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+
+Network Working Group J. Dunn
+Request for Comments: 2761 C. Martin
+Category: Informational ANC, Inc.
+ February 2000
+
+
+ Terminology for ATM Benchmarking
+
+Status of this Memo
+
+ This memo provides information for the Internet community. It does
+ not specify an Internet standard of any kind. Distribution of this
+ memo is unlimited.
+
+Copyright Notice
+
+ Copyright (C) The Internet Society (2000). All Rights Reserved.
+
+Abstract
+
+ This memo discusses and defines terms associated with performance
+ benchmarking tests and the results of these tests in the context of
+ Asynchronous Transfer Mode (ATM) based switching devices. The terms
+ defined in this memo will be used in addition to terms defined in
+ RFCs 1242, 2285, and 2544. This memo is a product of the Benchmarking
+ Methodology Working Group (BMWG) of the Internet Engineering Task
+ Force (IETF).
+
+Introduction
+
+ This document provides terminology for benchmarking ATM based
+ switching devices. It extends terminology already defined for
+ benchmarking network interconnect devices in RFCs 1242, 2285, and
+ 2544. Although some of the definitions in this memo may be applicable
+ to a broader group of network interconnect devices, the primary focus
+ of the terminology in this memo is on ATM cell relay and signaling.
+
+ 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, that contains performance metrics with inherent units.
+ The divisions of the measurement sub-section follow the BISDN model.
+
+
+
+
+
+
+
+
+
+Dunn & Martin Informational [Page 1]
+
+RFC 2761 Terminology for ATM Benchmarking February 2000
+
+
+ The BISDN model comprises four layers and two planes. This document
+ addresses the interactions between these layers and how they effect
+ IP and TCP throughput. A schematic of the B-ISDN model follows:
+
+ ---------|--------------------------|-------------------------------
+ | User Plane | Control Plane
+ ---------|--------------------------|--------------------------------
+ Services | IP | 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). This document covers only CBR, VBR and UBR traffic
+ types. ABR will be handled in a separate document. 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.
+
+Existing Definitions
+
+ RFC 1242, "Benchmarking Terminology for Network Interconnect Devices"
+ should be consulted before attempting to make use of this document.
+ RFC 2544, "Benchmarking Methodology for Network Interconnect Devices"
+ contains discussions of a number of terms relevant to the
+ benchmarking of switching devices and should be consulted. RFC 2285,
+ "Benchmarking Terminology for LAN Switching Devices" contains a
+ number of terms pertaining to traffic distributions and datagram
+ interarrival. 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
+
+
+
+Dunn & Martin Informational [Page 2]
+
+RFC 2761 Terminology for ATM Benchmarking February 2000
+
+
+ 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.
+
+Definitions
+
+ The definitions presented in this section have been divided into two
+ groups. The first group is formal definitions, which are required in
+ the definitions of the performance metrics but are not themselves
+ strictly metrics. These definitions are subsumed from other work
+ done in other working groups both inside and outside the IETF. They
+ are provided as a courtesy to the reader.
+
+1. Formal Definitions
+
+1.1. Definition Format (from RFC 1242)
+
+ Term to be defined.
+
+ Definition: The specific definition for the term.
+
+ Discussion: A brief discussion of the term, its application and any
+ restrictions on measurement procedures. These discussions pertain
+ solely to the impact of a particular ATM parameter on IP or TCP;
+ therefore, definitions which contain no configurable components or
+ whose components will have the discussion: None.
+
+ Specification: The working group and document in which the terms are
+ specified and are listed in the references section.
+
+1.2. Related Definitions
+
+1.2.1. ATM Adaptation Layer (AAL)
+
+ Definition: The layer in the B-ISDN reference model (see B-ISDN)
+ which adapts higher layer PDUs into the ATM layer.
+
+ Discussion: There are four types of adaptation layers: AAL 1: used
+ for circuit qemulation, 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
+
+
+
+
+
+
+
+
+
+Dunn & Martin Informational [Page 3]
+
+RFC 2761 Terminology for ATM Benchmarking February 2000
+
+
+ These AAL types are not measurements, but it is possible to measure
+ the time required for Segmentation and Reassembly (SAR).
+
+ Specification: I.363
+
+1.2.2. ATM Adaptation Layer Type 5 (AAL5)
+
+ Definition: AAL5 adapts multi-cell higher layer PDUs into ATM with
+ minimal error checking and no error detection. The AAL5 CPCS (Common
+ Paer Convergence Sub-layer) PDU is defined as follows:
+
+|---------------------------|---------------------------|--------------|
+| Higher Layer PDU | Padding (If needed) | Trailer |
+|---------------------------|---------------------------|--------------|
+
+ Where the padding is used to ensure that the trailer occupies the
+ final 8 octets of the last cell.
+
+ The trailer is defined as follows:
+
+ |--------------|--------------|--------------|--------------|
+ | CPCS-UU | CPI | Length | CRC-32 |
+ |--------------|--------------|--------------|--------------|
+
+ where:
+
+ CPCS-UU is the 1 octet Common Part Convergence Sub-layer User to User
+ Indication and may be used to communicate between two AAL5 entities.
+
+ CPI is the 1 octet Common Part Indicator and must be set to 0.
+
+ Length is the 2 octet length of the higher layer PDU.
+
+ CRC-32 is a 32 bit (4 octet) cyclic redundancy check over the entire
+ PDU.
+
+ Discussion: AAL5 is the adaptation layer for UNI signaling, ILMI,
+ PNNI signaling, and for IP PDUs. It is the most widely used AAL type
+ to date. AAL5 requires two distinct processes. The first is the
+ encapsulation, on the transmit side, and de-encapsulation, on the
+ receive side, of the higher layer PDU into the AAL5 CPCS PDU which
+ requires the computation of the length and the CRC-32. The time
+ required for this process depends on whether the CRC-32 computation
+ is done on the interface (on-board) or in machine central memory (in
+ core). On-board computation should produce only a small, constant
+ delay; however, in core computation will produce variable delay,
+ which will negatively effect TCP RTT computations. The second process
+ is segmentation and re-assembly (SAR) which is defined below (see
+
+
+
+Dunn & Martin Informational [Page 4]
+
+RFC 2761 Terminology for ATM Benchmarking February 2000
+
+
+ SAR).
+
+ Specification: I.363.5
+
+1.2.3. 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; however, unlike ISDN, ATM
+ uses fixed length (53 octet) cells. Because of the fixed length of
+ ATM PDUs, higher layer PDUs must be adapted into ATM using one of the
+ four ATM adaptation layers (see AAL).
+
+ Specification: AF-UNI3.1
+
+1.2.4. ATM Link
+
+ Definition: A virtual path link (VPL) or a virtual channel link
+ (VCL).
+
+ Discussion: none.
+
+ Specification: AF-UNI3.1
+
+1.2.5. ATM Peer-to-Peer Connection
+
+ Definition: A virtual channel connection (VCC) or a virtual path
+ connection (VPC).
+
+ Discussion: none.
+
+ Specification: AF-UNI3.1
+
+1.2.6. ATM Traffic Descriptor
+
+ Definition: A generic list of traffic parameters, which specify the
+ intrinsic traffic characteristics of a requested ATM connection (see
+ GCRA), which must include PCR and QoS and may include BT, SCR and
+ best effort (UBR) indicator.
+
+
+
+
+
+
+
+
+
+Dunn & Martin Informational [Page 5]
+
+RFC 2761 Terminology for ATM Benchmarking February 2000
+
+
+ Discussion: The effects of each traffic parameter will be discussed
+ individually.
+
+ Specification: AF-UNI3.1
+
+1.2.7. 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) is issued for both directions of a connection at an
+ interface.
+
+ Discussion: Because ATM is connection oriented, certain features of
+ IP (i.e. those which require multicast) are not available.
+
+ Specification: AF-UNI3.1
+
+1.2.8. 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: See discussion above.
+
+ Specification: I.321
+
+1.2.9. 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. BT will effect TCP and IP PDU
+ loss in that cells presented to an interface which violate the BT may
+ be dropped, which will cause AAL5 PDU corruption. BT will also effect
+ TCP RTT calculation. BT=(MBS-1)*(1/SCR 1/PCR) (see MBS, PCR, SCR).
+
+ Specification: AF-TM4.0
+
+
+
+
+
+
+
+
+Dunn & Martin Informational [Page 6]
+
+RFC 2761 Terminology for ATM Benchmarking February 2000
+
+
+1.2.10. 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
+
+1.2.11. 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
+
+1.2.12. Call-based
+
+ Definition: A transport requiring call setups - see CALL definition.
+
+ Discussion: none.
+
+ Specification: AF-UNI3.1
+
+1.2.13. 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 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 and cause SAR
+ timeout. See discussion under SAR.
+
+ Specification: AF-TM4.0
+
+
+
+
+
+
+Dunn & Martin Informational [Page 7]
+
+RFC 2761 Terminology for ATM Benchmarking February 2000
+
+
+1.2.14. 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 four octets
+
+ Each field is discussed in this document.
+
+ Specification: AF-UNI3.1
+
+1.2.15. 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. Specifically, two traffic contracts may apply to a
+ single connection: CLP=0, meaning only cells with CLP=0, and
+ CLP=0+1, meaning cells with CLP=0 or CLP=1.
+
+ Specification: AF-UNI3.1
+
+1.2.16. 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
+
+1.2.17. 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).
+
+
+
+
+
+
+Dunn & Martin Informational [Page 8]
+
+RFC 2761 Terminology for ATM Benchmarking February 2000
+
+
+ Discussion: CAC is based on the ATM traffic descriptor (see ATM
+ traffic descriptor) associated with the call as well as the presented
+ and existing load. It may also be based on administrative policies
+ such as calling party number required or access limitations. The
+ effect on performance of these policies is beyond the scope of this
+ document and will be handled in the BMWG document: Benchmarking
+ Terminology for Firewall Performance.
+
+ Specification: AF-UNI3.1
+
+1.2.18. Constant Bit Rate (CBR)
+
+ Definition: An ATM service category which supports a constant and
+ guaranteed rate to transport services such as video or voice as well
+ as circuit emulation which requires rigorous timing control and
+ performance parameters. CBR requires the specification of PCR and
+ QoS (see PCR and QoS).
+
+ Discussion: Because CBR provides minimal cell delay variation (see
+ CDV), it should improve TCP throughput by stabilizing the RTT
+ calculation. Further, as CBR generally provides a high priority
+ service, meaning that cells with a CBR traffic contract usually take
+ priority over other cells during congestion, TCP segment and IP
+ packet loss should be minimized. The cost associated with using CBR
+ is the loss of statistical multiplexing. Since CBR guarantees both
+ throughput and CDV control, the connections must be subscribed at
+ PCR. This is extremely wasteful as most protocols, e.g., TCP, only
+ utilize full bandwidth on one half of a bi-directional connection.
+
+ Specification: AF-UNI3.1
+
+1.2.19. 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, 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. See discussion
+ under AAL5.
+
+ Specification: AF-UNI3.1
+
+
+
+
+
+Dunn & Martin Informational [Page 9]
+
+RFC 2761 Terminology for ATM Benchmarking February 2000
+
+
+1.2.20. 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
+
+1.2.21. 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 adaptively 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: EFCI may be used to prevent congestion by alerting a
+ positive acknowledgement protocol and causing action to be taken. In
+ the case of TCP, when EFCI cells are received the driver software
+ could alert the TCP software of impending congestion. The TCP
+ receiver would then acknowledge the current segment and set the
+ window size to some very small number.
+
+ Specification: AF-TM4.0
+
+1.2.22. 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 (I) and the Limit (L).
+
+ Discussion: The GCRA increment and limit parameters are mapped to CBR
+ and VBR in the following fashion. For CBR, I=1/PCR and L=CDVT (CDV
+ tolerance). For VBR, there are two GCRA algorithms running (dual
+ leaky bucket). The first functions in the same fashion .bp as CBR,
+ I=1/PCR and L=CDVT. The second, which polices cells which are in
+ conformance with the first GCRA uses I=1/SCR and L=BT (see BT, CDV,
+
+
+
+Dunn & Martin Informational [Page 10]
+
+RFC 2761 Terminology for ATM Benchmarking February 2000
+
+
+ MBS, PCR and SCR).
+
+ Specification: AF-TM4.0
+
+1.2.23. 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
+
+1.2.24. Guaranteed Frame Rate (GFR)
+
+ Definition: The GFR service provides the user with a Minimum Cell
+ Rate (MCR) guarantee under the assumption of a given maximum frame
+ size (MFS) and a given Maximum Burst Size (MBS). The MFS and MBS are
+ both expressed in units of cells. GFR only applies to virtual
+ channel connections (VCCs).
+
+ Discussion: GFR is intended for users who are either not able to
+ specify the range of traffic parameters needed to request most ATM
+ services, or are not equipped to comply with the (source) behavior
+ rules required by existing ATM services. Specifically, GFR provides
+ the user with the following minimum service guarantee: When the
+ network is congested, all frames whose length is less than MFS and
+ presented to the ATM interface in bursts less than MBS and at a rate
+ less than PCR will be handled with minimum frame loss. When the
+ network is not congested, the user can burst at higher rates.
+
+ The effect of GFR on performance is somewhat problematic as the
+ policing algorithm associated with GFR depends on the network load;
+ however, under congested condition and assuming a user who is
+ following the GFR service agreement, it should improve performance.
+
+ Specification: AF-TM4.1
+
+
+
+
+
+
+
+
+
+
+
+
+Dunn & Martin Informational [Page 11]
+
+RFC 2761 Terminology for ATM Benchmarking February 2000
+
+
+1.2.25. Header Error Control (HEC)
+
+ Definition: A check character calculated using an 8 bit CRC computed
+ over 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
+
+1.2.26. 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 VPCs, VCCs, 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
+
+1.2.27. 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
+
+1.2.28. 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.
+
+ Discussion: There are two types of LB algorithms - single and dual.
+ Single LB is used in CBR; dual LB is used in VBR (see CBR and VBR).
+
+ Specification: AF-TM4.0
+
+
+
+Dunn & Martin Informational [Page 12]
+
+RFC 2761 Terminology for ATM Benchmarking February 2000
+
+
+1.2.29. 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 PCR determine the MBS that may be
+ transmitted at the peak rate and still is in conformance with the
+ GCRA.
+
+ Discussion: See the discussion under BT.
+
+ Specification: AF-TM4.0
+
+1.2.30. Maximum Frame Size (MFS)
+
+ Definition: The MFS is the maximum length of a frame, expressed in
+ units of cells, which in interface implementing GFR will accept
+ during congested conditions (see GFR).
+
+ Discussion: During congestion, frames whose size is in excess of the
+ MFS may be dropped or tagged. Assuming that the user is adhering to
+ the MFS limit, this behavior should improve performance by improving
+ congestion.
+
+ Specification: AF-TM4.1
+
+1.2.31. 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 loop back measurements.
+
+ Specification: AF-UNI3.1
+
+
+
+
+
+
+
+
+
+
+
+
+
+Dunn & Martin Informational [Page 13]
+
+RFC 2761 Terminology for ATM Benchmarking February 2000
+
+
+1.2.32. Payload Type Indicator (PTI)
+
+ Definition: Payload Type Indicator is the Payload Type field value
+ distinguishing the various management cells and user cells as well as
+ conveying explicit forward congestion indication (see EFCI).
+ 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
+
+1.2.33. 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: PCR directly limits the maximum data rate on an ATM
+ connection. If a user violates the PCR, cells may be dropped
+ resulting in Cell Loss. This in turn will negatively impact AAL5
+ PDUs, which may be carrying IP datagrams. See the discussion under
+ SAR.
+
+ Specification: AF-TM4.0
+
+1.2.34. 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
+
+1.2.35. 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
+
+
+
+
+
+
+Dunn & Martin Informational [Page 14]
+
+RFC 2761 Terminology for ATM Benchmarking February 2000
+
+
+1.2.36. Permanent Virtual Path Connection: (PVPC)
+
+ 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
+
+1.2.37. 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 cells between two separate, autonomous ATM
+ networks.
+
+ Specification: AF-PNNI1.0
+
+1.2.38. 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. PDUs 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: Common Usage
+
+1.2.39. Segmentation and Reassembly (SAR)
+
+ Definition: The process used by the AAL in the B-ISDN reference model
+ (see B-ISDN) which fragments higher layer PDUs 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. Although this
+ measurement is not included in this document, it should be noted that
+ the manner in which SAR is performed will greatly effect performance.
+ SAR can be performed either on the interface card (on board) or in
+ machine central memory (in core). On-board computation should
+
+
+
+Dunn & Martin Informational [Page 15]
+
+RFC 2761 Terminology for ATM Benchmarking February 2000
+
+
+ produce only a small, constant delay; however, in core computation
+ will produce variable delay, which will negatively effect TCP RTT
+ computations. This situation is further complicated by the location
+ of the CRC-32 calculation. Given an in core CRC-32 calculation, bus
+ contention may cause on board SAR to be slower than in core SAR.
+ Clearly, on board CRC-32 calculation and SAR will produce the most
+ favorable performance results.
+
+ SAR performance will also be effected by ATM layer impairments. Cell
+ error (CE), cell loss(CL), cell mis-insertion (CM) and cell delay
+ variation (CDV) will all negatively effect SAR. CE will cause an
+ AAL5 PDU to fail the CRC-32 check and be discarded, thus discarding
+ the packet which the PDU contained. CL and CM will both cause an
+ AAL5 PDU to fail the length check and be discarded. CL can have
+ other effects depending on whether the cell which was lost is the
+ final cell (PTI=1) of the AAL5 PDU. The following discussion
+ enumerates the possibilities.
+
+ 1. PTI=0 cell is lost. In this case, re-assembly registers a length
+ discrepancy and discards the PDU.
+
+ 2. PTI=1 cell is lost.
+
+ 2. A. The AAL5 re-assembly timer expires before the first cell,
+ PTI=0, of the next AAL5 PDU arrives. The AAL5 PDU with the missing
+ PTI=1 cell is discarded due to re-assembly timeout and one packet is
+ lost.
+
+ 2. B. The first cell of the next AAL5 PDU arrives before the re-
+ assembly timer expires. The AAL5 with the missing PTI=1 cell is
+ prepended to the next AAL5 PDU in the SAR engine. This yields two
+ possibilities:
+
+ 2. B. i. The AAL5 re-assembly timer expires before the last cell,
+ PTI=1, of the next AAL5 PDU arrives. The AAL5 PDU with the missing
+ PTI=1 cell and the next AAL5 PDU are discarded due to re-assembly
+ timeout and two packets are lost.
+
+ 2. B. ii. The last cell of the next AAL5 PDU arrives before the re-
+ assembly timer expires. In this case, AAL5 registers a length
+ discrepancy and discards the PDU; therefore, the AAL5 PDU with the
+ missing PTI=1 cell and the next AAL5 PDU are discarded due to their
+ concatenation and two packets are lost.
+
+
+
+
+
+
+
+
+Dunn & Martin Informational [Page 16]
+
+RFC 2761 Terminology for ATM Benchmarking February 2000
+
+
+ 2. C. Coupled with re-assembly, there exists some mechanism for
+ identifying the start of a higher layer PDU, e.g., IP, and the cells
+ associated with the first incomplete AAL5 PDU are discarded,
+ resulting in the loss of one packet.
+
+ Specification: AF-UNI3.1
+
+1.2.40. 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: SCR limits the average data rate on an ATM connection.
+ If a user violates the SCR, cells may be dropped resulting in Cell
+ Loss. This in turn will negatively impact AAL5 PDUs, which may be
+ carrying IP datagrams. See the discussion under SAR.
+
+ Specification: AF-TM4.0
+
+1.2.41. Switched Connection
+
+ Definition: A connection established via signaling.
+
+ Discussion: none.
+
+ Specification: AF-UNI3.1
+
+1.2.42. Switched Virtual Channel Connection (SVCC)
+
+ Definition: A Switched VCC is one that is established and taken down
+ 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
+
+
+
+
+
+
+
+
+
+
+Dunn & Martin Informational [Page 17]
+
+RFC 2761 Terminology for ATM Benchmarking February 2000
+
+
+1.2.43. Switched Virtual Circuit (SVC)
+
+ Definition: A connection established via signaling. The user defines
+ the endpoints when the call is initiated.
+
+ Discussion: SVCs 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
+ effect TCP round trip time calculation, effecting TCP throughput.
+ Specifically, there are two possibilities. In the case where Call
+ Proceeding is not implemented, there is only one timer, T310, with a
+ value of 10 seconds. In the case where Call Proceeding is
+ implemented, there are two timers, T303 and T310, with the values 4
+ and 10 seconds, respectively. In either case, if a timer, either
+ T303 or T310, expires after a Setup message is send, the calling
+ party has the option of re-transmitting the Setup. In the T303 case,
+ this yields a maximum setup time of 18 seconds and, In the T310 case,
+ a maximum setup time of 20 seconds. Thus, the initial TCP RTT
+ calculation will be on he order of 20 seconds.
+
+ Specification: AF-UNI3.1, AF-UNI4.0, AF-PNNI1.0
+
+1.2.44. 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
+
+1.2.45. Traffic Contract
+
+ Definition: A specification of the negotiated traffic characteristics
+ of an ATM connection.
+
+ Discussion: See discussions under BT, CAC, CDV, GCRA, PCR and SCR.
+
+ Specification: AF-TM4.0
+
+1.2.46. 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
+
+
+
+Dunn & Martin Informational [Page 18]
+
+RFC 2761 Terminology for ATM Benchmarking February 2000
+
+
+ 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
+ Priority Control
+ Traffic Shaping
+ Network Resource Management
+ Frame Discard
+ ABR Flow Control
+
+ Discussion: See CAC and traffic shaping.
+
+ Specification: AF-TM4.0
+
+1.2.47. 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 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 RTT
+ variations. As a result, TCP RTT calculations should be more stable.
+
+ Specification: AF-UNI3.1
+
+1.2.48. Transmission Convergence (TC)
+
+ 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.
+
+
+
+
+
+
+
+
+Dunn & Martin Informational [Page 19]
+
+RFC 2761 Terminology for ATM Benchmarking February 2000
+
+
+ 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; however, its value should be constant and
+ small with respect to cell inter-arrival at the maximum data rate.
+
+ Specification: AF-UNI3.1
+
+1.2.49. 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 (CL), cell
+ delay variation (CDV) or cell mis-insertion(CM), TCP RTT estimates
+ will be highly variable. Further, all negatively impact AAL5 re-
+ assembly, which in turn may cause packet loss. See discussions under
+ CDV and SAR.
+
+ Specification: AF-TM4.0
+
+1.2.50. 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 established connections, by detecting violations of negotiated
+ parameters and taking appropriate actions.
+
+ Discussion: See discussions under BT, CAC, CDV, GCRA, PCR and SCR.
+
+ Specification: AF-TM4.0
+
+1.2.51. 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.
+
+
+
+Dunn & Martin Informational [Page 20]
+
+RFC 2761 Terminology for ATM Benchmarking February 2000
+
+
+ Discussion: none.
+
+ Specification: AF-UNI3.1
+
+1.2.52. 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 RTT variations. This in turn will cause the TCP RTT
+ estimates to be unstable.
+
+ Specification: AF-TM4.0
+
+1.2.53. Virtual Channel (VC)
+
+ Definition: A communications channel that provides for the sequential
+ unidirectional transport of ATM cells.
+
+ Discussion: none.
+
+ Specification: AF-TM3.1
+
+1.2.54. Virtual Channel Connection (VCC)
+
+ Definition: A concatenation of VCIs 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. VCCs are unidirectional.
+
+ Discussion: none.
+
+ Specification: AF-TM3.1
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+Dunn & Martin Informational [Page 21]
+
+RFC 2761 Terminology for ATM Benchmarking February 2000
+
+
+1.2.55. 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
+
+1.2.56. Virtual Path (VP)
+
+ Definition: A unidirectional logical association or bundle of VCs.
+
+ Discussion: none.
+
+ Specification: AF-UNI3.1
+
+1.2.57. Virtual Path Connection (VPC)
+
+ Definition: A concatenation of VPIs between Virtual Path Terminators
+ (VPTs). VPCs are unidirectional
+
+ Discussion: none.
+
+ Specification: AF-TM3.1
+
+1.2.58. 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
+
+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.
+
+
+
+
+
+Dunn & Martin Informational [Page 22]
+
+RFC 2761 Terminology for ATM Benchmarking February 2000
+
+
+ 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 ATM 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.
+
+ 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
+
+
+
+
+
+
+
+
+
+
+
+Dunn & Martin Informational [Page 23]
+
+RFC 2761 Terminology for ATM Benchmarking February 2000
+
+
+2.2.2. ATM Layer
+
+2.2.2.1. Cell Delay Variation (CDV)
+
+ Definition: The variation in cell transfer delay (CTD) 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 and cause SAR timeout. See
+ discussion under SAR.
+
+ Measurement Units: seconds
+
+2.2.2.2. Cell Error Ratio (CER)
+
+ Definition: The ratio of cells with payload errors in a transmission
+ in relation to the total number of 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
+ cell header will cause cell loss at the ATM layer. Note further that
+ multiple errors in a payload will only be counted as one cell payload
+ error.
+
+ CER = Cells with payload errors / Total Cells Transmitted.
+
+ Discussion: The measurement is taken over a time interval and is
+ desirable to be measured on an in-service circuit. CER is closely
+ related to the number of corrupted AAL5 PDUs; however, there is not a
+ direct numerical correlation between the number of errored cells and
+ the number of corrupted AAL5 PDUs. There are two cases described
+ below.
+
+ 1. Only one cell in an AAL5 PDU contains payload errors. In this
+ case, there is a one-to-one correspondence between cell payload
+ errors and the number of corrupted AAL5 PDUs.
+
+
+
+
+
+Dunn & Martin Informational [Page 24]
+
+RFC 2761 Terminology for ATM Benchmarking February 2000
+
+
+ 2. Multiple cells in the AAL5 PDU contain payload errors. In this
+ case, there is not a one-to-one correspondence between cell payload
+ errors and the number of corrupted AAL5 PDUs.
+
+ Measurement Units: dimensionless.
+
+2.2.2.3. 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 indicates the number of ATM cells lost in relation to the total
+ number of cells sent. CLR is closely related to the number of
+ corrupted AAL5 PDUs; however, there is not a direct numerical
+ correlation between the number of cells lost and the number of
+ corrupted AAL5 PDUs. See the discussion under SAR.
+
+ Measurement Units: dimensionless.
+
+2.2.2.4. Cell Misinsertion Ratio (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 = Misinserted Cells / Total Cells Transmitted.
+
+ Discussion: The measurement is taken over a time interval and is
+ desirable to be measured on an in-service circuit. CMR is closely
+ related to the number of corrupted AAL5 PDUs; however, there is not a
+ direct numerical correlation between the number of mis-inserted cells
+ and the number of corrupted AAL5 PDUs. There are two cases described
+ below.
+
+
+
+
+
+Dunn & Martin Informational [Page 25]
+
+RFC 2761 Terminology for ATM Benchmarking February 2000
+
+
+ 1. Only one cell is mis-inserted into an AAL5 PDU. In this case,
+ there is a one-to-one correspondence between cell mis-insertion and
+ the number of corrupted AAL5 PDUs.
+
+ 2. Multiple cells are mis-inserted into an AAL5. In this case, there
+ is not a one-to-one correspondence between cell mis-insertion and the
+ number of corrupted AAL5 PDUs.
+
+ Measurement Units: dimensionless.
+
+2.2.2.5. 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: This measures the amount of provisioned bandwidth which
+ is not utilized. This lack of utilization may be caused by
+ encapsulation overhead, e.g., AAL5 trailer and padding, or by the
+ protocol itself, e.g., TCP usually transmits in only one direction.
+
+ Measurement units: Cells per second
+
+2.2.2.6. 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. Although this
+ will appear as cell loss at the ATM layer, this measurement can be
+ made in-service using a test probe which measures CRC errors at the
+ TC layer.
+
+ Measurement Units: dimensionless
+
+2.2.2.7. 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.
+
+
+
+
+
+
+
+
+Dunn & Martin Informational [Page 26]
+
+RFC 2761 Terminology for ATM Benchmarking February 2000
+
+
+ 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. While this number is a constant and
+ should not adversely effect performance, it is a component in RTT.
+
+ Measurement units: seconds
+
+2.2.3. ATM Adaptation Layer (AAL) Type 5 (AAL5)
+
+2.2.3.1. AAL5 Re-assembly Errors
+
+ Definition: AAL5 Re-assembly Errors constitute any error, which
+ causes the AAL5 PDU to be corrupted.
+
+ Discussion: AAL5 Re-assembly 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 PDUs payload
+ 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 cause AAL5 re-assembly errors. See
+ discussion under AAL5 re-assembly errors.
+
+ Measurement Units: dimensionless
+
+
+
+
+
+
+
+
+
+
+Dunn & Martin Informational [Page 27]
+
+RFC 2761 Terminology for ATM Benchmarking February 2000
+
+
+2.2.4. ATM Service: Signaling
+
+2.2.4.1. CAC Denial Time
+
+ Definition: The amount of time required for CAC to determine that a
+ call must be rejected.
+
+ Discussion: In the case where Call Proceeding is implemented, this
+ number will be less than 4 seconds. Otherwise, it will be less than
+ 10 seconds. Large values of this measurement will adversely effect
+ performance on systems where an alternate, non-NBMA, service is
+ available.
+
+ Measurement Units: seconds
+
+2.2.4.2. Connection Establishment Time
+
+ Definition: The amount of time between the first Setup message from
+ the calling party and the Connect message to the calling party.
+
+ Discussion: See discussion under SVC.
+
+ Measurement Units: seconds
+
+2.2.4.3. Connection Teardown Time
+
+ Definition: The amount of between the Release message being sent and
+ the Release Complete message being received.
+
+ Discussion: Large values of this measurement will adversely effect
+ performance in systems where the total number of open calls or VCs is
+ limited. Specifically, a new VC cannot be instantiated with the same
+ VPI/VCI before the old one is released.
+
+ Measurement Units: seconds
+
+2.2.4.4. Crankback Time
+
+ Definition: The amount of time between the issuance of the first
+ release or release complete message by the switch where the current
+ Designated Transit List (DTL) is blocked and the receipt of the SETUP
+ with the updated DTLs by the target switch.
+
+ Discussion: This measurement does not take into account the amount of
+ time associated with either the successful portion of the call setup
+ transit or the time required for the calling party to receive .bp a
+ response from the called party. As a result, the call may still fail
+ to complete if the call setup timer on the calling party expires.
+
+
+
+Dunn & Martin Informational [Page 28]
+
+RFC 2761 Terminology for ATM Benchmarking February 2000
+
+
+ See discussion under SVC.
+
+ Measurement Units: seconds
+
+2.2.4.5. Route Update Response Time
+
+ Definition: The amount of time between the receipt of a PNNI Topology
+ State Element (PTSE), which is the PNNI routing PDU, containing a
+ topology different from the current topology and the point at which
+ the switch begins to generate DTLs reflecting the routing change.
+
+ Discussion: This measurement provides a lower bound on the amount of
+ time during which SETUP messages will be forwarded along a sub-
+ optimal or blocked path.
+
+ Measurement Units: seconds
+
+2.2.5. ATM Service: ILMI
+
+2.2.5.1. MIB Alignment Time
+
+ Definition: The amount of time between the issuance of the final cold
+ start message and the final get response associated with the exchange
+ of static MIB information.
+
+ Discussion: This measurement reflects the amount of time required by
+ the switch and end system to exchange all information required to
+ characterize and align the capabilities of both systems. It does not
+ include address registration. It should also be noted that this
+ measurement will depend on the number of MIB elements implemented by
+ both systems.
+
+ Measurement Units: seconds
+
+2.2.5.2. Address Registration Time
+
+ Definition: The amount of time between the initial set request issued
+ by the switch and the final get response issued by the switch.
+
+ Discussion: This measurement assumes that the switch has checked the
+ network prefix status object and the end system has checked the ATM
+ address status object. In the case where the end system checks the
+ ATM address status object only after the switch has issued a set
+ request of the network prefix status object, this measurement will
+ not reflect the actual time required to complete the address
+ registration.
+
+ Measurement Units: seconds
+
+
+
+Dunn & Martin Informational [Page 29]
+
+RFC 2761 Terminology for ATM Benchmarking February 2000
+
+
+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.
+
+4. Notices
+
+ The IETF takes no position regarding the validity or scope of any
+ intellectual property or other rights that might be claimed to
+ pertain to the implementation or use of the technology described in
+ this document or the extent to which any license under such rights
+ might or might not be available; neither does it represent that it
+ has made any effort to identify any such rights. Information on the
+ IETFs procedures with respect to rights in standards-track and
+ standards-related documentation can be found in BCP-11. Copies of
+ claims of rights made available for publication and any assurances of
+ licenses to be made available, or the result of an attempt made to
+ obtain a general license or permission for the use of such
+ proprietary rights by implementors or users of this specification can
+ be obtained from the IETF Secretariat.
+
+ The IETF invites any interested party to bring to its attention any
+ copyrights, patents or patent applications, or other proprietary
+ rights which may cover technology that may be required to practice
+ this standard. Please address the information to the IETF Executive
+ Director.
+
+5. 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.
+
+ [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 (final ballot), btd-tm-01.02, July 1998.
+
+ [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.
+
+
+
+
+Dunn & Martin Informational [Page 30]
+
+RFC 2761 Terminology for ATM Benchmarking February 2000
+
+
+ [I.321] ITU-T, B-ISDN protocol reference model and its
+ application, April 1991.
+
+ [I.363] ITU-T, B-ISDN ATM Adaptation Layer Specification
+ series, 1996-1997.
+
+ [I.363.5] ITU-T, B-ISDN ATM Adaptation Layer Specification: Type
+ 5 AAL, August 1996.
+
+6. 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.
+ 11241-B Skilift Court
+ Columbia, MD 21044 USA
+
+ Phone: +1 (410) 730-6300
+ EMail: Cynthia.E.Martin@worldnet.att.net
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+Dunn & Martin Informational [Page 31]
+
+RFC 2761 Terminology for ATM Benchmarking February 2000
+
+
+7. Full Copyright Statement
+
+ Copyright (C) The Internet Society (2000). All Rights Reserved.
+
+ This document and translations of it may be copied and furnished to
+ others, and derivative works that comment on or otherwise explain it
+ or assist in its implementation may be prepared, copied, published
+ and distributed, in whole or in part, without restriction of any
+ kind, provided that the above copyright notice and this paragraph are
+ included on all such copies and derivative works. However, this
+ document itself may not be modified in any way, such as by removing
+ the copyright notice or references to the Internet Society or other
+ Internet organizations, except as needed for the purpose of
+ developing Internet standards in which case the procedures for
+ copyrights defined in the Internet Standards process must be
+ followed, or as required to translate it into languages other than
+ English.
+
+ The limited permissions granted above are perpetual and will not be
+ revoked by the Internet Society or its successors or assigns.
+
+ This document and the information contained herein is provided on an
+ "AS IS" basis and THE INTERNET SOCIETY AND THE INTERNET ENGINEERING
+ TASK FORCE DISCLAIMS ALL WARRANTIES, EXPRESS OR IMPLIED, INCLUDING
+ BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE INFORMATION
+ HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED WARRANTIES OF
+ MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE.
+
+Acknowledgement
+
+ Funding for the RFC Editor function is currently provided by the
+ Internet Society.
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+Dunn & Martin Informational [Page 32]
+