One document matched: draft-morton-ippm-registry-pdv-00.xml
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<rfc category="std" docName="draft-morton-ippm-registry-pdv-00"
ipr="trust200902">
<front>
<title abbrev="Round-trip Loss">A Registry Investigation for IPPM Packet
Delay Variation Metrics</title>
<author fullname="Al Morton" initials="A." surname="Morton">
<organization>AT&T Labs</organization>
<address>
<postal>
<street>200 Laurel Avenue South</street>
<city>Middletown,</city>
<region>NJ</region>
<code>07748</code>
<country>USA</country>
</postal>
<phone>+1 732 420 1571</phone>
<facsimile>+1 732 368 1192</facsimile>
<email>acmorton@att.com</email>
<uri>http://home.comcast.net/~acmacm/</uri>
</address>
</author>
<date day="26" month="August" year="2013"/>
<abstract>
<t>This memo investigates a scheme to organize registry entries,
primarily those defined in RFCs prepared in the IP Performance Metrics
(IPPM) Working Group of the IETF. Three aspects make IPPM metric
registration difficult: (1) Use of the Type-P notion to allow users to
specify their own packet types. (2) Use of Flexible input variables,
called Parameters in IPPM definitions, some which determine the quantity
measured and others which should not be specified until execution of the
measurement. (3) Allowing flexibility in choice of statistics to
summarize the results on a stream of measurement packets. Specifically,
this memo investigates registry entries that would follow from RFC 3393,
the specification IP Packet Delay Variation that allows for many
different forms of unique metrics, as a difficult and important test of
the registry structure.</t>
</abstract>
<note title="Requirements Language">
<t>The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in <xref
target="RFC2119">RFC 2119</xref>.</t>
<t/>
</note>
</front>
<middle>
<section title="Introduction">
<t>This memo investigates a scheme to organize registry entries,
primarily those defined in RFCs prepared in the IP Performance Metrics
(IPPM) Working Group of the IETF, according to their framework <xref
target="RFC2330"/>. Three aspects make IPPM metric registration
difficult: (1) Use of the Type-P notion to allow users to specify their
own packet types. (2) Use of Flexible input variables, called Parameters
in IPPM definitions, some which determine the quantity measured and
others which should not be specified until execution of the measurement.
(3) Allowing flexibility in choice of statistics to summarize the
results on a stream of measurement packets. Specifically, this memo
investigates registry entries that would follow from <xref
target="RFC3393"/>, the specification IP Packet Delay Variation that
allows for many different forms of unique metrics, as a difficult and
important test of the registry structure.</t>
<t>Although there are several standard templates for organizing
specifications of performance metrics (see <xref target="RFC2679"/> for
an example of the traditional IPPM template, based to large extent on
the Benchmarking Methodology Working Group's traditional template in
<xref target="RFC1242"/>, and <xref target="RFC6390"/> for a similar
template), none of these templates were intended to become the basis for
the columns of an IETF-wide registry of metrics. As we examine the
aspects of metric specifications which need to appear in the registry,
we will see that none of the existing metric templates fully satisfies
the needs of a registry.</t>
<t>The authors of [draft-bagnulo-ippm-new-registry] and
[draft-bagnulo-ippm-new-registry-independent] made important
contributions to this memo in the registry column structure, and the
problem of registry development in general. We also acknowledge input
from the authors of [draft-claise-ippm-perf-metric-registry], especially
the value of an Element ID and the need for naming conventions.</t>
</section>
<section title="Scope">
<t>This memo investigates the registry structure that best describes
IPPM delay variation metrics based on <xref target="RFC3393"/> using the
conventions of the IPPM framework <xref target="RFC2330"/>.</t>
<t>We find that the flexibility allowed in <xref target="RFC3393"/>
requires further specificity to have a metric worthy of registration,
and we refer to <xref target="RFC5481"/> for the needed definition
details.</t>
<t>In this memo, we attempt a combinatoric registry, where all factors
that can be reasonably specified ARE specified, and changing even one
factor would require a new registry entry (row). It is believed that
this exercise can also be instructive for a registry based on
independent factors, [draft-bagnulo-ippm-new-registry-independent] but
that topic is beyond the scope of this effort.</t>
</section>
<section title="List of Registry Columns">
<t>This section briefly describes the columns used by this draft, as
this is likely to be a topic for discussion and revision. Taken as a
whole, the entries in the columns give a registered instance of a metric
with sufficient specificity to promote comparable results across
independent implementations. In other words, a complete Metric
Description.</t>
<section title="Element ID">
<t>An integer having enough digits to uniquely identify each entry in
the Registry.</t>
</section>
<section title="Metric Name">
<t>A metric naming convention is TBD.</t>
<t>The current guidance from Section 13 of <xref target="RFC2330"/>,
where Type-P is a feature of all IPPM metric names, is:</t>
<t>"... we introduce the generic notion of a "packet of type P", where
in some contexts P will be explicitly defined (i.e., exactly what type
of packet we mean), partially defined (e.g., "with a payload of B
octets"), or left generic. Thus we may talk about generic
IP-type-P-connectivity or more specific IP-port-HTTP-connectivity.
Some metrics and methodologies may be fruitfully defined using generic
type P definitions which are then made specific when performing actual
measurements. Whenever a metric's value depends on the type of the
packets involved in the metric, the metric's name will include either
a specific type or a phrase such as "type-P". ..."</t>
<t>Registry entries are a context where Type-P must be defined.</t>
<t>IPPM Metric names have also included the typically included the
stream type, to distinguish between singleton and sample metrics (see
<xref target="RFC2330"/> for the definition of these terms).</t>
</section>
<section title="Run-time Parameters">
<t>Run-Time Parameters are input factors that must be determined,
configured into the measurement system, and reported with the results
for the context to be complete. However, the values of these
parameters is not specified in the Registry, rather these parameters
are listed as an aid to the measurement system implementor or user
(they must be left as variables, and supplied on execution).</t>
<t>Where metrics supply a list of Parameters as part of their
descriptive template, a sub-set of the Parameters will be designated
as Run-Time Parameters.</t>
</section>
<section title="Fixed Parameters">
<t>Fixed Parameters are input factors that must be determined and
embedded in the measurement system for use when needed. The values of
these parameters is specified in the Registry.</t>
<t>Where metrics supply a list of Parameters as part of their
descriptive template, a sub-set of the Parameters will be designated
as Fixed Parameters.</t>
<t>A Parameter which is Fixed for one Registry element may be
designated as a Run-time Parameter for another Registry element.</t>
</section>
<section title="Metric Definition">
<t>This entry provides references to relevant sections of the RFC(s)
defining the metric, as well as any supplemental information needed to
ensure an unambiguous definition for implementations.</t>
</section>
<section title="Metric Units (and Data Format?)">
<t>The results of a metric must be expressed using some standard
dimension or units of measure. This column provides the units (and if
possible, the data format, whose specification will simplify both
measurement implementation and collection/storage tasks).</t>
<t>When a sample of singletons is collected, this entry will include
the data format and units of measure for each measured value.</t>
</section>
<section title="Stream Type and Stream Parameters">
<t>Principally, two different streams are used in IPPM metrics,
Poisson distributed as described in <xref target="RFC2330"/> and
Periodic as described in <xref target="RFC3432"/>. Both Poisson and
Periodic have their own unique parameters, and the relevant set is
specified in as Fixed Parameters in this column.</t>
</section>
<section title="Method of Measurement">
<t>This entry provides references to relevant sections of the RFC(s)
describing the method of measurement, as well as any supplemental
information needed to ensure an unambiguous methods for
implementations.</t>
</section>
<section title="Output Statistic">
<t>For entries which involve a stream and many singleton measurements,
a statistic may be specified in this column to summarize the results
to a single value.</t>
</section>
<section title="Discussion/Remarks">
<t>Besides providing additional details which do not appear in other
columns, the Discussion/Remarks column allows for unforeseen issues to
be addressed by simply updating this Informational column.</t>
</section>
</section>
<section title="Registry Column Entries for PDV">
<t>This is a complete Metric Description for one Packet Delay Variation
(PDV) metric.</t>
<section title="Element ID">
<t>An integer with enough digits to uniquely identify the entry.</t>
</section>
<section title="Metric Name">
<t>A metric naming convention is TBD.</t>
<t>One possibility based on IPPM's framework is:</t>
<t>IP-UDP-One-way-pdv-95th-percentile-Poisson</t>
</section>
<section title="Run-time Parameters">
<t>Where metrics supply a list of Parameters as part of their
descriptive template, a sub-set of the Parameters will be designated
as Run-Time Parameters.</t>
<t><list style="symbols">
<t>Src, the IP address of a host</t>
<t>Dst, the IP address of a host</t>
<t>T, a time (start of test interval)</t>
<t>Tf, a time (end of test interval)</t>
<t>T1, the wire time of the first packet in a pair, measured at
MP(Src) as it leaves for Dst.</t>
<t>T2, the wire time of the second packet in a pair, measured at
MP(Src) as it leaves for Dst.</t>
<t>I(i),I(i+1), i >=0, pairs of times which mark the beginning
and ending of the intervals in which the packet stream from which
the measurement is taken occurs. Here, I(0) = T0 and assuming that
n is the largest index, I(n) = Tf.</t>
</list></t>
</section>
<section title="Fixed Parameters">
<t>Where metrics supply a list of Parameters as part of their
descriptive template, a sub-set of the Parameters will be designated
as Fixed Parameters.</t>
<t><list style="symbols">
<t>F, a selection function defining unambiguously the packets from
the stream selected for the metric. See section 4.2 of <xref
target="RFC5481"/> for the PDV form.</t>
<t>L, a packet length in bits. L = 200 bits.</t>
<t>Tmax, a maximum waiting time for packets to arrive at Dst, set
sufficiently long to disambiguate packets with long delays from
packets that are discarded (lost). Tmax = 3 seconds.</t>
<t>Type-P, as defined in <xref target="RFC2330"/>, which includes
any field that may affect a packet's treatment as it traverses the
network. The packets are IP/UDP, with DSCP = 0 (BE).</t>
</list></t>
</section>
<section title="Metric Definition">
<t>See sections 2.4 and 3.4 of <xref target="RFC3393"/>. Singleton
delay differences measured are referred to by the variable name
"ddT".</t>
</section>
<section title="Metric Units (and Data Format?)">
<t>See section 3.3 of <xref target="RFC3393"/> for singleton
elements.</t>
<t><xref target="RFC2330"/> recommends that when a time is given, it
will be expressed in UTC.</t>
<t>The timestamp format (for T, Tf, etc.) is the same as in <xref
target="RFC5905"/> (64 bits) and is as follows: the first 32 bits
represent the unsigned integer number of seconds elapsed since 0h on 1
January 1900; the next 32 bits represent the fractional part of a
second that has elapsed since then.</t>
<t>The result format for ddT is *similar to* the short format in <xref
target="RFC5905"/> (32 bits) and is as follows: the first 16 bits
represent the *signed* integer number of seconds; the next 16 bits
represent the fractional part of a second.</t>
</section>
<section title="Stream Type and Stream Parameters">
<t>Poisson distributed as described in <xref target="RFC2330"/>, with
the following Parameters.</t>
<t><list style="symbols">
<t>lambda, a rate in reciprocal seconds (for Poisson Streams).
lambda = 1 packet per second</t>
<t>Upper limit on Poisson distribution (values above this limit
will be clipped and set to the limit value). Upper limit = 30
seconds.</t>
</list></t>
</section>
<section title="Method of Measurement">
<t>See section 2.6 and 3.6 of <xref target="RFC3393"/> for singleton
elements.</t>
</section>
<section title="Output Statistic">
<t>See section 4.3 of <xref target="RFC3393"/> for details on the
percentile statistic. The percentile = 95.</t>
<t>Individual results (singletons) should be represented by the
following triple</t>
<t><list style="symbols">
<t>T1 and T2, times as described above</t>
<t>ddT as defined in section 2.4 of <xref target="RFC3393"/></t>
</list>if needed.</t>
</section>
<section title="Discussion/Remarks">
<t>Lost packets represent a challenge for delay variation metrics. See
section 4.1 of <xref target="RFC3393"/> and the delay variation
applicability statement<xref target="RFC5481"/> for extensive analysis
and comparison of PDV and IPDV.</t>
</section>
</section>
<section title="Registry Column Entries for IPDV">
<t>This is a complete Metric Description for one Inter-Packet Delay
Variation (IPDV) metric.</t>
<section title="Element ID">
<t>An integer with enough digits to uniquely identify the entry.</t>
</section>
<section title="Metric Name">
<t>A metric naming convention is TBD.</t>
<t>One possibility based on IPPM's framework is:</t>
<t>IP-UDP-One-way-ipdv-range-Periodic</t>
</section>
<section title="Run-time Parameters">
<t>Where metrics supply a list of Parameters as part of their
descriptive template, a sub-set of the Parameters will be designated
as Run-Time Parameters.</t>
<t><list style="symbols">
<t>Src, the IP address of a host</t>
<t>Dst, the IP address of a host</t>
<t>T, the beginning of a time interval where a periodic sample is
desired.</t>
<t>T0, a time that MUST be selected at random from the interval
[T, T+PdT] to start generating packets and taking measurements
(start of test interval)</t>
<t>Tf, a time, greater than T0, for stopping generation of packets
for a sample (Tf may be relative to T0 if desired).</t>
<t>T1, the wire time of the first packet in a pair, measured at
MP(Src) as it leaves for Dst.</t>
<t>T2, the wire time of the second packet in a pair, measured at
MP(Src) as it leaves for Dst.</t>
<t>I(i),I(i+1), i >=0, pairs of times which mark the beginning
and ending of the intervals in which the packet stream from which
the measurement is taken occurs. Here, I(0) = T0 and assuming that
n is the largest index, I(n) = Tf.</t>
</list></t>
</section>
<section title="Fixed Parameters">
<t>Where metrics supply a list of Parameters as part of their
descriptive template, a sub-set of the Parameters will be designated
as Fixed Parameters.</t>
<t><list style="symbols">
<t>F, a selection function defining unambiguously the packets from
the stream selected for the metric. See section 4.1 of <xref
target="RFC5481"/> for the IPDV form.</t>
<t>L, a packet length in bits. L = 200 bits.</t>
<t>Tmax, a maximum waiting time for packets to arrive at Dst, set
sufficiently long to disambiguate packets with long delays from
packets that are discarded (lost). Tmax = 3 seconds.</t>
<t>Type-P, as defined in <xref target="RFC2330"/>, which includes
any field that may affect a packet's treatment as it traverses the
network. The packets are IP/UDP, with DSCP = 0 (BE).</t>
</list></t>
</section>
<section title="Metric Definition">
<t>See section 3.4 of <xref target="RFC3393"/>.</t>
</section>
<section title="Metric Units (and Data Format?)">
<t>See section 3.3 of <xref target="RFC3393"/> for singleton
elements.</t>
<t><xref target="RFC2330"/> recommends that when a time is given, it
will be expressed in UTC.</t>
<t>The timestamp format (for T, Tf, etc.) is the same as in <xref
target="RFC5905"/> (64 bits) and is as follows: the first 32 bits
represent the unsigned integer number of seconds elapsed since 0h on 1
January 1900; the next 32 bits represent the fractional part of a
second that has elapsed since then.</t>
<t>The result format for ddT is *similar to* the short format in <xref
target="RFC5905"/> (32 bits) and is as follows: the first 16 bits
represent the *signed* integer number of seconds; the next 16 bits
represent the fractional part of a second (resolving 15
microseconds).</t>
</section>
<section title="Stream Type and Stream Parameters">
<t>Periodic distributed as described in <xref target="RFC3432"/>, with
the following Parameters.</t>
<t><list style="symbols">
<t>incT, the nominal duration of inter-packet interval, first bit
to first bit (for Periodic Streams). incT = 1 second (per
packet)</t>
<t>PdT, the duration of the interval for allowed sample start
times. T0 may be drawn from a uniform distribution, such as T0 = T
+ Unif(0,PdT), or other distribution for PdT.</t>
</list></t>
</section>
<section title="Method of Measurement">
<t>See section 2.6 and 3.6 of <xref target="RFC3393"/> for singleton
elements.</t>
</section>
<section title="Output Statistic">
<t>See sections 5.2 and 6.5 of <xref target="RFC5481"/> for details on
the range statistic, or max(ddT) - min(ddT). Note that min(ddT) will
almost always be a negative value.</t>
<t>Individual results (singletons) should be represented by the
following triple</t>
<t><list style="symbols">
<t>T1 and T2, times as described above</t>
<t>ddT as defined in section 2.4 of <xref target="RFC3393"/></t>
</list>if needed.</t>
</section>
<section title="Discussion/Remarks">
<t>Lost packets represent a challenge for delay variation metrics. See
section 4.1 of <xref target="RFC3393"/> and the delay variation
applicability statement<xref target="RFC5481"/> for extensive analysis
and comparison of PDV and IPDV.</t>
</section>
</section>
<section title="Security Considerations">
<t/>
<section title="Denial of Service Attacks">
<t>The metrics in this memo require a stream of packets sent from one
host (source) to another host (destination) through intervening
networks, and back. This method could be abused for denial of service
attacks directed at the destination and/or the intervening
network(s).</t>
<t>Administrators of source, destination, and the intervening
network(s) should establish bilateral or multi-lateral agreements
regarding the timing, size, and frequency of collection of sample
metrics. Use of this method in excess of the terms agreed between the
participants may be cause for immediate rejection or discard of
packets or other escalation procedures defined between the affected
parties.</t>
</section>
<section title="User Data Confidentiality">
<t>Active use of this method generates packets for a sample, rather
than taking samples based on user data, and does not threaten user
data confidentiality. </t>
</section>
<section title="Interference with the metrics">
<t>It may be possible to identify that a certain packet or stream of
packets is part of a sample. With that knowledge at the destination
and/or the intervening networks, it is possible to change the
processing of the packets (e.g. increasing or decreasing delay) in a
way that may distort the measured performance. It may also be possible
to generate additional packets that appear to be part of the sample
metric. These additional packets are likely to perturb the results of
the sample measurement.</t>
<t>Authentication or encryption techniques, such as digital
signatures, MAY be used where appropriate to guard against injected
traffic attacks. <xref target="RFC5357"/> includes both authentication
and encryption features.</t>
</section>
</section>
<section anchor="IANA" title="IANA Considerations">
<t>Metrics previously defined in IETF were registered in the IANA IPPM
METRICS REGISTRY, however this process was discontinued when the
registry structure was found to be inadequate, and the registry was
declared Obsolete <xref target="RFC6248"/>.</t>
<t>Although the metrics in this draft may be considered for some form of
registration in the future, no IANA Action is requested at this
time.</t>
</section>
<section title="Acknowledgements">
<t>The author thanks Brian Trammell for suggesting the term "Run-time
Parameters", which led to the distinction between run-time and fixed
parameters implemented in this memo.</t>
</section>
</middle>
<back>
<references title="Normative References">
<?rfc ?>
<?rfc include="reference.RFC.2119"?>
<?rfc include="reference.RFC.2330"?>
<?rfc include="reference.RFC.2679"?>
<?rfc include='reference.RFC.2680'?>
<?rfc include='reference.RFC.3393'?>
<?rfc include='reference.RFC.3432'?>
<?rfc include='reference.RFC.2681'?>
<?rfc include='reference.RFC.5905'?>
<?rfc include='reference.RFC.4737'?>
<?rfc include='reference.RFC.5357'?>
</references>
<references title="Informative References">
<?rfc include='reference.RFC.1242'?>
<?rfc include='reference.RFC.5481'?>
<?rfc include='reference.RFC.6248'?>
<?rfc include='reference.RFC.6390'?>
</references>
</back>
</rfc>
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