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Keywords: switching, devices, signaling
Network Working Group J. Dunn
Request for Comments: 3133 C. Martin
Category: Informational ANC, Inc.
June 2001
Terminology for Frame Relay Benchmarking
Status of this Memo
This memo provides information for the Internet community. It does
not specify an Internet standard of any kind. Distribution of this
memo is unlimited.
Copyright Notice
Copyright (C) The Internet Society (2001). All Rights Reserved.
Abstract
This memo discusses and defines terms associated with performance
benchmarking tests and the results of these tests in the context of
frame relay switching devices.
I. Background
1. Introduction
This document provides terminology for Frame Relay switching devices.
It extends terminology already defined for benchmarking network
interconnect devices in RFCs 1242, 1944 and 2285. Although some of
the definitions in this memo may be applicable to a broader group of
network interconnect devices, the primary focus of the terminology in
this memo is on Frame Relay Signaling.
This memo contains two major sections: Background and Definitions.
The background section provides the reader with an overview of the
technology and IETF formalisms. The definitions section is split
into two sub-sections. The formal definitions sub-section is
provided as a courtesy to the reader. The measurement definitions
sub-section contains performance metrics with inherent units.
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.
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For the purposes of computing several of the metrics, certain textual
conventions are required. Specifically:
1) The notation sum {i=1 to N} A_i denotes: the summation of N
instances of the observable A. For example, the set of observations
{1,2,3,4,5} would yield the result 15.
2) The notation max {I=1 to N} A_i and min {I=1 to N} A_i denotes:
the maximum or minimum of the observable A over N instances. For
example, given the set of observations {1,2,3,4,5}, max {i=1 to 5} =
5 and min {I=1 to 5} = 1.
The terms defined in this memo will be used in addition to terms
defined in RFCs 1242, 1944 and 2285. This memo is a product of the
Benchmarking Methodology Working Group (BMWG) of the Internet
Engineering Task Force(IETF).
2. Existing Definitions
RFC 1242, "Benchmarking Terminology for Network Interconnect
Devices", should be consulted before attempting to make use of this
document. RFC 1944, "Benchmarking Methodology for Network
Interconnect Devices", contains discussions of a number of terms
relevant to the benchmarking of switching devices and should also be
consulted. RFC 2285, "Benchmarking Terminology for LAN Switching
Devices", contains a number of terms pertaining to traffic
distributions and datagram interarrival. For the sake of clarity and
continuity this RFC adopts the template for definitions set out in
Section 2 of RFC 1242.
II. Definitions
The definitions presented in this section have been divided into two
groups. The first group is formal definitions, which are required in
the definitions of the performance metrics but are not themselves
strictly metrics. These definitions are subsumed from other work
done in other working groups both inside and outside the IETF. They
are provided as a courtesy to the reader.
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1. Formal Definitions
1.1. Definition Format (from RFC1242)
Term to be defined.
Definition: The specific definition for the term.
Discussion: A brief discussion of the term, its application and any
restrictions on measurement procedures.
Specification: The working group and document in which the term is
specified. Listed in the references.
1.2. Frame Relay Related Definitions
1.2.1. Access Channel
Definition: Access channel refers to the user access channel across
which frame relay data travels. Within a given DS-3, T1 or E1
physical line, a channel can be one of the following, depending of
how the line is configured. Possible line configurations are:
A. Unchannelized: The entire DS-3/T1/E1 line is considered a channel,
where:
The DS-3 line operates at speeds of 45 Mbps and is a single channel.
The T1 line operates at speeds of 1.536 Mbps and is a single channel
consisting of 24 T1 time slots. The E1 line operates at speeds of
1.984 Mbps and is a single channel consisting of 30 DS0 time slots.
B. Channelized: The channel is any one of N time slots within a given
line, where:
The T1 line consists of any one or more channels. Each channel is
any one of 24 time slots. The T1 line operates at speeds in
multiples of 56/64 Kbps to 1.536 Mbps, with aggregate speed not
exceeding 1.536 Mbps. The E1 line consists of one or more channels.
Each channel is any one of 31 time slots. The E1 line operates at
speeds in multiples of 64 Kbps to 1.984 Mbps, with aggregate speed
not exceeding 1.984 Mbps.
C. Fractional: The T1/E1 channel is one of the following groupings of
consecutively or non-consecutively assigned time slots:
N DS0 time slots (NX56/64Kbps where N = 1 to 24 DS0 time slots per
FT1 channel).
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N E1 time slots (NX64Kbps, where N = 1 to 30 DS0 time slots per E1
channel).
Discussion: Access channels specify the physical layer interface
speed of a DTE or DCE. In the case of a DTE, this may not correspond
to either the CIR or EIR. Specifically, based on the service level
agreement in place, the user may not be able to access the entire
bandwidth of the access channel.
Specification: FRF
1.2.2. Access Rate (AR)
Definition: The data rate of the user access channel. The speed of
the access channel determines how rapidly (maximum rate) the end user
can inject data into a frame relay network.
Discussion: See Access Channel.
Specification: FRF
1.2.3. Backward Explicit Congestion Notification (BECN)
Definition: BECN is a bit in the frame relay header. The bit is set
by a congested network node in any frame that is traveling in the
reverse direction of the congestion.
Discussion: When a DTE receives frames with the BECN bit asserted, it
should begin congestion avoidance procedures. Since the BECN frames
are traveling in the opposite direction as the congested traffic, the
DTE will be the sender. The frame relay layer may communicate the
possibility of congestion to higher layers, which have inherent
congestion avoidance procedures, such as TCP. See Frame Relay Frame.
Specification: FRF
1.2.4. Burst Excess(Be)
Definition: The maximum amount of uncommitted data (in bits) in
excess of Committed Burst Size (Bc) that a frame relay network can
attempt to deliver during a Committed Rate Measurement Interval (Tc).
This data (Be) generally is delivered with a lower probability than
Bc. The network treats Be data as discard eligible.
Discussion: See also Committed burst Size (Bc), Committed Rate
Measurement Interval (Tc) and Discard Eligible (De).
Specification: FRF
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1.2.5. Committed Burst Size (Bc)
Definition: The maximum amount of data (in bits) that the network
agrees to transfer, under normal conditions, during a time interval
Tc.
Discussion: See also Excess Burst Size (Be) and Committed Rate
Measurement Interval (Tc).
Specification: FRF
1.2.6. Committed Information Rate (CIR)
Definition: CIR is the transport speed the frame relay network will
maintain between service locations when data is presented.
Discussion: CIR specifies the guaranteed data rate between two frame
relay terminal connected by a frame relay network. Data presented to
the network in excess of this data rate and below the Excess
Information Rate (EIR) will be marked as Discard Eligible and may be
dropped.
Specification: FRF
1.2.7. Committed Rate Measurement Interval (Tc)
Definition: The time interval during which the user can send only
Bc-committed amount of data and Be excess amount of data. In
general, the duration of Tc is proportional to the "burstiness" of
the traffic. Tc is computed (from the subscription parameters of CIR
and Bc) as Tc = Bc/CIR. Tc is not a periodic time interval.
Instead, it is used only to measure incoming data, during which it
acts like a sliding window. Incoming data triggers the Tc interval,
which continues until it completes its computed duration.
Discussion: See also Committed Information Rate (CIR) and committed
Burst Size (Bc).
Specification: FRF
1.2.8. Cyclic Redundancy Check (CRC)
Definition: A computational means to ensure the accuracy of frames
transmitted between devices in a frame relay network. The
mathematical function is computed, before the frame is transmitted,
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at the originating device. Its numerical value is computed based on
the content of the frame. This value is compared with a recomputed
value of the function at the destination device. See also Frame
Check Sequence (FCS).
Discussion: CRC is not a measurement, but it is possible to measure
the amount of time to perform a CRC on a string of bits. This
measurement will not be addressed in this document.
Specification: FRF
1.2.9. Data Communications Equipment (DCE)
Definition: Term defined by both frame relay and X.25 committees,
that applies to switching equipment and is distinguished from the
devices that attach to the network (DTE).
Discussion: Also see DTE.
Specification: FRF
1.2.10. Data Link Connection Identifier (DLCI)
Definition: A unique number assigned to a PVC end point in a frame
relay network. Identifies a particular PVC endpoint within a user's
access channel in a frame relay network and has local significance
only to that channel.
Discussion: None.
Specification: FRF
1.2.11. Data Terminal Equipment (DTE)
Definition: Any network equipment terminating a network connection
and is attached to the network. This is distinguished from Data
Communications Equipment (DCE), which provides switching and
connectivity within the network.
Discussion: See also DCE.
Specification: FRF
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1.2.12. Discard Eligible (DE)
Definition: This is a bit in the frame relay header that provides a
two level priority indicator, used to bias discard frames in the
event of congestion toward lower priority frames. Similar to the CLP
bit in ATM.
Discussion: See Frame Relay Frame.
Specification: FRF
1.2.13. Discardable frames
Definition: Frames identified as being eligible to be dropped in the
event of congestion.
Discussion: The discard eligible field in the frame relay header is
the correct -- and by far the most common -- means of indicating
which frames may be dropped in the event of congestion. However, DE
is not the only means of identifying which frames may be dropped.
There are at least three other cases that apply.
In the first case, network devices may prioritize frame relay traffic
by non-DE means. For example, many service providers prioritize
traffic on a per-PVC basis. In this instance, any traffic from a
given DLCI (data link channel identifier) may be dropped during
congestion, regardless of whether DE is set.
In the second case, some implementations use upper-layer criteria,
such as IP addresses or TCP or UDP port numbers, to prioritize
traffic within a single PVC. In this instance, the network device
may evaluate discard eligibility based on upper-layer criteria rather
than the presence or absence of a DE bit.
In the third case, the frame is discarded because of an error in the
frame. Specifically, frames that are too long or too short, frames
that are not a multiple of 8 bits in length, frames with an invalid
or unrecognized DLCI, frames with an abort sequence, frames with
improper flag delimitation, and frames that fail FCS.
Specification: FRMIB
1.2.14. Discarded frames
Definition: Those frames dropped by a network device.
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Discussion: Discardable and discarded frames are not synonymous.
Some implementations may ignore DE bits or other criteria, even
though they supposedly use such criteria to determine which frames to
drop in the event of congestion.
In other cases, a frame with its DE bit set may not be dropped. One
example of this is in cases where congestion clears before the frame
can be evaluated.
Specification: DN
1.2.15. Forward Explicit Congestion Notification (FECN)
Definition: FECN is a bit in the frame relay header. The bit is set
by a congested network node in any frame that is traveling in the
same direction of the congestion.
Discussion: When a DTE receives frames with the FECN bit asserted, it
should begin congestion avoidance procedures. Since the FECN frames
are traveling in the same direction as the congested traffic, the DTE
will be the receiver. The frame relay layer may communicate the
possibility of congestion to higher layers, which have inherent
congestion avoidance procedures, such as TCP. See Frame Relay Frame.
Specification: FRF
1.2.16. Frame Check Sequence (FCS)
Definition: The standard 16-bit cyclic redundancy check used for HDLC
and frame relay frames. The FCS detects bit errors occurring in the
bits of the frame between the opening flag and the FCS, and is only
effective in detecting errors in frames no larger than 4096 octets.
See also Cyclic Redundancy Check (CRC).
Discussion: FCS is not a measurement, but it is possible to measure
the amount of time to perform a FCS on a string of bits. This
measurement will not be addressed in this document.
Specification: FRF
1.2.17. Frame Entry Event
Definition: Frame enters a network section or end system. The event
occurs when the last bit of the closing flag of the frame crosses the
boundary.
Discussion: None.
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Specification: FRF.13
1.2.18. Frame Exit Event
Definition: Frame exits a network section or end system. The event
occurs when the first bit of the address field of the frame crosses
the boundary.
Discussion: None.
Specification: FRF.13
1.2.19. Frame Relay
Definition: A high-performance interface for packet-switching
networks; considered more efficient that X.25. Frame relay
technology can handle "bursty" communications that have rapidly
changing bandwidth requirements.
Discussion: None.
Specification: FRF
1.2.20. Frame Relay Frame
Definition: A logical grouping of information sent as a link-layer
unit over a transmission medium. Frame relay frames consist of a
pair of flags, a header, a user data payload and a Frame Check
Sequence (FCS). Bit stuffing differentiates user data bytes from
flags. By default, the header is two octets, of which 10 bits are
the Data Link Connection Identifier (DLCI), 1 bit in each octet is
used for address extension (AE), and 1 bit each for Forward Explicit
Congestion Notification (FECN), Backward Explicit Congestion
Notification (BECN) Command/Response (C/R) and Discard Eligible (DE).
The EA bit is set to one in the final octet containing the DLCI. A
header may span 2, 3 or 4 octets.
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Bit 7 6 5 4 3 2 1 0
|---|---|---|---|---|---|---|---|
| FLAG |
|-------------------------------|
| Upper 6 bits of DLCI |C/R|AE |
|-------------------------------|
| DLCI |FE |BE |DE |AE |
| |CN |CN | | |
|-------------------------------|
| User Data up to |
| 1600 Octets |
|-------------------------------|
| First Octet of FCS |
|-------------------------------|
| Second Octet of FCS |
|-------------------------------|
| FLAG |
|-------------------------------|
Discussion: Frame Relay headers spanning 3 or 4 octets will not be
discussed in this document. Note, the measurements described later
in this document are based on 2 octet headers. If longer headers are
used, the metric values must take into account the associated
overhead. See BECN, DE, DLCI and FECN.
Specification: FRF
1.2.21. Excess Information Rate (EIR)
Definition: See Burst Excess.
Discussion: None.
Specification: FRF
1.2.22. Network Interworking (FRF.5)
Definition: FRF.5 defines a protocol mapping called Network
Interworking between
Frame Relay and Asynchronous Transfer Mode (ATM). Protocol mapping
occurs when the network performs conversions in such a way that
within a common layer service, the protocol information of one
protocol is extracted and mapped on protocol information of another
protocol. This means that each communication terminal supports
different protocols. The common layer service provided in this
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interworking scenario is defined by the functions, which are common
to the two protocols. Specifically, the ATM terminal must be
configured to interoperate with the Frame Relay network and vice
versa.
Discussion: None.
Specification: FRF.5
1.2.23. Port speed
Definition: See Access Rate
Discussion: None.
Specification: FRF
1.2.24. Service Interworking (FRF.8)
Definition: FRF.8 defines a protocol encapsulation called Service
Interworking. Protocol encapsulation occurs when the conversions in
the network or in the terminals are such that the protocols used to
provide one service make use of the layer service provided by another
protocol. This means that at the interworking point, the two
protocols are stacked. When encapsulation is performed by the
terminal, this scenario is also called interworking by port access.
Specifically, the ATM service user performs no Frame Relaying
specific functions, and Frame Relaying service user performs no ATM
service specific functions.
Discussion: None.
Specification: FRF.8
1.2.25. Service Availability Parameters
Definition: The service availability parameters report the
operational readiness of individual frame relay virtual connections.
Service availability is affected by service outages.
Discussion: Service availability parameters provide metrics for
assessment of frame relay network health and are used to monitor
compliance with service level agreements. See Services Outages.
Specification: FRF.13
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1.2.26. Service Outages
Definition: Any event that interrupts the transport of frame relay
traffic. Two types of outages are differentiated:
1) Fault outages: Outages resulting from faults in the network and
thus tracked by the service availability parameters, and
2) Excluded outages: Outages resulting from faults beyond the control
of the network as well as scheduled maintenance.
Discussion: Service availability can be defined on a per-VC basis
and/or on a per-port basis. Frame relay port-based service
availability parameters are not addressed in this document. See
Service Availability Parameters.
Specification: FRF.13
2. Performance Metrics
2.1. Definition Format (from RFC1242)
Metric to be defined.
Definition: The specific definition for the metric.
Discussion: A brief discussion of the metric, its application and
any restrictions on measurement procedures.
Measurement units: Intrinsic units used to quantify this metric.
This includes subsidiary units, e.g., microseconds are acceptable if
the intrinsic unit is seconds.
2.2. Definitions
2.2.1. Physical Layer-Plesiochronous Data Hierarchy (PDH)
2.2.1.1. Alarm Indication Signal (AIS)
Definition: An all 1's frame transmitted after the DTE or DCE detects
a defect for 2.5 s +/- 0.5 s.
Discussion: An AIS will cause loss of information in the PDH frame,
which contains a frame relay frame which may contain IP datagrams.
Measurement units: Dimensionless.
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2.2.1.2. Loss of Frame (LOF)
Definition: An NE transmits an LOF when an OOF condition persists.
Discussion: A LOF will cause loss of information in the PDH frame,
which contains a frame relay frame which may contain IP datagrams.
Measurement units: Dimensionless.
2.2.1.3. Loss of Signal (LOS)
Definition: Indicates that there are no transitions occurring in the
received signal.
Discussion: A LOS will cause loss of information in the PDH frame
which contains a frame relay frame which may contain IP datagrams.
Measurement units: Dimensionless.
2.2.1.4. Out of Frame (OOF)
Definition: An NE transmits an OOF downstream when it receives
framing errors in a specified number of consecutive frame bit
positions.
Discussion: An OOF will cause loss of information in the PDH frame
which contains a frame relay frame which may contain IP datagrams.
Measurement units: Dimensionless.
2.2.1.5. Remote Alarm Indication (RAI)
Definition: Previously called Yellow Alarm. Transmitted upstream by
an NE to indicate that it detected an LOS, LOF, or AIS.
Discussion: An RAI will cause loss of information in the transmitted
PDH frame, which may contain a frame relay frame, which, in turn, may
contain IP datagrams.
Measurement units: Dimensionless.
2.2.2. Frame Relay Layer
2.2.2.1. Data Delivery Ratio (DDR)
Definition: The DDR service level parameter reports the networks
effectiveness in transporting offered data (payload without address
field or FCS) in one direction of a single virtual connection. The
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DDR is a ratio of successful payload octets received to attempted
payload octets transmitted. Attempted payload octets transmitted are
referred to as DataOffered. Successfully delivered payload octets
are referred to as DataDelivered. These loads are further
differentiated as being within the committed information rate or as
burst excess.
Three data relay ratios may be reported:
Data Delivery Ratio (DDR):
(DataDelivered_c + DataDelivered_e DataDelivered_e+c
DDR = --------------------------------- = -----------------
(DataOffered_c + DataOffered_e) DataOffered_e+c
Data Delivery Ratio (DDR_c) for load consisting of frames within the
committed information rate:
DataDelivered_c
DDR_c = -------------
DataOffered_c
Data Delivery Ratio (DDR_e) for load in excess of the committed
information rate:
DataDelivered_e
DDR_e = ---------------
DataOffered_e
where
DataDelivered_c: Successfully delivered data payload octets within
committed information rate,
DataDelivered_e: Successfully delivered data payload octets in excess
of CIR,
DataDelivereD_e+c: Successfully delivered total data payload octets,
including those within committed information rate and those in excess
of CIR,
DataOffered_c: Attempted data payload octet transmissions within
committed information rate,
DataOffered_e: Attempted data payload octet transmissions in excess
of CIR
and
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DataOffered_e+c: Attempted total data payload octet transmissions,
including those within committed information rate and those in excess
of CIR
Each direction of a full duplex connection has a discrete set of data
delivery ratios.
Discussion: Data delivery ratio measurements may not be
representative of data delivery effectiveness for a given
application. For example, the discarding of a small frame containing
an acknowledgement message may result in the retransmission of a
large number of data frames. In such an event, a good data delivery
ratio would be reported while the user experienced poor performance.
Measurement units: dimensionless.
2.2.2.2. Frame Delivery Ratio (FDR)
Definition: The FDR service level parameter reports the networks
effectiveness in transporting an offered frame relay load in one
direction of a single virtual connection. The FDR is a ratio of
successful frame receptions to attempted frame transmissions.
Attempted frame transmissions are referred to as Frames Offered.
Successfully delivered frames are referred to as Frames Delivered.
These loads may be further differentiated as being within the
committed information rate or as burst excess.
Frame Delivery Ratio (FDR):
Frame Delivery Ratio (FDR):
(FramesDelivered_c + FramesDelivered_e) FramesDelivered_e+c
FDR = ------------------------------------- = -------------------
(FramesOffered_c + FramesOffered_e) FramesOffered_e+c
Frame Delivery Ratio (FDR_c) for load consisting of frames within the
committed information rate:
FramesDelivered_c
FDR_c = -----------------
FramesOffered_c
Frame Delivery Ratio (FDR_c) for load in excess of the committed
information rate:
FramesDelivered_e
FDR_e = -----------------
FramesOffered_e
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where
FramesDelivered_c: Successfully delivered frames within committed
information rate,
FramesDelivered_e: Successfully delivered frames in excess of CIR,
FramesDelivered_e+c: Successfully delivered total frames, including
those within committed information rate and those in excess of CIR,
FramesOffered_c: Attempted frame transmissions within committed
information rate,
FramesOffered_e: Attempted frame transmissions in excess of CIR
and
FramesOffered_e+c: Attempted total frame transmissions, including
those within committed information rate and those in excess of CIR.
An independent set of frame delivery ratios exists for each direction
of a full duplex connection.
Discussion: Frame delivery ratio measurements may not be
representative of frame delivery effectiveness for a given
application. For example, the discarding of a small frame containing
an acknowledgement message may result in the retransmission of a
large number of data frames. In such an event, a good data delivery
ratio would be reported while the user
Measurement units: dimensionless.
2.2.2.3. Frame Discard Ratio (FDR)
Definition: The number of received frames that are discarded because
of a frame error divided by the total number of transmitted frames in
one direction of a single virtual connection. Frame errors are
defined as follows:
1) frames that are too long or too short,
2) frames that are not a multiple of 8 bits in length,
3) frames with an invalid or unrecognized DLCI,
4) frames with an abort sequence,
5) frames with improper flag delimitation,
6) frames that fail FCS.
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The formal definition of frame discard ratio is as follows:
sum {i=1 to N} fr_i
FDR = -------------------
sum {i=1 to N} ft_i,
where
fr_i is the number of successfully delivered frames for a particular
DLCI at second i
and
ft_i is the total number of attempted frame transmissions within the
committed plus extended information rate for a particular DLCI at
second i.
Discussion: Frame discards can adversely effect applications running
on IP over FR. In general, frame discards will negatively impact TCP
throughput; however, in the case of frame discard due to frame error,
frame discard will improve performance by dropping errored frames.
As a result, these frames will not adversely effect the forwarding of
retransmitted frames
Measurement units: dimensionless.
2.2.2.4. Frame Error Ratio (FER)
Definition: The number of received frames that contain an error in
the frame payload divided by the total number of transmitted frames
in one direction of a single virtual connection.
The formal definition of frame error ratio is as follows:
sum {i=1 to N} fe_i
FER = -------------------
sum {i=1 to N} ft_i,
where
fe_i is the number of frames containing a payload error for a
particular DLCI at second i
and
ft_i is the total number of attempted frame transmissions within the
committed plus the extended information rate for a particular DLCI at
second i. This statistic includes those frames which have an error
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in the Frame Check Sequence (FCS). Frame errors in the absence of
FCS errors can be detected by sending frames containing a known
pattern; however, this indicates an equipment defect.
Discussion: The delivery of frames containing errors will adversely
effect applications running on IP over FR. Typically, these errors
are caused by transmission errors and flagged as failed FCS frames;
however, when Frame Relay to ATM Network interworking is used, an
error may be injected in the frame payload which, in turn, is
encapsulated into an AAL5 PDU (see RFC 2761 for a discussion of AAL5
related metrics).
Measurement units: dimensionless.
2.2.2.5. Frame Excess Ratio (FXR)
Definition: The number of frames received by the network and treated
as excess traffic divided by the total number of transmitted frames
in one direction of a single virtual connection. Frames which are
sent to the network with DE set to zero are treated as excess when
more than Bc bits are submitted to the network during the Committed
Information Rate Measurement Interval (Tc). Excess traffic may or
may not be discarded at the ingress if more than Bc + Be bits are
submitted to the network during Tc. Traffic discarded at the ingress
is not recorded in this measurement. Frames which are sent to the
network with DE set to one are also treated as excess traffic.
The formal definition of frame excess ratio is as follows:
sum {i=1 to N} fc_i
FXR = 1 - -------------------
sum {i=1 to N} ft_i,
where
fc_i is the total number of frames which were submitted within the
traffic contract for a particular DLCI at second i
and
ft_i is the total number of attempted frame transmissions for a
particular DLCI at second i.
Discussion: Frame discards can adversely effect applications running
on IP over FR. Specifically, frame discards will negatively impact
TCP throughput.
Measurement units: dimensionless.
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2.2.2.6. Frame Loss Ratio (FLR)
Definition: The FLR is a ratio of successful frame receptions to
attempted frame transmissions at the committed information rate, in
one direction of a single virtual connection. Attempted frame
transmissions are referred to as Frames Offered. Successfully
delivered frames are referred to as Frames Delivered.
The formal definition of frame loss ratio is as follows:
FramesDelivered_c
FLR = 1- -----------------
FramesOffered_c,
where
FramesDelivered_c is the successfully delivered frames within
committed information rate for a given DLCI
and
FramesOffered_c is the attempted frame transmissions within committed
information rate for a given DLCI
An independent set of frame delivery ratios exists for each direction
of a full duplex connection.
Discussion: Frame delivery loss measurements may not be
representative of frame delivery effectiveness for a given
application. For example, the loss of a small frame containing an
acknowledgement message may result in the retransmission of a large
number of data frames. In such an event, a good data delivery ratio
would be reported while the user
Measurement units: dimensionless.
2.2.2.7. Frame Policing Ratio (FPR)
Definition: The number of frames received by the network and treated
as excess traffic and dropped divided by the total number of received
frames, in one direction of a single virtual connection. Frames
which are sent to the network with DE set to zero are treated as
excess when more than Bc bits are submitted to the network during the
Committed Information Rate Measurement Interval (Tc). Excess traffic
may or may not be discarded at the ingress if more than Bc + Be bits
are submitted to the network during Tc. Traffic discarded at the
ingress is recorded in this measurement. Frames which are sent to
the network with DE set to one are also treated as excess traffic.
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The formal definition of frame excess ratio is as follows:
sum {i=1 to N} fr_i
FPR = 1- -------------------
sum {i=1 to N} ft_i,
where
fr_i is the successfully delivered frames for a particular DLCI at
second i
and
ft_i is the total number of attempted frame transmissions for a
particular DLCI
at second i.
Discussion: Frame discards can adversely effect applications running
on IP over FR. Specifically, frame discards will negatively impact
TCP throughput.
2.2.2.8. Frame Transfer Delay (FTD)
Definition: The time required to transport frame relay data from
measurement point 1 to measurement point 2. The frame transfer delay
is the difference in seconds between the time a frame exits
measurement point 1 and the time the same frame enters measurement
point 2, in one direction of a single virtual connection. The formal
definition of frame transfer delay is as follows:
FTD = 1/N * sum {i=1 to N} t2_i - t1_i,
where
t1_i is the time in seconds when the ith frame leaves measurement
point 1 (i.e., frame exit event),
t2 is the time in seconds when the ith frame arrives at measurement
point 2 (i.e., frame entry event)
and
N is the number of frames received during a measurement interval T.
FTD is computed for a specific DLCI and a specified integration
period of T seconds. The computation does not include frames which
are transmitted during the measurement period but not received.
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Discussion: While frame transfer delay is usually computed as an
average and, thus, can effect neither IP nor TCP performance,
applications such as voice over IP may be adversely effected by
excessive FTD.
Measurement units: seconds.
2.2.2.9. Frame Transfer Delay Variation (FTDV)
Definition: The variation in the time required to transport frame
relay data from measurement point 1 to measurement point 2. The
frame transfer delay variation is the difference in seconds between
maximum frame transfer delay and the minimum frame transfer delay, in
one direction of a single virtual connection. The formal definition
of frame transfer delay is as follows:
FTDV = max {i=1 to N} FTD_i - min {i=1 to N} FTD_i.
where
FTD and N are defined as above.
Discussion: Large values of FTDV can adversely effect TCP round trip
time calculation and, thus, TCP throughput.
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
Internet Engineering Task Force
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
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permission for the use of such proprietary rights by implementors
or users of this specification can be obtained from the IETF
Secretariat.
The IETF invites any interested party to bring to its attention
any copyrights, patents or patent applications, or other
proprietary rights, which may cover technology that may be
required to practice this standard. Please address the
information to the IETF Executive Director.
Frame Relay Forum
Copyright Frame Relay Forum 1998. All Rights Reserved.
References FRF, FRF.5, FRF.8 and FRF.13 and translations of them
may be copied and furnished to others, and works that comment on
or otherwise explain it or assist in their 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, these documents themselves may not be
modified in any way, such as by removing the copyright notice or
references to the Frame Relay Forum, except as needed for the
purpose of developing Frame Relay standards (in which case the
procedures for copyrights defined by the Frame Relay Forum must be
followed), or as required to translate it into languages other
than English.
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5. References
[DN] Private communication from David Newman, Network Test, Inc.
[FRF] Frame Relay Forum Glossary, http://www.frforum.com, 1999.
[FRF.5] Frame Relay Forum, Frame Relay/ATM PVC Network Interworking
Implementation Agreement, December 1994.
[FRF.8] Frame Relay Forum, Frame Relay/ATM PVC Service Interworking
Implementation Agreement, April 1995.
[FRF.13] Frame Relay Forum, Service Level Definitions Implementation
Agreement, August 1998.
[FRMIB] Rehbehn, K and D. Fowler, "Definitions of Managed Objects
for Frame Relay Service", RFC 2954, October 2000.
6. Editors' Addresses
Jeffrey Dunn
Advanced Network Consultants, Inc.
4214 Crest Place
Ellicott City, MD 21043 USA
Phone: +1 (410) 750-1700
EMail: Jeffrey.Dunn@worldnet.att.net
Cynthia Martin
Advanced Network Consultants, Inc.
4214 Crest Place
Ellicott City, MD 21043 USA
Phone: +1 (410) 750-1700
EMail: Cynthia.E.Martin@worldnet.att.net
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Full Copyright Statement
Copyright (C) The Internet Society (2001). 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
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"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
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Acknowledgement
Funding for the RFC Editor function is currently provided by the
Internet Society.
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