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Network Working Group                                        J. H. Dunn
INTERNET-DRAFT                                             C. E. Martin
Expires: August, 1999                                          ANC, Inc.

                                                         February, 1999
                  Terminology for Call/Cell Benchmarking
                       <draft-ietf-bmwg-call-04.txt>

Status of this Memo

   This  document  is an Internet-Draft and is in full conformance with all
   provisions of Section 10 of RFC2026.

   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."

   The    list    of   current   Internet-Drafts   can   be   accessed   at
   http://www.ietf.org/ietf/1id-abstracts.txt

   The list  of  Internet-Draft  Shadow  Directories  can  be  accessed  at
   http://www.ietf.org/shadow.html.

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).


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 RFC's 1242, 1944 and  2285.
   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  cell-based and call-based switches.
   Specifically, this includes Asynchronous Transfer Mode (ATM) cell  relay
   and signaling.



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   This  memo  contains  two  major  sections:  Background and Definitions.
   Within the definitions  section  is  a  formal  definitions  subsection,
   provided as a courtesy to the reader, and a measurement definitions sub-
   section, which contains performance metrics with  inherent  units.   The
   divisions of the measurement sub-section follow the BISDN model.

   The  BISDN  model  comprises  four layers and two planes.  This document
   addresses the interactions between these layers and how they effect  the
   performance of IP, TCP, etc.  A schematic of the model follows:


                    User Plane         |           Control Plane
   Services |                          |   ILMI    |       UNI, PNNI
   ---------|--------------------------|-----------|---------------------
   AAL      |AAL1, AAL2, AAL3/4, AAL5  |   AAL5    |          SAAL
   ---------|--------------------------|-----------|---------------------
   ATM      |        Cell Relay        |               OAM, RM
   ---------|--------------------------|---------------------------------
            |       Convergence        |
   Physical |--------------------------|---------------------------------
            |          Media           |
   ---------|--------------------------|---------------------------------



   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 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



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   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" go 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.

   Formal Definitions

   1.1. Definition Format (from RFC 1242)

   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.      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.




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   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.

   Discussion: Refer to AIR.

   Specification: AF-TM4.0

   1.2.5. ATM Adaptation Layer (AAL):

   Definition: The layer in the B-ISDN reference model (see B-ISDN) which
   adapts higher layer PDU's into the ATM layer.

   Discussion: There are 4 types of adaptation layers:
   AAL 1: used for circuit emulation, voice over ATM
   AAL2: used for sub-rated voice over ATM
   AAL3/4: used for data over noisy ATM lines
        AAL5: used for data over ATM, most widely used AAL type
   These AAL types are not measurements, but it is possible to measure the
   time required for Segmentation and Reassembly (SAR).




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   Specification: AF-TM3.1

   1.2.6. ATM Adaptation Layer Type 5 (AAL5):

   Definition: AAL5 functions in support of variable bit rate, delay-tolerant
   data traffic requiring minimal sequencing or error detection support.

   Discussion: AAL5 is the adaptation layer for UNI signaling, ILMI, PNNI
   signaling, and for IP PDU'S. It is the most widely used AAL type to date.

   Specification: AF-UNI3.1

   1.2.7. 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

   1.2.8. Asynchronous Transfer Mode (ATM)

   Definition: A transfer mode in which the information is organized into 53
   octet PDUs called cells. It is asynchronous in the sense that the
   recurrence of cells containing information from an individual user is not
   necessarily periodic.

   Discussion: ATM is based on the ISDN model.

   Specification: AF-UM3.1

   1.2.9. ATM Link:

   Definition: A virtual path link (VPL) or a virtual channel link (VCL).

   Discussion: none.

   Specification: AF-UNI3.1

   1.2.10. ATM Peer-to-Peer Connection:



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   Definition: A virtual channel connection (VCC) or a virtual path
   connection (VPC).

   Discussion: none.

   Specification: AF-UNI3.1

   1.2.11. ATM Traffic Descriptor:

   Definition: A generic list of traffic parameters, which specify the
   intrinsic traffic characteristics of a requested ATM connection. See GCRA
   and ABR.

   Discussion: none.

   Specification: AF-UNI3.1

   1.2.12. ATM User-User Connection:

   Definition: An association established by the ATM Layer to support
   communication between two or more ATM service users (i.e., between two or
   more next higher entities or between two or more ATM-entities). The
   communications over an ATM Layer connection may be either bi-directional
   or unidirectional. The same Virtual Channel Identifier (VCI) issued for
   both directions of a connection at an interface.

   Discussion: none.

   Specification: AF-UNI3.1

   1.2.13. Backward Explicit Congestion Notification (BECN):

   Definition: A Resource Management (RM) cell type generated by the network
   or the destination, indicating congestion or approaching congestion for
   traffic flowing in the direction opposite that of the BECN cell.

   Discussion:  none.

   Specification: AF-TM4.0

   1.2.14. BECN Cell (BN):

   Definition: A Resource Management (RM) cell type indicator. The network or
   the destination may generate a Backwards Explicit Congestion Notification
   (BECN) RM-cell. To do so, BN=l is set, to indicate the cell is not source-
   generated, and DIR=1 to indicate the backward flow. Source generated RM-
   cells are initialized with BN=O.




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   Discussion: none.

   Specification: AF-TM4.0

   1.2.15. Broadband ISDN (B-ISDN) Model:

   Definition: A layered service model that specifies the mapping of higher
   layer protocols onto ATM and its underlying physical layer. The model is
   composed of four layers: Physical, ATM, AAL and Service.

   Discussion: none.

   Specification: AF-UNI3.1

   1.2.16. Burst Tolerance (BT):

   Definition: A traffic parameter, which, along with the Sustainable Cell
   Rate (SCR), specifies the maximum number of cells which will be accepted
   at the Peak Cell Rate (PCR) on an ATM connection.

   Discussion: BT applies to ATM connections supporting VBR services and is
   the limit parameter of the GCRA.

   Specification: AF-TM4.0

   1.2.17. Connection Admission Control (CAC):

   Definition: Connection Admission Control is defined as the set of actions
   taken by the network during the call set-up phase (or during call re-
   negotiation phase) in order to determine whether a connection request can
   be accepted or should be rejected (or whether a request for re-allocation

   can be accommodated).

   Discussion: none

   Specification: AF-UNI3.1

   1.2.18. Call:

   Definition: A call is 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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   1.2.19. Call-based:

   Definition: A transport requiring call setups- see CALL definition.

   Discussion: none

   Specification: AF-UNI3.1

   1.2.20. Constant Bit Rate (CBR):

   Definition: An ATM service category which supports a constant or
   guaranteed rate to transport services such as video or voice as well as
   circuit emulation which requires rigorous timing control and performance
   parameters.

   Discussion: CBR reduces problems associated with TCP performance and
   throughput. **

   Specification: AF-UNI3.1

   1.2.21. 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

   1.2.22. Cell Header:

   Definition: ATM Layer protocol control information.

   Discussion: The ATM cell header is a 5-byte header that contains the
   following fields:
   Generic Flow Control (GFC): 4 bits
   Virtual Path Identifier (VPI): 8 bits
   Virtual Channel Identifier (VCI): 16 bits
   Payload Type (PT): 3 bits
   Cell Loss Priority (CLP): 1 bit
   Header Error Check (HEC): 8 bit CRC computed over the previous 4 octets

   Each field is discussed in this document.

   Specification: AF-UNI3.1

   1.2.23. Congestion Indicator (CI):




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   Definition: This is a field in a RM-cell, and is used to cause the source
   to decrease its ACR. The source sets CI=O when it sends a RM-cell.
   Setting CI=1 is typically how destinations indicate that Explicit Forward
   Congestion Indication (EFCI) has been received on a previous data cell.

   Discussion: none.

   Specification: AF-TM4.0

   1.2.24. Cell Loss Priority (CLP):

   Definition: This bit in the ATM cell header indicates two levels of
   priority for ATM cells. CLP=0 cells are higher priority than CLP=1 cells.
   CLP=1 cells may be discarded during periods of congestion to preserve the
   CLR of CLP=0 cells.

   Discussion: The CLP bit is used to determine GCRA contract compliance.

   Specification: AF-UNI3.1

   1.2.25. Connection:

   Definition: An ATM connection consists of concatenation of ATM Layer links
   in order to provide an end-to-end information transfer capability to
   access points.

   Discussion: none.

   Specification: AF-UNI3.1

   1.2.26. 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

   1.2.27. Current Cell Rate (CCR):

   Definition: The Current Cell Rate is an RM-cell field set by the source to
   its current ACR when it generates a forward RM-cell. This field may be
   used to facilitate the calculation of ER, and may not be changed by
   network elements. CCR is formatted as a rate.




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   Discussion: See actual cell rate.

   Specification: AF-TM4.0

   1.2.28. Cyclic Redundancy Check (CRC):

   Definition: A mathematical algorithm that computes a numerical value based
   on the bits in a block of data. This number is transmitted with the data
   and the receiver uses this information and the same algorithm to insure
   the accurate delivery of data by comparing the results of algorithm and
   the number received. If a mismatch occurs, an error in transmission is
   presumed.

   Discussion: CRC is not a measurement, but it is possible to measure the
   amount of time to perform a CRC on a string of bits. This measurement will
   not be addressed in this document.

   Specification: AF-UNI3.1

   1.2.29. DIR:

   Definition: This is a field in a RM-cell, which indicates the direction of
   the RM-cell with respect to the data flow with which it is associated.
   The source sets DIR=O and the destination sets DIR=1.

   Discussion: none

   Specification: AF-TM4.0

   1.2.30. Explicit Forward Congestion Indication (EFCI):

   Definition: EFCI is an indication in the PTI field of the ATM cell header.
   A network element in an impending-congested state or a congested state may
   set EFCI so that this indication may be examined by the destination end-
   system. For example, the end-system may use this indication to implement a
   protocol that adoptively lowers the cell rate of the connection during
   congestion or impending congestion. A network element that is not in a
   congestion state or an impending congestion state will not modify the
   value of this indication. Impending congestion is the state when network
   equipment is operating around its engineered capacity level.

   Discussion: none.

   Specification: AF-TM4.0

   1.2.3 1. Explicit Rate (ER):

   Definition: The Explicit Rate is a RM-cell field used to limit the source



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   ACR to a specific value. It is initially set by the source to a requested
   rate (such as PCR). It may be subsequently reduced by any network element
   in the path to a value that the element can sustain. ER is formatted as a
   rate.

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

   Specification: AF-TM4.0

   1.2.32. End System (ES):

   Definition: A system where an ATM connection is terminated or initiated.
   An originating end system initiates the ATM connection, and terminating
   end system terminates the ATM connection. OAM cells may be generated and
   received.

   Discussion: An ES can be the user side of a UNI signaling interface.

   Specification: AF-TEST-0022

   1.2.33. Generic Cell Rate Algorithm (GCRA):

   Definition: The GCRA is used to define conformance with respect to the
   traffic contract of the connection. For each cell arrival the GCRA
   determines whether the cell conforms to the traffic contract. The UPC
   function may implement the GCRA, or one or more equivalent algorithms to
   enforce conformance. The GCRA is defined with two parameters: the
   Increment (1) and the Limit (L).

   Discussion: GCRA is not a measurement, but there are a number of
   measurements that can be obtained using the GCRA and other parameters.

   Specification: AF-TM4.0

   1.2.34. Generic Flow Control (GFC):

   Definition: GFC is a field in the ATM header, which can be used to provide
   local functions (e.g., flow control). It has local significance only and
   the value encoded in the field is not carried end-to-end.

   Discussion: none

   Specification: AF-UNI3.1

   1.2.35. Header Error Control (HEC):

   Definition: A check character calculated using an 8 bit CRC computed over



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   the first 4 octets of the ATM cell header. This allows for single bit
   error correction or multiple bit error detection.

   Discussion: none

   Specification: AF-UNI3.1

   1.2.36. 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

   1.2.37. Integrated Local Management Interface

   Definition: A management protocol which uses SNMPv1 carried on AAL5 to
   provide ATM network devices with status and configuration information
   concerning VPC's, VCC's, registered ATM addresses and the capabilities of
   ATM interfaces.

   Discussion: ILMI is a conditionally required portion of UNI3.1; however,
   ILMI 4.0 has been issued as a separate specification.  This document will
   refer to ILMI 4.0.

   Specification: AF-ILMI4.0

   1.2.38. Intermediate System (IS):

   Definition: A system that provides forwarding functions or relaying
   functions or both for a specific ATM connection. OAM cells may be
   generated and received.

   Discussion: An IS can be either the user or network side of a UNI
   signaling interface, or the network side of a PNNI signaling interface.

   Specification: AF-TEST-0022

   1.2.39. Leaky Bucket (LB):

   Definition: Leaky Bucket is the term used as an analogous description of
   the algorithm used for conformance checking of cell flows from a user or
   network. See GCRA and UPC.  The "leaking hole in the bucket" applies to
   the sustained rate at which cells can be accommodated, while the "bucket
   depth" applies to the tolerance to cell bursting over a given time period.




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   Discussion: There are two types of LB algorithms- single and dual. Single
   LB defines a PCR; dual LB defines a PCR and SCR.

   Specification: AF-TM4.0

   1.2-40. Maximum Cell Rate (MCR):

   Definition: This is the maximum capacity usable by connections belonging
   to the specified service category.

   Discussion: none

   Specification: AF-TM4.0

   1.2.41. Maximum Burst Size (MBS):

   Definition: In the signaling message, the Burst Tolerance (BT) is conveyed
   through the MBS that is coded as a number of cells. The BT together with
   the SCR and the GCRA determine the MBS that may be transmitted at the peak
   rate and still is in conformance with the GCRA.

   Discussion: none

   Specification: AF-TM4.0

   1.2.42. 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: none

   Specification: AF-TM4.0

   1.2.43. Missing RM-Cell Count (CRM):

   Definition: CRM limits the number of forward RM-cells that may be sent in
   the absence of received backward RM-cells.

   Discussion: none.

   Specification: AF-TM4.0

   1.2.44. Mrm:

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




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   Discussion: none

   Specification: AF-TM4.0

   1.2.45. 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

   1.2.46. Operations, Administration, and Maintenance (OAM):

   Definition: A group of network management functions that provide network
   fault indication, performance information, and data and diagnosis
   functions.

   Discussion: There are four types of ATM OAM flows: segment or end-to-end
   VP termination management (i.e. F4 segment, F4 E2E) and segment or end-to-
   end VC termination management (i.e. F5 segment, F5 E2E). These OAM cells
   can be used to identify fault management, connection verification, and
   loopback measurements.

   Specification: AF-UNI3.1

   1.2.47. Protocol Data Unit (PDU):

   Definition: A PDU is a message of a given protocol comprising payload and
   protocol-specific control information, typically contained in a header.
   PDU's pass over the protocol interfaces that exist between the layers of
   protocols (per OSI model).

   Discussion: In ATM networks, a PDU can refer to an ATM cell, multiple ATM
   cells, an AAL segment, an IP datagram and others.

   Specification: -

   1.2.48. Private Network-Network Interface (PNNI):

   Definition: A routing information protocol that enables extremely,
   scalable, full function, dynamic multi-vendor ATM switches to be
   integrated in the same network.

   Discussion: PNNI consists of signaling and routing between ATM network
   devices. PNNI signaling is based on UNI 4.0 signaling between two network
   side interfaces, while PNNI routing provides a mechanism to route ATM



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   cells between two separate, autonomous ATM networks.

   Specification: AF-PNNI1.0

   1.2.49. Payload Type Indicator (PTI):

   Definition: Payload Type Indicator is the Payload Type field value
   distinguishing the various management cells and user cells.
   Example:
   Resource Management cell is indicated as PTI=110,
   end-to-end OAM F5 Flow cell is indicated as PTI=101.

   Discussion: none.

   Specification: AF-UNI3.1

   1.2-50. Peak Cell Rate (PCR):

   Definition: A traffic parameter, which specifies the upper bound on the
   rate at which ATM cells can be submitted to an ATM connection.  This
   parameter is used by the GCRA.

   Discussion: none.

   Specification: AF-TM4.0

   1.2.5 1. Permanent Virtual Circuit (PVC):

   Definition: This is a link with static route(s) defined in advance,
   usually by manual setup.

   Discussion: none.

   Specification: AF-UNI3.1

   1.2.52. Permanent Virtual Channel Connection (PVCC):

   Definition: A Virtual Channel Connection (VCC) is an ATM connection where
   switching is performed on the VPI/VCI fields of each cell. A permanent VCC
   is one that is provisioned through some network management function and
   left up indefinitely.

   Discussion: none.

   Specification: AF-UNI3.1

   1.2.53. Permanent Virtual Path Connection: (PVPC):




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   Definition: A Virtual Path Connection (VPC) is an ATM connection where
   switching is performed on the VPI field only of each cell. A permanent VPC
   is one that is provisioned through some network management function and
   left up indefinitely.

   Discussion: none.

   Specification: AF-UNI3.1

   1.2.54. 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

   1.2.55. 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

   1.2.56. Resource Management (RM):

   Definition: Resource Management is the management of critical resources in
   an ATM network. Two critical resources are buffer space and trunk
   bandwidth. Provisioning may be used to allocate network resources in order
   to separate traffic flows according to service characteristics. VPC's play
   a key role in resource management. By reserving capacity on VPCs, the
   processing required to establish individual VCC's is reduced. Refer to RM-
   cell.

   Discussion: none.

   Specification: AF-TM4.0

   1.2.57. Resource Management Cell (RM-Cell):




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   Definition: Information about the state of the network like bandwidth
   availability, state of congestion, and impending congestion, is conveyed
   to the source through special control cells called Resource Management
   Cells (RM-cells).

   Discussion: none.

   Specification: AF-TM4.0

   1.2-58. Segmentation and Reassembly (SAR):

   Definition: The process used by the AAL in the B-ISDN reference model (see
   B-ISDN) which fragments higher layer PDU's into ATM cells.

   Discussion: SAR is not a measurement, but the speed in which SAR can be
   completed on a bit stream can be measured. This measurement will not be
   discussed in this document.

   Specification: AF-UNI3.1

   1.2.59. Sustainable Cell Rate (SCR):

   Definition: The SCR is an upper bound on the conforming average rate of an
   ATM connection over time scales which are long relative to those for which
   the PCR is defined. Enforcement of this bound by the UPC could allow the
   network to allocate sufficient resources, but less than those based on the
   PCR, and still ensure that the performance objectives (e.g., for Cell Loss
   Ratio) can be achieved.

   Discussion: none.

   Specification: AF-TM4.0

   1.2.60. Switched Virtual Circuit (SVC):

   Definition: A connection established via signaling. The user defines the
   endpoints when the call is initiated.

   Discussion: SVC's are established using either UNI signaling or PNNI
   signaling.  The signaling state machine implements several timers, which
   can effect the time required for call establishment.  This will, in turn,
   effect TCP round trip time calculation, effecting TCP throughput.

   Specification: AF-UNI3.1, AF-UNI4.0, AF-PNNI1.0

   1.2.61. Switched Virtual Channel Connection (SVCC):

   Definition: A Switched VCC is one that is established and taken down



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   dynamically through control signaling. A Virtual Channel Connection  (VCC)
   is an ATM connection where switching is performed on the VPI/VCI fields of
   each cell.

   Discussion: none.

   Specification: AF-UNI3.1

   1.2.62. Switched Virtual Path Connection (SVPC):

   Definition: A Switched Virtual Path Connection is one that is established
   and taken down dynamically through control signaling. A Virtual Path
   Connection (VPC) is an ATM connection where switching is performed on the
   VPI field only of each cell.

   Discussion: none.

   Specification: AF-UNI3.1

   1.2.63. Switched Connection:

   Definition: A connection established via signaling.

   Discussion: none.

   Specification: AF-UNI3.1

   1.2.64. Tagged Cell Rate (TCR):

   Definition: An ABR service parameter, TCR limits the rate at which a
   source may send out-of-rate forward RM-cells. TCR is a constant fixed at
   10 cells/second.

   Discussion: none.

   Specification: AF-TM4.0

   1.2.65. Traffic Contract

   Definition: A specification of the negotiated traffic characteristics of
   an ATM connection.

   Discussion: none.

   Specification: AF-TM4.0

   1.2.66. Transmission Convergence (TC):




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   Definition: A sub-layer of the physical layer of the B-ISDN model
   transforms the flow of cells into a steady flow of bits and bytes for
   transmission over the physical medium. On transmit the TC sublayer maps
   the cells to the frame format, generates the Header Error Check (HEC), and
   sends idle cells when the ATM layer has none to send. On reception, the TC
   sublayer delineates individual cells in the received bit stream, and uses
   the HEC to detect and correct received errors.

   Discussion: TC is not a measurement, but the speed in which TC can occur
   on a bit stream can be measured. This measurement will not be discussed in
   this document.

   Specification: AF-UNI3.1

   1.2.67. TDF:

   Definition: An ABR service parameter, TDF controls the decrease in ACR
   associated with TOF. TDF is signaled as TDFF, where TDF=TDFF/RDF times the
   smallest power of 2 greater or equal to PCR. TDF is in units of 1/seconds.

   Discussion: For ABR traffic, TDF 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

   1.2.68. TDFF.

   Definition: 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.

   Specification: AF-TM4.0

   1.2.69. Traffic Management (TM):

   Definition: Traffic Management is the aspect of the traffic control and
   congestion control procedures for ATM. ATM layer traffic control refers to
   the set of actions taken by the network to avoid congestion conditions.
   ATM layer congestion control refers to the set of actions taken by the
   network to minimize the intensity, spread and duration of congestion. The
   following functions form a framework for managing and controlling traffic
   and congestion in ATM networks and may be used in appropriate
   combinations.
   Connection Admission Control
   Feedback Control
   Usage Parameter Control



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   Priority Control
   Traffic Shaping
   Network Resource Management
   Frame Discard
   ABR Flow Control

   Discussion: none.

   Specification: AF-TM4.0

   1.2.70. Time Out Factor (TOF):

   Definition: An ABR service parameter, TOF controls the maximum time
   permitted between sending forward RM-cells before a rate decrease is
   required. It is 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 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

   1.2.7 1. Time Out Factor (TOFF):

   Definition: Refer to TOF.

   Discussion: none

   Specification: AF-TM4.0

   1.2.72. Trm.

   Definition: An ABR service parameter that provides an upper bound on 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 of the
   ACR. This value effects TCP round trip time calculations, which in turn
   effects TCP throughput.

   Specification: AF-TM4.0

   1.2.73. Traffic Shaping (TS):

   Definition: Traffic Shaping is a mechanism that alters the traffic
   characteristics of a stream of cells on a connection to achieve better
   network efficiency, while meeting the QoS objectives, or to ensure



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   conformance at a subsequent interface. Traffic shaping must maintain cell
   sequence integrity on a connection. Shaping modifies traffic
   characteristics of a cell flow with the consequence of increasing the mean
   Cell Transfer Delay.

   Discussion: TS should improve TCP throughput by reducing round trip time
   variations.

   Specification: AF-UNI3.1

   1.2.74. Unspecified Bit Rate (UBR):

   Definition: UBR is an ATM service category, which does not specify traffic
   related service guarantees. Specifically, UBR does not include the notion
   of a per-connection-negotiated bandwidth.  No commitments are made with
   respect to the cell loss ratio experienced by a UBR connection, or as to
   the cell transfer delay experienced by cells on the connection.

   Discussion: RFC 2331 specifies UBR service class for IP over ATM.  UBR
   service models the best effort service type specified in RFC 791;
   however, UBR has specific drawbacks with respect to TCP service.  Since
   UBR makes no guarantee with respect to cell loss, cell delay variation or
   cell mis-insertion, TCP round trip time estimates may not be accurate.

   Specification: AF-TM4.0

   1.2.75. User-Network Interface (UNI):

   Definition: An interface point between ATM end users and a private ATM
   switch, or between a private ATM switch and the public carrier ATM
   network; defined by physical and protocol specifications per ATM Forum UNI
   documents. The standard adopted by the ATM Forum to define connections
   between users or end stations and a local switch.

   Discussion: none.

   Specification: AF-UNI3.1

   1.2.76. Usage Parameter Control (UPC):

   Definition: Usage Parameter Control is defined as the set of actions taken
   by the network to monitor and control traffic, in terms of traffic offered
   and validity of the ATM connection, at the end-system access. Its main
   purpose is to protect network resources from malicious as well as
   unintentional misbehavior, which can affect the QoS of other already
   established connections, by detecting violations of negotiated parameters
   and taking appropriate actions.




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   Discussion: none.

   Specification: AF-TM4.0

   1.2.77. Variable Bit Rate (VBR):

   Definition: An ATM Forum defined service category which supports variable
   bit rate data traffic with average and peak traffic parameters.

   Discussion: VBR may potentially adversely effect TCP throughput due to
   large round trip time variations.

   Specification: AF-TM4.0

   1.2.78. VC:

   Definition: A communications channel that provides for the sequential
   unidirectional transport of ATM cells.

   Discussion: none.

   Specification: AF-TM3.1

   1.2.79. Virtual Channel Connection (VCC):

   Definition: A concatenation of VCI's that extends between the points where
   the ATM service users access the ATM layer. The points at which the ATM
   cell payload is passed to, or received from, the users of the ATM Layer
   (i.e., a higher layer or ATM-entity) for processing signify the endpoints
   of a VCC. VCC's are unidirectional.

   Discussion: none.

   Specification: AF-TM3.1

   1.2.80. Virtual Channel Identifier (VCI):

   Definition: A unique numerical tag as defined by a 16 bit field in the ATM
   cell header that identifies a virtual channel, over which the cell is to
   travel.

   Discussion: none.

   Specification: AF-UNI3.1

   1.2.8 1. Virtual Path (VP):

   Definition: A unidirectional logical association or bundle of VCs.



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   Discussion: none.

   Specification: AF-UNI3.1

   1.2.82. Virtual Path Connection (VPC):

   Definition: A concatenation of VPIs between Virtual Path Terminators
   (VPT's). VPC's are unidirectional

   Discussion: none.

   Specification: AF-TM3.1

   1.2.83. Virtual Path Identifier (VPI):

   Definition: An eight-bit field in the ATM cell header that indicates the
   virtual path over which the cell should be routed.

   Discussion: none.

   Specification: AF-UNI3.1

   1.2.84. Virtual Source/Virtual Destination (VSND):

   Definition: An ABR connection may be divided into two or more separately
   controlled ABR segments. Each ABR control segment, except the first, is
   sourced by a virtual source. A virtual source implements the behavior of
   an ABR source endpoint. Backward RM-cells received by a virtual source are
   removed from the connection.  Each ABR control segment, except the last,
   is terminated by a virtual destination. A virtual destination assumes the
   behavior of an ABR destination endpoint. Forward RM-cells received by a
   virtual destination are turned around and not forwarded to the next
   segment of the connection.

   Discussion: none.

   Specification: AF-TM4.0

   1.2.85. Xrm Decrease Factor (XDM):

   Definition: An ABR service parameter, XDF controls the decrease in 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 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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   1.2.86. Xrm:

   Definition: An ABR service parameter, Xrm limits the number of forward RM-
   cells which may be sent in the absence of received backward PM-cells. The
   range is 0-255.

   Discussion: For ABR traffic, Xrm 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


   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. Physical Layer- SONET

   2.2.1.1. Pointer Movements

   Definition: Pointer Movements is the number of changes in a SONET pointer
   due to clock synchronization slips.

   Discussion: SONET Pointer Movements can cause loss of information in the
   SONET payload envelop (SPE) which contains IP datagrams, either in the
   form of cells or as PPP delimited PDUs.

   Measurement Units: Per second.

   2.2.1.2. Transport Overhead Error Count

   Definition: SONET Transport Overhead Error Count is the number of SONET
   transport overhead errors detected.



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   Discussion: SONET Transport Overhead Errors SONET Transport Overhead
   Errors cause SONET frames to be lost.  These frames may contain IP
   datagrams, either in the form of cells or as PPP delimited PDUs.

   Measurement Units: Positive integer

   2.2.1.3. Path Overhead Error Count

   Definition: SONET Path Overhead Error Count is the number of SONET path
   overhead errors detected.

   Discussion: SONET Path Overhead Errors cause SONET frames to be lost.
   These frames may contain IP datagrams, either in the form of cells or as
   PPP delimited PDUs.

   Measurement Units: Positive integer

   2.2.2. ATM Layer

   2.2.2.1. 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.

   CDV effects TCP round trip time calculations.  Large values of CDV will
   adversely effect TCP throughput.

   Measurement Units: seconds

   2.2.2.2. Cell Delay Variation Tolerance (CDVT):

   Definition: ATM layer functions may alter the traffic characteristics of
   ATM connections by introducing Cell Delay Variation. When cells from two
   or more ATM connections are multiplexed, cells of a given ATM connection
   may be delayed while cells of another ATM connection are being inserted at
   the output of the multiplexer. Similarly, some cells may be delayed while
   physical layer overhead or OAM cells are inserted. Consequently, some
   randomness may affect the inter-arrival time between consecutive cells of



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   a connection as monitored at the UNI. The upper bound on the "clumping"
   measure is the CDVT.

   Discussion:
   CDVT effects TCP round trip time calculations.  Large values of CDVT will
   adversely effect TCP throughput.

   Measurement units: seconds

   2.2.2.3. 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.

   CER causes ATM cells to be lost.  These cells may contain AAL5 segments of
   IP datagrams.

   Measurement Units: dimensionless.

   2.2.2.4. 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.

   CLR measures the number of ATM cells lost.  These cells may contain AAL5
   segments of IP datagrams.

   Measurement Units: dimensionless.

   2.2.2.5. 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



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   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:
   CMR causes ATM streams to be corrupted.  These streams may contain AAL5
   segments of IP datagrams.

   Measurement Units: dimensionless.

   2.2.2.6. Cell Rate Margin (CRM):

   Definition: This is a measure of the difference between the effective
   bandwidth allocation and the allocation for sustainable rate in cells per
   second.

   Discussion: none.

   Measurement units: Cells per second

   2.2.2.7. CRC Error Ratio:

   Definition: The ratio of PDUs received at an endpoint that which contain
   an invalid CRC 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.

   Discussion:
   CRC errors cause ATM cells to be lost.  These cells may contain AAL5
   segments of IP datagrams.

   Measurement Units: dimensionless

   2.2.2.8. 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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   2.2.3. ATM Adaptation Layer (AAL) Type 5 (AAL5)

   2.2.3.1. AAL5 Reassembly Errors

   Definition: AAL5 Reassembly Errors constitute any error which causes the
   AAL5 PDU to be corrupted.

   Discussion:
   AAL5 Reassembly errors cause AAL5 PDUs to be lost.  These PDUs may
   contain IP datagrams.

   Measurement Units: Positive Integer

   2.2.3.2. AAL5 Reassembly Time

   Definition: AAL5 Reassembly Time constitutes the time between the arrival
   of the final cell in the AAL5 PDU and the AAL5 PDU being made available to
   the service layer.

   Discussion:
   AAL5 Reassembly time directly effects TCP round trip time calculations.

   Measurement Units: seconds

   2.2.3.3. AAL5 CRC Error Ratio:

   Definition: The ratio of PDUs received at an endpoint that which contain
   an invalid CRC 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.

   Discussion:
   AAL5 CRC errors causes AAL5 PDUs to be dropped. These PDUs may contain
   IP datagrams.

   Measurement Units: dimensionless


   3. Security Considerations.
   As this document is solely for the purpose of providing terminology and
   describes neither a protocol nor an implementation, there are no security
   considerations associated with this document.

   4. References
   [AF-ILMI4.0] ATM Forum Integrated Local Management Interface Version 4.0,
   af-ilmi-0065.000, September 1996.
   [AF-TEST-0022] Introduction to ATM Forum Test Specifications, af-test-
   0022.00, December 1994.



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

   5. Editor's Addresses
   Jeffrey Dunn
   Advanced Network Consultants, Inc.
   11241-B Skilift Court, Columbia, MD 21044 USA
   Phone: +1 (410) 730-6300, E-mail: Jeffrey.Dunn@worldnet.att.net

   Cynthia Martin
   Advanced Network Consultants, Inc.
   11241-B Skilift Court, Columbia, MD 21044 USA
   Phone: +1 (410) 730-6300, E-mail: Cynthia.E.Martin@worldnet.att.net


































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