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Versions: 01 00 RFC 2761

Network Working Group                                      J. H. Dunn
INTERNET-DRAFT                                             C. E. Martin
Expires: February, 2000                                    ANC, Inc.

                                               August, 1999

                     Terminology for ATM Benchmarking
                     <draft-ietf-bmwg-atm-term-00.txt>

Status of this Memo

   This  document  is an Internet-Draft and is in full conformance with all
   provisions  of  Section  10  of  RFC2026.  Internet-Drafts  are  working
   documents  of the Internet Engineering Task Force (IETF), its areas, and
   its working groups.  Note that other groups may also distribute  working
   documents as Internet-Drafts.

   Internet-Drafts  are  draft  documents valid for a maximum of six months
   and may be updated, replaced, or obsoleted by  other  documents  at  any
   time.   It is inappropriate to use Internet-Drafts as reference material
   or to cite them other than as "work in progress."

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

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

Abstract

   This memo  discusses  and  defines  terms  associated  with  performance
   benchmarking  tests  and  the  results  of these tests in the context of
   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).


1. 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.




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

   The  BISDN  model  comprises  four layers and two planes.  This document
   addresses the interactions between these layers and how they  effect  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.

2. 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



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   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 reference.  The  key  words
   "MUST",  "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD
   NOT", "RECOMMENDED", "MAY", and "OPTIONAL" go in this document are to be
   interpreted as described in RFC 2119.

II. Definitions

   The  definitions  presented  in  this section have been divided into two
   groups.  The first group is formal definitions, which  are  required  in
   the  definitions  of  the  performance  metrics  but  are not themselves
   strictly metrics.  These definitions are subsumed from other  work  done
   in  other  working  groups  both  inside and outside the IETF.  They are
   provided as a courtesy to the reader.

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  emulation,  voice over ATM AAL2: used for sub-rated voice over ATM
AAL3/4: used for data over noisy ATM lines AAL5: used for  data  over  ATM,
most widely used AAL type




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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
SAR)




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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.

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



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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

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



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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

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)




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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).

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



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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

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



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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  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, 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



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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

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




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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

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.




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Specification: AF-UNI3.1

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

1.2.36. Permanent Virtual Path Connection: (PVPC)



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

Discussion: none.

Specification: AF-UNI3.1

1.2.37. 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 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,



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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.

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



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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

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



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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  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)




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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.

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




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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.

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



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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

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)




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Metric to be defined.

Definition: The specific definition for the metric.

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

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

2.2. Definitions

2.2.1. Physical Layer- SONET

2.2.1.1. Pointer Movements

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

Discussion: SONET Pointer Movements can cause loss of  information  in  the
SONET payload envelop (SPE) which contains IP datagrams, either in the form
of 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




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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.

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.



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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.

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.



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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.

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



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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

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.




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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  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.  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



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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

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



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   standard.    Please  address  the  information  to  the  IETF  Executive
   Director.

5. Disclaimer

   Copyright (C) The Internet Society (1999). 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.

6. 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.



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   [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.


7. Editors Addresses

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

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






























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