Network Working Group S. Randriamasy, Ed.
Internet-Draft Alcatel-Lucent Bell Labs
Intended status: Experimental October 15, 2010
Expires: April 18, 2011
Multi-Cost ALTO
draft-randriamasy-alto-multi-cost-00
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 by
providing a better mapping of the Selected Endpoints to needs of the
growing diversity of Content Networking Applications and to the
network conditions, secondly by producing a more robust choice of
multiple Endpoints, helping thus out for efficient Multi-Path
transfer.
There are 2 parts in this draft: the first part proposes protocol
extensions to support requests on multiple CostTypes in 1
transaction; the second part proposes additional CostTypes and Cost
attributes such as valitity period, timeframe and reliability.
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.
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/.
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Internet-Drafts are draft documents valid for a maximum of six months
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This Internet-Draft will expire on April 18, 2011.
Copyright Notice
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 4
2. Scope . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
3. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 5
4. Proposed ALTO services updates . . . . . . . . . . . . . . . . 6
4.1. Endpoint Cost Service with multiple Cost Types . . . . . . 6
4.2. All Costs Types in one response with vector cost values . 6
4.3. Proposed additional Cost Types . . . . . . . . . . . . . . 7
4.4. Statistical costs with a timeframe . . . . . . . . . . . . 7
5. Proposed ALTO protocol updates . . . . . . . . . . . . . . . . 7
5.1. Proposed updates for Multi-Cost ALTO . . . . . . . . . . . 8
5.1.1. Multi-Cost Attributes . . . . . . . . . . . . . . . . 8
5.2. Proposed additional Properties and Costs . . . . . . . . . 9
5.2.1. Proposed additional Endpoints properties . . . . . . . 9
5.2.2. Scoping ALTO information . . . . . . . . . . . . . . . 10
5.2.3. Proposed additional Cost Types . . . . . . . . . . . . 10
5.3. ALTO Status Codes for Multi-Cost ALTO . . . . . . . . . . 11
5.4. Examples of Multi-Cost ALTO messages . . . . . . . . . . . 11
6. Use case . . . . . . . . . . . . . . . . . . . . . . . . . . . 11
6.1. Scenario . . . . . . . . . . . . . . . . . . . . . . . . . 11
6.2. Illustrative ALTO use case . . . . . . . . . . . . . . . . 12
7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 15
8. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 15
9. References . . . . . . . . . . . . . . . . . . . . . . . . . . 15
9.1. Normative References . . . . . . . . . . . . . . . . . . . 15
9.2. Informative References . . . . . . . . . . . . . . . . . . 15
Author's Address . . . . . . . . . . . . . . . . . . . . . . . . . 15
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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-protocol5], gives the
possibility to query multiple Endpoint properties at once (see
S.7.7.4.1). However section 7.7.3.2 on Cost Map states about both
parameters Cost Type and Cost Mode that: "This parameter MUST NOT be
specified multiple times". The ALTO requirements draft, see
[ID-ALTO-Requirements] also 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 altogether.
Currently, the costs are provided in a scalar form, one by one. So
that an ALTO Client wanting information for several Cost Types must
place a request and receive a response as many times as desired Cost
Types. However, vector costs provide a robust and natural input to
multi-path connections and getting all costs in one single query/
response transaction saves time and ALTO traffic, thus ressources,
thus energy.
The ALTO Problem Statement, see [RFC5693] and the ALTO requirements
draft, see [ID-ALTO-Requirements] stress 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", as "ALTO is not an admission control system "and does not
necessarily know about the instant load of endpoints and links.
However, longer term statistics or empirical ratings on performance
oriented information may still be useful for a reliable choice of
candidate endpoints. In addition, given the QoE requirements of
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nowadays and future Internet applications, more and more NPs compute
and store such information to optimize their traffic. Last, specific
ALTO servers can be specified for mobile core networks, which have a
smaller scale and can afford and take advantage of using smaller
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. Besides, keeping the shortest or cheapest possible path,
in addition, saves resources, time and energy.
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. For P2P applications, the use case where
the ALTO Client is embedded in the P2P tracker is also applicable.
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.
The solution proposed in this draft is applicable to fixed networks.
It is also meant for smaller networks such as mobile networks.
3. Terminology
Endpoint (EP): can be a Peers, a CDN storage location, a Party in a
resource sharing swarm such as Grid or online gaming.
Endpoint Discovery (EP Discovery) : this term embraces the different
types of processes used to discover different types of endpoints.
Network provider: includes both ISPs, who provide means 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.
Application Client (AC): this term generalizes the case of a P2P
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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.
Traffic Engineered End Point Optimization Tool (TEEPOT): this is a
functional entity introduced in this draft, that is linked to an ALTO
Client and to an Application Client. Its role is to assist the
selection of Endpoints upon Allication needs and the ALTO responses.
It can be a specific group of functions or an already existing
function.
4. Proposed ALTO services updates
The currently available ALTO services supporting Endpoint evaluation
are: Endpoint Cost Service, Cost Map and Filtered Cost Map. The ALTO
client may want to simultaneously use a number N>1 of cost metrics
referred to as Cost Types in ALTO. The only possibility in the
current ALTO protocol is to sequentially place as many requests as
desired cost types. This draft proposes to add the following
features:
4.1. Endpoint Cost Service with multiple Cost Types
Some application clients may want to consider several metrics to
select the endpoints appropriately w.r.t. the application needs.
Clients may also want to use multiple paths for the transfer of
particular data bulks, possibly selected with several metrics.
Therefore the Endpoint Cost Lookup and the Cost Map Services should
have the possibility to handle several metrics.
4.2. All Costs Types in one response with vector cost values
Providing all the numerical costs simultaneously with only one
request and response exchange saves time, resources and energy. To
avoid overloading the network with ALTO traffic with multiple
requests for Cost Types, we propose that the Cost values provided by
the ALTO server be arranged in a vector. This requires:
o firstly to add an ALTO Cost Attribute called for instance "Cost
Length" that provides the number N of desired Cost Types,
o secondly to put the requested cost values in a vector having a
number N of components, where N is equal to Cost Length.
As specified in the ALTO Requirements [ID-ALTO-Requirements] "REQ.
ARv05-19: The ALTO reply message SHOULD allow the ALTO server to
express which rating criteria have been considered when generating
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the reply." That is, the ALTO response indicates the mapping between
vector components and Cost Types.
Note that in this case, the ALTO client MUST require the Cost Mode
"numerical" that is the Mode MUST NOT be "ordinal".
4.3. Proposed additional Cost Types
The current ALTO protocol draft provides examples of metrics in
section 5.1.1, that are: air miles, hop-counts or generic routing
costs. Statistics or longer term ratings on path bandwidth and
latency may also be considered. Additional Endpoint properties may
be useful, such as the memory capacity or statistical scores on the
load and possibilities of an Endpoint.
4.4. Statistical costs with a timeframe
The ALTO Requirements Draft [ID-ALTO-Requirements] advises against
instant performance-related cost metrics as they may be easily
captured by online mechanisms and in addition, the ALTO service does
not know how a Peer manages its sending rate. Application clients
however may have good reasons and wise ways to use performance
related information in the mid to long term ,on Endpoints that they
don't know in advance and on which they therefore cannot plan
measurements. Other applications may wisely use static performance
indicators such as nominal memory capacity.
Dynamic performance indicators can be represented by scores,
reflecting some overall performance, in a static way or with values
periodically updated according to a timeframe. A timeframe SHOULD be
sent along with the statistical Cost Types if the latter are
available. By default this timeframe corresponds to permanent
validity.
5. Proposed ALTO protocol updates
This section proposes updates or additions to the ALTO protocol to
support Multi Cost ALTO Services or provide additional ALTO
information. The applicable ALTO services are:
o Cost Map Service,
o Cost Map Filtering Service,
o Endpoint Property Lookup Service,
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o Endpoint Cost Lookup Service.
5.1. Proposed updates for Multi-Cost ALTO
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 transaction. The correspondence between the
components and the cost type MUST be indicated in the ALTO request.
The ALTO server then, provided it supports the desired cost, and
provided it supports the vector cost values, sends one single
response where for each {source, destination} pair, the cost values
are arranged in a vector, whose component each corresponds to a
specified Cost Type. The correspondence between the components and
the cost types MUST be indicated in the ALTO response.
The following ALTO protocol services and features need to be updated
to enable Multi Cost ALTO transactions.
o Endpoint (EP) Cost (see [ID-alto-protocol5], S. 3.2.4 and S.
7.7.5).
o Cost attributes (see [ID-alto-protocol5], S. 5.1).
o Cost Map (see [ID-alto-protocol5] S. 5 and 7.7.2.2):
* between Network Locations (that are groups of 1 or several
endpoints).
o Cost Map filtering: need the same updates as for the Cost Map.
5.1.1. Multi-Cost Attributes
To enable Multi-Cost ALTO Cost Services, we propose the following
updates to the Cost Attributes, described in [ID-alto-protocol5] S.
5.1.
o addition of attribute "Cost Length", a numerical value equal to
the number of requested EP Cost Types.
o extension of the attribute Cost Type from a single value to a
vector of N >= 1 values. If N > 1, then the values WILL be
interpreted as numerical values.
o addition of definitions that list and identify the Cost Types
supported by the acting ALTO server. These definitions can be
formulated with alphanumeric strings,
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o definition of the correspondence between an index "i_typecost" in
[1,N] in a cost vector and the ID of the defined alphanumeric cost
types.
o optional addition of a reliability vector having the same
dimension as the cost vector and that reflects, for each component
of the vector, the reliability of the provided cost value, for
instance in statistical terms or as a percentage. Values lying in
[0,1] can also be a good option.
* by default, the reliability is considered as total,
* the unit of validity values MUST be specified.
o optional association of a validity timeframe to the reliability
vector, indicating how long the information can be considered as
up to date.
* by default the validity timeframe WILL be considered infinite.
To the attribute Cost Mode in S.5.1: addition of a rule stipulating
that when multiple cost types are requested, then the requested Cost
Mode MUST be numerical. If the attribute Cost Length is > 1 and the
Cost Mode is set to "ordinal", then one option is that the ALTO
Server returns the 'Sucess' code "E_INVALID_COST_TYPE".
5.2. Proposed additional Properties and Costs
5.2.1. Proposed additional Endpoints properties
The Endpoint Properties given as example in [ID-alto-protocol5]
S.3.2.3 mostly apply to fixed end nodes. We propose to add other
properties, that are static, contribute to reflect the potential
physical abilities of end nodes and therefore may guide their
selection. In addition, these properties apply to end nodes
connected by any access technology. Example additional properties
include:
o EP capacity in memory,
o EP nominal bandwidth,
o EP access technology.
Note that if this service is not supported, it is possible although
less convenient to get the information at the overlay level, thus
without the ALTO server.
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5.2.2. Scoping ALTO information
One way to moderate the ALTO traffic load while maintaining some
reliability is to associate the following attributes to the
applicable ALTO information:
o a Time Frame attribute: this is the period during which an
information is considered applicable, for example 5 minutes, 2
hours, one month. When a time framed Property Service is
supported by the ALTO server, the Time Frame parameter can be by
default set to "permanent".
o a Time To Expire counter associated to some lifetime attribute and
the Time Frame as proposed in REQ ARv05-27 of
[ID-ALTO-Requirements] . By defaut, this parameter can be set to
infinity.
o RELIABILITY LEVEL: reflects the degree of likelihood of the
property, either a statistical value or a percentage.
The Time Frame and Time To Expire values can be used by the aging
mechanism as proposed in REQ ARv05-28 of [ID-ALTO-Requirements] for a
better synchronization of Cost Information collected at various times
and places.
5.2.3. Proposed additional Cost Types
Additional Cost Types may be used in either the Cost Map or the
Endpoint Cost Lookup Services and include:
o Endpoint availability: indicating how often an Endpoint is
reachable, preferebly as a percentage. To be further specified.
Possibly with associated Time frame and Time To Expire.
o Endpoint reliability: indicating how easily an Endpoint is
reachable, and / or the degree of continuity of its reachability,
preferebly as a percentage. To be further specified. Possibly
with associated Time frame and Time To Expire.
o Endpoint Load: indicating the average load, preferably as a
percentage, or a quantitative coarse grain index indicating
whether this Endpoint is in a rush period or calm period. To be
further specified. Possibly with associated Time frame and Time
To Expire.
o Path robustness: one or more timeframed indicators related to
statistical evaluations of the path performance on bandwidth,
delay, packet loss, or other such metrics. This Cost can also be
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represented by a quantitative coarse grain index indicating
whether this Endpoint is in a rush period or calm period. To be
further specified. Possibly with associated Time frame and Time
To Expire.
5.3. ALTO Status Codes for Multi-Cost ALTO
If the vector cost structure is not supported, 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 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 MUST be numerical. If the attribute Cost Length
is > 1 and the Cost Mode is set to "ordinal", an option is that the
ALTO Server returns the 'Sucess' code "E_INVALID_COST_TYPE".
5.4. Examples of Multi-Cost ALTO messages
Request and Response syntax. To be further specified.
6. Use case
6.1. Scenario
A Multi-Cost ALTO transaction is illustrated in a simple scenario,
where an application client in a terminal wants to use several paths
for a data transfer. This scenario applies to a terminal having
access to the network via one or several interfaces.
The application client for example wants 3 paths per transfer:
o 1 path optimising the Cost Type "routingcost",
o 2 paths optimizing 2 metrics: the Cost Type "routingcost" and an
Endpoint property named "EP memory".
* The application client in addition wants these 2 paths to
optimize the first criterion with a weight W_PATH_LENGTH equal
for example to 0.4 and the second criterion with a weight
W_EP_MEMORY equal to 0.6.
* If the EP Property Service provides the information on Endpoint
Load, then the application client wants this information in the
available time frame closest to 1 hour.
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A TEEPOT connected with the ALTO Client and the Application Client
takes in the list of candidate Endpoints from the Application Client
and prepares for the ALTO Client the request to the ALTO Server, in
particular the following values: EP Cost Length, vector EP Cost Type
[EP Cost Length], vector TimeFrame[EP Cost Length], with components
equal to either a value or an indication of "not applicable".
6.2. Illustrative ALTO use case
Figure 1 shows the example scenario in the last IETF ALTO protocol
draft, where the ALTO client is embedded in the P2P Client and
requires an ALTO server servicing its own ISP to provide the Endpoint
Cost for a list of gethered peers.
As written in [ID-alto-protocol5], the use case proceeds as follows:
1. The P2P Client discovers peers from sources such as Peer Exchange
(PEX) from other P2P Clients, Distributed Hash Tables (DHT), and
P2P Trackers.
2. The P2P Client queries the ALTO Server's Ranking Service,
including discovered peers as the set of Destination Endpoints,
and indicates the 'ordinal' Cost Mode. The response indicates
the ranking of the candidate peers.
3. The P2P Client connects to the peers in the order specified in
the ranking.
.---------. .---------------.
| | (2) Get Path Ranking | |
| ALTO | <----------------------> | [ALTO Client] |
| Server | | |
| | | P2P Client | .---------.
`---------' `---------------' <- | P2P |
.---------. / | ^ ^ | Tracker |
| Peer 1 | <-------------- | | \ `---------'
`---------' | (1) Gather Peers
. (3) Connect to | | \
. Selected Peers / .--------. .--------.
.---------. / | P2P | | DHT |
| Peer 50 | <---------------- | Client | `--------'
`---------' | (PEX) |
`--------'
Figure 1:example scenario in the last IETF ALTO protocol draft, where the
ALTO client is embedded in the P2P Client
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Figure 2 depicts the features and mechanisms added to the current
ALTO scenario for Multi-Cost ALTO services, for the use case of
Figure 1. The EPs have already been discovered. In this figure, the
term Peer is replaced by the term Endpoint (EP), the term P2P Client
by Application Client and an Endpoint Tracker for resource Sharing
Applications is added to the tools involved in Step (1) Gather
Endpoints .
We focus on the ALTO use case where the ALTO client is co-located
with an Application client in a terminal node, as not all P2P systems
use a P2P tracker for peer discovery and selection as written in
section 8.2 of [ID-alto-protocol5]. In Figure 2, the entity called
P2P Client mentionned in the current protocol draft is zoomed to an
entity called in this draft "Client Block" and that links: the
Application Client (AC), its ALTO Client and the Traffic Engineered
EP Optimization Tool (TEEPOT).
(3) Get EP Cost Client Block
Mode=Numerical, Dimension > 1 __________________________________________________
.---------. Cost Types=Hops,EP-mem | .---------------. |
| ALTO | <-------------------> | | ALTO Client | ---------------. |
| Server | | `---------------' <----. (4.a) Send EP cost |
| | | ^ (2.c)Send list of | vectors |
`---------' | | Cost Types | v |
| | .---------------. |
|(2.a)Send list of EPs | TEEPOT | |
| | `---------------' |
| | ^ (4.b)Send selected |
| | (2.b)Send EP Specs. and ranked EPs |
| .---------------. -------' | |
| |Appl. Client | <---------------' |
| `---------------' |
|__/_|______^______________________________________|
.---------. / | |
| EP 1 | <-------------- | |
`---------' | (1) Gather Endpoints (EPs)
. (5) Connect to | |
. Selected Endpoints / .-------------------.
.---------. / | PEX |
| EP 50 | <---------------' | Endpoint Tracker |
`---------' | DHT |
`-------------------'
Figure 2: features and mechanisms added to the current ALTO scenario for Multi-Cost ALTO services
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The use case in Figure 2 proceeds as follows:
1. The Application Client discovers Endpoints (EPs) from sources
such as Peer Exchange (PEX) from other P2P Clients, Distributed
Hash Tables (DHT), P2P Trackers or other types of EP trackers.
2. In the "Client Block" gathering the Application Client (AC), its
ALTO Client and the Traffic Engineered EP Optimization Tool
(TEEPOT):
A. the Application Client (AC) sends to the ALTO Client the list
of the discovered peers as the set of Destination Endpoints.
B. the Application Client (AC) sends to the TEEPOT the
specifications on the EPs to select, according to the needs
of the application. For example, AC needs 3 EPs, with 1 EP
optimizing the Path Length Metric and 2 EPs optimizing the
Path Length and the EP Memory Capacity Score, with respective
weights of 0.4 and 0.6.
C. the TEEPOT indicates to the ALTO Client that the Service to
request is EP Cost, with the Cost Mode set to "Numerical",
and the Cost Dimension equal to the number of requested
metrics and with the index of the requested Cost Types.
3. The ALTO Client queries the ALTO Server's EP Cost Service, sends
the list of the discovered peers as the set of Destination
Endpoints and indicates the 'numerical' Cost Mode, with a Cost
Dimension equal to 2 and the index of requested metrics,
corresponding in this example to: "Path Length" and "EP Memory
Capacity Score". The response is the set of metric values
associated to each EP.
4. In the Client block:
A. The ALTO Client hands to the TEEPOT the list of EPs and their
associated value set.
B. The TEEPOT ranks the EPs with some smart algorithm, given the
metric weights and then sends the ranked list to the
Application Client.
5. The Application Client connects to the selected EPs.
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7. IANA Considerations
This document makes no request of IANA.
Note to RFC Editor: this section may be removed on publication as an
RFC.
8. Acknowledgements
9. References
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-Requirements]
"draft-ietf-alto-reqs-05.txt", June 2010.
[ID-alto-protocol5]
""ALTO Protocol" draft-ietf-alto-protocol-05.txt",
July 2010.
Author's Address
Sabine Randriamasy (editor)
Alcatel-Lucent Bell Labs
Route de Villejust
NOZAY 91460
FRANCE
Email: Sabine.Randriamasy@alcatel-lucent.com
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