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ALTO WG K. Gao
Internet-Draft Sichuan University
Intended status: Standards Track Y. Lee
Expires: January 9, 2020 Huawei
S. Randriamasy
Nokia Bell Labs
Y. Yang
Yale University
J. Zhang
Tongji University
July 8, 2019
ALTO Extension: Path Vector Cost Type
draft-ietf-alto-path-vector-07
Abstract
The Application-Layer Traffic Optimization (ALTO) protocol [RFC7285]
has defined cost maps and endpoint cost maps to provide basic network
information. However, they provide only scalar (numerical or
ordinal) cost mode values, which are insufficient to satisfy the
demands of solving more complex network optimization problems. This
document introduces an extension to the base ALTO protocol, namely
the path-vector extension, which allows ALTO clients to query
information such as the capacity region for a given set of flows
(called co-flows). A non-normative example called co-flow scheduling
is presented to illustrate the limitations of existing ALTO endpoint
cost maps. After that, details of the extension are defined.
Requirements Language
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in RFC 2119 [RFC2119].
Status of This Memo
This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF). Note that other groups may also distribute
working documents as Internet-Drafts. The list of current Internet-
Drafts is at https://datatracker.ietf.org/drafts/current/.
Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any
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time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress."
This Internet-Draft will expire on January 9, 2020.
Copyright Notice
Copyright (c) 2019 IETF Trust and the persons identified as the
document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents
(https://trustee.ietf.org/license-info) in effect on the date of
publication of this document. Please review these documents
carefully, as they describe your rights and restrictions with respect
to this document. Code Components extracted from this document must
include Simplified BSD License text as described in Section 4.e of
the Trust Legal Provisions and are provided without warranty as
described in the Simplified BSD License.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 5
3. Use Case . . . . . . . . . . . . . . . . . . . . . . . . . . 5
3.1. Capacity Region for Co-Flow Scheduling . . . . . . . . . 5
3.2. In-Network Caching . . . . . . . . . . . . . . . . . . . 7
4. Overview . . . . . . . . . . . . . . . . . . . . . . . . . . 8
4.1. New Cost Mode to Encode Path Vectors . . . . . . . . . . 8
4.2. New ALTO Entity Domain for ANE Properties . . . . . . . . 8
4.3. Multipart/Related Resource for Consistency . . . . . . . 9
5. Basic Data Types . . . . . . . . . . . . . . . . . . . . . . 10
5.1. ANE Identifier . . . . . . . . . . . . . . . . . . . . . 10
5.2. Path Vector Cost Type . . . . . . . . . . . . . . . . . . 10
5.2.1. Cost Metric: ane-path . . . . . . . . . . . . . . . . 11
5.2.2. Cost Mode: array . . . . . . . . . . . . . . . . . . 11
5.3. ANE Domain . . . . . . . . . . . . . . . . . . . . . . . 11
5.3.1. Domain Name . . . . . . . . . . . . . . . . . . . . . 11
5.3.2. Domain-Specific Entity Identifier . . . . . . . . . . 11
5.3.3. Hierarchy and Inheritance . . . . . . . . . . . . . . 11
5.4. ANE Properties . . . . . . . . . . . . . . . . . . . . . 11
5.4.1. ANE Property: Maximum Reservable Bandwidth . . . . . 11
5.4.2. ANE Property: Persistent Entity . . . . . . . . . . . 12
6. Service Extensions . . . . . . . . . . . . . . . . . . . . . 12
6.1. Multipart Filtered Cost Map for Path Vector . . . . . . . 12
6.1.1. Media Type . . . . . . . . . . . . . . . . . . . . . 12
6.1.2. HTTP Method . . . . . . . . . . . . . . . . . . . . . 12
6.1.3. Accept Input Parameters . . . . . . . . . . . . . . . 12
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6.1.4. Capabilities . . . . . . . . . . . . . . . . . . . . 13
6.1.5. Uses . . . . . . . . . . . . . . . . . . . . . . . . 13
6.1.6. Response . . . . . . . . . . . . . . . . . . . . . . 13
6.2. Multipart Endpoint Cost Service for Path Vector . . . . . 15
6.2.1. Media Type . . . . . . . . . . . . . . . . . . . . . 15
6.2.2. HTTP Method . . . . . . . . . . . . . . . . . . . . . 15
6.2.3. Accept Input Parameters . . . . . . . . . . . . . . . 15
6.2.4. Capabilities . . . . . . . . . . . . . . . . . . . . 15
6.2.5. Uses . . . . . . . . . . . . . . . . . . . . . . . . 15
6.2.6. Response . . . . . . . . . . . . . . . . . . . . . . 16
7. Examples . . . . . . . . . . . . . . . . . . . . . . . . . . 17
7.1. Information Resource Directory Example . . . . . . . . . 17
7.2. Example: Multipart Filtered Cost Map . . . . . . . . . . 19
7.3. Example: Multipart Endpoint Cost Service . . . . . . . . 20
7.4. Example: Incremental Updates . . . . . . . . . . . . . . 22
8. Compatibility . . . . . . . . . . . . . . . . . . . . . . . . 24
8.1. Compatibility with Base ALTO Clients/Servers . . . . . . 24
8.2. Compatibility with Multi-Cost Extension . . . . . . . . . 24
8.3. Compatibility with Incremental Update . . . . . . . . . . 24
9. General Discussions . . . . . . . . . . . . . . . . . . . . . 25
9.1. Provide Calendar for Property Map . . . . . . . . . . . . 25
9.2. Constraint Tests for General Cost Types . . . . . . . . . 25
9.3. General Multipart Resources Query . . . . . . . . . . . . 25
10. Security Considerations . . . . . . . . . . . . . . . . . . . 26
11. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 27
11.1. ALTO Cost Mode Registry . . . . . . . . . . . . . . . . 27
11.2. ALTO Entity Domain Registry . . . . . . . . . . . . . . 27
11.3. ALTO Property Type Registry . . . . . . . . . . . . . . 27
12. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 27
13. References . . . . . . . . . . . . . . . . . . . . . . . . . 28
13.1. Normative References . . . . . . . . . . . . . . . . . . 28
13.2. Informative References . . . . . . . . . . . . . . . . . 28
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 29
1. Introduction
The base ALTO protocol [RFC7285] is designed to expose network
information through services such as cost maps and endpoint cost
service. These services use an extreme "single-node" network
abstraction, which represents a whole network as a single node, and
hosts as "endpoint groups" directly connected to the node.
Although the "single-node" abstraction works well in many settings,
it lacks the ability to support emerging use cases, such as co-flow
scheduling for large-scale data analytics. For such a use case,
applications require a more powerful network view abstraction beyond
the "single-node" abstraction.
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To support capabilities like co-flow scheduling, this document uses a
"path vector" abstraction to represent more detailed network graph
information like capacity regions. A path vector is a sequence of
abstract network elements (ANEs), and each ANE represents a network
device that end-to-end traffic goes through, such as links, switches,
middleboxes, and their aggregations. An ANE can have properties such
as "bandwidth", and "delay". Providing such information can help
both applications to achieve better application performance and
networks to avoid network congestion.
Providing path vector abstraction using ALTO introduces the following
additional requirements (ARs):
AR-1: The path vector abstraction requires the encoding of array-
like cost values rather than scalar cost values in cost maps or
endpoint cost maps.
Specifically, the path vector abstraction requires the
specification of the sequence of ANEs between sources and
destinations. Such a sequence, however, cannot be encoded by the
scalar types (numerical or ordinal) which the base ALTO protocol
supports.
AR-2: The path vector abstraction requires the encoding of the
properties of aforementioned ANEs.
Specifically, only the sequences of ANEs are not enough for
existing use cases. Properties of ANEs such as "bandwidth" and
"delay" are needed by applications to properly construct network
constraints or states.
AR-3: The path vector abstraction requires consistent encoding of
path vectors (AR-1) and the properties of the ANEs in a path
vector (AR-2).
Specifically, path vectors and the properties of ANEs in the
vectors are dependent. A mechanism to query both of them
consistently is necessary.
This document proposes the path vector extension to the ALTO protocol
to satisfy these additional requirements .
Specifically, the extension encodes the array (AR-1) of ANEs over an
end-to-end path using a new cost type, and conveys the properties of
ANEs (AR-2) using unified property map
[I-D.ietf-alto-unified-props-new]. The path vector and ANE
properties are conveyed in a single message encoded as a multipart/
related message to satisfy AR-3.
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The rest of this document is organized as follows. Section 3.1 gives
an example of co-flow scheduling and illustrates the limitations of
the base ALTO protocol in such a use case. Section 4 gives an
overview of the path vector extension. Section 5.2 introduces a new
cost type. Section 5.3 registers a new domain in Domain Registry.
Section 6.1 and Section 6.2 define new ALTO resources to support Path
Vector query by using the request format of Filtered Cost Map and
Endpoint Cost Service. Section 7 presents several examples.
Section 8 and Section 9 discusses compatibility issues with other
existing ALTO extensions and design decisions. Section 10 and
Section 11 review the security and IANA considerations.
2. Terminology
Besides the terms defined in [RFC7285] and
[I-D.ietf-alto-unified-props-new], this document also uses the
following additional terms: Abstract Network Element and Path Vector.
o Abstract Network Element (ANE): An abstract network element is an
abstraction of network components. It can be an aggregation of
links, middleboxes, virtualized network function (VNF), etc. An
abstract network element has two types of attributes: a name and a
set of properties.
o Path Vector: A path vector is an array of ANEs. It presents an
abstract network path between source/destination points such as
PIDs or endpoints.
3. Use Case
3.1. Capacity Region for Co-Flow Scheduling
Assume that an application has control over a set of flows, which may
go through shared links or switches and share a bottleneck. The
application hopes to schedule the traffic among multiple flows to get
better performance. The capacity region information for those flows
will benefit the scheduling. However, existing cost maps cannot
reveal such information.
Specifically, consider a network as shown in Figure 1. The network
has 7 switches (sw1 to sw7) forming a dumb-bell topology. Switches
sw1/sw3 provide access on one side, sw2/sw4 provide access on the
other side, and sw5-sw7 form the backbone. Endhosts eh1 to eh4 are
connected to access switches sw1 to sw4 respectively. Assume that
the bandwidth all links are 100 Mbps.
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+------+
| |
--+ sw6 +--
/ | | \
PID1 +-----+ / +------+ \ +-----+ PID2
eh1__| |_ / \ ____| |__eh2
| sw1 | \ +--|---+ +---|--+ / | sw2 |
+-----+ \ | | | |/ +-----+
\_| sw5 +---------+ sw7 |
PID3 +-----+ / | | | |\ +-----+ PID4
eh3__| |__/ +------+ +------+ \____| |__eh4
| sw3 | | sw4 |
+-----+ +-----+
Figure 1: Raw Network Topology.
The single-node ALTO topology abstraction of the network is shown in
Figure 2.
+----------------------+
{eh1} | | {eh2}
PID1 | | PID2
+------+ +------+
| |
| |
{eh3} | | {eh4}
PID3 | | PID4
+------+ +------+
| |
+----------------------+
Figure 2: Base Single-Node Topology Abstraction.
Consider an application overlay (e.g., a large data analysis system)
which wants to schedule the traffic among a set of end host source-
destination pairs, say eh1 -> eh2 and eh3 -> eh4. The application
can request a cost map providing end-to-end available bandwidth,
using 'availbw' as cost-metric and 'numerical' as cost-mode.
The application will receive from ALTO server that the bandwidth of
eh1 -> eh2 and eh3 -> eh4 are both 100 Mbps. But this information is
not enough. Consider the following two cases:
o Case 1: If eh1 -> eh2 uses the path eh1 -> sw1 -> sw5 -> sw6 ->
sw7 -> sw2 -> eh2 and eh3 -> eh4 uses path eh3 -> sw3 -> sw5 ->
sw7 -> sw4 -> eh4, then the application will obtain 200 Mbps.
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o Case 2: If eh1 -> eh2 uses the path eh1 -> sw1 -> sw5 -> sw7 ->
sw2 -> eh2 and eh3 -> eh4 uses the path eh3 -> sw3 -> sw5 -> sw7
-> sw4 -> eh4, then the application will obtain only 100 Mbps due
to the shared link from sw5 to sw7.
To allow applications to distinguish the two aforementioned cases,
the network needs to provide more details. In particular:
o The network needs to expose more detailed routing information to
show the shared bottlenecks;
o The network needs to provide the necessary abstraction to hide the
real topology information while providing enough information to
applications.
The path vector extension defined in this document provides a
solution to address the preceding issue.
See [I-D.bernstein-alto-topo] for a more comprehensive survey of use
cases where extended network topology information is needed.
3.2. In-Network Caching
Consider a network as shown in Figure 3. Two clients (C1/eh2 and C2/
eh3) are downloading data from a server (S/eh1) and the network
provides an HTTP proxy which can cache results. The clients and the
server are controlled by an ALTO client.
+---------+
| Caching |
-+ Proxy |
/ | |
S +-------+ / +---------+
eh1__| sub |_ /
| net 1 | \ +--|---+ +----------+
+-------+ ---| | | | C2
| Gate +---------+ Internet |__eh3
C1 +-------+ --| way | | |
eh2__| sub |__/ +------+ +----------+
| net 2 |
+-------+
Figure 3: Raw Topology for the In-Network Caching Use Case.
Without the traffic correlation information, the ALTO client cannot
know whether or how the traffic goes through the proxy. For example,
if subnet1 and subnet2 are directly connected and the traffic from
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eh1 to eh2 bypasses the gateway, the in-network cache can only be
used for traffic from C2 to S and is less effective.
4. Overview
This section presents an overview of approaches adopted by the path
vector extension. It assumes that the readers are familiar with cost
map and endpoint cost service defined in [RFC7285]. The path vector
extension also requires the support of Filtered Property Map defined
in [I-D.ietf-alto-unified-props-new].
The path vector extension is composed of three building blocks: (1) a
new cost mode to encode path vectors in a cost map or an endpoint
cost map; (2) a new ALTO entity domain to enable ANE property
encoding using the unified property extension
[I-D.ietf-alto-unified-props-new]; and (3) a generic mechanism to put
multiple ALTO information objects in a single response to enforce
consistency, to preserve modularity and to avoid complex linking of
multiple responses.
4.1. New Cost Mode to Encode Path Vectors
Existing cost modes defined in [RFC7285] allow only scalar cost
values. However, the "path vector" abstraction requires to convey
vector format information (AR-1). To fulfill this requirement, this
document defines a new "cost-mode" named path vector to indicate that
the cost value is an array of ANEs. A path vector abstraction should
be computed for a specific performance metric, and this is achieved
using the existing "cost-metric" component of cost type. The details
of the new "cost-mode" is given in Section 5.2.
4.2. New ALTO Entity Domain for ANE Properties
A path vector of ANEs contains only the abstracted routing elements
between a source and a destination. Hence, an application can find
shared ANEs of different source-destination pairs but cannot know the
shared ANEs' properties. For the capacity region use case in
Section 3.1, knowing that eh1->eh2 and eh3->eh4 share ANEs but not
the available bandwidth of the shared ANEs, is not enough.
To encode ANE properties like the available bandwidth in a path
vector query response, this document uses the unified property
extension defined in [I-D.ietf-alto-unified-props-new].
Specifically, for each path vector query, the ALTO server generates a
property map associated to the (endpoint) cost map as follows:
o a dynamic entity domain of an entity domain type "ane" is
generated to contain the generated ANEs. Each ANE has the same
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unique identifier in the path vectors and in the dynamic entity
domain;
o each entity in this dynamic entity domain has the properties
specified by the client.
Detailed information and specifications are given in Section 5.3.
4.3. Multipart/Related Resource for Consistency
Path vectors and the property map containing the ANEs are two
different types of objects, but they require strong consistency. One
approach to achieving strong consistency is to define a new media
type to contain both objects, but this violates modular design.
Another approach is to provide the objects in two different
information resources. Thus, an ALTO client needs to make separate
queries to get the information of related services. This may cause a
data synchronization problem between two queries. Also, as the
generation of ANE is dynamic, an ALTO server must cache the results
of a query before a client fully retrieves all related resources,
which hurts the scalability and security of an ALTO server.
This document uses standard-conforming usage of "multipart/related"
media type defined in [RFC2387] to elegantly solve the problem.
Specifically, using "multipart/related" needs to address two issues:
o ALTO uses media type to indicate the type of an entry in the
information resource directory (IRD) (e.g., "application/alto-
costmap+json" for cost map and "application/alto-
endpointcostmap+json" for endpoint cost map). Simply putting
"multipart/related" as the media type, however, makes it
impossible for an ALTO client to identify the type of service
provided by related entries.
o The ALTO SSE extension (see [I-D.ietf-alto-incr-update-sse])
depends on resource-id to identify push updates, but resource-id
is provided only in IRD and hence each entry in the IRD has only
one resource-id.
This design addresses the two issues as follows:
o To address the first issue, the multipart/related media type
includes the type parameter to allow type indication of the root
object. For a cost map service, the "media-type" will be
"multipart/related" with the parameter "type=application/alto-
costmap+json"; for an endpoint cost map service, the parameter
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will be "type=application/alto-endpointcostmap+json". This design
is highly extensible. The entries can still use "application/
alto-costmapfilter+json" or "application/alto-
endpointcostparams+json" as the accept input parameters, and hence
an ALTO client still sends the filtered cost map request or
endpoint cost service request. The ALTO server sends the response
as a "multipart/related" message. The body of the response
includes two parts: the first one is of the media type specified
by the "type" parameter; the second one is a property map
associated to the first map.
o To address the second issue, each part of the "multipart/related"
response message has the MIME part header information including
"Content-Type" and "Resource-Id". An ALTO server MAY generate
incremental updates (see [I-D.ietf-alto-incr-update-sse]) for each
part separately using the "Resource-Id" header.
By applying the design above, for each path vector query, an ALTO
server returns the path vectors and the associated property map
modularly and consistently. An ALTO server can reuse the data models
of the existing information resources. And an ALTO client can
subscribe to the incremental updates for the dynamic generated
information resources without any changes, if th ALTO server provides
incremental updates for them.
5. Basic Data Types
5.1. ANE Identifier
An ANE identifier is encoded as a JSON string. The string MUST be no
more than 64 characters, and it MUST NOT contain characters other
than US-ASCII alphanumeric characters (U+0030-U+0039, U+0041-U+005A,
and U+0061-U+007A), the hyphen ("-", U+002D), the colon (":",
U+003A), the at sign ("@", code point U+0040), the low line ("_",
U+005F), or the "." separator (U+002E). The "." separator is
reserved for future use and MUST NOT be used unless specifically
indicated in this document, or an extension document.
The type ANEIdentifier is used in this document to indicate a string
of this format.
5.2. Path Vector Cost Type
This document defines a new cost type, which is referred to as the
"path vector" cost type. An ALTO server MUST offer this cost type if
it supports the path vector extension.
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5.2.1. Cost Metric: ane-path
This cost metric conveys an array of ANE identifiers, where each
identifier uniquely represents an ANE traversed by traffic from a
source to a destination.
5.2.2. Cost Mode: array
This cost mode indicates that every cost value in a cost map or an
endpoint cost map MUST be interpreted as a JSON array object.
Note that this cost mode only requires the cost value to be a JSON
array of JSONValue. However, an ALTO server that enables this
extension MUST return a JSON array of ANEIdentifier (Section 5.1)
when the cost metric is "ane-path".
5.3. ANE Domain
This document specifies a new ALTO entity domain called "ane" in
addition to the ones in [I-D.ietf-alto-unified-props-new]. The ANE
domain associates property values with the ANEs in a network. The
entity in ANE domain is often used in the path vector by cost maps or
endpoint cost resources. Accordingly, the ANE domain always depends
on a cost map or an endpoint cost map.
5.3.1. Domain Name
ane
5.3.2. Domain-Specific Entity Identifier
The entity identifier of ANE domain uses the same encoding as
ANEIdentifier (Section 5.1).
5.3.3. Hierarchy and Inheritance
There is no hierarchy or inheritance for properties associated with
ANEs.
5.4. ANE Properties
5.4.1. ANE Property: Maximum Reservable Bandwidth
The maximum reservable bandwidth property conveys the maximum
bandwidth that can be reserved for traffic from a source to a
destination and is indicated by the property name "maxresbw". The
value MUST be encoded as a numerical cost value as defined in
Section 6.1.2.1 of [RFC7285] and the unit is bit per second.
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If this property is requested but is missing for a given ANE, it MUST
be interpreted as that the ANE does not support bandwidth reservation
but have sufficiently large bandwidth for all traffic that traverses
it.
5.4.2. ANE Property: Persistent Entity
The persistent entity property conveys the physical or logical
network entities (e.g., links, in-network caching service) that are
contained by an abstract network element. It is indicated by the
property name "persistent-entity". The value is encoded as a JSON
array of entity identifiers ([I-D.ietf-alto-unified-props-new]).
These entity identifiers are persistent so that a client CAN further
query their properties for future use.
If this property is requested but is missing for a given ANE, it MUST
be interpreted as that no such entities exist in this ANE.
6. Service Extensions
6.1. Multipart Filtered Cost Map for Path Vector
This document introduces a new ALTO resource called Multipart
Filtered Cost Map resource, which allows an ALTO server to provide
other ALTO resources associated to the Cost Map resource in the same
response.
6.1.1. Media Type
The media type of the Multipart Filtered Cost Map Resource is
"multipart/related;type=application/alto-costmap+json".
6.1.2. HTTP Method
The Multipart Filtered Cost Map is requested using the HTTP POST
method.
6.1.3. Accept Input Parameters
The input parameters of the Multipart Filtered Cost Map are supplied
in the body of an HTTP POST request. This document extends the input
parameters to a filtered Cost Map with a data format indicated by the
media type "application/alto-costmapfilter+json", which is a JSON
object of type PVReqFilteredCostMap, where:
object {
[PropertyName ane-properties<0..*>;]
} PVReqFilteredCostMap : ReqFilteredCostMap;
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with fields:
ane-properties: A list of properties that are associated with the
ANEs. Each property in this list MUST match one of the supported
ANE properties indicated in the resource's "ane-properties"
capability. If the field is NOT present, it MUST be interpreted
as an empty list, indicating that the ALTO server MUST NOT return
any property in the unified property part.
6.1.4. Capabilities
The Multipart Filtered Cost Map resource extends the capabilities
defined in Section 11.3.2.4 of [RFC7285]. The capabilities are
defined by a JSON object of type PVFilteredCostMapCapabilities:
object {
[PropertyName ane-properties<0..*>;]
} PVFilteredCostMapCapabilities : FilteredCostMapCapabilities;
with fields:
cost-type-names: The "cost-type-names" field MUST only include the
path vector cost type, unless explicitly documented by a future
extension. This also implies that the path vector cost type MUST
be defined in the "cost-types" of the Information Resource
Directory's "meta" field.
ane-properties: Defines a list of ANE properties that can be
returned. If the field is NOT present, it MUST be interpreted as
an empty list, indicating the ALTO server CANNOT provide any ANE
property.
6.1.5. Uses
The resource ID of the network map based on which the PIDs in the
returned cost map will be defined. If this resource supports
"persistent-entities", it MUST also include ALL the resources that
exposes the entities that MAY appear in the response.
6.1.6. Response
The response MUST indicate an error, using ALTO protocol error
handling, as defined in Section 8.5 of [RFC7285], if the request is
invalid.
The "Content-Type" header of the response MUST be "multipart/related"
as defined by [RFC2387] with the following parameters:
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type: The type parameter MUST be "application/alto-costmap+json".
Note that [RFC2387] permits both parameters with and without the
double quotes.
start: The start parameter MUST be a quoted string where the quoted
part has the same value as the "Resource-ID" header in the first
part.
boundary: The boundary parameter is as defined in [RFC2387].
The body of the response consists of two parts.
The first part MUST include "Resource-Id" and "Content-Type" in its
header. The value of "Resource-Id" MUST be prefixed by the resource
id of the Multipart Filtered Cost Map appended by a "." character.
The "Content-Type" MUST be "application/alto-costmap+json".
The body of the first part MUST be a JSON object with the same format
as defined in Section 11.2.3.6 of [RFC7285]. The JSON object MUST
include the "vtag" field in the "meta" field, which provides the
version tag of the returned cost map. The resource id of the version
tag MUST be the same as the value of the "Resource-Id" header. The
"meta" field MUST also include the "dependent-vtags" field, whose
value is a single-element array to indicate the version tag of the
network map used, where the network map is specified in the "uses"
attribute of the Multipart Cost Map resource in IRD.
The second part MUST also include "Resource-Id" and "Content-Type" in
its header. The value of "Resource-Id" MUST be prefixed by the
resource id of the Multipart Filtered Cost Map appended by a "."
character. The "Content-Type" MUST be "application/alto-
propmap+json".
The body of the second part MUST be a JSON object with the same
format as defined in Section 4.6 of
[I-D.ietf-alto-unified-props-new]. The JSON object MUST include the
"dependent-vtags" field in the "meta" field. The value of the
"dependent-vtags" field MUST be an array of VersionTag objects as
defined by Section 10.3 of [RFC7285]. The "vtag" of the first part
MUST be included in the "dependent-vtags". If "persistent-entities"
is requested, the version tags of the dependent resources that MAY
expose the entities in the response MUST also be included. The
PropertyMapData has one member for each ANE identifier that appears
in the first part, where the EntityProps has one member for each
property requested by the client if applicable.
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6.2. Multipart Endpoint Cost Service for Path Vector
This document introduces a new ALTO resource called Multipart
Endpoint Cost resource, which allows an ALTO server to provide other
ALTO resources associated to the Endpoint Cost resource in the same
response.
6.2.1. Media Type
The media type of the Multipart Endpoint Cost Resource is
"multipart/related;type=application/alto-endpointcostmap+json".
6.2.2. HTTP Method
The Multipart Endpoint Cost resource is requested using the HTTP POST
method.
6.2.3. Accept Input Parameters
The input parameters of the Multipart Endpoint Cost resource are
supplied in the body of an HTTP POST request. This document extends
the input parameters to an Endpoint Cost Map with a data format
indicated by the media type "application/alto-
endpointcostparams+json", which is a JSON object of type
PVEndpointCostParams, where
object {
[PropertyName ane-properties<0..*>;]
} PVReqEndpointCostMap : ReqEndpointCostMap;
with fields:
ane-properties: This document defines the "ane-properties" in
PVReqEndpointCostMap as the same as in PVReqFilteredCostMap. See
Section 6.1.3.
6.2.4. Capabilities
The capabilities of the Multipart Endpoint Cost Service are defined
by a JSON object of type PVEndpointCostMapCapabilities, which is
defined as the same as PVFilteredCostMapCapabilities. See
Section 6.1.4.
6.2.5. Uses
If a Multipart Endpoint Cost resource supports "persistent-entities",
the "uses" field in its IRD entry MUST include ALL the resources
which exposes the entities that MAY appear in the response.
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6.2.6. Response
The response MUST indicate an error, using ALTO protocol error
handling, as defined in Section 8.5 of [RFC7285], if the request is
invalid.
The "Content-Type" header of the response MUST be "multipart/related"
as defined by [RFC2387] with the following parameters:
type: The type parameter MUST be "application/alto-
endpointcostmap+json".
start: The start parameter MUST be a quoted string where the quoted
part has the same value as the "Resource-ID" header in the first
part.
boundary: The boundary parameter is as defined in [RFC2387].
The body consists of two parts:
The first part MUST include "Resource-Id" and "Content-Type" in its
header. The value of "Resource-Id" MUST be prefixed by the resource
id of the Multipart Endpoint Cost Service appended by a "." character
(U+002E). The "Content-Type" MUST be "application/alto-
endpointcostmap+json".
The body of the first part MUST be a JSON object with the same format
as defined in Section 11.5.1.6 of [RFC7285]; The JSON object MUST
include the "vtag" field in the "meta" field, which provides the
version tag of the returned endpoint cost map. The resource id of
the version tag MUST be the same as the value of the "Resource-Id"
header.
The second part MUST also include "Resource-Id" and "Content-Type" in
its header. The value of "Resource-Id" MUST be prefixed by the
resource id of the Multipart Filtered Cost Map appended by a "."
character (U+002E). The "Content-Type" MUST be "application/alto-
propmap+json".
The body of the second part MUST be a JSON object with the same
format as defined in Section 4.6 of
[I-D.ietf-alto-unified-props-new]. The JSON object MUST include the
"dependent-vtags" field in the "meta" field. The value of the
"dependent-vtags" field MUST be an array of VersionTag objects as
defined by Section 10.3 of [RFC7285]. The "vtag" of the first part
MUST be included in the "dependent-vtags". If "persistent-entities"
is requested, the version tags of the dependent resources that MAY
expose the entities in the response MUST also be included. The
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PropertyMapData has one member for each ANE identifier that appears
in the first part, where the EntityProps has one member for each
property requested by the client if applicable.
7. Examples
This section lists some examples of path vector queries and the
corresponding responses. Some long lines are truncated for better
readability.
7.1. Information Resource Directory Example
Below is an example of an Information Resource Directory which
enables the path vector extension. Some critical modifications
include:
o The "path-vector" cost type (Section 5.2) is defined in the "cost-
types" of the "meta" field.
o The "cost-map-pv" information resource provides a Multipart Cost
Map resource, which exposes the Maximum Reservable Bandwidth
("maxresbw") property.
o The "http-proxy-props" information resource provides a filtered
Unified Property Map resource, which exposes the HTTP proxy entity
domain (encoded as "http-proxy") and the "price" property. Note
that HTTP proxy is NOT a valid entity domain yet and is used here
only for demonstration.
o The "endpoint-cost-pv" information resource provides a Multipart
Endpoint Cost Service. It exposes the Maximum Reservable
Bandwidth ("maxresbw") property and the Persistent Entity
property. The persistent entities MAY come from the "http-proxy-
props" resource.
o The "update-pv" information resource provides the incremental
update ([I-D.ietf-alto-incr-update-sse]) service for the
"endpoint-cost-pv" resource.
{
"meta": {
"cost-types": {
"path-vector": {
"cost-mode": "array",
"cost-metric": "ane-path"
}
}
},
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"resources": {
"my-default-networkmap": {
"uri" : "http://alto.example.com/networkmap",
"media-type" : "application/alto-networkmap+json"
},
"cost-map-pv": {
"uri": "http://alto.example.com/costmap/pv",
"media-type": "multipart/related;
type=application/alto-costmap+json",
"accepts": "application/alto-costmapfilter+json",
"capabilities": {
"cost-type-names": [ "path-vector" ],
"ane-properties": [ "maxresbw" ]
},
"uses": [ "my-default-networkmap" ]
},
"http-proxy-props": {
"uri": "http://alto.example.com/proxy-props",
"media-type": "application/alto-propmap+json",
"accpets": "application/alto-propmapparams+json",
"capabilities": {
"mappings": {
"http-proxy": [ "price" ]
}
}
},
"endpoint-cost-pv": {
"uri": "http://alto.exmaple.com/endpointcost/pv",
"media-type": "multipart/related;
type=application/alto-endpointcost+json",
"accepts": "application/alto-endpointcostparams+json",
"capabilities": {
"cost-type-names": [ "path-vector" ],
"ane-properties": [ "maxresbw", "persistent-entities" ]
},
"uses": [ "http-proxy-props" ]
},
"update-pv": {
"uri": "http://alto.example.com/updates/pv",
"media-type": "text/event-stream",
"uses": [ "endpoint-cost-pv" ],
"accepts": "application/alto-updatestreamparams+json",
"capabilities": {
"support-stream-control": true
}
}
}
}
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7.2. Example: Multipart Filtered Cost Map
The following examples demonstrate the request to the "cost-map-pv"
resource and the corresponding response.
The request uses the path vector cost type in the "cost-type" field.
The "ane-properties" field is missing, indicating that the client
only requests for the path vector but not the ANE properties.
The response consists of two parts. The first part returns the array
of ANE identifiers for each source and destination pair. There are
three ANEs, where "ane:L001" is shared by traffic from "PID1" to both
"PID2" and "PID3".
The second part returns an empty property map. Note that the ANE
entries are omitted since they have no properties (See Section 3.1 of
[I-D.ietf-alto-unified-props-new]).
POST /costmap/pv HTTP/1.1
Host: alto.example.com
Accept: multipart/related;type=application/alto-costmap+json,
application/alto-error+json
Content-Length: [TBD]
Content-Type: application/alto-costmapfilter+json
{
"cost-type": {
"cost-mode": "array",
"cost-metric": "ane-path"
},
"pids": {
"srcs": [ "PID1" ],
"dsts": [ "PID2", "PID3" ]
}
}
HTTP/1.1 200 OK
Content-Length: [TBD]
Content-Type: multipart/related;
boundary=example-1;
start=cost-map-pv.costmap;
type=application/alto-costmap+json
--example-1
Resource-Id: cost-map-pv.costmap
Content-Type: application/alto-costmap+json
{
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"meta": {
"vtag": {
"resource-id": "cost-map-pv.costmap",
"tag": "d827f484cb66ce6df6b5077cb8562b0a"
},
"dependent-vtags": [
{
"resource-id": "my-default-networkmap",
"tag": "75ed013b3cb58f896e839582504f6228"
}
],
"cost-type": {
"cost-mode": "array",
"cost-metric": "ane-path"
}
},
"cost-map": {
"PID1": {
"PID2": [ "ane:L001", "ane:L003" ],
"PID3": [ "ane:L001", "ane:L004" ]
}
}
}
--example-1
Resource-Id: cost-map-pv.propmap
Content-Type: application/alto-propmap+json
{
"meta": {
"dependent-vtags": [
{
"resource-id": "cost-map-pv.costmap",
"tag": "d827f484cb66ce6df6b5077cb8562b0a"
}
]
},
"property-map": {
}
}
7.3. Example: Multipart Endpoint Cost Service
The following examples demonstrate the request to the "endpoint-cost-
pv" resource and the corresponding response.
The request uses the path vector cost type in the "cost-type" field,
and queries the Maximum Reservable Bandwidth ANE property and the
Persistent Entity property.
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The response consists of two parts. The first part returns the array
of ANE identifiers for each valid source and destination pair.
The second part returns the requested properties of ANEs in the first
part. The "ane:NET001" element contains an HTTP proxy entity, which
can be further used by the client. Since it does not contain a
"maxresbw" property, the client SHOULD assume it does NOT support
bandwidth reservation but will NOT become a traffic bottleneck, as
specified in Section 5.4.1.
POST /endpointcost/pv HTTP/1.1
Host: alto.example.com
Accept: multipart/related;
type=application/alto-endpointcost+json,
application/alto-error+json
Content-Length: [TBD]
Content-Type: application/alto-endpointcostparams+json
{
"cost-type": {
"cost-mode": "array",
"cost-metric": "ane-path"
},
"endpoints": {
"srcs": [ "ipv4:192.0.2.2" ],
"dsts": [ "ipv4:192.0.2.89",
"ipv4:203.0.113.45",
"ipv6:2001:db8::10" ]
},
"ane-properties": [ "maxresbw", "persistent-entities" ]
}
HTTP/1.1 200 OK
Content-Length: [TBD]
Content-Type: multipart/related; boundary=example-2;
start=endpoint-cost-pv.ecs;
type=application/alto-endpointcost+json
--example-2
Resource-Id: endpoint-cost-pv.ecs
Content-Type: application/alto-endpointcost+json
{
"meta": {
"vtags": {
"resource-id": "endpoint-cost-pv.ecs",
"tag": "bb6bb72eafe8f9bdc4f335c7ed3b10822a391cef"
},
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"cost-type": {
"cost-mode": "array",
"cost-metric": "ane-path"
}
},
"endpoint-cost-map": {
"ipv4:192.0.2.2": {
"ipv4:192.0.2.89": [ "ane:NET001", "ane:L002" ],
"ipv4:203.0.113.45": [ "ane:NET001", "ane:L003" ]
}
}
}
--example-2
Resource-Id: endpoint-cost-pv.propmap
Content-Type: application/alto-propmap+json
{
"meta": {
"dependent-vtags": [
{
"resource-id": "endpoint-cost-pv.ecs",
"tag": "bb6bb72eafe8f9bdc4f335c7ed3b10822a391cef"
},
{
"resource-id": "http-proxy-props",
"tag": "bf3c8c1819d2421c9a95a9d02af557a3"
}
]
},
"property-map": {
"ane:NET001": {
"persistent-entities": [ "http-proxy:192.0.2.1" ]
},
"ane:L002": { "maxresbw": 48000000 },
"ane:L003": { "maxresbw": 35000000 }
}
}
7.4. Example: Incremental Updates
In this example, an ALTO client subscribes to the incremental update
for the Multipart Endpoint Cost resource "endpoint-cost-pv".
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POST /updates/pv HTTP/1.1
Host: alto.example.com
Accept: text/event-stream
Content-Type: application/alto-updatestreamparams+json
Content-Length: [TBD]
{
"add": {
"ecspvsub1": {
"resource-id": "endpoint-cost-pv",
"input": <ecs-input>
}
}
}
Based on the server-side process defined in
[I-D.ietf-alto-incr-update-sse], the ALTO server will send the
"control-uri" first using Server-Sent Event (SSE), followed by the
full response of the multipart message.
HTTP/1.1 200 OK
Connection: keep-alive
Content-Type: text/event-stream
event: application/alto-updatestreamcontrol+json
data: {"control-uri": "http://alto.example.com/updates/streams/1414"}
event: multipart/related;boundary=example-3;start=pvmap;
type=application/alto-endpointcost+json,ecspvsub1
data: --example-3
data: Resource-ID: endpoint-cost-pv.ecsmap02695067
data: Content-Type: application/alto-endpointcost+json
data:
data: <endpoint-cost-map-entry>
data: --example-3
data: Resource-ID: endpoint-cost-pv.propmapbbc868aa
data: Content-Type: application/alto-propmap+json
data:
data: <property-map-entry>
data: --example-3--
When the contents change, the ALTO server will publish the updates
for each node in this tree separately.
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event: application/merge-patch+json,
ecspvsub1.endpoint-cost-pv.ecsmap02695067
data: <Merge patch for endpoint-cost-map-update>
event: application/merge-patch+json,
ecspvsub1.endpoint-cost-pv.propmapbbc868aa
data: <Merge patch for property-map-update>
8. Compatibility
8.1. Compatibility with Base ALTO Clients/Servers
The Multipart Filtered Cost Map resource and the Multipart Endpoint
Cost resource has no backward compatibility issue with the base ALTO
clients and servers. Although these two types of resources reuse the
media types defined in the base ALTO protocol for the accept input
parameters, they have different media types for responses. If the
ALTO server provides these two types of resources, but the ALTO
client does not support them, the ALTO client will ignore the
resources without conducting any incompatibility.
8.2. Compatibility with Multi-Cost Extension
This document does not specify how to integrate the "path-vector"
cost mode with the multi-cost extension [RFC8189]. Although there is
no reason why somebody has to compound the path vectors with other
cost types in a single query, there is no compatible issue doing it
without constraint tests.
8.3. Compatibility with Incremental Update
As this document still follows the basic request/response protocol
with JSON encoding, it is surely compatible with the incremental
update service as defined by [I-D.ietf-alto-incr-update-sse]. But
the following details are to be noticed:
o When using the compound response, updates on both cost map and
property map SHOULD be notified.
o When not using the compound response, because the cost map is in
the "uses" attribute of the property map, once the path vectors in
the cost map change, the ALTO server MUST send the updates of the
cost map before the updates of the property map.
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9. General Discussions
9.1. Provide Calendar for Property Map
Fetching the historical network information is useful for many
traffic optimization problem. [I-D.ietf-alto-cost-calendar] already
proposes an ALTO extension called Cost Calendar which provides the
historical cost values using Filtered Cost Map and Endpoint Cost
Service. However, the calendar for only path costs is not enough.
For example, as the properties of ANEs (e.g., available bandwidth and
link delay) are usually the real-time network states, they change
frequently in the real network. It is very helpful to get the
historical value of these properties. Applications may predicate the
network status using these information to better optimize their
performance.
So the coming requirement may be a general calendar service for the
ALTO information resources.
9.2. Constraint Tests for General Cost Types
The constraint test is a simple approach to query the data. It
allows users to filter the query result by specifying some boolean
tests. This approach is already used in the ALTO protocol.
[RFC7285] and [RFC8189] allow ALTO clients to specify the
"constraints" and "or-constraints" tests to better filter the result.
However, the current defined syntax is too simple and can only be
used to test the scalar cost value. For more complex cost types,
like the "array" mode defined in this document, it does not work
well. It will be helpful to propose more general constraint tests to
better perform the query.
In practice, it is too complex to customize a language for the
general-purpose boolean tests, and can be a duplicated work. So it
may be a good idea to integrate some already defined and widely used
query languages (or their subset) to solve this problem. The
candidates can be XQuery and JSONiq.
9.3. General Multipart Resources Query
Querying multiple ALTO information resources continuously MAY be a
general requirement. And the coming issues like inefficiency and
inconsistency are also general. There is no standard solving these
issues yet. So we need some approach to make the ALTO client request
the compound ALTO information resources in a single query.
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10. Security Considerations
This document is an extension of the base ALTO protocol, so the
Security Considerations [RFC7285] of the base ALTO protocol fully
apply when this extension is provided by an ALTO server.
The path vector extension requires additional considerations on two
security considerations discussed in the base protocol:
confidentiality of ALTO information (Section 15.3 of [RFC7285]) and
availability of ALTO service (Section 15.5 of [RFC7285]).
For confidentiality of ALTO information, a network operator should be
aware of that this extension may introduce a new risk: the path
vector information may make network attacks easier. For example, as
the path vector information may reveal more network internal
structures than the more abstract single-node abstraction, an ALTO
client may detect the bottleneck link and start a distributed denial-
of-service (DDoS) attack involving minimal flows to conduct the in-
network congestion.
To mitigate this risk, the ALTO server should consider protection
mechanisms to reduce information exposure or obfuscate the real
information, in particular, in settings where the network and the
application do not belong to the same trust domain. But the
implementation of path vector extension involving reduction or
obfuscation should guarantees the constraints on the requested
properties are still accurate.
For availability of ALTO service, an ALTO server should be cognizant
that using path vector extension might have a new risk: frequent
requesting for path vectors might conduct intolerable increment of
the server-side storage and break the ALTO server. It is known that
the computation of path vectors is unlikely to be cacheable, in that
the results will depend on the particular requests (e.g., where the
flows are distributed). Hence, the service providing path vectors
may become an entry point for denial-of-service attacks on the
availability of an ALTO server. To avoid this risk, authenticity and
authorization of this ALTO service may need to be better protected.
Even if there is no intentional attack, the dependent property map of
path vector might be still dynamically enriched, in that every new
request for path vectors will make the ALTO server generate a new
property map. So the properties of the abstract network elements can
consume a large amount of resources when cached. To avoid this, the
ALTO server providing the path vector extension should support a
time-to-live configuration for the property map, so that the outdated
entries can be removed from the property map resource.
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11. IANA Considerations
11.1. ALTO Cost Mode Registry
This document specifies a new cost mode "path-vector". However, the
base ALTO protocol does not have a Cost Mode Registry where new cost
mode can be registered. This new cost mode will be registered once
the registry is defined either in a revised version of [RFC7285] or
in another future extension.
11.2. ALTO Entity Domain Registry
As proposed in Section 9.2 of [I-D.ietf-alto-unified-props-new],
"ALTO Domain Entity Registry" is requested. Besides, a new domain is
to be registered, listed in Table 1.
+-------------+--------------------------+--------------------------+
| Identifier | Entity Address Encoding | Hierarchy & Inheritance |
+-------------+--------------------------+--------------------------+
| ane | See Section 5.3.2 | None |
+-------------+--------------------------+--------------------------+
Table 1: ALTO Entity Domain
11.3. ALTO Property Type Registry
The "ALTO Property Type Registry" is required by the ALTO Domain
"ane", listed in Table 2.
+-------------+------------+----------------------------------------+
| Identifier | Intended | Dependencies and Interpretation |
| | Semantics | |
+-------------+------------+----------------------------------------+
| ane:maxresb | The | application/alto-costmap+json, or |
| w | maximum | application/alto-endpointcostmap+json, |
| | reservable | where the ANE names are used. |
| | bandwidth | |
| | for the | |
| | ANE | |
+-------------+------------+----------------------------------------+
Table 2: ALTO Abstract Network Element Property Types
12. Acknowledgments
The authors would like to thank discussions with Andreas Voellmy,
Erran Li, Haibin Son, Haizhou Du, Jiayuan Hu, Qiao Xiang, Tianyuan
Liu, Xiao Shi, Xin Wang, and Yan Luo. The authors thank Greg
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Bernstein (Grotto Networks), Dawn Chen (Tongji University), Wendy
Roome, and Michael Scharf for their contributions to earlier drafts.
13. References
13.1. Normative References
[I-D.ietf-alto-incr-update-sse]
Roome, W. and Y. Yang, "ALTO Incremental Updates Using
Server-Sent Events (SSE)", draft-ietf-alto-incr-update-
sse-16 (work in progress), March 2019.
[I-D.ietf-alto-unified-props-new]
Roome, W., Randriamasy, S., Yang, Y., and J. Zhang,
"Unified Properties for the ALTO Protocol", draft-ietf-
alto-unified-props-new-07 (work in progress), March 2019.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119,
DOI 10.17487/RFC2119, March 1997,
<https://www.rfc-editor.org/info/rfc2119>.
[RFC2387] Levinson, E., "The MIME Multipart/Related Content-type",
RFC 2387, DOI 10.17487/RFC2387, August 1998,
<https://www.rfc-editor.org/info/rfc2387>.
[RFC7285] Alimi, R., Ed., Penno, R., Ed., Yang, Y., Ed., Kiesel, S.,
Previdi, S., Roome, W., Shalunov, S., and R. Woundy,
"Application-Layer Traffic Optimization (ALTO) Protocol",
RFC 7285, DOI 10.17487/RFC7285, September 2014,
<https://www.rfc-editor.org/info/rfc7285>.
[RFC8189] Randriamasy, S., Roome, W., and N. Schwan, "Multi-Cost
Application-Layer Traffic Optimization (ALTO)", RFC 8189,
DOI 10.17487/RFC8189, October 2017,
<https://www.rfc-editor.org/info/rfc8189>.
13.2. Informative References
[I-D.bernstein-alto-topo]
Bernstein, G., Yang, Y., and Y. Lee, "ALTO Topology
Service: Uses Cases, Requirements, and Framework", draft-
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Authors' Addresses
Kai Gao
Sichuan University
Chengdu 610000
China
Email: kai.gao@scu.edu.cn
Young Lee
Huawei
TX
USA
Email: leeyoung@huawei.com
Sabine Randriamasy
Nokia Bell Labs
Route de Villejust
NOZAY 91460
FRANCE
Email: Sabine.Randriamasy@nokia-bell-labs.com
Y. Richard Yang
Yale University
51 Prospect St
New Haven CT
USA
Email: yry@cs.yale.edu
Jingxuan Jensen Zhang
Tongji University
4800 Caoan Road
Shanghai 201804
China
Email: jingxuan.n.zhang@gmail.com
Gao, et al. Expires January 9, 2020 [Page 29]
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