One document matched: draft-randriamasy-alto-cost-schedule-01.txt
Differences from draft-randriamasy-alto-cost-schedule-00.txt
Network Working Group S. Randriamasy, Ed.
Internet-Draft N. Schwan
Intended status: Experimental Alcatel-Lucent Bell Labs
Expires: January 17, 2013 July 16, 2012
ALTO Cost Schedule
draft-randriamasy-alto-cost-schedule-01
Abstract
The goal of Application-Layer Traffic Optimization (ALTO) is to
bridge the gap between network and applications by provisioning
network related information. This allows applications to make
informed decisions, for example when selecting a target host from a
set of candidates. The ALTO problem statement [RFC5693] considers
typical applications as file sharing, real-time communication and
live streaming peer-to-peer networks. Recently other use cases
focused on Content Distribution Networks and Data Centers have
emerged [draft-jenkins-alto-cdn-use-cases-01].
The present draft proposes to extend the cost information provided by
the ALTO protocol. The purpose is to broaden the decision
possibilities of applications to not only decide 'where' to connect
to, but also 'when' to connect. This is useful to applications that
have a degree of freedom on when to schedule data transfers, such as
non-instantaneous data replication between data centers. The draft
therefore specifies a new cost mode, called the "schedule" mode. In
this mode the ALTO server offers cost maps that contain link ratings
that are valid for a given timeframe (e.g. hourly) for a period of
time (e.g. a day). Besides the functional time-shift enhancement
providing multi-timeframe cost values the extansion also allows the
saving of a number of ALTO transactions and thus resources on the
ALTO server and clients.
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
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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 January 17, 2013.
Copyright Notice
Copyright (c) 2012 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
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described in the Simplified BSD License.
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 4
2. Use cases for ALTO Cost Schedule . . . . . . . . . . . . . . . 5
2.1. Bulk Data Transfer scheduling . . . . . . . . . . . . . . 5
2.2. Endsystems with limited access to datacenters using
schedule mode . . . . . . . . . . . . . . . . . . . . . . 5
3. ALTO Cost Schedule . . . . . . . . . . . . . . . . . . . . . . 7
3.1. Cost Schedule Attributes . . . . . . . . . . . . . . . . . 7
3.1.1. ALTO Cost-Mode: Schedule . . . . . . . . . . . . . . . 7
3.2. ALTO Capability: Cost-Scope . . . . . . . . . . . . . . . 7
3.2.1. Example of time scope for a cost schedule . . . . . . 8
3.3. Example of scheduled information resources in the IRD . . 8
3.3.1. Example scenario and response with a cost schedule . . 11
4. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 12
4.1. Information for IANA on proposed Cost Types . . . . . . . 13
4.2. Information for IANA on proposed Endpoint Propeeries . . . 13
5. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 13
6. References . . . . . . . . . . . . . . . . . . . . . . . . . . 14
6.1. Normative References . . . . . . . . . . . . . . . . . . . 14
6.2. Informative References . . . . . . . . . . . . . . . . . . 14
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 14
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1. Introduction
IETF is currently standardizing the ALTO protocol which aims for
providing guidance to overlay applications, that need to select one
or several hosts from a set of candidates that are able to provide a
desired resource. This guidance is based on parameters that affect
performance and efficiency of the data transmission between the
hosts, e.g., the topological distance. The goal of ALTO is to
improve the Quality of Experience (QoE) in the application while
simultaneously optimizing resource usage in the underlying network
infrastructure.
The ALTO protocol therefore [ID-alto-protocol] specifies a Network
Map, which defines groupings of endpoints in a network region (called
a PID) as seen by the ALTO server. The Endpoint Cost Service and the
Endpoint (EP) Ranking Service then provide rankings for connections
between the specified network regions and thus incentives for
application clients to connect to ISP preferred endpoints, e.g. to
reduce costs imposed to the network provider. Thereby ALTO
intentionally avoids the provisioning of realtime information (cmp.
ALTO Problem Statement [RFC5693] and ALTO Requirements [RFC5693]), as
"Such information is better suited to be transferred through an in-
band technique at the transport layer instead". Thus the current
Cost Map and Endpoint Cost Service are providing, for a given Cost
Type, exactly one rating per link between two PIDs or to en Endpoint.
Applications are expected to query one of these two services in order
to retrieve the currently valid cost values. They therefore need to
plan their ALTO information requests according to the estimated
frequency of cost value change. In case these value changes are
predicable over a certain period of time and the application does not
require immediate data transfer, it would save time to get the whole
set of cost values over the period in one ALTO response and using
these values to schedule data transfers would allow to optimise the
network resources usage and QoE.
In this draft we introduce use cases that describe applications that
have a degree of freedom on scheduling data transfers over a period
of time, thus they do not need to start a transfer instantaneously on
a retrieved request. For this kind of applications we propose to
extend the Cost Map and Endpoint Cost Services by adding a schedule
on the cost values, allowing applications to time-shift data
transfers.
In addition to this functional ALTO enhancement, we expect to further
gain by gathering multiple Cost Values for one cost type as one Cost
Map reporting on N Cost Values is less bulky than N Cost Maps
containing one Cost value each, in addition to reducing N ALTO
transactions to a single one. This is valuable for both the storage
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of these maps and their transfer. Similar gains can be obtained for
the ALTO Endpoint Cost Service.
The remainder of this draft first provides use cases that motivate
the need for a 'schedule' cost mode. It then specifies the needed
extensions to the ALTO protocol and details some example messages.
2. Use cases for ALTO Cost Schedule
2.1. Bulk Data Transfer scheduling
Some CDNs are prepopulating caches with content before it actually
gets available for the user and thus there is a degree of freedom on
when the content is transmitted from the origin server to the
chaching node. Other 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. Typically the usage pattern of these data centers or
caches follows a location dependent diurnal pattern.
In the examples above data 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.
While this usage data today already is gathered and also used for the
scheduling of data transfer, provisioning this data gets increasingly
complex with the number of CDN nodes and in particular the number of
datacenter operators that are involved. For example, privacy
concerns prevent that this kind of data is shared across
administrative domains. Therefore the Cost schedule specified later
in this document avoids this problem by presenting an abstracted view
of time sensitive utilization maps through a dedicated ALTO service
to allow CDN operators a mutual scheduling of such data transfers
across administrative domains.
2.2. Endsystems with limited access to datacenters using schedule mode
Another use case that benefits from the availability of multi-
timeframe cost information is based on applications that are limited
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by their connectivity either in time or resources or both. For
example applications running on devices in remote locations or in
developing countries that need to synchronize their state with a data
center periodically, in particular if sometimes there is no
connection at all. Example applications is enterprise database
update, remote learning, remote computation.
Another challenge arises with endsystems using resources located in
datacenters and trading content and resources scattered around the
world. For non-real time applications, the interaction with
Endpoints can be scheduled at the time slots corresponding to the
best possible QoE. For instance, resource Ra downloaded from
Endpoint (EP) 1 at time Ta, Resource Rb uploaded to EP2 at time Tb,
some batch computation results RC downloaded from EP3 at Tc. Example
applications are similar to the ones cited in the previous paragraph.
These examples describe situations where a client has the choice of
trading content or resources with several Endpoints and needs to
decide with which Endpoint it will trade and at what time. For
instance, one may assume that the Endpoints are spread over different
time-zones, or have intermittent access. The ALTO schedule mode
specified below allows these clients to retrieve Endpoint cost maps
valid for a certain timeframe (e.g. 24 hours), and get a set of
values, each applicable on a (e.g. hourly) slot. Thus the
application can optimize the needed data transfer according to this
information.
Let us assume an Application Client is located in an end sytem with
limited resources and/or has an access to the network that is either
intermittent or provides an acceptable QoE in limited but predictable
time periods. Therefore, it needs to both schedule its resources
demanding networking activities. Instead of carefully schedule
multiple ALTO requests for Cost values and having to figure out when
the cost values may change it could benefit from relying on Cost
attributes indicating the time granularity, the validity and time
scope of the cost information, together with the values themselves.
Suppose that for some Cost Types, the ALTO cost values are available
in the "schedule" mode. If the values of Cost type 'routingcost'
and/or another time-sensitive Cost Type named for example
'pathoccupationcost' are available in the "schedule" mode for the 24
following the last update, the ALTO Client embedded in the
Application Client may query ALTO information on 'routingcost' or
'pathoccupationcost' for these 24 hours, and get a set of values,
each applicable to an hour slot. If appropriate Cost Attributes are
provided together with the cost values, the Application client also
knows the date of their last update. An example ALTO transaction is
provided later in this draft.
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3. ALTO Cost Schedule
One example of non-realtime information that can be provisioned in a
'schedule' is the expected path bandwidth. While the transmission
rate can be measured in real time by end systems the operator of a
data center is in the position of formulating preferences for given
paths at given time periods on given time scales, for example to
avoid hotspots due to diurnal usage patterns. The entity managing
the ALTO Server values can decide to integrate path bandwidth in the
ALTO 'routingcost' metric. However to better highlight the purpose
of the cost schedule we will use the Cost Type name
'pathoccupationcost' in the remainder of this document.
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
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.
3.1. Cost Schedule Attributes
For further extensions, specifications on the cost "schedule" are
proposed and will be completed in further versions of this draft.
3.1.1. ALTO Cost-Mode: Schedule
The "schedule" mode applies to Costs that are eligible for a single-
valued Cost Mode and can also be expressed as such. In that sense,
when the "numerical" mode is available for a Cost-Type, the cost
expressed in the "schedule" mode is an extension of its expression in
the "numerical" mode to an array of several values varying over time.
Types of Cost values such as JSONBool can also be expressed in the
"schedule" mode, as states may be "true" or "false" depending on
given time periods. It may be expressed as a single value which is
either "true" or "false" following a decision rule outside the ALTO
protocol.
3.2. ALTO Capability: Cost-Scope
To ensure that the application client uses the NP provided
information in the cost schedule in an unambiguous way we define the
Cost Scope capability, which defines the validity of the "scheduled"
cost values.
For Cost Types whose values are provided in a mode different than
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'schedule', the Cost Scope capability is specified by the string
"permanent". The Cost Scope attributes provided for the 'schedule'
mode are listed below. The reference time zone for the provided
values is UTC.
o Unit: expresses the time interval applicable to each value. A 2
element array where the first element is the time unit, ranging
from "second" to "year", and the second one the number of units of
this duration. For example: '["minute", 5]' means that each value
is provided on a time interval lasting 5 minutes.
o Size: the number of values of the cost schedule array,
o Begin: the index of the first unit in the array,
o Reference time zone: set to "UTC",
o Next update: the date at which the sample will be re-computed,
o Last update: the last re-computation date.
The reference time zone is UTC.
Attributes 'Last update 'and 'Next update' report on the update
frequency and age of the information.
3.2.1. Example of time scope for a cost schedule
For example: a metric called 'pathoccupationcost' (POC for short) is
computed for 24 hours, on time intervals lasting 2 hours, with the
first interval starting at 0h00. The ALTO Server thus provides an
array 12 values. This information is then used to enable
applications to see which time intervals in a day are the most
favorable to operate, and which "busy " time intervals should be
avoided. If the "Begin" date is past, the application can also use
the information to compute statistics or infer a some customized
prediction.
3.3. Example of scheduled information resources in the IRD
The example IRD given in this Section includes 2 particular URIs:
o "http://alto.example.com/endpointcost/lookup", in which the ALTO
Server offers several Endpoint Cost Types, including a Cost called
"pathoccupationcost" for which the "schedule" Cost Mode is
available. The Endpoint Costs available are the "hopcount",
"routingcost" and "pathoccupationcost" Cost Types, with the two
first ones in the "numerical" Cost Mode and "pathoccupationcost"
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in the "schedule" Cost Mode.
o "http://custom.alto.example.com/endpointcost/lookup", in which the
ALTO Server provides the 'routingcost' in both "numerical" and
"schedule" modes. This resource is accessible via a separate
subdomain called "custom.alto.example.com". The ALTO Client may
either get the last update of the 'routingcost' value or request
for a previsonal sample of 24 values established each for 1 hour.
An ALTO Client can discover the services available at
"custom.alto.example.com" by successfully performing an OPTIONS
request to "http://custom.alto.example.com/endpointcost".
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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
{
... usual ALTO resources ...
"resources" : [
{
"uri" : "http://alto.example.com/endpointcost/lookup",
"media-types" : [ "application/alto-endpointcost+json" ],
"accepts" : [ "application/alto-endpointcostparams+json" ],
"capabilities" : {
"cost-constraints" : true,
"cost-modes" : [ "numerical", "numerical", "schedule" ],
"cost-types" : [ "routingcost", "hopcount", "pathoccupationcost" ],
"cost-scope": [ "permanent", "permanent",
{"unit": ["hour", 1], "size": 24, "begin": 0,
"time zone": "UTC",
"lastupdate": mm/hh/dd/mm/yyyy,
"nextupdate": mm/hh/dd/mm/yyyy}
]
},
{
"uri" : "http://custom.alto.example.com/endpointcost/lookup",
"media-types" : [ "application/alto-endpointcost+json" ],
"accepts" : [ "application/alto-endpointcostparams+json" ],
"capabilities" : {
"cost-constraints" : true,
"cost-modes" : [ "numerical", "schedule" ],
"cost-types" : [ "routingcost", "routingcost" ],
"cost-scope": [ "permanent",
{"unit": ["hour", 1], "size": 24, "begin": 0,
"time zone": "UTC",
"lastupdate": mm/hh/dd/mm/yyyy,
"nextupdate": mm/hh/dd/mm/yyyy}
]
}
}
]
}
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3.3.1. Example scenario and response with a cost schedule
The Application Client is located in an end sytem with limited
resources and has an access to the network that is either
intermittent or provides an acceptable quality in limited but
possibly predictable time periods. Therefore, it needs to both
schedule its resources demanding networking activities and minimize
its ALTO transactions.
The Application Client has the choice to trade content or resources
with a set of Endpoints of moderate 'routingcost', and needs to
decide with which Endpoint it will trade at what time. For instance,
one may assume that the Endpoints are spread on different time-zones,
or have intermittent access. In this example, the 'routingcost' is
assumed constant for the scheduling period and the time sentitive
decision metric is the path bandwidth reflected by a Cost type called
'pathoccupationcost'.
The ALTO Client embedded in the Application Client queries ALTO
information on 'pathoccupationcost' for the 24 hours following
(implicitely) the date of "lastupdate", as this resource is listed in
the IRD.
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POST /endpointcost/lookup HTTP/1.1
Host: alto.example.com
Content-Length: [TODO]
Content-Type: application/alto-endpointcostparams+json
Accept: application/alto-endpointcost+json,application/alto-error+json
{
"cost-type" : ["pathoccupationcost"],
"cost-mode" : ["schedule"],
"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-endpointcost+json
{
"meta" : {},
"data" : {
"cost-type" : ["pathoccupationcost"],
"cost-mode" : ["schedule"],
"map" : {
"ipv4:192.0.2.2": {
"ipv4:192.0.2.89" : [7, ... 24 values],
"ipv4:198.51.100.34" : [4, ... 24 values],
"ipv4:203.0.113.45" : [2, ... 24 values]
}
}
}
}
4. 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],
4.1. 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.
4.2. 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.
5. Acknowledgements
Thank you to the ALTO WG for fruitful discussions.
Sabine Randriamasy is partially supported by the MEVICO project (http
://www.celtic-initiative.org/Projects/Celtic-projects/Call7/MEVICO/
mevico-default.asp), a research project supported by the European
Commission under its 7th Framework Program CELTIC initiative (project
no. CP 07-011). 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 MEVICO 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.
6. References
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6.1. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC5693] Seedorf, J. and E. Burger, "Application-Layer Traffic
Optimization (ALTO) Problem Statement", RFC 5693,
October 2009.
6.2. Informative References
[ID-alto-protocol]
, Eds., ""ALTO Protocol" draft-ietf-alto-protocol-10.txt",
October 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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