Network Working Group J. Alvarez-Hamelin
Internet-Draft Universidad de Buenos Aires
Updates: 2330 (if approved) A. Morton
Intended status: Standards Track AT&T Labs
Expires: September 10, 2019 J. Fabini
TU Wien
C. Pignataro
Cisco Systems, Inc.
R. Geib
Deutsche Telekom
March 9, 2019
Advanced Unidirectional Route Assessment (AURA)
draft-ietf-ippm-route-04
Abstract
This memo introduces an advanced unidirectional route assessment
(AURA) metric and associated measurement methodology, based on the IP
Performance Metrics (IPPM) Framework RFC 2330. This memo updates RFC
2330 in the areas of path-related terminology and path description,
primarily to include the possibility of parallel subpaths between a
given Source and Destination pair, owing to the presence of multi-
path technologies.
Requirements Language
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
"OPTIONAL" in this document are to be interpreted as described in BCP
14[RFC2119] [RFC8174] when, and only when, they appear in all
capitals, as shown here.
Status of This Memo
This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF). Note that other groups may also distribute
working documents as Internet-Drafts. The list of current Internet-
Drafts is at https://datatracker.ietf.org/drafts/current/.
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."
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This Internet-Draft will expire on September 10, 2019.
Copyright Notice
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document authors. All rights reserved.
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described in the Simplified BSD License.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3
1.1. Issues with Earlier Work to define Route . . . . . . . . 3
2. Scope . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4
3. Route Metric Terms and Definitions . . . . . . . . . . . . . 5
3.1. Formal Name . . . . . . . . . . . . . . . . . . . . . . . 6
3.2. Parameters . . . . . . . . . . . . . . . . . . . . . . . 6
3.3. Metric Definitions . . . . . . . . . . . . . . . . . . . 7
3.4. Related Round-Trip Delay and Loss Definitions . . . . . . 9
3.5. Discussion . . . . . . . . . . . . . . . . . . . . . . . 9
3.6. Reporting the Metric . . . . . . . . . . . . . . . . . . 10
4. Route Assessment Methodologies . . . . . . . . . . . . . . . 10
4.1. Active Methodologies . . . . . . . . . . . . . . . . . . 10
4.1.1. Temporal Composition for Route Metrics . . . . . . . 12
4.1.2. Routing Class C Identification . . . . . . . . . . . 13
4.1.3. Intermediate Observation Point Route Measurement . . 14
4.2. Hybrid Methodologies . . . . . . . . . . . . . . . . . . 15
4.3. Combining Different Methods . . . . . . . . . . . . . . . 15
5. Background on Round-Trip Delay Measurement Goals . . . . . . 16
6. Tools to Measure Delays in the Internet . . . . . . . . . . . 17
7. RTD Measurements Statistics . . . . . . . . . . . . . . . . . 18
8. Conclusions . . . . . . . . . . . . . . . . . . . . . . . . . 20
9. Security Considerations . . . . . . . . . . . . . . . . . . . 20
10. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 20
11. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 20
12. Appendix I MPLS Methods for Route Assessment . . . . . . . . 21
13. References . . . . . . . . . . . . . . . . . . . . . . . . . 21
13.1. Normative References . . . . . . . . . . . . . . . . . . 22
13.2. Informative References . . . . . . . . . . . . . . . . . 24
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 26
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1. Introduction
The IETF IP Performance Metrics (IPPM) working group first created a
framework for metric development in [RFC2330]. This framework has
stood the test of time and enabled development of many fundamental
metrics. It has been updated in the area of metric composition
[RFC5835], and in several areas related to active stream measurement
of modern networks with reactive properties [RFC7312].
The [RFC2330] framework motivated the development of "performance and
reliability metrics for paths through the Internet," and Section 5 of
[RFC2330] defines terms that support description of a path under
test. However, metrics for assessment of path components and related
performance aspects had not been attempted in IPPM when the [RFC2330]
framework was written.
This memo takes-up the route measurement challenge and specifies a
new route metric, two practical frameworks for methods of measurement
(using either active or hybrid active-passive methods [RFC7799]), and
round-trip delay and link information discovery using the results of
measurements. All route measurements are limited by the willingness
of hosts along the path to be discovered, to cooperate with the
methods used, or to recognize that the measurement operation is
taking place (such as when tunnels are present).
1.1. Issues with Earlier Work to define Route
Section 7 of [RFC2330] presented a simple example of a "route" metric
along with several other examples. The example is reproduced below
(where the reference is to Section 5 of [RFC2330]):
"route: The path, as defined in Section 5, from A to B at a given
time."
This example provides a starting point to develop a more complete
definition of route. Areas needing clarification include:
Time: In practice, the route will be assessed over a time interval,
because active path detection methods like [PT] rely on TTL limits
for their operation and cannot accomplish discovery of all hosts
using a single packet.
Type-P: The legacy route definition lacks the option to cater for
packet-dependent routing. In this memo, we assess the route for a
specific packet of Type-P, and reflect this in the metric
definition. The methods of measurement determine the specific
Type-P used.
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Parallel Paths: This a reality of Internet paths and a strength of
advanced route assessment methods, so the metric must acknowledge
this possibility. Use of Equal Cost Multi-Path (ECMP) and Unequal
Cost Multi-Path (UCMP) technologies are common sources of parallel
subpaths.
Cloud Subpath: May contain hosts that do not decrement TTL or Hop
Limit, but may have two or more exchange links connecting
"discoverable" hosts or routers. Parallel subpaths contained
within clouds cannot be discovered. The assessment methods only
discover hosts or routers on the path that decrement TTL or Hop
Count, or cooperate with interrogation protocols. The presence of
tunnels and nested tunnels further complicate assessment by hiding
hops.
Hop: Although the [RFC2330] definition was a link-host pair, only
hosts are discoverable or have the capability to cooperate with
interrogation protocols where link information may be exposed.
The refined definition of Route metrics begins in the sections that
follow.
2. Scope
The purpose of this memo is to add new route metrics and methods of
measurement to the existing set of IPPM metrics.
The scope is to define route metrics that can identify the path taken
by a packet or a flow traversing the Internet between two hosts.
Although primarily intended for hosts communicating on the Internet
with IP, the definitions and metrics are constructed to be applicable
to other network domains, if desired. The methods of measurement to
assess the path may not be able to discover all hosts comprising the
path, but such omissions are often deterministic and explainable
sources of error.
Also, to specify a framework for active methods of measurement which
use the techniques described in [PT] at a minimum, and a framework
for hybrid active-passive methods of measurement, such as the Hybrid
Type I method [RFC7799] described in
[I-D.ietf-ippm-ioam-data](intended only for single administrative
domains), which do not rely on ICMP and provide a protocol for
explicit interrogation of nodes on a path. Combinations of active
methods and hybrid active-passive methods are also in-scope.
Further, this memo provides additional analysis of the round-trip
delay measurements made possible by the methods, in an effort to
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discover more details about the path, such as the link technology in
use.
This memo updates Section 5 of [RFC2330] in the areas of path-related
terminology and path description, primarily to include the
possibility of parallel subpaths between a given Source and
Destination address pair (possibly resulting from Equal Cost Multi-
Path (ECMP) and Unequal Cost Multi-Path (UCMP) technologies).
There are several simple non-goals of this memo. There is no attempt
to assess the reverse path from any host on the path to the host
attempting the path measurement. The reverse path contribution to
delay will be that experienced by ICMP packets (in active methods),
and may be different from delays experienced by UDP or TCP packets.
Also, the round trip delay will include an unknown contribution of
processing time at the host that generates the ICMP response.
Therefore, the ICMP-based active methods are not supposed to yield
accurate, reproducible estimations of the round-trip delay that UDP
or TCP packets will experience.
3. Route Metric Terms and Definitions
This section sets requirements for the following components to
support the Route Metric:
Host Identity The unique address for hosts communicating within the
network domain. For hosts communicating on the Internet with IP,
it is the globally routable IP address(es) which the host uses
when communicating with other hosts under normal or error
conditions. The Host Identity revealed (and its connection to a
Host Name through reverse DNS) determines whether interfaces to
parallel links can be associated with a single host, or appear to
identify unique hosts.
Discoverable Host Hosts that convey their Host Identity according to
the requirements of their network domain, such as when error
conditions are detected by that host. For hosts communicating
with IP packets, compliance with Section 3.2.2.4 of [RFC1122] when
discarding a packet due to TTL or Hop Limit Exceeded condition,
MUST result in sending the corresponding Time Exceeded message
(containing a form of host identity) to the source. This
requirement is also consistent with section 5.3.1 of [RFC1812] for
routers.
Cooperating Host Hosts MUST respond to direct queries for their host
identity as part of a previously agreed and established
interrogation protocol. Hosts SHOULD also provide information
such as arrival/departure interface identification, arrival
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timestamp, and any relevant information about the host or specific
link which delivered the query to the host.
Hop A Hop MUST contain a Host Identity, and MAY contain arrival and/
or departure interface identification, round trip delay, and an
arrival timestamp.
3.1. Formal Name
Type-P-Route-Ensemble-Method-Variant, abbreviated as Route Ensemble.
Note that Type-P depends heavily on the chosen method and variant.
3.2. Parameters
This section lists the REQUIRED input factors to specify a Route
metric.
o Src, the address of a host (such as the globally routable IP
address).
o Dst, the address of a host (such as the globally routable IP
address).
o i, the limit on the number of Hops a specific packet may visit as
it traverses from the host at Src to the host at Dst (such as the
TTL or Hop Limit).
o MaxHops, the maximum value of i used, (i=1,2,3,...MaxHops).
o T0, a time (start of measurement interval)
o Tf, a time (end of measurement interval)
o T, the host time of a packet as measured at MP(Src), meaning
Measurement Point at the Source.
o Ta, the host time of a reply packet's *arrival* as measured at
MP(Src), assigned to packets that arrive within a "reasonable"
time (see parameter below).
o Tmax, a maximum waiting time for reply packets to return to the
source, set sufficiently long to disambiguate packets with long
delays from packets that are discarded (lost), such that the
distribution of round-trip delay is not truncated.
o F, the number of different flows simulated by the method and
variant.
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o flow, the stream of packets with the same n-tuple of designated
header fields that (when held constant) result in identical
treatment in a multi-path decision (such as the decision taken in
load balancing). Note: The IPv6 flow label MAY be included in the
flow definition when routers have complied with [RFC6438]
guidelines at the Tunnel End Points (TEP), and the source of the
measurement is a TEP.
o Type-P, the complete description of the packets for which this
assessment applies (including the flow-defining fields).
3.3. Metric Definitions
This section defines the REQUIRED measurement components of the Route
metrics (unless otherwise indicated):
M, the total number of packets sent between T0 and Tf.
N, the smallest value of i needed for a packet to be received at Dst
(sent between T0 and Tf).
Nmax, the largest value of i needed for a packet to be received at
Dst (sent between T0 and Tf). Nmax may be equal to N.
Next, define a *singleton* definition for a Hop on the path, with
sufficient indexes to identify all Hops identified in a measurement
interval.
A Hop, designated h(i,j), the IP address and/or identity of one of j
Discoverable Hosts (or Cooperating Hosts) that are i hops away from
the host with address = Src during the measurement interval, T0 to
Tf. As defined above, a Hop singleton measurement MUST contain a
Host Identity, hid(i,j), and MAY contain one or more of the following
attributes:
o a(i,j) Arrival Interface ID (e.g., when [RFC5837] is supported)
o d(i,j) Departure Interface ID (e.g., when [RFC5837] is supported)
o t(i,j) Arrival Timestamp (where t(i,j) is ideally supplied by the
hop, or approximated from the sending time of the packet that
revealed the hop)
o Measurements of Round Trip Delay (for each packet that reveals the
same Host Identity and attributes, but not timestamp of course,
see next section)
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Now that Host Identities and related information can be positioned
according to their distance from the host with address Src in hops,
we introduce two forms of Routes:
A Route Ensemble is defined as the combination of all routes
traversed by different flows from the host at Src address to the host
at Dst address. The route traversed by each flow (with addresses Src
and Dst, and other fields which constitute flow criteria) is a member
of the ensemble and called a Member Route.
Using h(i,j) and components and parameters, further define:
When considering the set of Hops in the context of a single flow, a
Member Route j is an ordered list {h(1,j), ... h(Nj, j)} where h(i-1,
j) and h(i, j) are by 1 hop away from each other and Nj satisfying
h(Nj,j)=Dst is the minimum count of hops needed by the packet on
Member Route j to reach Dst. Member Routes must be unique. The
uniqueness property requires that any two Member routes j and k that
are part of the same Route Ensemble differ either in terms of minimum
hop count Nj and Nk to reach the destination Dst, or, in the case of
identical hop count Nj=Nk, they have at least one distinct hop:
h(i,j) != h(i, k) for at least one i (i=1..Nj).
All the optional information collected to describe a Member Route,
such as the arrival interface, departure interface, and Round Trip
Delay at each Hop, turs each list item into a rich structure. There
may be information on the links between Hops, possibly information on
the routing (arrival int. to departure int.), an estimate of distance
between Hops based on Round Trip Delay measurements and calculations,
and a time stamp indicating when all the additional detail was valid.
The Route Ensemble from Src to Dst, during the measurement interval
T0 to Tf, is the aggregate of all m distinct Member Routes discovered
between the two hosts with Src and Dst addresses. More formally,
with the host having address Src omitted:
Route Ensemble = {
{h(1,1), h(2,1), h(3,1), ... h(N1,1)=Dst},
{h(1,2), h(2,2), h(3,2),..., h(N2,2)=Dst},
...
{h(1,m), h(2,m), h(3,m), ....h(Nm,m)=Dst}
}
where the following conditions apply: i <= Nj <= Nmax (j=1..m)
Note that some h(i,j) may be empty (null) in the case that systems do
not reply (not discoverable, or not cooperating).
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h(i-1,j) and h(i,j) are the Hops on the same Member Route one hop
away from each other.
Hop h(i,j) may be identical with h(k,l) for i!=k and j!=l ; which
means there may be portions shared among different Member Routes
(parts of various routes may overlap).
3.4. Related Round-Trip Delay and Loss Definitions
RTD(i,j,T) is defined as a singleton of the [RFC2681] Round-trip
Delay between the host with address = Src and the host at Hop h(i,j)
at time T.
RTL(i,j,T) is defined as a singleton of the [RFC6673] Round-trip Loss
between the host with address = Src and the host at Hop h(i,j) at
time T.
3.5. Discussion
Depending on the way that Host Identity is revealed, it may be
difficult to determine parallel subpaths between the same pair of
hosts (i.e. multiple parallel links). It is easier to detect
parallel subpaths involving different hosts.
o If a pair of discovered hosts identify two different addresses,
then they will appear to be different hosts.
o If a pair of discovered hosts identify two different IP addresses,
and the IP addresses resolve to the same host name (in the DNS),
then they will appear to be the same hosts.
o If a discovered host always replies using the same network
address, regardless of the interface a packet arrives on, then
multiple parallel links cannot be detected in that network domain.
o If parallel links between routers are aggregated below the IP
layer, In other words, all links share the same pair of IP
addresses, then the existence of these parallel links can't be
detected at IP layer. This applies to other network domains with
layers below them, as well.
@@@@ This paragraph on Temporal Composition moved to support a more
complete section on Methodology (section 4).
When a route assessment employs IP packets (for example), the reality
of flow assignment to parallel subpaths involves layers above IP.
Thus, the measured Route Ensemble is applicable to IP and higher
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layers (as described in the methodology's packet of Type-P and flow
parameters).
@@@@ The Temporal Measurement and Route Class C (unrelated to address
classes of the past) is now partly addressed in Section 4.
3.6. Reporting the Metric
@@@@ now partly addressed, based on feedback at IETF-101:
An Information Model and an XML Data Model for Storing Traceroute
Measurements is available in [RFC5388]. The measured information at
each hop includes four pieces of information: a one-dimensional hop
index, host symbolic address, host IP address, and RTD for each
response.
The description of Hop information that may be collected according to
this memo covers more dimensions, as defined in Section 3.3 above.
For example, the Hop index is two-dimensional to capture the
complexity of a Route Ensemble, and it contains corresponding host
identities at a minimum. The models need to be expanded to include
these features, as well as Arrival Interface ID, Departure Interface
ID, and Arrival Timestamp, when available.
@@@@ can we leave updates to RFC 5388 for further work? Or, do we
need to take-on this topic in an Appendix here?
4. Route Assessment Methodologies
There are two classes of methods described in this section, active
methods relying on the reaction to TTL or Hop Limit Exceeded
condition to discover hosts on a path, and Hybrid active-passive
methods that involve direct interrogation of cooperating hosts
(usually within a single domain). Description of these methods
follow.
@@@@ Editor's Note: We need to incorporate description of Type-P
packets (with the flow parameters) used in each method below (done
for Active).
4.1. Active Methodologies
We have chosen to describe the method based on that employed in
current open source tools, thereby providing a practical framework
for further advanced techniques to be included as method variants.
This method is applicable to use across multiple administrative
domains.
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Paris-traceroute [PT] provides some measure of protection from path
variation generated by ECMP load balancing, and it ensures traceroute
packets will follow the same path in 98% of cases according to
[SCAMPER]. If it is necessary to find every path possible between
two hosts, Paris-traceroute provides "exhaustive" mode while scamper
provides "tracelb" (stands for traceroute load balance).
The Type-P of packets used could be ICMP (as in the original
traceroute), UDP or TCP. The later are used when a particular
characteristic needs to be to verified, such as filtering or traffic
shaping on specific ports (i.e., services). [SCAMPER] supports IPv6
traceroute measurements, keeping the FlowLable constant in all
packets.
The advanced route assessment methods used in Paris-traceroute [PT]
keep the critical fields constant for every packet to maintain the
appearance of the same flow. Since route assessment can be conducted
using TCP, UDP or ICMP packets, this method REQUIRES the Diffserv
field, the protocol number, IP source and destination addresses, and
the port settings for TCP or UDP kept constant. For ICMP probes, the
method additionally REQUIRES keeping the type, code, and ICMP
checksum constant; which occupy the corresponding positions in the
header of an IP packet, e.g., bytes 20 to 23 when the header IP has
no options.
Maintaining a constant checksum in ICMP is most challenging because
the ICMP Sequence Number is part of the calculation. The advanced
traceroute method requires calculations using the IP Sequence Number
Field and the Identifier Field, yielding a constant ICMP checksum in
successive packets. For an example of calculations to maintain a
constant checksum, see Appendix A of [RFC7820], where revision of a
timestamp field is complemented by modifying the 2 octet checksum
complement field (these fields take the roles of the ICMP Sequence
Number and Identifier Fields, respectively).
For TCP and UDP packets, the checksum must also be kept constant.
Therefore, the first four bytes of UDP (or TCP) data field are
modified to compensate for fields that change from packet to packet.
@@@@ Note: other variants of advanced traceroute are planned be
described.
Finally, the return path is also important to check. Taking into
account that it is an ICMP time exceeded (during transit) packet, the
source and destination IP are constant for every reply. Then, we
should consider the fields in the first 32 bits of the protocol on
the top of IP: the type and code of ICMP packet, and its checksum.
Again, to maintain the ICMP checksum constant for the returning
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packets, we need to consider the whole ICMP message. It contains the
IP header of the discarded packet plus the first 8 bytes of the IP
payload; that is some of the fields of TCP header, the UDP header
plus four data bytes, the ICMP header plus four bytes. Therefore,
for UDP case the data field is used to maintain the ICMP checksum
constant in the returning packet. For the ICMP case, the identifier
and sequence fields of the sent ICMP probe are manipulated to be
constant. The TCP case presents no problem because its first eight
bytes will be the same for every packet probe.
Formally, to maintain the same flow in the measurements to a certain
hop, the Type-P-Route-Ensemble-Method-Variant packets should be[PT]:
o TCP case: Fields Src, Dst, port-Src, port_Dst, and Diffserv Field
should be the same.
o UDP case: Fields Src, Dst, port-Src, port-Dst, and Diffserv Field
should be the same, the UDP-checksum should change to maintain
constant the IP checksum of the ICMP time exceeded reply. Then,
the data length should be fixed, and the data field is used to
fixing it (consider that ICMP checksum uses its data field, which
contains the original IP header plus 8 bytes of UDP, where TTL, IP
identification, IP checksum, and UDP checksum changes).
o ICMP case: The Data field should compensate variations on TTL, IP
identification, and IP checksum for every packet.
Then, the way to identify different hops and attempts of the same
flow is:
o TCP case: The IP identification field.
o UDP case: The IP identification field.
o ICMP case: The IP identification field, and ICMP Sequence number.
4.1.1. Temporal Composition for Route Metrics
The Active Route Assessment Methods described above have the ability
to discover portions of a path where ECMP load balancing is present,
observed as two or more unique Member Routes having one or more
distinct Hops which are part of the Route Ensemble. Likewise,
attempts to deliberately vary the flow characteristics to discover
all Member Routes will reveal portions of the path which are flow-
invariant.
Section 9.2 of [RFC2330] describes Temporal Composition of metrics,
and introduces the possibility of a relationship between earlier
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measurement results and the results for measurement at the current
time (for a given metric). There is value in establishing a Temporal
Composition relationship for Route Metrics. However, this
relationship does not represent a forecast of future route conditions
in any way.
For Route Metric measurements, the value of Temporal Composition is
to reduce the measurement iterations required with repeated
measurements. Reduced iterations are possible by inferring that
current measurements using fixed and previously measured flow
characteristics:
o will have many common hops with previous measurements.
o will have relatively time-stable results at the ingress and egress
portions of the path when measured from user locations, as opposed
to measurements of backbone networks and across inter-domain
gateways.
o may have greater potential for time-variation in path portions
where ECMP load balancing is observed (because increasing or
decreasing the pool of links changes the hash calculations).
Optionally, measurement systems may take advantage of the inferences
above when seeking to reduce measurement iterations, after exhaustive
measurements indicate that the time-stable properties are present.
Repetitive Active Route measurement systems:
1. SHOULD occasionally check path portions which have exhibited
stable results over time, particularly ingress and egress
portions of the path.
2. SHOULD continue testing portions of the path that have previously
exhibited ECMP load balancing.
3. SHALL trigger re-assessment of the complete path and Route
Ensemble, if any change in hops is observed for a specific (and
previously tested) flow.
@@@@ Comments on this material are very welcome!
4.1.2. Routing Class C Identification
There is an opportunity to apply the [RFC2330] notion of equal
treatment for a class of packets, "...very useful to know if a given
Internet component treats equally a class C of different types of
packets", as it applies to Route measurements. Knowledge of "class
C" parameters (unrelated to address classes of the past) on a path
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potentially reduces the number of flows required for a given method
to assess a Route Ensemble over time.
First, recognize that each Member Route of a Route Ensemble will have
a corresponding Routing Class C. Class C can be discovered by
testing with multiple flows, all of which traverse the unique set of
hops that comprise a specific Member Route.
Second, recognize that the different Routing Classes depend primarily
on the hash functions used at each instance of ECMP load balancing on
the path.
Third, recognize the synergy with Temporal Composition methods
(described above) where evaluation intends to discover time-stable
portions of each Member Route so that more emphasis can be placed on
ECMP portions that also determine Class C.
The methods to assess the various Routing Class C characteristics
benefit from the following measurement capabilities:
o flows designed to determine which n-tuple header fields are
considered by a given hash function and ECMP hop on the path, and
which are not. This operation immediately narrows the search
space, where possible, and partially defines a Routing Class C.
o a priori knowledge of the possible types of hash functions in use
also helps to design the flows for testing (major router vendors
publish information about these hash functions, examples are here
https://www.researchgate.net/
publication/281571413_COMPARISON_OF_HASH_STRATEGIES_FOR_FLOW-
BASED_LOAD_BALANCING ).
o ability to direct the emphasis of current measurements on ECMP
portions of the path, based on recent past measurement results
(the Routing Class C of some portions of the path is essentially
"all packets").
@@@@ Comments on this material are very welcome! Especially
suggestions for tools that might lend themselves to support these
measurements.
4.1.3. Intermediate Observation Point Route Measurement
There are many examples where passive monitoring of a flow at an
Observation Point within the network can detect unexpected Round Trip
Delay or Delay Variation. But how can the cause of the anomolous
dely be investigated further --from the Observation Point -- possibly
located at an intermediate point on the path?
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In this case, knowledge that the flow of interest belongs to a
specific Routing Class C will enable mesurement of the route where
anomolous delay has been observed. Specifically, Round Trip Delay
assessment to each Hop on the path between the Observation Point and
the Destination for the flow of interest may discover high or
variable delay on a specific link and Hop combination.
The determination of a Routing Class C which includes the flow of
interest is as described in the section above, aided by computation
of the relevant hash function output as the target.
@@@@ Comments on this new material are very welcome!
@@@@ This is a topic for investigation at the Hackfest-103
Measurements and Standards table.
4.2. Hybrid Methodologies
The Hybrid Type I methods provide an alternative method for Route
Member assessment. As mentioned in the Scope section,
[I-D.ietf-ippm-ioam-data] provides a possible set of data fields that
would support route identification.
In general, nodes in the measured domain would be equipped with
specific abilities:
o Support of the "Loopback" Flag (L-bit), where a copy of the packet
is returned to the source, and the packet is processed like any
other IOAM packet on the return transfer.
In addition to node identity, nodes may also identify the ingress and
egress interfaces utilized by the tracing packet, the time of day
when the packet was processed, and other generic data (as described
in section 4 of [I-D.ietf-ippm-ioam-data]).
4.3. Combining Different Methods
In principle, there are advantages if the entity conducting Route
measurements can utilize both forms of advanced methods (active and
hybrid), and combine the results. For example, if there are hosts
involved in the path that qualify as Cooperating Hosts, but not as
Discoverable Hosts, then a more complete view of hops on the path is
possible when a hybrid method (or interrogation protocol) is applied
and the results are combined with the active method results collected
across all other domains.
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In order to combine the results of active and hybrid/interrogation
methods, the network hosts that are part of a domain supporting an
interrogation protocol have the following attributes:
1. Hosts at the ingress to the domain SHOULD be both Discoverable
and Cooperating, and SHOULD reveal the same Host Identity in
response to both active and hybrid methods.
2. Any Hosts within the domain that are both Discoverable and
Cooperating SHOULD reveal the same Host Identity in response to
both active and hybrid methods.
3. Hosts at the egress to the domain SHOULD be both Discoverable and
Cooperating, and SHOULD reveal the same Host Identity in response
to both active and hybrid methods.
When Hosts follow these requirements, it becomes a simple matter to
match single domain measurements with the overlapping results from a
multidomain measurement.
In practice, Internet users do not typically have the ability to
utilize the OAM capabilities of networks that their packets traverse,
so the results from a remote domain supporting an interrogation
protocol would not normally be accessible. However, a network
operator could combine interrogation results from their access domain
with other measurements revealing the path outside their domain.
5. Background on Round-Trip Delay Measurement Goals
The aim of this method is to use packet probes to unveil the paths
between any two end-hosts of the network. Moreover, information
derived from RTD measurements might be meaningful to identify:
1. Intercontinental submarine links
2. Satellite communications
3. Congestion
4. Inter-domain paths
This categorization is widely accepted in the literature and among
operators alike, and it can be trusted with empirical data and
several sources as ground of truth (e.g., [RTTSub] ) but it is an
inference measurement nonetheless [bdrmap][IDCong].
The first two categories correspond to the physical distance
dependency on Round Trip Delay (RTD) while the last one binds RTD
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with queueing delay on routers. Due to the significant contribution
of propagation delay in long distance hops, RTD will be on the order
of 100ms on transatlantic hops, depending on the geolocation of the
vantage points. Moreover, RTD is typically greater than 480ms when
two hops are connected using geostationary satellite technology
(i.e., their orbit is at 36000km). Detecting congestion with latency
implies deeper mathematical understanding since network traffic load
is not stationary. Nonetheless, as the first approach, a link seems
to be congested if after sending several traceroute probes, it is
possible to detect congestion observing different statistics
parameters (e.g., see [IDCong]).
6. Tools to Measure Delays in the Internet
Internet routing is complex because it depends on the policies of
thousands Autonomous Systems (AS). While most of the routers perform
load balancing on flows using Equal Cost Multiple Path (ECMP), a few
still divide the workload through packet-based techniques. The
former scenario is defined according to [RFC2991] while the latter
generates a round-robin scheme to deliver every new outgoing packet.
ECMP keeps flow state in the router to ensure every packet of a flow
is delivered by the same path, and this avoids increasing the packet
delay variation and possibly producing overwhelming packet reordering
in TCP flows.
Taking into account that Internet protocol was designed under the
"end-to-end" principle, the IP payload and its header do not provide
any information about the routes or path necessary to reach some
destination. For this reason, the well-known tool traceroute was
developed to gather the IP addresses of each hop along a path using
the ICMP protocol [RFC0792]. Besides, traceroute adds the measured
RTD from each hop. However, the growing complexity of the Internet
makes it more challenging to develop accurate traceroute
implementation. For instance, the early traceroute tools would be
inaccurate in the current network, mainly because they were not
designed to retain flow state. However, evolved traceroute tools,
such as Paris-traceroute [PT] [MLB] and Scamper [SCAMPER], expect to
encounter ECMP and achieve more accurate results when they do.
Paris-traceroute-like tools operate in the following way: every
packet should follow the same path because the sensitive fields of
the header are controlled to appear as the same flow. This means
that source and destination IP addresses, source and destination port
numbers are the same in every packet. Additionally, Differentiated
Services Code Point (DSCP), checksum and ICMP code should remain
constant since they may affect the path selection.
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Today's traceroute tools can send either UDP, TCP or ICMP packet
probes. Since ICMP header does not include transport layer
information, there are no fields for source and destination port
numbers. For this reason, these tools keep constant ICMP type, code,
and checksum fields to generate a kind of flow. However, the
checksum may vary in every packet, therefore when probes use ICMP
packets, ICMP Identifier and Sequence Number are manipulated to
maintain constant checksum in every packet. On the other hand, when
UDP probes are generated, the expected variation in the checksum of
each packet is again compensated by manipulating the payload.
Paris-traceroute allows its users to measure RTD in every hop of the
path for a particular flow. Furthermore, either Paris-traceroute or
Scamper is capable of unveiling the many available paths between a
source and destination (which are visible to this method). This task
is accomplished by repeating complete traceroute measurements with
different flow parameters for each measurement. The Framework for IP
Performance Metrics (IPPM) ([RFC2330] updated by[RFC7312]) has the
flexibility to require that the round-trip delay measurement
[RFC2681] uses packets with the constraints to assure that all
packets in a single measurement appear as the same flow. This
flexibility covers ICMP, UDP, and TCP. The accompanying methodology
of [RFC2681] needs to be expanded to report the sequential hop
identifiers along with RTD measurements, but no new metric definition
is needed.
7. RTD Measurements Statistics
Several articles have shown that network traffic presents a self-
similar nature [SSNT] [MLRM] which is accountable for filling the
queues of the routers. Moreover, router queues are designed to
handle traffic bursts, which is one of the most remarkable features
of self-similarity. Naturally, while queue length increases, the
delay to traverse the queue increases as well and leads to an
increase on RTD. Due to traffic bursts generate short-term overflow
on buffers (spiky patterns), every RTD only depicts the queueing
status on the instant when that packet probe was in transit. For
this reason, several RTD measurements during a time window could
begin to describe the random behavior of latency. Loss must also be
accounted for in the methodology.
To understand the ongoing process, examining the quartiles provides a
non-parametric way of analysis. Quartiles are defined by five
values: minimum RTD (m), RTD value of the 25% of the Empirical
Cumulative Distribution Function (ECDF) (Q1), the median value (Q2),
the RTD value of the 75% of the ECDF (Q3) and the maximum RTD (M).
Congestion can be inferred when RTD measurements are spread apart,
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and consequently, the Inter-Quartile Range (IQR), the distance
between Q3 and Q1, increases its value.
This procedure requires to compute quartile values "on the fly" using
the algorithm presented in [P2].
This procedure allow us to update the quartiles value whenever a new
measurement arrives, which is radically different from classic
methods of computing quartiles because they need to use the whole
dataset to compute the values. This way of calculus provides savings
in memory and computing time.
To sum up, the proposed measurement procedure consists in performing
traceroutes several times to obtain samples of the RTD in every hop
from a path, during a time window (W) and compute the quantiles for
every hop. This could be done for a single path flow or for every
detected path flow.
Even though a particular hop may be understood as the amount of hops
away from the source, a more detailed classification could be used.
For example, a possible classification may be identify ICMP Time
Exceeded packets coming from the same routers to those who have the
same hop distance, IP address of the router which is replying and TTL
value of the received ICMP packet.
Thus, the proposed methodology is based on this algorithm:
================================================================
1 input: W (window time of the measurement)
2 i_t (time between two measurements)
3 E (True: exhaustive, False: a single path)
4 Dst (destination IP address)
5 output: Qs (quartiles for every hop and alt in the path(s) to Dst)
----------------------------------------------------------------
6 T <? start_timer(W)
7 while T is not finished do:
8 | start_timer(i_t)
9 | RTD(hop,alt) = advanced-traceroute(Dst,E)
10 | for each hop and alt in RTD do:
11 | | Qs[Dst,hop,alt] <? ComputeQs(RTD(hop,alt))
12 | done
13 | wait until i_t timer is expired
14 done
15 return (Qs)
================================================================
In line 9 the advance-traceroute could be either Paris-traceroute or
Scamper, which will use "exhaustive" mode or "tracelb" option if E is
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set True, respectively. The procedure returns a list of tuples
(m,Q1,Q2,Q3,M) for each intermediate hop in the path towards the Dst.
Additionally, it could also return path variations using "alt"
variable.
8. Conclusions
Combining the method proposed in Section 4 and statistics in
Section 7, we can measure the performance of paths interconnecting
two endpoints in Internet, and attempt the categorization of link
types and congestion presence based on RTD.
9. Security Considerations
The security considerations that apply to any active measurement of
live paths are relevant here as well. See [RFC4656] and [RFC5357].
The active measurement process of "changing several fields to keep
the checksum of different packets identical" does not require special
security considerations because it is part of synthetic traffic
generation, and is designed to have minimal to zero impact on network
processing (to process the packets for ECMP).
@@@@ add reference to security considerations from
[I-D.ietf-ippm-ioam-data].
When considering privacy of those involved in measurement or those
whose traffic is measured, the sensitive information available to
potential observers is greatly reduced when using active techniques
which are within this scope of work. Passive observations of user
traffic for measurement purposes raise many privacy issues. We refer
the reader to the privacy considerations described in the Large Scale
Measurement of Broadband Performance (LMAP) Framework [RFC7594],
which covers active and passive techniques.
10. IANA Considerations
This memo makes no requests of IANA. We thank the good folks at IANA
for having checked this section anyway.
11. Acknowledgements
The original 3 authors acknowledge Ruediger Geib, for his penetrating
comments on the initial draft, and his initial text for the
Appendix on MPLS. Carlos Pignataro challenged the authors to
consider a wider scope, and applied his substantial expertise with
many technologies and their measurement features in his extensive
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comments. Frank Brockners also shared useful comments. We thank
them all!
12. Appendix I MPLS Methods for Route Assessment
A host assessing an MPLS path must be part of the MPLS domain where
the path is implemented. When this condition is met, RFC 8029
provides a powerful set of mechanisms to detect "correct operation of
the data plane, as well as a mechanism to verify the data plane
against the control plane" [RFC8029].
MPLS routing is based on the presence of a Forwarding Equivalence
Class (FEC) Stack in all visited hosts. Selecting one of several
Equal Cost Multi Path (ECMP) is however based on information hidden
deeper in the stack. Early deployments may support a so called
"Entropy label" for this purpose. State of the art deployments base
their choice of an ECMP member based on the IP addresses (see
Section 2.4 of [RFC7325]). Both methods allow load sharing
information to be decoupled from routing information. Thus, an MPLS
traceroute is able to check how packets with a contiguous number of
ECMP relevant addresses (and the same destination) are routed by a
particular router. The minimum number of MPLS paths traceable at a
router should be 32. Implementations supporting more paths are
available.
The MPLS echo request and reply messages offering this feature must
support the Downstream Detailed Mapping TLV (was Downstream Mapping
initially, but the latter has been deprecated). The MPLS echo
response includes the incoming interface where a router received the
MPLS Echo request. The MPLS Echo reply further informs which of the
n addresses relevant for the load sharing decision results in a
particular next hop interface and contains the next hop's interface
address (if available). This ensures that the next hop will receive
a properly coded MPLS Echo request in the next step route of
assessment.
RFC to be 8403 (draft-ietf-spring-oam-usecase-10) explains how a
central Path Monitoring System could be used to detect arbitrary MPLS
paths between any routers within a single MPLS domain. The
combination of MPLS forwarding, Segment Routing and MPLS traceroute
offers a simple architecture and a powerful mechanism to detect and
validate (segment routed) MPLS paths.
13. References
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13.1. Normative References
[I-D.ietf-ippm-ioam-data]
Brockners, F., Bhandari, S., Pignataro, C., Gredler, H.,
Leddy, J., Youell, S., Mizrahi, T., Mozes, D., Lapukhov,
P., Chang, R., daniel.bernier@bell.ca, d., and J. Lemon,
"Data Fields for In-situ OAM", draft-ietf-ippm-ioam-
data-04 (work in progress), October 2018.
[RFC0792] Postel, J., "Internet Control Message Protocol", STD 5,
RFC 792, DOI 10.17487/RFC0792, September 1981,
<https://www.rfc-editor.org/info/rfc792>.
[RFC1122] Braden, R., Ed., "Requirements for Internet Hosts -
Communication Layers", STD 3, RFC 1122,
DOI 10.17487/RFC1122, October 1989,
<https://www.rfc-editor.org/info/rfc1122>.
[RFC1812] Baker, F., Ed., "Requirements for IP Version 4 Routers",
RFC 1812, DOI 10.17487/RFC1812, June 1995,
<https://www.rfc-editor.org/info/rfc1812>.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119,
DOI 10.17487/RFC2119, March 1997,
<https://www.rfc-editor.org/info/rfc2119>.
[RFC2330] Paxson, V., Almes, G., Mahdavi, J., and M. Mathis,
"Framework for IP Performance Metrics", RFC 2330,
DOI 10.17487/RFC2330, May 1998,
<https://www.rfc-editor.org/info/rfc2330>.
[RFC2460] Deering, S. and R. Hinden, "Internet Protocol, Version 6
(IPv6) Specification", RFC 2460, DOI 10.17487/RFC2460,
December 1998, <https://www.rfc-editor.org/info/rfc2460>.
[RFC2675] Borman, D., Deering, S., and R. Hinden, "IPv6 Jumbograms",
RFC 2675, DOI 10.17487/RFC2675, August 1999,
<https://www.rfc-editor.org/info/rfc2675>.
[RFC2681] Almes, G., Kalidindi, S., and M. Zekauskas, "A Round-trip
Delay Metric for IPPM", RFC 2681, DOI 10.17487/RFC2681,
September 1999, <https://www.rfc-editor.org/info/rfc2681>.
[RFC2991] Thaler, D. and C. Hopps, "Multipath Issues in Unicast and
Multicast Next-Hop Selection", RFC 2991,
DOI 10.17487/RFC2991, November 2000,
<https://www.rfc-editor.org/info/rfc2991>.
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[RFC4494] Song, JH., Poovendran, R., and J. Lee, "The AES-CMAC-96
Algorithm and Its Use with IPsec", RFC 4494,
DOI 10.17487/RFC4494, June 2006,
<https://www.rfc-editor.org/info/rfc4494>.
[RFC4656] Shalunov, S., Teitelbaum, B., Karp, A., Boote, J., and M.
Zekauskas, "A One-way Active Measurement Protocol
(OWAMP)", RFC 4656, DOI 10.17487/RFC4656, September 2006,
<https://www.rfc-editor.org/info/rfc4656>.
[RFC5357] Hedayat, K., Krzanowski, R., Morton, A., Yum, K., and J.
Babiarz, "A Two-Way Active Measurement Protocol (TWAMP)",
RFC 5357, DOI 10.17487/RFC5357, October 2008,
<https://www.rfc-editor.org/info/rfc5357>.
[RFC5388] Niccolini, S., Tartarelli, S., Quittek, J., Dietz, T., and
M. Swany, "Information Model and XML Data Model for
Traceroute Measurements", RFC 5388, DOI 10.17487/RFC5388,
December 2008, <https://www.rfc-editor.org/info/rfc5388>.
[RFC5644] Stephan, E., Liang, L., and A. Morton, "IP Performance
Metrics (IPPM): Spatial and Multicast", RFC 5644,
DOI 10.17487/RFC5644, October 2009,
<https://www.rfc-editor.org/info/rfc5644>.
[RFC5835] Morton, A., Ed. and S. Van den Berghe, Ed., "Framework for
Metric Composition", RFC 5835, DOI 10.17487/RFC5835, April
2010, <https://www.rfc-editor.org/info/rfc5835>.
[RFC5837] Atlas, A., Ed., Bonica, R., Ed., Pignataro, C., Ed., Shen,
N., and JR. Rivers, "Extending ICMP for Interface and
Next-Hop Identification", RFC 5837, DOI 10.17487/RFC5837,
April 2010, <https://www.rfc-editor.org/info/rfc5837>.
[RFC6282] Hui, J., Ed. and P. Thubert, "Compression Format for IPv6
Datagrams over IEEE 802.15.4-Based Networks", RFC 6282,
DOI 10.17487/RFC6282, September 2011,
<https://www.rfc-editor.org/info/rfc6282>.
[RFC6437] Amante, S., Carpenter, B., Jiang, S., and J. Rajahalme,
"IPv6 Flow Label Specification", RFC 6437,
DOI 10.17487/RFC6437, November 2011,
<https://www.rfc-editor.org/info/rfc6437>.
[RFC6438] Carpenter, B. and S. Amante, "Using the IPv6 Flow Label
for Equal Cost Multipath Routing and Link Aggregation in
Tunnels", RFC 6438, DOI 10.17487/RFC6438, November 2011,
<https://www.rfc-editor.org/info/rfc6438>.
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[RFC6564] Krishnan, S., Woodyatt, J., Kline, E., Hoagland, J., and
M. Bhatia, "A Uniform Format for IPv6 Extension Headers",
RFC 6564, DOI 10.17487/RFC6564, April 2012,
<https://www.rfc-editor.org/info/rfc6564>.
[RFC6673] Morton, A., "Round-Trip Packet Loss Metrics", RFC 6673,
DOI 10.17487/RFC6673, August 2012,
<https://www.rfc-editor.org/info/rfc6673>.
[RFC7045] Carpenter, B. and S. Jiang, "Transmission and Processing
of IPv6 Extension Headers", RFC 7045,
DOI 10.17487/RFC7045, December 2013,
<https://www.rfc-editor.org/info/rfc7045>.
[RFC7312] Fabini, J. and A. Morton, "Advanced Stream and Sampling
Framework for IP Performance Metrics (IPPM)", RFC 7312,
DOI 10.17487/RFC7312, August 2014,
<https://www.rfc-editor.org/info/rfc7312>.
[RFC7799] Morton, A., "Active and Passive Metrics and Methods (with
Hybrid Types In-Between)", RFC 7799, DOI 10.17487/RFC7799,
May 2016, <https://www.rfc-editor.org/info/rfc7799>.
[RFC7820] Mizrahi, T., "UDP Checksum Complement in the One-Way
Active Measurement Protocol (OWAMP) and Two-Way Active
Measurement Protocol (TWAMP)", RFC 7820,
DOI 10.17487/RFC7820, March 2016,
<https://www.rfc-editor.org/info/rfc7820>.
[RFC8029] Kompella, K., Swallow, G., Pignataro, C., Ed., Kumar, N.,
Aldrin, S., and M. Chen, "Detecting Multiprotocol Label
Switched (MPLS) Data-Plane Failures", RFC 8029,
DOI 10.17487/RFC8029, March 2017,
<https://www.rfc-editor.org/info/rfc8029>.
[RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
May 2017, <https://www.rfc-editor.org/info/rfc8174>.
13.2. Informative References
[bdrmap] Luckie, M., Dhamdhere, A., Huffaker, B., Clark, D., and
KC. Claffy, "bdrmap: Inference of Borders Between IP
Networks", In Proceedings of the 2016 ACM on Internet
Measurement Conference, pp. 381-396. ACM, 2016.
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[IDCong] Luckie, M., Dhamdhere, A., Clark, D., and B. Huffaker,
"Challenges in inferring Internet interdomain congestion",
In Proceedings of the 2014 Conference on Internet
Measurement Conference, pp. 15-22. ACM, 2014.
[MLB] Augustin, B., Friedman, T., and R. Teixeira, "Measuring
load-balanced paths in the Internet", Proceedings of the
7th ACM SIGCOMM conference on Internet measurement, pp.
149-160. ACM, 2007., 2007.
[MLRM] Fontugne, R., Mazel, J., and K. Fukuda, "An empirical
mixture model for large-scale RTT measurements", 2015
IEEE Conference on Computer Communications (INFOCOM), pp.
2470-2478. IEEE, 2015., 2015.
[P2] Jain, R. and I. Chlamtac, "The P 2 algorithm for dynamic
calculation of quantiles and histograms without storing
observations", Communications of the ACM 28.10 (1985):
1076-1085, 2015.
[PT] Augustin, B., Cuvellier, X., Orgogozo, B., Viger, F.,
Friedman, T., Latapy, M., Magnien, C., and R. Teixeira,
"Avoiding traceroute anomalies with Paris traceroute",
Proceedings of the 6th ACM SIGCOMM conference on Internet
measurement, pp. 153-158. ACM, 2006., 2006.
[RFC7325] Villamizar, C., Ed., Kompella, K., Amante, S., Malis, A.,
and C. Pignataro, "MPLS Forwarding Compliance and
Performance Requirements", RFC 7325, DOI 10.17487/RFC7325,
August 2014, <https://www.rfc-editor.org/info/rfc7325>.
[RFC7594] Eardley, P., Morton, A., Bagnulo, M., Burbridge, T.,
Aitken, P., and A. Akhter, "A Framework for Large-Scale
Measurement of Broadband Performance (LMAP)", RFC 7594,
DOI 10.17487/RFC7594, September 2015,
<https://www.rfc-editor.org/info/rfc7594>.
[RTTSub] Bischof, Z., Rula, J., and F. Bustamante, "In and out of
Cuba: Characterizing Cuba's connectivity", In Proceedings
of the 2015 ACM Conference on Internet Measurement
Conference, pp. 487-493. ACM, 2015.
[SCAMPER] Matthew Luckie, M., "Scamper: a scalable and extensible
packet prober for active measurement of the Internet",
Proceedings of the 10th ACM SIGCOMM conference on
Internet measurement, pp. 239-245. ACM, 2010., 2010.
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[SSNT] Park, K. and W. Willinger, "Self-Similar Network Traffic
and Performance Evaluation (1st ed.)", John Wiley & Sons,
Inc., New York, NY, USA, 2000.
Authors' Addresses
Jose Ignacio Alvarez-Hamelin
Universidad de Buenos Aires
Av. Paseo Colon 850
Buenos Aires C1063ACV
Argentine
Phone: +54 11 5285-0716
Email: ihameli@cnet.fi.uba.ar
URI: http://cnet.fi.uba.ar/ignacio.alvarez-hamelin/
Al Morton
AT&T Labs
200 Laurel Avenue South
Middletown, NJ 07748
USA
Phone: +1 732 420 1571
Fax: +1 732 368 1192
Email: acm@research.att.com
Joachim Fabini
TU Wien
Gusshausstrasse 25/E389
Vienna 1040
Austria
Phone: +43 1 58801 38813
Fax: +43 1 58801 38898
Email: Joachim.Fabini@tuwien.ac.at
URI: http://www.tc.tuwien.ac.at/about-us/staff/joachim-fabini/
Carlos Pignataro
Cisco Systems, Inc.
7200-11 Kit Creek Road
Research Triangle Park, NC 27709
USA
Email: cpignata@cisco.com
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Ruediger Geib
Deutsche Telekom
Heinrich Hertz Str. 3-7
Darmstadt 64295
Germany
Phone: +49 6151 5812747
Email: Ruediger.Geib@telekom.de
Alvarez-Hamelin, et al.Expires September 10, 2019 [Page 27]