Subject: Terminology for Call/Cell Benchmarking

From: Kevin Dubray <[email-masked]>
Date: Tue, 04 Aug 1998 15:34:57 -0400

Network Working Group                                        J. H. Dunn 
INTERNET-DRAFT                                          Hewlett-Packard 
Expires in six months                                      C. E.
Martin        
                                                       
Hewlett-Packard    
                                                            August 1998

                 Terminology for Call/Cell Benchmarking

Status of this Memo

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   This memo provides information for the Internet community.  This memo
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Abstract

This memo discusses and defines terms associated with performance 
benchmarking tests and the results of these tests in the context 
of cell-based and call-based switching devices.  The terms defined 
in this memo will be used in addition to terms defined in RFCs 
1242, 1944 and 2285.  This memo is a product of the Benchmarking 
Methodology Working Group (BMWG) of the Internet Engineering Task 
Force (IETF).

I.  Background

1.  Introduction
 
This document provides terminology for benchmarking cell-based and 
call-based switching devices.  It extends terminology already 
defined for benchmarking network interconnect devices in RFCs 
1242, 1944 and 2285.  Although some of the definitions in this 

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memo may be applicable to a broader group of network interconnect 
devices, the primary focus of the terminology in this memo is on 
cell-based and call-based switches.  Specifically, this includes 
Asynchronous Transfer Mode (ATM) cell relay and signaling and 
Frame Relay (FR) signaling.

This memo contains two major sections: Background and Definitions.  
Within the definitions section are a formal definitions sub-
section, provided as a courtesy to the reader, and a measurement 
definitions sub-section which contains performance metrics with 
inherent units.

2.  Existing Definitions

   RFC 1242 "Benchmarking Terminology for Network Interconnect 
Devices" should be consulted before attempting to make use of this 
document.   RFC 1944 "Benchmarking Methodology for Network 
Interconnect Devices" contains discussions of a number of terms 
relevant to the benchmarking of switching devices and should also 
be consulted.  RFC 2285 "Benchmarking Terminology for LAN 
Switching Devices" contains a number of terms pertaining to 
traffic distributions and datagram interarrival.
   For the sake of clarity and continuity this RFC adopts the 
template for definitions set out in Section 2 of RFC 1242.  
Definitions are indexed and grouped together in sections for ease 
of reference.
   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL 
NOT",   "SHOULD", "SHOULD NOT", "RECOMMENDED",  "MAY", and 
"OPTIONAL" in this document are to be interpreted as described in 
RFC 2119.

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.

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1.  Formal Definitions

1.1.  Definition Format (from RFC1242)

Term to be defined.

Definition: The specific definition for the term.

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

Specification:  The working group and document in which the term 
is specified.  Listed in the references.

1.2 Definitions

1.2.1 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-TM4.0

1.2.2 Call-based

Definition:  An association between two or more users or between a 
user and a network entity that is established by the use of 
network capabilities.  This association may have zero or more 
connections.

Discussion:  none

Specification: AF-UNI3.1

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1.2.3 Cell 

Definition: A unit of transmission in ATM.  A fixed size frame 
consisting of a 5 octet header and a 48 octet payload.

Discussion:  none

Specification: AF-UNI3.1   

2. Performance Metrics

2.1.  Definition Format (from RFC1242)

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 Cell Transfer Delay (CTD)

Definition:  The elapsed time between a cell exit event at the 
measurement point 1 (e.g., at the source UNI) and the 
corresponding cell entry event at a measurement point 2 (e.g., the 
destination UNI) for a particular connection. 

Discussion: The 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.

Measurement units: seconds

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2.2.2 Cell Delay Variation (CDV)

Definition:  The variation in cell transfer delay associated with 
a given traffic load, orientation and distribution, as well as an 
integration period.  CDV = max(CTD) - min(CTD) where max and min 
indicate the maximum  and minimum over the integration period, 
respectively.

Discussion: CDV is a component of cell transfer delay, induced by 
buffering and cell scheduling. Peak-to-peak CDV is a QoS delay 
parameter associated with CBR and VBR services. The peak-to-peak 
CDV is the ((1-a) quantile of the CTD) minus the fixed CTD that  
could be experienced by any delivered cell on a connection during 
the entire connection holding time. The parameter "a" is the 
probability of a cell arriving late. 

Measurement Units: seconds.

2.2.3 Cell Error Ratio (CER)

Definition:  The ratio of errored cells in a transmission in 
relation to the total cells sent in a transmission associated with 
a given traffic load, orientation and distribution, as well as an 
integration period.   CER = Errored Cells / Total Cells 
Transmitted.

Discussion:  The measurement is taken over a time interval and is 
desirable to be measured on an in-service circuit.

Measurement Units: dimensionless.

2.2.4  Cell Loss Ratio (CLR)

Definition:  The ratio of lost cells in a transmission in relation 
to the total cells sent in a transmission associated with a given 
traffic load, orientation and distribution, as well as an 
integration period.  CLR = Lost Cells / Total Cells Transmitted.

Discussion:  CLR is a negotiated QoS parameter and acceptable 
values are network specific. The objective is to minimize CLR 
provided the end-system adapts the traffic to the changing ATM 
layer transfer characteristics. The CLR parameter is the value of 
CLR that the network agrees to offer as an objective over the 
lifetime of the connection. It is expressed as an order of 
magnitude, having a range of 10-1 to 10-15 and unspecified.

Measurement Units: dimensionless.

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2.2.5 Cell Misinsertion Rate (CMR)

Definition: The ratio of cells received at an endpoint that were 
not originally transmitted by the source end in relation to the 
total number of cells properly transmitted associated with a given 
traffic load, orientation and distribution, as well as an 
integration period.  CMR = Mis-inserted Cells / Total Cells 
Transmitted.

Discussion:  none

Measurement Units: dimensionless.

3.  Security Considerations
   Security issues are not addressed in this memo.

4.  References

[AF-TM4.0] ATM Forum, Traffic Management Specification Version 
4.0, af-tm-0056.00, April 1996.

[AF-UNI3.1] ATM Forum, User Network Interface Specification 
Version 3.1, September 1994.

5. Editor's Addresses

Jeffrey Dunn   
Hewlett-Packard   
3701 Koppers St.   
Baltimore, MD 21227 USA 

Phone: +1 (410) 362-7612
E-mail:  [email-masked]      

Cynthia Martin   
Hewlett-Packard   
3701 Koppers St.   
Baltimore, MD 21227   

Phone +1 (410) 362-7631
E-mail:  [email-masked]

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