throughput.

   Specification: AF-TM4.0

1.2.2. ACR Decrease Time Factor (ADTF)

   Definition: This is the time permitted between sending RM-cells
   before the rate is decreased to ICR (Initial Cell Rate). The time
   units are .01 to 10.23 seconds with a granularity of 10 ms.

   Discussion: For ABR traffic, ADTF constitutes the time rate of the
   ACR.  This value effects TCP round trip time calculations, which in
   turn effects TCP throughput.

   Specification: AF-TM4.0

1.2.3. Additive Increase Rate (AIR)

   Definition: An ABR service parameter, AIR controls the rate at which
   the cell transmission rate increases.  It is signaled as AIRF, where

       AIRF = AIR*Nrm/PCR.

   Discussion: For ABR traffic, AIR effects the time rate of change of
   the ACR.  This value effects TCP round trip time calculations, which
   in turn effects TCP throughput.

   Specification: AF-TM4.0

1.2.4. Additive Increase Rate Factor (AIRF)

   Definition: Refer to AIR.



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   Discussion: Refer to AIR.

   Specification: AF-TM4.0

1.2.5. Available Bit Rate (ABR)

   Definition: ABR is an ATM layer service category for which the
   limiting ATM layer transfer characteristics provided by the network
   may change subsequent to connection establishment.  A flow control
   mechanism is specified which supports several types of feedback to
   control the source rate in response to changing ATM layer transfer
   characteristics.

   Discussion: It is expected that an end-system that adapts its traffic
   in accordance with the feedback will experience a low cell loss ratio
   and obtain a fair share of the available bandwidth according to a
   network specific allocation policy.  Cell delay variation is not
   controlled in this service, although admitted cells are not delayed
   unnecessarily.

   Specification: AF-TM4.1

1.2.6. Available Bit Rate (ABR) Compliance (Conformance)

   Definition: ABR connection conformance refers to the behavior
   specified for ABR destination and switches, but allows for delays
   between the source and the UNI [UNI3.1, UNI4.0], which may perturb
   the traffic flow.

   Discussion: The cells on an ABR connection applies to CLP=0 cells,
   which are tested upon arrival.  At the arrival point, each cell is
   identified as conforming or non-conforming.  The minimal conformance
   definition for ABR is GCRA((1/PCR),t1), where PCR is defined for
   CLP=0 flow.

   Specification: AF-TM4.1

1.2.7. BN

   Definition: The BN bit in the RM-cell indicated whether the RM-cell
   is a BECN cell or not.

   Discussion: If BN=0, the RM cells were generated by the source.  If
   BN=1, the RM cells were generated by the destination or a switch.

   Specification: AF-TM4.1





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1.2.8. CCR

   Definition: The CCR field in the RM-cell is set by the source to its
   current ACR.  CCR is formatted as a rate.

   Discussion: For BECN cells, CCR=0.

   Specification: AF-TM4.1

1.2.9. Cell Blocks (CB)

   Definition: Cell blocks are a sequence of N cells transmitted
   consecutively on a given connection.

   Discussion: A cell block will normally correspond to the number of
   information cells transmitted between successive OAM cells.

   Specification: AF-TM4.1

1.2.10. Congestion Indication (CI)

   Definition: The CI bit in the RM-cell allows a network element to
   indicate that there is congestion in the network.

   Discussion: When the source receives a backward RM-cell with CI=1,
   ACR is decreased.  When the destination turns around a forward RM-
   cell, the CI is set to 1 to indicate that the previously received
   data cell had the EFCI state set.

   Specification: AF-TM4.1

1.2.11. Cutoff Decrease Factor (CDF)

   Definition: CDF controls the decrease in ACR (Allowed Cell Rate)
   associated with CRM (missing RM cell count).

   Discussion: For ABR traffic, CDF effects the time rate of change of
   the ACR.  This value effects TCP round trip time calculations, which
   in turn effects TCP throughput.

   Specification: AF-TM4.0










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1.2.12. DIR

   Definition: The DIR bit in the RM-cell indicates which direction of
   data flow is associated with the RM-cell.  DIR is changed from 0 to 1
   when an RM-cell is turned around at the destination.

   Discussion: A forward RM-cell is indicated by DIR=0 and is associated
   with data cells flowing in the same direction.  A backward RM-cell is
   indicated by DIR=1 and is associated with data cells flowing in the
   opposite direction.

   Specification: AF-TM4.1

1.2.13. Explicit Rate (ER)

   Definition: The ER field in the RM-cell is used to limit the source
   ACR to a specific value.  For each RM-cell, ER is set by the source
   to a requested rate (e.g., PCR).  It may be reduced by any network
   element in the path to a value that the element can sustain.  ER is
   formatted as a rate.

   Discussion: None.

   Specification: AF-TM4.1

1.2.14. Feedback

   Definition: Information carried in the backward RM-cells provided by
   the network elements and/or the destination back to the source.

   Discussion: Feedback may include information in the ER field, or the
   CI or NI bits of each backward RM-cell.

   Specification: AF-TM4.1

1.2.15. Ideal Transmission Time (ITT)

   Definition: The transmission time for ABR CLP=0 cells, if the
   difference between itself and the transmission time for the previous
   CLP=0 cell on the connection is greater than or equal to the minimum:
   a) the inverse of the ACR in effect immediately after the
   transmission time of the first of the two cells b) the inverse of the
   ACR in effect immediately before the transmission time of the second
   of the two cells.

   Discussion: The transmission time for the first cell on the
   connection is automatically an ITT.




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   Specification: AF-TM4.1

1.2.16. Initial Cell Rate (ICR)

   Definition: An ABR service parameter, in cells/sec, that is the rate
   at which a source should send initially and after an idle period.

   Discussion: none.

   Specification: AF-TM4.0

1.2.17. In-Rate Cells

   Definition: In-Rate ABR cells are sent with CLP=0.

   Discussion: ABR RM-cells shall be sent with CLP=0 except in certain
   circumstances, See Out-of-Rate Cells.  All other ABR cells shall be
   sent with CLP=0.

   Specification: AF-TM4.1

1.2.18. Minimum Cell Rate (MCR)

   Definition: An ABR service traffic descriptor, in cells/sec, that is
   the rate at which the source is always allowed to send.

   Discussion: MCR may be set to zero.  The bandwidth available from the
   network may vary, but shall not become less than MCR.

   Specification: AF-TM4.1

1.2.19. Mrm

   Definition: An ABR service parameter that controls allocation of
   bandwidth between forward W-cells, backward RM-cells, and data cells.

   Discussion: none.

   Specification: AF-TM4.0

1.2.20. No Increase (NI)

   Definition: The NI bit in the RM-cell is used to prevent a source
   from increasing its ACR.  NI does not require any decrease in value.

   Discussion: None.

   Specification: AF-TM4.0



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1.2.21. Nrm

   Definition: An ABR service parameter, Nrm is the maximum number of
   cells a source may send for each forward RM-cell.

   Discussion: none.

   Specification: AF-TM4.0

1.2.22. Out-of-Rate Cells

   Definition: Out-of-Rate ABR cells are sent with CLP=1.

   Discussion: This may be used to enable a rate increase for a
   connection that has an ACR=0.  The source would generate out-of-rate
   cells to probe the network to learn when it may increase its rate.

   Specification: AF-TM4.1

1.2.23. Rate Decrease Factor (RDF)

   Definition: An ABR service parameter, RDF controls the decrease in
   the cell transmission rate.  RDF is a power of 2 from 1/32,768 to 1.

   Discussion: For ABR traffic, RDF effects the time rate of change of
   the ACR.  This value effects TCP round trip time calculations, which
   in turn effects TCP throughput.

   Specification: AF-TM4.0

1.2.24. Rate Increase Factor (RIF)

   Definition: This controls the amount by which the cell transmission
   rate may increase upon receipt of a RM-cell.  The additive increase
   rate AIR=PCR*RIF.  RIF is a power of 2, ranging from 1/32,768 to 1.

   Discussion: For ABR traffic, RIF effects the time rate of change of
   the ACR.  This value effects TCP round trip time calculations, which
   in turn effects TCP throughput.

   Specification: AF-TM4.0

1.2.25. Resource Management (RM) Cells

   Definition: RM cells are used to convey network status  (available
   bandwidth, congestion levels) and request peak cell rates for ATM
   blocks.  The RM cell has the following format:




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