As per Relevance of the word terminology, we have this rfc below:
Network Working Group J.
Request for Comments: 3134 C.
Category: Informational ANC, Inc
June 2001
Terminology for ATM ABR
Status of this
This memo provides information for the Internet community. It
not specify an Internet standard of any kind. Distribution of
memo is unlimited
Copyright
Copyright (C) The Internet Society (2001). All Rights Reserved
This memo discusses and defines terms associated with
benchmarking tests and the results of these tests in the context
Asynchronous Transfer Mode (ATM) based switching devices
ABR (Available Bit Rate). The terms defined in this memo will
used in addition to terms defined in RFCs 1242, 2285, and 2544
2761. This memo is a product of the Benchmarking Methodology
Group (BMWG) of the Internet Engineering Task Force (IETF).
1.
This document provides terminology for benchmarking ATM
switching devices supporting ABR. It extends terminology
defined for benchmarking network interconnect devices in RFC's 1242,
2285, and 2544 and 2761. Although some of the definitions in
memo may be applicable to a broader group of network
devices, the primary focus of the terminology in this memo is on
ABR
This memo contains two major sections: Background and Definitions
The background section provides the reader with an overview of
technology and IETF formalisms. The definitions section is
into two sub-sections. The formal definitions sub-section
provided as a courtesy to the reader. The measurement
sub-section contains performance metrics with inherent units
This document assumes that necessary services are available
active. For example, IP connectivity requires SSCOP
between signaling entities. Further, it is assumed that the SUT
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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,
has the ability to perform signaled call setups (via UNI or
signaling). Finally, this document presents only the
associated with benchmarking IP performance over ATM; therefore,
does not represent a total compilation of ATM test terminology
The BMWG produces two major classes of documents:
Terminology documents and Benchmarking Methodology documents.
Terminology documents present the benchmarks and other related terms
The Methodology documents define the procedures required to
the benchmarks cited in the corresponding Terminology documents
2. Existing Definitions
RFC 1242, "Benchmarking Terminology for Network
Devices", should be consulted before attempting to make use of
document. RFC 2544, "Benchmarking Methodology for
Interconnect Devices", contains discussions of a number of
relevant to the benchmarking of switching devices and should
consulted. RFC 2285, "Benchmarking Terminology for LAN
Devices", contains a number of terms pertaining to
distributions and datagram interarrival. RFC 2761, "Terminology
ATM Benchmarking", contains a number terms pertaining to
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
benchmarking. These metrics will not be redefined in this document
For the sake of clarity and continuity, this RFC adopts the
for definitions set out in Section 2 of RFC 1242.
II.
The definitions presented in this section have been divided into
groups. The first group is formal definitions, which are required
the definitions of the performance metrics but are not
strictly metrics. These definitions are subsumed from other
done in other working groups both inside and outside the IETF.
are provided as a courtesy to the reader
1. Formal
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
restrictions on measurement procedures
Specification: The working group and document in which the terms
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
(cells/second) at which a source is allowed to send
Discussion: For ABR traffic, ACR constitutes the actual
throughput for a particular VC. The time change of this
effects TCP round trip time calculations, which in turn effects
throughput
Specification: AF-TM4.0
1.2.2. ACR Decrease Time Factor (ADTF
Definition: This is the time permitted between sending RM-
before the rate is decreased to ICR (Initial Cell Rate). The
units are .01 to 10.23 seconds with a granularity of 10 ms
Discussion: For ABR traffic, ADTF constitutes the time rate of
ACR. This value effects TCP round trip time calculations, which
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
the cell transmission rate increases. It is signaled as AIRF,
AIRF = AIR*Nrm/PCR
Discussion: For ABR traffic, AIR effects the time rate of change
the ACR. This value effects TCP round trip time calculations,
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
limiting ATM layer transfer characteristics provided by the
may change subsequent to connection establishment. A flow
mechanism is specified which supports several types of feedback
control the source rate in response to changing ATM layer
characteristics
Discussion: It is expected that an end-system that adapts its
in accordance with the feedback will experience a low cell loss
and obtain a fair share of the available bandwidth according to
network specific allocation policy. Cell delay variation is
controlled in this service, although admitted cells are not
unnecessarily
Specification: AF-TM4.1
1.2.6. Available Bit Rate (ABR) Compliance (Conformance
Definition: ABR connection conformance refers to the
specified for ABR destination and switches, but allows for
between the source and the UNI [UNI3.1, UNI4.0], which may
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
identified as conforming or non-conforming. The minimal
definition for ABR is GCRA((1/PCR),t1), where PCR is defined
CLP=0 flow
Specification: AF-TM4.1
1.2.7.
Definition: The BN bit in the RM-cell indicated whether the RM-
is a BECN cell or not
Discussion: If BN=0, the RM cells were generated by the source.
BN=1, the RM cells were generated by the destination or a switch
Specification: AF-TM4.1
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1.2.8.
Definition: The CCR field in the RM-cell is set by the source to
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
consecutively on a given connection
Discussion: A cell block will normally correspond to the number
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
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
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
the ACR. This value effects TCP round trip time calculations,
in turn effects TCP throughput
Specification: AF-TM4.0
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1.2.12.
Definition: The DIR bit in the RM-cell indicates which direction
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
with data cells flowing in the same direction. A backward RM-cell
indicated by DIR=1 and is associated with data cells flowing in
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
ACR to a specific value. For each RM-cell, ER is set by the
to a requested rate (e.g., PCR). It may be reduced by any
element in the path to a value that the element can sustain. ER
formatted as a rate
Discussion: None
Specification: AF-TM4.1
1.2.14.
Definition: Information carried in the backward RM-cells provided
the network elements and/or the destination back to the source
Discussion: Feedback may include information in the ER field, or
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
difference between itself and the transmission time for the
CLP=0 cell on the connection is greater than or equal to the minimum
a) the inverse of the ACR in effect immediately after
transmission time of the first of the two cells b) the inverse of
ACR in effect immediately before the transmission time of the
of the two cells
Discussion: The transmission time for the first cell on
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
at which a source should send initially and after an idle period
Discussion: none
Specification: AF-TM4.0
1.2.17. In-Rate
Definition: In-Rate ABR cells are sent with CLP=0.
Discussion: ABR RM-cells shall be sent with CLP=0 except in
circumstances, See Out-of-Rate Cells. All other ABR cells shall
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
the rate at which the source is always allowed to send
Discussion: MCR may be set to zero. The bandwidth available from
network may vary, but shall not become less than MCR
Specification: AF-TM4.1
1.2.19.
Definition: An ABR service parameter that controls allocation
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
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.
Definition: An ABR service parameter, Nrm is the maximum number
cells a source may send for each forward RM-cell
Discussion: none
Specification: AF-TM4.0
1.2.22. Out-of-Rate
Definition: Out-of-Rate ABR cells are sent with CLP=1.
Discussion: This may be used to enable a rate increase for
connection that has an ACR=0. The source would generate out-of-
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
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
the ACR. This value effects TCP round trip time calculations,
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
rate may increase upon receipt of a RM-cell. The additive
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
the ACR. This value effects TCP round trip time calculations,
in turn effects TCP throughput
Specification: AF-TM4.0
1.2.25. Resource Management (RM)
Definition: RM cells are used to convey network status (
bandwidth, congestion levels) and request peak cell rates for
blocks. The RM cell has the following format
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Header: 5 bytes, same as the ATM cell header Protocol ID: 3 bytes
protocol ID value is 1 for ABR service Function specific field: 45
bytes, data required for the specific protocol (See DIR, BN, CI, NI
ER, CCR, and MCR for field information.) Rsvd: 6 bytes, reserved
future specification EDC: 10 bytes, CRC-10 error detection
computed over the cell payload .ti6 (except the CRC-10 field)
used to check for data
Discussion: RM information can exist at the VP and/or VC level.
level cells are identified with a VCI value of 6. VC level cells
identified with a PT of 6. See DIR, BN, CI, NI, ER, CCR, and MCR
additional protocol field information
Specification: AF-TM4.0
1.2.26. Severely Errored Cell Block (SECB
Definition: A severely cell block outcome occurs when more than
errored cells, lost cells, or misinserted cell outcomes are
in a received cell block
Discussion: none
Specification: AF-TM4.1
1.2.27. Tagged Cell Rate (TCR
Definition: An ABR service parameter, TCR limits the rate at which
source may send out-of-rate forward RM-cells. TCR is a
fixed at 10 cells/second
Discussion: none
Specification: AF-TM4.0
1.2.28.
Definition: An ABR service parameter, TDF controls the decrease
ACR associated with TOF. TDF is signaled as TDFF, where TDF=TDFF/
times the smallest power of 2 greater or equal to PCR. TDF is
units of 1/seconds
Discussion: For ABR traffic, TDF effects the time rate of change
the ACR. This value effects TCP round trip time calculations,
in turn effects TCP throughput
Specification: AF-TM4.0
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1.2.29.
Definition: Refer to TDF. TDFF is either zero or a power of two
the range 1/64 to 1 in units of 1 /cells
Discussion: Refer to TDF
Specification: AF-TM4.0
1.2.30. Time Out Factor (TOF
Definition: An ABR service parameter, TOF controls the maximum
permitted between sending forward RM-cells before a rate decrease
required. It is signaled as TOFF where TOF=TOFF+1. TOFF is a
of 2 in the range: 1/8 to 4,096.
Discussion: For ABR traffic, TOF effects the time rate of change
the ACR. This value effects TCP round trip time calculations,
in turn effects TCP throughput
Specification: AF-TM4.0
1.2.31. Time Out Factor (TOFF
Definition: Refer to TOF
Discussion: none
Specification: AF-TM4.0
1.2.32.
Definition: An ABR service parameter that provides an upper bound
the time between forward RM-cells for an active source. It is 100
times a power of two with a range of 100*2-7 to 100*20
Discussion: For ABR traffic, Trm effects the time rate of change
the ACR. This value effects TCP round trip time calculations,
in turn effects TCP throughput
Specification: AF-TM4.0
1.2.33. Virtual Source/Virtual Destination (VSND
Definition: An ABR connection may be divided into two or
separately controlled ABR segments. Each ABR control segment,
the first, is sourced by a virtual source. A virtual
implements the behavior of an ABR source endpoint. Backward RM-
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received by a virtual source are removed from the connection.
ABR control segment, except the last, is terminated by a
destination. A virtual destination assumes the behavior of an
destination endpoint. Forward RM-cells received by a
destination are turned around and not forwarded to the next
of the connection
Discussion: none
Specification: AF-TM4.0
1.2.34. Xrm Decrease Factor (XDM
Definition: An ABR service parameter, XDF controls the decrease
ACR associated with Xrm. It is a power of two in range: [0, 1].
Discussion: For ABR traffic, XDM effects the time rate of change
the ACR. This value effects TCP round trip time calculations,
in turn effects TCP throughput
Specification: AF-TM4.0
1.2.35.
Definition: An ABR service parameter, Xrm limits the number
forward RM-cells which may be sent in the absence of
backward PM-cells. The range is 0-255.
Discussion: For ABR traffic, Xrm effects the time rate of change
the ACR. This value effects TCP round trip time calculations,
in turn effects TCP throughput
Specification: AF-TM4.0
2. Performance
2.1. Definition Format (from RFC 1242)
Metric to be defined
Definition: The specific definition for the metric
Discussion: A brief discussion of the metric, its application and
restrictions on measurement procedures
Measurement units: Intrinsic units used to quantify this metric
This includes subsidiary units; e.g., microseconds are acceptable
the intrinsic unit is seconds
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2.2.
2.2.1. ABR Rate Decrease Response Time (ARDRT
Definition: The amount of time required by the SUT to adjust
transmission rate based on an ABR rate decrease request
Discussion: During the ARDRT, cells transmitted by the SUT may
dropped by the network due to traffic policing. These dropped
may contain a portion of an IP datagram. This may cause IP and
packet loss
Measurement Units:
2.2.2. ABR Rate Increase Response Time (ARIRT
Definition: The amount of time required by the SUT to adjust
transmission rate based on an ABR rate increase request
Discussion: During the ARIRT, the SUT will not fully utilize
available bandwidth. This will negatively impact IP and
throughput
Measurement Units:
2.2.3. RM-Cell Delay Variation (RM-CDV
Definition: The variation in RM-cell transfer delay (RM-CTD) of RM
cells associated with a given traffic load, orientation
distribution, as well as an integration period. RM-CDV = max (RM
CTD) - min (RM-CTD) where max and min indicate the maximum
minimum over the integration period, respectively
Discussion: RM-CDV is a component of RM-cell transfer delay,
by buffering and RM-cell scheduling
RM-CDV effects the time required to notify the source of a change
the condition of the network. This in turn effects TCP round
time calculations. Large values of RM-CDV will adversely effect
throughput and cause SAR timeout
Measurement Units:
2.2.4. RM-Cell Error Ratio (RM-CER
Definition: The ratio of RM-cells with payload errors in
transmission in relation to the total number of RM-cells sent in
transmission associated with a given traffic load, orientation
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distribution, as well as an integration period. Note that
occurring in the RM-cell header will cause RM-cell loss at the
layer. Note further that multiple errors in a payload will only
counted as one cell payload error
RM-CER = RM-Cells with payload errors / Total RM-Cells Transmitted
Discussion: The measurement is taken over a time interval and
desirable to be measured on an in-service circuit. RM-CER effects
time required to notify the source of a change in the condition
the network. This in turn effects TCP round trip time calculations
Large values of RM-CER will adversely effect TCP throughput and
SAR timeout
Measurement Units: dimensionless
2.2.5. RM-Cell Loss Ratio (RM-CLR
Definition: The ratio of lost RM-cells in a transmission in
to the total RM-cells sent in a transmission associated with a
traffic load, orientation and distribution, as well as an
period
RM-CLR = Lost RM-Cells / Total RM-Cells Transmitted
Discussion: The objective is to minimize RM-CLR. It is expressed
an order of magnitude, having a range of 10^-1 to 10^-15
unspecified
RM-CLR effects the time required to notify the source of a change
the condition of the network. This in turn effects TCP round
time calculations. Large values of RM-CLR will adversely effect
throughput and cause SAR timeout
Measurement Units: dimensionless
2.2.6. RM-Cell Misinsertion Ratio (RM-CMR
Definition: The ratio of RM-cells received at an endpoint that
not originally transmitted by the source end in relation to the
number of RM-cells properly transmitted associated with a
traffic load, orientation and distribution, as well as an
period
RM-CMR = Misinserted RM-Cells / Total RM-Cells Transmitted
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Discussion: The measurement is taken over a time interval and
desirable to be measured on an in-service circuit
RM-CMR effects the time required to notify the source of a change
the condition of the network. This in turn effects TCP round
time calculations. Large values of RM-CMR will adversely effect
throughput and cause SAR timeout
Measurement Units: dimensionless
2.2.7. RM-CRC Error
Definition: The ratio of RM-cells received at an endpoint
contain an invalid CRC in relation to the total number of RM-
properly transmitted associated with a given traffic load
orientation and distribution, as well as an integration period
Discussion: RM-CRC errors cause ATM RM-cells to be lost
RM-CRC effects the time required to notify the source of a change
the condition of the network. This in turn effects TCP round
time calculations. Large values of RM-CRC will adversely effect
throughput and cause SAR timeout
Measurement Units:
2.2.8. RM-Cell Transfer Delay (RM-CTD
Definition: The elapsed time between a RM-cell exit event at
measurement point 1 (e.g., at the source UNI) and the
RM-cell entry event at a measurement point 2 (e.g., the
UNI) for a particular connection
Discussion: The RM-cell transfer delay between two measurement
is the sum of the total inter-ATM node transmission delay and
total ATM node processing delay. This number is a constant
should not adversely effect performance
Measurement units:
2.2.9. Severely Errored Cell Block Ratio (SECBR
Definition: The ratio of severely errored cell blocks in
transmission in relation to the total cell blocks sent in
transmission associated with a given traffic load, orientation
distribution, as well as an integration period
SECBR = Severely Errored Cell Blocks/Total Transmitted Cell
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Discussion: SECBR may cause the SUT to drop cells that may contain
portion of an IP datagram. This may cause IP and TCP packet loss
Measurement Units: dimensionless
3. Security
As this document is solely for providing terminology and
neither a protocol nor an implementation, there are no
considerations associated with this document
4.
[AF-TM4.0] ATM Forum, Traffic Management Specification Version 4.0,
af-tm-0056.00, April 1996.
[AF-TM4.1] ATM Forum, Traffic Management Specification Version 4.1,
af-tm-0121.000, March 1999.
[AF-UNI3.1] ATM Forum, User Network Interface Specification
3.1, September 1994.
[AF-UNI4.0] ATM Forum, User Network Interface Specification
4.0, July 1996.
5. Editors'
Jeffrey
Advanced Network Consultants, Inc
4214 Crest
Ellicott City, MD 21043
Phone: +1 (410) 750-1700
EMail: Jeffrey.Dunn@worldnet.att.
Cynthia
Advanced Network Consultants, Inc
4214 Crest
Ellicott City, MD 21043
Phone: +1 (410) 750-1700
EMail: Cynthia.E.Martin@worldnet.att.
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Dunn & Martin Informational [Page 16]
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