As per Relevance of the word terminology, we have this rfc below:
Network Working Group J.
Request for Comments: 2761 C.
Category: Informational ANC, Inc
February 2000
Terminology for ATM
Status of this
This memo provides information for the Internet community. It
not specify an Internet standard of any kind. Distribution of
memo is unlimited
Copyright
Copyright (C) The Internet Society (2000). All Rights Reserved
This memo discusses and defines terms associated with
benchmarking tests and the results of these tests in the context
Asynchronous Transfer Mode (ATM) based switching devices. The
defined in this memo will be used in addition to terms defined
RFCs 1242, 2285, and 2544. This memo is a product of the
Methodology Working Group (BMWG) of the Internet Engineering
Force (IETF).
This document provides terminology for benchmarking ATM
switching devices. It extends terminology already defined
benchmarking network interconnect devices in RFCs 1242, 2285,
2544. Although some of the definitions in this memo may be
to a broader group of network interconnect devices, the primary
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
sub-section, that contains performance metrics with inherent units
The divisions of the measurement sub-section follow the BISDN model
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The BISDN model comprises four layers and two planes. This
addresses the interactions between these layers and how they
IP and TCP throughput. A schematic of the B-ISDN model follows
---------|--------------------------|-------------------------------
| User Plane | Control
---------|--------------------------|--------------------------------
Services | IP | ILMI | UNI,
---------|--------------------------|----------|---------------------
AAL | AAL1, AAL2, AAL3/4, AAL5 | AAL5 |
---------|--------------------------|----------|---------------------
ATM | Cell Relay | OAM,
---------|--------------------------|--------------------------------
| Convergence |
Physical |--------------------------|--------------------------------
| Media |
---------|--------------------------|--------------------------------
This document assumes that necessary services are available
active. For example, IP connectivity requires SSCOP
between signaling entities. Further, it is assumed that the SUT
the ability to configure ATM addresses (via hard coded addresses
ILMI or PNNI neighbor discovery), has the ability to run SSCOP,
has the ability to perform signaled call setups (via UNI or
signaling). This document covers only CBR, VBR and UBR
types. ABR will be handled in a separate document. Finally,
document presents only the terminology associated with
IP performance over ATM; therefore, it does not represent a
compilation of ATM test terminology
The BMWG produces two major classes of documents:
Terminology documents and Benchmarking Methodology documents.
Terminology documents present the benchmarks and other related terms
The Methodology documents define the procedures required to
the benchmarks cited in the corresponding Terminology documents
Existing
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
benchmarking of switching devices and should be consulted. RFC 2285,
"Benchmarking Terminology for LAN Switching Devices" contains
number of terms pertaining to traffic distributions and
interarrival. For the sake of clarity and continuity, this
adopts the template for definitions set out in Section 2 of RFC 1242.
Definitions are indexed and grouped together in sections for ease
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reference. The key words "MUST", "MUST NOT", "REQUIRED", "SHALL",
"SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY",
"OPTIONAL" go in this document are to be interpreted as described
RFC 2119.
The definitions presented in this section have been divided into
groups. The first group is formal definitions, which are required
the definitions of the performance metrics but are not
strictly metrics. These definitions are subsumed from other
done in other working groups both inside and outside the IETF.
are provided as a courtesy to the reader
1. Formal
1.1. Definition Format (from RFC 1242)
Term to be defined
Definition: The specific definition for the term
Discussion: A brief discussion of the term, its application and
restrictions on measurement procedures. These discussions
solely to the impact of a particular ATM parameter on IP or TCP
therefore, definitions which contain no configurable components
whose components will have the discussion: None
Specification: The working group and document in which the terms
specified and are listed in the references section
1.2. Related
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:
for circuit qemulation, voice over ATM AAL2: used for sub-rated
over ATM AAL3/4: used for data over noisy ATM lines AAL5: used
data over ATM, most widely used AAL
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These AAL types are not measurements, but it is possible to
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
minimal error checking and no error detection. The AAL5 CPCS (
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
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
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
PDU
Discussion: AAL5 is the adaptation layer for UNI signaling, ILMI
PNNI signaling, and for IP PDUs. It is the most widely used AAL
to date. AAL5 requires two distinct processes. The first is
encapsulation, on the transmit side, and de-encapsulation, on
receive side, of the higher layer PDU into the AAL5 CPCS PDU
requires the computation of the length and the CRC-32. The
required for this process depends on whether the CRC-32
is done on the interface (on-board) or in machine central memory (
core). On-board computation should produce only a small,
delay; however, in core computation will produce variable delay
which will negatively effect TCP RTT computations. The second
is segmentation and re-assembly (SAR) which is defined below (
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SAR).
Specification: I.363.5
1.2.3. Asynchronous Transfer Mode (ATM
Definition: A transfer mode in which the information is
into 53 octet PDUs called cells. It is asynchronous in the sense
the recurrence of cells containing information from an
user is not necessarily periodic
Discussion: ATM is based on the ISDN model; however, unlike ISDN,
uses fixed length (53 octet) cells. Because of the fixed length
ATM PDUs, higher layer PDUs must be adapted into ATM using one of
four ATM adaptation layers (see AAL).
Specification: AF-UNI3.1
1.2.4. ATM
Definition: A virtual path link (VPL) or a virtual channel
(VCL).
Discussion: none
Specification: AF-UNI3.1
1.2.5. ATM Peer-to-Peer
Definition: A virtual channel connection (VCC) or a virtual
connection (VPC).
Discussion: none
Specification: AF-UNI3.1
1.2.6. ATM Traffic
Definition: A generic list of traffic parameters, which specify
intrinsic traffic characteristics of a requested ATM connection (
GCRA), which must include PCR and QoS and may include BT, SCR
best effort (UBR) indicator
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Discussion: The effects of each traffic parameter will be
individually
Specification: AF-UNI3.1
1.2.7. ATM User-User
Definition: An association established by the ATM Layer to
communication between two or more ATM service users (i.e.,
two or more next higher entities or between two or more ATM
entities). The communications over an ATM Layer connection may
either bi-directional or unidirectional. The same Virtual
Identifier (VCI) is issued for both directions of a connection at
interface
Discussion: Because ATM is connection oriented, certain features
IP (i.e. those which require multicast) are not available
Specification: AF-UNI3.1
1.2.8. Broadband ISDN (B-ISDN)
Definition: A layered service model that specifies the mapping
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
Cell Rate (SCR), specifies the maximum number of cells which will
accepted at the Peak Cell Rate (PCR) on an ATM connection
Discussion: BT applies to ATM connections supporting VBR services
is the limit parameter of the GCRA. BT will effect TCP and IP
loss in that cells presented to an interface which violate the BT
be dropped, which will cause AAL5 PDU corruption. BT will also
TCP RTT calculation. BT=(MBS-1)*(1/SCR 1/PCR) (see MBS, PCR, SCR).
Specification: AF-TM4.0
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1.2.10.
Definition: A call is an association between two or more users
between a user and a network entity that is established by the use
network capabilities. This association may have zero or
connections
Discussion: none
Specification: AF-UNI3.1
1.2.11.
Definition: A unit of transmission in ATM. A fixed-size
consisting of a 5-octet header and a 48-octet payload
Discussion: none
Specification: AF-UNI3.1
1.2.12. Call-
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
of ATM connections by introducing Cell Delay Variation. When
from two or more ATM connections are multiplexed, cells of a
ATM connection may be delayed while cells of another ATM
are being inserted at the output of the multiplexer. Similarly,
cells may be delayed while physical layer overhead or OAM cells
inserted. Consequently, some randomness may affect the inter-
time between consecutive cells of a connection as monitored at
UNI. The upper bound on the "clumping" measure is the CDVT
Discussion: CDVT effects TCP round trip time calculations.
values of CDVT will adversely effect TCP throughput and cause
timeout. See discussion under SAR
Specification: AF-TM4.0
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1.2.14. Cell
Definition: ATM Layer protocol control information
Discussion: The ATM cell header is a 5-byte header that contains
following fields: Generic Flow Control (GFC) 4 bits Virtual
Identifier (VPI) 8 bits Virtual Channel Identifier (VCI) 16
Payload Type (PT) 3 bits Cell Loss Priority (CLP) 1 bit Header
Check (HEC) 8 bit CRC computed over the previous four
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
priority for ATM cells. CLP=0 cells are higher priority than CLP=1
cells. CLP=1 cells may be discarded during periods of congestion
preserve the CLR of CLP=0 cells
Discussion: The CLP bit is used to determine GCRA
compliance. Specifically, two traffic contracts may apply to
single connection: CLP=0, meaning only cells with CLP=0,
CLP=0+1, meaning cells with CLP=0 or CLP=1.
Specification: AF-UNI3.1
1.2.16.
Definition: An ATM connection consists of concatenation of ATM
links in order to provide an end-to-end information
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
actions taken by the network during the call set-up phase (or
call re-negotiation phase) in order to determine whether a
request can be accepted or should be rejected (or whether a
for re-allocation can be accommodated).
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Discussion: CAC is based on the ATM traffic descriptor (see
traffic descriptor) associated with the call as well as the
and existing load. It may also be based on administrative
such as calling party number required or access limitations.
effect on performance of these policies is beyond the scope of
document and will be handled in the BMWG document:
Terminology for Firewall Performance
Specification: AF-UNI3.1
1.2.18. Constant Bit Rate (CBR
Definition: An ATM service category which supports a constant
guaranteed rate to transport services such as video or voice as
as circuit emulation which requires rigorous timing control
performance parameters. CBR requires the specification of PCR
QoS (see PCR and QoS).
Discussion: Because CBR provides minimal cell delay variation (
CDV), it should improve TCP throughput by stabilizing the
calculation. Further, as CBR generally provides a high
service, meaning that cells with a CBR traffic contract usually
priority over other cells during congestion, TCP segment and
packet loss should be minimized. The cost associated with using
is the loss of statistical multiplexing. Since CBR guarantees
throughput and CDV control, the connections must be subscribed
PCR. This is extremely wasteful as most protocols, e.g., TCP,
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
based on the bits in a block of data. This number is transmitted
the data, the receiver uses this information and the same
to insure the accurate delivery of data by comparing the results
algorithm, and the number received. If a mismatch occurs, an
in transmission is presumed
Discussion: CRC is not a measurement, but it is possible to
the amount of time to perform a CRC on a string of bits.
measurement will not be addressed in this document. See
under AAL5.
Specification: AF-UNI3.1
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1.2.20. End System (ES
Definition: A system where an ATM connection is terminated
initiated. An originating end system initiates the ATM connection
and terminating end system terminates the ATM connection. OAM
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
header. A network element in an impending-congested state or
congested state may set EFCI so that this indication may be
by the destination end-system. For example, the end-system may
this indication to implement a protocol that adaptively lowers
cell rate of the connection during congestion or
congestion. A network element that is not in a congestion state
an impending congestion state will not modify the value of
indication. Impending congestion is the state when network
is operating around its engineered capacity level
Discussion: EFCI may be used to prevent congestion by alerting
positive acknowledgement protocol and causing action to be taken.
the case of TCP, when EFCI cells are received the driver
could alert the TCP software of impending congestion. The
receiver would then acknowledge the current segment and set
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
the traffic contract of the connection. For each cell arrival,
GCRA determines whether the cell conforms to the traffic contract
The UPC function may implement the GCRA, or one or more
algorithms to enforce conformance. The GCRA is defined with
parameters: the Increment (I) and the Limit (L).
Discussion: The GCRA increment and limit parameters are mapped to
and VBR in the following fashion. For CBR, I=1/PCR and L=CDVT (
tolerance). For VBR, there are two GCRA algorithms running (
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
conformance with the first GCRA uses I=1/SCR and L=BT (see BT, CDV
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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
provide local functions (e.g., flow control). It has
significance only and the value encoded in the field is not
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
Rate (MCR) guarantee under the assumption of a given maximum
size (MFS) and a given Maximum Burst Size (MBS). The MFS and MBS
both expressed in units of cells. GFR only applies to
channel connections (VCCs).
Discussion: GFR is intended for users who are either not able
specify the range of traffic parameters needed to request most
services, or are not equipped to comply with the (source)
rules required by existing ATM services. Specifically, GFR
the user with the following minimum service guarantee: When
network is congested, all frames whose length is less than MFS
presented to the ATM interface in bursts less than MBS and at a
less than PCR will be handled with minimum frame loss. When
network is not congested, the user can burst at higher rates
The effect of GFR on performance is somewhat problematic as
policing algorithm associated with GFR depends on the network load
however, under congested condition and assuming a user who
following the GFR service agreement, it should improve performance
Specification: AF-TM4.1
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1.2.25. Header Error Control (HEC
Definition: A check character calculated using an 8 bit CRC
over the first 4 octets of the ATM cell header. This allows
single bit error correction or multiple bit error detection
Discussion: none
Specification: AF-UNI3.1
1.2.26. Integrated Local Management
Definition: A management protocol which uses SNMPv1 carried on AAL
to provide ATM network devices with status and
information concerning VPCs, VCCs, registered ATM addresses and
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.
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
functions or both for a specific ATM connection. OAM cells may
generated and received
Discussion: An IS can be either the user or network side of a
signaling interface, or the network side of a PNNI
interface
Specification: AF-TEST-0022
1.2.28. Leaky Bucket (LB
Definition: Leaky Bucket is the term used as an analogous
of the algorithm used for conformance checking of cell flows from
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
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
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1.2.29. Maximum Burst Size (MBS
Definition: In the signaling message, the Burst Tolerance (BT)
conveyed through the MBS that is coded as a number of cells. The
together with the SCR and the PCR determine the MBS that may
transmitted at the peak rate and still is in conformance with
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
units of cells, which in interface implementing GFR will
during congested conditions (see GFR).
Discussion: During congestion, frames whose size is in excess of
MFS may be dropped or tagged. Assuming that the user is adhering
the MFS limit, this behavior should improve performance by
congestion
Specification: AF-TM4.1
1.2.31. Operations, Administration, and Maintenance (OAM
Definition: A group of network management functions that
network fault indication, performance information, and data
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)
segment or end-to-end VC termination management (i.e. F5 segment, F
E2E). These OAM cells can be used to identify fault management
connection verification, and loop back measurements
Specification: AF-UNI3.1
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1.2.32. Payload Type Indicator (PTI
Definition: Payload Type Indicator is the Payload Type field
distinguishing the various management cells and user cells as well
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
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
connection. If a user violates the PCR, cells may be
resulting in Cell Loss. This in turn will negatively impact AAL
PDUs, which may be carrying IP datagrams. See the discussion
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
where switching is performed on the VPI/VCI fields of each cell.
permanent VCC is one that is provisioned through some
management function and left up indefinitely
Discussion: none
Specification: AF-UNI3.1
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1.2.36. Permanent Virtual Path Connection: (PVPC
Definition: A Virtual Path Connection (VPC) is an ATM
where switching is performed on the VPI field only of each cell.
permanent VPC is one that is provisioned through some
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
integrated in the same network
Discussion: PNNI consists of signaling and routing between
network devices. PNNI signaling is based on UNI 4.0
between two network side interfaces, while PNNI routing provides
mechanism to route ATM cells between two separate, autonomous
networks
Specification: AF-PNNI1.0
1.2.38. Protocol Data Unit (PDU
Definition: A PDU is a message of a given protocol comprising
and protocol-specific control information, typically contained in
header. PDUs pass over the protocol interfaces that exist
the layers of protocols (per OSI model).
Discussion: In ATM networks, a PDU can refer to an ATM cell,
ATM cells, an AAL segment, an IP datagram and others
Specification: Common
1.2.39. Segmentation and Reassembly (SAR
Definition: The process used by the AAL in the B-ISDN reference
(see B-ISDN) which fragments higher layer PDUs into ATM cells
Discussion: SAR is not a measurement, but the speed in which SAR
be completed on a bit stream can be measured. Although
measurement is not included in this document, it should be noted
the manner in which SAR is performed will greatly effect performance
SAR can be performed either on the interface card (on board) or
machine central memory (in core). On-board computation
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produce only a small, constant delay; however, in core
will produce variable delay, which will negatively effect TCP
computations. This situation is further complicated by the
of the CRC-32 calculation. Given an in core CRC-32 calculation,
contention may cause on board SAR to be slower than in core SAR
Clearly, on board CRC-32 calculation and SAR will produce the
favorable performance results
SAR performance will also be effected by ATM layer impairments.
error (CE), cell loss(CL), cell mis-insertion (CM) and cell
variation (CDV) will all negatively effect SAR. CE will cause
AAL5 PDU to fail the CRC-32 check and be discarded, thus
the packet which the PDU contained. CL and CM will both cause
AAL5 PDU to fail the length check and be discarded. CL can
other effects depending on whether the cell which was lost is
final cell (PTI=1) of the AAL5 PDU. The following
enumerates the possibilities
1. PTI=0 cell is lost. In this case, re-assembly registers a
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
PTI=1 cell is discarded due to re-assembly timeout and one packet
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
prepended to the next AAL5 PDU in the SAR engine. This yields
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
PTI=1 cell and the next AAL5 PDU are discarded due to re-
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
discrepancy and discards the PDU; therefore, the AAL5 PDU with
missing PTI=1 cell and the next AAL5 PDU are discarded due to
concatenation and two packets are lost
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2. C. Coupled with re-assembly, there exists some mechanism
identifying the start of a higher layer PDU, e.g., IP, and the
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
of an ATM connection over time scales which are long relative
those for which the PCR is defined. Enforcement of this bound by
UPC could allow the network to allocate sufficient resources,
less than those based on the PCR, and still ensure that
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
Loss. This in turn will negatively impact AAL5 PDUs, which may
carrying IP datagrams. See the discussion under SAR
Specification: AF-TM4.0
1.2.41. Switched
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
dynamically through control signaling. A Virtual Channel
(VCC) is an ATM connection where switching is performed on
VPI/VCI fields of each cell
Discussion: none
Specification: AF-UNI3.1
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1.2.43. Switched Virtual Circuit (SVC
Definition: A connection established via signaling. The user
the endpoints when the call is initiated
Discussion: SVCs are established using either UNI signaling or
signaling. The signaling state machine implements several timers
which can effect the time required for call establishment. This
effect TCP round trip time calculation, effecting TCP throughput
Specifically, there are two possibilities. In the case where
Proceeding is not implemented, there is only one timer, T310, with
value of 10 seconds. In the case where Call Proceeding
implemented, there are two timers, T303 and T310, with the values 4
and 10 seconds, respectively. In either case, if a timer,
T303 or T310, expires after a Setup message is send, the
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
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
established and taken down dynamically through control signaling.
Virtual Path Connection (VPC) is an ATM connection where switching
performed on the VPI field only of each cell
Discussion: none
Specification: AF-UNI3.1
1.2.45. Traffic
Definition: A specification of the negotiated traffic
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
and congestion control procedures for ATM. ATM layer traffic
refers to the set of actions taken by the network to avoid
conditions. ATM layer congestion control refers to the set
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actions taken by the network to minimize the intensity, spread
duration of congestion. The following functions form a framework
managing and controlling traffic and congestion in ATM networks
may be used in appropriate combinations
Connection Admission
Feedback
Usage Parameter
Priority
Traffic
Network Resource
Frame
ABR Flow
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
characteristics of a stream of cells on a connection to
better network efficiency, while meeting the QoS objectives, or
ensure conformance at a subsequent interface. Traffic shaping
maintain cell sequence integrity on a connection. Shaping
traffic characteristics of a cell flow with the consequence
increasing the mean Cell Transfer Delay
Discussion: TS should improve TCP throughput by reducing
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
transforms the flow of cells into a steady flow of bits and bytes
transmission over the physical medium. On transmit the TC
maps the cells to the frame format, generates the Header Error
(HEC), and sends idle cells when the ATM layer has none. to send.
reception, the TC sublayer delineates individual cells in
received bit stream, and uses the HEC to detect and correct
errors
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Discussion: TC is not a measurement, but the speed in which TC
occur on a bit stream can be measured. This measurement will not
discussed in this document; however, its value should be constant
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
traffic related service guarantees. Specifically, UBR does
include the notion of a per-connection-negotiated bandwidth.
commitments are made with respect to the cell loss ratio
by a UBR connection, or as to the cell transfer delay experienced
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
791; however, UBR has specific drawbacks with respect to TCP service
Since UBR makes no guarantee with respect to cell loss (CL),
delay variation (CDV) or cell mis-insertion(CM), TCP RTT
will be highly variable. Further, all negatively impact AAL5 re
assembly, which in turn may cause packet loss. See discussions
CDV and SAR
Specification: AF-TM4.0
1.2.50. Usage Parameter Control (UPC
Definition: Usage Parameter Control is defined as the set of
taken by the network to monitor and control traffic, in terms
traffic offered and validity of the ATM connection, at the end-
access. Its main purpose is to protect network resources
malicious as well as unintentional misbehavior, which can affect
QoS of established connections, by detecting violations of
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
ATM switch, or between a private ATM switch and the public
ATM network; defined by physical and protocol specifications per
Forum UNI documents. The standard adopted by the ATM Forum to
connections between users or end stations and a local switch
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Discussion: none
Specification: AF-UNI3.1
1.2.52. Variable Bit Rate (VBR
Definition: An ATM Forum defined service category which
variable bit rate data traffic with average and peak
parameters
Discussion: VBR may potentially adversely effect TCP throughput
to large RTT variations. This in turn will cause the TCP
estimates to be unstable
Specification: AF-TM4.0
1.2.53. Virtual Channel (VC
Definition: A communications channel that provides for the
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
where the ATM service users access the ATM layer. The points at
the ATM cell payload is passed to, or received from, the users of
ATM Layer (i.e., a higher layer or ATM-entity) for processing
the endpoints of a VCC. VCCs are unidirectional
Discussion: none
Specification: AF-TM3.1
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1.2.55. Virtual Channel Identifier (VCI
Definition: A unique numerical tag as defined by a 16 bit field
the ATM cell header that identifies a virtual channel, over which
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
(VPTs). VPCs are
Discussion: none
Specification: AF-TM3.1
1.2.58. Virtual Path Identifier (VPI
Definition: An eight-bit field in the ATM cell header that
the virtual path over which the cell should be routed
Discussion: none
Specification: AF-UNI3.1
2. Performance
2.1. Definition Format (from RFC 1242)
Metric to be defined
Definition: The specific definition for the metric
Discussion: A brief discussion of the metric, its application and
restrictions on measurement procedures
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Measurement units: Intrinsic units used to quantify this metric.
includes subsidiary units; e.g., microseconds are acceptable if
intrinsic unit is seconds
2.2.
2.2.1. Physical Layer -
2.2.1.1. Pointer
Definition: Pointer Movements is the number of changes in a
pointer due to clock synchronization slips
Discussion: SONET Pointer Movements can cause loss of information
the SONET payload envelop (SPE) which contains IP datagrams,
in the form of ATM cells or as PPP delimited PDUs
Measurement Units: Per second
2.2.1.2. Transport Overhead Error
Definition: SONET Transport Overhead Error Count is the number
SONET transport overhead errors detected
Discussion: SONET Transport Overhead Errors SONET Transport
Errors cause SONET frames to be lost. These frames may contain
datagrams; either in the form of cells or as PPP delimited PDUs
Measurement Units: Positive
2.2.1.3. Path Overhead Error
Definition: SONET Path Overhead Error Count is the number of
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
as PPP delimited PDUs
Measurement Units: Positive
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2.2.2. ATM
2.2.2.1. Cell Delay Variation (CDV
Definition: The variation in cell transfer delay (CTD)
with a given traffic load, orientation and distribution, as well
an integration period. CDV = max (CTD) - min (CTD) where max and
indicate the maximum and minimum over the integration period
respectively
Discussion: CDV is a component of cell transfer delay, induced
buffering and cell scheduling. Peak-to-peak CDV is a QoS
parameter associated with CBR and VBR services. The peak-to-peak
is the ((1-a) quantile of the CTD) minus the fixed CTD that could
experienced by any delivered cell on a connection during the
connection holding time. The parameter "a" is the probability of
cell arriving late
CDV effects TCP round trip time calculations. Large values of
will adversely effect TCP throughput and cause SAR timeout.
discussion under SAR
Measurement Units:
2.2.2.2. Cell Error Ratio (CER
Definition: The ratio of cells with payload errors in a
in relation to the total number of cells sent in a
associated with a given traffic load, orientation and distribution
as well as an integration period. Note that errors occurring in
cell header will cause cell loss at the ATM layer. Note further
multiple errors in a payload will only be counted as one cell
error
CER = Cells with payload errors / Total Cells Transmitted
Discussion: The measurement is taken over a time interval and
desirable to be measured on an in-service circuit. CER is
related to the number of corrupted AAL5 PDUs; however, there is not
direct numerical correlation between the number of errored cells
the number of corrupted AAL5 PDUs. There are two cases
below
1. Only one cell in an AAL5 PDU contains payload errors. In
case, there is a one-to-one correspondence between cell
errors and the number of corrupted AAL5 PDUs
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2. Multiple cells in the AAL5 PDU contain payload errors. In
case, there is not a one-to-one correspondence between cell
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
the total cells sent in a transmission associated with a
traffic load, orientation and distribution, as well as an
period
CLR = Lost Cells / Total Cells Transmitted
Discussion: CLR is a negotiated QoS parameter and acceptable
are network specific. The objective is to minimize CLR provided
end-system adapts the traffic to the changing ATM layer
characteristics. The CLR parameter is the value of CLR that
network agrees to offer as an objective over the lifetime of
connection. It is expressed as an order of magnitude, having a
of 10^-1 to 10^-15 and unspecified
CLR indicates the number of ATM cells lost in relation to the
number of cells sent. CLR is closely related to the number
corrupted AAL5 PDUs; however, there is not a direct
correlation between the number of cells lost and the number
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
originally transmitted by the source end in relation to the
number of cells properly transmitted associated with a given
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
desirable to be measured on an in-service circuit. CMR is
related to the number of corrupted AAL5 PDUs; however, there is not
direct numerical correlation between the number of mis-inserted
and the number of corrupted AAL5 PDUs. There are two cases
below
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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
the number of corrupted AAL5 PDUs
2. Multiple cells are mis-inserted into an AAL5. In this case,
is not a one-to-one correspondence between cell mis-insertion and
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
bandwidth allocation and the allocation for sustainable rate in
per second
Discussion: This measures the amount of provisioned bandwidth
is not utilized. This lack of utilization may be caused
encapsulation overhead, e.g., AAL5 trailer and padding, or by
protocol itself, e.g., TCP usually transmits in only one direction
Measurement units: Cells per
2.2.2.6. CRC Error
Definition: The ratio of PDUs received at an endpoint that
contain an invalid CRC in relation to the total number of
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
will appear as cell loss at the ATM layer, this measurement can
made in-service using a test probe which measures CRC errors at
TC layer
Measurement Units:
2.2.2.7. Cell Transfer Delay (CTD
Definition: The elapsed time between a cell exit event at
measurement point 1 (e.g., at the source UNI) and the
cell entry event at a measurement point 2 (e.g., the destination UNI
for a particular connection
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Discussion: The cell transfer delay between two measurement points
the sum of the total inter-ATM node transmission delay and the
ATM node processing delay. While this number is a constant
should not adversely effect performance, it is a component in RTT
Measurement units:
2.2.3. ATM Adaptation Layer (AAL) Type 5 (AAL5)
2.2.3.1. AAL5 Re-assembly
Definition: AAL5 Re-assembly Errors constitute any error,
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
2.2.3.2. AAL5 Reassembly
Definition: AAL5 Reassembly Time constitutes the time between
arrival of the final cell in the AAL5 PDU and the AAL5 PDUs
being made available to the service layer
Discussion: AAL5 Reassembly time directly effects TCP round trip
calculations
Measurement Units:
2.2.3.3. AAL5 CRC Error
Definition: The ratio of PDUs received at an endpoint that
contain an invalid CRC in relation to the total number of
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.
discussion under AAL5 re-assembly errors
Measurement Units:
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2.2.4. ATM Service:
2.2.4.1. CAC Denial
Definition: The amount of time required for CAC to determine that
call must be rejected
Discussion: In the case where Call Proceeding is implemented,
number will be less than 4 seconds. Otherwise, it will be less
10 seconds. Large values of this measurement will adversely
performance on systems where an alternate, non-NBMA, service
available
Measurement Units:
2.2.4.2. Connection Establishment
Definition: The amount of time between the first Setup message
the calling party and the Connect message to the calling party
Discussion: See discussion under SVC
Measurement Units:
2.2.4.3. Connection Teardown
Definition: The amount of between the Release message being sent
the Release Complete message being received
Discussion: Large values of this measurement will adversely
performance in systems where the total number of open calls or VCs
limited. Specifically, a new VC cannot be instantiated with the
VPI/VCI before the old one is released
Measurement Units:
2.2.4.4. Crankback
Definition: The amount of time between the issuance of the
release or release complete message by the switch where the
Designated Transit List (DTL) is blocked and the receipt of the
with the updated DTLs by the target switch
Discussion: This measurement does not take into account the amount
time associated with either the successful portion of the call
transit or the time required for the calling party to receive .bp
response from the called party. As a result, the call may still
to complete if the call setup timer on the calling party expires
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See discussion under SVC
Measurement Units:
2.2.4.5. Route Update Response
Definition: The amount of time between the receipt of a PNNI
State Element (PTSE), which is the PNNI routing PDU, containing
topology different from the current topology and the point at
the switch begins to generate DTLs reflecting the routing change
Discussion: This measurement provides a lower bound on the amount
time during which SETUP messages will be forwarded along a sub
optimal or blocked path
Measurement Units:
2.2.5. ATM Service:
2.2.5.1. MIB Alignment
Definition: The amount of time between the issuance of the final
start message and the final get response associated with the
of static MIB information
Discussion: This measurement reflects the amount of time required
the switch and end system to exchange all information required
characterize and align the capabilities of both systems. It does
include address registration. It should also be noted that
measurement will depend on the number of MIB elements implemented
both systems
Measurement Units:
2.2.5.2. Address Registration
Definition: The amount of time between the initial set request
by the switch and the final get response issued by the switch
Discussion: This measurement assumes that the switch has checked
network prefix status object and the end system has checked the
address status object. In the case where the end system checks
ATM address status object only after the switch has issued a
request of the network prefix status object, this measurement
not reflect the actual time required to complete the
registration
Measurement Units:
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3. Security
As this document is solely for providing terminology and
neither a protocol nor an implementation, there are no
considerations associated with this document
4.
The IETF takes no position regarding the validity or scope of
intellectual property or other rights that might be claimed
pertain to the implementation or use of the technology described
this document or the extent to which any license under such
might or might not be available; neither does it represent that
has made any effort to identify any such rights. Information on
IETFs procedures with respect to rights in standards-track
standards-related documentation can be found in BCP-11. Copies
claims of rights made available for publication and any assurances
licenses to be made available, or the result of an attempt made
obtain a general license or permission for the use of
proprietary rights by implementors or users of this specification
be obtained from the IETF Secretariat
The IETF invites any interested party to bring to its attention
copyrights, patents or patent applications, or other
rights which may cover technology that may be required to
this standard. Please address the information to the IETF
Director
5.
[AF-ILMI4.0] ATM Forum Integrated Local Management
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
4.0, af-tm-0056.00, April 1996.
[AF-TM4.1] ATM Forum, Traffic Management Specification
4.1 (final ballot), btd-tm-01.02, July 1998.
[AF-UNI3.1] ATM Forum, User Network Interface
Version 3.1, September 1994.
[AF-UNI4.0] ATM Forum, User Network Interface
Version 4.0, July 1996.
Dunn & Martin Informational [Page 30]
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[I.321] ITU-T, B-ISDN protocol reference model and
application, April 1991.
[I.363] ITU-T, B-ISDN ATM Adaptation Layer
series, 1996-1997.
[I.363.5] ITU-T, B-ISDN ATM Adaptation Layer Specification:
5 AAL, August 1996.
6. Editors'
Jeffrey
Advanced Network Consultants, Inc
4214 Crest
Ellicott City, MD 21043
Phone: +1 (410) 750-1700
EMail: Jeffrey.Dunn@worldnet.att.
Cynthia
Advanced Network Consultants, Inc
11241-B Skilift
Columbia, MD 21044
Phone: +1 (410) 730-6300
EMail: Cynthia.E.Martin@worldnet.att.
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7. Full Copyright
Copyright (C) The Internet Society (2000). All Rights Reserved
This document and translations of it may be copied and furnished
others, and derivative works that comment on or otherwise explain
or assist in its implementation may be prepared, copied,
and distributed, in whole or in part, without restriction of
kind, provided that the above copyright notice and this paragraph
included on all such copies and derivative works. However,
document itself may not be modified in any way, such as by
the copyright notice or references to the Internet Society or
Internet organizations, except as needed for the purpose
developing Internet 