ALTO WG G. Bernstein
Internet-Draft Grotto Networking
Intended status: Standards Track S. Chen
Expires: June 21, 2018 Tongji University
K. Gao
Tsinghua University
Y. Lee
Huawei
W. Roome
M. Scharf
Nokia
Y. Yang
Yale University
J. Zhang
Tongji University
December 18, 2017
ALTO Extension: Path Vector Cost Type
draft-ietf-alto-path-vector-02.txt
Abstract
The Application-Layer Traffic Optimization (ALTO) protocol [RFC7285]
has defined several resources and services to provide clients with
basic network information. However, the base ALTO protocol and
latest extensions only provide end-to-end metrics, 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 capacity regions for a
given set of flows. A non-normative example called multi-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.
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This Internet-Draft will expire on June 21, 2018.
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Copyright (c) 2017 IETF Trust and the persons identified as the
document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal
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the Trust Legal Provisions and are provided without warranty as
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 4
3. Use Case: Capacity Region for Multi-Flow Scheduling . . . . . 5
4. Overview of Path Vector Extensions . . . . . . . . . . . . . 7
4.1. Path Vector Cost Type Extensions . . . . . . . . . . . . 7
4.1.1. New Cost Metric for Path Vector . . . . . . . . . . . 7
4.1.2. New Cost Mode for Path Vector . . . . . . . . . . . . 8
4.1.3. Path Vector Cost Type Semantics . . . . . . . . . . . 8
4.2. ANE Property Map . . . . . . . . . . . . . . . . . . . . 8
4.3. media type for path vector: multipart/related . . . . . . 9
4.4. Applicable ALTO services for Path Vector costs . . . . . 9
4.5. Impact of backwards compatibility on the PV design . . . 10
4.6. Requirements for PV on Clients and Servers . . . . . . . 10
5. Path-Vector Extension: Basic Data Types . . . . . . . . . . . 10
5.1. Cost Type . . . . . . . . . . . . . . . . . . . . . . . . 10
5.1.1. Cost Mode: array . . . . . . . . . . . . . . . . . . 11
5.1.2. Cost Metric: ane-path . . . . . . . . . . . . . . . . 11
5.2. ANE Domain . . . . . . . . . . . . . . . . . . . . . . . 11
5.3. Abstract Network Element Name . . . . . . . . . . . . . . 11
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6. Path-Vector Extension: Services . . . . . . . . . . . . . . . 11
6.1. Filtered Cost Map Extensions . . . . . . . . . . . . . . 11
6.1.1. Capabilities . . . . . . . . . . . . . . . . . . . . 12
6.1.2. Accept Input Parameters . . . . . . . . . . . . . . . 12
6.1.3. Response . . . . . . . . . . . . . . . . . . . . . . 12
6.2. Endpoint Cost Service Extensions . . . . . . . . . . . . 13
6.2.1. Capabilities . . . . . . . . . . . . . . . . . . . . 13
6.2.2. Accept Input Parameters . . . . . . . . . . . . . . . 13
6.2.3. Response . . . . . . . . . . . . . . . . . . . . . . 13
6.3. Multipart Cost Property Service . . . . . . . . . . . . . 13
6.3.1. Media Type . . . . . . . . . . . . . . . . . . . . . 14
6.3.2. HTTP Method . . . . . . . . . . . . . . . . . . . . . 14
6.3.3. Accept Input Parameters . . . . . . . . . . . . . . . 14
6.3.4. Capabilities . . . . . . . . . . . . . . . . . . . . 14
6.3.5. Uses . . . . . . . . . . . . . . . . . . . . . . . . 14
6.3.6. Response . . . . . . . . . . . . . . . . . . . . . . 15
7. Examples . . . . . . . . . . . . . . . . . . . . . . . . . . 15
7.1. Workflow . . . . . . . . . . . . . . . . . . . . . . . . 15
7.2. Information Resource Directory Example . . . . . . . . . 16
7.3. Example # 1 . . . . . . . . . . . . . . . . . . . . . . . 17
7.4. Example # 2 . . . . . . . . . . . . . . . . . . . . . . . 18
8. Compatibility . . . . . . . . . . . . . . . . . . . . . . . . 20
8.1. Compatibility with Legacy ALTO Clients/Servers . . . . . 20
8.2. Compatibility with Multi-Cost Extensions . . . . . . . . 20
8.3. Compatibility with Incremental Update . . . . . . . . . . 20
9. Design Decisions and Discussions . . . . . . . . . . . . . . 21
9.1. Provide More General Calendar Extension . . . . . . . . . 21
10. Security Considerations . . . . . . . . . . . . . . . . . . . 21
10.1. Privacy Concerns . . . . . . . . . . . . . . . . . . . . 21
10.2. Resource Consumption on ALTO Servers . . . . . . . . . . 22
11. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 22
11.1. ALTO Cost Mode Registry . . . . . . . . . . . . . . . . 22
11.2. ALTO Cost Metric Registry . . . . . . . . . . . . . . . 22
11.3. ALTO Network Element Property Type Registry . . . . . . 22
12. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 23
13. References . . . . . . . . . . . . . . . . . . . . . . . . . 23
13.1. Normative References . . . . . . . . . . . . . . . . . . 23
13.2. Informative References . . . . . . . . . . . . . . . . . 23
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 24
1. Introduction
The base ALTO protocol [RFC7285] is designed for exposing network
information through services such as the Network Map service and the
Cost Map service. These services use an extreme "single-node"
network view abstraction, which represents the whole network with a
single node and hosts with "endpoint groups" directly connected to
the node.
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Although the "single-node" network view abstraction works well in
many settings, it lacks the ability to support new emerging use
cases, such as inter-datacenter flow scheduling, scientific high-
performance computing data transfers and end-to-end paths crossing
heterogeneous technologies. For these use cases, more powerful
network view abstraction is required. To provide a better network
view abstraction, ALTO services need to support the following
additional functionalities:
o Providing path vector rather than a simple path cost of endpoint
to endpoint. The path vector exposes the network elements (e.g.,
links, switches, middle boxes and their aggregations) that
endpoint to endpoint traffic goes through.
o Providing information of the network elements in the path vector.
The information can be "bandwidth" for links, "delay" between
neighboring switches and other properties of network elements.
These information may help the application avoid network
congestion, achieving better application performance.
To support these new functionalities, this document proposes the
path-vector extension, which introduces a qualitative cost type
listing selected groups of one or more abstracted network elements in
an e2e path and optionally conveys some of their properties.
The rest of this document is organized as follows. Section 3 gives
an example of 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, before specifying the details of the
extension in Section 5 and Section 6. Section 7 presents several
examples, and Section 9 explains some design decisions. Section 8
discusses compatibility issues with some other ALTO extensions.
Section 10 and Section 11 discusses about security and IANA
considerations.
2. Terminology
This document uses the same terms as defined in [RFC7285], [RFC8189]
and [I-D.ietf-alto-unified-props-new] with the following additional
terms: Abstract Network Element, Abstract Network Element Name,
Abstract Network Element Property, Abstract Network Element Property
Map 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, middle boxes, Virtualized Network Function (VNF), or even a
sub-network. An abstract network element has two attributes:
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abstract network element name and abstract network element
property, which are defined below.
o Abstract Network Element Name (ANEN): An abstract network element
name is an identifier which uniquely identifies an abstract
network element, as defined in Section 5.3.
o Abstract Network Element Property (ANEP): An abstract network
element property is a specific metric associated with a given
abstract network element, as introduced in Section 4.2. An
abstract network element can have several network element
properties.
o Abstract Network Element Property Map (ANE Property Map): An
abstract network element property map is a Filtered Property Map
defined in [I-D.ietf-alto-unified-props-new] which supports the
"ane" domain in its "domain-types" capability.
o Path Vector (PV): A path vector is an array of ALTO Abstract
Network Elements (ANEs), which presents an abstract network path
between entities such as PIDs or endpoints. An ANE represents a
selected part of an end-to-end path that the ALTO Server considers
worth exposing. An ANE is a set of one or more network elements
such as links, switches, middle boxes and their aggregations, it
is expected to have properties that may influence the applications
e.g. when they select an endpoint or want to estimate their
performance.
3. Use Case: Capacity Region for Multi-Flow Scheduling
Once routing has been configured in the network, application-layer
traffic optimization may want to schedule traffic among application-
layer paths. Specifically, assume that an application has control
over a set of flows F = {f_1, f_2, ..., f_|F|}. If routing is given,
what the application can control is x_1, x_2, ..., x_|F|, where x_i
is the amount of traffic for flow i. Let x = [x_1, ..., x_|F|] be
the vector of the flow traffic amounts. Due to shared links,
feasible values of x where link capacities are not exceeded can be a
complex polytype.
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. End hosts eh1 to eh4 are
connected to access switches sw1 to sw4 respectively. Assume that
the bandwidth of link eh1 -> sw1 and link sw1 -> sw5 are 150 Mbps,
and the bandwidth of the rest 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 eh1 -> 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 eh1 -> 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 eh1 -> eh4 uses path eh1 -> sw1 -> sw5 ->
sw7 -> sw4 -> eh4, then the application will obtain 150 Mbps.
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o Case 2: If eh1 -> eh2 uses the path eh1 -> sw1 -> sw5 -> sw7 ->
sw2 -> eh2 and eh1 -> eh4 uses the path eh1 -> sw1 -> sw5 -> sw7
-> sw4 -> eh4, then the application will obtain only 100 Mbps.
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 meets all the
requirements.
See [I-D.bernstein-alto-topo] for a survey of use-cases where
extended network topology information is needed.
4. Overview of Path Vector Extensions
This section presents the approaches taken to support the path-vector
extension. It assumes the readers are familiar with (Filtered) Cost
Map and Endpoint Cost Service defined in [RFC7285] and their
extensions defined in [RFC8189]. It also uses features such as
Filtered Property Map defined in [I-D.ietf-alto-unified-props-new].
4.1. Path Vector Cost Type Extensions
None of current cost types defined in [RFC7285] can be used to convey
path vector information. So, a new cost type with a new cost metric
"ane-path" and a new cost mode "array" is defined in this document.
Below are brief descriptions. Detailed information and
specifications are given in Section 5.1.1 and Section 5.1.2.
4.1.1. New Cost Metric for Path Vector
To represent an abstract network path, this document introduces a new
cost metric named "ane-path". A cost value in this metric is a list
containing the names of the ALTO ANEs that the ALTO Server has
specified as describing the network path elements. The ANE names
array is organized as a sequence beginning at the source of the path
and ending at its destination.
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4.1.2. New Cost Mode for Path Vector
A cost mode as defined in Section 6.1.2 of [RFC7285], a cost mode is
either "numerical" or "ordinal" and none of these can be used to
present a list of ANE names. Therefore, this document specifies a
new cost mode named "array" for the cost metric "ane-path". The new
cost mode "array" means each cost value in the cost maps is a list.
4.1.3. Path Vector Cost Type Semantics
The new cost type follows the convention of the cost types in the
legacy ALTO protocol. Table 1 lists some of the current defined cost
types and their semantics.
+------------+--------------+---------------------------------------+
| Cost Mode | Cost Metric | Semantics |
+------------+--------------+---------------------------------------+
| numerical | routingcost | a number representing the routing |
| | | cost |
| numerical | hopcount | a number representing the hop count |
| ordinal | routingcost | a ranking representing the routing |
| | | cost |
| ordinal | hopcount | a ranking representing the hop count |
| array | ane-path | a list representing the ane path |
+------------+--------------+---------------------------------------+
Table 1: Cost Types and Their Semantics
The "routingcost" and "hopcount" can encoded in "numerical" or
"ordinal", however, the cost metric "ane-path" can only be applied to
the cost mode "array" defined in this document to convey path vector
information. The cost metric "ane-path" can not be used in
"numerical" or "ordinal" unless it is defined in future extensions.
If the ALTO server declares that it support cost type with cost
metric being "ane-path" and cost mode not being "array", the ALTO
client SHOULD ignore them.
4.2. ANE Property Map
Given that Cost Map and Endpoint Cost service now provide the
abstract network element names along a flow path, ALTO clients can
learn that there exist bottlenecks shared by different flows.
However, only providing the abstract network element names without
abstract network element properties is not enough, some ALTO clients
may want to have information on specific ANE properties such as link
capacity or delay. This document adopts the property map resources
defined in [I-D.ietf-alto-unified-props-new] to encode the properties
of ANEs. Draft [I-D.ietf-alto-unified-props-new] defines a new
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entity domain called "ane" and each entity in the "ane" domain has an
identifier of an ANE. An ANE identifier is the ANE name used in the
values of the "ane-path" metric defined in the present draft. ANE
properties are provided in information resources called "Property Map
Resource" and "Filtered Property Map Resource". The "Filtered
Property Map" resource which support the "ane" domain is used to
encode the properties of ane entities, and it is called an ANE
Property Map in this document.
4.3. media type for path vector: multipart/related
In the legacy ALTO protocol, ALTO servers use media types in the HTTP
header to indicate the type of the response. Typically one response
only contains a single media type, such as "application/alto-
costmap+json" or "application/alto-propmap+json". This has limited
the capability of ALTO servers to return multiple services in a
single response.
Thus, an ALTO client needs to make separate queries to get the
information of related services. This may cause a data
synchronization problem between dependent ALTO services because when
making the second query, the result for the first query may have
already changed. The very same problem can happen to Network Map and
Cost Map resources. However, unlike Network Map and Cost Map which
are considered more stable, Path Vectors and the dependent ANE
Property Maps might change more frequently.
Instead of introducing a new media type to encapsulate multiple types
in a single response, this document adopts the "multipart/related"
media type defined in [RFC2387]. In this way, a response can contain
both the Path Vectors in a Filtered Cost Map (or Endpoint Cost Map)
and the associated ANE Property Map. The media types of the cost map
and the property map can still be retrieved from the response. The
interpretation of each media type in the "multipart/related" response
is consistent with the base ALTO protocol.
4.4. Applicable ALTO services for Path Vector costs
This document defines Filtered Cost Map and Endpoint Cost Map are
applicable for path vector costs. Although the new cost type for
path vector can also be used in the GET-mode Cost Map service from
[RFC7285], the behaviours of the ALTO server and client for such a
GET-mode service is not defined. So it is not recommended to apply
path vector costs to the GET-mode Cost Map service.
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4.5. Impact of backwards compatibility on the PV design
The path vector extension on Filtered Cost Map and Endpoint Cost
Service is backward compatible with the base ALTO protocol. If the
ALTO server provides path vector extended Filtered Cost Map or
Endpoint Cost Service, but the client is a base ALTO client, then the
client will ignore the path vector cost type without conducting any
incompatibility. If the client sents a request with path vector cost
type, but the server is a base ALTO server, the server will return an
"E_INVALID_FIELD_VALUE" error.
4.6. Requirements for PV on Clients and Servers
A path vector extended ALTO server MUST implement the legacy ALTO
protocol specified in [RFC7285] with the following additional
requirements:
o If an ALTO server supports path vector extension, it MUST support
the Unified Property Map defined in
[I-D.ietf-alto-unified-props-new].
o If an ALTO server supports path vector extended Filtered Cost Map
or Endpoint Cost Service, the server MUST provide the associated
Property Map simultaneously.
o If an ALTO server provides "multipart/related" media type for path
vector, the server MUST provide the associated Filtered Cost Map
or Endpoint Cost Service and the Property Map simultaneously.
An ALTO client supported path vector extension MUST be able to
interpret Unified Property Map correctly. If the ALTO client wants
to interpret "multipart/related" path vector response, the client
MUST implement the path vector extension on Filtered Cost Map or
Endpoint Cost Service at first.
5. Path-Vector Extension: Basic Data Types
This section formally specifies a new cost type.
5.1. Cost Type
This document extends the cost types defined in Section 6.1 of
[RFC7285] by introducing a new cost mode "array" and a new cost
metric "ane-path".
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5.1.1. Cost Mode: array
This document extends the CostMode defined in Section 10.5 of
[RFC7285] with a new cost mode: "array". This cost mode indicates
that every cost value in a cost map represents an array rather than a
simple value. The values are arrays of JSONValue. The specific type
of each element in the array depends on the cost metric.
5.1.2. Cost Metric: ane-path
This document specifies a new cost metric: "ane-path". This cost
metric indicates that the cost value is a list of abstract network
elements which the path from a source to a destination goes across.
The values are arrays of ANE Names which are defined in Section 5.3.
The cost metric "ane-path" SHOULD NOT be used when the cost mode is
not "array" unless it is explicitly specified by a future extension.
If an ALTO client send queries with the cost metric "ane-path" and a
non "array" cost mode, the ALTO server SHOULD return an error with
the error code "E_INVALID_FIELD_VALUE"; If an ALTO server declares
the support of a cost type with the cost metric "ane-path" and a non
"array" cost mode, the ALTO client SHOULD assume such a cost type is
invalid and ignore it.
5.2. ANE Domain
This document uses the same definition of entity domain name 'ane' as
defined in Section 3.4 of [I-D.ietf-alto-unified-props-new].
5.3. Abstract Network Element Name
An Abstract Network Element Name is encoded as an EntityAddr of the
"ane" domain as defined in Section 3.4.2 of
[I-D.ietf-alto-unified-props-new].
6. Path-Vector Extension: Services
This section extends Filtered Cost Map Service and Endpoint Cost
Service.
6.1. Filtered Cost Map Extensions
This document extends the Filtered Cost Map defined in Section 4.1 of
[RFC8189].
The specifications for the "media type", "HTTP method" and "uses" are
the same as defined in Section 4.1 of [RFC8189].
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6.1.1. Capabilities
The FilteredCostMapCapabilities object is extended with a new member
"property-map":
object {
[ResourceID property-map;]
} PathVectorFilteredCostMapCapabilities : FilteredCostMapCapabilities
property-map: A resource ID defined in the same IRD pointing to an
ANE Property Map as defined in Section 2. This field MUST be
present if the path vector cost type is present in the "cost-type-
names" field.
Other fields of the FilteredCostMapCapabilities object has the same
format as defined in Section 4.1.1 of [RFC8189] with the following
constraint:
testable-cost-type-names: The path vector cost type with "ane-path"
as the cost metric and "array" as the cost mode MUST NOT be
included in "testable-cost-type-names".
6.1.2. Accept Input Parameters
The ReqFilteredCostMap uses the same format as defined in
Section 4.1.2 of [RFC8189], with the following constraints:
constraints, or-constraints: If the path vector cost type is
included in either "cost-type" or "multi-cost-types", ALTO clients
MUST NOT use it in "constraints" or "or-constraints". Otherwise,
the ALTO server MUST return an error with error code
"E_INVALID_FIELD_VALUE".
testable-cost-types: The path vector cost type MUST NOT be included
in the "testable-cost-types" field. Otherwise, the ALTO server
MUST return an error with error code "E_INVALID_FIELD_VALUE".
6.1.3. Response
If the ALTO client includes the path vector cost type in the "cost-
type" or "multi-cost-types" field of the input parameter, the
response use the same format as defined in Section 4.1.3 of
[RFC8189], but the corresponding cost value MUST be encoded as a
JSONArray of AbstractNetworkElementName.
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6.2. Endpoint Cost Service Extensions
This document extends the Endpoint Cost Service defined in
Section 4.2 in [RFC8189].
The specifications for "HTTP method" and "uses" are the same as
defined in Section 4.2 in [RFC8189].
6.2.1. Capabilities
The same as defined in Section 6.1.1.
6.2.2. Accept Input Parameters
The ReqEndpointCostMap uses the same format as defined in
Section 4.2.2 of [RFC8189], with the following constraints:
cost-type, multi-cost-types: ALTO clients MUST include the path
vector cost type, e.g. the one with "ane-path" as cost metric and
"array" as cost mode, in either "cost-type" or "multi-cost-types"
to activate the path vector extension.
constraints, or-constraints: If the path vector cost type is
included in either "cost-type" or "multi-cost-types", ALTO clients
MUST NOT use it in "constraints" or "or-constraints". Otherwise,
the ALTO server MUST return an error with error code
"E_INVALID_FIELD_VALUE".
testable-cost-types: The path vector cost type MUST NOT be included
in the "testable-cost-types" field. Otherwise, the ALTO server
MUST return an error with error code "E_INVALID_FIELD_VALUE".
6.2.3. Response
If the ALTO client specifies the path vector cost type in the "cost-
type" or "multi-cost-types" field of the input parameter, the
response use the same format as defined in Section 4.2.3 of
[RFC8189], but the corresponding cost value MUST be encoded as a
JSONArray of AbstractNetworkElementName.
6.3. Multipart Cost Property Service
This document introduces a new ALTO service called "Multipart Cost
Property Service", which provides the path vector information and the
associated ANE property information in the same response.
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6.3.1. Media Type
The media type of the Multipart Cost Property service is "multipart/
related".
6.3.2. HTTP Method
The Multipart Cost Property service is requested using the HTTP POST
method.
6.3.3. Accept Input Parameters
The input parameters of the Multipart Cost Property service MUST be
encoded as a JSON object in the body of an HTTP POST request. The
media type of the request SHOULD be one of "application/alto-
costmapfilter+json" and "application/alto-endpointcostparams+json".
The format of the request body depends on the media type:
o If the media type of the request is "application/alto-
costmapfilter+json", the request body MUST be the same type as
defined by Section 6.1.2.
o If the media type of the request is "application/alto-
endpointcostparams+json", the request body MUST be the same type
as defined by Section 6.2.2.
The path vector cost type MUST be the only cost type in the input
parameter.
6.3.4. Capabilities
TBD
6.3.5. Uses
The "uses" attribute MUST be an array with at least one resource id.
The first resource id MUST point to a Filtered Cost Map or an
Endpoint Cost Service resource. And the path vector cost type MUST
be in its "cost-type" capability. If there are more than one
resource id in the "uses" attribute, the ALTO client SHOULD ignore
any additional resource ids.
According to Section 6.1.1, the "property-map" field MUST be present
in the first resource. So the ALTO client MUST infer that the
Property Map pointed by the "property-map" field of the first
resource is also a dependent resource.
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6.3.6. Response
If an ALTO client sends a request of the media type "application/
alto-costmapfilter+json" and accepts "multipart/related", the HTTP
body of the response MUST consist of two parts with the media types
"application/alto-costmap+json" and "application/alto-propmap+json"
accordingly. The part with media type "application/alto-
costmap+json" MUST be the first part. The content of the
"application/alto-endpointcost+json" part has the same format as
defined in Section 6.1.3.
If an ALTO client sends a request of the media type "application/
alto-endpointcostparams+json" and accepts "multipart/related", the
HTTP body of the response MUST consist of two parts with the media
types "application/alto-endpointcost+json" and "application/alto-
propmap+json" accordingly. The part with media type "application/
alto-endpointcost+json" MUST be the first part. The content of the
"application/alto-endpointcost+json" part has the same format as
defined in Section 6.2.3.
7. Examples
This section lists some examples of path vector queries and the
corresponding responses.
7.1. Workflow
This section gives a typical workflow of an ALTO client using the
path-vector extension.
1. Send a GET request for the whole Information Resource Directory.
2. Look for the resource of the (Filtered) Cost Map/Endpoint Cost
Service which contains the path vector cost type and get the
resource ID of the dependent abstract network element property
map.
3. Check whether the capabilities of the property map includes the
desired "prop-types".
4. Send a path-vector request which accepts "multipart/related"
media type following "application/alto-costmap+json" or
"application/endpointcost+json".
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7.2. Information Resource Directory Example
Here is an example of an Information Resource Directory. In this
example, filtered cost map "cost-map-pv" doesn't support the multi-
cost extension but support the path-vector extension, "endpoint-
multicost-map" supports both multi-cost extension and path-vector
extension. Filtered Property Map "propmap-delay-availbw" supports
properties "availbw" and "delay", and "propmap-location" supports
property "location".
{
"meta": {
"cost-types": {
"pv": {
"cost-mode": "array",
"cost-metric": "ane-path"
},
"num-routingcost": {
"cost-mode": "numerical",
"cost-metric": "routingcost"
},
"num-hopcount": {
"cost-mode": "numerical",
"cost-metric": "hopcount"
}
}
},
"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": "application/alto-costmap+json",
"accepts": "application/alto-costmapfilter+json",
"capabilities": {
"cost-type-names": [ "pv", "num-hopcount" ]
},
"property-map": "propmap-delay",
"uses": [ "my-default-networkmap" ]
},
"endpoint-multicost-map" : {
"uri": "http://alto.exmaple.com/endpointcostmap/multicost",
"media-type": "application/alto-endpointcost+json",
"accepts": "application/alto-endpointcostparams+json",
"capabilities": {
"cost-constraints": true,
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"cost-type-names": [ "pv", "num-routingcost" ],
"max-cost-types": 2
},
"property-map": "propmap-availbw"
},
"propmap-availbw-delay" : {
"uri": "http://alto.exmaple.com/propmap/availbw",
"media-type": "application/alto-propmap+json",
"accepts": "application/alto-propmapparams+json",
"capabilities": {
"domain-types": [ "ane" ],
"prop-types": [ "availbw" ]
}
},
"propmap-location" : {
"uri": "http://alto.exmaple.com/propmap/delay",
"media-type": "application/alto-propmap+json",
"accepts": "application/alto-propmapparams+json",
"capabilities": {
"domain-types": [ "pid" ],
"prop-types": [ "location" ]
}
}
}
}
7.3. Example # 1
POST /costmap/pv HTTP/1.1
Host: alto.example.com
Accept: multipart/related, application/alto-costmap+json,
application/alto-propmap+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]
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Content-Type: multipart/related; boundary=42
--42
Content-Type: application/alto-costmap+json
{
"meta": {
"dependent-vtags": [
{
"resource-id": "default-network-map",
"tag": "75ed013b3cb58f896e839582504f622838ce670f"
}
],
"cost-type": {
"cost-mode": "array",
"cost-metric": "ane-path"
},
},
"cost-map": {
"PID1": {
"PID2": [ "ane:L001", "ane:L003" ],
"PID3": [ "ane:L001", "ane:L004" ]
}
}
}
--42
Content-Type: application/alto-propmap+json
{
"property-map": {
"ane:L001": { "delay": 46},
"ane:L003": { "delay": 50},
"ane:L004": { "delay": 70}
}
}
--42--
7.4. Example # 2
POST /endpointcostmap/multicost HTTP/1.1
Host: alto.example.com
Accept: multipart/related, application/alto-endpointcost+json,
application/alto-propmap+json, application/alto-error+json
Content-Length: [TBD]
Content-Type: application/alto-endpointcostparams+json
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{
"multi-cost-types": [
{
"cost-mode": "array",
"cost-metric": "ane-path"
},
{
"cost-mode": "numerical",
"cost-metric": "routingcost"
}
],
"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
--example-2
Content-Type: application/alto-endpointcost+json
{
"meta": {
"multi-cost-types": [
{"cost-mode": "array", "cost-metric": "ane-path"},
{"cost-mode": "numerical", "cost-metric": "routingcost"}
]
},
"endpoint-cost-map": {
"ipv4:192.0.2.2": {
"ipv4:192.0.2.89": [[ "ane:L001", "ane:L003", "ane:L004" ], 77],
"ipv4:203.0.113.45": [[ "ane:L001", "ane:L004", "ane:L005" ], 68],
"ipv6:2001:db8::10": [[ "ane:L001", "ane:L005", "ane:L007" ], 98]
}
}
}
--example-2
Content-Type: application/alto-propmap+json
{
"property-map": {
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"ane:L001": { "availbw": 50 },
"ane:L003": { "availbw": 48 },
"ane:L004": { "availbw": 55 },
"ane:L005": { "availbw": 60 },
"ane:L007": { "availbw": 35 }
}
}
--example-2--
8. Compatibility
8.1. Compatibility with Legacy ALTO Clients/Servers
Legacy ALTO clients SHOULD NOT send queries with the path-vector
extension and ALTO servers with this extension SHOULD NOT have any
compatibility issue. Legacy ALTO servers do not support cost types
with cost mode being "array" and cost metric being "ane-path", so
they MUST NOT announce the extended cost types in IRD. Thus, ALTO
clients MUST NOT send queries specified in this extension to base
ALTO servers according to Section 11.3.2.3 [RFC7285].
8.2. Compatibility with Multi-Cost Extensions
Path Vector is not a testable cost type. Any format of constraints
SHOULD NOT be applied to cost type path-vector in order for multi-
cost to support the path-vector extension. Specifically,
o Cost type path-vector MUST NOT be included in "testable-cost-
types-names" or "testable-cost-types".
o When "testable-cost-types-names" is omitted in the "capabilities"
and "testable-cost-types" is omitted in the input parameters,
"constraints" or "or-constraints" SHOULD NOT add any format of
constraints on cost type path-vector.
8.3. Compatibility with Incremental Update
Without considering the incremental update of multipart/related
information, there is no compatibility issue with incremental update
extension. Compatibility issue with the incremental update of
multipart/related information will be discussed and addressed in the
next version.
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9. Design Decisions and Discussions
9.1. Provide More General Calendar Extension
Cost Calendar is proposed as a useful ALTO extension to provide the
historical cost values for Filtered Cost Map Service and Endpoint
Cost Service. Since path vector is an extension to these services,
it SHOULD be compatible with Cost Calendar extension.
However, the calendar of a path-vector (Endpoint) Cost Map is
insufficient for the application which requires the historical data
of routing state information. The (Endpoint) Cost Map can only
provide the changes of the paths. But more useful information is the
history of network element properties which are recorded in the
dependent Network Element Property Map.
Before the Unified Property Map is introduced as an ALTO extension,
Filtered Cost Map Service and Endpoint Cost Service are the only
resources which require the calendar supported. Because other
resources don't have to be updated frequently. But Network Element
Property Map as a use case of Unified Property Map will collect the
real-time information of the network. It SHOULD be updated as soon
as possible once the metrics of network elements change.
So the requirement is to provide a general calendar extension which
not only meets the Filtered Cost Map and Endpoint Cost Service but
also applies to the Property Map Service.
10. Security Considerations
10.1. Privacy Concerns
We can identify multiple potential security issues. A main security
issue is network privacy, as the path-vector information may reveal
more network internal structures than the more abstract single-node
abstraction. The network should consider protection mechanisms to
reduce information exposure, in particular, in settings where the
network and the application do not belong to the same trust domain.
On the other hand, in a setting of the same trust domain, a key
benefit of the path-vector abstraction is reduced information
transfer from the network to the application.
The path-vector query may also reveal more information about the
application. In particular, the application may reveal all potential
transfers sites (e.g., where the data source is replicated, and where
the potential replication sites are). The application should
evaluate the potential privacy concerns.
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Beyond the privacy issues, the computation of the path-vector is
unlikely to be cachable, in that the results will depend on the
particular requests (e.g., where the flows are distributed). Hence,
this service may become an entry point for denial of service attacks
on the availability of an ALTO server. Hence, authenticity and
authorization of this ALTO service may need to be better protected.
10.2. Resource Consumption on ALTO Servers
The Abstract Network Element Property Map is dynamically enriched
when the (Filtered) Cost Map/Endpoint Cost Service is queried of the
path-vector information. The properties of the abstract network
elements can consume a large amount of resources when cached. So, a
time-to-live is needed to remove outdated entries in the Network
Element Property Map.
11. IANA Considerations
11.1. ALTO Cost Mode Registry
This document specifies a new cost mode "array". 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 Cost Metric Registry
A new cost metric needs to be registered in the "ALTO Cost Metric
Registry", listed in Table 2.
+-------------+---------------------+
| Identifier | Intended Semantics |
+-------------+---------------------+
| ane-path | See Section 5.1.2 |
+-------------+---------------------+
Table 2: ALTO Cost Metrics
11.3. ALTO Network Element Property Type Registry
The "ALTO Abstract Network Element Property Type Registry" is
required by the ALTO Entity Domain "ane", listed in Table 3.
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+-------------+--------------------------+
| Identifier | Intended Semantics |
+-------------+--------------------------+
| availbw | The available bandwidth |
| delay | The transmission delay |
+-------------+--------------------------+
Table 3: ALTO Abstract Network Element Property Types
12. Acknowledgments
The authors would like to thank discussions with Randriamasy Sabine,
Andreas Voellmy, Erran Li, Haibin Son, Haizhou Du, Jiayuan Hu, Qiao
Xiang, Tianyuan Liu, Xiao Shi, Xin Wang, and Yan Luo.
13. References
13.1. 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>.
13.2. Informative References
[I-D.amante-i2rs-topology-use-cases]
Medved, J., Previdi, S., Lopez, V., and S. Amante,
"Topology API Use Cases", draft-amante-i2rs-topology-use-
cases-01 (work in progress), October 2013.
[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.clemm-i2rs-yang-network-topo]
Clemm, A., Medved, J., Tkacik, T., Varga, R., Bahadur, N.,
and H. Ananthakrishnan, "A YANG Data Model for Network
Topologies", draft-clemm-i2rs-yang-network-topo-01 (work
in progress), October 2014.
[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.
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[I-D.ietf-alto-unified-props-new]
Roome, W. and Y. Yang, "Extensible Property Maps for the
ALTO Protocol", draft-ietf-alto-unified-props-new-00 (work
in progress), July 2017.
[I-D.lee-alto-app-net-info-exchange]
Lee, Y., Bernstein, G., Choi, T., and D. Dhody, "ALTO
Extensions to Support Application and Network Resource
Information Exchange for High Bandwidth Applications",
draft-lee-alto-app-net-info-exchange-02 (work in
progress), July 2013.
[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
Greg Bernstein
Grotto Networking
Fremont, CA
USA
Email: gregb@grotto-networking.com
Shiwei Dawn Chen
Tongji University
4800 Caoan Road
Shanghai 201804
China
Email: dawn_chen_f@hotmail.com
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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
Wendy Roome
Nokia/Bell Labs
600 Mountain Ave, Rm 3B-324
Murray Hill, NJ 07974
USA
Phone: +1-908-582-7974
Email: wendy.roome@nokia.com
Michael Scharf
Nokia
Germany
Email: michael.scharf@nokia.com
Y. Richard Yang
Yale University
51 Prospect St
New Haven CT
USA
Email: yry@cs.yale.edu
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Jingxuan Jensen Zhang
Tongji University
4800 Caoan Road
Shanghai 201804
China
Email: jingxuan.n.zhang@gmail.com
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