ALTO Working Group Q. Wu
Internet-Draft Huawei
Intended status: Standards Track Y. Yang
Expires: December 13, 2020 Yale University
Y. Lee
Samsung
D. Dhody
Huawei
S. Randriamasy
Nokia Bell Labs
L. Contreras
Telefonica
June 11, 2020
ALTO Performance Cost Metrics
draft-ietf-alto-performance-metrics-11
Abstract
Cost metric is a basic concept in Application-Layer Traffic
Optimization (ALTO), and is used in basic ALTO services including
both the cost map service and the endpoint cost service.
Different applications may use different cost metrics, but the ALTO
base protocol [RFC7285] defines only a single cost metric, i.e., the
generic "routingcost" metric; see Sec. 14.2 of [RFC7285]. Hence, if
the ALTO client of an application wants to issue a cost map or an
endpoint cost request to determine the resource provider that offers
better delay performance (i.e., low-delay) to a resource consumer,
the base protocol does not define the cost metric to be used.
This document addresses the issue by introducing network performance
metrics, including network delay, jitter, packet loss rate, hop
count, and bandwidth. The ALTO server may derive and aggregate such
performance metrics from routing protocols such as BGP-LS, OSPF-TE
and ISIS-TE, or from end-to-end traffic management tools, and then
expose the information to allow applications to determine "where" to
connect based on network performance criteria.
There are multiple sources to derive the performance metrics. For
example, whether the metric reported is an estimation based on
measurements or it is a service-level agreement (SLA) can define the
meaning of the performance metric. Hence, an application may need
additional contextual information beyond the metric value. This
document introduces an additional "cost-context" field to the ALTO
"cost-type" field to convey such information.
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Requirements Language 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
[RFC2119].
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 http://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."
This Internet-Draft will expire on December 13, 2020.
Copyright Notice
Copyright (c) 2020 IETF Trust and the persons identified as the
document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents
(http://trustee.ietf.org/license-info) in effect on the date of
publication of this document. Please review these documents
carefully, as they describe your rights and restrictions with respect
to this document. Code Components extracted from this document must
include Simplified BSD License text as described in Section 4.e of
the Trust Legal Provisions and are provided without warranty as
described in the Simplified BSD License.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 4
2. Performance Metric Attributes . . . . . . . . . . . . . . . . 5
2.1. Performance Metric Context: cost-context . . . . . . . . 5
2.2. Performance Metric Statistics . . . . . . . . . . . . . . 7
3. Packet Performance Metrics . . . . . . . . . . . . . . . . . 8
3.1. Cost Metric: One-Way Delay (delay-ow) . . . . . . . . . . 9
3.1.1. Base Identifier . . . . . . . . . . . . . . . . . . . 9
3.1.2. Value Representation . . . . . . . . . . . . . . . . 9
3.1.3. Intended Semantics and Use . . . . . . . . . . . . . 9
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3.1.4. Cost-Context Specification Considerations . . . . . . 11
3.2. Cost Metric: Round-trip Delay (delay-rt) . . . . . . . . 11
3.2.1. Base Identifier . . . . . . . . . . . . . . . . . . . 11
3.2.2. Value Representation . . . . . . . . . . . . . . . . 11
3.2.3. Intended Semantics and Use . . . . . . . . . . . . . 11
3.2.4. Cost-Context Specification Considerations . . . . . . 13
3.3. Cost Metric: Delay Variation (delay-variation) . . . . . 13
3.3.1. Base Identifier . . . . . . . . . . . . . . . . . . . 13
3.3.2. Value Representation . . . . . . . . . . . . . . . . 13
3.3.3. Intended Semantics and Use . . . . . . . . . . . . . 13
3.3.4. Cost-Context Specification Considerations . . . . . . 15
3.4. Cost Metric: Hop Count (hopcount) . . . . . . . . . . . . 15
3.4.1. Base Identifier . . . . . . . . . . . . . . . . . . . 15
3.4.2. Value Representation . . . . . . . . . . . . . . . . 15
3.4.3. Intended Semantics and Use . . . . . . . . . . . . . 15
3.4.4. Cost-Context Specification Considerations . . . . . . 17
3.5. Cost Metric: Loss Rate (lossrate) . . . . . . . . . . . . 17
3.5.1. Base Identifier . . . . . . . . . . . . . . . . . . . 17
3.5.2. Value Representation . . . . . . . . . . . . . . . . 17
3.5.3. Intended Semantics and Use . . . . . . . . . . . . . 17
3.5.4. Cost-Context Specification Considerations . . . . . . 18
4. Bandwidth Performance Metrics . . . . . . . . . . . . . . . . 19
4.1. Cost Metric: TCP Throughput (tput) . . . . . . . . . . . 19
4.1.1. Base Identifier . . . . . . . . . . . . . . . . . . . 19
4.1.2. Value Representation . . . . . . . . . . . . . . . . 19
4.1.3. Intended Semantics and Use . . . . . . . . . . . . . 19
4.1.4. Cost-Context Specification Considerations . . . . . . 20
4.2. Cost Metric: Residue Bandwidth . . . . . . . . . . . . . 21
4.2.1. Base Identifier . . . . . . . . . . . . . . . . . . . 21
4.2.2. Value Representation . . . . . . . . . . . . . . . . 21
4.2.3. Intended Semantics and Use . . . . . . . . . . . . . 21
4.2.4. Cost-Context Specification Considerations . . . . . . 22
4.3. Cost Metric: Maximum Reservable Bandwidth . . . . . . . . 23
4.3.1. Base Identifier . . . . . . . . . . . . . . . . . . . 23
4.3.2. Value Representation . . . . . . . . . . . . . . . . 23
4.3.3. Intended Semantics and Use . . . . . . . . . . . . . 23
4.3.4. Cost-Context Specification Considerations . . . . . . 24
5. Operational Considerations . . . . . . . . . . . . . . . . . 25
5.1. Source Considerations . . . . . . . . . . . . . . . . . . 25
5.2. Metric Timestamp Consideration . . . . . . . . . . . . . 26
5.3. Backward Compatibility Considerations . . . . . . . . . . 26
5.4. Computation Considerations . . . . . . . . . . . . . . . 26
5.4.1. Configuration Parameters Considerations . . . . . . . 26
5.4.2. Availability Considerations . . . . . . . . . . . . . 27
6. Security Considerations . . . . . . . . . . . . . . . . . . . 27
7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 27
8. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 28
9. References . . . . . . . . . . . . . . . . . . . . . . . . . 28
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9.1. Normative References . . . . . . . . . . . . . . . . . . 28
9.2. Informative References . . . . . . . . . . . . . . . . . 29
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 30
1. Introduction
Cost Metric is a basic concept in Application-Layer Traffic
Optimization (ALTO). It is used in both the ALTO cost map service
and the ALTO endpoint cost service in the ALTO base protocol
[RFC7285].
Since different applications may use different cost metrics, the ALTO
base protocol introduces an ALTO Cost Metric Registry (Section 14.2
of [RFC7285]), as a systematic mechanism to allow different metrics
to be specified. For example, a delay-sensitive application may want
to use latency related metrics, and a bandwidth-sensitive application
may want to use bandwidth related metrics. The ALTO base protocol,
however, has registered only one single cost metric, i.e., the
generic "routingcost" metric; no latency or bandwidth related metrics
are defined.
This document registers a set of new cost metrics specified in
Table 1, to allow applications to better determine "where" to connect
based on network performance criteria. This document follows the
guideline defined in Section 14.2 of the ALTO base protocol
[RFC7285]) on registering ALTO cost metrics. Hence it specifies the
identifier, the intended semantics, and the security considerations
of each one of the metrics defined in Table 1.
+--------------------------+-------------+-------------------+
| Metric | Definition | Origin Example |
+--------------------------+-------------+-------------------+
| One-way Delay | Section 3.1 | [RFC7679] |
| Round-trip Delay | Section 3.2 | [RFC2681] |
| Delay Variation | Section 3.3 | [RFC3393] |
| Hop Count | Section 3.4 | [RFC7285] |
| Loss Rate | Section 3.5 | [RFC7680] |
| | | |
| TCP Throughput | Section 4.1 | [RFC6349] |
| Residue Bandwidth | Section 4.2 | [RFC7810] |
| Max Reservable Bandwidth | Section 4.3 | [RFC5305] |
+------------+-----------------------------------------------+
Table 1. Cost Metrics Defined in this Document.
The purpose of this document is to ensure proper usage of the
performance metrics defined in Table 1; it does not claim novelty of
the metrics. For each performance metric, the Origin column of
Table 1 gives an earlier RFC which has defined the metric. We can
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rough classify the performance metrics into two categories: those
derived from the performance of individual packets (i.e., one-way
delay, round-trip delay, delay variation, hop count, and loss rate),
and those related with bandwidth (TCP throughput, residue bandwidth
and max reservable bandwidth). These two categories are defined in
Section 3 and Section 4 respectively. Note that all metrics except
round trip delay are unidirectional. Hence, a client will need to
query both directions if needed.
An ALTO server may provide only a subset of the metrics described in
this document. For example, those that are subject to privacy
concerns should not be provided to unauthorized ALTO clients. Hence,
all cost metrics defined in this document are optional and not all of
them need to be exposed to a given application. When an ALTO server
supports a cost metric defined in this document, it should announce
this metric in its information resource directory (IRD).
An ALTO server introducing these metrics should consider security
issues. As a generic security consideration on the reliability and
trust in the exposed metric values, applications SHOULD rapidly give
up using ALTO-based guidance if they detect that the exposed
information does not preserve their performance level or even
degrades it. This document discusses security considerations in more
details in Section 6.
Following the ALTO base protocol, this document uses JSON to specify
the value type of each defined metric. See [RFC8259] for JSON data
type specification.
2. Performance Metric Attributes
2.1. Performance Metric Context: cost-context
The semantics of a performance metric depends on the source of the
information. Specifically, this document defines four information
sources when defining performance metrics: "nominal", and "sla"
(service level agreement), "import", and "estimation".
Even given the source, precise interpretation of a performance metric
value, if needed, depends on an additional set of measurement and
computation parameters. For example, see Section 3.8 of [RFC7679] on
items which a more complete measurement-based report should include.
To make it possible to specify both the source and the additional
parameters, this document introduces an optional "cost-context" field
to the "cost-type" field defined by the ALTO base protocol
(Section 10.7 of [RFC7285]) as the following:
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object {
CostMetric cost-metric;
CostMode cost-mode;
[CostContext cost-context;]
[JSONString description;]
} CostType;
object {
JSONString cost-source;
[JSONValue parameters;]
} CostContext;
The "cost-source" field of the "cost-context" field MUST be one of
four category values: "nominal", "sla", "import", and "estimation".
"cost-context" will not be used as a key to distinguish among
performance metrics. Hence, an ALTO information resource SHOULD NOT
announce multiple CostType with the same "cost-metric" and "cost-
mode". They can be placed into different information resources.
The "nominal" category indicates that the value of the metric is
statically configured by the underlying devices. Not all metrics
have reasonable "nominal" values. For example, throughput can have a
nominal value, which indicates the configured transmission rate of
the devices; latency typically do not have a nominal value.
The "sla" category indicates that the value of the metric is derived
from some commitment which this document refers to as service-level
agreement (SLA). Some operators also use terms such as "target" or
"committed" values. For a "sla" metric, it is RECOMMENDED that the
"parameters" field provides a link to the SLA definition.
The "import" category indicates that the value of the metric is
derived from importing from a specific existing protocol or system.
For an "import" metric, it is RECOMMENDED that the "parameters" field
provides details to the system from which raw data is imported. In
particular, one may notice that the set of end-to-end metrics defined
in Table 1 has large overlap with the set defined in [RFC8571], in
the setting of IGP traffic engineering performance metrics for each
link (i.e., unidirectional link delay, min/max unidirectional link
delay, unidirectional delay variation, unidirectional link loss,
unidirectional residual bandwidth, unidirectional available
bandwidth, unidirectional utilized bandwidth). Hence, an ALTO server
may use "import" to indicate that its end-to-end metrics are computed
from link metrics imported from [RFC8571].
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The "estimation" category indicates that the value of the metric is
computed through an estimation process. An ALTO server may compute
"estimation" values by retrieving and/or aggregating information from
routing protocols (e.g., [RFC8571]) and traffic measurement
management tools (e.g., TWAMP), with corresponding operational
issues. A potential architecture on estimating these metrics is
shown in Figure 1 below. Section 5 will discuss in more detail the
operational issues and how a network may address them.
+--------+ +--------+ +--------+
| Client | | Client | | Client |
+----^---+ +---^----+ +---^----+
| | |
+-----------|-----------+
NBI |ALTO protocol
|
|
+--+-----+ retrieval +-----------+
| ALTO |<----------------| Routing |
| Server | and aggregation| |
| |<-------------+ | Protocols |
+--------+ | +----------+
|
| +-----------+
| |Management |
---| |
| Tool |
+-----------+
Figure 1. Potential framework to compute estimation to performance metrics
There can be overlap in deciding the cost-source category. It is the
operator of an ALTO server who chooses the category. If a metric
does not include a "cost-source" value, the application MUST assume
that the value of "cost-source" is "estimation".
2.2. Performance Metric Statistics
Even with a specified cost context, a performance metric may be
observed with values from an observation distribution. To address
this issue, this document allows each performance metric's identifier
to indicate a summary statistics of the distribution, to become
<metric-base-identifier>-<stat>, where <stat> MUST be one of the
following:
letter p followed by a number:
the value represents the percentile: less than or equal to number
percent of observations are lower than the value (for example,
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delay-ow-p75 gives the value that 75% of observed one-way delays
will be less or equal to it). To avoid complex identifiers, the
number MUST be a JSON number (Section 6 of [RFC8259]) without the
minus or the exp component.
max:
the maximal value of the observation distribution.
min:
the minimal value of the observation distribution.
median:
the mid point of the observation distribution.
mean:
the arithmetic mean value of the observations.
stand-deviation:
the standard deviation of the observations.
If a metric has no <stat> (and hence no - as well), the metric is the
50 percentile (median). Since this scheme is common for all metrics
defined in this document, below we only specify the base identifier.
3. Packet Performance Metrics
This section introduces ALTO network performance metrics including
one way delay, round trip delay, delay variation, hop count, and
packet loss rate. They measure the "quality of experience" of the
stream of packets sent from a resource provider to a resource
consumer. The measures of each individual packet (pkt) can include
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the delay from the time that the packet enters the network to the
time that the packet leaves the network (pkt.delay); the number of
network hops that the packet traverses (pkt.hopcount); and whether
the packet is dropped before reaching destination (pkt.dropped). The
semantics of the performance metrics defined in this section is that
they are statistics (percentiles) computed from these measures; for
example, the x-percentile of the one-way delay is the x-percentile of
the set of delays {pkt.delay} for the packets in the stream.
3.1. Cost Metric: One-Way Delay (delay-ow)
3.1.1. Base Identifier
The base identifier for this performance metric is "delay-ow".
3.1.2. Value Representation
The metric value type is a single 'JSONNumber' type value conforming
to the number specification of [RFC8259] Section 6. The unit is
expressed in milliseconds. Hence, the number can be a floating point
number to express delay that is smaller than milliseconds. The
number MUST be non-negative.
3.1.3. Intended Semantics and Use
Intended Semantics: To specify spatial and temporal aggregated delay
of a stream of packets from the specified source and the specified
destination. The spatial aggregation level is specified in the query
context (e.g., PID to PID, or endpoint to endpoint).
Use: This metric could be used as a cost metric constraint attribute
or as a returned cost metric in the response.
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Example 1: Delay value on source-destination endpoint pairs
POST /endpointcost/lookup HTTP/1.1
Host: alto.example.com
Content-Length: TBA
Content-Type: application/alto-endpointcostparams+json
Accept:
application/alto-endpointcost+json,application/alto-error+json
{
"cost-type": {"cost-mode" : "numerical",
"cost-metric" : "delay-ow"},
"endpoints" : {
"srcs": [ "ipv4:192.0.2.2" ],
"dsts": [
"ipv4:192.0.2.89",
"ipv4:198.51.100.34",
"ipv6:2000::1:2345:6789:abcd"
]
}
}
HTTP/1.1 200 OK
Content-Length: TBA
Content-Type: application/alto-endpointcost+json
{
"meta" :{
"cost-type": {"cost-mode" : "numerical",
"cost-metric" : "delay-ow"
}
},
"endpoint-cost-map" : {
"ipv4:192.0.2.2": {
"ipv4:192.0.2.89" : 10,
"ipv4:198.51.100.34" : 20,
"ipv6:2000::1:2345:6789:abcd" : 30,
}
}
}
Comment: Since the "cost-type" does not include the "cost-source"
field, the values are based on "estimation". Since the identifier
does not include the -<percentile> component, the values will
represent median values.
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3.1.4. Cost-Context Specification Considerations
"nominal": Typically network one-way delay does not have a nominal
value.
"sla": Many networks provide delay in their application-level service
level agreements. It is RECOMMENDED that the "parameters" field of
an "sla" one-way delay metric provides a link ("link") to the SLA
definition.
"import": There can be multiple sources to import one-way delay. For
example, if the import is from [RFC8571] (by using unidirectional
link delay, min/max unidirectional link delay), it is RECOMMENDED
that "parameters" provides "protocol" as a field and "RFC8571" as the
value. During import, the server should be cognizant of potential
issues when computing an end-to-end summary statistics from a link
statistics. Another example import source is the IPPM framework.
For IPPM, it is recommended that "parameters" provides "protocol" as
a field and "ippm" as the value; see Section 4 of [I-D.ietf-ippm-
initial-registry] for additional fields which can be specified for
"ippm" in "parameters".
"estimation": The exact estimation method is out of the scope of this
document. It is RECOMMENDED that the "parameters" field of an
"estimation" one-way delay metric provides a link ("link") to a
description of the "estimation" method.
3.2. Cost Metric: Round-trip Delay (delay-rt)
3.2.1. Base Identifier
The base identifier for this performance metric is "delay-rt".
3.2.2. Value Representation
The metric value type is a single 'JSONNumber' type value conforming
to the number specification of [RFC8259] Section 6. The number MUST
be non-negative. The unit is expressed in milliseconds.
3.2.3. Intended Semantics and Use
Intended Semantics: To specify spatial and temporal aggregated round-
trip delay between the specified source and specified destination.
The spatial aggregation level is specified in the query context
(e.g., PID to PID, or endpoint to endpoint).
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Note that it is possible for a client to query two one-way delays and
then compute the round-trip delay. The server should be cognizant of
the consistency of values.
Use: This metric could be used either as a cost metric constraint
attribute or as a returned cost metric in the response.
Example 2: Round-trip Delay value on source-destination endpoint pairs
POST /endpointcost/lookup HTTP/1.1
Host: alto.example.com
Content-Length: TBA
Content-Type: application/alto-endpointcostparams+json
Accept:
application/alto-endpointcost+json,application/alto-error+json
{
"cost-type": {"cost-mode" : "numerical",
"cost-metric" : "delay-rt"},
"endpoints" : {
"srcs": [ "ipv4:192.0.2.2" ],
"dsts": [
"ipv4:192.0.2.89",
"ipv4:198.51.100.34",
"ipv6:2000::1:2345:6789:abcd"
]
}
}
HTTP/1.1 200 OK
Content-Length: TBA
Content-Type: application/alto-endpointcost+json
{
"meta" :{
"cost-type": {"cost-mode" : "numerical",
"cost-metric" : "delay-rt"
}
},
"endpoint-cost-map" : {
"ipv4:192.0.2.2": {
"ipv4:192.0.2.89" : 4,
"ipv4:198.51.100.34" : 3,
"ipv6:2000::1:2345:6789:abcd" : 2,
}
}
}
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3.2.4. Cost-Context Specification Considerations
"nominal": Typically network round-trip delay does not have a nominal
value.
"sla": It is RECOMMENDED that the "parameters" field of an "sla"
round-trip delay metric provides a link ("link") to the SLA
definition.
"import": There can be multiple sources to import round-trip delay.
If the import is from [RFC8571] (by using unidirectional link delay,
min/max unidirectional link delay), it is RECOMMENDED that
"parameters" provides "protocol" as a field and "RFC8571" as the
value; see Section 3.1.4 for discussions on summing up link metrics
to obtain end-to-end metrics. If the import is from the IPPM
framework, it is recommended that "parameters" provides "protocol" as
a field and "ippm" as the value; see Section 4 of [I-D.ietf-ippm-
initial-registry] for additional fields which can be specified for
"ippm" in "parameters".
"estimation": The exact estimation method is out of the scope of this
document. It is RECOMMENDED that the "parameters" field of an
"estimation" round-trip delay metric provides a link ("link") to a
description of the "estimation" method.
3.3. Cost Metric: Delay Variation (delay-variation)
3.3.1. Base Identifier
The base identifier for this performance metric is "delay-variation".
3.3.2. Value Representation
The metric value type is a single 'JSONNumber' type value conforming
to the number specification of [RFC8259] Section 6. The number MUST
be non-negative. The unit is expressed in milliseconds.
3.3.3. Intended Semantics and Use
Intended Semantics: To specify spatial and temporal aggregated delay
variation (also called delay jitter)) with respect to the minimum
delay observed on the stream over the specified source and
destination. The spatial aggregation level is specified in the query
context (e.g., PID to PID, or endpoint to endpoint).
Note that in statistics, variations are typically evaluated by the
distance from samples relative to the mean. In networking context,
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it is more commonly defined from samples relative to the min. This
definition follows the networking convention.
Use: This metric could be used either as a cost metric constraint
attribute or as a returned cost metric in the response.
Example 3: Delay variation value on source-destination endpoint pairs
POST /endpointcost/lookup HTTP/1.1
Host: alto.example.com
Content-Length: TBA
Content-Type: application/alto-endpointcostparams+json
Accept:
application/alto-endpointcost+json,application/alto-error+json
{
"cost-type": {"cost-mode" : "numerical",
"cost-metric" : "delay-var"},
"endpoints" : {
"srcs": [ "ipv4:192.0.2.2" ],
"dsts": [
"ipv4:192.0.2.89",
"ipv4:198.51.100.34",
"ipv6:2000::1:2345:6789:abcd"
]
}
}
HTTP/1.1 200 OK
Content-Length: TBA
Content-Type: application/alto-endpointcost+json
{
"meta": {
"cost type": {
"cost-mode": "numerical",
"cost-metric":"delay-var"
}
},
"endpoint-cost-map": {
"ipv4:192.0.2.2": {
"ipv4:192.0.2.89" : 0
"ipv4:198.51.100.34" : 1
"ipv6:2000::1:2345:6789:abcd" : 5
}
}
}
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3.3.4. Cost-Context Specification Considerations
"nominal": Typically network delay variation does not have a nominal
value.
"sla": It is RECOMMENDED that the "parameters" field of an "sla"
delay variation metric provides a link ("link") to the SLA
definition.
"import": There can be multiple sources to import delay variation.
If the import is from [RFC8571] (by using unidirectional delay
variation), it is RECOMMENDED that "parameters" provides "protocol"
as a field and "RFC8571" as the value; see Section 3.1.4 for
discussions on summing up link metrics to obtain end-to-end metrics.
If the import is from the IPPM framework, it is recommended that
"parameters" provides "protocol" as a field and "ippm" as the value;
see Section 4 of [I-D.ietf-ippm-initial-registry] for additional
fields which can be specified for "ippm" in "parameters".
"estimation": The exact estimation method is out of the scope of this
document. It is RECOMMENDED that the "parameters" field of an
"estimation" delay variation metric provides a link ("link") to a
description of the "estimation" method.
3.4. Cost Metric: Hop Count (hopcount)
The metric hopcount is mentioned in [RFC7285] Section 9.2.3 as an
example. This section further clarifies its properties.
3.4.1. Base Identifier
The base identifier for this performance metric is "hopcount".
3.4.2. Value Representation
The metric value type is a single 'JSONNumber' type value conforming
to the number specification of [RFC8259] Section 6. The number MUST
be a non-negative integer (greater than or equal to 0). The value
represents the number of hops.
3.4.3. Intended Semantics and Use
Intended Semantics: To specify the number of hops in the path from
the specified source to the specified destination. The hop count is
a basic measurement of distance in a network and can be exposed as
router hops, in direct relation to the routing protocols originating
this information. The spatial aggregation level is specified in the
query context (e.g., PID to PID, or endpoint to endpoint).
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Use: This metric could be used as a cost metric constraint attribute
or as a returned cost metric in the response.
Example 4: hopcount value on source-destination endpoint pairs
POST /endpointcost/lookup HTTP/1.1
Host: alto.example.com
Content-Length: TBA
Content-Type: application/alto-endpointcostparams+json
Accept:
application/alto-endpointcost+json,application/alto-error+json
{
"cost-type": {"cost-mode" : "numerical",
"cost-metric" : "hopcount"},
"endpoints" : {
"srcs": [ "ipv4:192.0.2.2" ],
"dsts": [
"ipv4:192.0.2.89",
"ipv4:198.51.100.34",
"ipv6:2000::1:2345:6789:abcd"
]
}
}
HTTP/1.1 200 OK
Content-Length: TBA
Content-Type: application/alto-endpointcost+json
{
"meta": {
"cost type": {
"cost-mode": "numerical",
"cost-metric":"hopcount"}
}
},
"endpoint-cost-map": {
"ipv4:192.0.2.2": {
"ipv4:192.0.2.89" : 5,
"ipv4:198.51.100.34": 3,
"ipv6:2000::1:2345:6789:abcd" : 2,
}
}
}
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3.4.4. Cost-Context Specification Considerations
"nominal": Typically hop count does not have a nominal value.
"sla": Typically hop count does not have an SLA value.
"import": There can be multiple sources to import hop count such as
IGP routing protocols.
"estimation": The exact estimation method is out of the scope of this
document. It is RECOMMENDED that the "parameters" field of an
"estimation" hop count metric provides a link ("link") to a
description of the "estimation" method.
3.5. Cost Metric: Loss Rate (lossrate)
3.5.1. Base Identifier
The base identifier for this performance metric is "lossrate".
3.5.2. Value Representation
The metric value type is a single 'JSONNumber' type value conforming
to the number specification of [RFC8259] Section 6. The number MUST
be non-negative. The value represents the percentage of packet
losses.
3.5.3. Intended Semantics and Use
Intended Semantics: To specify spatial and temporal aggregated packet
loss rate from the specified source and the specified destination.
The spatial aggregation level is specified in the query context
(e.g., PID to PID, or endpoint to endpoint).
Use: This metric could be used as a cost metric constraint attribute
or as a returned cost metric in the response.
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Example 5: Loss rate value on source-destination endpoint pairs
POST /endpointcost/lookup HTTP/1.1
Host: alto.example.com
Content-Length: TBA
Content-Type: application/alto-endpointcostparams+json
Accept:
application/alto-endpointcost+json,application/alto-error+json
{
"cost-type": {"cost-mode" : "numerical",
"cost-metric" : "lossrate"
},
"endpoints" : {
"srcs": [ "ipv4:192.0.2.2" ],
"dsts": [
"ipv4:192.0.2.89",
"ipv4:198.51.100.34",
"ipv6:2000::1:2345:6789:abcd"
]
}
}
HTTP/1.1 200 OK
Content-Length: TBA
Content-Type: application/alto-endpointcost+json
{
"meta": {
"cost-type": {
"cost-mode": "numerical",
"cost-metric":"lossrate"
}
},
"endpoint-cost-map": {
"ipv4:192.0.2.2": {
"ipv4:192.0.2.89" : 0,
"ipv4:198.51.100.34": 0,
"ipv6:2000::1:2345:6789:abcd" : 0,
}
}
}
3.5.4. Cost-Context Specification Considerations
"nominal": Typically packet loss rate does not have a nominal value,
although some networks may specify zero losses.
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"sla": It is RECOMMENDED that the "parameters" field of an "sla"
packet loss rate provides a link ("link") to the SLA definition.
"import": There can be multiple sources to import packet loss rate.
If the import is from [RFC8571] (by using unidirectional link loss),
it is RECOMMENDED that "parameters" provides "protocol" as a field
and "RFC8571" as the value; see Section 3.1.4 for discussions on
summing up link metrics to obtain end-to-end metrics. If the import
is from the IPPM framework, it is recommended that "parameters"
provides "protocol" as a field and "ippm" as the value; see Section 4
of [I-D.ietf-ippm-initial-registry] for additional fields which can
be specified for "ippm" in "parameters".
"estimation": The exact estimation method is out of the scope of this
document. It is RECOMMENDED that the "parameters" field of an
"estimation" packet loss rate metric provides a link ("link") to a
description of the "estimation" method.
4. Bandwidth Performance Metrics
This section introduces three bandwidth related metrics. Given a
specified source to a specified destination, these metrics reflect
the volume of traffic that the network can carry from the source to
the destination.
4.1. Cost Metric: TCP Throughput (tput)
4.1.1. Base Identifier
The base identifier for this performance metric is "tput".
4.1.2. Value Representation
The metric value type is a single 'JSONNumber' type value conforming
to the number specification of [RFC8259] Section 6. The number MUST
be non-negative. The unit is bytes per second.
4.1.3. Intended Semantics and Use
Intended Semantics: To give the throughput of a TCP flow from the
specified source to the specified destination. The spatial
aggregation level is specified in the query context (e.g., PID to
PID, or endpoint to endpoint).
Use: This metric could be used as a cost metric constraint attribute
or as a returned cost metric in the response.
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Example 5: TCP throughput value on source-destination endpoint pairs
POST /endpointcost/lookup HTTP/1.1
Host: alto.example.com
Content-Length: TBA
Content-Type: application/alto-endpointcostparams+json
Accept:
application/alto-endpointcost+json,application/alto-error+json
{
"cost-type": {"cost-mode" : "numerical",
"cost-metric" : "tput"},
"endpoints" : {
"srcs": [ "ipv4:192.0.2.2" ],
"dsts": [
"ipv4:192.0.2.89",
"ipv4:198.51.100.34",
"ipv6:2000::1:2345:6789:abcd"
]
}
}
HTTP/1.1 200 OK
Content-Length: TBA
Content-Type: application/alto-endpointcost+json
{
"meta": {
"cost type": {
"cost-mode": "numerical",
"cost-metric":"tput"
}
}
"endpoint-cost-map": {
"ipv4:192.0.2.2": {
"ipv4:192.0.2.89" : 256000,
"ipv4:198.51.100.34": 128000,
"ipv6:2000::1:2345:6789:abcd" : 428000,
}
}
4.1.4. Cost-Context Specification Considerations
"nominal": Typically TCP throughput does not have a nominal value.
"sla": Typically TCP throughput does not have an SLA value.
"import": Typically there is not a routing protocol through which one
can import TCP throughput. If the import is from the IPPM framework,
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it is recommended that "parameters" provides "protocol" as a field
and "ippm" as the value; see Section 4 of [I-D.ietf-ippm-initial-
registry] for additional fields which can be specified for "ippm" in
"parameters".
"estimation": The exact estimation method is out of the scope of this
document. See [ProphetINFOCOM18] for a method to estimate TCP
throughput. It is RECOMMENDED that the "parameters" field of an
"estimation" TCP throughput metric provides a link ("link") to a
description of the "estimation" method.
4.2. Cost Metric: Residue Bandwidth
4.2.1. Base Identifier
The base identifier for this performance metric is "bw-residue".
4.2.2. Value Representation
The metric value type is a single 'JSONNumber' type value that is
non-negative. The unit of measurement is bytes per second.
4.2.3. Intended Semantics and Use
Intended Semantics: To specify spatial and temporal residual
bandwidth from the specified source and the specified destination.
The value is calculated by subtracting tunnel reservations from
Maximum Bandwidth (motivated from [RFC7810], Section 4.5.). The
spatial aggregation unit is specified in the query context (e.g., PID
to PID, or endpoint to endpoint).
Use: This metric could be used either as a cost metric constraint
attribute or as a returned cost metric in the response.
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Example 7: bw-residue value on source-destination endpoint pairs
POST/ endpointcost/lookup HTTP/1.1
Host: alto.example.com
Content-Length: TBA
Content-Type: application/alto-endpointcostparams+json
Accept:
application/alto-endpointcost+json,application/alto-error+json
{
"cost-type": { "cost-mode": "numerical",
"cost-metric": "bw-residue"},
"endpoints": {
"srcs": [ "ipv4 : 192.0.2.2" ],
"dsts": [
"ipv4:192.0.2.89",
"ipv4:198.51.100.34",
"ipv6:2000::1:2345:6789:abcd"
]
}
}
HTTP/1.1 200 OK
Content-Length: TBA
Content-Type: application/alto-endpointcost+json
{
"meta": {
"cost-type" {
"cost-mode": "numerical",
"cost-metric": "bw-residue"
}
},
"endpoint-cost-map" {
"ipv4:192.0.2.2" {
"ipv4:192.0.2.89" : 0,
"ipv4:198.51.100.34": 2000,
"ipv6:2000::1:2345:6789:abcd": 5000,
}
}
}
4.2.4. Cost-Context Specification Considerations
"nominal": Typically residue bandwidth does not have a nominal value.
"sla": Typically residue bandwidth does not have an "sla" value.
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"import": There can be multiple sources to import residue bandwidth.
If the import is from [RFC8571] (by using unidirectional residue
bandwidth), it is RECOMMENDED that "parameters" provides "protocol"
as a field and "RFC8571" as the value. The server should be
cognizant of issues when computing end-to-end summary statistics from
link statistics. For example, the min of the end-to-end path residue
bandwidth is the min of all links on the path.
"estimation": The exact estimation method is out of the scope of this
document. It is RECOMMENDED that the "parameters" field of an
"estimation" residue bandwidth metric provides a link ("link") to a
description of the "estimation" method.
4.3. Cost Metric: Maximum Reservable Bandwidth
4.3.1. Base Identifier
The base identifier for this performance metric is "bw-maxres".
4.3.2. Value Representation
The metric value type is a single 'JSONNumber' type value that is
non-negative. The unit of measurement is bytes per second.
4.3.3. Intended Semantics and Use
Intended Semantics: To specify spatial and temporal maximum
reservable bandwidth from the specified source to the specified
destination. The value is corresponding to the maximum bandwidth
that can be reserved (motivated from RFC 3630 Sec. 2.5.7.). The
spatial aggregation unit is specified in the query context (e.g., PID
to PID, or endpoint to endpoint).
Use: This metric could be used either as a cost metric constraint
attribute or as a returned cost metric in the response.
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Example 6: bw-maxres value on source-destination endpoint pairs
POST/ endpointcost/lookup HTTP/1.1
Host: alto.example.com
Content-Length: TBA
Content-Type: application/alto-endpointcostparams+json
Accept:
application/alto-endpointcost+json,application/alto-error+json
{
"cost-type" { "cost-mode": "numerical",
"cost-metric": "bw-maxres"},
"endpoints": {
"srcs": [ "ipv4 : 192.0.2.2" ],
"dsts": [
"ipv4:192.0.2.89",
"ipv4:198.51.100.34",
"ipv6:2000::1:2345:6789:abcd"
]
}
}
HTTP/1.1 200 OK
Content-Length: TBA
Content-Type: application/alto-endpointcost+json
{
"meta": {
"cost-type": {
"cost-mode": "numerical",
"cost-metric": "bw-maxres"
}
},
"endpoint-cost-map": {
"ipv4:192.0.2.2" {
"ipv4:192.0.2.89" : 0,
"ipv4:198.51.100.34": 2000,
"ipv6:2000::1:2345:6789:abcd": 5000,
}
}
}
4.3.4. Cost-Context Specification Considerations
"nominal": Typically maximum reservable bandwidth does not have a
nominal value.
"sla": Typically maximum reservable bandwidth does not have an "sla"
value.
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"import": There can be multiple sources to import maximum reservable
bandwidth. For example, Maximum reservable bandwidth is defined by
IS-IS/OSPF TE, and measures the reservable bandwidth between two
directly connected IS-IS neighbors or OSPF neighbors; see Section 3.5
of [RFC5305]. If the import is from [RFC8571] (by using
unidirectional maximum reservable bandwidth), it is RECOMMENDED that
"parameters" provides "protocol" as a field and "RFC8571" as the
value.
"estimation": The exact estimation method is out of the scope of this
document. It is RECOMMENDED that the "parameters" field of an
"estimation" maximum reservable bandwidth metric provides a link
("link") to a description of the "estimation" method.
5. Operational Considerations
The exact measurement infrastructure, measurement condition and
computation algorithms can vary from different networks, and are
outside the scope of this document. Both the ALTO server and the
ALTO clients, however, need to be cognizant of the operational issues
discussed below.
Also, the performance metrics specified in this document are similar,
in that they may use similar data sources and have similar issues in
their calculation. Hence, we specify common issues unless one metric
has its unique challenges.
5.1. Source Considerations
The addition of the "cost-source" field is to solve a key issue: An
ALTO server needs data sources to compute the cost metrics described
in this document and an ALTO client needs to know the data sources to
better interpret the values.
To avoid too fine-grained information, this document introduces
"cost-source" to indicate only the high-level type of data sources:
"estimation" or "sla", where "estimation" is a type of measurement
data source and "sla" is a type that is more based on policy.
For estimation, for example, the ALTO server may use log servers or
the OAM system as its data source [RFC7971]. In particular, the cost
metrics defined in this document can be computed using routing
systems as the data sources. Mechanisms defined in [RFC2681],
[RFC3393], [RFC7679], [RFC7680], [RFC3630], [RFC3784], [RFC7471],
[RFC7810], [RFC7752] and [I-D.ietf-idr-te-pm-bgp] that allow an ALTO
Server to retrieve and derive the necessary information to compute
the metrics that we describe in this document.
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5.2. Metric Timestamp Consideration
Despite the introduction of the additional cost-context information,
there is no built-in field to indicate the timestamps of the data
used to compute a metric. To indicate this attribute, the ALTO
server SHOULD return HTTP "Last-Modified", to indicate the freshness
of the data used to compute the performance metrics.
If the ALTO client obtains updates through an incremental update
mechanism (e.g., [ALTO SSE]), the client SHOULD assume that the
metric is computed using a snapshot at the time that is approximated
by the receiving time.
5.3. Backward Compatibility Considerations
One potential issue introduced by the optional "cost-source" field is
backward compatibility. Consider that an IRD which defines two cost-
types with the same "cost-mode" and "cost-metric", but one with
"cost-source" being "estimation" and the other being "sla". Then an
ALTO client that is not aware of the extension will not be able to
distinguish between these two types. A similar issue can arise even
with a single cost-type which has "cost-source" being "sla", but the
backward client will ignore this field and consider the metric
estimation.
To address this issue, the only defined "routingcost" metric can be
ONLY "estimation".
5.4. Computation Considerations
The metric values exposed by an ALTO server may result from
additional processing on measurements from data sources to compute
exposed metrics. This may involve data processing tasks such as
aggregating the results across multiple systems, removing outliers,
and creating additional statistics. There are two challenges on the
computation of ALTO performance metrics.
5.4.1. Configuration Parameters Considerations
Performance metrics often depend on configuration parameters. For
example, the value of packet loss rate depends on the measurement
interval and varies over time. To handle this issue, an ALTO server
may collect data on time periods covering the previous and current
time or only collect data on present time. The ALTO server may
further aggregate these data to provide an abstract and unified view
that can be more useful to applications. To make the ALTO client
better understand how to use these performance data, the ALTO server
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may provide the client with the validity period of the exposed metric
values.
5.4.2. Availability Considerations
Applications value information relating to bandwidth availability
whereas bandwidth related metrics can often be only measured at the
link level. This document specifies a set of link-level bandwidth
related values that may be exposed as such by an ALTO server. The
server may also expose other metrics derived from their aggregation
and having different levels of endpoint granularity, e.g., link
endpoints or session endpoints. The metric specifications may also
expose the utilized aggregation laws.
6. Security Considerations
The properties defined in this document present no security
considerations beyond those in Section 15 of the base ALTO
specification [RFC7285].
However concerns addressed in Sections "15.1 Authenticity and
Integrity of ALTO Information", "15.2 Potential Undesirable Guidance
from Authenticated ALTO Information" and "15.3 Confidentiality of
ALTO Information" remain of utmost importance. Indeed, TE
performance is a highly sensitive ISP information, therefore, sharing
TE metric values in numerical mode requires full mutual confidence
between the entities managing the ALTO Server and Client. Numerical
TE performance information will most likely be distributed by ALTO
Servers to Clients under strict and formal mutual trust agreements.
On the other hand, ALTO Clients must be cognizant on the risks
attached to such information that they would have acquired outside
formal conditions of mutual trust.
7. IANA Considerations
IANA has created and now maintains the "ALTO Cost Metric Registry",
listed in Section 14.2, Table 3 of [RFC7285]. This registry is
located at <http://www.iana.org/assignments/alto-protocol/alto-
protocol.xhtml#cost-metrics>. This document requests to add the
following entries to "ALTO Cost Metric Registry".
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+------------+--------------------+
| Identifier | Intended Semantics |
+------------+--------------------+
| delay-ow | See Section 3.1 |
| delay-rt | See Section 3.2 |
| delay-var | See Section 3.3 |
| hopcount | See Section 3.4 |
| lossrate | See Section 3.5 |
| tput | See Section 4.1 |
| bw-residue | See Section 4.2 |
| bw-maxres | See Section 4.3 |
+------------+--------------------+
This document requests the creation of the "ALTO Cost Source
Registry" with the following currently defined values:
+------------+-----------------------------+
| Identifier | Intended Semantics |
+------------+-----------------------------+
| nominal | Values in nominal cases |
| sla | Values reflecting service |
| | level agreement |
| import | Values from a given protocol|
| estimation | Values by estimation |
+------------+-----------------------------+
8. Acknowledgments
The authors of this document would also like to thank Brian Trammell,
Haizhou Du, Kai Gao, Lili Liu, Geng Li, Danny Alex Lachos Perez for
the reviews and comments. Young Lee is an author of an earlier
version of the document.
9. References
9.1. Normative References
[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>.
[RFC2679] Almes, G., Kalidindi, S., and M. Zekauskas, "A One-way
Delay Metric for IPPM", RFC 2679, DOI 10.17487/RFC2679,
September 1999, <https://www.rfc-editor.org/info/rfc2679>.
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[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>.
[RFC3393] Demichelis, C. and P. Chimento, "IP Packet Delay Variation
Metric for IP Performance Metrics (IPPM)", RFC 3393, DOI
10.17487/RFC3393, November 2002, <https://www.rfc-
editor.org/info/rfc3393>.
[RFC5305] Li, T. and H. Smit, "IS-IS Extensions for Traffic
Engineering", RFC 5305, DOI 10.17487/RFC5305, October
2008, <https://www.rfc-editor.org/info/rfc5305>.
[RFC6349] Constantine, B., Forget, G., Geib, R., and R. Schrage,
"Framework for TCP Throughput Testing", RFC 6349, DOI
10.17487/RFC6349, August 2011, <https://www.rfc-
editor.org/info/rfc6349>.
[RFC7285] Alimi, R., Ed., Penno, R., Ed., Yang, Y., Ed., Kiesel, S.,
Previdi, S., Roome, W., Shalunov, S., and R. Woundy,
"Application-Layer Traffic Optimization (ALTO) Protocol",
RFC 7285, DOI 10.17487/RFC7285, September 2014,
<https://www.rfc-editor.org/info/rfc7285>.
[RFC7810] Previdi, S., Ed., Giacalone, S., Ward, D., Drake, J., and
Q. Wu, "IS-IS Traffic Engineering (TE) Metric Extensions",
RFC 7810, DOI 10.17487/RFC7810, May 2016,
<https://www.rfc-editor.org/info/rfc7810>.
[RFC8259] Bray, T., Ed., "The JavaScript Object Notation (JSON) Data
Interchange Format", STD 90, RFC 8259, DOI 10.17487/
RFC8259, December 2017, <https://www.rfc-editor.org/info/
rfc8259>.
9.2. Informative References
[ProphetINFOCOM18]
Gao, K., Zhang, J., and YR. Yang, "Prophet: Fast, Accurate
Throughput Prediction with Reactive Flows", IEEE INFOCOM
2018 - IEEE Conference on Computer Communications 16-19
April 2018, 2018.
[RFC6390] Clark, A. and B. Claise, "Guidelines for Considering New
Performance Metric Development", BCP 170, RFC 6390, DOI
10.17487/RFC6390, October 2011, <https://www.rfc-
editor.org/info/rfc6390>.
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[RFC7971] Stiemerling, M., Kiesel, S., Scharf, M., Seidel, H., and
S. Previdi, "Application-Layer Traffic Optimization (ALTO)
Deployment Considerations", RFC 7971, DOI 10.17487/
RFC7971, October 2016, <https://www.rfc-editor.org/info/
rfc7971>.
Authors' Addresses
Qin Wu
Huawei
101 Software Avenue, Yuhua District
Nanjing, Jiangsu 210012
China
Email: bill.wu@huawei.com
Y. Richard Yang
Yale University
51 Prospect St
New Haven, CT 06520
USA
Email: yry@cs.yale.edu
Young Lee
Samsung
1700 Alma Drive, Suite 500
Plano, TX 75075
USA
Email: leeyoung@huawei.com
Dhruv Dhody
Huawei
Leela Palace
Bangalore, Karnataka 560008
INDIA
Email: dhruv.ietf@gmail.com
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Sabine Randriamasy
Nokia Bell Labs
Route de Villejust
Nozay 91460
FRANCE
Email: sabine.randriamasy@nokia-bell-labs.com
Luis Miguel Contreras Murillo
Telefonica
Email: luismiguel.contrerasmurillo@telefonica.com
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