Multi-Cost ALTO
draft-randriamasy-alto-multi-cost-05
The information below is for an old version of the document.
| Document | Type |
This is an older version of an Internet-Draft whose latest revision state is "Replaced".
|
|
|---|---|---|---|
| Authors | Sabine Randriamasy , Nico Schwan | ||
| Last updated | 2011-10-31 (Latest revision 2011-07-11) | ||
| Replaced by | draft-ietf-alto-multi-cost, RFC 8189 | ||
| RFC stream | (None) | ||
| Formats | |||
| Stream | Stream state | (No stream defined) | |
| Consensus boilerplate | Unknown | ||
| RFC Editor Note | (None) | ||
| IESG | IESG state | I-D Exists | |
| Telechat date | (None) | ||
| Responsible AD | (None) | ||
| Send notices to | (None) |
draft-randriamasy-alto-multi-cost-05
Network Working Group S. Randriamasy, Ed.
Internet-Draft N. Schwan
Intended status: Experimental Alcatel-Lucent Bell Labs
Expires: May 3, 2012 October 31, 2011
Multi-Cost ALTO
draft-randriamasy-alto-multi-cost-05
Abstract
IETF is designing a new service called ALTO (Application Layer
traffic Optimization) that includes a "Network Map Service", an
"Endpoint Cost Service" and an "Endpoint (EP) Ranking Service" and
thus incentives for application clients to connect to ISP preferred
Endpoints. These services provide a view of the Network Provider
(NP) topology to overlay clients.
The present draft proposes a light way to extend the information
provided by the current ALTO protocol. The purpose is to broaden the
possibilities of the Application Clients in two ways. Firstly it
proposes to include information on multiple cost types in a single
ALTO transaction, providing a better mapping of the Selected
Endpoints to needs of the growing diversity of Content Networking
Applications and to the network conditions. Secondly it proposes new
cost types, that are an abstraction of time-sensitive network
information as viewed by the Network Provider. All this also helps
producing a more robust choice when multiple Endpoints must be
selected.
There are 2 parts in this draft: the first part initiates protocol
extensions to support requests on multiple Cost Types in one single
transaction. These first extensions also integrate the discussions
within the ALTO Working Group. The second part proposes use cases
motivating further definitions of additional CostTypes and Cost
related attributes and capabilities.
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 RFC 2119 [RFC2119].
Status of this Memo
This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79.
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This Internet-Draft will expire on May 3, 2012.
Copyright Notice
Copyright (c) 2011 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
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the Trust Legal Provisions and are provided without warranty as
described in the Simplified BSD License.
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 5
2. Scope . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6
3. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 6
4. Proposed ALTO protocol updates for multi-cost transactions . . 7
4.1. Information Resources Directory . . . . . . . . . . . . . 8
4.1.1. Example Multi-Cost specific resources . . . . . . . . 8
4.2. Multi-Cost Map Service . . . . . . . . . . . . . . . . . . 10
4.2.1. Media Type . . . . . . . . . . . . . . . . . . . . . . 10
4.2.2. HTTP Method . . . . . . . . . . . . . . . . . . . . . 10
4.2.3. Input Parameters . . . . . . . . . . . . . . . . . . . 10
4.2.4. Capabilities . . . . . . . . . . . . . . . . . . . . . 10
4.2.5. Response . . . . . . . . . . . . . . . . . . . . . . . 11
4.2.6. Example . . . . . . . . . . . . . . . . . . . . . . . 13
4.3. Filtered Multi-Cost Map . . . . . . . . . . . . . . . . . 13
4.3.1. Media Type . . . . . . . . . . . . . . . . . . . . . . 14
4.3.2. HTTP Method . . . . . . . . . . . . . . . . . . . . . 14
4.3.3. Input Parameters . . . . . . . . . . . . . . . . . . . 14
4.3.4. Capabilities . . . . . . . . . . . . . . . . . . . . . 16
4.3.5. Response . . . . . . . . . . . . . . . . . . . . . . . 16
4.3.6. Example . . . . . . . . . . . . . . . . . . . . . . . 16
4.4. Endpoint Multi-Cost Service . . . . . . . . . . . . . . . 17
4.4.1. Endpoint Multi-Cost . . . . . . . . . . . . . . . . . 18
4.4.2. Media Type . . . . . . . . . . . . . . . . . . . . . . 18
4.4.3. HTTP Method . . . . . . . . . . . . . . . . . . . . . 18
4.4.4. Input Parameters . . . . . . . . . . . . . . . . . . . 18
4.4.5. Capabilities . . . . . . . . . . . . . . . . . . . . . 19
4.4.6. Response . . . . . . . . . . . . . . . . . . . . . . . 19
4.4.7. Example . . . . . . . . . . . . . . . . . . . . . . . 20
4.5. ALTO Status Codes for Multi-Cost ALTO . . . . . . . . . . 21
5. Use cases for further Cost Types and Endpoint Properties . . . 22
5.1. Delay Sensitive Overlay Applications . . . . . . . . . . . 22
5.2. CDN Surrogate Selection . . . . . . . . . . . . . . . . . 23
5.3. Bulk Data Transfer scheduling . . . . . . . . . . . . . . 24
6. Proposed additional Properties and Costs . . . . . . . . . . . 25
6.1. For further extensions: dynamic Costs . . . . . . . . . . 25
6.1.1. Path Occupation Cost and Endpointoccupationcost . . . 26
6.1.2. Dynamic Cost Attributes . . . . . . . . . . . . . . . 26
6.1.2.1. The dynamic Cost Mode . . . . . . . . . . . . . . 26
6.1.3. Proposed dynamic Cost Scope capability . . . . . . . 27
6.1.3.1. Example of time scope for a dynamic cost . . . . . 27
6.1.4. Example of dynamic information resources in the IRD . 27
6.1.4.1. Example of response with a "dynamic" cost . . . . 28
7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 29
7.1. Information for IANA on proposed Cost Types . . . . . . . 30
7.2. Information for IANA on proposed Endpoint Propeeries . . . 30
8. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 30
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9. References . . . . . . . . . . . . . . . . . . . . . . . . . . 31
9.1. Normative References . . . . . . . . . . . . . . . . . . . 31
9.2. Informative References . . . . . . . . . . . . . . . . . . 31
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 31
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1. Introduction
IETF is designing a new service called ALTO that provides guidance to
P2P applications, which have to select one or several hosts from a
set of candidates that are able to provide a desired resource. This
guidance shall be based on parameters that affect performance and
efficiency of the data transmission between the hosts, e.g., the
topological distance. The ultimate goal is to improve Quality of
Experience (QoE) in the application while reducing resource
consumption in the underlying network infrastructure. The ALTO
protocol conveys the Internet View from the perspective of a Provider
Network region that spans from a region to one or more Autonomous
System (AS). Together with this Network Map, it provides the
Provider determined Cost Map between locations of the Network Map.
Last, it provides the Ranking of Endpoints w.r.t. their routing cost.
The term Network Provider in this document includes both ISPs, who
provide means to transport the data and Content Delivery Network
(CDN) operators who care for the dissemination, persistent storage
and possibly identification of the best/closest content copy.
The last ALTO protocol draft see [ID-alto-protocol], gives the
possibility to query multiple Endpoint properties at once. On the
other hand, the Endpoint Cost service in its input specification
allows only one Cost Type and Cost mode per request. The ALTO
requirements draft, see [ID-ALTO-Requirements7] states in REQ.
ARv05-14: "The ALTO client protocol MUST support the usage of several
different rating criteria types". In the current protocol draft,
there is no specified way to get values for several Cost Types
simultaneously. Currently, the costs are provided in a scalar form,
one by one. So that an ALTO Client wanting information for several
Cost Types must request and receive a response as many times as
desired Cost Types.
Getting all costs in one single query/response transaction saves time
and ALTO traffic load, thus ressources, thus energy. Besides, vector
costs provide a robust and natural input to multi-variate path
computation as well as robust multi-variate selection multiple
Endpoints. Other savings in resources can be obtained by gathering
multiple Cost Types in the Cost map and Filtered Cost Map services.
Indeed, one Cost Map reporting on N Cost Types is less bulky than N
Cost Maps containing one Cost Type each. This is valuable for both
the storage of these maps and their transfer. Last, as it is most
likely that nowadays applications need information on several cost
types, having them gathered in one map will save time.
The ALTO Problem Statement, see [RFC5693] and the ALTO requirements
draft, see [RFC5693] stress that: "information that can change very
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rapidly, such as transport-layer congestion, is out of scope for an
ALTO service. Such information is better suited to be transferred
through an in-band technique at the transport layer instead", as
"ALTO is not an admission control system "and does not necessarily
know about the instant load of endpoints and links. However, non-
real time abstraction of performance oriented information is useful
for a reliable choice of candidate endpoints. In addition, given the
QoE requirements of nowadays and future Internet applications, more
and more NPs compute and store such information to optimize their
traffic. Besides specific ALTO servers can be specified for small
networks including mobile core networks, which have a smaller scale
and can afford and take advantage of using small time-scale network
information. Adding QoE-enabling metrics to the Network Provider
established routing cost could meet the interests of both the end
users and the Providers.
2. Scope
This draft generalizes the case of a P2P client to include the case
of a CDN client, a GRID application client and any Client having the
choice in several connection points for data or resource exchange.
To do so, it uses the term "Application Client" (AC).
This draft focuses on the use case where the ALTO client is embedded
in the Application Client or in some Application Endpoint tracker in
the network, such as a P2P tracker, a CDN location tracker or a cloud
computing orchestration system implemented in a logically centralized
management system.
It is assumed that Applications likely to use the ALTO service have a
choice in connection endpoints as it is the case for most of them.
The ALTO service is managed by the Network Provider and reflects its
preferences for the choice of endpoints. The NP defines in
particular the network map, the routing cost among Network Locations,
and which ALTO services are available at a given ALTO server.
3. Terminology
Endpoint (EP): can be a Peer, a CDN storage location, a Party in a
resource sharing swarm such as a computation Grid or an online multi-
party game.
Endpoint Discovery (EP Discovery) : this term covers the different
types of processes used to discover different types of endpoints.
Network Service Provider (NSP): includes both ISPs, who provide means
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to transport the data and Content Delivery Network (CDN) who care for
the dissemination, persistent storage and possibly identification of
the best/closest content copy.
ALTO transaction: a request/response exchange between an ALTO Client
and an ALTO Server.
Application Client (AC): this term generalizes the case of a P2P
client to include the case of a CDN client and of any Client having
the choice in several connection points for data or resource
exchange.
4. Proposed ALTO protocol updates for multi-cost transactions
This section proposes updates of the ALTO protocol to support Multi
Cost ALTO Services or provide additional ALTO information. It
integrates discussions on the ALTO mailing list.
If an ALTO client desires several Cost Types, instead of placing as
many requests as costs, it may request and receive all the desired
cost types in one single transaction.
The ALTO server then, provided it supports the requested Cost Types,
and provided it supports multi-cost ALTO transactions, sends one
single response where for each {source, destination} pair, the cost
values are arranged in a vector, where each component corresponds to
a specified Cost Type. The correspondence between the components and
the cost types MUST be indicated either in the ALTO response or
available via the resource directory.
The following ALTO services get corresponding services with Multi-
Cost extensions:
o Information Resources Directory: extended with multi-cost related
URIs and associated capabilities.
o Cost Map Service: extended with the Multi-Cost Map Service,
o Cost Map Filtering Service: extended with the Multi-Cost Map
Filtering Service,
o Endpoint Cost Lookup Service: extended with the Endpoint Multi-
Cost Lookup Service.
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4.1. Information Resources Directory
When the ALTO server supports the provision of information on
multiple costs in a single transactions, the Information Resources
will list the corresponding resources. The media type and encoding
specificarions remain the same as in the current ALTO protocol.
4.1.1. Example Multi-Cost specific resources
The following is an example Information Resource Directory returned
by an ALTO Server and containing Multi-Cost specific services: the
Multi-Cost Map Service, Filtered Multi-Cost Map and the Endpoint
Multi-Cost Service. It is assumed that the IRD contains usual ALTO
Services as described in the example IRD of the current ALTO
protocol. In this example, the ALTO Server provides additional
Multi-Cost Services in a specific folder of "alto.example.com" called
"multi". This folder contains the Multi-Cost Maps, Filtered Multi-
Cost Maps as well as the Endpoint Multi-Cost Service.
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GET /directory HTTP/1.1
Host: alto.example.com
Accept: application/alto-directory+json,application/alto-error+json
HTTP/1.1 200 OK
Content-Length: [TODO]
Content-Type: application/alto-directory+json
{
"resources" : [
{
.....
Usual ALTO "single-cost" Services as described in ALTO Protocol
.....
}, {
"uri" : "http://alto.example.com/multi/maps",
"media-types" : ["application/alto-multicostmap+json"],
"accepts" : ["application/alto-multicostmapfilter+json"],
"capabilities" : {
"cost-constraints" : true,
"cost-types" : [ "routingcost", "hopcount" ],
"cost-modes" : [ "numerical", "numerical" ]
}
}, {
"uri" : "http://alto.example.com/multi/endpointmulticost/lookup",
"media-types" : [ "application/alto-endpointmulticost+json" ],
"accepts" : [ "application/alto-endpointmulticostparams+json" ],
"capabilities" : {
"cost-constraints" : true,
"cost-types" : [ "routingcost", "hopcount" ],
"cost-modes" : [ "numerical", "numerical" ]
}
}, {
"uri" : "http://custom.alto.example.com/multi/endpointmulticost/lookup",
"media-types" : [ "application/alto-endpointmulticost+json" ],
"accepts" : [ "application/alto-endpointmulticostparams+json" ],
}
]
}
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4.2. Multi-Cost Map Service
This section introduces a new media-type for the Multi-Cost map. For
each source/destination pair of PIDs, it provides the value of the
different Cost Type supported for the Multi-cost map, in the same
order as in the list of cost-types specified in the capabilities.
A Multi-Cost Map MAY be provided by an ALTO Server.
This resource MUST be provided for at least the 'routingcost' Cost
Type with the 'numerical' Cost Mode. It is assumed that an ALTO
Server supporting multi-cost maps supports the 'numerical' Cost Mode
for all Cost Types encoded in the 'JSONnumber' type.
Note that the capabilities specify implicitly the order in which the
different Cost Type values will be listed in the Cost Map.
The Cost Type values in the responses are encoded in with a JSONArray
of cost values for the different required cost types.
Note also that contrary to the Cost Map service, the returned Multi
Cost Map is not required to include the required Path Costs for each
pair of Source and Destination PID known to the ALTO Server. The
reason is that for a given source/destination pair, the ALTO Server
may not have the information on certain Cost Types. As a
consequence, contrary to the Cost Map service, the Multi-Cost Map
service introduces a particular value that unambiguously indicates
that the information is not available. This way, the order in which
the cost values are provided for a source/destination pair is
unambiguous.
4.2.1. Media Type
The media type is "application/alto-multicostmap+json".
4.2.2. HTTP Method
This resource is requested using the HTTP GET method.
4.2.3. Input Parameters
None.
4.2.4. Capabilities
This resource may be defined for multiple Cost Types and Cost Modes.
The capabilities of an ALTO Server URI providing this resource are
defined by a JSON Object of type MultiCostMapCapability:
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object {
CostType cost-types<1..*>;
CostMode cost-modes<0..*>;
} MultiCostMapCapability;
with members
cost-types The Cost Types ( Section 5.1.1) supported by the
corresponding URI. This member MUST at least include the
type 'routingcost'. The order in which the Cost Type values
for a source/destination pair will be listed in the Multi-Cost
Map provided to an ALTO Client MUST be the order in which these
Cost Types are listed in this member.
cost-modes The Cost Mode ( Section 5.1.2) supported for each of
the supported Cost Types listed in the "cost-types".
For Cost types encoded with the 'JSONnumber' type, the
Cost Mode MUST be numerical. It will be interpreted as such
if this member is not present.
An ALTO Server MUST support all of the Cost Types listed here for
each of the listed Cost Modes. Note that an ALTO Server may provide
multiple Cost Map Information Resources, each with different
capabilities.
An ALTO Server supporting the Multi-Cost Map service, MUST support
the Cost mode 'numerical' for all supported Cost Types encoded with
the 'JSONnumber' type. It also MUST list the Cost Type values
associated to a source/destination pair in the same order as in the
"cost-types" member of the capabilities specified the Multi-Cost Map
resource.
4.2.5. Response
The returned InfoResourceEntity object has "data" member of type
InfoResourceMultiCostMap:
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object DstMultiCosts {
JSONArray [PIDName];
...
};
object {
DstMultiCosts [PIDName]<0..*>;
...
} MultiCostMapData;
object {
CostType cost-type<1..*>;
CostMode cost-mode<1..*>;
JSONString map-vtag;
MultiCostMapData map;
} InfoResourceMultiCostMap;
with members:
cost-mode Cost Mode (Section 5.1.2) used in the Cost Map where each
member of the cost-mode list is the Cost Mode provided for the
Cost Type at the same place in the list.
cost-type Cost Type (Section 5.1.1) used in the Multi Cost Map.
map-vtag The Version Tag (Section 5.3) of the Network Map used to
generate the Cost Map.
map The Multi Cost Map data itself.
MultiCostMapData is a JSON object with each member representing a single
Source PID; the name for a member is the PIDName string identifying
the corresponding Source PID. For each Source PID, a DstMultiCosts
object denotes the associated multiple costs to a set of destination
PIDs (Section 5.2); the name for each member in the object is the PIDName
string identifying the corresponding Destination PID. DstMultiCosts are
listed in the same order as in the 'cost-type' array.
The returned Cost Map MUST include the required Path Costs for each
pair of Source and Destination PID for which this information is
available.
The members cost-mode and cost-type MUST be arrays with the same
number of elements.
Note also that the Multi-Cost Map service needs a particular value
that unambiguously indicates that the information is not available.
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As an example this value is referred here to as NAv for "Not
available". Note that the type of NAv still needs to be specified:
preferably a numerical value for numerical costs that unambiguously
means: "not available" and can distiguished from "infinite" or
"invalid something" or any "pathological" value.
4.2.6. Example
This example illustrates a 'static' multi-cost' ALTO trasaction,
where the utilized cost-types all have 'static' values. We assume
here that the Cost Types available at the ALTO Server are
"routingcost" and "hopcount" and the 'numerical' mode is available
for both of them. The "routingcost" may be based on monetary
considerations where as the "hopcount" is used to account on the path
delay.
GET /multicostmap/num HTTP/1.1
Host: alto.example.com
Accept: application/alto-multicostmap+json,application/alto-error+json
HTTP/1.1 200 OK
Content-Length: [TODO]
Content-Type: application/alto-multicostmap+json
{
"meta" : {},
"data" : {
"cost-mode" : ["numerical", "numerical"]
"cost-type" : ["routingcost", "hopcount"]
"map-vtag" : "1266506139",
"map" : {
"PID1": { "PID1": [1,6], "PID2": [5,23], "PID3": [10,5] },
"PID2": { "PID1": [5,5], "PID2": [1,11], "PID3": [15,9] },
"PID3": { "PID1": [20,12], "PID2": [15,1], "PID3": [1,18] }
}
}
}
4.3. Filtered Multi-Cost Map
A Multi-Cost Map may reach a huge volume and also, an Application
Client assisted by the ALTO Client does not necessarily need
information on all the Cost Types for all the source/destination
pairs of PIDs.
Therefore, applications may more likely use Cost Map information
filtered w.r.t. the Cost types as well as the source/destination
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pairs of PIDs. This section specifies filtered Multi-Cost Maps.
A Filtered Cost Map is a Cost Map Information Resource (Section
7.7.2.2) for which an ALTO Client may supply additional parameters
limiting the scope of the resulting Cost Map. A Filtered Cost Map MAY
be provided by an ALTO Server.
4.3.1. Media Type
The media type is "application/alto-multicostmap+json", see Section
4.2.1 of this draft.
4.3.2. HTTP Method
This resource is requested using the HTTP POST method
4.3.3. Input Parameters
Input parameters are supplied in the entity body of the POST request.
This document specifies the input parameters with a data format
indicated by the media type "application/
alto-multicostmapfilter+json", which is a JSON Object of type
ReqFilteredCostMap, where:
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object {
PIDName srcs<0..*>;
PIDName dsts<0..*>;
} PIDFilter;
object {
CostType cost-type<0..*>;
CostMode cost-mode<0..*>;
JSONString constraints<0..*>; [OPTIONAL]
PIDFilter pids; [OPTIONAL]
} ReqFilteredMultiCostMap;
with members:
cost-type The Cost Type ( Section 5.1.1) for the returned costs.
Each listed cost-type MUST be one of the supported Cost Types indicated
in this resource's capabilities ( Section 7.7.3.2.4).
cost-mode The Cost Mode ( Section 5.1.2) for each of the returned cost-types.
For Cost types encoded with the 'JSONnumber' type, the
Cost Mode MUST be numerical. It will be interpreted as such
if this member is not present.
constraints Defines a list of additional constraints on which
elements of the Cost Map are returned. This parameter MUST NOT be
specified if this resource's capabilities ( Section 7.7.3.2.4)
indicate that constraint support is not available. A constraint
contains two entities separated by whitespace: (1) an operator
either 'gt' for greater than or 'lt' for less than (2) a target
numerical cost. The numerical cost is a number that MUST be
defined in the same units as the Cost Type indicated by the cost-
type parameter. ALTO Servers SHOULD use at least IEEE 754 double-
precision floating point [IEEE.754.2008] to store the numerical
cost, and SHOULD perform internal computations using double-
precision floating-point arithmetic. If multiple 'constraint'
parameters are specified, they are interpreted as being related to
each other with a logical AND.
pids A list of Source PIDs and a list of Destination PIDs for which
Path Costs are to be returned. If a list is empty, the ALTO
Server MUST interpret it as the full set of currently-defined
PIDs. The ALTO Server MUST interpret entries appearing in a list
multiple times as if they appeared only once. If the "pids"
member is not present, both lists MUST be interpreted by the ALTO
Server as containing the full set of currently-defined PIDs.
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4.3.4. Capabilities
The URI providing this resource supports all capabilities documented
in Section 7.7.2.2.4 (with identical semantics), plus additional
capabilities. In particular, the capabilities are defined by a JSON
object of type FilteredMultiCostMapCapability:
object {
CostMode cost-modes<0..*>;
CostType cost-types<0..*>;
JSONBool cost-constraints;
} FilteredMultiCostMapCapability;
with members:
cost-modes See Section 4.2.5 of this MC draft
cost-types See Section 4.2.5 of this MC draft
cost-constraints If true, then the ALTO Server allows cost
constraints to be included in requests to the corresponding URI.
If not present, this member MUST be interpreted as if it specified
false.
4.3.5. Response
See Section of this draft for the format. The returned Cost Map MUST
NOT contain any source/destination pair that was not indicated
(implicitly or explicitly) in the input parameters. If the input
parameters contain a PID name that is not currently defined by the
ALTO Server, the ALTO Server MUST behave as if the PID did not appear
in the input parameters. If any constraints are specified, Source/
Destination pairs that do for which the Path Costs do not meet the
constraints MUST NOT be included in the returned Cost Map. If no
constraints were specified, then all Path Costs are assumed to meet
the constraints.
4.3.6. Example
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POST multi/multicostmap/filtered HTTP/1.1
Host: alto.example.com
Content-Type: application/alto-multicostmapfilter+json
Accept: application/alto-multicostmap+json,application/alto-error+json
{
"cost-mode" : "numerical", "numerical"],
"cost-type" : "routingcost", "hopcount"],
"pids" : {
"srcs" : [ "PID1" ],
"dsts" : [ "PID1", "PID2", "PID3" ]
}
}
HTTP/1.1 200 OK
Content-Length: [TODO]
Content-Type: application/alto-costmap+json
{
"meta" : {},
"data" : {
"cost-mode" : ["numerical", "numerical"],
"cost-type" : ["routingcost", "hopcount"],
"map-vtag" : "1266506139",
"map" : {
"PID1": { "PID1": [1,6], "PID2": [5,23], "PID3": [10,5] }
}
}
}
4.4. Endpoint Multi-Cost Service
The Endpoint Multi-Cost Service provides information about several
costs between individual Endpoints.
This service does not allow lists of Endpoint prefixes (and
addresses, as a special case) to be ranked (ordered) by an ALTO
Server, as firstly the costs encoded with the JSONnumber 'type' are
provided in the numerical Mode and secondly the choice among various
existing methods to rank Endpoints upon multiple costs (criteria) is
out of scope of this protocol and in the responsability of the
Application Client using the ALTO Endpoint Multi-Cost information.
However common sense lead to warn that a necessary condition for
methods that rank vectors to be reliable is that the components
(costs) of the processed vectors be numerical Cost Mode.
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This Service introduces a new media type to define the service and
the input parameters.
4.4.1. Endpoint Multi-Cost
The Endpoint Multi-Cost resource provides information about multiple
costs between individual endpoints.
This service MAY be provided by an ALTO Server. If it is provided.
It is important to note that although this resource allows an ALTO
Server to reveal costs between individual endpoints, an ALTO Server
is not required to do so. A simple alternative would be to compute
the cost between two endpoints as the cost between the PIDs
corresponding to the endpoints +++ if this service is available for
the requested Cost Types +++ . See Section 12.1 for additional
details.
4.4.2. Media Type
The media type is "application/alto-endpointmulticost+json".
4.4.3. HTTP Method
This resource is requested using the HTTP POST method
4.4.4. Input Parameters
Input parameters are supplied in the entity body of the POST request.
This document specifies input parameters with a data format indicated
by media type "application/alto-endpointmulticostparams+json", which
is a JSON Object of type ReqEndpointMultiCostMap:
object {
TypedEndpointAddr srcs<0..*>; [OPTIONAL]
TypedEndpointAddr dsts<1..*>;
} EndpointFilter;
object{
CostType cost-type<0..*>;
CostMode cost-mode<0..*>;
JSONString constraints; [OPTIONAL]
EndpointFilter endpoints;
} ReqEndpointMultiCostMap;
with members:
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cost-mode The Cost Mode ( Section 5.1.2) to use for returne costs that
are encoded with the 'JSONnumber' type. For Multi-Cost requests
this Cost Mode MUST be numerical for any Cost Type encoded with
the 'JSONnumber' type, provided that the Cost Mode 'numerical'
is available for this Cost Type. Remember (Section 5.1.2) that
ALTO Clients SHOULD be cognizant of operations applicable to different
Cost Modes.
cost-type The Cost Type ( Section 5.1.1) to use for returned costs.
All the listed the Cost Types MUST be indicated in this
resource's capabilities ( Section 7.7.5.1.4).
constraints Defined equivalently to the "constraints" input parameter
of a Filtered Multi Cost Map (see Section 7.7.3.2).
endpoints A list of Source Endpoints and Destination Endpoints for
which Path Costs are to be returned. If the list of Source Endpoints
is empty (or not included), the ALTO Server MUST interpret it as if
it contained the Endpoint Address corresponding to the client IP
address from the incoming connection (see Section 10.3 for discussion
and considerations regarding this mode). The list of destination
Endpoints MUST NOT be empty. The ALTO Server MUST interpret entries
appearing multiple times in a list as if they appeared only once.
4.4.5. Capabilities
See section 4.3.4 of this draft.
4.4.6. Response
The returned InfoResourceEntity object has "data" member equal to
InfoResourceEndpointMultiCostMap, where:
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object EndpointDstMultiCosts {
JSONArray [TypedEndpointAddr];
...
};
object {
EndpointDstMultiCosts [TypedEndpointAddr]<0..*>;
...
} EndpointMultiCostMapData;
object {
CostMode cost-mode<0..*>;
CostType cost-type<0..*>;
EndpointMultiCostMapData map;
} InfoResourceEndpointMultiCostMap;
InfoResourceEndpointMultiCostMap has members:
cost-type<0..*> The Cost Types used in the returned Cost Map.
cost-mode<0..*> The Cost Mode for each of the Cost Types used in the returned Cost Map.
map The Endpoint Multi-Cost Map data itself.
EndpointMultiCostMapData is a JSON object with each member representing a
single Source Endpoint specified in the input parameters; the name
for a member is the TypedEndpointAddr string identifying the
corresponding Source Endpoint. For each Source Endpoint, a
EndpointDstMultiCosts object denotes the cost vector associated to each
Destination Endpoint specified in the input parameters; the name for
each member in the object is the TypedEndpointAddr string identifying
the corresponding Destination Endpoint.
4.4.7. Example
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POST /endpointcost/lookup HTTP/1.1
Host: alto.example.com
Content-Length: [TODO]
Content-Type: application/alto-endpointmulticostparams+json
Accept: application/alto-endpointmulticost+json,application/alto-error+json
{
"cost-type" : ["routingcost", "hopcount"],
"cost-mode" : ["numerical", "numerical"],
"endpoints" : {
"srcs": [ "ipv4:192.0.2.2" ],
"dsts": [
"ipv4:192.0.2.89",
"ipv4:198.51.100.34",
"ipv4:203.0.113.45"
]
}
}
HTTP/1.1 200 OK
Content-Length: [TODO]
Content-Type: application/alto-endpointmulticost+json
{
"meta" : {},
"data" : {
"cost-type" : ["routingcost", "hopcount"],
"cost-mode" : ["numerical", "numerical"],
"map" : {
"ipv4:192.0.2.2": {
"ipv4:192.0.2.89" : [1, 7],
"ipv4:198.51.100.34" : [2, 4],
"ipv4:203.0.113.45" : [3, 2]
}
}
}
}
4.5. ALTO Status Codes for Multi-Cost ALTO
If the Multi-cost Service is not supported for either the Cost Map or
the Endpoint Service, then the ALTO server sends an ALTO status code
7 corresponding to HTTP status code 501 indicating "Invalid cost
structure". The ALTO client may then needs to place as many requests
as needed Cost Types, and the ALTO server sends as many cost maps or
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EP cost as needed.
To the attribute Cost Mode in S.5.1 should be associated a rule
stipulating that when multiple cost types are requested, then the
requested Cost Mode SHOULD be numerical.
5. Use cases for further Cost Types and Endpoint Properties
The current ALTO protocol [ID-alto-protocol] specification requests
the creation of two registries maintained by IANA. The ALTO Cost
Type registry ensures that the Cost Types that are represented by an
ALTO Cost Map are unique identifiers, and it further contains
references to the semantics of the Cost Type. The current
specification registers 'routingcost' as a generic measure for
routing traffic from a source to a destination. In a similar way the
ALTO Endpoint Property Registry ensures uniqueness of ALTO Endpoint
Property identifiers and provides references to particular semantics
of the allocated Enpoint Properties. Currently the 'pid' identifier
is registered, which serves as an identifier that allows aggregation
of network endpoints into network regions. Both registries accept
new entries after Expert Review [[ID-alto-protocol]]. New entries
are requested to be conform to the respective syntactical
requirements, and must include information about the new identifier,
the intended semantics as well as security considerations.
The current protocol specification concentrates on the basic use case
of optimizing routing costs in NSPs networks. Upcoming use cases
however will require both, new Cost Types and new Endpoint
Properties. The goal of this section is to describe further forward
looking use case scenarios that are likely to benefit from ALTO, and,
in future iterations, to convey new Cost Types and Endpoint
Properties that are likely to be beneficial for ALTO clients in these
scenarios.
5.1. Delay Sensitive Overlay Applications
The ALTO working group has been created to allow P2P applications and
NSPs a mutual cooperation, in particular because P2P bulk file-
transfer applications have created a huge amount of intra-domain and
congestion on low-speed uplink traffic. By aligning overlay
topologies according to the 'routingcost' of the underlying network
both layers are expected to benefit in terms of reduced costs and
improved Quality-of-Experience.
However other types of overlay applications might benefit from a
different set of path metrics. In particular for real-time sensitive
applications, such as gaming, interactive video conferencing or
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medical services, creating an overlay topology with respect to a
minimized delay is preferable. However it is very hard for a NSP to
give accurate guidance for this kind of realtime information, instead
probing through end-to-end measurements on the application layer has
proven to be the superior mechanism. Still, a NSP might give some
guidance to the overlay application, for example by providing
statistically preferable paths with respect to the time of a day.
Also static information like hopcount can be seen as an indicator for
the delay that can be expected. In the following iterations this
draft will thus analyse which metrics can realistically be provided
through ALTO to give delay sensitive applications guidance for peer
selection.
5.2. CDN Surrogate Selection
A second use case is motivated through draft
[draft-jenkins-alto-cdn-use-cases-01]. The request router in today's
CDNs makes a decision about to which surrogate or cache node a
content request should be forwarded to. Typically this decision is
based on locality aspects, i.e. the surrogate node which is closest
to the client is preferred by the request router. An ALTO server
hereby is one promising option to allow NSPs to give guidance to the
CDN about which cache node would be preferable according to the view
of the network by the 'routingcost' Cost Type. Providing this kind
of information is in particular important as one trend is to place
cache nodes deeper into the network (i.e., closer to the end user),
which results in the need for finer grained information.
While distance today is the predominant metric used for routing
decisions, other metrics might allow sophisticated request routing
strategies. For example the load a cache node sees in terms of CPU
utilization, memory usage or bandwidth utilization might influence
routing decisions for load-balancing reasons. There exist numerous
ways of gathering and feeding this kind of information into the
request routing mechanism.
Typically, information reporting on the occupation of a cache could
be based on:
o an Endpoint Property called : "EPCapacity" and reflecting the
nominal capacity of this endpoint. This capacity could be
splitted in:
* EP Nominal Memory : denoting the nominal storage capacity
* EP Nominal Bandwidth: denoting the computation resources of the
Endpoint.
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o an Endpoint Cost called: "EP occupied Capacity" and reflecting the
currently available resources wrt their nominal capacity and
splitted in the same way as for the EP Capacity:
* EP Occupied Memory: denoting the remaining storage capacity,
* EP Occupied Bandwidth: denoting the remaining computation
resources.
As ALTO is likely to become a standardized interface to provide
network topology information, for simplicity other information that
is used by a request router could be provided by the ALTO server as
well. In the next iterations of this draft we will analyse which of
these metrics is suitable to be provided as Cost Type or Endpoint
Property for the use case of CDN Surrogate Selection and propose to
register them in the respective registries.
5.3. Bulk Data Transfer scheduling
Applications like Facebook or YouTube rely on data replication across
multiple sites for several reasons, such as offloading the core
network or increasing user experience through short latency.
As content is generated constantly data also needs to be replicated
across the various locations of a CDN provider, leading to bulk data
transfers between datacenters. Scheduling these data transfers is a
non-trivial task as the transfer should not infer with the user peak
demand to avoid degradation of user experience and to decrease
billing costs for the datacenter operator by leveraging off-peak
hours for the transfer. This peak demand typically follows a diurnal
pattern according to the geographic region of the datacenter. One
precondition to schedule transfers however is to have a good
knowledge about the demand and link utilization patterns between the
different datacenters and networks. Provisioning this data gets
increasingly complex with the number of CDN nodes and in particular
the number of datacenter operators that are involved. ALTO can
provide time sensitive utilization maps through a dedicated service
to allow CDN operators a mutual scheduling of such data transfers
across administrative domains, which becomes even more significant
through the CDNi protocol.
Another use case that stresses the need for multi-timeframe
information is the one of private users or user groups having
limitations in their connectivity either in time or resources or
both. These kind of users definitely need to plan their data
transfers to and from various locations an be sure to optimize for
example the 'routingcost' jointly with some 'pathoccupationcost' and
possibly the 'hopcount'. These users often have very poor means to
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have any information on the network that may provide them some
guidance and the ALTO protocol could greatly help them while
optimizing traffic on networks that face continuous resources and/or
connectivity challenges.
In the next iteration of this draft we plan specify a multi-timeframe
map service for ALTO to allow the targeted scheduling of data
transfers between datacenter locations or other types of locations.
6. Proposed additional Properties and Costs
This section proposes further extensions on new Costs Types, to be
discussed in the WG.
6.1. For further extensions: dynamic Costs
It is agreed in the ALTO requirements that: "information that can
change very rapidly, such as transport-layer congestion, is out of
scope for an ALTO service. Such information is better suited to be
transferred through an in-band technique at the transport layer
instead". However NP managing ALTO Servers as well as Application
Client using ALTO information have common interests to use some
information on time (or space) varying information that is not
provided in real time, which is neither desirable nor feasible, but
rather a synthetis of such information. Such information is made
available for ALTO Servers in order to reflect how the NP wishes the
information to be used by the Applicaton Client.
One example of such information is the path bandwidth. This can be
captured in real time by end systems, in terms of transmission rate.
On the other hand, the NSP can formulate preferences on given paths,
at given time periods on given time scales.
One way for the NSP to provide guidance on highly dynamic network
state information such as delay and load while preserving
confidentiality and moderating processing load, is to provide them in
a synthetic or abstract form, for example as a numerical indicator.
It is important to have the possibility to reflect that the provided
values are applicable for a given time period, for example busy hours
or days, and are subject to changes over time. Also, how the NP has
evaluated the cost associated to a given network state information is
out of scope ot the ALTO protocol.
The usage of a time related cost is more proactive in that it can be
used like a "time table" to figure out the best time to schedule data
transfer and also anticipate predictable events including predictable
flash crowds. The time-related information is not necessarily
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historical and statistic. This is why the proposed time-sensitive
Costs should be viewed as synthetic or as abstraction of real
measurements rather than as statistics.
6.1.1. Path Occupation Cost and Endpointoccupationcost
The 'pathoccupationcost' can be used to reflect the NP view on the
utilized path bandwidth at given time slots of given timeframes. For
example, during daytime in the PC time zone, or between hh/mm and
hh/mm in another time zone.
A Cost metric called 'endpointoccupationcost' and that accounts for
the computation resources usage can be provided with the "dynamic"
mode as well with a similar time scope updated for example with the
knowledge of the NSP operating the CDN.
Both of these metrics are encoded with the 'JSONNumber' type.
Their optimal value is their minimal value.
They should also be provided in the numerical mode, that is as one
single value, if requested so by the ALTO Client. This could be the
case for an ALTO Server providing values at a short time scale (e.g.
some minutes), or in the opposite, providing a timeless cost.
6.1.2. Dynamic Cost Attributes
For further extensions, specifications around "dynamic" costs are
proposed and will be completed in further versions of this draft.
6.1.2.1. The dynamic Cost Mode
The "dynamic" mode applies to Costs that are eligible for the
"numerical" Cost Mode and can also be expressed as such. In that
sense, the "dynamic" mode is an extension of the "numerical" mode.
Example are "pathoccupationcost" and "pathlosscost" that respectively
report on the occupied bandwidth and packet loss on a path.
Other Cost Types such as JSONBool could also claim the "dynamic"
mode, as states may be "true" or "false" depending on given periods.
To stick to the target usage of Costs which is to be integrated in
some evaluation process, an alternative could be to assign a
numerical value to boolean costs and carefully map "true" and "false"
with values '0' and '1'.
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6.1.3. Proposed dynamic Cost Scope capability
To ensure that the Application Client uses the NP provided
information on dynamic Costs in an inambuguous way, a capability
called Cost Scope is introduced here, to report on the validity of
the "dynamic" cost values. This draft focuses on the time related
scope. Indeed, one may as well imagine some costs proposed in the
future that could also be scoped w.r.t. space.
o Unit: ranging from "seconds" to "year", expresses the granularity
of the information,
o Size: the scope of the dynamic cost, that is the number of units
of the dynamic cost sample,
o Reference time zone,
o Begin: the index of the first unit in the sample,
o Next update: the date at which the sample will be re-computed,
o Last update: the last re-computation day.
Attributes 'Last update 'and 'Next update' report on the update
frequency and age of the information.
6.1.3.1. Example of time scope for a dynamic cost
An example is: a metric called 'pathoccupationcost' (POC for short)
is computed with a granularity of 2 hours, starting a 0h00, for 24
hours, with reference time GMT. The goal is to enable applications
to see which time intervals in a day are the most favorable to
operate.
6.1.4. Example of dynamic information resources in the IRD
The example IRD given in Section 4.1.1 includes an URI called
"http://custom.alto.example.com/multi/endpointmulticost/lookup", in
which the ALTO Server provides additional Mutliple Endpoint Costs
including a Cost called "pathoccupationcost" for which the Cost Mode
is "dynamic". This resource is accessible with other costs, via a
separate subdomain called "custom.alto.example.com". The Endpoint
Costs available via this subdomain are the "hopcount", "routingcost"
and "pathoccupationcost" Cost Types, with the two first ones in the
"numerical" Cost Mode and "pathoccupationcost" in the "dynamic" cost
mode.
An ALTO Client can discover the services available by
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"custom.alto.example.com" by successfully performing an OPTIONS
request to "http://custom.alto.example.com/multi/endpointmulticost".
OPTIONS /multi/endpointmulticost HTTP/1.1
Host: custom.alto.example.com
Accept: application/alto-directory+json,application/alto-error+json
HTTP/1.1 200 OK
Content-Length: [TODO]
Content-Type: application/alto-directory+json
{
"resources" : [
{
"uri" : "http://custom.alto.example.com/multi/endpointmulticost",
"media-types" : [ "application/alto-endpointmulticost+json" ],
"accepts" : [ "application/alto-endpointmulticostparams+json" ],
"capabilities" : {
"cost-constraints" : true,
"cost-modes" : [ "numerical", "numerical", "dynamic" ],
"cost-types" : [ "routingcost", "hopcount", "pathoccupationcost" ],
"cost-scope": [ "permanent", "permanent",
{"unit": "hour", "size": 24, "begin": 0,
"time zone": "GMT",
"lastupdate": mm/hh/dd/mm/yyyy,
"nextupdate": mm/hh/dd/mm/yyyy}
]
}
}
]
}
6.1.4.1. Example of response with a "dynamic" cost
To be completed
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POST /endpointcost/lookup HTTP/1.1
Host: alto.example.com
Content-Length: [TODO]
Content-Type: application/alto-endpointmulticostparams+json
Accept: application/alto-endpointmulticost+json,application/alto-error+json
{
"cost-type" : ["routingcost", "pathoccupationcost"],
"cost-mode" : ["numerical", "dynamic"],
"endpoints" : {
"srcs": [ "ipv4:192.0.2.2" ],
"dsts": [
"ipv4:192.0.2.89",
"ipv4:198.51.100.34",
"ipv4:203.0.113.45"
]
}
}
HTTP/1.1 200 OK
Content-Length: [TODO]
Content-Type: application/alto-endpointmulticost+json
{
"meta" : {},
"data" : {
"cost-type" : ["routingcost", "pathoccupationcost"],
"cost-mode" : ["numerical", "dynamic"],
"map" : {
"ipv4:192.0.2.2": {
"ipv4:192.0.2.89" : [1, [7, ..., 24 values]],
"ipv4:198.51.100.34" : [2, [4, ..., 24 values]],
"ipv4:203.0.113.45" : [3, [2, ..., 24 values]]
}
}
}
}
7. IANA Considerations
Information for the ALTO Endpoint property registry maintained by the
IANA and related to the new Endpoints supported by the acting ALTO
server. These definitions will be formulated according to the syntax
defined in Section on "ALTO Endpoint Property Registry" of
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[ID-alto-protocol],
Information for the ALTO Cost Type Registry maintained by the IANA
and related to the new Cost Types supported by the acting ALTO
server. These definitions will be formulated according to the syntax
defined in Section on "ALTO Cost Type Registry" of
[ID-alto-protocol],
7.1. Information for IANA on proposed Cost Types
When a new ALTO Cost Type is defined, accepted by the ALTO working
group and requests for IANA registration MUST include the following
information, detailed in Section 11.2: Identifier, Intended
Semantics, Security Considerations.
7.2. Information for IANA on proposed Endpoint Propeeries
Likewise, an ALTO Endpoint Property Registry could serve the same
purposes as the ALTO Cost Type registry. Application to IANA
registration for Endpoint Properties would follow a similar process.
8. Acknowledgements
Thank you to Dave Mac Dysan (Verizon) for fruitful discussions and
comments on the last draft.
Sabine Randriamasy is partially supported by the MEDIEVAL project
(http://www.ict-medieval.eu/), a research project supported by the
European Commission under its 7th Framework Program (contract no.
248565). The views and conclusions contained herein are those of the
authors and should not be interpreted as necessarily representing the
official policies or endorsements, either expressed or implied, of
the MEDIEVAL project or the European Commission.
Nico Schwan is partially supported by the ENVISION project
(http://www.envision-project.org), a research project supported by
the European Commission under its 7th Framework Program (contract no.
248565). The views and conclusions contained herein are those of the
authors and should not be interpreted as necessarily representing the
official policies or endorsements, either expressed or implied, of
the ENVISION project or the European Commission.
9. References
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9.1. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC5693] "Application Layer Traffic Optimization (ALTO) Problem
Statement", October 2009.
9.2. Informative References
[ID-ALTO-Requirements7]
"draft-ietf-alto-reqs-07.txt", January 2011.
[ID-alto-protocol]
, Eds., ""ALTO Protocol" draft-ietf-alto-protocol-09.txt",
June 2011.
[draft-jenkins-alto-cdn-use-cases-01]
""Use Cases for ALTO within CDNs"
draft-jenkins-alto-cdn-use-cases-01", June 2011.
Authors' Addresses
Sabine Randriamasy (editor)
Alcatel-Lucent Bell Labs
Route de Villejust
NOZAY 91460
FRANCE
Email: Sabine.Randriamasy@alcatel-lucent.com
Nico Schwan
Alcatel-Lucent Bell Labs
Lorenzstrasse 10
STUTTGART 70435
GERMANY
Email: Nico.Schwan@alcatel-lucent.com
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