RFC 3134

Terminology for ATM ABR Benchmarking

📅 published June 2001, from ietf

RFC 3134: Terminology for ATM ABR Benchmarking ✨

Okay bestie, this one is all about ATM ABR benchmarking terminology 💅 It's a glossary, so we're basically learning the vocab before anyone can talk about performance testing. Let's get into it 🦋

Here's the title block, all in one place 🎀 It's an Informational RFC from the Network Working Group, numbered 3134. J. Dunn and C. Martin wrote it at ANC, Inc., and it's dated June 2001. The header doesn't list anything it obsoletes or updates.

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

Abstract

Okay so this memo defines terms for performance benchmarking tests and their results 🔥 The focus is ATM-based switching devices that support ABR (Available Bit Rate). The terms here get used alongside the ones from RFCs 1242, 2285, and 2544 and 2761. It's a product of the Benchmarking Methodology Working Group (BMWG) of the Internet Engineering Task Force (IETF) 🌈

1. Introduction

Bestie, this doc gives you the terminology for benchmarking ATM-based switching devices that support ABR ✨ It builds on the terms already defined for benchmarking network interconnect devices in RFC's 1242, 2285, and 2544 and 2761. Some definitions here could apply to a wider group of network interconnect devices, but the main vibe is ATM ABR 💖

The memo has two big sections, Background and Definitions 📚 The background gives you the tech overview and the IETF formalisms. The definitions section has two sub-sections. The formal definitions sub-section is just there as a courtesy to you 🫶 The measurement definitions sub-section has the performance metrics, and those come with inherent units.

This document assumes the necessary services are available and active 💅 For example, IP connectivity needs SSCOP connectivity between signaling entities. The SUT is also assumed to be able to configure ATM addresses (via hard coded addresses, ILMI or PNNI neighbor discovery), to run SSCOP, and to perform signaled call setups (via UNI or PNNI signaling). Last but not least, this document only covers the terminology for benchmarking IP performance over ATM, so it is not a complete list of ATM test terms 🙈

The BMWG makes two major kinds of documents 🍓 Benchmarking Terminology documents present the benchmarks and related terms. Benchmarking Methodology documents define the procedures you need to collect the benchmarks cited in the matching Terminology documents.

2. Existing Definitions.

Before you touch this doc, you should check out RFC 1242, "Benchmarking Terminology for Network Interconnect Devices" 📖 RFC 2544, "Benchmarking Methodology for Network Interconnect Devices", discusses a bunch of terms that matter for benchmarking switching devices, so it's worth a look too. RFC 2285, "Benchmarking Terminology for LAN Switching Devices", has terms about traffic distributions and datagram interarrival. RFC 2761, "Terminology for ATM Benchmarking", has terms about traffic management [TM4.0, TM4.1]. Lots of the metrics in RFC 2761 (for example CDV, CER, CLR, CMR, and CTD) also apply to ABR performance benchmarking, so they aren't redefined here 🧚 For the sake of clarity and continuity, this RFC uses the definition template from Section 2 of RFC 1242 💅

II. Definitions

Okay this section is split into two groups 👑 The first group is the formal definitions. They're required to define the performance metrics, but they aren't strictly metrics themselves. They're borrowed from other work done in other working groups, both inside and outside the IETF, and they're here as a courtesy to you 🫶

1. Formal Definitions

1.1. Definition Format (from RFC 1242)

Every entry uses the same four labels. First up is the term being defined. Then you get the Definition, the Discussion (a brief talk about the term, how it's used, and any restrictions on measurement procedures), and finally the Specification, which names the working group and document where the term is specified. Those documents are listed in the references section 📚

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 is the actual data throughput for a particular VC. Its value changes over time, which affects TCP round trip time calculations, and that in turn affects 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 is the time rate of the ACR. This value affects TCP round trip time calculations, which in turn affects 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 affects the time rate of change of the ACR. This value affects TCP round trip time calculations, which in turn affects TCP throughput 🌸

Specification: AF-TM4.0

1.2.4. Additive Increase Rate Factor (AIRF)

Definition: Refer to AIR.

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 after 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's expected that an end-system that adapts its traffic to the feedback will see a low cell loss ratio and get a fair share of the available bandwidth, according to a network specific allocation policy. Cell delay variation isn't controlled in this service, although admitted cells aren't 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 apply to CLP=0 cells, which get tested when they arrive. 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

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 match 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 lets a network element say 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, CI is set to 1 to show 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 affects the time rate of change of the ACR. This value affects TCP round trip time calculations, which in turn affects TCP throughput 🌈

Specification: AF-TM4.0

1.2.12. DIR

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

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

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) 🦋

Okay so NI is the bit inside the RM-cell that stops a source from raising its ACR 🙅‍♀️ It doesn't need the rate to go down though, so it's a pure "hold up, not yet" vibe ✨

Discussion: None.

Specification: AF-TM4.0

1.2.21. Nrm 🎀

Nrm is an ABR service parameter, and it's the max number of cells a source is allowed to send for each forward RM-cell. Think of it as a little sending budget per RM-cell 💅

Discussion: none.

Specification: AF-TM4.0

1.2.22. Out-of-Rate Cells 🌸

Out-of-rate ABR cells are the ones sent with CLP=1 🙈

Discussion: This one is super clever ngl 🧠 It can be used to enable a rate increase for a connection whose ACR=0. The source sends out-of-rate cells to probe the network and figure out when it's safe to speed up. It's giving "sneak a peek before you commit" energy 👀

Specification: AF-TM4.1

1.2.23. Rate Decrease Factor (RDF) 🍓

RDF is an ABR service parameter that controls how much the cell transmission rate goes down. It's a power of 2, anywhere from 1/32,768 up to 1 📉

Discussion: For ABR traffic, RDF affects how fast the ACR changes over time ⏱️ And since that matters, it also affects TCP round trip time calculations, which then affects TCP throughput. It's all connected, bestie 🫶

Specification: AF-TM4.0

1.2.24. Rate Increase Factor (RIF) 🌈

This one controls how much the cell transmission rate is allowed to go up when a RM-cell comes in. The additive increase rate is AIR=PCR*RIF, and RIF is a power of 2 from 1/32,768 up to 1 📈

Discussion: For ABR traffic, RIF affects how fast the ACR changes over time, just like RDF does. And yep, that feeds into TCP round trip time calculations, which then affects TCP throughput 💖

Specification: AF-TM4.0

1.2.25. Resource Management (RM) Cells 👑

RM cells are the messengers 💌 They carry network status info (available bandwidth and congestion levels) and request peak cell rates for ATM blocks. The RM cell has the following format:

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 for future specification
EDC: 10 bytes, CRC-10 error detection code computed over the cell
payload .ti6 (except the CRC-10 field) and used to check for data
corruption

Discussion: RM information can live at the VP level and/or the VC level 🗺️ VP-level cells are identified with a VCI value of 6. VC-level cells are identified with a PT of 6. Check out DIR, BN, CI, NI, ER, CCR, and MCR for the extra protocol field details 🔍

Specification: AF-TM4.0

1.2.26. Severely Errored Cell Block (SECB) 💀

A severely errored cell block outcome happens when more than M errored cells, lost cells, or misinserted cell outcomes show up in a received cell block. That's a lot of drama 😭

Discussion: none.

Specification: AF-TM4.1

1.2.27. Tagged Cell Rate (TCR) 🧚

TCR is an ABR service parameter that limits how fast a source can send out-of-rate forward RM-cells. It's a constant, fixed at 10 cells/second, so it's not moving 🔒

Discussion: none.

Specification: AF-TM4.0

1.2.28. TDF 🦋

TDF is an ABR service parameter that controls the decrease in ACR tied to TOF. It's signaled as TDFF, where TDF=TDFF/RDF times the smallest power of 2 that is greater than or equal to PCR. TDF is measured in units of 1/seconds ⏳

Discussion: For ABR traffic, TDF affects how fast the ACR changes over time, and that feeds into TCP round trip time calculations and then TCP throughput. Same storyline, different character 💅

Specification: AF-TM4.0

1.2.29. TDFF 🌟

Refer to TDF! TDFF is either zero or a power of two in the range 1/64 to 1, in units of 1/cells ✨

Discussion: Refer to TDF. (Yes, I'm sending you back up one 😌)

Specification: AF-TM4.0

1.2.30. Time Out Factor (TOF) ⏰

TOF is an ABR service parameter that controls the maximum time allowed between sending forward RM-cells before a rate decrease is required. It's signaled as TOFF, where TOF=TOFF+1. TOFF is a power of 2 in the range 1/8 to 4,096 💖

Discussion: For ABR traffic, TOF affects how fast the ACR changes over time, which then affects TCP round trip time calculations and TCP throughput. It's the same chain of drama every time 🎀

Specification: AF-TM4.0

1.2.31. Time Out Factor (TOFF) 🌙

Refer to TOF 🔁

Discussion: none.

Specification: AF-TM4.0

1.2.32. Trm 🍒

Trm is an ABR service parameter that gives an upper bound on the time between forward RM-cells for an active source. It's 100 times a power of two, with a range of 100*2-7 to 100*20 ⏱️

Discussion: For ABR traffic, Trm affects how fast the ACR changes over time, which feeds into TCP round trip time calculations and then TCP throughput 💜

Specification: AF-TM4.0

1.2.33. Virtual Source/Virtual Destination (VSND) 🪞

Okay, this one is iconic 👑 An ABR connection can be split into two or more separately controlled ABR segments. Each ABR control segment, except the first, is sourced by a virtual source, and a virtual source acts like an ABR source endpoint. Backward RM-cells that a virtual source receives get removed from the connection 🗑️

Each ABR control segment, except the last, is ended by a virtual destination, and a virtual destination acts like an ABR destination endpoint. Forward RM-cells that a virtual destination receives get turned around and are not forwarded to the next segment of the connection. Plot twist 🔄

Discussion: none.

Specification: AF-TM4.0

1.2.34. Xrm Decrease Factor (XDM) 🌺

XDF is an ABR service parameter that controls the decrease in ACR tied to Xrm. It's a power of two in the range [0, 1] 🌷

Discussion: For ABR traffic, XDM affects how fast the ACR changes over time, and then TCP round trip time calculations and TCP throughput get pulled into the chat too 💬

Specification: AF-TM4.0

1.2.35. Xrm 🧁

Xrm is an ABR service parameter that limits the number of forward RM-cells that can be sent when no backward PM-cells have been received. The range is 0-255 🔢

Discussion: For ABR traffic, Xrm affects how fast the ACR changes over time, which feeds into TCP round trip time calculations and TCP throughput. Literally everything is connected in ABR land 🕸️

Specification: AF-TM4.0

2. Performance Metrics ✨

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 any restrictions on measurement procedures.

Measurement units: Intrinsic units used to quantify this metric. This includes subsidiary units, e.g., microseconds are acceptable if the intrinsic unit is seconds.

2.2. Definitions 🔬

2.2.1. ABR Rate Decrease Response Time (ARDRT) 📉

Definition: The amount of time the SUT needs to adjust its transmission rate based on an ABR rate decrease request.

Discussion: During the ARDRT, cells transmitted by the SUT may get dropped by the network due to traffic policing 😬 Those dropped cells may contain a portion of an IP datagram, which may cause IP and TCP packet loss. Not the vibe 💀

Measurement Units: seconds

2.2.2. ABR Rate Increase Response Time (ARIRT) 📈

Definition: The amount of time the SUT needs to adjust its transmission rate based on an ABR rate increase request.

Discussion: During the ARIRT, the SUT will not fully utilize the available bandwidth. That will negatively impact IP and TCP throughput 🥲

Measurement Units: seconds

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, and distribution, as well as an integration period. RM-CDV = max (RM-CTD) - min (RM-CTD), where max and min indicate the maximum and minimum over the integration period, respectively.

Discussion: RM-CDV is a component of RM-cell transfer delay, induced by buffering and RM-cell scheduling 📦

RM-CDV effects the time required to notify the source of a change in the condition of the network. That in turn effects TCP round trip time calculations. Large values of RM-CDV will adversely effect TCP throughput and cause SAR timeout 🚨

Measurement Units: seconds

2.2.4. RM-Cell Error Ratio (RM-CER) ❌

Definition: The ratio of RM-cells with payload errors in a transmission, in relation to the total number of RM-cells sent in a transmission, associated with a given traffic load, orientation, and distribution, as well as an integration period. Note that errors occurring in the RM-cell header will cause RM-cell loss at the ATM layer. Note further that multiple errors in a payload will only be 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 it's desirable to measure it on an in-service circuit 🔌 RM-CER effects the time required to notify the source of a change in the condition of the network. That in turn effects TCP round trip time calculations. Large values of RM-CER will adversely effect TCP throughput and cause 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 relation to the total RM-cells sent in a transmission, associated with a given traffic load, orientation, and distribution, as well as an integration period.

RM-CLR = Lost RM-Cells / Total RM-Cells Transmitted.

Discussion: The objective is to minimize RM-CLR 🎯 It is expressed as an order of magnitude, having a range of 10^-1 to 10^-15 and unspecified.

RM-CLR effects the time required to notify the source of a change in the condition of the network. That in turn effects TCP round trip time calculations. Large values of RM-CLR will adversely effect TCP 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 were not originally transmitted by the source end, in relation to the total number of RM-cells properly transmitted, associated with a given traffic load, orientation, and distribution, as well as an integration period.

RM-CMR = Misinserted RM-Cells / Total RM-Cells Transmitted.

Discussion: The measurement is taken over a time interval, and it's desirable to measure it on an in-service circuit 🔌

RM-CMR effects the time required to notify the source of a change in the condition of the network. That in turn effects TCP round trip time calculations. Large values of RM-CMR will adversely effect TCP throughput and cause SAR timeout 🙃

Measurement Units: dimensionless.

2.2.7. RM-CRC Error Ratio 🧾

Definition: The ratio of RM-cells received at an endpoint which contain an invalid CRC, in relation to the total number of RM-cells 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 in the condition of the network. That in turn effects TCP round trip time calculations. Large values of RM-CRC will adversely effect TCP throughput and cause SAR timeout 🌪️

Measurement Units: dimensionless

2.2.8. RM-Cell Transfer Delay (RM-CTD) 🦋

Definition: okay so this one is the time it takes an RM-cell to get from one spot to another 🚀. It's the elapsed time between an RM-cell leaving at measurement point 1 (like the source UNI) and that same RM-cell showing up at measurement point 2 (like the destination UNI) for a particular connection ✨.

Discussion: the RM-cell transfer delay between two measurement points is the sum of the total inter-ATM node transmission delay and the total ATM node processing delay 💅. bestie, this number is a constant, so it should not adversely effect performance 🌸.

Measurement units: seconds ⏱️

2.2.9. Severely Errored Cell Block Ratio (SECBR) 💀

Definition: this is basically the ratio of severely errored cell blocks to the total cell blocks sent in a transmission 🧁. It's measured against a given traffic load, orientation and distribution, plus an integration period, so the context matters a lot 🎀.

SECBR = Severely Errored Cell Blocks/Total Transmitted Cell Blocks

Discussion: okay this one is kinda scary 😭. SECBR may cause the SUT to drop cells that may contain a portion of an IP datagram. And that may cause IP and TCP packet loss, which is a whole mess 🙈.

Measurement Units: dimensionless. no units needed, it's just a ratio 🌈.

3. Security Considerations 🔐

As this document is solely for providing terminology and describes neither a protocol nor an implementation, there are no security considerations associated with this document. ✨ no protocol, no implementation, so nothing to panic about here 🫶.

4. References 📚

  • [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 Version 3.1, September 1994.
  • [AF-UNI4.0] ATM Forum, User Network Interface Specification Version 4.0, July 1996.

5. Editors' Addresses 💌

Jeffrey Dunn
Advanced Network Consultants, Inc.
4214 Crest Place
Ellicott City, MD 21043 USA

Phone: +1 (410) 750-1700
EMail: Jeffrey.Dunn@worldnet.att.net
Cynthia Martin
Advanced Network Consultants, Inc.
4214 Crest Place
Ellicott City, MD 21043 USA

Phone: +1 (410) 750-1700
EMail: Cynthia.E.Martin@worldnet.att.net

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