Network Working Group S. Randriamasy
Internet-Draft W. Roome
Intended status: Standards Track Alcatel-Lucent
Expires: September 10, 2015 N. Schwan
Thales Deutschland
March 9, 2015
Multi-Cost ALTO
draft-randriamasy-alto-multi-cost-10
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 simple way to extend the information
provided by the current ALTO protocol in two ways. First, including
information on multiple Cost Types in a single ALTO transaction
provides a better mapping of the Selected Endpoints to needs of the
growing diversity of Content and Resources Networking Applications
and to the network conditions. Second, one ALTO query and response
exchange on N Cost Types is faster and more efficient than N single
cost transactions. All this also helps producing a faster and more
robust choice when multiple Endpoints need to be selected. Last, the
draft proposes to enrich the filtering capabilities by allowing
constraints involving several metrics combined by several types of
logical operators. This allows the applications to set finer
requirements and above all to include compromises on those
requirements.
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-
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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 September 10, 2015.
Copyright Notice
Copyright (c) 2015 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
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 4
2. Application Scope And Terminology . . . . . . . . . . . . . . 5
3. Uses Cases For Using Multiple Costs . . . . . . . . . . . . . 6
3.1. Use Cases For Using Additional Costs . . . . . . . . . . 6
3.1.1. Delay Sensitive Overlay Applications . . . . . . . . 7
3.1.2. Selection Of Physical Servers Involved In Virtualized
Applications . . . . . . . . . . . . . . . . . . . . 7
3.1.3. CDN Surrogate Selection . . . . . . . . . . . . . . . 8
3.1.4. Some Proposed Additional Properties And Costs . . . . 9
3.2. Use Cases For Multi-Cost ALTO Transactions . . . . . . . 10
3.2.1. Optimized Endpoint Cost Service . . . . . . . . . . . 10
3.2.2. Optimized Filtered Cost Map Service . . . . . . . . . 11
3.2.3. Cases Of Unpredicable Endpoint Cost Value Changes . . 11
3.2.3.1. Case Of A Multi-Cost ALTO Query Upon A Route
Change . . . . . . . . . . . . . . . . . . . . . 12
3.2.3.2. Case Of A Multi-Cost ALTO Query Upon A Cost Value
Change . . . . . . . . . . . . . . . . . . . . . 13
4. ALTO Protocol Updates Needed To Support Multi-Cost
Transactions . . . . . . . . . . . . . . . . . . . . . . . . 14
4.1. List Of ALTO Protocol Updates Required And Recommended . 15
4.2. Updates Required In The Member Format Of Objects . . . . 16
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4.2.1. Cost Value Encoded In array of JSON values . . . . . 16
4.2.2. Scalar 'cost-type' Member Replaced By Array 'multi-
cost-types' Member . . . . . . . . . . . . . . . . . 16
4.2.3. Rule On Cost Value Order In ALTO Reponses . . . . . . 17
4.3. Updates Recommended In The Object Structure . . . . . . . 17
5. Extended Constraints On Multi-Cost Values . . . . . . . . . . 17
5.1. Use Cases For Multi-Cost Multi-Operator Constraints . . . 18
5.2. Extended constraints in Multi-Cost ALTO . . . . . . . . . 19
6. Protocol Extensions for Multi-Cost ALTO Transactions . . . . 19
6.1. Information Resources Directory . . . . . . . . . . . . . 20
6.1.1. Example of Multi-Cost specific resources in the IRD . 20
6.2. Multi-Cost Map Service . . . . . . . . . . . . . . . . . 23
6.2.1. Media Type . . . . . . . . . . . . . . . . . . . . . 23
6.2.2. HTTP Method . . . . . . . . . . . . . . . . . . . . . 23
6.2.3. Input Parameters . . . . . . . . . . . . . . . . . . 23
6.2.4. Capabilities . . . . . . . . . . . . . . . . . . . . 23
6.2.5. Uses . . . . . . . . . . . . . . . . . . . . . . . . 24
6.2.6. Response . . . . . . . . . . . . . . . . . . . . . . 24
6.2.7. Example . . . . . . . . . . . . . . . . . . . . . . . 25
6.3. Filtered Multi-Cost Map . . . . . . . . . . . . . . . . . 26
6.3.1. Media Type . . . . . . . . . . . . . . . . . . . . . 26
6.3.2. HTTP Method . . . . . . . . . . . . . . . . . . . . . 26
6.3.3. Input Parameters . . . . . . . . . . . . . . . . . . 26
6.3.4. Capabilities . . . . . . . . . . . . . . . . . . . . 28
6.3.5. Uses . . . . . . . . . . . . . . . . . . . . . . . . 29
6.3.6. Response . . . . . . . . . . . . . . . . . . . . . . 29
6.3.7. Example 1 . . . . . . . . . . . . . . . . . . . . . . 30
6.3.8. Example 2 . . . . . . . . . . . . . . . . . . . . . . 31
6.4. Endpoint Multi-Cost Service . . . . . . . . . . . . . . . 32
6.4.1. Media Type . . . . . . . . . . . . . . . . . . . . . 32
6.4.2. HTTP Method . . . . . . . . . . . . . . . . . . . . . 32
6.4.3. Input Parameters . . . . . . . . . . . . . . . . . . 32
6.4.4. Capabilities . . . . . . . . . . . . . . . . . . . . 33
6.4.5. Uses . . . . . . . . . . . . . . . . . . . . . . . . 33
6.4.6. Response . . . . . . . . . . . . . . . . . . . . . . 34
6.4.7. Example . . . . . . . . . . . . . . . . . . . . . . . 34
7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 35
7.1. Information for IANA on proposed Cost Types . . . . . . . 35
7.2. Information for IANA on proposed Endpoint Properties . . 36
8. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 36
9. References . . . . . . . . . . . . . . . . . . . . . . . . . 36
9.1. Normative References . . . . . . . . . . . . . . . . . . 36
9.2. Informative References . . . . . . . . . . . . . . . . . 36
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 37
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1. Introduction
IETF has designed a new service called ALTO that provides guidance to
overlay applications, which have 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 purpose of ALTO 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.
Current ALTO Costs and their modes provide values that are seen to be
stable over a longer period of time, such as hopcount and
administrative routing cost to reflect ISP routing preferences.
Recently, new use cases have extended the usage scope of ALTO to
Content Delivery Networks, Data centers and applications that need
additional information to select their Endpoints or handle their
PIDs.
Thus a multitude of new Cost Types that better reflect the
requirements of these applications are expected to be specified, in
particular cost values that change more frequently than previously
assumed.
The ALTO protocol [RFC7285] restricts ALTO Cost Maps and Endpoint
Cost services to only one Cost Type and Cost Mode per ALTO request.
To retrieve information for several Cost Types, an ALTO client must
send several separate requests to the server.
It would be far more efficient, in terms of RTT, traffic, and
processing load on the ALTO client and server, to get all costs with
a single query/response transaction. Vector costs provide a robust
and natural input to multi-variate path computation as well as robust
multi-variate selection of multiple Endpoints. In particular, one
Cost Map reporting on N Cost Types is less bulky than N Cost Maps
containing one Cost Type each. This is valuable for both the storage
of these maps and their transmission. Additionally, for many
emerging applications that need information on several Cost Types,
having them gathered in one map will save time.
Along with multi-cost values queries, the filtering capabilities need
to be extended to allow constraints on multiple metrics. The base
protocol allows optional constraints in the input parameters to a
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request for a Filtered Cost Map or the Endpoint Cost Service. The
'constraints' member is an AND-combination of expressions that all
apply to the (single) requested Cost Type. It is therefore necessary
to allow constraints on multiple metrics. Beyond that, applications
that are sensitive to several metrics and struggle with complicated
network conditions may need to arbitrate between conflicting
objectives such as routing cost and network performance. To address
this issue, this draft proposes to extend the base protocol by both
allowing to combine constraints on multiple metrics and relating
these constraints with a logical 'AND' and a logical 'OR'. This
allows an application to make compromises such as: "select solutions
with either (moderate 'hopcount' AND high 'routingcost') OR (higher
'hopcount' AND moderate 'routingcost')".
This draft is organized as follows: section 3 exposes use cases
motivating the introduction of new Cost Types and why multi-cost
transactions are useful. Section 4 identifies the core ALTO protocol
extensions that are required or recommended to support requests and
responses on multiple Cost Types in one single transaction.
Section 5 specifies the extended constraints on mutli-cost values.
Section 6 specifies the protocol extensions for Multi-Cost ALTO
transactions and provides examples.
2. Application Scope And Terminology
This draft generalizes the case of a P2P client to include the case
of a CDN client, a client of an application running on a virtual
server, a GRID application client and any Client having the choice in
several connection points for data or resource exchange. To do so,
it uses the term "Application Client" (AC).
This draft focuses on the use case where the ALTO client is embedded
in the Application Client or in some Application Endpoint tracker in
the network, such as a P2P tracker, a CDN request router or a cloud
computing orchestration system implemented in a logically centralized
management system.
It is assumed that Applications likely to use the ALTO service have a
choice in connection endpoints as it is the case for most of them.
The ALTO service is managed by the Network Provider (NP) and reflects
its preferences for the choice of endpoints. The NP defines in
particular the network map, the routing cost among Network Locations,
the cost types used to reflect it, and which ALTO services are
available at a given ALTO server.
This draft uses terms defined as follows:
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o Endpoint (EP): can be a Peer, a CDN storage location, a physical
server involved in a virtual server-supported application, a Party
in a resource sharing swarm such as a computation Grid or an
online multi-party game.
o Endpoint Discovery (EP Discovery) : this term covers the different
types of processes used to discover the eligible endpoints.
o Network Service Provider (NSP): includes both ISPs, who provide
means to transport the data, and Content Delivery Networks (CDNs)
who care for the dissemination, persistent storage and possibly
identification of the best/closest content copy.
o ALTO transaction: a request/response exchange between an ALTO
Client and an ALTO Server.
o Application Client (AC): this term generalizes the case of a P2P
client to include the case of a CDN client, a client of an
application running on a virtual server, a GRID application client
and any Client having the choice in several connection points for
data or resource exchange.
3. Uses Cases For Using Multiple Costs
The ALTO protocol specification in [RFC7285] focuses on the basic use
case of optimizing routing costs in NSP networks. Upcoming use cases
however will require both new Cost Types and new Endpoint Properties.
Recent ALTO use cases now extend to CDNs, Data centers and other
applications that need additional information to select their
Endpoints or handle their PIDs. The needed Cost Types depend on the
QoE requirements that are specific to the applications. Moreover,
the cost values that they may use may change more rapidly than
assumed up to now.
The goal of this section is to describe forward looking use case
scenarios that are likely to benefit from ALTO, in order to motivate
the introduction of new Cost Types and Endpoint Properties as well as
the ALTO Multi-Cost extension.
3.1. Use Cases For Using Additional Costs
ALTO Cost Types and Endpoint Properties are registered in two
registries maintained by IANA. The ALTO Cost Type registry ensures
that the Cost Types that are represented by an ALTO Cost Map are
unique identifiers, and it further contains references to the
semantics of the Cost Type. The ALTO specification registers
'routingcost' as a generic measure for routing traffic from a source
to a destination. In a similar way the ALTO Endpoint Property
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Registry ensures uniqueness of ALTO Endpoint Property identifiers and
provides references to particular semantics of the allocated Endpoint
Properties. Currently the 'pid' identifier is registered, which
serves as an identifier that allows aggregation of network endpoints
into network regions. Both registries accept new entries after
Expert Review. New entries should conform to the respective
syntactical requirements, and must include information about the new
identifier, the intended semantics, and the security considerations.
One basic example advocating for multiple Cost Type transactions is
an Application Client looking for destination Endpoints or Source/
Destination PID pairs yielding jointly the lowest 'routingcost' and
path delay. We hereby assume that 'routingcost' values report some
monetary cost and that the Application Client chooses to rely on the
hopcount to reflect the path delay.
3.1.1. Delay Sensitive Overlay Applications
The ALTO working group has been created to allow P2P applications and
NSPs a mutual cooperation, in particular because P2P bulk file-
transfer applications have created a huge amount of intra-domain and
congestion on low-speed uplink traffic. By aligning overlay
topologies according to the 'routingcost' of the underlying network,
both layers are expected to benefit in terms of reduced costs and
improved Quality-of-Experience.
Other types of overlay applications might benefit from a different
set of path metrics. In particular for real-time sensitive
applications, such as gaming, interactive video conferencing or
medical services, creating an overlay topology with respect to a
minimized delay is preferable. However it is very hard for an NSP to
give accurate guidance for this kind of realtime information, instead
probing through end-to-end measurements on the application layer has
proven to be the superior mechanism. Still, a NSP might give some
guidance to the overlay application, for example by providing
statistically preferable paths, possibly with respect to the time of
day. Also static information like hopcount can serve as an indicator
for the delay that can be expected. Thus a Cost Type that can
indicate latency, without the need for end-to-end measurements
between endpoints, is likely to be useful.
3.1.2. Selection Of Physical Servers Involved In Virtualized
Applications
Virtualized applications in large Datacenters are supported by
virtualized servers that actually gather resources distributed on
several physical servers. The federation of these resources is often
orchestrated by a centralized entity that needs to select the
physical servers from or to which it will take resources. This
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entity can be co-located with an ALTO Client that will request and
get the ALTO information on the network formed by the physical
servers. The physical servers can be assimilated to endpoints with
which the orchestration entity trades application resources or
content. These resources include computation resources, storage
capacity and path bandwidth between the physical servers.
Here too, the applications that are ran are diverse and may have
different and specific QoE requirements. The Endpoint selection
typically needs to consider both the computational resources at the
Endpoints and the resources e.g. in bandwidth on the transmission
paths to or among Endpoints. Thus the application QoE requirements
drive the Endpoint selection with more or less weight on QoE specific
metrics such as hopcount/delay, bandwidth and other resources, that
are typically combined with the routing cost and need to jointly
integrate the Endpoint and transmission path perspective in the
decision process, which is difficult to do with one single Cost Type.
3.1.3. CDN Surrogate Selection
Another use case is motivated through draft
[draft-jenkins-alto-cdn-use-cases-01]. The request router in today's
CDNs makes a decision about the surrogate or cache node to which a
content request should be forwarded. Typically this decision is
based on locality aspects, i.e. the request router tries to select
the surrogate node losest to the client. By using the 'routingcost'
Cost Type, an ALTO server allows an NSP to guide the CDN in selecting
the best cache node. This is particularly important as CDNs place
cache nodes deeper into the network (i.e., closer to the end user),
which requires finer grained information. Finally the provisioning
of abstracted network topology information across administrative
boundaries gains importance for cache federations.
While distance today is the predominant metric used for routing
decisions, other metrics might allow sophisticated request routing
strategies. For example the load a cache node sees in terms of CPU
utilization, memory usage or bandwidth utilization might influence
routing decisions for load-balancing reasons. There exist numerous
ways of gathering and feeding this kind of information into the
request routing mechanism.
For example, information reporting on the occupation level of a cache
could be based on a cost reflecting: its remaining computation
resources, its remaining storage capacity w.r.t its capacity in
storage or computation resources.
As ALTO is likely to become a standardized interface to provide
network topology information, the ALTO server could also provide
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other information that a request router needs. In the next
iterations of this draft we will analyse which of these metrics is
suitable as a Cost Type or Endpoint Property for CDN Surrogate
Selection, and propose to register them in the respective registries.
3.1.4. Some Proposed Additional Properties And Costs
In addition to CDN caches, Endpoint Properties and Costs can be
useful to report an Endpoint's load, given that an Endpoint can as
well be a physical server in a datacenter or any entity as defined in
Section 2 of this draft.
Proposed new Endpoint properties and costs include:
o an Endpoint Property called "EP-Capacity", reflecting the nominal
capacity of this endpoint. This capacity could be split into:
* EP-Nominal-Memory: the storage capacity of the Endpoint.
* EP-Nominal-Bandwidth: the capacity of the computation resources
of the Endpoint.
o an Endpoint Cost called "EP-Occupied-Capacity", reflecting the
currently available resources w.r.t. their nominal capacity. As
with EP-Capacity, this can be split into:
* EP-Occupied-Memory: the remaining storage capacity,
* EP-Occupied-Bandwidth: the remaining computation resources.
Likewise, new Cost Types are needed to describe the resources of the
network paths needed for content transport, in particular the
utilized network path bandwidth.
o A Cost Type named 'pathoccupationcost' (POC) can be used to
reflect the NP view of the utilized path bandwidth. Such an ALTO
Cost Type is likely to have values that change frequently. By no
means, as stated in the ALTO requirements, are ALTO Cost types
expected to reflect real-time values, as these can be gathered by
other mechanisms. Instead, a Cost Type such as
'pathoccupationcost' should be used as an abstraction that may be
represented by a statistical value, or be updated regularly at a
frequency lower than 'real-time', or be provided according to
different time periods or other parameters. A provision mode for
time dependent cost values is proposed in
[draft-randriamasy-alto-cost-schedule-01]
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3.2. Use Cases For Multi-Cost ALTO Transactions
Different Cost Types are suitable for different applications. For
example, delay sensitive applications look for both low routing cost
and low delay, where as other applications, such as non real time
content download, look for moderate delay and minimal losses. On the
other hand, applications or entities managing application input
information may want, for various reasons to update their ALTO
information on several Cost Types. So an ALTO Client may want to mix
Cost Types in either 'numerical' and 'ordinal' mode, for Cost Types
values that can be represented by numerical values.
The Multi-Cost ALTO Services propose to:
o include several Cost Types (and/or Cost Modes) in an ALTO client's
Cost Map and Endpoint Cost request,
o provide several Cost Type values (and/or Cost Mode) in an ALTO
server's response, instead of one.
The primary reasons to use Multi-Cost ALTO are:
o Optimizing time and bandwidth: a single ALTO response with a
Multi-Cost cost map with three separate Cost Type values takes
much less network bandwidth, and fewer CPU cycles, than three
separate ALTO requests for three complete single-cost cost maps.
The motivation also holds for the Endpoint Cost Service. Multi-
Cost ALTO services can straightforwardly provide a more complete
set of cost information.
o Facing unpredictable and/or rapid value changes: an ALTO client
can get a consistent snapshot of several different rapidly-varying
Cost Type values.
3.2.1. Optimized Endpoint Cost Service
The Endpoint Cost Service (ECS) provides cost information about both
the application Endpoint resources and the networking resources used
to access those Endpoints. In addition, the ECS may be invoked in
"short term" situations, that is for frequent requests and/or
requests requiring fast responses. For the ECS, the server's
response is restricted to the requested Endpoints, and so is much
smaller than a complete Cost Map. Therefore the ECS can be invoked
for 'nearly-instant' information requests, and is particularly well
suited for multi-cost ALTO transactions, supporting requests and
responses on several Cost Type values simultaneously.
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3.2.2. Optimized Filtered Cost Map Service
The set of ALTO Cost Types is not restricted to 'routingcost': ALTO
Servers may provide a broader set of metrics. One thing to consider
is that the frequency of updates can vary from a Cost Type to another
one. Additionally the volume of an entire cost map with values of
all available Cost Types, may get rapidly prohibitive for frequent
downloads. Given these considerations the Application Client may
take better advantage when:
o requesting multi-cost maps filtered w.r.t. Cost Types of
compatible update frequencies or dates, which is the
responsibility of the Application Client,
o requesting multi-cost maps filtered w.r.t. a restricted set of PID
pairs.
In such a case, as with the Endpoint Cost Service, the purpose of a
Multi-Cost transaction is to gain time with whatever future use of
the received ALTO information. In this case, the Client may mix Cost
Types in either 'numerical' and 'ordinal' mode, for Cost Type values
that can be represented by numerical values.
3.2.3. Cases Of Unpredicable Endpoint Cost Value Changes
Querying all Endpoint cost values simultaneously is always more time
and resources efficient than doing it sequentially.
It becomes a necessity in case of unpredictable and/or rapid value
changes on at least one of the ALTO Cost Types. The term 'rapid'
here means "Typical update intervals [that] may be several orders of
magnitude longer than the typical network-layer packet round-trip
time (RTT)", as described in [RFC6708], up to a couple of minutes.
This section provides two examples of a delay sensitive application
using 'routingcost' and 'hopcount' to select an Endpoint. The
application can choose between two candidate Endpoints, EP1 and EP2.
The initial choice at T=1 is EP1. It is assumed that at T=2 events
in the network occur that impact both 'routingcost' and 'hopcount'.
These examples illustrate the need to query 'hopcount' and
'routingcost' values at the same time in order to re-evaluate the EP
costs w.r.t. the QoE needs of the application. It is assumed that
the application triggers regular ALTO requests to get the latest cost
values for a list of candidate Endpoints.
In some cases the Application client wants to use the ALTO
information to perform multi-variate optimization on several Cost
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Type values. In order for the optimization to be reliable, it is
recommended that the Cost Type values are provided in 'numerical'
Cost Mode. Therefore the requested Cost Mode for the applicable Cost
Types SHOULD be 'numerical'.
3.2.3.1. Case Of A Multi-Cost ALTO Query Upon A Route Change
In Figure 1, initially at time T=1, the application has chosen EP1
rather than EP2, despite the higher routing cost, because EP1 has a
"better" (lower) 'hopcount' value and despite the higher routing cost
and possibly because the application has set a higher weight to
'hopcount'.
At a time T=2, the route to EP1 changes. The ALTO Server information
is accordingly updated. The ALTO client makes its next request to
update the cost values for 'routingcost' and 'hopcount' on EP1 and
EP2. It appears that EP1 has now a hopcount value of 3, the same
than for EP2 while its routing cost is higher.
The application realizes that there is no more benefit in keeping
interacting with EP1 and therefore switches to EP2, that now has the
same hopcount but a lower routing cost.
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T = 1 : EP1: routingcost = 40, hopcount = 2
EP2: routingcost = 30, hopcount = 3
EP1 is selected because application is time-sensitive and
metric 'hopcount' has a higher weight
.-----.
O ---------- O ------------- | EP2 |
/ `-----'
/
/ .-----.
Source ----------------------- O ---- | EP1 |
`-----'
T = 2 : EP1: routingcost = 40, hopcount = 3
EP2: routingcost = 30, hopcount = 3
- Route to EP1 has changed. Hopcount is now 3
==> EP2 is selected because routingcost is lower than for
EP1, with the same hopcount value
.-----.
O ---------- O -------------| EP2 |
/ \ `-----'
/ `-----.
/ `------. .-----.
Source ---------- X --------- [O] ---- | EP1 |
`-----'
Figure 1: Endpoint re-selection using Multi-Cost ALTO request on
updated cost values, upon a chnage in the route.
3.2.3.2. Case Of A Multi-Cost ALTO Query Upon A Cost Value Change
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T = 1 : EP1: routingcost = 30, hopcount = 2
EP2: routingcost = 30, hopcount = 3
==> EP1 is selected because application is time-sensitive and
hopcount metrics has higher weight
.-----.
O ---------- O ------------- | EP2 |
/ `-----'
/
/ .-----.
O ------------------------ O ---- | EP1 |
`-----'
T = 2 : EP1: routingcost = 40, hopcount = 2
EP2: routingcost = 30, hopcount = 3
Routingcost to EP1 has increased. Hopcount is the same.
==> Delay sensitive applications willing to minimize hopcount
remain with EP1 while other applications may remain
with EP2, that now has a lower routingcost.
.-----.
O ---------- O -------------| EP2 |
/ `-----'
/
/ .-----.
O ------------------------ O ---- | EP1 |
`-----'
Figure 2: Endpoint selection using 2 Cost Types with joint request on
updated cost values and for delay sensitive applications.
4. ALTO Protocol Updates Needed To Support Multi-Cost Transactions
To allow running Multi-Cost ALTO Services some minor changes in the
base protocol are needed. The main updates consist of changing the
JSON type of the value taken by the costs and add a few members to
the objects describing the information resources, client requests and
server responses to Multi-Cost information services.
As written in the introduction, this section relies on
Section {11.2.3.6} of the ALTO protocol draft, see [RFC7285] , which
allows protocol extensions to encode cost values as the 'JSONValue'
data type.
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4.1. List Of ALTO Protocol Updates Required And Recommended
The following updates to the ALTO protocol ([RFC7285]) are required
or recommended to support multi-cost ALTO transactions. The new
resulting JSON formats are specified in the next sections.
Section references ({##}) are to the ALTO protocol document.
The applicable ALTO information resources are: Cost Map, Filtrered
Cost Map and Endpoint Cost Map, becoming respectively Multi-Cost Map,
Filtered Multi-Cost Map and Endpoint Multicost Map provided with the
same media-type.
o Updates required in the format of objects member(s):
* Objects DstCosts (to destination PIDs, {11.2.3.6}) and
EndpointDstCosts (to destination Endpoints, {11.5.1.6}): the
cost value member evolves to an array of JSONValues.
* Object ReqFilteredCostMap {11.3.2.3} and ReqEndpointCostMap
{11.5.1.3}: a new member named "multi-cost-types" is
introduced. This member is an array of 1 or more cost types
for which a Multi-Cost ALTO Client requests values. Each cost
type of the array is encoded as specified in {10.7}.
o Updates recommended in the object structure:
* The capabilities for the Filtered Cost Map Service {11.3.2.4}
and the Endpoint Cost Map Service {11.5.1.4} need to be
extended with a new member entitled "max-cost-types" giving the
maximum number of Cost Types allowed in a Multi-Cost request
and response.
* The capabilities for the Multi Cost Map Service need to include
a new member named "multi-cost-type-names" and giving the list
of Cost Types that are provided in a Multi-Cost Map requested
via a GET method.
* The capabilities for the Cost Map Service, the Filtered Cost
Map Service {11.3.2.4} and the Endpoint Cost Map Service
{11.5.1.4} need to be extended with a new member named "multi-
cost-type-names" and giving the list of Cost Types that may be
included in the constraints member of a request.
* In a Server response to {11.3.2.6} filtered cost map request
and {11.5.1.6} and to filtered endpoint cost service request: a
new member named "multi-cost-types" and described above is
added to the "meta" field of the response.
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o Rules required on object member description:
* Order in which the multiple cost values are provided in the
responses.
4.2. Updates Required In The Member Format Of Objects
This section specifies the changes in the object member format that
are required to enable multi-cost ALTO transactions.
The term Single Cost qualifies the items as they are specified in the
current ALTO protocol.
4.2.1. Cost Value Encoded In array of JSON values
The fundamental change to support multi-cost is to encode the cost
values as an array of JSONValues. This way, the cost between two
PIDs or two Endpoints can be represented in a generic way:
o with several Cost Types,
o with Cost Types whose value can each be encoded with any type of
JSON value.
For example, a multi-cost value represented with Cost Types (assuming
they are supported by the ALTO Server):
["num-routingcost", "num-hopcount", "string-status"]
will be encoded in the following JSON Array in a Multi Cost ALTO
response:
[23, 6, "medium"]
The objects impacted by the encoding of ALTO Multi-Cost values in a
JSONArray are: DstCosts and EndpointDstCosts. Full specification
will be provided in later sections of this draft.
4.2.2. Scalar 'cost-type' Member Replaced By Array 'multi-cost-types'
Member
In the base protocol, the various single-cost-map services use a
scalar "cost-type" member in the "meta" section to indicate the cost
metric and cost mode of the returned values.
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In Multi-Cost ALTO, the multi-cost-map services use an array member
named "cost-types" instead. The array elements are in the same
format as the "cost-type" member in single cost maps, and the order
corresponds to the order of values in the array values in the multi-
cost map.
Alternatively, we could use the same member name, but define it as an
array for multi-cost services. This would simplify some things for a
client, but complicate others. Overall, we believe it is easier for
a client to use a new member name than to overload the type of an
existing member name.
4.2.3. Rule On Cost Value Order In ALTO Reponses
The cost values each Source/Destination pair MUST be provided in the
same order as in the array of Cost Types. This way, the cost type
values are provided without any ambiguity on the Cost Type they
report on.
4.3. Updates Recommended In The Object Structure
Objects MultiCostMapCapability {11.2.3.4} and
FilteredMultiCostMapCapability {11.3.2.4}: are extended with:
o a new member a new member entitled "max-cost-types" giving the
maximum number of Cost Types allowed in a Multi-Cost request and
response and giving the maximum number of Cost Types in a
response. The default value is set to 1 to avoid a multi-cost
aware client requesting a multi-cost map from a server that does
not support them.
o a new member named "multi-cost-type-names" and giving the list of
Cost Types that are provided in a Multi-Cost Map requested via a
GET method.
5. Extended Constraints On Multi-Cost Values
This draft proposes to extend the constraint tests in the base
protocol to allow tests on the various costs in a request, and to
allow more general predicates.
NOTE: Constraint tests on multiple cost metrics are useful even when
retrieving single costs, and we expect there will be proposals to add
multi-cost constraint tests to the ALTO protocol, relating to the
extensions proposed in this draft. Draft
[draft-lee-alto-app-net-info-exchange] proposes in particular
extensions to query values on a metric M1 with constraints on other
metrics {M2, ... Mk}, that adds an interesting feature to extend ALTO
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constraints. This motivates the need to augment the capabilities in
the IRD of the Filteredt Multi-Cost Map and Endpoint Multi-Cost Map
with the extensive list of Cost-Types that may be included in the
constraints of requests.
The base ALTO protocol allows optional contraints in the input
parameters to a request for a Filtered Cost Map or the Endpoint Cost
Service. The 'constraints' member is an array of expressions that
all apply to the (single) requested Cost Type. The encoding of
'constraints' member, is fully specified in Section 11.3.2.3 of the
base protocol as follows:
A constraint contains two entities separated by whitespace:
(1) an operator,'gt' for greater than, 'lt' for less than,
'ge' for greater than or equal to, 'le' for less than or equal to,
or 'eq' for equal to
(2) a target cost value. The cost value is a number that MUST be
defined in the same units as the Cost Type indicated by the costtype
parameter
...
If multiple 'constraint' parameters are specified, they are
interpreted as being related to each other with a logical AND.
Such a specification covers multiple predicates on one metric such
as:
'routingcost' values belong to [6, 20)
5.1. Use Cases For Multi-Cost Multi-Operator Constraints
Suppose that an application uses information on the ALTO Cost Types
'hopcount' and 'routingcost'. This application may want to select
paths or Endpoints with bounds on values for both 'hopcount' and
'routingcost'. For instance solutions meeting a constraint like:
'hopcount' values in [6,20) OR 'routingcost' values in [100,200]
Moreover, this application may be ready to make compromises and to
select paths or Endpoints by bounding their cost values according to
two options:
1. either solutions with moderate 'hopcount' and high 'routingcost',
for instance: 'hopcount' values in [6,20] AND 'routingcost'
values in [100,200],
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2. or solutions with higher 'hopcount' and moderate 'routingcost',
for instance: 'hopcount' values in [20,50] AND 'routingcost'
values in [30,100].
5.2. Extended constraints in Multi-Cost ALTO
This draft proposes to support the two above mentioned use cases by
extending the scope of constraints in two ways:
o allow the 'constraint' member to be applicable to multiple Cost
Types,
o allow the multiple constraints to be related to each other by both
logical AND and logical OR.
The two options would be covered by a logical expression like:
[('hopcount' ge 6) AND ('hopcount' lt 20) AND
('routingcost' ge 100) AND ('routingcost' le 200)]
OR
[('hopcount' ge 20) AND ('hopcount' le 50) AND
('routingcost' ge 30) AND ('routingcost' le 100)]
A simple encoding of multi-cost constraints for such expressions is
specified in Section 5.3.3 of this draft, describing the input
parameters to request for Filtered Cost Map. This specification is
applicable to the EP Cost service as well.
6. Protocol Extensions for Multi-Cost ALTO Transactions
This section proposes extensions of the ALTO protocol to support
Multi Cost ALTO Services or provide additional ALTO information. It
integrates discussions on the ALTO mailing list.
If an ALTO client desires information on several Cost Types, then
instead of placing as many requests as costs, it may request and
receive all the desired Cost Types in one single transaction.
The ALTO server then, provided it supports the requested Cost Types,
and provided it supports multi-cost ALTO transactions, sends one
single response where for each {source, destination} pair, the cost
values are arranged in an array, where each component corresponds to
a specified Cost Type. The correspondence between the components and
the Cost Types is implicitly indicated in the ALTO response. Indeed,
the values in the Cost values MUST be provided in the same order as
in the array of cost types indicated in the response.
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The following ALTO services have corresponding Multi-Cost extensions:
o Information Resources Directory: extended with multi-cost related
URIs and associated capabilities.
o Cost Map Service: extended with the Multi-Cost Map Service,
o Cost Map Filtering Service: extended with the Multi-Cost Map
Filtering Service,
o Endpoint Cost Lookup Service: extended with the Endpoint Multi-
Cost Lookup Service.
6.1. Information Resources Directory
When the ALTO server supports the provision of information on
multiple costs in a single transaction, the Information Resources
Directory will list the corresponding resources. The media type
remains the same as in the current ALTO protocol.
6.1.1. Example of Multi-Cost specific resources in the IRD
The following is an example Information Resource Directory returned
by an ALTO Server and containing Multi-Cost specific services: the
Multi-Cost Map Service, Filtered Multi-Cost Map and the Endpoint
Multi-Cost Service. It is assumed that the IRD contains usual ALTO
Services as described in the example IRD of the current ALTO
protocol. In this example, the ALTO Server can additionally provide
Multi-Cost Services in a specific folder of "alto.example.com" called
"multi". This folder contains the Multi-Cost Maps, Filtered Multi-
Cost Maps as well as the Endpoint Multi-Cost Service.
In this example, the ALTO IRD exposes Multi-Cost capabilities on cost
types "num-routingcost", "num-hopcount", "num-pathoccupationcost",
that can be combined in a request. The values on these metrics are
provided in numerical mode. Values provided for cost-type string are
in "string" mode.
For the "filtered-multicost-map" resource and the "endpoint-
multicost-map" resource, the IRD exposes in its capabilities a member
noted "testable-cost-types" that is the list of cost-types that are
allowed to be included in the constraints of a request. Note that
this set may be different than the set "multi-cost-type-names". The
"endpoint-multicost-map" resource provides cost-values for Cost Types
"num-routingcost", "num-hopcount" and "str-status" and supports
constraints on "num-routingcost", "num-hopcount", "num-
pathoccupationcost" where as it does not provide values on "num-
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pathoccupationcost" and does not supports constraints on "str-
status".
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-pathoccupationcost" : {
"cost-mode" : "numerical",
"cost-metric" : "pathoccupationcost"
},
"str-status" : {
"cost-mode" : "string",
"cost-metric" : "status"
},
"num-routing" : {
"cost-mode" : "numerical",
"cost-metric" : "routingcost"
},
"num-hopcount" : {
"cost-mode" : "numerical",
"cost-metric" : "hopcount"
},
.....
Other ALTO cost types as described
in current ALTO Protocol
.....
},
"default-alto-network-map" : "my-default-network-map"
},
"resources" : {
"my-default-network-map" : {
"uri" : "http://alto.example.com/networkmap",
"media-type" : "application/alto-networkmap+json"
},
"numerical-routing-cost-map" : {
.....
Single-cost Services as described
in current ALTO Protocol
.....
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},
"rc-hc-multicost-map" : {
"uri" : "http://alto.example.com/multi/costmap",
"media-types" : ["application/alto-costmap+json"],
"uses" : [ "my-default-network-map" ],
"capabilities" : {
"multi-cost-type-names" : [ "num-routing", "num-hopcount" ]
}
},
"filtered-multicost-map" : {
"uri" : "http://alto.example.com/multi/costmap/filtered",
"media-types" : ["application/alto-costmap+json" ],
"accepts" : ["application/alto-costmapfilter+json" ],
"uses" : [ "my-default-network-map" ],
"capabilities" : {
"cost-constraints" : true,
"max-cost-types" : 3,
"cost-type-names" : [ "num-routingcost",
"num-hopcount",
"num-pathoccupationcost" ],
"testable-cost-types": ["num-routingcost",
"num-hopcount",
"num-pathoccupationcost" ]
}
},
"endpoint-multicost-map" : {
"uri" : "http://alto.example.com/multi/endpointcost/lookup",
"media-types" : [ "application/alto-endpointcost+json" ],
"accepts" : [ "application/alto-endpointcostparams+json" ],
"uses" : [ "my-default-network-map" ],
"capabilities" : {
"cost-constraints" : true,
"max-cost-types" : 3,
"cost-type-names" : [ "num-routingcost",
"num-hopcount",
"str-status" ],
"multi-cost-type-names" : [ "num-routingcost",
"num-hopcount",
"str-status"],
"testable-cost-types": ["num-routingcost",
"num-hopcount",
"num-pathoccupationcost" ]
}
}
}
}
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6.2. Multi-Cost Map Service
This section introduces a new media-type for the Multi-Cost map. For
each source/destination pair of PIDs, it provides the values of the
different Cost Types supported for the Multi-Cost map, in the same
order as in the list of Cost Types specified in the capabilities.
A Multi-Cost Map MAY be provided by an ALTO Server.
Note that the capabilities specify implicitly the order in which the
different Cost Type values will be listed in the Cost Map.
The Cost Type values in the responses are encoded as a JSONArray of
cost values for the different Cost Types.
Note that values in a Multi-Cost map are arrays of values of the
various Cost Types. If the ALTO server does not have the value for a
particular Cost Type for a source/destination PID pair, the server
MUST use 'null' (a reserved JSON symbol) for that location in the
array. If the ALTO server does not have a value for any of the Cost
Types for a given source/destination pair -- that is, if the array
would be a list of nulls -- then the ALTO server MAY omit the array
for that source/destination pair.
6.2.1. Media Type
The media type is "application/alto-costmap+json".
6.2.2. HTTP Method
This resource is requested using the HTTP GET method.
6.2.3. Input Parameters
None.
6.2.4. Capabilities
The capabilities of the URI providing this resource are defined by a
JSON object of type FilteredCostMapCapabilities::
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object {
JSONString multi-cost-type-names<1..*>;
} MultiCostMapCapabilities;
with members
multi-cost-type-names The Cost Type names returned by this map.
An ALTO Server MUST support all of the Cost Types listed here. Note
that an ALTO Server may provide multiple Cost Map Information
Resources, each with different capabilities.
An ALTO Server supporting the Multi-Cost Map service MUST support the
Cost mode 'numerical' for all supported Cost Types encoded with the
'JSONNumber' type.
A full cost map resource capabilities has either "cost-type-names" or
"multi-cost-type-names", but not both. The former means it returns a
Single Cost Map, the latter means it returns a multi-cost Map. Since
this resource is requested via the GET method, the Server returns
what it returns and the client has no choice.
6.2.5. Uses
The Resource ID of the Network Map which defines the PIDs used in
this Multi Cost Map. An ALTO Server MUST NOT define two Multi Cost
Maps with the same Network Map and set of Cost Types.
6.2.6. Response
The "meta" field of a Cost Map response MUST include the "dependent-
vtags" key, whose value is a single-element array to indicate the
Version Tag of the Network Map used, where the Network Map is
specified in "uses" of the IRD.
The "meta" MUST also include the member "multi-cost-types", which is
a JSONArray of the CostTypes in this Multi Cost Map.
The data component of a Multi Cost Map response is named "cost-map",
which is a JSON object of type CostMapData, as defined in {11.2.3.6}
of the ALTO protocol. This is identical to the format of the ALTO
Cost Map response, except that the JSONValues are arrays rather than
numbers. The values in the arrays correspond to the Cost Type listed
at the same place in the 'multi-cost-types' array. This array MUST
have the same size as the 'multi-cost-types' array, and the provided
values MUST be in the same order as in the 'multi-cost-types' array.
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The returned Multi Cost Map MUST include the required Path Costs for
each pair of Source and Destination PID for which this information is
available. If a cost value is not defined, the ALTO Server MUST
replace that value in the array with the reserved JSON symbol 'null'.
If no costs are defined for a pair of Source and Destination PIDs, so
the Path Cost would be an array of nulls, the ALTO Server MAY omit
the array for that pair.
6.2.7. Example
This example illustrates a 'static' multi-cost ALTO transaction,
where the utilized Cost Types all have 'static' values. We assume
here that the Cost Types available at the ALTO Server are
"routingcost" and "hopcount" and the 'numerical' mode is available
for both of them. The "routingcost" may be based on monetary
considerations where as the "hopcount" is used to report on the path
delay. We also assume that ALTO server does not know the value of
the "routingcost" between PID2 and PID3, and hence uses 'null' for
those costs.
GET /multicostmap/num HTTP/1.1
Host: alto.example.com
Accept: application/alto-costmap+json,application/alto-error+json
HTTP/1.1 200 OK
Content-Length: [TODO]
Content-Type: application/alto-costmap+json
{
"meta" : {
"dependent-vtags" : [
{"resource-id": "my-default-network-map",
"tag": "3ee2cb7e8d63d9fab71b9b34cbf764436315542e"
}
],
"multi-cost-types" : [
{"cost-mode": "numerical", "cost-metric": "routingcost"},
{"cost-mode": "numerical", "cost-metric": "hopcount"}
]
}
"cost-map" : {
"PID1": { "PID1":[1,0], "PID2":[5,23], "PID3":[10,5] },
"PID2": { "PID1":[null,5], "PID2":[1,0], "PID3":[15,9] },
"PID3": { "PID1":[20,12], "PID2":[null,1], "PID3":[1,0] }
}
}
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6.3. Filtered Multi-Cost Map
A Multi-Cost Map may be very large. In addition, an Application
Client assisted by the ALTO Client does not necessarily need the Cost
Types for all the source/destination PID pairs.
Therefore applications may more likely use Cost Map information
filtered w.r.t. the Cost types as well as the source/destination
pairs of PIDs. This section specifies Filtered Multi-Cost Maps.
A Filtered Multi Cost Map is a Cost Map Information Resource for
which an ALTO Client may supply additional parameters limiting the
scope of the resulting Cost Map. A Filtered Multi Cost Map MAY be
provided by an ALTO Server.
6.3.1. Media Type
The media type is "application/alto-costmap+json".
6.3.2. HTTP Method
This resource is requested using the HTTP POST method.
6.3.3. Input Parameters
Input parameters are supplied in the entity body of the POST request.
This document specifies the input parameters with a data format
indicated by the media type "application/alto-costmapfilter+json",
which is a JSON Object of type ReqFilteredMultiCostMap, where:
object {
PIDName srcs<0..*>;
PIDName dsts<0..*>;
} PIDFilter;
object {
CostType multi-cost-types<1..*>;
JSONString constraints<0..*>; [OPTIONAL] - TO BE UPDATED
JSONArray or-constraints<0..*>; [OPTIONAL]
PIDFilter pids; [OPTIONAL]
} ReqFilteredMultiCostMap;
with members:
multi-cost-type-names The array of requested Cost Types for the returned costs.
Each listed Cost Type MUST be one of the supported Cost Types
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indicated in this resource's capabilities.
constraints
As specified in section {11.3.2.3} of RFC7285.
The Client MUST specify this member in its requests for
single cost services as specified in RFC7285.
The Client MUST NOT specify this member in requests for
multi-cost services.
The Client MUST NOT specify both a 'constraint' and
an 'or-constraints' parameter.
NB: THIS TEXT ON SUPPORT OF BASE PROTOCOL SINGLE COST CONSTRAINTS
WILL BE UPDATED IN NEXT VERSIONS
or-constraints
Defines an array of arrays of constraint strings.
This parameter MUST NOT be specified if this resource's capabilities
indicate that constraint support is not available.
A constraint string is an array of additional constraints.
That is the constraint strings of the array are related by
logical ANDs. Each string in the
constraint array MUST contain three entities separated by
whitespace, in the following format:
[index] op value
'Index' is a number between 0 and the number of Testable Cost
Types minus 1, and indicates the Cost Type to which this
constraint applies. (The square brackets ([]) surrounding
'index' are required syntactic sugar. They serve as a
reminder that 'index' is an array index, not a value to test,
and they avoid unusual-looking constraints such as "1 ge 5".)
'Op' is an operator: 'gt' for greater than, 'lt' for less
than, 'ge' for greater than or equal to, 'le' for less than
or equal to, 'eq' for equal to, or 'ne' for not equal to.
'Value' is a target cost value to compare against the
indicated Cost Type. For numeric Cost Types, 'value' MUST be
a number defined in the same units as the Cost Type indicated
by 'index'. ALTO servers SHOULD use at least IEEE 754
doubleprecision floating point [IEEE.754.2008] to store the
cost value, and SHOULD perform internal computations using
double-precision floating-point arithmetic. For string Cost
Types, 'value' MUST be a string enclosed in single quotes (').
For array-valued Cost Types, 'eq' is true iff one of the
Cost Type values is equal to 'value', and 'ne' is true iff
none of the Cost Type values are equal to 'value'. The other
operators are not defined for array-valued Cost Types.
The "or-constraints" member defines an array of arrays of
constraint strings in the format : [index] op value
The ALSO server MUST return costs that satisfy all constraints
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in one or more of the inner lists, and no other costs. That is,
'or-constraints' is the logical OR of ANDs.
pids A list of Source PIDs and a list of Destination PIDs for which
Path Costs are to be returned. If a list is empty, the ALTO
Server MUST interpret it as the full set of currently-defined
PIDs. The ALTO Server MUST interpret entries appearing in a list
multiple times as if they appeared only once. If the "pids"
member is not present, both lists MUST be interpreted by the ALTO
Server as containing the full set of currently-defined PIDs.
6.3.4. Capabilities
The URI providing this resource supports all capabilities documented
in Section 6.2.4 (with identical semantics), plus additional
capabilities. In particular, the capabilities are defined by a JSON
object of type FilteredMultiCostMapCapability:
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object {
JSONString cost-type-names<1..*>;
JSONString multi-cost-type-names<1..*>;
JSONBool cost-constraints;
JSONNumber max-cost-types; [OPTIONAL]
} FilteredMultiCostMapCapability;
with members:
cost-type-names
The array of cost types available from this service.
multi-cost-type-names
The array of cost types available from this service.
Its resence means that this resource can return
a multi-cost map. A filtered cost map resource can have
either "cost-type-names" or "multi-cost-type-names" or both
in its capabilities. The former means it can return a single
cost map, the latter a multi cost. The Client selects which.
max-cost-types Indicates the maximum number of cost values
the ALTO Server can provide in a multi-cost array of a
Multi-Cost Map.
cost-constraints If true, then the ALTO Server allows cost
constraints to be included in requests to the corresponding URI.
If not present, this member MUST be interpreted as if it specified
false.
Note that a filtered cost map resource can have either "cost-type-
names" or "multi-cost-type-names" or both in its capabilities. The
former means it can return a single cost map, the latter a multi
cost. The Client selects which one its wants.
6.3.5. Uses
The Resource ID of the Network Map which defines the PIDs used in
this Filtered Multi Cost Map.
6.3.6. Response
The response is the same format as for the Multi Cost Map Service
(Section 6.2.6). The returned Cost Map MUST NOT contain any source/
destination pair that was not indicated (implicitly or explicitly) in
the input parameters. If the input parameters contain a PID name
that is not currently defined by the ALTO Server, the ALTO Server
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MUST behave as if the PID did not appear in the input parameters. If
any constraints are specified, Source/Destination pairs for which the
Path Costs do not meet the constraints MUST NOT be included in the
returned Cost Map. If no constraints were specified, then all Path
Costs are assumed to meet the constraints.
6.3.7. Example 1
POST multi/multicostmap/filtered HTTP/1.1
Host: alto.example.com
Content-Type: application/alto-costmapfilter+json
Accept: application/alto-costmap+json,application/alto-error+json
{
"multi-cost-types" : [
{"cost-mode": "numerical", "cost-metric": "routingcost"},
{"cost-mode": "numerical", "cost-metric": "hopcount"}
],
"pids" : {
"srcs" : [ "PID1" ],
"dsts" : [ "PID1", "PID2", "PID3" ]
}
}
HTTP/1.1 200 OK
Content-Length: [TODO]
Content-Type: application/alto-costmap+json
{
"meta" : {
"dependent-vtags" : [
{"resource-id": "my-default-network-map",
"tag": "3ee2cb7e8d63d9fab71b9b34cbf764436315542e"
}
],
"multi-cost-types" : [
{"cost-mode": "numerical", "cost-metric": "routingcost"},
{"cost-mode": "numerical", "cost-metric": "hopcount"}
]
}
"cost-map" : {
"PID1": { "PID1": [1,6], "PID2": [5,23], "PID3": [10,5] }
}
}
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6.3.8. Example 2
This is an example of using constraints to restrict returned source/
destination PID pairs to those with 'routingcost' between 5 and 10,
or 'hopcount' equal to 0.
POST multi/multicostmap/filtered HTTP/1.1
Host: alto.example.com
Content-Type: application/alto-costmapfilter+json
Accept: application/alto-costmap+json,application/alto-error+json
{
"multi-cost-types" : [
{"cost-mode": "numerical", "cost-metric": "routingcost"},
{"cost-mode": "numerical", "cost-metric": "hopcount"}
],
"or-constraints" : [ ["[0] ge 5", "[0] le 10"],
["[1] eq 0"] ]
"pids" : {
"srcs" : [ "PID1", "PID2" ],
"dsts" : [ "PID1", "PID2", "PID3" ]
}
}
HTTP/1.1 200 OK
Content-Length: [TODO]
Content-Type: application/alto-costmap+json
{
"meta" : {
"dependent-vtags" : [
{"resource-id": "my-default-network-map",
"tag": "3ee2cb7e8d63d9fab71b9b34cbf764436315542e"
}
],
"multi-cost-types" : [
{"cost-mode": "numerical", "cost-metric": "routingcost"},
{"cost-mode": "numerical", "cost-metric": "hopcount"}
]
}
"cost-map" : {
"PID1": { "PID2": [5,23], "PID3": [10,5] }
"PID2": { "PID2": [1,0] },
}
}
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6.4. Endpoint Multi-Cost Service
The Endpoint Multi-Cost Service provides information on several Cost
Types between individual Endpoints.
This service MAY be provided by an ALTO Server. It is important to
note that although this resource allows an ALTO Server to reveal
costs between individual endpoints, an ALTO Server is not required to
do so. A simple alternative would be to compute the cost between two
endpoints as the costs between the PIDs corresponding to the
endpoints if these values are available for the requested Cost Types.
When the cost values are requested to perform multi-variate numerical
optimization and are each available in the 'numerical' mode, then the
ALTO Client SHOULD request the 'numerical' mode in order to get a
reliable result. Note that this consideration is outside the scope
of the ALTO protocol as it relates to the responsibility of the ALTO
Client and related entries. However common sense lead to warn that a
necessary condition for vector ranking method to be reliable is that
the components of the processed vectors are numerical and not ordinal
values.
6.4.1. Media Type
The media type is "application/alto-endpointcost+json".
6.4.2. HTTP Method
This resource is requested using the HTTP POST method
6.4.3. Input Parameters
Input parameters are supplied in the entity body of the POST request.
This document specifies input parameters with a data format indicated
by media type "application/alto-endpointmulticostparams+json", which
is a JSON Object of type ReqEndpointMultiCostMap:
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object {
TypedEndpointAddr srcs<0..*>; [OPTIONAL]
TypedEndpointAddr dsts<1..*>;
} EndpointFilter;
object{
CostType multi-cost-types<1..*>;
JSONString constraints<0..*>; [OPTIONAL] // TO BE UPDATED
JSONArray or-constraints<0..*>; [OPTIONAL]
EndpointFilter endpoints;
} ReqEndpointMultiCostMap;
with members:
multi-cost-types Defined equivalently to the "cost-types"
input parameter of a Filtered Multi Cost Map.
constraints Defined equivalently to the "constraints"
input parameter of a Filtered Multi Cost Map.
or-constraints Defined equivalently to the "or-constraints"
input parameter of a Filtered Multi Cost Map.
endpoints A list of Source Endpoints and Destination Endpoints for
which Path multiple Costs are to be returned. If the list
of Source Endpoints is empty (or not included), the ALTO Server
MUST interpret it as if it contained the Endpoint Address
corresponding to the client IP address from the incoming
connection (see Section 10.3 for discussion and considerations
regarding this mode). The list of destination Endpoints
MUST NOT be empty. The ALTO Server MUST interpret entries
appearing multiple times in a list as if they appeared only once.
6.4.4. Capabilities
The capabilities are the same as described in Section 6.3.4.
6.4.5. Uses
As with the ALTO Endpoint Cost Service, the Endpoint Multi Cost
Service MUST NOT use a Network Map.
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6.4.6. Response
The "meta" field of an Endpoint Multi Cost response MUST include the
"multi-cost-types" key, to indicate the Cost Types used.
The data component of an Endpoint Multi Cost response is named
"endpoint-cost-map", which is a JSON object of type
EndpointCostMapData, as defined in Section 11.5.1.6 of the ALTO
protocol. This is identical to the format of the ALTO Cost Map
response, except that the JSONValues are arrays rather than numbers.
The values in the arrays correspond to the Cost Type listed at the
same place in the 'multi-cost-types' array. This array MUST have the
same size as the 'multi-cost-types' array, and the values in the MUST
be in the same order as in the 'multi-cost-types' array.
6.4.7. Example
This is an example of requesting jointly cost values for
"routingcost" and "hopcount" while using constraints to restrict the
returned source/destination endpoints to those with
'pathoccupationcost' between 5 and 10, or 'hopcount' equal to 0,
where 'pathoccupationcost' and 'hopcount' respectively have index 2
and 1 in the "testable-cost-types" member of the IRD capabilities of
the "endpoint-multicost-map" resource. Only 2 of the 3 requested
source/destination pairs meet the constraints.
POST multi/endpointmulticost/lookup HTTP/1.1
Host: alto.example.com
Content-Length: [TODO]
Content-Type: application/alto-endpoincostparams+json
Accept: application/alto-endpointcost+json,application/alto-error+json
{
"multi-cost-types" : [
{"cost-mode": "numerical", "cost-metric": "routingcost"},
{"cost-mode": "numerical", "cost-metric": "hopcount"}
],
"or-constraints" : [ ["[2] ge 5", "[2] le 10"],
["[1] eq 0"] ],
"endpoints" : {
"srcs": [ "ipv4:192.0.2.2" ],
"dsts": [
"ipv4:192.0.2.89",
"ipv4:198.51.100.34",
"ipv4:203.0.113.45"
]
}
}
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HTTP/1.1 200 OK
Content-Length: [TODO]
Content-Type: application/alto-endpointcost+json
{
"meta" : {
"dependent-vtags" : [
{"resource-id": "my-default-network-map",
"tag": "3ee2cb7e8d63d9fab71b9b34cbf764436315542e"
}
],
"multi-cost-types" : [
{"cost-mode": "numerical", "cost-metric": "routingcost"},
{"cost-mode": "numerical", "cost-metric": "hopcount"}
]
}
"endpoint-cost-map" : {
"ipv4:192.0.2.2": {
"ipv4:192.0.2.89" : [1, 7],
"ipv4:203.0.113.45" : [3, 2]
}
}
}
7. IANA Considerations
Information for the ALTO Endpoint property registry maintained by the
IANA and related to the new Endpoints supported by the acting ALTO
server. These definitions will be formulated according to the syntax
defined in Section on "ALTO Endpoint Property Registry" of [RFC7285],
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],
7.1. Information for IANA on proposed Cost Types
When a new ALTO Cost Type is defined, accepted by the ALTO working
group and requests for IANA registration MUST include the following
information, detailed in Section 11.2: Identifier, Intended
Semantics, Security Considerations.
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7.2. Information for IANA on proposed Endpoint Properties
Likewise, an ALTO Endpoint Property Registry could serve the same
purposes as the ALTO Cost Type registry. Application to IANA
registration for Endpoint Properties would follow a similar process.
8. Acknowledgements
The authors would like to thank Vijay Gurbani, Dave Mac Dysan, Dhruv
Dhodi and Young Lee for fruitful discussions and comments on this
draft and previous versions.
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-protocol]
""ALTO Protocol" RFC 7285", September 2014.
[RFC6708] "Application-Layer Traffic Optimization (ALTO)
Requirements", February 2012.
[RFC7285] R. Alimi, R. Yang, R. Penno (Eds.), , "ALTO Protocol",
September 2014.
[draft-jenkins-alto-cdn-use-cases-01]
""Use Cases for ALTO within CDNs" draft-jenkins-alto-cdn-
use-cases-01", June 2011.
[draft-lee-alto-app-net-info-exchange]
"Information Exchange for High Bandwidth Applications in
TE networks", October 2013.
[draft-randriamasy-alto-cost-schedule-01]
"ALTO Cost Schedule", July 2012.
[draft-randriamasy-alto-multi-cost-05]
"Multi-Cost ALTO", October 2011.
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Authors' Addresses
Sabine Randriamasy
Alcatel-Lucent/Bell Labs
Route de Villejust
NOZAY 91460
FRANCE
Email: Sabine.Randriamasy@alcatel-lucent.com
Wendy Roome
Alcatel-Lucent/Bell Labs
600 Mountain Ave, Rm 3B-324
Murray Hill, NJ 07974
USA
Phone: +1-908-582-7974
Email: w.roome@alcatel-lucent.com
Nico Schwan
Thales Deutschland
Lorenzstrasse 10
Stuttgart 70435
Germany
Email: nico.schwan@thalesgroup.com
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