ALTO WG K. Gao
Internet-Draft Tsinghua University
Intended status: Standards Track Y. Lee
Expires: September 12, 2019 Huawei
S. Randriamasy
Nokia Bell Labs
Y. Yang
Yale University
J. Zhang
Tongji University
March 11, 2019
ALTO Extension: Path Vector Cost Type
draft-ietf-alto-path-vector-05
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 http://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 September 12, 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
(http://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 Type to Encode Path Vectors . . . . . . . . . . 7
4.2. New ALTO Entity Domain to Provide ANE Properties . . . . 8
4.3. Extended Cost Map/Endpoint Cost Service for Compound
Resources . . . . . . . . . . . . . . . . . . . . . . . . 8
5. Cost Type . . . . . . . . . . . . . . . . . . . . . . . . . . 8
5.1. Cost Mode: array . . . . . . . . . . . . . . . . . . . . 9
5.2. Cost Metric: ane-path . . . . . . . . . . . . . . . . . . 9
5.3. Path Vector Cost Type Semantics . . . . . . . . . . . . . 9
6. ANE Domain . . . . . . . . . . . . . . . . . . . . . . . . . 10
6.1. Domain Name . . . . . . . . . . . . . . . . . . . . . . . 10
6.2. Domain-Specific Entity Addresses . . . . . . . . . . . . 10
6.3. Hierarchy and Inheritance . . . . . . . . . . . . . . . . 10
7. Protocol Extensions for Path Vector . . . . . . . . . . . . . 10
7.1. Filtered Cost Map Extensions . . . . . . . . . . . . . . 11
7.1.1. Accept Input Parameters . . . . . . . . . . . . . . . 11
7.1.2. Capabilities . . . . . . . . . . . . . . . . . . . . 11
7.1.3. Response . . . . . . . . . . . . . . . . . . . . . . 12
7.2. Endpoint Cost Service Extensions . . . . . . . . . . . . 12
7.2.1. Accept Input Parameters . . . . . . . . . . . . . . . 13
7.2.2. Capabilities . . . . . . . . . . . . . . . . . . . . 13
7.2.3. Response . . . . . . . . . . . . . . . . . . . . . . 13
8. Examples . . . . . . . . . . . . . . . . . . . . . . . . . . 13
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8.1. Workflow . . . . . . . . . . . . . . . . . . . . . . . . 13
8.2. Information Resource Directory Example . . . . . . . . . 14
8.3. Example # 1 . . . . . . . . . . . . . . . . . . . . . . . 16
8.4. Example # 2 . . . . . . . . . . . . . . . . . . . . . . . 18
8.5. Example #3 . . . . . . . . . . . . . . . . . . . . . . . 20
9. Compatibility . . . . . . . . . . . . . . . . . . . . . . . . 22
9.1. Compatibility with Base ALTO Clients/Servers . . . . . . 22
9.2. Compatibility with Multi-Cost Extension . . . . . . . . . 23
9.3. Compatibility with Incremental Update . . . . . . . . . . 23
10. General Discussions . . . . . . . . . . . . . . . . . . . . . 23
10.1. Provide Calendar for Property Map . . . . . . . . . . . 23
10.2. Constraint Tests for General Cost Types . . . . . . . . 24
10.3. General Compound Resources Query . . . . . . . . . . . . 24
11. Security Considerations . . . . . . . . . . . . . . . . . . . 24
12. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 25
12.1. ALTO Cost Mode Registry . . . . . . . . . . . . . . . . 25
12.2. ALTO Cost Metric Registry . . . . . . . . . . . . . . . 26
12.3. ALTO Entity Domain Registry . . . . . . . . . . . . . . 26
12.4. ALTO Network Element Property Type Registry . . . . . . 26
13. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 26
14. References . . . . . . . . . . . . . . . . . . . . . . . . . 27
14.1. Normative References . . . . . . . . . . . . . . . . . . 27
14.2. Informative References . . . . . . . . . . . . . . . . . 27
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 27
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. The path vector abstraction uses
path vectors with abstract network elements to provide network graph
view for applications. A path vector consists of a sequence of
abstract network elements (ANEs) that end-to-end traffic goes
through. Example ANEs include links, switches, middleboxes, and
their aggregations. An ANE can have properties such as "bandwidth",
"delay". Providing such information can help both applications to
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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 capacity
regions.
AR-3: The path vector abstraction requires consistent encoding of
path vectors (AR-1) and the properties of the elements in a path
vector (AR-2).
Specifically, path vectors and the properties of abstract network
elements in the vectors are dependent. A mechanism to query both
of them consistently is necessary.
This document proposes the path vector extension which satisfies
these additional requirements to the ALTO protocol. Specifically,
the ALTO protocol encodes the array of ANEs over an end-to-end path
using a new cost type, and conveys the properties of ANEs using
unified property map [I-D.ietf-alto-unified-props-new]. We also
provide an optional solution to query separated path vectors and
properties of ANEs in a consistent way. But querying general
separated resources consistently is not the scope in this document.
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 extends Filtered Cost Map and Endpoint Cost Service to
support the compound resource query. Section 8 presents several
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examples. Section 9 and Section 10 discusses compatibility issues
with other existing ALTO extensions and design decisions. Section 11
and Section 12 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, 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), 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 can not
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 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 at
most.
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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 at
most.
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 propose a solution
to provide these details.
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 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 type to encode path vectors; (2) a new ALTO entity domain
for unified property extension [I-D.ietf-alto-unified-props-new] to
encode properties of ANEs; and (3) an extension to the cost map and
endpoint cost resource to provide path vectors and properties of ANEs
in a single response.
4.1. New Cost Type to Encode Path Vectors
Existing cost types defined in [RFC7285] allow only scalar cost
values. However, the "path vector" abstraction requires to convey
vector format information. To achieve this requirement, this
document defines a new cost mode to enable the cost value to carry an
array of elements, and a new cost metric to take names of ANEs as
elements in the array. We call such an array of ANEs a path vector.
In this way, the cost map and endpoint cost service can convey the
path vector to represent the routing information. Detailed
information and specifications are given in Section 5.1 and
Section 5.2.
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4.2. New ALTO Entity Domain to Provide ANE Properties
The path vector can only represent the route between the source and
the destination. Although the application can find the shared ANEs
among different paths, it is not enough for most use cases, which
requires the bandwidth or delay information of the ANEs. So this
document adopts the property map defined in
[I-D.ietf-alto-unified-props-new] to provide the general properties
of ANEs. The document registers a new entity domain called "ane" to
represent the ANE. The address of the ANE entity is just the ANE
name used by the path vector. By requesting the property map of
entities in the "ane" domain, the client can retrieve the properties
of ANEs in path vectors.
4.3. Extended Cost Map/Endpoint Cost Service for Compound Resources
Providing the path vector information and the ANE properties by
separated resources have several known benefits: (1) can be better
compatible with the base ALTO protocol; (2) can make different
property map resources reuse the same cost map or endpoint cost
resource. However, it conducts two issues:
o Efficiency: The separated resources will require the ALTO client
to invoke multiple requests/responses to collect all needed
information. It increases the communication overhead.
o Consistency: The path vectors and properties of ANEs are
correlated. So querying them one by one may conduct consistency
issue. Once the path vector changes during the client requests
the ANE properties, the ANE properties may be inconsistent with
the previous path vector.
To solve these issues, this document introduces an extension to cost
map and endpoint cost service, which allows the ALTO server to attach
a property map in the data entry of a cost map or an endpoint cost
service response.
These issues may exist in all general cases for querying separated
ALTO information resources. But solving this general problem is not
in the scope of this document.
5. 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". In the rest content, this document uses "path-
vector" to indicate the combination cost type of the cost mode
"array" and the cost metric "ane-path".
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5.1. 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.
5.2. 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 ANEs which the path
from a source to a destination goes across. The values are arrays of
ANE names which are defined in Section 6.2.
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.
5.3. Path Vector Cost Type Semantics
The new cost type follows the convention of the cost types in the
base 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
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"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.
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.
6.1. Domain Name
ane
6.2. Domain-Specific Entity Addresses
The entity address 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
address 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. Protocol Extensions for Path Vector
To make the ALTO client query the path vectors and properties of ANEs
efficiently and consistently, this document extends the Filtered Cost
Map and Endpoint Cost Service.
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7.1. Filtered Cost Map Extensions
This document extends Filtered Cost Map, as defined in Section 11.3.2
of [RFC7285], by adding new input parameters and capabilities, and by
augmenting the property map into the data entry of the response.
The "media type", "HTTP method", and "uses" specifications (described
in Sections 11.3.2.1, 11.3.2.2, and 11.3.2.5 of [RFC7285],
respectively) remain the same.
7.1.1. Accept Input Parameters
The ReqFilteredCostMap object in Section 11.3.2.3 of [RFC7285] is
extended as follows:
object {
[PropertyName compound-properties<1..*>;]
} ReqPVFilteredCostMap : ReqFilteredCostMap;
compound-properties: If the capability "allow-compound-response" is
false, the ALTO client MUST NOT specify this field, and the ALTO
server MUST reject the request and return "E_INVALID_FILED_VALUE"
error when it receives a request including this field. If this
field is specified and accepted, the ALTO server MUST augment the
dependent property map with the properties in this field into the
response automatically.
7.1.2. Capabilities
The Filtered Cost Map capabilities are extended with two new members:
o dependent-property-map
o allow-compound-response
The capability "dependent-property-map" indicates which property map
this resource depends on, and the capability "allow-compound-
response" indicates whether the ALTO server supports the resource to
compound the property map with its own response data. With these two
additional members, the FilteredCostMapCapabilities object in
Section 11.3.2.4 of [RFC7285] is extended as follows:
object {
[ResourceID dependent-property-map;]
[JSONBool allow-compound-response;]
} PVFCMCapabilities : FilteredCostMapCapabilities;
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dependent-property-map: This field MUST be specified when the "cost-
type-names" includes a cost type name indicating a "ane-path"
metric. Its value MUST be a resource id indicating a property map
including "ane" domain. If not, the ALTO client SHOULD consider
this resource is invalid.
allow-compound-response: If present, the true value means the ALTO
client can request the resource to augment its dependent property
map into the response automatically; the false value means the
ALTO client cannot request the compound response. If omitted, the
default value is false;
To be noticed that the capability "cost-constraints" is unexpected
for the "array" cost mode. The syntax and semantics of constraint
tests on the "array" cost mode depends on the implementation and can
be defined in the future documents. But it is not in the scope of
this document.
7.1.3. Response
If the ALTO client specifies the "cost-type" input parameter with
"ane-path" metric, the "dependent-vtags" field in the "meta" field of
the response MUST include the version tag of its dependent property
map following its dependent network map.
If the ALTO client specifies the "compound-properties" input
parameter which is accepted by the ALTO server, the response MUST
include a "property-map" field following the "cost-map" field, and
its value MUST be a PropertyMapData object. This PropertyMapData
object MUST be equivalent to the result when query the dependent
property map resource using the following request: the "entities"
field includes all the ANE names appearing in the cost values of the
"cost-map" field, the "properties" field has the same value as the
"compound-properties" field does. The properties shown in the
"compound-properties" input parameter but are not supported by the
dependent property map SHOULD be omitted from the response.
7.2. Endpoint Cost Service Extensions
This document extends the Endpoint Cost Service, as defined in
Section 11.5.1 of [RFC7285], by adding new input parameters and
capabilities and by augmenting the property map into the data entry
of the response.
The media type, HTTP method, and "uses" specifications (described in
Sections 11.5.1.1, 11.5.1.2, and 11.5.1.5 of [RFC7285], respectively)
are unchanged.
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7.2.1. Accept Input Parameters
The ReqEndpointCostMap object in Section 11.5.1.3 of [RFC7285] is
extended as follows:
object {
[PropertyName compound-properties<1..*>;]
} ReqPVEndpointCostMap : ReqEndpointCostMap;
The "compound-properties" has the same interpretation as defined in
Section 7.1.1.
7.2.2. Capabilities
The extensions to the Endpoint Cost Service capabilities are
identical to the extensions to the Filtered Cost Map (see
Section 7.1.2).
7.2.3. Response
If the ALTO client specifies the "cost-type" input parameter with
"ane-path" metric, the response MUST include the "meta" field with
the "dependent-vtags" in it, and the "dependent-vtags" field MUST
include the version tag of its dependent property map.
If the ALTO client specifies the "compound-properties" input
parameter which is accepted by the ALTO server, the response MUST
include a "property-map" field following the "endpoint-cost-map"
field, and its value MUST be a PropertyMapData object. This
PropertyMapData object MUST be equivalent to the result when query
the dependent property map resource using the following request: the
"entities" field includes all the ANE names appearing in the cost
values of the "endpoint-cost-map" field, the "properties" field has
the same value as the "compound-properties" field does. The
properties shown in the "compound-properties" input parameter but are
not supported by the dependent property map SHOULD be omitted from
the response.
8. Examples
This section lists some examples of path vector queries and the
corresponding responses.
8.1. Workflow
This section gives a typical workflow of how an ALTO client query
path vectors using the extension.
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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 supports the "ane-path" cost metric and get the
resource ID of the dependent property map.
3. Check whether the capabilities of the property map includes the
desired "prop-types".
4. Check whether the (Filtered) Cost Map/Endpoint Cost Service
allows the compound response.
5. If allowed, the ALTO client can send a request including the
desired ANE properties to the ALTO server and receive a compound
response with the cost map/endpoint cost map and the property
map.
6. If not allowed, the ALTO client sends a query for the cost map/
endpoint cost map first. After receiving the response, the ALTO
client interprets all the ANE names appearing in the response and
sends another query for the property map on those ANE names.
8.2. 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-availbw-delay" supports
properties "availbw" and "delay".
{
"meta": {
"cost-types": {
"path-vector": {
"cost-mode": "array",
"cost-metric": "ane-path"
},
"num-routingcost": {
"cost-mode": "numerical",
"cost-metric": "routingcost"
},
"num-hopcount": {
"cost-mode": "numerical",
"cost-metric": "hopcount"
}
}
},
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"resources": {
"my-default-networkmap": {
"uri" : "http://alto.example.com/networkmap",
"media-type" : "application/alto-networkmap+json"
},
"my-default-cost-map": {
"uri": "http://alto.example.com/costmap/pv",
"media-type": "application/alto-costmap+json",
"accepts": "application/alto-costmapfilter+json",
"capabilities": {
"cost-type-names": [ "num-hopcount",
"num-routingcost" ]
},
"uses": [ "my-default-networkmap" ]
},
"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": [ "path-vector" ],
"dependent-property-map": "propmap-availbw-delay"
},
"uses": [ "my-default-networkmap" ]
},
"endpoint-cost-pv": {
"uri": "http://alto.exmaple.com/endpointcost/pv",
"media-type": "application/alto-endpointcost+json",
"accepts": "application/alto-endpointcostparams+json",
"capabilities": {
"cost-type-names": [ "path-vector" ],
"dependent-property-map": "propmap-availbw-delay",
"allow-compound-response": true
}
},
"invalid-cost-map" : {
"uri": "http://alto.example.com/costmap/invalid",
"media-type": "application/alto-costmap+json",
"accepts": "application/alto-costmapfilter+json",
"capabilities": {
"cost-type-names": [ "path-vector" ],
"allow-compound-response": true
},
"uses": [ "my-default-networkmap" ]
},
"propmap-availbw-delay": {
"uri": "http://alto.exmaple.com/propmap/ane-prop",
"media-type": "application/alto-propmap+json",
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"accepts": "application/alto-propmapparams+json",
"capabilities": {
"domain-types": [ "ane" ],
"prop-types": [ "availbw", "delay" ]
},
"uses": [ "cost-map-pv", "endpoint-cost-pv" ]
}
}
}
8.3. Example # 1
Query filtered cost map to get the path vectors.
POST /costmap/pv HTTP/1.1
Host: alto.example.com
Accept: 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" ]
}
}
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HTTP/1.1 200 OK
Content-Length: [TBD]
Content-Type: application/alto-costmap+json
{
"meta": {
"dependent-vtags": [
{
"resource-id": "my-default-networkmap",
"tag": "75ed013b3cb58f896e839582504f622838ce670f"
}
],
"cost-type": {
"cost-mode": "array",
"cost-metric": "ane-path"
}
},
"cost-map": {
"PID1": {
"PID2": [ "ane:L001", "ane:L003" ],
"PID3": [ "ane:L001", "ane:L004" ]
}
}
}
Then query the properties of ANEs in path vectors.
POST /propmap/ane-prop HTTP/1.1
Host: alto.example.com
Accept: application/alto-propmap+json,
application/alto-error+json
Content-Length: [TBD]
Content-Type: application/alto-propmapparams+json
{
"entities": [ "ane:L001", "ane:L003", "ane:L004" ],
"properties": [ "delay" ]
}
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HTTP/1.1 200 OK
Content-Length: [TBD]
Content-Type: application/alto-propmap+json
{
"meta": {
"dependent-vtags": [
{
"resource-id": "cost-map-pv",
"tag": "a7d57e120ab63124e3c9a82f7a54bc120fc96216"
}
]
},
"property-map": {
"ane:L001": { "delay": 46},
"ane:L003": { "delay": 50},
"ane:L004": { "delay": 70}
}
}
8.4. Example # 2
POST /endpointcost/pv HTTP/1.1
Host: alto.example.com
Accept: application/alto-endpointcost+json,
application/alto-error+json
Content-Length: [TBD]
Content-Type: application/alto-endpointcostparams+json
{
"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" ]
}
}
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HTTP/1.1 200 OK
Content-Length: [TBD]
Content-Type: application/alto-endpointcost+json
{
"meta": {
"cost-type": [
{"cost-mode": "array", "cost-metric": "ane-path"}
]
},
"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" ],
"ipv6:2001:db8::10": [ "ane:L001", "ane:L005",
"ane:L007" ]
}
}
}
POST /endpointcost/pv HTTP/1.1
Host: alto.example.com
Accept: application/alto-endpointcost+json,
application/alto-error+json
Content-Length: [TBD]
Content-Type: application/alto-endpointcostparams+json
{
"entities": [ "ane:L001", "ane:L003", "ane:L004",
"ane:L005", "ane:L007" ],
"properties": [ "availbw" ]
}
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HTTP/1.1 200 OK
Content-Length: [TBD]
Content-Type: application/alto-propmap+json
{
"meta": {
"dependent-vtags": [
{
"resource-id": "endpoint-cost-pv",
"tag": "12c0889c3c0892bb67df561ed16d93f5d1fa75cf"
}
]
},
"property-map": {
"ane:L001": { "availbw": 50 },
"ane:L003": { "availbw": 48 },
"ane:L004": { "availbw": 55 },
"ane:L005": { "availbw": 60 },
"ane:L007": { "availbw": 35 }
}
}
8.5. Example #3
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POST /endpointcost/pv HTTP/1.1
Host: alto.example.com
Accept: application/alto-endpointcost+json,
application/alto-error+json
Content-Length: [TBD]
Content-Type: application/alto-endpointcostparams+json
{
"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" ]
},
"properties": [ "delay", "availbw" ]
}
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HTTP/1.1 200 OK
Content-Length: [TBD]
Content-Type: application/alto-endpointcost+json
{
"meta": {
"dependent-vtags": [
{
"resource-id": "propmap-availbw-delay",
"tag": "bb6bb72eafe8f9bdc4f335c7ed3b10822a391cef"
}
],
"cost-type": [
{"cost-mode": "array", "cost-metric": "ane-path"}
]
},
"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" ],
"ipv6:2001:db8::10": [ "ane:L001", "ane:L005",
"ane:L007" ]
}
},
"property-map": {
"ane:L001": { "availbw": 50, "delay": 46 },
"ane:L003": { "availbw": 48, "delay": 50 },
"ane:L004": { "availbw": 55, "delay": 70 },
"ane:L005": { "availbw": 60, "delay": 100 },
"ane:L007": { "availbw": 35, "delay": 100 }
}
}
9. Compatibility
9.1. Compatibility with Base ALTO Clients/Servers
The path vector extension on Filtered Cost Map and Endpoint Cost
Service is backward compatible with the base ALTO protocol:
o If the ALTO server provides extended capabilities "dependent-
property-map" and "allow-compound-response" for Filtered Cost Map
or Endpoint Cost Service, but the client only supports the base
ALTO protocol, then the client will ignore those capabilities
without conducting any incompatibility.
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o If the client sends a request with the input parameter
"properties", but the server only supports the base ALTO protocol,
the server will ignore this field.
9.2. Compatibility with Multi-Cost Extension
This document does not specify how to integrate the "array" cost mode
and the "ane-path" cost metric 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.
As Section 7.1.2 mentions, the syntax and semantics of whether
"constraints" or "or-constraints" field for the "array" cost mode is
not specified in this document. So if an ALTO server provides a
resource with the "array" cost mode and the capability "cost-
constraints" or "testable-cost-types-names", the ALTO client MAY
ignore the capability "cost-constraints" or "testable-cost-types-
names" unless the implementation or future documents specify the
behavior.
9.3. 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.
10. General Discussions
10.1. 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
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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.
10.2. 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.
10.3. General Compound Resources Query
As the last paragraph of Section 4.3 mentions, querying multiple ALTO
information resources continuously is 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.
11. Security Considerations
This document is an extension of the base ALTO protocol, so the
Security Considerations 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]).
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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.
12. IANA Considerations
12.1. 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.
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12.2. 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 5.2 |
+-------------+---------------------+
Table 2: ALTO Cost Metrics
12.3. 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 3.
+-------------+--------------------------+--------------------------+
| Identifier | Entity Address Encoding | Hierarchy & Inheritance |
+-------------+--------------------------+--------------------------+
| ane | See Section 6.2 | None |
+-------------+--------------------------+--------------------------+
Table 3: ALTO Entity Domain
12.4. ALTO Network Element Property Type Registry
The "ALTO Abstract Network Element Property Type Registry" is
required by the ALTO Domain "ane", listed in Table 4.
+-------------+--------------------------+
| Identifier | Intended Semantics |
+-------------+--------------------------+
| availbw | The available bandwidth |
| delay | The transmission delay |
+-------------+--------------------------+
Table 4: ALTO Abstract Network Element Property Types
13. 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.
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14. References
14.1. 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>.
14.2. 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., Yang, Y., and S. Chen, "ALTO Incremental
Updates Using Server-Sent Events (SSE)", draft-ietf-alto-
incr-update-sse-15 (work in progress), December 2018.
[I-D.ietf-alto-unified-props-new]
Roome, W., Chen, S., xinwang2014@hotmail.com, x., Yang,
Y., and J. Zhang, "Extensible Property Maps for the ALTO
Protocol", draft-ietf-alto-unified-props-new-01 (work in
progress), December 2017.
[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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