ALTO Extension: Path Vector
draft-ietf-alto-path-vector-10
The information below is for an old version of the document.
| Document | Type |
This is an older version of an Internet-Draft that was ultimately published as RFC 9275.
|
|
|---|---|---|---|
| Authors | Kai Gao , Sabine Randriamasy , Y. Richard Yang , Jingxuan Zhang | ||
| Last updated | 2020-03-09 (Latest revision 2019-11-03) | ||
| Replaces | draft-yang-alto-path-vector | ||
| RFC stream | Internet Engineering Task Force (IETF) | ||
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draft-ietf-alto-path-vector-10
ALTO K. Gao
Internet-Draft Sichuan University
Intended status: Standards Track Y. Lee
Expires: 10 September 2020
S. Randriamasy
Nokia Bell Labs
Y.R. Yang
Yale University
J. Zhang
Tongji University
9 March 2020
ALTO Extension: Path Vector
draft-ietf-alto-path-vector-10
Abstract
This document is an extension to the base Application-Layer Traffic
Optimization protocol [RFC7285]. The current ALTO Cost Services
allow applications to obtain cost values on an end-to-end path
defined by its source and destination. The present extension
provides abstracted information on particular network parts or
elements traversed by a path between its source and destination.
Examples of such abstracted parts are networks, data centers or
links. This is useful for applications whose performance is impacted
by particular network parts they traverse or by their properties.
Applications having the choice among several connection paths may use
this information to select paths accordingly and improve their
performance. In particular, they may infer that several paths share
common links and prevent traffic bottlenecks by avoiding such paths.
This document introduces a new cost type called Path Vector. A Path
Vector is an array of entities that each identifies an abstracted
representation of a network part and that are called Abstract Network
Element (ANE). Each ANE is defined by a set of properties. ANE
properties are conveyed by an ALTO information resource called
"Property Map", that can be packed together with the Path Vectors in
a multipart response. They can also be obtained via a separate ALTO
request to a Property Map. An ALTO Property Map is an extension to
the ALTO protocol, that is specified in another document entitled
"Unified Properties for the ALTO Protocol"
[I-D.ietf-alto-unified-props-new].
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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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
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 10 September 2020.
Copyright Notice
Copyright (c) 2020 IETF Trust and the persons identified as the
document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents (https://trustee.ietf.org/
license-info) in effect on the date of publication of this document.
Please review these documents carefully, as they describe your rights
and restrictions with respect to this document. Code Components
extracted from this document must include Simplified BSD License text
as described in Section 4.e of the Trust Legal Provisions and are
provided without warranty as described in the Simplified BSD License.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 4
2. Use Cases . . . . . . . . . . . . . . . . . . . . . . . . . . 5
2.1. Capacity Region for Multi-Flow Scheduling . . . . . . . . 6
2.2. Recent Use Cases . . . . . . . . . . . . . . . . . . . . 7
2.2.1. Large-scale Data Analytics . . . . . . . . . . . . . 8
2.2.2. Context-aware Data Transfer . . . . . . . . . . . . . 8
2.2.3. CDN and Service Edge . . . . . . . . . . . . . . . . 8
2.3. Terminology . . . . . . . . . . . . . . . . . . . . . . . 8
3. Overview . . . . . . . . . . . . . . . . . . . . . . . . . . 9
3.1. Abstract Network Element . . . . . . . . . . . . . . . . 10
3.1.1. ANE Name . . . . . . . . . . . . . . . . . . . . . . 10
3.1.2. ANE Properties . . . . . . . . . . . . . . . . . . . 11
3.2. Path Vector . . . . . . . . . . . . . . . . . . . . . . . 12
3.3. Multipart Path Vector Response . . . . . . . . . . . . . 12
3.3.1. Identifying the Media Type of the Root Object . . . . 13
3.3.2. References to Part Messages . . . . . . . . . . . . . 14
3.3.3. Order of Part Messages . . . . . . . . . . . . . . . 15
4. Basic Data Types . . . . . . . . . . . . . . . . . . . . . . 15
4.1. ANE Name . . . . . . . . . . . . . . . . . . . . . . . . 15
4.2. ANE Domain . . . . . . . . . . . . . . . . . . . . . . . 15
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4.2.1. Entity Domain Type . . . . . . . . . . . . . . . . . 15
4.2.2. Domain-Specific Entity Identifier . . . . . . . . . . 15
4.2.3. Hierarchy and Inheritance . . . . . . . . . . . . . . 15
4.3. New Resource-Specific Entity Domain Exports . . . . . . . 16
4.3.1. ANE Domain of Cost Map Resource . . . . . . . . . . . 16
4.3.2. ANE Domain of Endpoint Cost Service Resource . . . . 16
4.4. ANE Property Name . . . . . . . . . . . . . . . . . . . . 16
4.4.1. ANE Property: Maximum Reservable Bandwidth . . . . . 16
4.4.2. ANE Property: Persistent Entities . . . . . . . . . . 17
4.5. Path Vector Cost Type . . . . . . . . . . . . . . . . . . 17
4.5.1. Cost Metric: ane-path . . . . . . . . . . . . . . . . 17
4.5.2. Cost Mode: array . . . . . . . . . . . . . . . . . . 17
4.6. Part Resource ID . . . . . . . . . . . . . . . . . . . . 17
5. Service Extensions . . . . . . . . . . . . . . . . . . . . . 18
5.1. Multipart Filtered Cost Map for Path Vector . . . . . . . 18
5.1.1. Media Type . . . . . . . . . . . . . . . . . . . . . 18
5.1.2. HTTP Method . . . . . . . . . . . . . . . . . . . . . 18
5.1.3. Accept Input Parameters . . . . . . . . . . . . . . . 18
5.1.4. Capabilities . . . . . . . . . . . . . . . . . . . . 18
5.1.5. Uses . . . . . . . . . . . . . . . . . . . . . . . . 19
5.1.6. Response . . . . . . . . . . . . . . . . . . . . . . 19
5.2. Multipart Endpoint Cost Service for Path Vector . . . . . 20
5.2.1. Media Type . . . . . . . . . . . . . . . . . . . . . 21
5.2.2. HTTP Method . . . . . . . . . . . . . . . . . . . . . 21
5.2.3. Accept Input Parameters . . . . . . . . . . . . . . . 21
5.2.4. Capabilities . . . . . . . . . . . . . . . . . . . . 21
5.2.5. Uses . . . . . . . . . . . . . . . . . . . . . . . . 21
5.2.6. Response . . . . . . . . . . . . . . . . . . . . . . 21
6. Examples . . . . . . . . . . . . . . . . . . . . . . . . . . 22
6.1. Example: Information Resource Directory . . . . . . . . . 23
6.2. Example: Multipart Filtered Cost Map . . . . . . . . . . 24
6.3. Example: Multipart Endpoint Cost Resource . . . . . . . . 26
6.4. Example: Incremental Updates . . . . . . . . . . . . . . 28
7. Compatibility . . . . . . . . . . . . . . . . . . . . . . . . 29
7.1. Compatibility with Legacy ALTO Clients/Servers . . . . . 29
7.2. Compatibility with Multi-Cost Extension . . . . . . . . . 30
7.3. Compatibility with Incremental Update . . . . . . . . . . 30
7.4. Compatibility with Cost Calendar . . . . . . . . . . . . 30
8. General Discussions . . . . . . . . . . . . . . . . . . . . . 30
8.1. Constraint Tests for General Cost Types . . . . . . . . . 31
8.2. General Multipart Resources Query . . . . . . . . . . . . 31
9. Security Considerations . . . . . . . . . . . . . . . . . . . 31
10. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 32
10.1. ALTO Cost Mode Registry . . . . . . . . . . . . . . . . 32
10.2. ALTO Entity Domain Registry . . . . . . . . . . . . . . 32
10.3. ALTO Entity Property Type Registry . . . . . . . . . . . 32
10.4. ALTO Resource Entity Domain Export Registries . . . . . 33
10.4.1. costmap . . . . . . . . . . . . . . . . . . . . . . 33
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10.4.2. endpointcost . . . . . . . . . . . . . . . . . . . . 33
11. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 33
12. References . . . . . . . . . . . . . . . . . . . . . . . . . 33
12.1. Normative References . . . . . . . . . . . . . . . . . . 33
12.2. Informative References . . . . . . . . . . . . . . . . . 34
Appendix A. Changes since -08 . . . . . . . . . . . . . . . . . 36
Appendix B. Changes Since Version -06 . . . . . . . . . . . . . 36
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 36
1. Introduction
Network performance metrics are crucial to the Quality of Experience
(QoE) of today's applications. The ALTO protocol allows Internet
Service Providers (ISPs) to provide guidance, such as topological
distance between different end hosts, to overlay applications. Thus,
the overlay applications can potentially improve the QoE by better
orchestrating their traffic to utilize the resources in the
underlying network infrastructure.
The base protocol [RFC7285] defines Cost Map and Endpoint Cost
Service that expose the topological distances of a set of <source,
destination> pairs. Various extensions have been proposed extend the
capability of these services to express other performance metrics
[I-D.ietf-alto-performance-metrics], to query multiple costs
simultaneously [RFC8189], and to obtain the time-varying values
[I-D.ietf-alto-cost-calendar].
Existing ALTO services provide only cost information on an end-to-end
path defined by its <source, destination> endpoints. However, the
QoE of many overlay applications depends not only on the end-to-end
costs, but also on some intermediate network components and their
properties. For example, job completion time, which is an important
QoE metric for a large scale data analytics application, is impacted
by shared bottlenecks inside the carrier network.
Predicting such information can be very complex without the help of
the ISP [AAAI2019]. On the other hand, ISPs are not likely to expose
details on their network paths: first for the sake of
confidentiality, second because it may represent a huge volume and
overhead and last, because it is difficult for ISPs to figure out
what information and what details an application needs. Likewise,
applications do not necessarily need all the network path details and
are likely not able to understand them.
It may be helpful as well for ISPs if applications could avoid using
bottlenecks or challenging the network with poorly scheduled traffic.
Therefore, it is beneficial for both parties if an ALTO server
provides ALTO clients with an "abstract network state" that provides
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the necessary details to applications, while hiding the network
complexity and confidential information. An "abstract network state"
is a selected set of abstract representations of intermediate network
components traversed by the paths between <source, destination> pairs
combined with properties of these components that are relevant to the
overlay applications' QoE. Both an application via its ALTO Client
and the ISP via the ALTO server can achieve better confidentiality
and resource utilization by appropriately abstracting relevant path
components. The pressure on the server scalability can also be
reduced by abstracting components and their properties and combining
them in a single response.
This document extends [RFC7285] to allow an ALTO server convey
"abstract network state", for paths defined by their <source,
destination> pairs. To this end, it introduces a new cost type
called "Path Vector". A Path Vector is an array of identifiers of
so-called Abstract Network Element (ANE). An ANE represents an
abstract intermediate component traversed by a path. It can be
associated with various properties. The associations between ANEs
and their properties are encoded in an ALTO information resource
called Unified Property Map, which is specified in
[I-D.ietf-alto-unified-props-new].
For better confidentiality, this document aims to minimize
information exposure. In particular, this document enables and
recommends that first ANEs are constructed on demand, and second an
ANE is only associated with properties that are requested by an ALTO
client. A Path Vector response involved two ALTO Maps: the Cost Map
that contains the Path Vector results and the up to date Unified
Property Map that contains the properties requested for these ANEs.
To enforce consistency and improve server scalability, this document
uses the "multipart/related" message defined in [RFC2387] to return
the two maps in a single response.
The rest of the document are organized as follows. Section 3 gives
an overview of the protocol design. Section 4 and Section 5 specify
the Path Vector extension to the ALTO IRD and the information
resources, with some concrete examples presented in Section 6.
Section 7 discusses the backward compatibility with the base protocol
and existing extensions. Security and IANA considerations are
discussed in Section 9 and Section 10 respectively.
2. Use Cases
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2.1. Capacity Region for Multi-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.
+------+
| |
--+ 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
+------+ +------+
| |
+----------------------+
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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:
* 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.
* 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:
* The network needs to expose more detailed routing information to
show the shared bottlenecks.
* 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.
2.2. Recent Use Cases
This section highlights some recent use cases that are reported in
IETF and ALTO working group. See [I-D.bernstein-alto-topo] for a
more comprehensive survey of use cases where extended network
topology information is needed.
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2.2.1. Large-scale Data Analytics
One potential use case of the Path Vector extension is for large-
scale data analytics such as [SENSE] and [LHC], where data of
Gigabytes, Terabytes and even Petabytes are transferred. For these
applications, the QoE is usually measured as the job completion time,
which is related to the completion time of the slowest data transfer.
With the Path Vector extension, an ALTO client can identify
bottlenecks inside the network. Therefore, the overlay application
can make optimal traffic distribution or resource reservation (i.e.,
proportional to the size of the transferred data), leading to optimal
job completion time and network resource utilization.
2.2.2. Context-aware Data Transfer
It is sometimes important to know how the capabilities of various
network components between two end hosts. With the Path Vector
extension, an ALTO client may query the "network context"
information, i.e., whether the two hosts are connected to the access
network through a wireless link or a wire, and the capabilities of
the access network. Thus, the client may use different data transfer
mechanisms, or even deploy different 5G User Plane Functions (UPF)
[I-D.ietf-dmm-5g-uplane-analysis] to optimize the data transfer.
2.2.3. CDN and Service Edge
A growing trend in today's applications is to bring storage and
computation closer to the end user for better QoE, such as Content
Delivery Network (CDN), AR/VR, and cloud gaming, as reported in
various recent documents ([I-D.contreras-alto-service-edge],
[I-D.huang-alto-mowie-for-network-aware-app], and
[I-D.yang-alto-deliver-functions-over-networks]).
With the Path Vector extension, an ALTO server can selectively reveal
the CDNs and service edges that reside along the paths between
different end hosts, together with their properties such as available
Service Level Agreement (SLA) plans. Otherwise, the ALTO client may
have to make multiple queries and potentially with the complete list
of CDNs and/or service edges. While both approaches offer the same
information, making multiple queries introduce larger delay and more
overhead on both the ALTO server and the ALTO client.
2.3. Terminology
This document extends the ALTO base protocol [RFC7285] and the
Unified Property Map extension [I-D.ietf-alto-unified-props-new]. In
addition to the terms defined in these documents, this document also
uses the following additional terms:
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* Abstract Network Element (ANE): An Abstract Network Element is an
abstraction representation of network components. It can be a
link, a middlebox, a virtualized network function (VNF), etc., or
their aggregations. An ANE can be constructed either statically
in advance or on demand based on the requested information. In a
response, each ANE is represented by a unique ANE Name. Note that
an ALTO client MUST NOT assume ANEs in different responses but
with the same ANE Name refer to the same aggregation of network
components.
* Path Vector: A Path Vector, or an ANE Path Vector, is a JSON array
of ANE Names. It conveys the information that the path between a
source and a destination traverses the ANEs in the same order as
they appear in the Path Vector.
* Path Vector resource: A Path Vector resource refers to an ALTO
resource which supports the extension defined in this document.
* Path Vector cost type: The Path Vector cost type is a special cost
type, which is specified in Section 4.5. When this cost type is
present in an IRD entry, it indicates that the information
resource is a Path Vector resource. When this cost type is
present in a Cost Map or an Endpoint Cost Map, it indicates each
cost value must be interpreted as a Path Vector.
* Path Vector request: A Path Vector request refers to the POST
message sent to an ALTO Path Vector resource.
* Path Vector response: A Path Vector response refers to the
multipart/related message returned by a Path Vector resource.
3. Overview
This section gives a non-normative overview of the Path Vector
extension. It is assumed that readers are familiar with both the
base protocol [RFC7285] and the Unified Property Map extension
[I-D.ietf-alto-unified-props-new].
Fundamentally, this extension conveys two pieces of information:
1. The abstract network state: The abstract network state is modeled
as an annotated graph, where each node is an Abstract Network
Element (ANE) and each annotation is a property associated with
an ANE.
2. Routing information: The routing information is modeled as an
array of nodes in the annotated graph that is traversed by the
path between a source and a destination.
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However, it can be observed that the routing information already
conveys the connectivity of the abstract network. Thus, this
extensions allows an ALTO server to provide the routing information
and the association between ANEs and their properties. Specifically,
this document uses the following designs:
1. This extension conveys the routing information in the abstract
network in an ALTO Cost Map or Endpoint Cost Map which accepts a
Path Vector, i.e., a JSON array of ANEs traversed by the path
between a source and a destination, as the cost value. With the
Path Vectors, an ALTO client can simultaneously reconstruct the
structure of the abstract network and the routing for the paths
between endpoints.
2. This extension uses the ALTO Unified Property Map to convey the
properties associated with the ANEs, which offers more fine-
grained abstract network state for overlay applications.
3. This extension uses the multipart message TBD-ALTO-MULTIPART to
include both information resources in the same Path Vector
response.
3.1. Abstract Network Element
This extension introduce Abstract Network Element (ANE) as an
indirect and network-agnostic way to specify an aggregation of
intermediate network components which can be treated as if they are
placed in the same location in the network, based on geo-location,
OSPF domain, service type, algebraic properties, or other criteria.
3.1.1. ANE Name
Each ANE is uniquely identified by a string of type ANEName as
specified in Section 4.1. An important observation is that for
different requests, an ALTO server may selectively apply different
methods to create the abstract network state based on confidentiality
and performance considerations. Thus, the ANEs inside the abstract
network may be constructed on demand. This indicates that the scope
of an ANEName is limited to the Path Vector response.
Since each ANE is also an entity in the Unified Property Map, the ANE
Name MUST conform to the encoding of an Entity Identifier. Thus,
this document also specifies a new EntityDomainName following the
instructions in [I-D.ietf-alto-unified-props-new].
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3.1.2. ANE Properties
In this extension, the associations between ANE and the properties
are conveyed in a Unified Property Map. Thus, they MUST follow the
mechanisms specified in the [I-D.ietf-alto-unified-props-new] with
some additional considerations.
1. As a property may not exist in every ANE, it must be interpreted
in the same way by the ALTO server and the ALTO client. Thus,
when an ANE property is specified, its intended semantics MUST
specify how to interpret the case that a requested ANE property
does not exist in an ANE.
2. As each ANE is an aggregation of multiple network components, its
properties are the aggregated results of the components'
properties. For different ALTO server implementations, different
properties MAY have different rules when they are aggregated into
a single ANE. For example, if an ANE is the aggregation of two
networks where each network contains a CDN, an ALTO server may
selectively expose one CDN, expose none, or expose both in the
ANE, according to its own aggregation policies.
However, it is common that an ALTO client needs to compute the
aggregated property value of some ANEs, e.g., to infer the end-
to-end property for a <source, destination> pair. It is
RECOMMENDED that the intended semantics of an ANE property
specifies how to compute the aggregated value without loss of
information. Thus, the information is interpreted by the ALTO
server and the ALTO client in the same way. For example,
properties with algebraic properties can be aggregated following
the algebraic rules [TON2019].
NOTE: The aggregation rule ONLY specifies how to compute the
aggregated property for a Path Vector, NOT how the ANEs can be
aggregated in the Path Vector response. This is because the
change of Path Vectors may change the routing information and the
abstract network topology, leading to inaccurate results.
3. An ALTO Path Vector resource MAY only support a set of ANE
properties. Meanwhile, an ALTO client MAY only require a subset
of the available properties. Thus, a property negotiation
process is required.
This document uses a similar approach as the negotiation process
of cost types: the available properties for a given resource are
announced in the Information Resource Directory as a new
capability called "ane-property-names"; the selected properties
SHOULD be specified in a new filter called "ane-property-names"
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in the request body; the response MUST return and only return the
selected properties for the ANEs in the response, if applicable.
3.2. Path Vector
For an ALTO client to correctly interpret the Path Vector, this
extension specifies a new cost type called the Path Vector cost type,
which MUST be included both in the Information Resource Directory and
the ALTO Cost Map or Endpoint Cost Map so that an ALTO client can
correct interpret the cost values.
The Path Vector cost type MUST convey both the interpretation and
semantics in the "cost-mode" and "cost-metric" respectively.
Unfortunately, a single "cost-mode" value cannot fully specify the
interpretation of a Path Vector, which is a compound data type. For
example, in programming languages such as Java, a Path Vector will
have the type of JSONArray[ANEName].
Instead of extending the "type system" of ALTO, this document takes a
simple and backward compatible approach. Specifically, the "cost-
mode" of the Path Vector cost type is "array", which indicates the
value is a JSON array. Then, an ATLO client MUST check the value of
the "cost-metric". If the value is "ane-path", meaning the JSON
array should be further interpreted as a path of ANENames.
The Path Vector cost type is specified in Section 4.5
3.3. Multipart Path Vector Response
For a basic ALTO information resource, the response contains only one
type of ALTO resources, e.g., Network Map, Cost Map, or Property Map.
Thus, only one round of communication is required: An ALTO client
sends a request to an ALTO server, and the ALTO server returns a
response, as shown in Figure 3.
ALTO Client ALTO Server
|-------------- Request ---------------->|
|<------------- Response ----------------|
Figure 3: A Typical ALTO Request and Response
ALTO Client ALTO Server
|------------- PV Request -------------->|
|<----- PV Response (Cost Map Part) -----|
|<--- PV Response (Property Map Part) ---|
Figure 4: The Path Vector Extension Request and Response
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The Path Vector extension, on the other hand, involves two types of
information resources: Path Vectors conveyed in a Cost Map or an
Endpoint Cost Map, and ANE properties conveyed in a Unified Property
Map. Instead of two consecutive message exchanges, the Path Vector
extension enforces one round of communication. Specifically, the
Path Vector extension requires the ALTO client to include the source
and destination pairs and the requested ANE properties in a single
request, and encapsulates both Path Vectors and properties associated
with the ANEs in a single response, as shown in Figure 4.
This design is based on the following considerations:
1. Since ANEs MAY be constructed on demand, and potentially based on
the requested properties (See Section 3.1 for more details). If
sources and destinations are not in the same request as the
properties, an ALTO server either CANNOT construct ANEs on-
demand, or MUST wait until both requests are received.
2. As ANEs MAY be constructed on demand, mappings of each ANE to its
underlying network devices and resources CAN be specific to the
request. In order to respond to the second request correctly, an
ALTO server MUST store the mapping of each Path Vector request
until the client fully retrieves the property information. The
"stateful" behavior CAN substantially harm the server scalability
and potentially lead to Denial-of-Service attacks.
One approach to realize the one-round communication is to define a
new media type to contain both objects, but this violates modular
design. This document uses standard-conforming usage of "multipart/
related" media type defined in [RFC2387] to elegantly combine the
objects. Path Vectors are encoded as a Cost Map or an Endpoint Cost
Map, and the Property Map is encoded as a Unified Propert Map. They
are encapsulated as parts of a multipart message. The modular
composition allows ALTO servers and clients to reuse the data models
of the existing information resources. Specifically, this document
addresses the following practical issues using "multipart/related".
3.3.1. Identifying the Media Type of the Root Object
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-endpointcost+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.
To address this issue, this document uses the "type" parameter to
indicate the root object of a multipart/related message. For a Cost
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Map resource, the "media-type" in the IRD entry MUST be "multipart/
related" with the parameter "type=application/alto-costmap+json"; for
an Endpoint Cost Service, the parameter MUST be "type=application/
alto-endpointcost+json".
3.3.2. References to Part Messages
The ALTO SSE extension (see [I-D.ietf-alto-incr-update-sse]) uses
"client-id" to demultiplex push updates. However, "client-id" is
provided for each request, which introduces ambiguity when applying
SSE to a Path Vector resource.
To address this issue, an ALTO server MUST assign a unique identifier
to each part of the "multipart/related" response message. This
identifier, referred to as a Part Resource ID (See Section 4.6 for
details), MUST be present in the part message's "Resource-Id" header.
The MIME part header MUST also contain the "Content-Type" header,
whose value is the media type of the part (e.g., "application/alto-
costmap+json", "application/alto-endpointcost+json", or "application/
alto-propmap+json").
If an ALTO server provides incremental updates for this Path Vector
resource, it MUST generate incremental updates for each part
separately. The client-id MUST have the following format:
pv-client-id '.' part-resource-id
where pv-client-id is the client-id assigned to the Path Vector
request, and part-resource-id is the "Resource-Id" header value of
the part. The media-type MUST match the "Content-Type" of the part.
The same problem happens inside the part messages as well. The two
parts MUST contain a version tag, which SHOULD contain a unique
Resource ID. This document requires the resource-id in a Version Tag
to have the following format:
pv-resource-id '.' part-resource-id
where pv-resource-id is the resource ID of the Path Vector resource
in the IRD entry, and the part-resource-id has the same value as the
"Resource-Id" header of the part.
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3.3.3. Order of Part Messages
According to RFC 2387 [RFC2387], the Path Vector part, whose media
type is the same as the "type" parameter of the multipart response
message, is the root object. Thus, it is the element the application
processes first. Even though the "start" parameter allows it to be
placed anywhere in the part sequence, it is RECOMMENDED that the
parts arrive in the same order as they are processed, i.e., the Path
Vector part is always put as the first part, followed by the property
map part. It is also RECOMMENDED that when doing so, an ALTO server
SHOULD NOT set the "start" parameter, which implies the first part is
the root object.
4. Basic Data Types
4.1. ANE Name
An ANE Name is encoded as a JSON string, which has the same format as
EntityIdentifer (Section 3.1.3 of [I-D.ietf-alto-unified-props-new])
and the EntityDomainName MUST be "ane", indicating that this entity
belongs to the "ane" Entity Domain.
The type ANEName is used in this document to indicate a string of
this format.
4.2. 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 Map or
Endpoint Cost Service resources. Accordingly, the ANE domain always
depends on a Cost Map or an Endpoint Cost Map.
4.2.1. Entity Domain Type
ane
4.2.2. Domain-Specific Entity Identifier
The entity identifier of ANE domain uses the same encoding as ANEName
(Section 4.1).
4.2.3. Hierarchy and Inheritance
There is no hierarchy or inheritance for properties associated with
ANEs.
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4.3. New Resource-Specific Entity Domain Exports
4.3.1. ANE Domain of Cost Map Resource
If an ALTO Cost Map resource supports the Path Vector cost type, it
can export an "ane" typed entity domain defined by the union of all
sets of ANE names, where each set of ANE names are an "ane-path"
metric cost value in this ALTO Cost Map resource.
4.3.2. ANE Domain of Endpoint Cost Service Resource
If an ALTO Endpoint Cost Service resource supports the Path Vector
cost type, it can export an "ane" typed entity domain defined by the
union of all sets of ANE names, where each set of ANE names are an
"ane-path" metric cost value in this ALTO Endpoint Cost Service
resource.
4.4. ANE Property Name
An ANE Property Name is encoded as an Entity Property Name
(Section 3.2.2 of [I-D.ietf-alto-unified-props-new]) where
* the ResourceID part of an ANE Property Name MUST be empty;
* the EntityPropertyType part MUST be a valid property of an ANE
entity, i.e., the mapping of the ANE domain type and the Entity
Property Type MUST be registered to the ALTO Resource Entity
Property Mapping Registries (Section 11.5 in
[I-D.ietf-alto-unified-props-new]).
4.4.1. ANE Property: Maximum Reservable Bandwidth
The maximum reservable bandwidth property conveys the maximum
bandwidth that can be reserved for all the traffic that traverses an
ANE. The Entity Property Type of the maximum reservable bandwidth is
"maxresbw", and the value MUST be encoded as a non-negative numerical
cost value as defined in Section 6.1.2.1 of [RFC7285] and the unit is
bit per second.
If this property is requested but not present in an ANE, it MUST be
interpreted as that the ANE has sufficiently large bandwidth to be
reserved. If the ANE does not support bandwidth reservation, the
value MUST be present and be set to 0.
The aggregated value of a Path Vector is the minimum value of all the
ANEs in the Path Vector.
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4.4.2. ANE Property: Persistent Entities
The persistent entities property conveys the physical or logical
network entities (e.g., links, in-network caching service) that are
contained by an ANE. It is indicated by the property name
"persistent-entities". The value is encoded as a JSON array of
entity identifiers ([I-D.ietf-alto-unified-props-new]). These entity
identifiers are persistent so that a client CAN further query their
properties for future use.
If this property is requested but is missing for a given ANE, it MUST
be interpreted as that no such entities exist in this ANE.
4.5. Path Vector Cost Type
This document defines a new cost type, which is referred to as the
"Path Vector" cost type. An ALTO server MUST offer this cost type if
it supports the Path Vector extension.
4.5.1. Cost Metric: ane-path
This cost metric conveys an array of ANE names, where each ANE name
uniquely represents an ANE traversed by traffic from a source to a
destination.
4.5.2. Cost Mode: array
This cost mode indicates that every cost value in a Cost Map or an
Endpoint Cost Map MUST be interpreted as a JSON array object.
Note that this cost mode only requires the cost value to be a JSON
array of JSONValue. However, an ALTO server that enables this
extension MUST return a JSON array of ANEName (Section 4.1) when the
cost metric is "ane-path".
4.6. Part Resource ID
A Part Resource ID is encoded as a JSON string with the same format
as that of the Resource ID (Section 10.2 of [RFC7285]).
WARNING: Even though the client-id assigned to a Path Vector request
and the Part Resource ID MAY contain up to 64 characters by their own
definition. Their concatenation (see Section 3.3.2) MUST also
conform to the same length constraint. The same requirement applies
to the resource ID of the Path Vector resource, too. Thus, it is
RECOMMENDED to limit the length of resource ID and client ID related
to a Path Vector resource to 31 characters.
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5. Service Extensions
5.1. Multipart Filtered Cost Map for Path Vector
This document introduces a new ALTO resource called multipart
filtered cost map resource, which allows an ALTO server to provide
other ALTO resources associated to the cost map resource in the same
response.
5.1.1. Media Type
The media type of the multipart filtered cost map resource is
"multipart/related;type=application/alto-costmap+json".
5.1.2. HTTP Method
The multipart filtered cost map is requested using the HTTP POST
method.
5.1.3. Accept Input Parameters
The input parameters of the multipart filtered cost map are supplied
in the body of an HTTP POST request. This document extends the input
parameters to a filtered cost map with a data format indicated by the
media type "application/alto-costmapfilter+json", which is a JSON
object of type PVReqFilteredCostMap, where:
object {
[EntityPropertyName ane-property-names<0..*>;]
} PVReqFilteredCostMap : ReqFilteredCostMap;
with fields:
ane-property-names: A list of properties that are associated with
the ANEs. Each property in this list MUST match one of the
supported ANE properties indicated in the resource's "ane-
property-names" capability. If the field is NOT present, it MUST
be interpreted as an empty list, indicating that the ALTO server
MUST NOT return any property in the unified property part.
5.1.4. Capabilities
The multipart filtered cost map resource extends the capabilities
defined in Section 11.3.2.4 of [RFC7285]. The capabilities are
defined by a JSON object of type PVFilteredCostMapCapabilities:
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object {
[EntityPropertyName ane-property-names<0..*>;]
} PVFilteredCostMapCapabilities : FilteredCostMapCapabilities;
with fields:
cost-type-names: The "cost-type-names" field MUST only include the
Path Vector cost type, unless explicitly documented by a future
extension. This also implies that the Path Vector cost type MUST
be defined in the "cost-types" of the Information Resource
Directory's "meta" field.
cost-constraints: If the "cost-type-names" field includes the Path
Vector cost type, "cost-constraints" field MUST be "false" or not
present unless specifically instructed by a future document.
testable-cost-type-names: If the "cost-type-names" field includes
the Path Vector cost type, the Path Vector cost type MUST NOT be
included in the "testable-cost-type-names" field unless
specifically instructed by a future document.
ane-property-names: Defines a list of ANE properties that can be
returned. If the field is NOT present, it MUST be interpreted as
an empty list, indicating the ALTO server CANNOT provide any ANE
property.
5.1.5. Uses
The resource ID of the network map based on which the PIDs in the
returned cost map will be defined. If this resource supports
"persistent-entities", it MUST also include ALL the resources that
exposes the entities that MAY appear in the response.
5.1.6. Response
The response MUST indicate an error, using ALTO protocol error
handling, as defined in Section 8.5 of [RFC7285], if the request is
invalid.
The "Content-Type" header of the response MUST be "multipart/related"
as defined by [RFC2387] with the following parameters:
type: The type parameter MUST be "application/alto-costmap+json".
Note that [RFC2387] permits both parameters with and without the
double quotes.
start: The start parameter MUST be a quoted string where the quoted
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part has the same value as the "Resource-ID" header in the first
part.
boundary: The boundary parameter is as defined in [RFC2387].
The body of the response consists of two parts.
The first part MUST include "Resource-Id" and "Content-Type" in its
header. The value of "Resource-Id" MUST has the format of a Part
Resource ID. The "Content-Type" MUST be "application/alto-
costmap+json".
The body of the first part MUST be a JSON object with the same format
as defined in Section 11.2.3.6 of [RFC7285]. The JSON object MUST
include the "vtag" field in the "meta" field, which provides the
version tag of the returned cost map. The resource ID of the version
tag MUST follow the format in Section 3.3.2. 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 filtered cost map resource in IRD.
The second part MUST also include "Resource-Id" and "Content-Type" in
its header. The value of "Resource-Id" has the format of a Part
Resource ID. The "Content-Type" MUST be "application/alto-
propmap+json".
The body of the second part MUST be a JSON object with the same
format as defined in Section 4.6 of
[I-D.ietf-alto-unified-props-new]. The JSON object MUST include the
"dependent-vtags" field in the "meta" field. The value of the
"dependent-vtags" field MUST be an array of VersionTag objects as
defined by Section 10.3 of [RFC7285]. The "vtag" of the first part
MUST be included in the "dependent-vtags". If "persistent-entities"
is requested, the version tags of the dependent resources that MAY
expose the entities in the response MUST also be included. The
PropertyMapData has one member for each ANEName that appears in the
first part, where the EntityProps has one member for each property
requested by the client if applicable.
5.2. Multipart Endpoint Cost Service for Path Vector
This document introduces a new ALTO resource called multipart
endpoint cost resource, which allows an ALTO server to provide other
ALTO resources associated to the endpoint cost resource in the same
response.
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5.2.1. Media Type
The media type of the multipart endpoint cost resource is
"multipart/related;type=application/alto-endpointcost+json".
5.2.2. HTTP Method
The multipart endpoint cost resource is requested using the HTTP POST
method.
5.2.3. Accept Input Parameters
The input parameters of the multipart endpoint cost resource are
supplied in the body of an HTTP POST request. This document extends
the input parameters to an endpoint cost map with a data format
indicated by the media type "application/alto-
endpointcostparams+json", which is a JSON object of type
PVEndpointCostParams, where
object {
[EntityPropertyName ane-property-names<0..*>;]
} PVReqEndpointcost : ReqEndpointcost;
with fields:
ane-property-names: This document defines the "ane-property-names"
in PVReqEndpointcost as the same as in PVReqFilteredCostMap. See
Section 5.1.3.
5.2.4. Capabilities
The capabilities of the multipart endpoint cost resource are defined
by a JSON object of type PVEndpointcostCapabilities, which is defined
as the same as PVFilteredCostMapCapabilities. See Section 5.1.4.
5.2.5. Uses
If a multipart endpoint cost resource supports "persistent-entities",
the "uses" field in its IRD entry MUST include ALL the resources
which exposes the entities that MAY appear in the response.
5.2.6. Response
The response MUST indicate an error, using ALTO protocol error
handling, as defined in Section 8.5 of [RFC7285], if the request is
invalid.
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The "Content-Type" header of the response MUST be "multipart/related"
as defined by [RFC7285] with the following parameters:
type: The type parameter MUST be "application/alto-
endpointcost+json".
start: The start parameter MUST be a quoted string where the quoted
part has the same value as the "Resource-ID" header in the first
part.
boundary: The boundary parameter is as defined in [RFC2387].
The body consists of two parts:
The first part MUST include "Resource-Id" and "Content-Type" in its
header. The value of "Resource-Id" MUST has the format of a Part
Resource ID. The "Content-Type" MUST be "application/alto-
endpointcost+json".
The body of the first part MUST be a JSON object with the same format
as defined in Section 11.5.1.6 of [RFC7285]. The JSON object MUST
include the "vtag" field in the "meta" field, which provides the
version tag of the returned endpoint cost map. The resource ID of
the version tag MUST follow the format in Section 3.3.2.
The second part MUST also include "Resource-Id" and "Content-Type" in
its header. The value of "Resource-Id" MUST has the format of a Part
Resource ID. The "Content-Type" MUST be "application/alto-
propmap+json".
The body of the second part MUST be a JSON object with the same
format as defined in Section 4.6 of
[I-D.ietf-alto-unified-props-new]. The JSON object MUST include the
"dependent-vtags" field in the "meta" field. The value of the
"dependent-vtags" field MUST be an array of VersionTag objects as
defined by Section 10.3 of [RFC7285]. The "vtag" of the first part
MUST be included in the "dependent-vtags". If "persistent-entities"
is requested, the version tags of the dependent resources that MAY
expose the entities in the response MUST also be included. The
PropertyMapData has one member for each ANEName that appears in the
first part, where the EntityProps has one member for each property
requested by the client if applicable.
6. Examples
This section lists some examples of path vector queries and the
corresponding responses. Some long lines are truncated for better
readability.
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6.1. Example: Information Resource Directory
Below is an example of an Information Resource Directory which
enables the path vector extension. Some critical modifications
include:
* The "path-vector" cost type (Section 4.5) is defined in the "cost-
types" of the "meta" field.
* The "cost-map-pv" information resource provides a multipart
filtered cost map resource, which exposes the Maximum Reservable
Bandwidth ("maxresbw") property.
* The "http-proxy-props" information resource provides a filtered
unified property map resource, which exposes the HTTP proxy entity
domain (encoded as "http-proxy") and the "price" property. Note
that HTTP proxy is NOT a valid entity domain yet and is used here
only for demonstration.
* The "endpoint-cost-pv" information resource provides a multipart
endpoint cost resource. It exposes the Maximum Reservable
Bandwidth ("maxresbw") property and the Persistent Entity property
("persistent-entities"). The persistent entities MAY come from
the "http-proxy-props" resource.
* The "update-pv" information resource provides the incremental
update ([I-D.ietf-alto-incr-update-sse]) service for the
"endpoint-cost-pv" resource.
{
"meta": {
"cost-types": {
"path-vector": {
"cost-mode": "array",
"cost-metric": "ane-path"
}
}
},
"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",
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"capabilities": {
"cost-type-names": [ "path-vector" ],
"ane-property-names": [ "maxresbw" ]
},
"uses": [ "my-default-networkmap" ]
},
"http-proxy-props": {
"uri": "http://alto.example.com/proxy-props",
"media-type": "application/alto-propmap+json",
"accepts": "application/alto-propmapparams+json",
"capabilities": {
"mappings": {
"http-proxy": [ "price" ]
}
}
},
"endpoint-cost-pv": {
"uri": "http://alto.exmaple.com/endpointcost/pv",
"media-type": "multipart/related;
type=application/alto-endpointcost+json",
"accepts": "application/alto-endpointcostparams+json",
"capabilities": {
"cost-type-names": [ "path-vector" ],
"ane-property-names": [ "maxresbw", "persistent-entities" ]
},
"uses": [ "http-proxy-props" ]
},
"update-pv": {
"uri": "http://alto.example.com/updates/pv",
"media-type": "text/event-stream",
"uses": [ "endpoint-cost-pv" ],
"accepts": "application/alto-updatestreamparams+json",
"capabilities": {
"support-stream-control": true
}
}
}
}
6.2. Example: Multipart Filtered Cost Map
The following examples demonstrate the request to the "cost-map-pv"
resource and the corresponding response.
The request uses the path vector cost type in the "cost-type" field.
The "ane-property-names" field is missing, indicating that the client
only requests for the path vector but not the ANE properties.
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The response consists of two parts. The first part returns the array
of ANEName for each source and destination pair. There are three
ANEs, where "ane:L001" is shared by traffic from "PID1" to both
"PID2" and "PID3".
The second part returns an empty property map. Note that the ANE
entries are omitted since they have no properties (See Section 3.1 of
[I-D.ietf-alto-unified-props-new]).
POST /costmap/pv HTTP/1.1
Host: alto.example.com
Accept: multipart/related;type=application/alto-costmap+json,
application/alto-error+json
Content-Length: [TBD]
Content-Type: application/alto-costmapfilter+json
{
"cost-type": {
"cost-mode": "array",
"cost-metric": "ane-path"
},
"pids": {
"srcs": [ "PID1" ],
"dsts": [ "PID2", "PID3" ]
}
}
HTTP/1.1 200 OK
Content-Length: [TBD]
Content-Type: multipart/related; boundary=example-1;
type=application/alto-costmap+json
--example-1
Resource-Id: 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"
}
],
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"cost-type": {
"cost-mode": "array",
"cost-metric": "ane-path"
}
},
"cost-map": {
"PID1": {
"PID2": [ "ane:L001", "ane:L003" ],
"PID3": [ "ane:L001", "ane:L004" ]
}
}
}
--example-1
Resource-Id: propmap
Content-Type: application/alto-propmap+json
{
"meta": {
"dependent-vtags": [
{
"resource-id": "cost-map-pv.costmap",
"tag": "d827f484cb66ce6df6b5077cb8562b0a"
}
]
},
"property-map": {
}
}
6.3. Example: Multipart Endpoint Cost Resource
The following examples demonstrate the request to the "endpoint-cost-
pv" resource and the corresponding response.
The request uses the path vector cost type in the "cost-type" field,
and queries the Maximum Reservable Bandwidth ANE property and the
Persistent Entity property.
The response consists of two parts. The first part returns the array
of ANEName for each valid source and destination pair.
The second part returns the requested properties of ANEs in the first
part. The "ane:NET001" element contains an HTTP proxy entity, which
can be further used by the client. Since it does not contain a
"maxresbw" property, the client SHOULD assume it does NOT support
bandwidth reservation but will NOT become a traffic bottleneck, as
specified in Section 4.4.1.
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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": "array",
"cost-metric": "ane-path"
},
"endpoints": {
"srcs": [ "ipv4:192.0.2.2" ],
"dsts": [ "ipv4:192.0.2.89",
"ipv4:203.0.113.45",
"ipv6:2001:db8::10" ]
},
"ane-property-names": [ "maxresbw", "persistent-entities" ]
}
HTTP/1.1 200 OK
Content-Length: [TBD]
Content-Type: multipart/related; boundary=example-2;
type=application/alto-endpointcost+json
--example-2
Resource-Id: ecs
Content-Type: application/alto-endpointcost+json
{
"meta": {
"vtags": {
"resource-id": "endpoint-cost-pv.ecs",
"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:NET001", "ane:L002" ],
"ipv4:203.0.113.45": [ "ane:NET001", "ane:L003" ]
}
}
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}
--example-2
Resource-Id: propmap
Content-Type: application/alto-propmap+json
{
"meta": {
"dependent-vtags": [
{
"resource-id": "endpoint-cost-pv.ecs",
"tag": "bb6bb72eafe8f9bdc4f335c7ed3b10822a391cef"
},
{
"resource-id": "http-proxy-props",
"tag": "bf3c8c1819d2421c9a95a9d02af557a3"
}
]
},
"property-map": {
"ane:NET001": {
"persistent-entities": [ "http-proxy:192.0.2.1" ]
},
"ane:L002": { "maxresbw": 48000000 },
"ane:L003": { "maxresbw": 35000000 }
}
}
6.4. Example: Incremental Updates
In this example, an ALTO client subscribes to 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-side process defined in
[I-D.ietf-alto-incr-update-sse], the ALTO server will send the
"control-uri" first using Server-Sent Event (SSE), followed by the
full response of the multipart message.
HTTP/1.1 200 OK
Connection: keep-alive
Content-Type: text/event-stream
event: application/alto-updatestreamcontrol+json
data: {"control-uri": "http://alto.example.com/updates/streams/1414"}
event: multipart/related;boundary=example-3;
type=application/alto-endpointcost+json,ecspvsub1
data: --example-3
data: Resource-ID: ecsmap
data: Content-Type: application/alto-endpointcost+json
data:
data: <endpoint-cost-map-entry>
data: --example-3
data: Resource-ID: propmap
data: Content-Type: application/alto-propmap+json
data:
data: <property-map-entry>
data: --example-3--
When the contents change, the ALTO server will publish the updates
for each node in this tree separately.
event: application/merge-patch+json, ecspvsub1.ecsmap
data: <Merge patch for endpoint-cost-map-update>
event: application/merge-patch+json, ecspvsub1.propmap
data: <Merge patch for property-map-update>
7. Compatibility
7.1. Compatibility with Legacy ALTO Clients/Servers
The multipart filtered cost map resource and the multipart endpoint
cost resource has no backward compatibility issue with legacy ALTO
clients and servers. Although these two types of resources reuse the
media types defined in the base ALTO protocol for the accept input
parameters, they have different media types for responses. If the
ALTO server provides these two types of resources, but the ALTO
client does not support them, the ALTO client will ignore the
resources without conducting any incompatibility.
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7.2. 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.
7.3. Compatibility with Incremental Update
The extension specified in this document is NOT compatible with the
original incremental update extension
[I-D.ietf-alto-incr-update-sse]. A legacy ALTO client CANNOT
recognize the compound client-id, and a legacy ALTO server MAY use
the same client-id for updates of both parts.
ALTO clients and servers MUST follow the specifications given in this
document to ensure compatibility with the incremental update
extension.
7.4. Compatibility with Cost Calendar
The extension specified in this document is compatible with the Cost
Calendar extension [I-D.ietf-alto-cost-calendar]. When used together
with the Cost Calendar extension, the cost value between a source and
a destination is an array of path vectors, where the k-th path vector
refers to the abstract network paths traversed in the k-th time
interval by traffic from the source to the destination.
When used with time-varying properties, e.g., maximum reservable
bandwidth (maxresbw), a property of a single entity may also have
different values in different time intervals. In this case, an ANE
with different property values MUST be considered as different ANEs.
The two extensions combined together CAN provide the historical
network correlation information for a set of source and destination
pairs. A network broker or client MAY use this information to derive
other resource requirements such as Time-Block-Maximum Bandwidth,
Bandwidth-Sliding-Window, and Time-Bandwidth-Product (TBP) (See
[SENSE] for details.)
8. General Discussions
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8.1. 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.
8.2. 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.
9. 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 fine-grained internal
network structures than the base protocol, 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 guarantee 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.
10. IANA Considerations
10.1. 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.
10.2. ALTO Entity Domain Registry
This document registers a new entry to the ALTO Domain Entity
Registry, as instructed by Section 9.2 of
[I-D.ietf-alto-unified-props-new]. See below in Table 1.
+------------+-------------------------+-------------------------+
| Identifier | Entity Address Encoding | Hierarchy & Inheritance |
+============+=========================+=========================+
| ane | See Section 4.2.2 | None |
+------------+-------------------------+-------------------------+
Table 1: ALTO Entity Domain
10.3. ALTO Entity Property Type Registry
Two initial entries are registered to the ALTO Domain "ane" in the
"ALTO Entity Property Type Registry". See below in Table 2.
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+-------------------------+--------------------+
| Identifier | Intended Semantics |
+=========================+====================+
| ane:maxresbw | See Section 4.4.1 |
+-------------------------+--------------------+
| ane:persistent-entities | See Section 4.4.2 |
+-------------------------+--------------------+
Table 2: Initial Entries for ane Domain in
the ALTO Entity Property Types Registry
10.4. ALTO Resource Entity Domain Export Registries
10.4.1. costmap
+--------------------+-------------------+
| Entity Domain Type | Export Function |
+====================+===================+
| ane | See Section 4.3.1 |
+--------------------+-------------------+
Table 3: ALTO Cost Map Entity Domain
Export
10.4.2. endpointcost
+--------------------+-------------------+
| Entity Domain Type | Export Function |
+====================+===================+
| ane | See Section 4.3.2 |
+--------------------+-------------------+
Table 4: ALTO Endpoint Cost Entity
Domain Export
11. Acknowledgments
The authors would like to thank discussions with Andreas Voellmy,
Erran Li, Haibin Song, 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.
12. References
12.1. Normative References
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[I-D.ietf-alto-cost-calendar]
Randriamasy, S., Yang, Y., WU, Q., Lingli, D., and N.
Schwan, "Application-Layer Traffic Optimization (ALTO)
Cost Calendar", Work in Progress, Internet-Draft, draft-
ietf-alto-cost-calendar-19, 2 March 2020,
<http://www.ietf.org/internet-drafts/draft-ietf-alto-cost-
calendar-19.txt>.
[I-D.ietf-alto-incr-update-sse]
Roome, W. and Y. Yang, "ALTO Incremental Updates Using
Server-Sent Events (SSE)", Work in Progress, Internet-
Draft, draft-ietf-alto-incr-update-sse-20, 20 February
2020, <http://www.ietf.org/internet-drafts/draft-ietf-
alto-incr-update-sse-20.txt>.
[I-D.ietf-alto-performance-metrics]
WU, Q., Yang, Y., Lee, Y., Dhody, D., and S. Randriamasy,
"ALTO Performance Cost Metrics", Work in Progress,
Internet-Draft, draft-ietf-alto-performance-metrics-08, 4
November 2019, <http://www.ietf.org/internet-drafts/draft-
ietf-alto-performance-metrics-08.txt>.
[I-D.ietf-alto-unified-props-new]
Roome, W., Randriamasy, S., Yang, Y., Zhang, J., and K.
Gao, "Unified Properties for the ALTO Protocol", Work in
Progress, Internet-Draft, draft-ietf-alto-unified-props-
new-10, 4 November 2019, <http://www.ietf.org/internet-
drafts/draft-ietf-alto-unified-props-new-10.txt>.
[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>.
12.2. Informative References
[AAAI2019] Xiang, Q., Yu, H., Aspnes, J., Le, F., Kong, L., and Y.R.
Yang, "Optimizing in the dark: Learning an optimal
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solution through a simple request interface", Proceedings
of the AAAI Conference on Artificial Intelligence 33,
1674-1681 , 2019.
[I-D.bernstein-alto-topo]
Bernstein, G., Yang, Y., and Y. Lee, "ALTO Topology
Service: Uses Cases, Requirements, and Framework", Work in
Progress, Internet-Draft, draft-bernstein-alto-topo-00, 21
October 2013, <http://www.ietf.org/internet-drafts/draft-
bernstein-alto-topo-00.txt>.
[I-D.contreras-alto-service-edge]
Contreras, L., Perez, D., and C. Rothenberg, "Use of ALTO
for Determining Service Edge", Work in Progress, Internet-
Draft, draft-contreras-alto-service-edge-00, 4 November
2019, <http://www.ietf.org/internet-drafts/draft-
contreras-alto-service-edge-00.txt>.
[I-D.huang-alto-mowie-for-network-aware-app]
"TBD", 2020.
[I-D.ietf-dmm-5g-uplane-analysis]
Homma, S., Miyasaka, T., Matsushima, S., and D. Voyer,
"User Plane Protocol and Architectural Analysis on 3GPP 5G
System", Work in Progress, Internet-Draft, draft-ietf-dmm-
5g-uplane-analysis-03, 3 November 2019,
<http://www.ietf.org/internet-drafts/draft-ietf-dmm-5g-
uplane-analysis-03.txt>.
[I-D.yang-alto-deliver-functions-over-networks]
Yang, S., Cui, L., Xu, M., Shen, H., and L. Chen,
"Delivering Functions over Networks: Traffic and
Performance Optimization for Edge Computing using ALTO",
Work in Progress, Internet-Draft, draft-yang-alto-deliver-
functions-over-networks-00, 29 November 2019,
<http://www.ietf.org/internet-drafts/draft-yang-alto-
deliver-functions-over-networks-00.txt>.
[LHC] "CERN - LHC", 2019, <https://atlas.cern/tags/lhc>.
[SENSE] "Services - SENSE", 2019, <http://sense.es.net/services>.
[TON2019] Gao, K., Xiang, Q., Wang, X., Yang, Y.R., and J. Bi, "An
objective-driven on-demand network abstraction for
adaptive applications", IEEE/ACM Transactions on
Networking (TON) Vol 27, no. 2 (2019): 805-818., 2019.
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Appendix A. Changes since -08
This revision
* fixes a few spelling errors
* emphasizes that abstract network elements can be generated on
demand in both introduction and motivating use cases
Appendix B. Changes Since Version -06
* We emphasize the importance of the path vector extension in two
aspects:
1. It expands the problem space that can be solved by ALTO, from
preferences of network paths to correlations of network paths.
2. It is motivated by new usage scenarios from both application's
and network's perspectives.
* More use cases are included, in addition to the original capacity
region use case.
* We add more discussions to fully explore the design space of the
path vector extension and justify our design decisions, including
the concept of abstract network element, cost type (reverted to
-05), newer capabilities and the multipart message.
* Fix the incremental update process to be compatible with SSE -16
draft, which uses client-id instead of resource-id to demultiplex
updates.
* Register an additional ANE property (i.e., persistent-entities) to
cover all use cases mentioned in the draft.
Authors' Addresses
Kai Gao
China
610000
Chengdu
No.24 South Section 1, Yihuan Road
Sichuan University
Email: kaigao@scu.edu.cn
Young Lee
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Sabine Randriamasy
Nokia Bell Labs
Route de Villejust
91460 Nozay
France
Email: sabine.randriamasy@nokia-bell-labs.com
Yang Richard Yang
Yale University
51 Prospect Street
New Haven, CT
United States of America
Email: yry@cs.yale.edu
Jingxuan Jensen Zhang
China
201804
Shanghai
4800 Caoan Road
Tongji University
Email: jingxuan.n.zhang@gmail.com
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