Network Working Group S. Randriamasy, Ed.
Internet-Draft Alcatel-Lucent Bell Labs
Intended status: Standards Track R. Yang
Expires: April 30, 2015 Yale University
Q. Wu
Huawei
L. Deng
China Mobile
N. Schwan
Thales Deutschland
October 27, 2014
ALTO Cost Calendar
draft-randriamasy-alto-cost-calendar-02
Abstract
The goal of Application-Layer Traffic Optimization (ALTO) is to
bridge the gap between network and applications by provisioning
network related information in order to allow applications to make
informed decisions. 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'. 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 or service
provisioning to end systems with irregular connectivity. ALTO
guidance to schedule application traffic can also efficiently help
for load balancing and resources efficiency.
The draft specifies a new Cost Mode, "Calendar" Mode, that is
applicable to time-sensitive ALTO metrics and allows Applications to
carefully schedule their connections or data transfers. In the
Calendar Mode, an ALTO Server exposes ALTO Cost Values in JSON arrays
where each value corresponds to a given time interval. The time
intervals as well as other Calendar attributes are specified in the
IRD. Besides the functional time-shift enhancement the ALTO Cost
Calendar also allows to schedule the ALTO requests themselves and
thus save a number of ALTO transactions.
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].
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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
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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 30, 2015.
Copyright Notice
Copyright (c) 2014 IETF Trust and the persons identified as the
document authors. All rights reserved.
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Motivating use cases for ALTO Cost Schedule . . . . . . . . . 4
2.1. Bulk Data Transfer scheduling . . . . . . . . . . . . . . 5
2.2. Endsystems with limited connectivity or access to
datacenters . . . . . . . . . . . . . . . . . . . . . . . 6
2.3. SDN Controller guided access to application endpoints . . 7
2.4. Large flow scheduling on extended ALTO topologies . . . . 8
2.5. Time-sensitve TE metrics Calendaring . . . . . . . . . . 9
3. Design considerations for an ALTO calendar . . . . . . . . . 10
3.1. Purpose of an ALTO calendar . . . . . . . . . . . . . . . 11
3.2. Design requirements for an ALTO calendar . . . . . . . . 12
4. ALTO extensions for a Cost Calendar . . . . . . . . . . . . . 13
4.1. ALTO Cost-Mode: Calendar . . . . . . . . . . . . . . . . 13
4.2. ALTO Calendar attributes in the IRD . . . . . . . . . . . 14
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4.3. Example of calendared information resources in the IRD . 15
4.3.1. Example IRD with ALTO cost Calendars . . . . . . . . 16
4.4. ALTO Calendar information in ALTO responses . . . . . . . 18
4.4.1. Example transaction for a routingcost Calendar to
face intermittent connectivity . . . . . . . . . . . 20
4.4.2. Example transaction for a bandwidth calendar . . . . 21
5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 23
5.1. Information for IANA on proposed Cost Types . . . . . . . 24
5.2. Information for IANA on proposed Endpoint Propeeries . . 24
6. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 24
7. References . . . . . . . . . . . . . . . . . . . . . . . . . 24
7.1. Normative References . . . . . . . . . . . . . . . . . . 24
7.2. Informative References . . . . . . . . . . . . . . . . . 24
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 25
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 [RFC7285] 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 as explained in the ALTO
Problem Statement [RFC5693] and ALTO Requirements [RFC5693]) drafts
that write "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
an 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
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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 calendar
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 firstly
one Cost Map reporting on N Cost Values is less bulky than N Cost
Maps containing one Cost value each and secondly, this reduces N ALTO
transactions to a single one. This is valuable for both the storage
of these ALTO maps and their transfer. Similar gains can be obtained
for the ALTO Endpoint Cost Service.
In this draft an "ALTO Calendar" is presented as a Cost Mode that is
applicable to time-sensitive ALTO metrics and allows applications
using such metrics to carefully schedule their connections or data
transfers. In the Calendar Mode, an ALTO Server exposes ALTO Cost
Values in JSON arrays where each value corresponds to a given time
interval. The time intervals as well as other Calendar attributes
(the ones suggested by Richard) are specified in the IRD and allow
the ALTO Client to interpret the received ALTO values. This draft
proposes a set of Calendar attributes to be added to the IRD, for
discussion in the ALTO WG.
The remainder of this draft first provides a variety of use cases
that motivate the need for a 'calendar' cost mode. It then specifies
the needed extensions to the ALTO protocol and details some example
messages.
2. Motivating use cases for ALTO Cost Schedule
This section introduces use cases showing the benefits of providing
ALTO Cost values in 'calendar' mode. Most likely, the ALTO Cost
Calendar would be used for the Endpoint Cost Service, assuming that a
limited set of feasible Endpoints for a non-real time application is
already identified, that they do not need to be accessed immediately
and that their access can be scheduled within a given time period.
The Cost Map service, filtered or not, is also applicable as long as
the size of the Map is manageable.
Last, the ALTO Cost calendar is beneficial to optimizing ALTO
transactions themselves. Indeed, let us assume that an Application
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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. In that
case, it needs to both schedule its resources demanding networking
activities and its ALTO requests. Instead of having to figure out
when the cost values may change and having to carefully schedule
multiple ALTO requests, it could aviod this by relying on Cost
Shedule attributes that indicate the time granularity, the validity
and time scope of the cost information, together with the time
related cost values themselves.
2.1. Bulk Data Transfer scheduling
Large Internet Content Providers (ICPs) like Facebook or YouTube, as
well as CDNs rely on data replication across multiple sites to
offload the core site and increase user experience through shorter
latency from a local site. 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 Internet Content Provider (ICP), leading to bulk data
transfers between datacenters on a diurnal pattern.
In the mean time, there is a degree of freedom on when the content is
transmitted from the origin server to the caching node, or from the
core site to a local site. However, 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.
As a result, it would be very helpful to let these ICPs to have a
good knowledge about the link utilization patterns between the
different datacenters from the networks before making a more
intelligent scheduling decision. 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. The ALTO Cost
Calendar 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 ICPs a coherent scheduling
of such data transfers across administrative domains.
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2.2. Endsystems with limited connectivity or access to datacenters
Another use case that benefits from the availability of multi-
timeframe cost information is based on applications that are limited
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 distributed on several
data center endpoints.
Wireless connections have a variable quality and may even be
intermittent. On the other hand, the wireless network conditions are
often predicable and have a rapid impact on applications. Non real
time applications and time-insensitive data transfers such as client
patching, archive syncing, etc. can benefit from careful scheduling.
It is thus desirable to provide ALTO clients with routing costs to
connection nodes (i.e. Application Endpoints) over different time
periods. This would allow end systems using ALTO aware application
clients to schedule their connections to application endpoints.
Another challenge arises with end systems 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 network conditions in order to improve the QoE. For
instance, resource Ra downloaded from Endpoint EPa at time t1,
Resource Rb uploaded to EPb at time t2, some batch computation
involving Ra and Rb done on EPc at time t3 and results R(A,B)
downloaded to EPd and EPe at time t4. Example applications are
similar to the ones cited in the previous paragraph.
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+-----+ +-----+
| EPa | | EPb | <----- Rb
+-----+ +-----+ (t2=50)
| +-------+ |
Ra --------------> | EPc | |
(time t1=10) | | |
|t3=100 | <----------------- Rb
+-------+
| \
| \
R(Ra,Rb)
(t4=200)
| \
| -------------------.
V V
+-----+ +-----+
| EPd | | EPe |
+-----+ +-----+
2.3. SDN Controller guided access to application endpoints
The Software Defined Networking (SDN), see [sdnrg], is a model that
attempts to manage and reconfigure networks in a more flexible way in
order to better cope with the traffic challenges posed by nowadays
resources greedy applications. To this end, one option is "moving
the control plane out of the network elements into "controllers", see
[SDN charter, http://www.1-4-5.net/~dmm/sdnrg/sdnrg.html], that
implements the network control and management. The SDN Controllers
are deemed to gather the network state information and provide it in
an abstracted form to SDN aware applications while gathering their
requirements in QoE and exchanging other application "management"
information and commands.
The relevance of ALTO to perform a number of SDN functions has been
recently highlighted. An ALTO Server can assist an SDN Controller by
hosting abstracted network information that can be provided to SDN
aware applications via an ALTO Client. It can also assist other SDN
Control operations using information in and outside the ALTO scope.
The SDN primitive "Get network resources" provides applications with
informations allowing them to evaluate the expected QoE. QoE related
information includes delay and bandwidth at the application endpoints
as well as on the network paths. Such information may be provided
via the ALTO Service by proposed extensions of the ALTO protocol that
define new ALTO Cost Types allowing to abstract and report QoE to
applications.
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One key objective of an SDN controller is the ability to balance the
application traffic whenever possible. For non real time
applications, data and resources transfer can be time shifted,
resources availability may often be predicable and last, strong
incentives for applications to time shift their traffic may be given
by network operators appropriately setting routing cost values at
different time values, according to their policy to cope with network
occupation over time.
To achieve this objective, the SDN controller can:
1. get the network state history from its controlled network
elements through its southbound API
2. possibly derive an estimation or a prediction of these values
over given time frames
3. compute estimates and/or network provider preferences on end to
end paths and store their abstraction in an ALTO Server in the
form of ALTO Cost Calendar values defined for different time
periods
4. deliver these values to the SDN applications via the ALTO
Endpoint Cost Service, as estimations covering the past and/or
the future and/or preferences.
This way:
o On one hand, the applications get the best possible QoE, as they
can pick the best time for them to access one or more Endpoints,
o One the other hand the SDN controller achieves load balancing as
it may guide the application traffic so as to better distribute
the traffic over time, and thus optimize its resources usage.
2.4. Large flow scheduling on extended ALTO topologies
[draft-yang-alto-topology-00] presents initial thinking on extending
ALTO for topology exposure services, that would provide flexible
abstractions based on the raw network topology. Among other
features, an ALTO topology may expose several paths between a source
(src) and destination (dst), or topology details may be provided on
restricted parts. This work was presented to the ALTO WG at IETF88.
The presentation slides [slides-88-alto-5-topology] on
[draft-yang-alto-topology-00] expose a use case entitled "Large Flow
Scheduling". This case includes a "daylife example" where a Google
Map service proposes multiple routes between 2 points A and B, each
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calculated w.r.t. length and estimated time. For each of these
selected paths, the map service exposes a time-sensitive qualitative
value taking 4 values between Slow and Fast. A user of this
application may thus organize its transfer w.r.t. metrics, paths and
time, provided s/he does not have to commute immediately.
The use case on Large flow scheduling on extended ALTO topologies in
the present section illustrates one modality of ALTO topology
service, that would expose several paths between end to end (src,
dst) pairs, computed w.r.t. one of more metrics, possibly under given
constraints. On top of this enriched topology service, non real-time
applications may also choose the time of data/resources transfer,
taking thus advantage of a richer set of decision variables.
The use case "Large Flow Scheduling" of presentation
[slides-88-alto-5-topology]can thus be adapted as follows:
o Step1 - obtain the set T transfer tasks {(src, dest, data)}
o Step2 - identify one or more paths for each (src, dst): several
information sources exist among which:
* (a) ALTO CostMap with a "path" metric, // not specified here
* (b) an ALTO Topology Service providing a path computation hint
(e.g. w.r.t. routingcost and/or other metrics)
o Step 3 - while T not empty:
* 1 - query for example values for some metric 'available
bandwidth' on paths:
+ to this end, query the values in the ALTO 'calendar' Mode:
on the selected (src, dst) for a set of time intervals.
With this mode, the ALTO client will receive an array of
values, each applicable to a time slot .
* 2 - schedule data transfer at the time slots corresponding to
the preferred value.
2.5. Time-sensitve TE metrics Calendaring
Draft [draft-wu-alto-te-metrics] , proposes to extend the set of ALTO
metrics with 11 ALTO traffic engineering (TE) metrics to reflect
measurement on network delay, jitter, packet loss, hop count, and
bandwidth. ALTO TE metrics that are time-sensitive, either by nature
such as bandwidth and delay related metrics, or due to "normally"
changing network conditions or both.
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The values of ALTO TE metrics are typically collected from routing
protocols and provided in a non-real time manner. In "normally"
changing network conditions, TE metric values remain uniformly
distributed over given time intervals and can be aggregated over
bigger time intervals of periodic patterns. For example, an ALTO
Server may collect values for e.g. delay from a routing protocol
produced by measurements done every second over a measurement period
of 30 seconds. The ALTO Server may then aggregate these values over
two measurement periods (i.e. 60 seconds) and repeat the operation as
it wishes. Then every hour, the ALTO Server provides these delay
values in 'calendar' mode, encoded as an array of 60 values, assumed
to estimate network performance statistics on each minute of this
hour.
Another example is Bandwidth Calendaring. Bandwidth Calendaring
allows network operators to reserve resources in advance according to
agreements with their customers, enabling them to transmit data with
specified starting time and duration, for example, for a scheduled
bulk data replication between data centers. Traditionally, this can
be supported by a Network Management System operation such as path
pre-establishment and activation on the agreed starting time.
However, this does not provide efficient network usage since the
established paths exclude the possibility of being used by other
services even when they are not used for undertaking any service.
A Cost calendar provided by an ALTO server can support the scheduled
bulk data replication application with better efficiency since it can
alleviate the burden of processing on network elements. This
requires the ALTO server to maintain the calendared TE cost metrics
on the end to end paths associated to data transfer.
To support cost calendaring for these time-sensitive ALTO TE metrics,
the network topology and the dynamicity of the traffic need to be
considered. For example, a small topology with low density and low
capacity that carries inpredictable, heavy and bursty traffic has few
chances to exhibit stationary TE metric value patterns over large
periods and would benefit to use the ALTO Calendar over smaller time
slots. Some ALTO TE metric values, even aggregated over time may
need to be updated at a frequency that would require doing ALTO
request at a pace that would be overload both the ALTO Client and the
Server.
3. Design considerations for an ALTO calendar
This section enumerates a set of challenges in designing the
calendaring specifications, and will be updated upon discussions in
the ALTO WG.
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An ALTO Cost calendar provided by the ALTO Server is an array of
values for a given metric, where each value corresponds to a time
interval which length is specified for this metric in the IRD,
together with other attributes describing the time scope of the
calendar. Most likely, the ALTO Cost Calendar would be used for the
Endpoint Cost Service, assuming that a limited set of feasible
Endpoints for a non-real time application is already identified, that
they do not need to be accessed immediately and that their access can
be scheduled within a given time period. The Cost Map service,
filtered or not, is also applicable as long as the size of the Map is
manageable.
3.1. Purpose of an ALTO calendar
A calendar is used to schedule transfers of application data or
services and has several characteristics:
o the Calendar values are assumed to be stationary on each time
interval,
o the ALTO Server may provide values on past time periods that can
be interpreted as historical experience and used to anticipate
future cost values,
o the ALTO Server may provide stationary values on present or future
time periods that can be interpreted as predictions on cost
values,
o the ALTO Server may provide stationary values on time intervals
covering the past, and/or present and/or future.
o for metrics provided with units and claiming to be aggregated from
network measurements, the values can be interpreted as
estimations.
o For abstracted metrics provided with no units such as the
'routingcost' defined in the base ALTO protocol or abstracted
unitless scores on network performances such as some potential
'bandwidth score' or 'unreliability cost', the values can be
interpreted as network provider preferences.
Note that we distinguish between "estimates" that we see as value
aggregations represented with units such as bytes, seconds,
percentage and "preferences" that we see as abstracted costs or
scores w.r.t. a metric or state such as 'routingcost',
'bandwidthscore', 'link quality'.
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The method used to generate the estimation and aggregation of
measured values is currently outside the scope of this draft and
expected to be documented in the applicable metric definition
document.
3.2. Design requirements for an ALTO calendar
TO BE COMPLETED IN FURTHER DRAFT VERSIONS
An ALTO Calendar can be seen as a cyclic value array pattern that is
valid for a certain time period with specified beginning date,
duration and number of time intervals.
o needs to convey cyclic network provider preferences expressed
w.r.t. given ALTO metric values (e.g., hourly, daily, weekly
measurement/prediction)
o needs to convey cyclic network status if the ALTO Server claims to
provide aggregated information on network status (e.g., hourly,
daily, weekly measurement/prediction)
o needs to be able to convey the result of a particular instance of
time (e.g., to convey predicted network status during a
maintenance outage on July 4, 2014 from 5-7pm)
o needs at least the following attributes to report on cyclic
patterns:
* generic time zone,
* applicable time interval for each calendar value (measurement
estimation with units or unitless preference value) : combining
<nb-int-unit> and <interval-unit> to reflect for example:
1hour, 2minutes, 1week, 1month
* date range of the Calendar, e.g. number of intervals allowing
to derive the calendar time range in terms of: year, month,
week, day, hour, min, secs
o needs to expose validity period of the calendar: indicating when
the next ALTO Calendar for this date range should be fetched if
needed,
o needs to provide time stamps:
* last-update-time: specifying when the metric values were last
computed ,
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* next-update-time: specifying when the calendar values will be
re-computed, indicating thus when an ALTO client should fetch
an update if it uses a Calendar.
* calendar-start-date: specifying when the current already
computed calendar starts,
* next-calendar-start-date: specifying when the already computed
calendar will have different values, indicating thus that the
ALTO client should fetch the next pre-computed calendar
It may be useful to keep a cyclic network status with date, in case
of exceptional predicted events such as New Year evening on a Tuesday
or any worldwide event generating a lot of traffic.Traffic calendars
may be particularly useful in such cases.
4. ALTO extensions for a Cost Calendar
The usage of a time-related ALTO Cost Calendar is rather 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. An ALTO Cost Calendar should be
viewed as a synthetic abstraction of real measurements that can be
historic or be a prediction for upcoming time periods.
Specifications on the cost "calendar" attributes are proposed here
and will be completed in further versions of this draft, upon
discussion with the ALTO WG.
The format of ALTO requests and responses will be specified in
further versions of this draft, as in particular it may be necessary
that the ALTO response indicates the computation and validity dates
of the provided ALTO Calendar.
4.1. ALTO Cost-Mode: Calendar
This draft introduces a new ALTO Cost Mode called "calendar". This
mode applies preferably to Costs that can be expressed in a single-
valued Cost Mode. In that sense, when the "numerical" mode is
available for a Cost-Type, the cost expressed in the "calendar" mode
is an extension of its expression from one value 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
"calendar" mode, as states may be "true" or "false" depending on
given time periods. They may be expressed as a single value which is
either "true" or "false" following a decision rule outside the ALTO
protocol.
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4.2. ALTO Calendar attributes in the IRD
To ensure that the application client understands the provided
information in the cost calendar in an unambiguous way, we specify
the Calendar attributes in the ALTO IRD "meta" information, that
defines the time scope of the "calendared" cost values. The Calendar
attributes in the IRD are meant to carry constant dateless values.
o time-interval-size:
* expresses the unit in which the duration of an ALTO calendar
time interval duration is expressed appended to the number of
these units. The time unit, ranges from "second" to "year".
The number is encoded with an integer. Example values are: "5
minute" , "2 hour". These vales mean that each calendar value
is provided on a time interval that lasts respectively 5
minutes and 2 hours.
o numb-intervals:
* the integer number of values of the cost calendar array, at
least equal to 1.
o calendar-update-frequency:
* the frequency at which ALTO Calendar values are updated in the
ALTO Server. Must be not sooner than 'next-calendar-start-
time'. The value is expressed in the same format as for 'time-
interval-size'.
o numb-calendars: (OPTIONAL)
* the number of calendars with deffering values, of duration
'time-interval-size' multiplied by 'numb-intervals' available
in the ALTO Server during the period equal to 'calendar-update-
frequency'.
- Attributes 'time-interval-size' and 'numb-intervals', when
mutlipled, reflect the duration of the provided calendar. For
example an ALTO Server may provide a calendar for ALTO values
changing every 'time-interval-size' equal to 5 minutes. If 'numb-
intervals' has the value 12, then the duration of the provided
calendar is "1 hour". Note also that in this example, a 5 minutes
interval may cover the aggregation of real TE measurements done every
30 seconds, but this latter aspect is outside the scope of this draft
as it is to be specified in the definition of the ALTO metric.
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- Attribute 'calendar-update-frequency' indicates the frequency at
which the calendar values are computed and made available to the ALTO
Client. The value is not necessarily constant and may change in
given periods when particular events and related usage patterns
occur. The ALTO Client should just consider that the ALTO Server
does not find it necessary to update the Calendar values more often
than indicated by the current value. The ALTO Client may thus assume
that the ALTO Server considers the values as valid or stationary
during this period.
- Attribute 'max-numb-calendars': this optional attribute stresses
the fact that an ALTO Server may for example offer daily cost
patterns conveying a number 'num-intervals' of 12 values valid on a
time interval of size 'time-interval-size' equal to 2 hours. The
calendars are updated at an 'calendar-update-frequency' of 7 days.
However for example the ALTO Server may identify in some period a
common daily pattern C1 for Monday, Tuesday, and Friday, another one
C2 for Saturday and Sunday and a specific one C3 for Wednesday for
instance due to maintenance or due to an important holiday. In this
case, the number of different daily patterns thus calendars is equal
to 3.
4.3. Example of calendared information resources in the IRD
This section describes an example IRD and related ALTO calendar
transaction in a scenario where an ALTO Server offers the Calendar
Mode for several Cost Types that are either specified in the base
ALTO protocol or proposed in other drafts see
[draft-wu-alto-te-metrics] or suggested here as examples, like a cost
metric reporting on measured packet loss and called 'TEpktloss. The
provided example transactions are based on the use cases of section
2.
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 Calendar 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 specified time interval (e.g. 1 hour).
Thus the application can optimize the needed data transfer according
to this information.
In the example IRD of the present draft, the available Endpoint Costs
metrics are: "routingcost", "AShopcount", 'TEpktloss' and
'Availbandwidth'. "routingcost" and "AShopcount" are available in the
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"numerical" Cost Mode. 'TEpktloss' , 'Availbandwidth' and
"routingcost" as well are available in the "calendar" Cost Mode.
We suppose that the ALTO Client GETs the IRD on Tuesday July 1st 2014
at 13:00
o The Calendar for 'TEpktloss'': is an hourly pattern that consists
of 12 values provided each on a time interval of 5 minutes,
provided for each hour, and the 24 calendars are updated every day
at 0:00 GMT.
o The Calendar for 'Availbandwidth': is a daily pattern that
consists of 12 values provided each on time intervals of 2 hours,
with the first interval starting at 0h00. It is computed every
day and updated at 0:00 GMT. This information is typically 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.
o The Calendar for 'routingcost': is a daily pattern that consists
of an array of 24 time intervals lasting each 1 hour. The
routingcost calendar covers a 1 day period, starting at midnight.
The daily patterns are updated every week on sunday at 23:59 GMT.
An ALTO Client can thus store and use the needed routingcost
calendars for maximum 1 week. This may be applicable for networks
with poor or intermittent connectivity where the operator may
integrate monetary as well as network performance metrics in the
provided 'routingcost' values.
4.3.1. Example IRD with ALTO cost Calendars
The example IRD given in this section includes 2 particular URIs:
o "http://alto.example.com/endpointcost/lookup", in which the ALTO
Server offers the numerical mode for metrics "routingcost" and
"AShopcount".
o "http://alto.example.com/endpointcost/calendar/lookup", in which
the ALTO Server provides "calendar" mode for metrics 'TEpktloss'
and 'Availbandwidth' and 'routingcost'.
For Cost Type 'calendar-routing', this example assumes that the ALTO
Server has defined 3 different daily patterns each represented by a
Calendar, to cover the week of Monday June 30th at 00:00 to Sunday
July 6th 23:59:
- C1 for Monday, Tuesday, Wednesday, Thursday, (week days)
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- C2 for Saturday, Sunday, (week end)
- C3 for Friday (maintenance outage on July 4, 2014 from 02:00:00 GMT
to 04:00:00 GMT, or big holiday such as New Year evening)
The example ALTO response shown in a further section also illustrates
how specific calendar attributes allow an ALTO client to fetch 3
Calendars instead of 7 and thus to reduce the volume of on-the-wire
data exchange. For Cost Type 'calendar-routing' , the IRD provides a
value for attribute 'num-calendars' which is equal to 3.
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
{
"meta" : {
"cost-types": {
"num-routingcost": {
"cost-mode" : "numerical",
"cost-metric" : "routingcost"
},
"num-AShopcount": {
"cost-mode" : "numerical",
"cost-metric" : "hopcount"
},
"calendar-TEpktloss": {
"cost-mode" : "calendar",
"cost-metric": "TEpktloss",
"description": {
"time-interval-size" : "5 minute",
"numb-intervals" : 12,
"calendar-update-frequency" : "1 day"
}
},
"calendar-bw": {
"cost-mode" : "calendar",
"cost-metric": "Availbandwidth",
"description": {
"time-interval-size" : "2 hour",
"numb-intervals" : 12,
"calendar-update-frequency" : "1 day"
}
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},
"calendar-routing": {
"cost-mode" : "calendar",
"cost-metric": "routingcost",
"description": {
"time-interval-size" : "1 hour",
"numb-intervals" : 24,
"calendar-update-frequency" : "1 week",
"num-calendars" : 3
}
... other meta ...
},
"resources" : {
... usual ALTO resources such as Network Map, Cost Maps ...
"endpoint-cost" : {
"uri" : "http://alto.example.com/endpointcost/lookup",
"media-types" : [ "application/alto-endpointcost+json" ],
"accepts" : [ "application/alto-endpointcostparams+json" ],
"capabilities" : {
"cost-constraints" : true,
"cost-type-names" : [ "num-routingcost", "num-AShopcount" ]
}
},
"endpoint-cost-calendar-map" : {
"uri" : "http://alto.example.com/endpointcost/calendar/lookup",
"media-types" : [ "application/alto-endpointcost+json" ],
"accepts" : [ "application/alto-endpointcostparams+json" ],
"capabilities" : {
"cost-constraints" : true,
"cost-type-names" : [ "calendar-routingcost",
"calendar-TEpktloss",
"calendar-bw"]
}
}
}
}
4.4. ALTO Calendar information in ALTO responses
ALTO responses convey additional attributes with usually non constant
values that inform the ALTO Client about the next date at which the
calendar values stored in the ALTO Server will change and at which
time updates calendar values will be uploaded in the ALTO Server. A
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number of Calendar attributes in ALTO responses are dates. The
reference time zone for the provided values is GMT. Indeed, the
option chosen to express the time format is the HTTP header fields
formats such as:
Date: Tue, 15 Nov 1994 08:12:31 GMT
o calendar-start-time:
* the date corresponding to the first value in the calendar
values array
o next-calendar-start-time:
* the starting date of the next calendar. To limit the number of
provided calendars and schedule the next ALTO Calendar query.
For example, a daily calendar may have the same values for the
next 3 days. So the ALTO Client does not need to get one every
day.
o last-calendar-update:
* the last date at which ALTO Calendar values were updated in the
ALTO Server. Must be no later than 'calendar-start-time'.
o 'time-interval-size': as specified for the IRD
o 'numb-intervals': as specified for the IRD
- Attribute 'calendar-start-time' indicates when the calendar
provided to the ALTO client starts. If the 'calendar-start-time'
date is past, the application can also use the information to compute
statistics on values provided by ALTO over time to guide
applications. Besides estimating some customized prediction the ALTO
Client may use these values to assess their reliability w.r.t. some
real measures of QoE.
- Attribute 'next-calendar-start-time' is useful for clients to
schedule their requests for calendars. For example: an ALTO Server
may provide calendars lasting 24 hours and decide to estimate and
update these daily patterns every week on Sunday. Suppose that in
the coming week, the patterns are the same for Monday through
Tursday. Then the calendar values will only change on Friday. It
the ALTO Client gets a calendar on Tuesday, it may keep it until
Thursday included and get another one the on the next Friday if
needed. An example illustrating the usefulness of 'next-calendar-
start-time' is provided in following sections.
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- Attributes 'last-calendar-update' indicates when the calendar
values are last updated and uploaded in the ALTO Server. This
attribute reflects the age of the ALTO Calendar information. Given
the update frequency indicated in the IRD by the 'calendar-update-
frequency' attribute, the ALTO Client can figure when the next value
update will occur.
DISCUSSION: can the ALTO responses omit repeating the values of
'time-interval-size' and 'numb-intervals', as they are already in the
IRD?
4.4.1. Example transaction for a routingcost Calendar to face
intermittent connectivity
Let us assume an Application Client located in an end sytem with
limited resources and having 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 to be the time sentitive decision metric, with values
provided in the ALTO Calendar Mode.
The ALTO Client embedded in the Application Client queries an ALTO
Calendar on 'routingcost' and will get the Calendar covering the 24
hours time period "containing" the date and time of the ALTO client
request. We suppose in this example that the ALTO Client sends its
request on Tuesday July 1st 2014 at 13:15
The present example also illustrates how attributes 'calendar-start-
time' and 'next-start-time' allow an ALTO client to fetch 3 Calendars
instead of 7 and thus to reduce the volume of on-the-wire data
exchange, because the ALTO Server has defined 3 different daily
patterns each represented by a Calendar, to cover the week of Monday
June 30th at 00:00 to Sunday July 6th 23:59:
- C1 for Monday, Tuesday, Wednesday, Thursday, (week days)
- C2 for Saturday, Sunday, (week end)
- C3 for Friday (maintenance outage on July 4, 2014 from 5-7pm, or
holiday such as New Year evening)
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POST endpointcost/calendar/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" : {"cost-mode" : "calendar", "cost-metric" : "routingcost"},
"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" : {
"calendar-start-time" : Tue, 1 Jul 2014 00:00:00 GMT,
"next-start-time" : Fri, 4 Jul 2014 00:00:00 GMT,
"last-calendar-update" : Sun, 29 Jun 2014 00:00:00 GMT,
"time-interval-size" : "1 hour",
"numb-intervals" : 24
},
"cost-type" : {"cost-mode" : "calendar", "cost-metric" : "routingcost"},
"endpoint-cost-calendar-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]
}
}
}
4.4.2. Example transaction for a bandwidth calendar
An example of non-real time information that can be provisioned in a
'calendar' is the expected path bandwidth. While the transmission
rate can be measured in real time by end systems, the operator of a
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data center is in the position of formulating preferences for given
paths, at given time periods for example to avoid traffic peaks due
to diurnal usage patterns. In this example, we assume that an ALTO
Client requests a bandwidth calendar as specified in the IRD to
shedule its bulk data transfers as described in the use cases of
sections 2.1 and 2.5.
We suppose in this example that the ALTO Client sends its request on
Tuesday July 1st 2014 at 13:15
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POST endpointcost/calendar/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" : {"cost-mode" : "calendar", "cost-metric" : "Availbandwidth"},
"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" : {
"calendar-start-time" : Tue, 1 Jul 2014 00:00:00 GMT,
"next-start-time" : Wed, 2 Jul 2014 00:00:00 GMT ,
"last-calendar-update" : Tue, 1 Jul 2014 00:00:00 GMT,
"time-interval-size" : "2 hour",
"numb-intervals" : 12
},
"cost-type" : {"cost-mode" : "calendar", "cost-metric" : "Availbandwidth"},
"endpoint-cost-calendar-map" : {
"ipv4:192.0.2.2": {
"ipv4:192.0.2.89" : [7, ... 12 values],
"ipv4:198.51.100.34" : [4, ... 12 values],
"ipv4:203.0.113.45" : [2, ... 12 values]
}
}
}
5. 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
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defined in Section on "ALTO Endpoint Property Registry" of
[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 [RFC7285],
5.1. 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.
5.2. 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.
6. Acknowledgements
Thank you to Diego Lopez, He Peng and Haibin Song and the ALTO WG for
fruitful discussions.
7. References
7.1. 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.
7.2. Informative References
[ID-alto-protocol]
R.Alimi, R. Penno, Y. Yang, Eds., "ALTO Protocol, RFC
7285", September 2014.
[RFC7285] R. Alimi, R. Yang, R. Penno, Eds., "ALTO Protocol",
September 2014.
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[article-gslh-alto-sdn]
V. Gurbani, M. Scharf, T.Lakshman, and V. Hilt, ,
"Abstracting network state in Software Defined Networks
(SDN) for rendezvous services, IEEE International
Conference on Communications (ICC) Workshop on Software
Defined Networks (SDN)", June 2012.
[draft-jenkins-alto-cdn-use-cases-01]
B. Niven-Jenkins (Ed.), G. Watson, N. Bitar, J. Medved, S.
Previdi, , "Use Cases for ALTO within CDNs, draft-jenkins-
alto-cdn-use-cases-01", June 2011.
[draft-randriamasy-multi-cost-alto]
S. Randriamasy, Ed., W. Roome, N. Schwan, , "Multi-Cost
ALTO (work in progress), draft-randriamasy-alto-multi-
cost-07", October 2012.
[draft-wu-alto-te-metrics]
Q. Wu, Y. Yang, Y. Lee, D. Dhody, S. Randriamasy, , "ALTO
Traffic Engineering Cost Metrics (work in progress)",
October 2014.
[draft-xie-alto-sdn]
H. Xie, T. Tsou, D. Lopez, H. Yin, , "Use Cases for ALTO
with Software Defined Networks (work in progress), draft-
xie-alto-sdn-extension-use-cases-01", January 2013.
[draft-yang-alto-topology-00]
Y. Yang, , "ALTO Topology Considerations (work in
progress)", July 2013.
[sdnrg] "Software Defined Network Research Group,
http://trac.tools.ietf.org/group/irtf/trac/wiki/sdnrg", .
[slides-88-alto-5-topology]
G. Bernstein, Y. Lee, Y. Yang, , , "ALTO Topology Service:
Use Cases, Requirements and Framework (presentation slides
IETF88 ALTO WG session),
http://tools.ietf.org/agenda/88/slides/
slides-88-alto-5.pdf", November 2013.
Authors' Addresses
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Sabine Randriamasy (editor)
Alcatel-Lucent Bell Labs
Route de Villejust
NOZAY 91460
FRANCE
Email: Sabine.Randriamasy@alcatel-lucent.com
Richard Yang
Yale University
51 Prospect st
New Haven, CT 06520
USA
Email: yry@cs.yale.edu
Qin Wu
Huawei
101 Software Avenue, Yuhua District
Nanjing, Jiangsu 210012
China
Email: sunseawq@huawei.com
Lingli Deng
China Mobile
China
Email: denglingli@chinamobile.com
Nico Schwan
Thales Deutschland
Email: ietf@nico-schwan.de
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