ALTO WG K. Gao
Internet-Draft Tsinghua University
Intended status: Standards Track Y. Lee
Expires: December 20, 2019 Huawei
S. Randriamasy
Nokia Bell Labs
Y. Yang
Yale University
J. Zhang
Tongji University
June 18, 2019
ALTO Extension: Path Vector Cost Type
draft-ietf-alto-path-vector-06
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 December 20, 2019.
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
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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: Capacity Region for Co-Flow Scheduling . . . . . . 5
4. Overview of Path Vector Extensions . . . . . . . . . . . . . 7
4.1. New Cost Mode to Encode Path Vectors . . . . . . . . . . 7
4.2. New ALTO Entity Domain for ANE Properties . . . . . . . . 8
4.3. Multipart/Related Resource for Consistency . . . . . . . 8
5. Path-Vector Cost Type . . . . . . . . . . . . . . . . . . . . 9
5.1. Cost Mode: path-vector . . . . . . . . . . . . . . . . . 10
5.2. Cost Metric: Link Maximum Reservable Bandwidth . . . . . 10
6. ANE Domain . . . . . . . . . . . . . . . . . . . . . . . . . 10
6.1. Domain Name . . . . . . . . . . . . . . . . . . . . . . . 11
6.2. Domain-Specific Entity Identifier . . . . . . . . . . . . 11
6.3. Hierarchy and Inheritance . . . . . . . . . . . . . . . . 11
7. Multipart Filtered Cost Map for Path Vector . . . . . . . . . 11
7.1. Media Type . . . . . . . . . . . . . . . . . . . . . . . 11
7.2. HTTP Method . . . . . . . . . . . . . . . . . . . . . . . 11
7.3. Accept Input Parameters . . . . . . . . . . . . . . . . . 12
7.4. Capabilities . . . . . . . . . . . . . . . . . . . . . . 12
7.5. Uses . . . . . . . . . . . . . . . . . . . . . . . . . . 12
7.6. Response . . . . . . . . . . . . . . . . . . . . . . . . 12
8. Multipart Endpoint Cost Service for Path Vector . . . . . . . 13
8.1. Media Type . . . . . . . . . . . . . . . . . . . . . . . 13
8.2. HTTP Method . . . . . . . . . . . . . . . . . . . . . . . 13
8.3. Accept Input Parameters . . . . . . . . . . . . . . . . . 13
8.4. Capabilities . . . . . . . . . . . . . . . . . . . . . . 13
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8.5. Uses . . . . . . . . . . . . . . . . . . . . . . . . . . 14
8.6. Response . . . . . . . . . . . . . . . . . . . . . . . . 14
9. Examples . . . . . . . . . . . . . . . . . . . . . . . . . . 14
9.1. Information Resource Directory Example . . . . . . . . . 14
9.2. Example #1 . . . . . . . . . . . . . . . . . . . . . . . 16
9.3. Example #2 . . . . . . . . . . . . . . . . . . . . . . . 17
9.4. Example for Incremental Update . . . . . . . . . . . . . 19
10. Compatibility . . . . . . . . . . . . . . . . . . . . . . . . 20
10.1. Compatibility with Base ALTO Clients/Servers . . . . . . 20
10.2. Compatibility with Multi-Cost Extension . . . . . . . . 21
10.3. Compatibility with Incremental Update . . . . . . . . . 21
11. General Discussions . . . . . . . . . . . . . . . . . . . . . 21
11.1. Provide Calendar for Property Map . . . . . . . . . . . 21
11.2. Constraint Tests for General Cost Types . . . . . . . . 22
11.3. General Multipart Resources Query . . . . . . . . . . . 22
12. Security Considerations . . . . . . . . . . . . . . . . . . . 22
13. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 23
13.1. ALTO Cost Mode Registry . . . . . . . . . . . . . . . . 23
13.2. ALTO Entity Domain Registry . . . . . . . . . . . . . . 23
13.3. ALTO Property Type Registry . . . . . . . . . . . . . . 24
14. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 24
15. References . . . . . . . . . . . . . . . . . . . . . . . . . 24
15.1. Normative References . . . . . . . . . . . . . . . . . . 24
15.2. Informative References . . . . . . . . . . . . . . . . . 25
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 25
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.
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
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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.
The rest of this document is organized as follows. Section 3 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 introduces a new
cost type. Section 6 registers a new domain in Domain Registry.
Section 7 and Section 8 define new ALTO resources to support Path
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Vector query by using the request format of Filtered Cost Map and
Endpoint Cost Service. Section 9 presents several examples.
Section 10 and Section 11 discusses compatibility issues with other
existing ALTO extensions and design decisions. Section 12 and
Section 13 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: 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.
4. Overview of Path Vector Extensions
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.
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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, 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
unique identifier in the path vectors and in the dynamic entity
domain;
o each entity in this dynamic entity domain has the property defined
by the "cost-metric" that generated the ANEs in the query.
Detailed information and specifications are given in Section 6.
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-
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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
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. Path-Vector Cost Type
This document extends the cost types defined in Section 6.1 of
[RFC7285] by introducing a new cost mode "path-vector". In the rest
of the document, we use "path-vector" to indicate the cost type with
the cost-mode "path-vector" for short.
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5.1. Cost Mode: path-vector
This document extends the CostMode defined in Section 10.5 of
[RFC7285] with a new cost mode: "path-vector". This cost mode
indicates that every cost value in a cost map represents an array of
ANEs which are defined in Section 6.2, rather than a JSON number or a
ranking order.
The ANEs computed by the ALTO server associate to the cost metric for
the "path-vector" cost mode. This document re-defines some cost
metrics for "path-vector", which are motivated by the co-flow
scheduling use case. The ALTO client SHOULD ignore the "path-vector"
cost mode with any other cost metrics, unless the future documents
define other cost metrics or specify the semantics of existing cost
metrics for "path-vector" cost mode for some additional requirements.
5.2. Cost Metric: Link Maximum Reservable Bandwidth
This document uses the same metric name, units of measurement and
measurement point(s) with potential measurement domain defined by
section 4.1 of [I-D.ietf-alto-performance-metrics], but specifies
different metric description and method of measurement or calculation
for "path-vector" cost mode only.
Metric Description: When used with "path-vector" cost mode, it is to
specify the path vector computed by using the spatial and temporal
maximum reservable bandwidth over each network link. The value of
the maximum reservable bandwidth of each ANE in the path vector is
specified in the associated property map.
Method of Measurement or Calculation: The value of Maximum
Reservable Bandwidth is the bandwidth measured between two
directly connected IS-IS neighbors, OSPF neighbors or BGP
neighbors. The associated ANEs are computed by some algorithm
which can guarantee the equivalent Maximum Reservable Bandwidth
constraints.
6. 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.
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6.1. Domain Name
ane
6.2. Domain-Specific Entity Identifier
The entity identifier of ane domain 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.
To simplify the description, we use "ANE name" to indicate the
identifier of an entity in ANE domain in this document.
The ANE name is usually unrelated to the physical device information.
It is usually generated by the ALTO server on demand and used to
distinguish from other ANEs in its dependent cost map or endpoint
cost map.
6.3. Hierarchy and Inheritance
There is no hierarchy or inheritance for properties associated with
ANEs.
7. 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.
7.1. Media Type
The media type of the Multipart Filtered Cost Map Resource is
"multipart/related;type=application/alto-costmap+json".
7.2. HTTP Method
The Multipart Filtered Cost Map is requested using the HTTP POST
method.
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7.3. Accept Input Parameters
The input parameters of the Multipart Filtered Cost Map MUST be
encoded as a JSON object in the body of an HTTP POST request. The
media type of the request MUST be one of "application/alto-
costmapfilter+json". The format of the request body MUST be the same
type as defined by section 11.3.2.3 of [RFC7285].
7.4. Capabilities
The Multipart Filtered Cost Map resource uses the same capabilities
as defined by section 11.3.2.4 of [RFC7285]. But the "cost-type-
names" field SHOULD only includes cost types in "path-vector" cost
mode. Otherwise, the ALTO client SHOULD ignore a cost type in other
cost mode, unless additional documents define the specification of it
for the Multipart Filtered Cost Map resource.
7.5. Uses
The resource ID of the network map based on which the PIDs in the
returned cost map will be defined.
7.6. 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 response to a valid request MUST be a "multipart/related" message
as defined by [RFC2387]. The body consists of two parts:
o 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 body of this 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 as 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.
o 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 "."
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character. The body of this 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 with a single VersionTag
object as defined by section 10.3 of [RFC7285]. The "resource-id"
of this VersionTag MUST be the value of "Resource-Id" header of
the first part. The "tag" of this VersionTag MUST be the "tag" of
"vtag" of the first part body.
8. 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.
8.1. Media Type
The media type of the Multipart Endpoint Cost Resource is
"multipart/related;type=application/alto-endpointcostmap+json".
8.2. HTTP Method
The Multipart Endpoint Cost resource is requested using the HTTP POST
method.
8.3. Accept Input Parameters
The input parameters of the Multipart Endpoint Cost resource MUST be
encoded as a JSON object in the body of an HTTP POST request. The
media type of the request MUST be one of "application/alto-
endpointcostparams+json". The format of the request body MUST be the
same type as defined by section 11.5.1.3 of [RFC7285].
8.4. Capabilities
The Multipart Endpoint Cost resource uses the same capabilities as
defined by section 11.3.2.4 of [RFC7285]. But the "cost-type-names"
field SHOULD only includes cost types in "path-vector" cost mode.
Otherwise, the ALTO client SHOULD ignore a cost type in other cost
mode, unless additional documents define the specification of it for
the Multipart Endpoint Cost resource.
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8.5. Uses
The Multipart Endpoint Cost resource MUST NOT specify the "uses"
attribute.
8.6. 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 response to a valid request MUST be a "multipart/related" message
as defined by [RFC2387]. The body consists of two parts:
o 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 (U+002E). The body of this 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 as same as the value of
the "Resource-Id" header.
o 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 body of this 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 with a single VersionTag
object as defined by section 10.3 of [RFC7285]. The "resource-id"
of this VersionTag MUST be the value of "Resource-Id" header of
the first part. The "tag" of this VersionTag MUST be the "tag" of
"vtag" of the first part body.
9. Examples
This section lists some examples of path vector queries and the
corresponding responses.
9.1. Information Resource Directory Example
Here is an example of an Information Resource Directory. In this
example, the "cost-map-pv" information resource provides a Multipart
Cost Map resource for path-vector; the "endpoint-cost-pv" information
resource provides a MultipartEndpoint Cost resource for path-vector.
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Both of them support the Maximum Reservable Bandwidth ("maxresbw")
cost metric in "path-vector" cost mode.
{
"meta": {
"cost-types": {
"pv-maxresbw": {
"cost-mode": "path-vector",
"cost-metric": "maxresbw"
}
}
},
"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": [ "pv-maxresbw" ]
},
"uses": [ "my-default-networkmap" ]
},
"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": [ "pv-maxresbw" ]
}
},
"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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9.2. Example #1
Query filtered cost map to get the path vectors.
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": "path-vector",
"cost-metric": "maxresbw"
},
"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
{
"meta": {
"vtag": {
"resource-id": "cost-map-pv.costmap",
"tag": "d827f484cb66ce6df6b5077cb8562b0a"
},
"dependent-vtags": [
{
"resource-id": "my-default-networkmap",
"tag": "75ed013b3cb58f896e839582504f6228"
}
],
"cost-type": {
"cost-mode": "path-vector",
"cost-metric": "maxresbw"
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}
},
"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": {
"ane:L001": { "maxresbw": 100000000},
"ane:L003": { "maxresbw": 150000000},
"ane:L004": { "maxresbw": 50000000}
}
}
9.3. Example #2
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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": "path-vector",
"cost-metric": "maxresbw"
},
"endpoints": {
"srcs": [ "ipv4:192.0.2.2" ],
"dsts": [ "ipv4:192.0.2.89",
"ipv4:203.0.113.45",
"ipv6:2001:db8::10" ]
}
}
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"
},
"cost-type": {
"cost-mode": "path-vector",
"cost-metric": "maxresbw"
}
},
"endpoint-cost-map": {
"ipv4:192.0.2.2": {
"ipv4:192.0.2.89": [ "ane:L001", "ane:L003",
"ane:L004" ],
"ipv4:203.0.113.45": [ "ane:L001", "ane:L004",
"ane:L005" ],
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"ipv6:2001:db8::10": [ "ane:L001", "ane:L005",
"ane:L007" ]
}
}
}
--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"
}
]
},
"property-map": {
"ane:L001": { "maxresbw": 50000000 },
"ane:L003": { "maxresbw": 48000000 },
"ane:L004": { "maxresbw": 55000000 },
"ane:L005": { "maxresbw": 60000000 },
"ane:L007": { "maxresbw": 35000000 }
}
}
9.4. Example for Incremental Update
In this example, an ALTO client subscribe the incremental update for
the Multipart Endpoint Cost resource "endpoint-cost-pv".
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>
}
}
}
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Based on the server process defined in
[I-D.ietf-alto-incr-update-sse], the ALTO server will send the
control-uri first using Server-Sent Event (SSE), and follow 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: Content-ID: pvmap
data: Content-Type: application/alto-endpointcost+json
data:
data: <endpoint-cost-map-entry>
data: --example-3
data: Content-ID: nepmap
data: Content-Type: application/alto-propmap+json
data:
data: <property-map-entry>
data: --example-3--
Then, the ALTO server will subscribe the whole tree of the multipart
message automatically.
When the data updated, the ALTO server will publish the data updates
for each node in this tree separately.
event: application/merge-patch+json,ecspvsub1.pvmap
data: <Merge patch for endpoint-cost-map-update>
event: application/merge-patch+json,ecspvsub2.nepmap
data: <Merge patch for property-map-update>
10. Compatibility
10.1. 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
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client does not support them, the ALTO client will ignore the
resources without conducting any incompatibility.
10.2. 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.
10.3. 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.
11. General Discussions
11.1. 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.
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11.2. 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.
11.3. 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.
12. 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.
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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.
13. IANA Considerations
13.1. 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.
13.2. 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.
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+-------------+--------------------------+--------------------------+
| Identifier | Entity Address Encoding | Hierarchy & Inheritance |
+-------------+--------------------------+--------------------------+
| ane | See Section 6.2 | None |
+-------------+--------------------------+--------------------------+
Table 1: ALTO Entity Domain
13.3. 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
14. 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
Bernstein (Grotto Networks), Dawn Chen (Tongji University), Wendy
Roome, and Michael Scharf for their contributions to earlier drafts.
15. References
15.1. Normative References
[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>.
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15.2. Informative References
[I-D.bernstein-alto-topo]
Bernstein, G., Yang, Y., and Y. Lee, "ALTO Topology
Service: Uses Cases, Requirements, and Framework", draft-
bernstein-alto-topo-00 (work in progress), October 2013.
[I-D.ietf-alto-cost-calendar]
Randriamasy, S., Yang, Y., Wu, Q., Lingli, D., and N.
Schwan, "ALTO Cost Calendar", draft-ietf-alto-cost-
calendar-01 (work in progress), February 2017.
[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-performance-metrics]
Wu, Q., Yang, Y., Lee, Y., Dhody, D., and S. Randriamasy,
"ALTO Performance Cost Metrics", draft-ietf-alto-
performance-metrics-06 (work in progress), November 2018.
[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.
[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>.
Authors' Addresses
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Kai Gao
Tsinghua University
Beijing Beijing
China
Email: gaok12@mails.tsinghua.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
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