rfc9275
Internet Engineering Task Force (IETF) K. Gao
Request for Comments: 9275 Sichuan University
Category: Experimental Y. Lee
ISSN: 2070-1721 Samsung
S. Randriamasy
Nokia Bell Labs
Y. Yang
Yale University
J. Zhang
Tongji University
September 2022
An Extension for Application-Layer Traffic Optimization (ALTO):
Path Vector
Abstract
This document is an extension to the base Application-Layer Traffic
Optimization (ALTO) protocol. It extends the ALTO cost map and ALTO
property map services so that an application can decide to which
endpoint(s) to connect based not only on numerical/ordinal cost
values but also on fine-grained abstract information regarding the
paths. This is useful for applications whose performance is impacted
by specific components of a network on the end-to-end paths, e.g.,
they may infer that several paths share common links and prevent
traffic bottlenecks by avoiding such paths. This extension
introduces a new abstraction called the "Abstract Network Element"
(ANE) to represent these components and encodes a network path as a
vector of ANEs. Thus, it provides a more complete but still abstract
graph representation of the underlying network(s) for informed
traffic optimization among endpoints.
Status of This Memo
This document is not an Internet Standards Track specification; it is
published for examination, experimental implementation, and
evaluation.
This document defines an Experimental Protocol for the Internet
community. This document is a product of the Internet Engineering
Task Force (IETF). It represents the consensus of the IETF
community. It has received public review and has been approved for
publication by the Internet Engineering Steering Group (IESG). Not
all documents approved by the IESG are candidates for any level of
Internet Standard; see Section 2 of RFC 7841.
Information about the current status of this document, any errata,
and how to provide feedback on it may be obtained at
https://www.rfc-editor.org/info/rfc9275.
Copyright Notice
Copyright (c) 2022 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
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include Revised BSD License text as described in Section 4.e of the
Trust Legal Provisions and are provided without warranty as described
in the Revised BSD License.
Table of Contents
1. Introduction
2. Requirements Language
3. Terminology
4. Requirements and Use Cases
4.1. Design Requirements
4.2. Sample Use Cases
4.2.1. Exposing Network Bottlenecks
4.2.2. Resource Exposure for CDNs and Service Edges
5. Path Vector Extension: Overview
5.1. Abstract Network Element (ANE)
5.1.1. ANE Entity Domain
5.1.2. Ephemeral and Persistent ANEs
5.1.3. Property Filtering
5.2. Path Vector Cost Type
5.3. Multipart Path Vector Response
5.3.1. Identifying the Media Type of the Object Root
5.3.2. References to Part Messages
6. Specification: Basic Data Types
6.1. ANE Name
6.2. ANE Entity Domain
6.2.1. Entity Domain Type
6.2.2. Domain-Specific Entity Identifier
6.2.3. Hierarchy and Inheritance
6.2.4. Media Type of Defining Resource
6.3. ANE Property Name
6.4. Initial ANE Property Types
6.4.1. Maximum Reservable Bandwidth
6.4.2. Persistent Entity ID
6.4.3. Examples
6.5. Path Vector Cost Type
6.5.1. Cost Metric: "ane-path"
6.5.2. Cost Mode: "array"
6.6. Part Resource ID and Part Content ID
7. Specification: Service Extensions
7.1. Notation
7.2. Multipart Filtered Cost Map for Path Vector
7.2.1. Media Type
7.2.2. HTTP Method
7.2.3. Accept Input Parameters
7.2.4. Capabilities
7.2.5. Uses
7.2.6. Response
7.3. Multipart Endpoint Cost Service for Path Vector
7.3.1. Media Type
7.3.2. HTTP Method
7.3.3. Accept Input Parameters
7.3.4. Capabilities
7.3.5. Uses
7.3.6. Response
8. Examples
8.1. Sample Setup
8.2. Information Resource Directory
8.3. Multipart Filtered Cost Map
8.4. Multipart Endpoint Cost Service Resource
8.5. Incremental Updates
8.6. Multi-Cost
9. Compatibility with Other ALTO Extensions
9.1. Compatibility with Legacy ALTO Clients/Servers
9.2. Compatibility with Multi-Cost Extension
9.3. Compatibility with Incremental Update Extension
9.4. Compatibility with Cost Calendar Extension
10. General Discussion
10.1. Constraint Tests for General Cost Types
10.2. General Multi-Resource Query
11. Security Considerations
12. IANA Considerations
12.1. "ALTO Cost Metrics" Registry
12.2. "ALTO Cost Modes" Registry
12.3. "ALTO Entity Domain Types" Registry
12.4. "ALTO Entity Property Types" Registry
12.4.1. New ANE Property Type: Maximum Reservable Bandwidth
12.4.2. New ANE Property Type: Persistent Entity ID
13. References
13.1. Normative References
13.2. Informative References
Acknowledgments
Authors' Addresses
1. Introduction
Network performance metrics are crucial for assessing the Quality of
Experience (QoE) of applications. The Application-Layer Traffic
Optimization (ALTO) protocol allows Internet Service Providers (ISPs)
to provide guidance, such as topological distances between different
end hosts, to overlay applications. Thus, the overlay applications
can potentially improve the perceived QoE by better orchestrating
their traffic to utilize the resources in the underlying network
infrastructure.
The existing ALTO cost map (Section 11.2.3 of [RFC7285]) and Endpoint
Cost Service (Section 11.5 of [RFC7285]) provide only cost
information for an end-to-end path defined by its <source,
destination> endpoints: the base protocol [RFC7285] allows the
services to expose the topological distances of end-to-end paths,
while various extensions have been proposed to extend the capability
of these services, e.g., to express other performance metrics
[ALTO-PERF-METRICS], to query multiple costs simultaneously
[RFC8189], and to obtain time-varying values [RFC8896].
While numerical/ordinal cost values for end-to-end paths provided by
the existing extensions are sufficient to optimize the QoE of many
overlay applications, the QoE of some overlay applications also
depends on the properties of particular components on the paths. For
example, job completion time, which is an important QoE metric for a
large-scale data analytics application, is impacted by shared
bottleneck links inside the carrier network, as link capacity may
impact the rate of data input/output to the job. We refer to such
components of a network as Abstract Network Elements (ANEs).
Predicting such information can be very complex without the help of
ISPs; for example, [BOXOPT] has shown that finding the optimal
bandwidth reservation for multiple flows can be NP-hard without
further information than whether a reservation succeeds. With proper
guidance from the ISP, an overlay application may be able to schedule
its traffic for better QoE. In the meantime, it may be helpful as
well for ISPs if applications could avoid using bottlenecks or
challenging the network with poorly scheduled traffic.
Despite the claimed benefits, ISPs are not likely to expose raw
details on their network paths: first because ISPs have requirements
to hide their network topologies, second because these details may
increase volume and computation overhead, and last because
applications do not necessarily need all the network path details and
are likely not able to understand them.
Therefore, it is beneficial for both ISPs and applications if an ALTO
server provides ALTO clients with an "abstract network state" that
provides the necessary information to applications, while hiding
network complexity and confidential information. An "abstract
network state" is a selected set of abstract representations of ANEs
traversed by the paths between <source, destination> pairs combined
with properties of these ANEs 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 ANEs.
Server scalability can also be improved by combining ANEs and their
properties in a single response.
This document extends the ALTO base protocol [RFC7285] to allow an
ALTO server to convey "abstract network state" for paths defined by
their <source, destination> pairs. To this end, it introduces a new
cost type called a "Path Vector", following the cost metric
registration specified in [RFC7285] and the updated cost mode
registration specified in [RFC9274]. A Path Vector is an array of
identifiers that identifies an ANE, which can be associated with
various properties. The associations between ANEs and their
properties are encoded in an ALTO information resource called the
"entity property map", which is specified in [RFC9240].
For better confidentiality, this document aims to minimize
information exposure of an ALTO server when providing Path Vector
services. In particular, this document enables the capability, and
also recommends that 1) ANEs be constructed on demand and 2) an ANE
only be associated with properties that are requested by an ALTO
client. A Path Vector response involves two ALTO maps: the cost map,
which contains the Path Vector results; and the up-to-date entity
property map, which contains the properties requested for these ANEs.
To enforce consistency and improve server scalability, this document
uses the "multipart/related" content type as defined in [RFC2387] to
return the two maps in a single response.
As a single ISP may not have knowledge of the full Internet paths
between arbitrary endpoints, this document is mainly applicable when
* there is a single ISP between the requested source and destination
Provider-defined Identifiers (PIDs) or endpoints -- for example,
ISP-hosted Content Delivery Network (CDN) / edge, tenant
interconnection in a single public cloud platform, etc., or
* the Path Vectors are generated from end-to-end measurement data.
2. Requirements Language
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
"OPTIONAL" in this document are to be interpreted as described in
BCP 14 [RFC2119] [RFC8174] when, and only when, they appear in all
capitals, as shown here.
3. Terminology
This document extends the ALTO base protocol [RFC7285] and the entity
property map extension [RFC9240]. In addition to the terms defined
in those documents, this document also uses the following terms:
Abstract Network Element (ANE): An abstract representation for a
component in a network that handles data packets and whose
properties can potentially have an impact on the end-to-end
performance of traffic. An ANE can be a physical device such as a
router, a link, or an interface; or an aggregation of devices such
as a subnetwork or a data center.
The definition of an ANE is similar to that for a network element
as defined in [RFC2216] in the sense that they both provide an
abstract representation of specific components of a network.
However, they have different criteria on how these particular
components are selected. Specifically, a network element requires
the components to be capable of exercising QoS control, while an
ANE only requires the components to have an impact on end-to-end
performance.
ANE name: A string that uniquely identifies an ANE in a specific
scope. An ANE can be constructed either statically in advance or
on demand based on the requested information. Thus, different
ANEs may only be valid within a particular scope, either ephemeral
or persistent. Within each scope, an ANE is uniquely identified
by an ANE name, as defined in Section 6.1. Note that an ALTO
client must not assume ANEs in different scopes but with the same
ANE name refer to the same component(s) of the network.
Path Vector (or ANE Path Vector): Refers to a JSON array of ANE
names. It is a generalization of a BGP path vector. While a
standard BGP path vector (Section 5.1.2 of [RFC4271]) specifies a
sequence of Autonomous Systems (ASes) for a destination IP prefix,
the Path Vector defined in this extension specifies a sequence of
ANEs for either 1) a source PID and a destination PID, as in the
CostMapData object (Section 11.2.3.6 of [RFC7285]) or 2) a source
endpoint and a destination endpoint, as in the EndpointCostMapData
object (Section 11.5.1.6 of [RFC7285]).
Path Vector resource: An ALTO information resource (Section 8.1 of
[RFC7285]) that supports the extension defined in this document.
Path Vector cost type: A special cost type, which is specified in
Section 6.5. When this cost type is present in an Information
Resource Directory (IRD) entry, it indicates that the information
resource is a Path Vector resource. When this cost type is
present in a filtered cost map request or an Endpoint Cost Service
request, it indicates that each cost value must be interpreted as
a Path Vector.
Path Vector request: The POST message sent to an ALTO Path Vector
resource.
Path Vector response: Refers to the multipart/related message
returned by a Path Vector resource.
4. Requirements and Use Cases
4.1. Design Requirements
This section gives an illustrative example of how an overlay
application can benefit from the extension defined in this document.
Assume that an application has control over a set of flows, which may
go through shared links/nodes and share bottlenecks. The application
seeks to schedule the traffic among multiple flows to get better
performance. The constraints of feasible rate allocations of those
flows will benefit the scheduling. However, cost maps as defined in
[RFC7285] cannot reveal such information.
Specifically, consider the example network shown in Figure 1. The
network has seven switches ("sw1" to "sw7") forming a dumbbell
topology. Switches "sw1", "sw2", "sw3", and "sw4" are access
switches, and "sw5-sw7" form the backbone. End hosts "eh1" to "eh4"
are connected to access switches "sw1" to "sw4", respectively.
Assume that the bandwidth of link "eh1 -> sw1" and link "sw1 -> sw5"
is 150 Mbps and the bandwidth of the other links is 100 Mbps.
+-----+
| |
--+ sw6 +--
/ | | \
PID1 +-----+ / +-----+ \ +-----+ PID2
eh1__| |_ / \ ____| |__eh2
192.0.2.2 | sw1 | \ +--|--+ +--|--+ / | sw2 | 192.0.2.3
+-----+ \ | | | |/ +-----+
\_| sw5 +---------+ sw7 |
PID3 +-----+ / | | | |\ +-----+ PID4
eh3__| |__/ +-----+ +-----+ \____| |__eh4
192.0.2.4 | sw3 | | sw4 | 192.0.2.5
+-----+ +-----+
bw(eh1--sw1) = bw(sw1--sw5) = 150 Mbps
bw(eh2--sw2) = bw(eh3--sw3) = bw(eh4--sw4) = 100 Mbps
bw(sw1--sw5) = bw(sw3--sw5) = bw(sw2--sw7) = bw(sw4--sw7) = 100 Mbps
bw(sw5--sw6) = bw(sw5--sw7) = bw(sw6--sw7) = 100 Mbps
Figure 1: Raw Network Topology
The base ALTO topology abstraction of the network is shown in
Figure 2. Assume that the cost map returns a hypothetical cost type
representing the available bandwidth between a source and a
destination.
+----------------------+
{eh1} | | {eh2}
PID1 | | PID2
+------+ +------+
| |
| |
{eh3} | | {eh4}
PID3 | | PID4
+------+ +------+
| |
+----------------------+
Figure 2: Base Topology Abstraction
Now, assume that the application wants to maximize the total rate of
the traffic among a set of <source, destination> pairs -- say, "eh1
-> eh2" and "eh1 -> eh4". Let "x" denote the transmission rate of
"eh1 -> eh2" and "y" denote the rate of "eh1 -> eh4". The objective
function is
max(x + y).
With the ALTO cost map, the costs between PID1 and PID2 and between
PID1 and PID4 will both be 100 Mbps. The client can get a capacity
region of
x <= 100 Mbps
y <= 100 Mbps.
With this information, the client may mistakenly think it can achieve
a maximum total rate of 200 Mbps. However, this rate is infeasible,
as there are only two potential cases:
Case 1: "eh1 -> eh2" and "eh1 -> eh4" take different path segments
from "sw5" to "sw7". For example, if "eh1 -> eh2" uses path "eh1
-> sw1 -> sw5 -> sw6 -> sw7 -> sw2 -> eh2" and "eh1 -> eh4" uses
path "eh1 -> sw1 -> sw5 -> sw7 -> sw4 -> eh4", then the shared
bottleneck links are "eh1 -> sw1" and "sw1 -> sw5". In this case,
the capacity region is:
x <= 100 Mbps
y <= 100 Mbps
x + y <= 150 Mbps
and the real optimal total rate is 150 Mbps.
Case 2: "eh1 -> eh2" and "eh1 -> eh4" take the same path segment
from "sw5" to "sw7". For example, if "eh1 -> eh2" uses path "eh1
-> sw1 -> sw5 -> sw7 -> sw2 -> eh2" and "eh1 -> eh4" also uses
path "eh1 -> sw1 -> sw5 -> sw7 -> sw4 -> eh4", then the shared
bottleneck link is "sw5 -> sw7". In this case, the capacity
region is:
x <= 100 Mbps
y <= 100 Mbps
x + y <= 100 Mbps
and the real optimal total rate is 100 Mbps.
Clearly, with more accurate and fine-grained information, the
application can better predict its traffic and may orchestrate its
resources accordingly. However, to provide such information, the
network needs to expose abstract information beyond the simple cost
map abstraction. In particular:
* The ALTO server must expose abstract information about the network
paths that are traversed by the traffic between a source and a
destination beyond a simple numerical value, which allows the
overlay application to distinguish between Cases 1 and 2 and to
compute the optimal total rate accordingly.
* The ALTO server must allow the client to distinguish the common
ANE shared by "eh1 -> eh2" and "eh1 -> eh4", e.g., "eh1--sw1" and
"sw1--sw5" in Case 1.
* The ALTO server must expose abstract information on the properties
of the ANEs used by "eh1 -> eh2" and "eh1 -> eh4". For example,
an ALTO server can either expose the available bandwidth between
"eh1--sw1", "sw1--sw5", "sw5--sw7", "sw5--sw6", "sw6--sw7",
"sw7--sw2", "sw7--sw4", "sw2--eh2", "sw4--eh4" in Case 1 or expose
three abstract elements "A", "B", and "C", which represent the
linear constraints that define the same capacity region in Case 1.
In general, we can conclude that to support the use case for multiple
flow scheduling, the ALTO framework must be extended to satisfy the
following additional requirements (ARs):
AR1: An ALTO server must provide the ANEs that are important for
assessing the QoE of the overlay application on the path of a
<source, destination> pair.
AR2: An ALTO server must provide information to identify how ANEs
are shared on the paths of different <source, destination> pairs.
AR3: An ALTO server must provide information on the properties that
are important for assessing the QoE of the application for ANEs.
The extension defined in this document specifies a solution to expose
such abstract information.
4.2. Sample Use Cases
While the problem related to multiple flow scheduling is used to help
identify the additional requirements, the extension defined in this
document can be applied to a wide range of applications. This
section highlights some of the reported use cases.
4.2.1. Exposing Network Bottlenecks
One important use case for the Path Vector extension is to expose
network bottlenecks. Applications that need to perform large-scale
data transfers can benefit from being aware of the resource
constraints exposed by this extension even if they have different
objectives. One such example is the Worldwide LHC Computing Grid
(WLCG) (where "LHC" means "Large Hadron Collider"), which is the
largest example of a distributed computation collaboration in the
research and education world.
Figure 3 illustrates an example of using an ALTO Path Vector as an
interface between the job optimizer for a data analytics system and
the network manager. In particular, we assume that the objective of
the job optimizer is to minimize the job completion time.
In such a setting, the network-aware job optimizer (e.g., [CLARINET])
takes a query and generates multiple query execution plans (QEPs).
It can encode the QEPs as Path Vector requests that are sent to an
ALTO server. The ALTO server obtains the routing information for the
flows in a QEP and finds links, routers, or middleboxes (e.g., a
stateful firewall) that can potentially become bottlenecks for the
QEP (e.g., see [NOVA] and [G2] for mechanisms to identify bottleneck
links under different settings). The resource constraint information
is encoded in a Path Vector response and returned to the ALTO client.
With the network resource constraints, the job optimizer may choose
the QEP with the optimal job completion time to be executed. It must
be noted that the ALTO framework itself does not offer the capability
to control the traffic. However, certain network managers may offer
ways to enforce resource guarantees, such as on-demand tunnels (e.g.,
[SWAN]), demand vectors (e.g., [HUG], [UNICORN]), etc. The traffic
control interfaces and mechanisms are out of scope for this document.
Data schema Queries
| |
\ /
+-------------+ +-----------------+
| ALTO Client | <===============> | Job Optimizer |
+-------------+ +-----------------+
PV | ^ PV |
Request | | Response |
| | On-demand resource |
(Potential | | (Network allocation, demand |
Data | | Resource vectors, etc. |
Transfers) | | Constraints) (Non-ALTO interfaces)|
v | v
+-------------+ +-----------------+
| ALTO Server | <===============> | Network Manager |
+-------------+ +-----------------+
/ | \
| | |
WAN DC1 DC2
Figure 3: Example Use Case for Data Analytics
Another example is illustrated in Figure 4. Consider a network
consisting of multiple sites and a non-blocking core network, i.e.,
the links in the core network have sufficient bandwidth that they
will not become a bottleneck for the data transfers.
Ongoing transfers New transfer requests
\----\ |
| |
v v
+-------------+ +---------------+
| ALTO Client | <===========> | Data Transfer |
+-------------+ | Scheduler |
^ | ^ | PV Request +---------------+
| | | \--------------\
| | \--------------\ |
| v PV Response | v
+-------------+ +-------------+
| ALTO Server | | ALTO Server |
+-------------+ +-------------+
|| ||
+---------+ +---------+
| Network | | Network |
| Manager | | Manager |
+---------+ +---------+
. .
. _~_ __ . . .
. ( )( ) .___
~v~v~ /--( )------------( )
( )-----/ ( ) ( )
~w~w~ ~^~^~^~ ~v~v~
Site 1 Non-blocking Core Site 2
Figure 4: Example Use Case for Cross-Site Bottleneck Discovery
With the Path Vector extension, a site can reveal the bottlenecks
inside its own network with necessary information (such as link
capacities) to the ALTO client, instead of providing the full
topology and routing information, or no bottleneck information at
all. The bottleneck information can be used to analyze the impact of
adding/removing data transfer flows, e.g., using the framework
defined in [G2]. For example, assume that hosts "a", "b", and "c"
are in Site 1 and hosts "d", "e", and "f" are in Site 2, and there
are three flows in two sites: "a -> b", "c -> d", and "e -> f"
(Figure 5).
Site 1:
[c]
.
........................................> [d]
+---+ 10 Gbps +---+ 10 Gbps +----+ 50 Gbps
| A |---------| B |---------| GW |--------- Core
+---+ +---+ +----+
...................
. .
. v
[a] [b]
Site 2:
[d] <........................................ [c]
+---+ 5 Gbps +---+ 10 Gbps +----+ 20 Gbps
| X |--------| Y |---------| GW |--------- Core
+---+ +---+ +----+
....................
. .
. v
[e] [f]
Figure 5: Example: Three Flows in Two Sites
For these flows, Site 1 returns:
a: { b: [ane1] },
c: { d: [ane1, ane2, ane3] }
ane1: bw = 10 Gbps (link: A->B)
ane2: bw = 10 Gbps (link: B->GW)
ane3: bw = 50 Gbps (link: GW->Core)
and Site 2 returns:
c: { d: [anei, aneii, aneiii] }
e: { f: [aneiv] }
anei: bw = 5 Gbps (link Y->X)
aneii: bw = 10 Gbps (link GW->Y)
aneiii: bw = 20 Gbps (link Core->GW)
aneiv: bw = 10 Gbps (link Y->GW)
With this information, the data transfer scheduler can use algorithms
such as the theory on bottleneck structure [G2] to predict the
potential throughput of the flows.
4.2.2. Resource Exposure for CDNs and Service Edges
At the time of this writing, a growing trend in today's applications
is to bring storage and computation closer to the end users for
better QoE, such as CDNs, augmented reality / virtual reality, and
cloud gaming, as reported in various documents (e.g., [SEREDGE] and
[MOWIE]). ISPs may deploy multiple layers of CDN caches or, more
generally, service edges, with different latencies and available
resources, including the number of CPU cores, memory, and storage.
For example, Figure 6 illustrates a typical edge-cloud scenario where
memory is measured in gigabytes (GB) and storage is measured in
terabytes (TB). The "on-premise" edge nodes are closest to the end
hosts and have the lowest latency, and the site-radio edge node and
access central office (CO) have higher latencies but more available
resources.
+-------------+ +----------------------+
| ALTO Client | <==========> | Application Provider |
+-------------+ +----------------------+
PV | ^ PV |
Request | | Response | Resource allocation,
| | | service establishment,
(End hosts | | (Edge nodes | etc.
and cloud | | and metrics) |
servers) | | |
v | v
+-------------+ +---------------------+
| ALTO Server | <=========> | Cloud-Edge Provider |
+-------------+ +---------------------+
____________________________________/\___________
/ \
| (((o |
|
/_\ _~_ __ __
a (/\_/\) ( ) ( )~( )_
\ /------( )---------( )----\\---( )
_|_ / (______) (___) ( )
|_| -/ Site-radio Access CO (__________)
/---\ Edge Node 1 | Cloud DC
On premise |
/---------/
(((o /
| /
Site-radio /_\ /
Edge Node 2(/\_/\)-----/
/(_____)\
___ / \ ---
b--|_| -/ \--|_|--c
/---\ /---\
On premise On premise
Figure 6: Example Use Case for Service Edge Exposure
With the extension defined in this document, an ALTO server can
selectively reveal the CDNs and service edges that reside along the
paths between different end hosts and/or the cloud servers, together
with their properties (e.g., storage capabilities or Graphics
Processing Unit (GPU) capabilities) and available Service Level
Agreement (SLA) plans. See Figure 7 for an example where the query
is made for sources [a, b] and destinations [b, c, DC]. Here, each
ANE represents a service edge, and the properties include access
latency, available resources, etc. Note that the properties here are
only used for illustration purposes and are not part of this
extension.
a: { b: [ane1, ane2, ane3, ane4, ane5],
c: [ane1, ane2, ane3, ane4, ane6],
DC: [ane1, ane2, ane3] }
b: { c: [ane5, ane4, ane6], DC: [ane5, ane4, ane3] }
ane1: latency = 5 ms cpu = 2 memory = 8 GB storage = 10 TB
(On premise, a)
ane2: latency = 20 ms cpu = 4 memory = 8 GB storage = 10 TB
(Site-radio Edge Node 1)
ane3: latency = 100 ms cpu = 8 memory = 128 GB storage = 100 TB
(Access CO)
ane4: latency = 20 ms cpu = 4 memory = 8 GB storage = 10 TB
(Site-radio Edge Node 2)
ane5: latency = 5 ms cpu = 2 memory = 8 GB storage = 10 TB
(On premise, b)
ane6: latency = 5 ms cpu = 2 memory = 8 GB storage = 10 TB
(On premise, c)
Figure 7: Example Service Edge Query Results
With the service edge information, an ALTO client may better conduct
CDN request routing or offload functionalities from the user
equipment to the service edge, with considerations in place for
customized quality of experience.
5. Path Vector Extension: Overview
This section provides a non-normative overview of the Path Vector
extension defined in this document. It is assumed that readers are
familiar with both the base protocol [RFC7285] and the entity
property map extension [RFC9240].
To satisfy the additional requirements listed in Section 4.1, this
extension:
1. introduces the concept of an ANE as the abstraction of components
in a network whose properties may have an impact on end-to-end
performance of the traffic handled by those components,
2. extends the cost map and Endpoint Cost Service to convey the ANEs
traversed by the path of a <source, destination> pair as Path
Vectors, and
3. uses the entity property map to convey the association between
the ANEs and their properties.
Thus, an ALTO client can learn about the ANEs that are important for
assessing the QoE of different <source, destination> pairs by
investigating the corresponding Path Vector value (AR1) and can also
(1) identify common ANEs if an ANE appears in the Path Vectors of
multiple <source, destination> pairs (AR2) and (2) retrieve the
properties of the ANEs by searching the entity property map (AR3).
5.1. Abstract Network Element (ANE)
This extension introduces the ANE as an indirect and network-agnostic
way to specify a component or an aggregation of components of a
network whose properties have an impact on end-to-end performance for
application traffic between endpoints.
ANEs allow ALTO servers to focus on common properties of different
types of network components. For example, the throughput of a flow
can be constrained by different components in a network: the capacity
of a physical link, the maximum throughput of a firewall, the
reserved bandwidth of an MPLS tunnel, etc. In the example below,
assume that the throughput of the firewall is 100 Mbps and the
capacity for link (A, B) is also 100 Mbps; they result in the same
constraint on the total throughput of f1 and f2. Thus, they are
identical when treated as an ANE.
f1 | ^ f1
| | ----------------->
+----------+ +---+ +---+
| Firewall | | A |-----| B |
+----------+ +---+ +---+
| | ----------------->
v | f2 f2
When an ANE is defined by an ALTO server, it is assigned an
identifier by the ALTO server, i.e., a string of type ANEName as
specified in Section 6.1, and a set of associated properties.
5.1.1. ANE Entity Domain
In this extension, the associations between ANEs and their properties
are conveyed in an entity property map. Thus, ANEs must constitute
an "entity domain" (Section 5.1 of [RFC9240]), and each ANE property
must be an entity property (Section 5.2 of [RFC9240]).
Specifically, this document defines a new entity domain called "ane"
as specified in Section 6.2; Section 6.4 defines two initial property
types for the ANE entity domain.
5.1.2. Ephemeral and Persistent ANEs
By design, ANEs are ephemeral and not to be used in further requests
to other ALTO resources. More precisely, the corresponding ANE names
are no longer valid beyond the scope of a Path Vector response or the
incremental update stream for a Path Vector request. Compared with
globally unique ANE names, ephemeral ANEs have several benefits,
including better privacy for the ISP's internal structure and more
flexible ANE computation.
For example, an ALTO server may define an ANE for each aggregated
bottleneck link between the sources and destinations specified in the
request. For requests with different sources and destinations, the
bottlenecks may be different but can safely reuse the same ANE names.
The client can still adjust its traffic based on the information, but
it is difficult to infer the underlying topology with multiple
queries.
However, sometimes an ISP may intend to selectively reveal some
"persistent" network components that, as opposed to being ephemeral,
have a longer life cycle. For example, an ALTO server may define an
ANE for each service edge cluster. Once a client chooses to use a
service edge, e.g., by deploying some user-defined functions, it may
want to stick to the service edge to avoid the complexity of state
transition or synchronization, and continuously query the properties
of the edge cluster.
This document provides a mechanism to expose such network components
as persistent ANEs. A persistent ANE has a persistent ID that is
registered in a property map, together with its properties. See
Sections 6.2.4 and 6.4.2 for more detailed instructions on how to
identify ephemeral ANEs and persistent ANEs.
5.1.3. Property Filtering
Resource-constrained ALTO clients (see Section 4.1.2 of [RFC7285])
may benefit from the filtering of Path Vector query results at the
ALTO server, as an ALTO client may only require a subset of the
available properties.
Specifically, the available properties for a given resource are
announced in the Information Resource Directory (IRD) as a new
filtering capability called "ane-property-names". The properties
selected by a client as being of interest are specified in the
subsequent Path Vector queries using the "ane-property-names" filter.
The response only includes the selected properties for the ANEs.
The "ane-property-names" capability for the cost map and the Endpoint
Cost Service is specified in Sections 7.2.4 and 7.3.4, respectively.
The "ane-property-names" filter for the cost map and the Endpoint
Cost Service is specified in Sections 7.2.3 and 7.3.3 accordingly.
5.2. Path Vector Cost Type
For an ALTO client to correctly interpret the Path Vector, this
extension specifies a new cost type called the "Path Vector cost
type".
The Path Vector cost type must convey both the interpretation and
semantics in the "cost-mode" and "cost-metric" parameters,
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 C++, if there
existed a JSON array type named JSONArray, a Path Vector would 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 that
the value is a JSON array. Then, an ALTO client must check the value
of the "cost-metric" parameter. If the value is "ane-path", it means
that the JSON array should be further interpreted as a path of
ANENames.
The Path Vector cost type is specified in Section 6.5.
5.3. Multipart Path Vector Response
For a basic ALTO information resource, a response contains only one
type of ALTO resource, 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 8.
ALTO client ALTO server
|-------------- Request ---------------->|
|<------------- Response ----------------|
Figure 8: A Typical ALTO Request and Response
The extension defined in this document, on the other hand, involves
two types of information resources: Path Vectors conveyed in an
InfoResourceCostMap data component (defined in Section 11.2.3.6 of
[RFC7285]) or an InfoResourceEndpointCostMap data component (defined
in Section 11.5.1.6 of [RFC7285]), and ANE properties conveyed in an
InfoResourceProperties data component (defined in Section 7.6 of
[RFC9240]).
Instead of two consecutive message exchanges, the extension defined
in this document enforces one round of communication. Specifically,
the ALTO client must include the source and destination pairs and the
requested ANE properties in a single request, and the ALTO server
must return a single response containing both the Path Vectors and
properties associated with the ANEs in the Path Vectors, as shown in
Figure 9. Since the two parts are bundled together in one response
message, their orders are interchangeable. See Sections 7.2.6 and
7.3.6 for details.
ALTO client ALTO server
|------------- PV Request -------------->|
|<----- PV Response (Cost Map Part) -----|
|<--- PV Response (Property Map Part) ---|
Figure 9: The Path Vector Extension Request and Response
This design is based on the following considerations:
1. ANEs may be constructed on demand and, potentially, based on the
requested properties (see Section 5.1 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 property map request
correctly, an ALTO server must store the mapping of each Path
Vector request until the client fully retrieves the property
information. This "stateful" behavior may substantially harm
server scalability and potentially lead to denial-of-service
attacks.
One approach for realizing the one-round communication is to define a
new media type to contain both objects, but this violates modular
design. This document follows the standard-conforming usage of the
"multipart/related" media type as defined in [RFC2387] to elegantly
combine the objects. Path Vectors are encoded in an
InfoResourceCostMap data component or InfoResourceEndpointCostMap
data component, and the property map is encoded in an
InfoResourceProperties data component. They are encapsulated as
parts of a multipart message. This 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".
5.3.1. Identifying the Media Type of the Object Root
ALTO uses a media type to indicate the type of an entry in the IRD
(e.g., "application/alto-costmap+json" for the cost map and
"application/alto-endpointcost+json" for the Endpoint Cost Service).
Simply using "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 object root of a multipart/related message. For a cost
map resource, the "media-type" field in the IRD entry is "multipart/
related" with the parameter "type=application/alto-costmap+json"; for
an Endpoint Cost Service, the parameter is "type=application/alto-
endpointcost+json".
5.3.2. References to Part Messages
As the response of a Path Vector resource is a multipart message with
two different parts, it is important that each part can be uniquely
identified. Following the design provided in [RFC8895], this
extension requires that an ALTO server assign a unique identifier to
each part of the multipart response message. This identifier,
referred to as a Part Resource ID (see Section 6.6 for details), is
present in the part message's "Content-ID" header field. By
concatenating the Part Resource ID to the identifier of the Path
Vector request, an ALTO server/client can uniquely identify the Path
Vector part or the property map part.
6. Specification: Basic Data Types
6.1. ANE Name
An ANE name is encoded as a JSON string with the same format as that
of the type PIDName (Section 10.1 of [RFC7285]).
The type ANEName is used in this document to indicate a string of
this format.
6.2. ANE Entity Domain
The ANE entity domain associates property values with the ANEs in a
property map. Accordingly, the ANE entity domain always depends on a
property map.
It must be noted that the term "domain" here does not refer to a
network domain. Rather, it is inherited from the entity domain as
defined in Section 3.2 of [RFC9240]; the entity domain represents the
set of valid entities defined by an ALTO information resource (called
the "defining information resource").
6.2.1. Entity Domain Type
The entity domain type is "ane".
6.2.2. Domain-Specific Entity Identifier
The entity identifiers are the ANE names in the associated property
map.
6.2.3. Hierarchy and Inheritance
There is no hierarchy or inheritance for properties associated with
ANEs.
6.2.4. Media Type of Defining Resource
The defining resource for entity domain type "ane" MUST be a property
map, i.e., the media type of defining resources is:
application/alto-propmap+json
Specifically, for ephemeral ANEs that appear in a Path Vector
response, their entity domain names MUST be exactly ".ane", and the
defining resource of these ANEs is the property map part of the
multipart response. Meanwhile, for any persistent ANE whose defining
resource is a property map resource, its entity domain name MUST have
the format of "PROPMAP.ane", where PROPMAP is the resource ID of the
defining resource. Persistent entities are "persistent" because
standalone queries can be made by an ALTO client to their defining
resource(s) when the connection to the Path Vector service is closed.
For example, the defining resource of an ephemeral ANE whose entity
identifier is ".ane:NET1" is the property map part that contains this
identifier. The defining resource of a persistent ANE whose entity
identifier is "dc-props.ane:DC1" is the property map with the
resource ID "dc-props".
6.3. ANE Property Name
An ANE property name is encoded as a JSON string with the same format
as that of an entity property name (Section 5.2.2 of [RFC9240]).
6.4. Initial ANE Property Types
Two initial ANE property types are specified: "max-reservable-
bandwidth" and "persistent-entity-id".
Note that these property types do not depend on any information
resources. As such, the "EntityPropertyName" parameter MUST only
have the EntityPropertyType part.
6.4.1. Maximum Reservable Bandwidth
The maximum reservable bandwidth property ("max-reservable-
bandwidth") stands for the maximum bandwidth that can be reserved for
all the traffic that traverses an ANE. 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 bits per second (bps). If this property
is requested by the ALTO client but is not present for an ANE in the
server response, it MUST be interpreted as meaning that the property
is not defined for the ANE.
This property can be offered in a setting where the ALTO server is
part of a network system that provides on-demand resource allocation
and the ALTO client is part of a user application. One existing
example is [NOVA]: the ALTO server is part of a Software-Defined
Networking (SDN) controller and exposes a list of traversed network
elements and associated link bandwidth to the client. The encoding
in [NOVA] differs from the Path Vector response defined in this
document in that the Path Vector part and property map part are
placed in the same JSON object.
In such a framework, the ALTO server exposes resource availability
information (e.g., reservable bandwidth) to the ALTO client. How the
client makes resource requests based on the information, and how the
resource allocation is achieved, respectively, depend on interfaces
between the management system and the users or a higher-layer
protocol (e.g., SDN network intents [INTENT-BASED-NETWORKING] or MPLS
tunnels), which are out of scope for this document.
6.4.2. Persistent Entity ID
This document enables the discovery of a persistent ANE by exposing
its entity identifier as the persistent entity ID property of an
ephemeral ANE in the path vector response. The value of this
property is encoded with the EntityID format defined in Section 5.1.3
of [RFC9240].
In this format, the entity ID combines:
* a defining information resource for the ANE on which a
"persistent-entity-id" is queried, which is the property map
resource defining the ANE as a persistent entity, together with
the properties.
* the persistent name of the ANE in that property map.
With this format, the client has all the needed information for
further standalone query properties on the persistent ANE.
6.4.3. Examples
To illustrate the use of "max-reservable-bandwidth", consider the
following network with five nodes. Assume that the client wants to
query the maximum reservable bandwidth from H1 to H2. An ALTO server
may split the network into two ANEs: "ane1", which represents the
subnetwork with routers A, B, and C; and "ane2", which represents the
subnetwork with routers B, D, and E. The maximum reservable
bandwidth for "ane1" is 15 Mbps (using path A->C->B), and the maximum
reservable bandwidth for "ane2" is 20 Mbps (using path B->D->E).
20 Mbps 20 Mbps
10 Mbps +---+ +---+ +---+
/----| B |---| D |----| E |---- H2
+---+/ +---+ +---+ +---+
H1 ----| A | 15 Mbps|
+---+\ +---+
\----| C |
15 Mbps +---+
To illustrate the use of "persistent-entity-id", consider the
scenario in Figure 6. As the life cycles of service edges are
typically long, the service edges may contain information that is not
specific to the query. Such information can be stored in an
individual entity property map and can later be accessed by an ALTO
client.
For example, "ane1" in Figure 7 represents the on-premise service
edge closest to host "a". Assume that the properties of the service
edges are provided in an entity property map called "se-props" and
the ID of the on-premise service edge is "9a0b55f7-7442-4d56-8a2c-
b4cc6a8e3aa1"; the "persistent-entity-id" setting for "ane1" will be
"se-props.ane:9a0b55f7-7442-4d56-8a2c-b4cc6a8e3aa1". With this
persistent entity ID, an ALTO client may send queries to the "se-
props" resource with the entity ID ".ane:9a0b55f7-7442-4d56-8a2c-
b4cc6a8e3aa1".
6.5. 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 extension defined in this document.
6.5.1. Cost Metric: "ane-path"
The cost metric "ane-path" indicates that the value of such a cost
type conveys an array of ANE names, where each ANE name uniquely
represents an ANE traversed by traffic from a source to a
destination.
An ALTO client MUST interpret the Path Vector as if the traffic
between a source and a destination logically traverses the ANEs in
the same order as they appear in the Path Vector.
When the Path Vector procedures defined in this document are in use,
an ALTO server using the "ane-path" cost metric and the "array" cost
mode (see Section 6.5.2) MUST return as the cost value a JSON array
of data type ANEName, and the client MUST also check that each
element contained in the array is an ANEName (Section 6.1).
Otherwise, the client MUST discard the response and SHOULD follow the
guidance in Section 8.3.4.3 of [RFC7285] to handle the error.
6.5.2. Cost Mode: "array"
The cost mode "array" indicates that every cost value in the response
body of a (filtered) cost map or an Endpoint Cost Service MUST be
interpreted as a JSON array object. While this cost mode can be
applied to all cost metrics, additional specifications will be needed
to clarify the semantics of the "array" cost mode when combined with
cost metrics other than "ane-path".
6.6. Part Resource ID and Part Content ID
A Part Resource ID is encoded as a JSON string with the same format
as that of the type ResourceID (Section 10.2 of [RFC7285]).
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 5.3.2) 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 the resource ID and client ID
related to a Path Vector resource to 31 characters.
A Part Content ID conforms to the format of "msg-id" as specified in
[RFC2387] and [RFC5322]. Specifically, it has the following format:
"<" PART-RESOURCE-ID "@" DOMAIN-NAME ">"
PART-RESOURCE-ID: PART-RESOURCE-ID has the same format as the Part
Resource ID. It is used to identify whether a part message is a
Path Vector or a property map.
DOMAIN-NAME: DOMAIN-NAME has the same format as "dot-atom-text" as
specified in Section 3.2.3 of [RFC5322]. It must be the domain
name of the ALTO server.
7. Specification: Service Extensions
7.1. Notation
This document uses the same syntax and notation as those introduced
in Section 8.2 of [RFC7285] to specify the extensions to existing
ALTO resources and services.
7.2. Multipart Filtered Cost Map for Path Vector
This document introduces a new ALTO resource called the "multipart
filtered cost map resource", which allows an ALTO server to provide
other ALTO resources associated with the cost map resource in the
same response.
7.2.1. Media Type
The media type of the multipart filtered cost map resource is
"multipart/related", and the required "type" parameter MUST have a
value of "application/alto-costmap+json".
7.2.2. HTTP Method
The multipart filtered cost map is requested using the HTTP POST
method.
7.2.3. 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, which is defined as a JSON object
of type ReqFilteredCostMap in Section 4.1.2 of [RFC8189], with a data
format indicated by the media type "application/alto-
costmapfilter+json", which is a JSON object of type
PVReqFilteredCostMap:
object {
[EntityPropertyName ane-property-names<0..*>;]
} PVReqFilteredCostMap : ReqFilteredCostMap;
with field:
ane-property-names: This field provides a list of selected ANE
properties to be included in the response. Each property in this
list MUST match one of the supported ANE properties indicated in
the resource's "ane-property-names" capability (Section 7.2.4).
If the field is not present, it MUST be interpreted as an empty
list.
Example: Consider the network in Figure 1. If an ALTO client wants
to query the "max-reservable-bandwidth" setting between PID1 and
PID2, it can submit the following request.
POST /costmap/pv HTTP/1.1
Host: alto.example.com
Accept: multipart/related;type=application/alto-costmap+json,
application/alto-error+json
Content-Length: 212
Content-Type: application/alto-costmapfilter+json
{
"cost-type": {
"cost-mode": "array",
"cost-metric": "ane-path"
},
"pids": {
"srcs": [ "PID1" ],
"dsts": [ "PID2" ]
},
"ane-property-names": [ "max-reservable-bandwidth" ]
}
7.2.4. Capabilities
The multipart filtered cost map resource extends the capabilities
defined in Section 4.1.1 of [RFC8189]. The capabilities are defined
by a JSON object of type PVFilteredCostMapCapabilities:
object {
[EntityPropertyName ane-property-names<0..*>;]
} PVFilteredCostMapCapabilities : FilteredCostMapCapabilities;
with field:
ane-property-names: This field provides a list of ANE properties
that can be returned. If the field is not present, it MUST be
interpreted as an empty list, indicating that the ALTO server
cannot provide any ANE properties.
This extension also introduces additional restrictions for the
following fields:
cost-type-names: The "cost-type-names" field MUST 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 IRD's "meta" field.
cost-constraints: If the "cost-type-names" field includes the Path
Vector cost type, the "cost-constraints" field MUST be either
"false" or not present, unless specifically instructed by a future
document.
testable-cost-type-names (Section 4.1.1 of [RFC8189]): If the "cost-
type-names" field includes the Path Vector cost type and the
"testable-cost-type-names" field is present, the Path Vector cost
type MUST NOT be included in the "testable-cost-type-names" field
unless specifically instructed by a future document.
7.2.5. Uses
This member MUST include the resource ID of the network map based on
which the PIDs are defined. If this resource supports "persistent-
entity-id", it MUST also include the defining resources of persistent
ANEs that may appear in the response.
7.2.6. Response
The response MUST indicate an error, using ALTO Protocol error
handling as defined in Section 8.5 of [RFC7285], if the request is
invalid.
The "Content-Type" header field of the response MUST be "multipart/
related" as defined by [RFC2387], with the following parameters:
type: The "type" parameter is mandatory and MUST be "application/
alto-costmap+json". Note that [RFC2387] permits parameters both
with and without double quotes.
start: The "start" parameter is as defined in [RFC2387] and is
optional. If present, it MUST have the same value as the
"Content-ID" header field of the Path Vector part.
boundary: The "boundary" parameter is as defined in Section 5.1.1 of
[RFC2046] and is mandatory.
The body of the response MUST consist of two parts:
* The Path Vector part MUST include "Content-ID" and "Content-Type"
in its header. The "Content-Type" MUST be "application/alto-
costmap+json". The value of "Content-ID" MUST have the same
format as the Part Content ID as specified in Section 6.6.
The body of the Path Vector part MUST be a JSON object with the
same format as that defined in Section 11.2.3.6 of [RFC7285] when
the "cost-type" field is present in the input parameters and MUST
be a JSON object with the same format as that defined in
Section 4.1.3 of [RFC8189] if the "multi-cost-types" field is
present. The JSON object MUST include the "vtag" field in the
"meta" field, which provides the version tag of the returned
CostMapData object. The resource ID of the version tag MUST
follow the format of
resource-id '.' part-resource-id
where "resource-id" is the resource ID of the Path Vector resource
and "part-resource-id" has the same value as the PART-RESOURCE-ID
in the "Content-ID" of the Path Vector part. 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 the IRD.
* The entity property map part MUST also include "Content-ID" and
"Content-Type" in its header. The "Content-Type" MUST be
"application/alto-propmap+json". The value of "Content-ID" MUST
have the same format as the Part Content ID as specified in
Section 6.6.
The body of the entity property map part is a JSON object with the
same format as that defined in Section 7.6 of [RFC9240]. 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 Path Vector part MUST be included in the
"dependent-vtags" field. If "persistent-entity-id" is requested,
the version tags of the dependent resources that may expose the
entities in the response MUST also be included.
The PropertyMapData object has one member for each ANEName that
appears in the Path Vector part, which is an entity identifier
belonging to the self-defined entity domain as defined in
Section 5.1.2.3 of [RFC9240]. The EntityProps object for each ANE
has one member for each property that is both 1) associated with
the ANE and 2) specified in the "ane-property-names" field in the
request. If the Path Vector cost type is not included in the
"cost-type" field or the "multi-cost-type" field, the "property-
map" field MUST be present and the value MUST be an empty object
({}).
A complete and valid response MUST include both the Path Vector part
and the property map part in the multipart message. If any part is
*not* present, the client MUST discard the received information and
send another request if necessary.
The Path Vector part, whose media type is the same as the "type"
parameter of the multipart response message, is the root body part as
defined in [RFC2387]. Thus, it is the element that 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 placed as the first part, followed by the
property map part. When doing so, an ALTO server MAY choose not to
set the "start" parameter, which implies that the first part is the
object root.
Example: Consider the network in Figure 1. The response to the
example request in Section 7.2.3 is as follows, where "ANE1"
represents the aggregation of all the switches in the network.
HTTP/1.1 200 OK
Content-Length: 911
Content-Type: multipart/related; boundary=example-1;
type=application/alto-costmap+json
--example-1
Content-ID: <costmap@alto.example.com>
Content-Type: application/alto-costmap+json
{
"meta": {
"vtag": {
"resource-id": "filtered-cost-map-pv.costmap",
"tag": "fb20b76204814e9db37a51151faaaef2"
},
"dependent-vtags": [
{
"resource-id": "my-default-networkmap",
"tag": "75ed013b3cb58f896e839582504f6228"
}
],
"cost-type": { "cost-mode": "array", "cost-metric": "ane-path" }
},
"cost-map": {
"PID1": { "PID2": [ "ANE1" ] }
}
}
--example-1
Content-ID: <propmap@alto.example.com>
Content-Type: application/alto-propmap+json
{
"meta": {
"dependent-vtags": [
{
"resource-id": "filtered-cost-map-pv.costmap",
"tag": "fb20b76204814e9db37a51151faaaef2"
}
]
},
"property-map": {
".ane:ANE1": { "max-reservable-bandwidth": 100000000 }
}
}
--example-1
7.3. Multipart Endpoint Cost Service for Path Vector
This document introduces a new ALTO resource called the "multipart
Endpoint Cost Service", which allows an ALTO server to provide other
ALTO resources associated with the Endpoint Cost Service resource in
the same response.
7.3.1. Media Type
The media type of the multipart Endpoint Cost Service resource is
"multipart/related", and the required "type" parameter MUST have a
value of "application/alto-endpointcost+json".
7.3.2. HTTP Method
The multipart Endpoint Cost Service resource is requested using the
HTTP POST method.
7.3.3. Accept Input Parameters
The input parameters of the multipart Endpoint Cost Service resource
are supplied in the body of an HTTP POST request. This document
extends the input parameters to an Endpoint Cost Service, which is
defined as a JSON object of type ReqEndpointCostMap in Section 4.2.2
of [RFC8189], with a data format indicated by the media type
"application/alto-endpointcostparams+json", which is a JSON object of
type PVReqEndpointCostMap:
object {
[EntityPropertyName ane-property-names<0..*>;]
} PVReqEndpointCostMap : ReqEndpointCostMap;
with field:
ane-property-names: This document defines the "ane-property-names"
field in PVReqEndpointCostMap as being the same as in
PVReqFilteredCostMap. See Section 7.2.3.
Example: Consider the network in Figure 1. If an ALTO client wants
to query the "max-reservable-bandwidth" setting between "eh1" and
"eh2", it can submit the following request.
POST /ecs/pv HTTP/1.1
Host: alto.example.com
Accept: multipart/related;type=application/alto-endpointcost+json,
application/alto-error+json
Content-Length: 238
Content-Type: application/alto-endpointcostparams+json
{
"cost-type": {
"cost-mode": "array",
"cost-metric": "ane-path"
},
"endpoints": {
"srcs": [ "ipv4:192.0.2.2" ],
"dsts": [ "ipv4:192.0.2.18" ]
},
"ane-property-names": [ "max-reservable-bandwidth" ]
}
7.3.4. Capabilities
The capabilities of the multipart Endpoint Cost Service resource are
defined by a JSON object of type PVEndpointCostCapabilities, which is
defined as being the same as PVFilteredCostMapCapabilities. See
Section 7.2.4.
7.3.5. Uses
If this resource supports "persistent-entity-id", it MUST also
include the defining resources of persistent ANEs that may appear in
the response.
7.3.6. 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 field of the response MUST be "multipart/
related" as defined by [RFC2387], with the following parameters:
type: The "type" parameter MUST be "application/alto-
endpointcost+json" and is mandatory.
start: The "start" parameter is as defined in Section 7.2.6.
boundary: The "boundary" parameter is as defined in Section 5.1.1 of
[RFC2046] and is mandatory.
The body of the response MUST consist of two parts:
* The Path Vector part MUST include "Content-ID" and "Content-Type"
in its header. The "Content-Type" MUST be "application/alto-
endpointcost+json". The value of "Content-ID" MUST have the same
format as the Part Content ID as specified in Section 6.6.
The body of the Path Vector part MUST be a JSON object with the
same format as that defined in Section 11.5.1.6 of [RFC7285] when
the "cost-type" field is present in the input parameters and MUST
be a JSON object with the same format as that defined in
Section 4.2.3 of [RFC8189] if the "multi-cost-types" field is
present. The JSON object MUST include the "vtag" field in the
"meta" field, which provides the version tag of the returned
EndpointCostMapData object. The resource ID of the version tag
MUST follow the format of
resource-id '.' part-resource-id
where "resource-id" is the resource ID of the Path Vector resource
and "part-resource-id" has the same value as the PART-RESOURCE-ID
in the "Content-ID" of the Path Vector part.
* The entity property map part MUST also include "Content-ID" and
"Content-Type" in its header. The "Content-Type" MUST be
"application/alto-propmap+json". The value of "Content-ID" MUST
have the same format as the Part Content ID as specified in
Section 6.6.
The body of the entity property map part MUST be a JSON object
with the same format as that defined in Section 7.6 of [RFC9240].
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 Path Vector part MUST be included in
the "dependent-vtags" field. If "persistent-entity-id" is
requested, the version tags of the dependent resources that may
expose the entities in the response MUST also be included.
The PropertyMapData object has one member for each ANEName that
appears in the Path Vector part, which is an entity identifier
belonging to the self-defined entity domain as defined in
Section 5.1.2.3 of [RFC9240]. The EntityProps object for each ANE
has one member for each property that is both 1) associated with
the ANE and 2) specified in the "ane-property-names" field in the
request. If the Path Vector cost type is not included in the
"cost-type" field or the "multi-cost-type" field, the "property-
map" field MUST be present and the value MUST be an empty object
({}).
A complete and valid response MUST include both the Path Vector part
and the property map part in the multipart message. If any part is
*not* present, the client MUST discard the received information and
send another request if necessary.
The Path Vector part, whose media type is the same as the "type"
parameter of the multipart response message, is the root body part as
defined in [RFC2387]. Thus, it is the element that 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 placed as the first part, followed by the
property map part. When doing so, an ALTO server MAY choose not to
set the "start" parameter, which implies that the first part is the
object root.
Example: Consider the network in Figure 1. The response to the
example request in Section 7.3.3 is as follows.
HTTP/1.1 200 OK
Content-Length: 899
Content-Type: multipart/related; boundary=example-1;
type=application/alto-endpointcost+json
--example-1
Content-ID: <ecs@alto.example.com>
Content-Type: application/alto-endpointcost+json
{
"meta": {
"vtag": {
"resource-id": "ecs-pv.ecs",
"tag": "ec137bb78118468c853d5b622ac003f1"
},
"dependent-vtags": [
{
"resource-id": "my-default-networkmap",
"tag": "677fe5f4066848d282ece213a84f9429"
}
],
"cost-type": { "cost-mode": "array", "cost-metric": "ane-path" }
},
"cost-map": {
"ipv4:192.0.2.2": { "ipv4:192.0.2.18": [ "ANE1" ] }
}
}
--example-1
Content-ID: <propmap@alto.example.com>
Content-Type: application/alto-propmap+json
{
"meta": {
"dependent-vtags": [
{
"resource-id": "ecs-pv.ecs",
"tag": "ec137bb78118468c853d5b622ac003f1"
}
]
},
"property-map": {
".ane:ANE1": { "max-reservable-bandwidth": 100000000 }
}
}
--example-1
8. Examples
This section lists some examples of Path Vector queries and the
corresponding responses. Some long lines are truncated for better
readability.
8.1. Sample Setup
Figure 10 illustrates the network properties and thus the message
contents. There are three subnetworks (NET1, NET2, and NET3) and two
interconnection links (L1 and L2). It is assumed that each
subnetwork has sufficiently large bandwidth to be reserved.
----- L1
/
PID1 +----------+ 10 Gbps +----------+ PID3
192.0.2.0/28+-+ +------+ +---------+ +--+192.0.2.32/28
| | MEC1 | | | | 2001:db8::3:0/16
| +------+ | +-----+ |
PID2 | | | +----------+
192.0.2.16/28+-+ | | NET3
| | | 15 Gbps
| | | \
+----------+ | -------- L2
NET1 |
+----------+
| +------+ | PID4
| | MEC2 | +--+192.0.2.48/28
| +------+ | 2001:db8::4:0/16
+----------+
NET2
Figure 10: Examples of ANE Properties
8.2. Information Resource Directory
To give a comprehensive example of the extension defined in this
document, we consider the network in Figure 10. Assume that the ALTO
server provides the following information resources:
"my-default-networkmap": A network map resource that contains the
PIDs in the network.
"filtered-cost-map-pv": A multipart filtered cost map resource for
the Path Vector. Exposes the "max-reservable-bandwidth" property
for the PIDs in "my-default-networkmap".
"ane-props": A filtered entity property resource that exposes the
information for persistent ANEs in the network.
"endpoint-cost-pv": A multipart Endpoint Cost Service for the Path
Vector. Exposes the "max-reservable-bandwidth" and "persistent-
entity-id" properties.
"update-pv": An update stream service that provides the incremental
update service for the "endpoint-cost-pv" service.
"multicost-pv": A multipart Endpoint Cost Service with both the
Multi-Cost extension and Path Vector extension enabled.
Below is the IRD of the example ALTO server. To enable the extension
defined in this document, the Path Vector cost type (Section 6.5),
represented by "path-vector" below, is defined in the "cost-types" of
the "meta" field and is included in the "cost-type-names" of
resources "filtered-cost-map-pv" and "endpoint-cost-pv".
{
"meta": {
"cost-types": {
"path-vector": {
"cost-mode": "array",
"cost-metric": "ane-path"
},
"num-rc": {
"cost-mode": "numerical",
"cost-metric": "routingcost"
}
}
},
"resources": {
"my-default-networkmap": {
"uri": "https://alto.example.com/networkmap",
"media-type": "application/alto-networkmap+json"
},
"filtered-cost-map-pv": {
"uri": "https://alto.example.com/costmap/pv",
"media-type": "multipart/related;
type=application/alto-costmap+json",
"accepts": "application/alto-costmapfilter+json",
"capabilities": {
"cost-type-names": [ "path-vector" ],
"ane-property-names": [ "max-reservable-bandwidth" ]
},
"uses": [ "my-default-networkmap" ]
},
"ane-props": {
"uri": "https://alto.example.com/ane-props",
"media-type": "application/alto-propmap+json",
"accepts": "application/alto-propmapparams+json",
"capabilities": {
"mappings": {
".ane": [ "cpu" ]
}
}
},
"endpoint-cost-pv": {
"uri": "https://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": [
"max-reservable-bandwidth", "persistent-entity-id"
]
},
"uses": [ "ane-props" ]
},
"update-pv": {
"uri": "https://alto.example.com/updates/pv",
"media-type": "text/event-stream",
"uses": [ "endpoint-cost-pv" ],
"accepts": "application/alto-updatestreamparams+json",
"capabilities": {
"support-stream-control": true
}
},
"multicost-pv": {
"uri": "https://alto.exmaple.com/endpointcost/mcpv",
"media-type": "multipart/related;
type=application/alto-endpointcost+json",
"accepts": "application/alto-endpointcostparams+json",
"capabilities": {
"cost-type-names": [ "path-vector", "num-rc" ],
"max-cost-types": 2,
"testable-cost-type-names": [ "num-rc" ],
"ane-property-names": [
"max-reservable-bandwidth", "persistent-entity-id"
]
},
"uses": [ "ane-props" ]
}
}
}
8.3. Multipart Filtered Cost Map
The following examples demonstrate the request to the "filtered-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 the Path Vector and not the ANE properties.
The response consists of two parts:
* The first part returns the array of data type ANEName for each
source and destination pair. There are two ANEs, where "L1"
represents interconnection link L1 and "L2" represents
interconnection link L2.
* The second part returns the property map. Note that the
properties of the ANE entries are equal to the literal string "{}"
(see Section 8.3 of [RFC9240]).
POST /costmap/pv HTTP/1.1
Host: alto.example.com
Accept: multipart/related;type=application/alto-costmap+json,
application/alto-error+json
Content-Length: 163
Content-Type: application/alto-costmapfilter+json
{
"cost-type": {
"cost-mode": "array",
"cost-metric": "ane-path"
},
"pids": {
"srcs": [ "PID1" ],
"dsts": [ "PID3", "PID4" ]
}
}
HTTP/1.1 200 OK
Content-Length: 952
Content-Type: multipart/related; boundary=example-1;
type=application/alto-costmap+json
--example-1
Content-ID: <costmap@alto.example.com>
Content-Type: application/alto-costmap+json
{
"meta": {
"vtag": {
"resource-id": "filtered-cost-map-pv.costmap",
"tag": "d827f484cb66ce6df6b5077cb8562b0a"
},
"dependent-vtags": [
{
"resource-id": "my-default-networkmap",
"tag": "c04bc5da49534274a6daeee8ea1dec62"
}
],
"cost-type": {
"cost-mode": "array",
"cost-metric": "ane-path"
}
},
"cost-map": {
"PID1": {
"PID3": [ "L1" ],
"PID4": [ "L1", "L2" ]
}
}
}
--example-1
Content-ID: <propmap@alto.example.com>
Content-Type: application/alto-propmap+json
{
"meta": {
"dependent-vtags": [
{
"resource-id": "filtered-cost-map-pv.costmap",
"tag": "d827f484cb66ce6df6b5077cb8562b0a"
}
]
},
"property-map": {
".ane:L1": {},
".ane:L2": {}
}
}
--example-1
8.4. Multipart Endpoint Cost Service 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 ID property for two IPv4 source and destination
pairs (192.0.2.34 -> 192.0.2.2 and 192.0.2.34 -> 192.0.2.50) and one
IPv6 source and destination pair (2001:db8::3:1 -> 2001:db8::4:1).
The response consists of two parts:
* The first part returns the array of data type ANEName for each
valid source and destination pair. As one can see in Figure 10,
flow 192.0.2.34 -> 192.0.2.2 traverses NET3, L1, and NET1; and
flows 192.0.2.34 -> 192.0.2.50 and 2001:db8::3:1 -> 2001:db8::4:1
traverse NET2, L2, and NET3.
* The second part returns the requested properties of ANEs. Assume
that NET1, NET2, and NET3 have sufficient bandwidth and their
"max-reservable-bandwidth" values are set to a sufficiently large
number (50 Gbps in this case). On the other hand, assume that
there are no prior reservations on L1 and L2 and their "max-
reservable-bandwidth" values are the corresponding link capacity
(10 Gbps for L1 and 15 Gbps for L2).
Both NET1 and NET2 have a mobile edge deployed, i.e., MEC1 in NET1
and MEC2 in NET2. Assume that the ANEName values for MEC1 and MEC2
are "MEC1" and "MEC2" and their properties can be retrieved from the
property map "ane-props". Thus, the "persistent-entity-id" property
values for NET1 and NET2 are "ane-props.ane:MEC1" and "ane-
props.ane:MEC2", respectively.
POST /endpointcost/pv HTTP/1.1
Host: alto.example.com
Accept: multipart/related;
type=application/alto-endpointcost+json,
application/alto-error+json
Content-Length: 383
Content-Type: application/alto-endpointcostparams+json
{
"cost-type": {
"cost-mode": "array",
"cost-metric": "ane-path"
},
"endpoints": {
"srcs": [
"ipv4:192.0.2.34",
"ipv6:2001:db8::3:1"
],
"dsts": [
"ipv4:192.0.2.2",
"ipv4:192.0.2.50",
"ipv6:2001:db8::4:1"
]
},
"ane-property-names": [
"max-reservable-bandwidth",
"persistent-entity-id"
]
}
HTTP/1.1 200 OK
Content-Length: 1508
Content-Type: multipart/related; boundary=example-2;
type=application/alto-endpointcost+json
--example-2
Content-ID: <ecs@alto.example.com>
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": {
"ipv4:192.0.2.34": {
"ipv4:192.0.2.2": [ "NET3", "L1", "NET1" ],
"ipv4:192.0.2.50": [ "NET3", "L2", "NET2" ]
},
"ipv6:2001:db8::3:1": {
"ipv6:2001:db8::4:1": [ "NET3", "L2", "NET2" ]
}
}
}
--example-2
Content-ID: <propmap@alto.example.com>
Content-Type: application/alto-propmap+json
{
"meta": {
"dependent-vtags": [
{
"resource-id": "endpoint-cost-pv.ecs",
"tag": "bb6bb72eafe8f9bdc4f335c7ed3b10822a391cef"
},
{
"resource-id": "ane-props",
"tag": "bf3c8c1819d2421c9a95a9d02af557a3"
}
]
},
"property-map": {
".ane:NET1": {
"max-reservable-bandwidth": 50000000000,
"persistent-entity-id": "ane-props.ane:MEC1"
},
".ane:NET2": {
"max-reservable-bandwidth": 50000000000,
"persistent-entity-id": "ane-props.ane:MEC2"
},
".ane:NET3": {
"max-reservable-bandwidth": 50000000000
},
".ane:L1": {
"max-reservable-bandwidth": 10000000000
},
".ane:L2": {
"max-reservable-bandwidth": 15000000000
}
}
}
--example-2
In certain scenarios where the traversal order is not crucial, an
ALTO server implementation may choose not to strictly follow the
physical traversal order and may even obfuscate the order
intentionally to preserve its own privacy or conform to its own
policies. For example, an ALTO server may choose to aggregate NET1
and L1 as a new ANE with ANE name "AGGR1" and aggregate NET2 and L2
as a new ANE with ANE name "AGGR2". The "max-reservable-bandwidth"
property of "AGGR1" takes the value of L1, which is smaller than that
of NET1, and the "persistent-entity-id" property of "AGGR1" takes the
value of NET1. The properties of "AGGR2" are computed in a similar
way; the obfuscated response is as shown below. Note that the
obfuscation of Path Vector responses is implementation specific and
is out of scope for this document. Developers may refer to
Section 11 for further references.
HTTP/1.1 200 OK
Content-Length: 1333
Content-Type: multipart/related; boundary=example-2;
type=application/alto-endpointcost+json
--example-2
Content-ID: <ecs@alto.example.com>
Content-Type: application/alto-endpointcost+json
{
"meta": {
"vtags": {
"resource-id": "endpoint-cost-pv.ecs",
"tag": "bb975862fbe3422abf4dae386b132c1d"
},
"cost-type": {
"cost-mode": "array",
"cost-metric": "ane-path"
}
},
"endpoint-cost-map": {
"ipv4:192.0.2.34": {
"ipv4:192.0.2.2": [ "NET3", "AGGR1" ],
"ipv4:192.0.2.50": [ "NET3", "AGGR2" ]
},
"ipv6:2001:db8::3:1": {
"ipv6:2001:db8::4:1": [ "NET3", "AGGR2" ]
}
}
}
--example-2
Content-ID: <propmap@alto.example.com>
Content-Type: application/alto-propmap+json
{
"meta": {
"dependent-vtags": [
{
"resource-id": "endpoint-cost-pv.ecs",
"tag": "bb975862fbe3422abf4dae386b132c1d"
},
{
"resource-id": "ane-props",
"tag": "bf3c8c1819d2421c9a95a9d02af557a3"
}
]
},
"property-map": {
".ane:AGGR1": {
"max-reservable-bandwidth": 10000000000,
"persistent-entity-id": "ane-props.ane:MEC1"
},
".ane:AGGR2": {
"max-reservable-bandwidth": 15000000000,
"persistent-entity-id": "ane-props.ane:MEC2"
},
".ane:NET3": {
"max-reservable-bandwidth": 50000000000
}
}
}
--example-2
8.5. Incremental Updates
In this example, an ALTO client subscribes to the incremental update
for the multipart Endpoint Cost Service 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: 120
{
"add": {
"ecspvsub1": {
"resource-id": "endpoint-cost-pv",
"input": <ecs-input>
}
}
}
Based on the server-side process defined in [RFC8895], the ALTO
server will send the "control-uri" first, using a 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": "https://alto.example.com/updates/streams/123"}
event: multipart/related;boundary=example-3;
type=application/alto-endpointcost+json,ecspvsub1
data: --example-3
data: Content-ID: <ecsmap@alto.example.com>
data: Content-Type: application/alto-endpointcost+json
data:
data: <endpoint-cost-map-entry>
data: --example-3
data: Content-ID: <propmap@alto.example.com>
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, based on Section 6.7.3 of
[RFC8895].
event: application/merge-patch+json,
ecspvsub1.ecsmap@alto.example.com
data: <Merge patch for endpoint-cost-map-update>
event: application/merge-patch+json,
ecspvsub1.propmap@alto.example.com
data: <Merge patch for property-map-update>
8.6. Multi-Cost
The following examples demonstrate the request to the "multicost-pv"
resource and the corresponding response.
The request asks for two cost types: the first is the Path Vector
cost type, and the second is a numerical routing cost. It also
queries the maximum reservable bandwidth ANE property and the
persistent entity ID property for two IPv4 source and destination
pairs (192.0.2.34 -> 192.0.2.2 and 192.0.2.34 -> 192.0.2.50) and one
IPv6 source and destination pair (2001:db8::3:1 -> 2001:db8::4:1).
The response consists of two parts:
* The first part returns a JSONArray that contains two JSONValue
entries for each requested source and destination pair: the first
JSONValue is a JSONArray of ANENames, which is the value of the
Path Vector cost type; and the second JSONValue is a JSONNumber,
which is the value of the routing cost.
* The second part contains a property map that maps the ANEs to
their requested properties.
POST /endpointcost/mcpv HTTP/1.1
Host: alto.example.com
Accept: multipart/related;
type=application/alto-endpointcost+json,
application/alto-error+json
Content-Length: 454
Content-Type: application/alto-endpointcostparams+json
{
"multi-cost-types": [
{ "cost-mode": "array", "cost-metric": "ane-path" },
{ "cost-mode": "numerical", "cost-metric": "routingcost" }
],
"endpoints": {
"srcs": [
"ipv4:192.0.2.34",
"ipv6:2001:db8::3:1"
],
"dsts": [
"ipv4:192.0.2.2",
"ipv4:192.0.2.50",
"ipv6:2001:db8::4:1"
]
},
"ane-property-names": [
"max-reservable-bandwidth",
"persistent-entity-id"
]
}
HTTP/1.1 200 OK
Content-Length: 1419
Content-Type: multipart/related; boundary=example-4;
type=application/alto-endpointcost+json
--example-4
Content-ID: <ecs@alto.example.com>
Content-Type: application/alto-endpointcost+json
{
"meta": {
"vtags": {
"resource-id": "endpoint-cost-pv.ecs",
"tag": "84a4f9c14f9341f0983e3e5f43a371c8"
},
"multi-cost-types": [
{ "cost-mode": "array", "cost-metric": "ane-path" },
{ "cost-mode": "numerical", "cost-metric": "routingcost" }
]
},
"endpoint-cost-map": {
"ipv4:192.0.2.34": {
"ipv4:192.0.2.2": [[ "NET3", "AGGR1" ], 3],
"ipv4:192.0.2.50": [[ "NET3", "AGGR2" ], 2]
},
"ipv6:2001:db8::3:1": {
"ipv6:2001:db8::4:1": [[ "NET3", "AGGR2" ], 2]
}
}
}
--example-4
Content-ID: <propmap@alto.example.com>
Content-Type: application/alto-propmap+json
{
"meta": {
"dependent-vtags": [
{
"resource-id": "endpoint-cost-pv.ecs",
"tag": "84a4f9c14f9341f0983e3e5f43a371c8"
},
{
"resource-id": "ane-props",
"tag": "be157afa031443a187b60bb80a86b233"
}
]
},
"property-map": {
".ane:AGGR1": {
"max-reservable-bandwidth": 10000000000,
"persistent-entity-id": "ane-props.ane:MEC1"
},
".ane:AGGR2": {
"max-reservable-bandwidth": 15000000000,
"persistent-entity-id": "ane-props.ane:MEC2"
},
".ane:NET3": {
"max-reservable-bandwidth": 50000000000
}
}
}
--example-4
9. Compatibility with Other ALTO Extensions
9.1. Compatibility with Legacy ALTO Clients/Servers
The multipart filtered cost map resource and the multipart Endpoint
Cost Service resource have no backward-compatibility issues 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 incurring any incompatibility problems.
9.2. Compatibility with Multi-Cost Extension
The extension defined in this document is compatible with the multi-
cost extension [RFC8189]. Such a resource has a media type of either
"multipart/related; type=application/alto-costmap+json" or
"multipart/related; type=application/alto-endpointcost+json". Its
"cost-constraints" field must be either "false" or not present, and
the Path Vector cost type must be present in the "cost-type-names"
capability field but must not be present in the "testable-cost-type-
names" field, as specified in Sections 7.2.4 and 7.3.4.
9.3. Compatibility with Incremental Update Extension
This extension is compatible with the incremental update extension
[RFC8895]. ALTO clients and servers MUST follow the specifications
given in Sections 5.2 and 6.7.3 of [RFC8895] to support incremental
updates for a Path Vector resource.
9.4. Compatibility with Cost Calendar Extension
The extension specified in this document is compatible with the Cost
Calendar extension [RFC8896]. 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, a property of a single ANE may also have different values
in different time intervals. In this case, if such an ANE has
different property values in two time intervals, it MUST be treated
as two different ANEs, i.e., with different entity identifiers.
However, if it has the same property values in two time intervals, it
MAY use the same identifier.
This rule allows the Path Vector extension to represent both changes
of ANEs and changes of the ANEs' properties in a uniform way. The
Path Vector part is calendared in a compatible way, and the property
map part is not affected by the Cost Calendar extension.
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).
10. General Discussion
10.1. Constraint Tests for General Cost Types
The constraint test is a simple approach for querying the data. It
allows users to filter query results by specifying some boolean
tests. This approach is already used in the ALTO Protocol. ALTO
clients are permitted to specify either the "constraints" test
[RFC7285] [RFC8189] or the "or-constraints" test [RFC8189] to better
filter the results.
However, the current syntax can only be used to test scalar cost
types and cannot easily express constraints on complex cost types,
e.g., the Path Vector cost type defined in this document.
In practice, developing a bespoke language for general-purpose
boolean tests can be a complex undertaking, and it is conceivable
that such implementations already exist (the authors have not done an
exhaustive search to determine whether such implementations exist).
One avenue for developing such a language may be to explore extending
current query languages like XQuery [XQuery] or JSONiq [JSONiq] and
integrating these with ALTO.
Filtering the Path Vector results or developing a more sophisticated
filtering mechanism is beyond the scope of this document.
10.2. General Multi-Resource Query
Querying multiple ALTO information resources continuously is a
general requirement. Enabling such a capability, however, must
address general issues like efficiency and consistency. The
incremental update extension [RFC8895] supports submitting multiple
queries in a single request and allows flexible control over the
queries. However, it does not cover the case introduced in this
document where multiple resources are needed for a single request.
The extension specified in this document gives an example of using a
multipart message to encode the responses from two specific ALTO
information resources: a filtered cost map or an Endpoint Cost
Service, and a property map. By packing multiple resources in a
single response, the implication is that servers may proactively push
related information resources to clients.
Thus, it is worth looking into extending the SSE mechanism as used in
the incremental update extension [RFC8895]; or upgrading to HTTP/2
[RFC9113] and HTTP/3 [RFC9114], which provides the ability to
multiplex queries and to allow servers to proactively send related
information resources.
Defining a general multi-resource query mechanism is out of scope for
this document.
11. Security Considerations
This document is an extension of the base ALTO Protocol, so the
security considerations provided for the base ALTO Protocol [RFC7285]
fully apply when this extension is provided by an ALTO server.
The Path Vector extension requires additional scrutiny of three
security considerations discussed in the base protocol:
confidentiality of ALTO information (Section 15.3 of [RFC7285]),
potential undesirable guidance from authenticated ALTO information
(Section 15.2 of [RFC7285]), and availability of ALTO services
(Section 15.5 of [RFC7285]).
For confidentiality of ALTO information, a network operator should be
aware that this extension may introduce a new risk: the Path Vector
information, when used together with sensitive ANE properties such as
capacities of bottleneck links, 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 attacker may
identify the bottleneck link or links and start a distributed denial-
of-service (DDoS) attack involving minimal flows, triggering in-
network congestion. Given the potential risk of leaking sensitive
information, the Path Vector extension is mainly applicable in
scenarios where 1) the ANE structures and ANE properties do not
impose security risks on the ALTO service provider (e.g., they do not
carry sensitive information) or 2) the ALTO server and client have
established a reliable trust relationship (e.g., they operate in the
same administrative domain or are managed by business partners with
legal contracts).
Three risk types are identified in Section 15.3.1 of [RFC7285]:
(1) excess disclosure of the ALTO service provider's data to an
unauthorized ALTO client,
(2) disclosure of the ALTO service provider's data (e.g., network
topology information or endpoint addresses) to an unauthorized
third party, and
(3) excess retrieval of the ALTO service provider's data by
collaborating ALTO clients.
To mitigate these risks, an ALTO server MUST follow the guidelines in
Section 15.3.2 of [RFC7285]. Furthermore, an ALTO server MUST follow
the following additional protections strategies for risk types (1)
and (3).
For risk type (1), an ALTO server MUST use the authentication methods
specified in Section 15.3.2 of [RFC7285] to authenticate the identity
of an ALTO client and apply access control techniques to restrict the
retrieval of sensitive Path Vector information by unprivileged ALTO
clients. For settings where the ALTO server and client are not in
the same trust domain, the ALTO server should reach agreements with
the ALTO client regarding protection of confidentiality before
granting access to Path Vector services with sensitive information.
Such agreements may include legal contracts or Digital Rights
Management (DRM) techniques. Otherwise, the ALTO server MUST NOT
offer Path Vector services that carry sensitive information to the
clients, unless the potential risks are fully assessed and mitigated.
For risk type (3), an ALTO service provider must be aware that
persistent ANEs may be used as "landmarks" in collaborative
inferences. Thus, they should only be used when exposing public
service access points (e.g., API gateways, CDN Interconnections) and/
or when the granularity is coarse grained (e.g., when an ANE
represents an AS, a data center, or a WAN). Otherwise, an ALTO
server MUST use dynamic mappings from ephemeral ANE names to
underlying physical entities. Specifically, for the same physical
entity, an ALTO server SHOULD assign a different ephemeral ANE name
when the entity appears in the responses to different clients or even
for different requests from the same client. A RECOMMENDED
assignment strategy is to generate ANE names from random numbers.
Further, to protect the network topology from graph reconstruction
(e.g., through isomorphic graph identification [BONDY]), the ALTO
server SHOULD consider protection mechanisms to reduce information
exposure or obfuscate the real information. When doing so, the ALTO
server must be aware that information reduction/obfuscation may lead
to a potential risk of undesirable guidance from authenticated ALTO
information (Section 15.2 of [RFC7285]).
Thus, implementations of ALTO servers involving reduction or
obfuscation of the Path Vector information SHOULD consider reduction/
obfuscation mechanisms that can preserve the integrity of ALTO
information -- for example, by using minimal feasible region
compression algorithms [NOVA] or obfuscation protocols [RESA]
[MERCATOR]. However, these obfuscation methods are experimental, and
their practical applicability to the generic capability provided by
this extension has not been fully assessed. The ALTO server MUST
carefully verify that the deployment scenario satisfies the security
assumptions of these methods before applying them to protect Path
Vector services with sensitive network information.
For availability of ALTO services, an ALTO server should be cognizant
that using a Path Vector extension might introduce a new risk:
frequent requests for Path Vectors might consume intolerable amounts
of server-side computation and storage. This behavior can break the
ALTO server. For example, if an ALTO server implementation
dynamically computes the Path Vectors for each request, the service
that provides the Path Vectors may become an entry point for denial-
of-service attacks on the availability of an ALTO server.
To mitigate this risk, an ALTO server may consider using such
optimizations as precomputation-and-projection mechanisms [MERCATOR]
to reduce the overhead for processing each query. An ALTO server may
also protect itself from malicious clients by monitoring client
behavior and stopping service to clients that exhibit suspicious
behavior (e.g., sending requests at a high frequency).
The ALTO service providers must be aware that providing incremental
updates of "max-reservable-bandwidth" may provide information about
other consumers of the network. For example, a change in value may
indicate that one or more reservations have been made or changed. To
mitigate this risk, an ALTO server can batch the updates and/or add a
random delay before publishing the updates.
12. IANA Considerations
12.1. "ALTO Cost Metrics" Registry
This document registers a new entry in the "ALTO Cost Metrics"
registry, per Section 14.2 of [RFC7285]. The new entry is as shown
below in Table 1.
+============+====================+===========+
| Identifier | Intended Semantics | Reference |
+============+====================+===========+
| ane-path | See Section 6.5.1 | RFC 9275 |
+------------+--------------------+-----------+
Table 1: "ALTO Cost Metrics" Registry
12.2. "ALTO Cost Modes" Registry
This document registers a new entry in the "ALTO Cost Modes"
registry, per Section 5 of [RFC9274]. The new entry is as shown
below in Table 2.
+============+=========================+=============+===========+
| Identifier | Description | Intended | Reference |
| | | Semantics | |
+============+=========================+=============+===========+
| array | Indicates that the cost | See Section | RFC 9275 |
| | value is a JSON array | 6.5.2 | |
+------------+-------------------------+-------------+-----------+
Table 2: "ALTO Cost Modes" Registry
12.3. "ALTO Entity Domain Types" Registry
This document registers a new entry in the "ALTO Entity Domain Types"
registry, per Section 12.3 of [RFC9240]. The new entry is as shown
below in Table 3.
+============+============+=============+===================+=======+
| Identifier |Entity |Hierarchy and| Media Type of |Mapping|
| |Identifier |Inheritance | Defining Resource |to ALTO|
| |Encoding | | |Address|
| | | | |Type |
+============+============+=============+===================+=======+
| ane |See Section |None | application/alto- |false |
| |6.2.2 | | propmap+json | |
+------------+------------+-------------+-------------------+-------+
Table 3: "ALTO Entity Domain Types" Registry
Identifier: See Section 6.2.1.
Entity Identifier Encoding: See Section 6.2.2.
Hierarchy: None
Inheritance: None
Media Type of Defining Resource: See Section 6.2.4.
Mapping to ALTO Address Type: This entity type does not map to an
ALTO address type.
Security Considerations: In some usage scenarios, ANE addresses
carried in ALTO Protocol messages may reveal information about an
ALTO client or an ALTO service provider. If a naming schema is
used to generate ANE names, either used privately or standardized
by a future extension, how (or if) the naming schema relates to
private information and network proximity must be explained to
ALTO implementers and service providers.
12.4. "ALTO Entity Property Types" Registry
Two initial entries -- "max-reservable-bandwidth" and "persistent-
entity-id" -- are registered for the ALTO domain "ane" in the "ALTO
Entity Property Types" registry, per Section 12.4 of [RFC9240]. The
two new entries are shown below in Table 4, and their details can be
found in Sections 12.4.1 and 12.4.2 of this document.
+==========================+====================+===================+
| Identifier | Intended | Media Type of |
| | Semantics | Defining Resource |
+==========================+====================+===================+
| max-reservable-bandwidth | See Section | application/alto- |
| | 6.4.1 | propmap+json |
+--------------------------+--------------------+-------------------+
| persistent-entity-id | See Section | application/alto- |
| | 6.4.2 | propmap+json |
+--------------------------+--------------------+-------------------+
Table 4: Initial Entries for the "ane" Domain in the "ALTO Entity
Property Types" Registry
12.4.1. New ANE Property Type: Maximum Reservable Bandwidth
Identifier: "max-reservable-bandwidth"
Intended Semantics: See Section 6.4.1.
Media Type of Defining Resource: application/alto-propmap+json
Security Considerations: To make better choices regarding bandwidth
reservation, this property is essential for applications such as
large-scale data transfers or an overlay network interconnection.
It may reveal the bandwidth usage of the underlying network and
can potentially be leveraged to reduce the cost of conducting
denial-of-service attacks. Thus, the ALTO server MUST consider
such protection mechanisms as providing the information to
authorized clients only and applying information reduction and
obfuscation as discussed in Section 11.
12.4.2. New ANE Property Type: Persistent Entity ID
Identifier: "persistent-entity-id"
Intended Semantics: See Section 6.4.2.
Media Type of Defining Resource: application/alto-propmap+json
Security Considerations: This property is useful when an ALTO server
wants to selectively expose certain service points whose detailed
properties can be further queried by applications. As mentioned
in Section 12.3.2 of [RFC9240], the entity IDs may reveal
sensitive information about the underlying network. An ALTO
server should follow the security considerations provided in
Section 11 of [RFC9240].
13. References
13.1. Normative References
[RFC2046] Freed, N. and N. Borenstein, "Multipurpose Internet Mail
Extensions (MIME) Part Two: Media Types", RFC 2046,
DOI 10.17487/RFC2046, November 1996,
<https://www.rfc-editor.org/info/rfc2046>.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119,
DOI 10.17487/RFC2119, March 1997,
<https://www.rfc-editor.org/info/rfc2119>.
[RFC2387] Levinson, E., "The MIME Multipart/Related Content-type",
RFC 2387, DOI 10.17487/RFC2387, August 1998,
<https://www.rfc-editor.org/info/rfc2387>.
[RFC5322] Resnick, P., Ed., "Internet Message Format", RFC 5322,
DOI 10.17487/RFC5322, October 2008,
<https://www.rfc-editor.org/info/rfc5322>.
[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>.
[RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
May 2017, <https://www.rfc-editor.org/info/rfc8174>.
[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>.
[RFC8895] Roome, W. and Y. Yang, "Application-Layer Traffic
Optimization (ALTO) Incremental Updates Using Server-Sent
Events (SSE)", RFC 8895, DOI 10.17487/RFC8895, November
2020, <https://www.rfc-editor.org/info/rfc8895>.
[RFC8896] Randriamasy, S., Yang, R., Wu, Q., Deng, L., and N.
Schwan, "Application-Layer Traffic Optimization (ALTO)
Cost Calendar", RFC 8896, DOI 10.17487/RFC8896, November
2020, <https://www.rfc-editor.org/info/rfc8896>.
[RFC9240] Roome, W., Randriamasy, S., Yang, Y., Zhang, J., and K.
Gao, "An Extension for Application-Layer Traffic
Optimization (ALTO): Entity Property Maps", RFC 9240,
DOI 10.17487/RFC9240, July 2022,
<https://www.rfc-editor.org/info/rfc9240>.
[RFC9274] Boucadair, M. and Q. Wu, "A Cost Mode Registry for the
Application-Layer Traffic Optimization (ALTO) Protocol",
RFC 9274, DOI 10.17487/RFC9274, July 2022,
<https://www.rfc-editor.org/info/rfc9274>.
13.2. Informative References
[ALTO-PERF-METRICS]
Wu, Q., Yang, Y., Lee, Y., Dhody, D., Randriamasy, S., and
L. Contreras, "ALTO Performance Cost Metrics", Work in
Progress, Internet-Draft, draft-ietf-alto-performance-
metrics-28, 21 March 2022,
<https://datatracker.ietf.org/doc/html/draft-ietf-alto-
performance-metrics-28>.
[BONDY] Bondy, J.A. and R.L. Hemminger, "Graph reconstruction--a
survey", Journal of Graph Theory, Volume 1, Issue 3, pp.
227-268, DOI 10.1002/jgt.3190010306, 1977,
<https://onlinelibrary.wiley.com/doi/10.1002/
jgt.3190010306>.
[BOXOPT] Xiang, Q., Yu, H., Aspnes, J., Le, F., Kong, L., and Y.R.
Yang, "Optimizing in the Dark: Learning an Optimal
Solution through a Simple Request Interface", Proceedings
of the AAAI Conference on Artificial Intelligence 33,
1674-1681, DOI 10.1609/aaai.v33i01.33011674, July 2019,
<https://ojs.aaai.org//index.php/AAAI/article/view/3984>.
[CLARINET] Viswanathan, R., Ananthanarayanan, G., and A. Akella,
"CLARINET: WAN-aware optimization for analytics queries",
Proceedings of the 12th USENIX conference on Operating
Systems Design and Implementation (OSDI'16), Savannah, GA,
pp. 435-450, November 2016,
<https://dl.acm.org/doi/abs/10.5555/3026877.3026911>.
[G2] Ros-Giralt, J., Bohara, A., Yellamraju, S., Langston,
M.H., Lethin, R., Jiang, Y., Tassiulas, L., Li, J., Tan,
Y., and M. Veeraraghavan, "On the Bottleneck Structure of
Congestion-Controlled Networks", Proceedings of the ACM on
Measurement and Analysis of Computing Systems, Volume 3,
Issue 3, pp. 1-31, DOI 10.1145/3366707, December 2019,
<https://dl.acm.org/doi/10.1145/3366707>.
[HUG] Chowdhury, M., Liu, Z., Ghodsi, A., and I. Stoica, "HUG:
multi-resource fairness for correlated and elastic
demands", Proceedings of the 13th USENIX Conference on
Networked Systems Design and Implementation (NSDI'16),
Santa Clara, CA, pp. 407-424, March 2016,
<https://dl.acm.org/doi/10.5555/2930611.2930638>.
[INTENT-BASED-NETWORKING]
Clemm, A., Ciavaglia, L., Granville, L. Z., and J.
Tantsura, "Intent-Based Networking - Concepts and
Definitions", Work in Progress, Internet-Draft, draft-
irtf-nmrg-ibn-concepts-definitions-09, 24 March 2022,
<https://datatracker.ietf.org/doc/html/draft-irtf-nmrg-
ibn-concepts-definitions-09>.
[JSONiq] JSONiq, "The JSON Query Language", 2022,
<https://www.jsoniq.org/>.
[MERCATOR] Xiang, Q., Zhang, J., Wang, X., Liu, Y., Guok, C., Le, F.,
MacAuley, J., Newman, H., and Y.R. Yang, "Toward Fine-
Grained, Privacy-Preserving, Efficient Multi-Domain
Network Resource Discovery", IEEE/ACM, IEEE Journal on
Selected Areas in Communications, Volume 37, Issue 8, pp.
1924-1940, DOI 10.1109/JSAC.2019.2927073, August 2019,
<https://ieeexplore.ieee.org/document/8756056>.
[MOWIE] Zhang, Y., Li, G., Xiong, C., Lei, Y., Huang, W., Han, Y.,
Walid, A., Yang, Y.R., and Z. Zhang, "MoWIE: Toward
Systematic, Adaptive Network Information Exposure as an
Enabling Technique for Cloud-Based Applications over 5G
and Beyond", Proceedings of the Workshop on Network
Application Integration/CoDesign (NAI '20), ACM, Virtual
Event USA, pp. 20-27, DOI 10.1145/3405672.3409489, August
2020, <https://dl.acm.org/doi/10.1145/3405672.3409489>.
[NOVA] 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, Issue 2, pp. 805-818,
DOI 10.1109/TNET.2019.2899905, April 2019,
<https://doi.org/10.1109/TNET.2019.2899905>.
[RESA] Xiang, Q., Zhang, J., Wang, X., Liu, Y., Guok, C., Le, F.,
MacAuley, J., Newman, H., and Y.R. Yang, "Fine-Grained,
Multi-Domain Network Resource Abstraction as a Fundamental
Primitive to Enable High-Performance, Collaborative Data
Sciences", SC18: International Conference for High
Performance Computing, Networking, Storage and Analysis,
pp. 58-70, DOI 10.1109/SC.2018.00008, November 2018,
<https://ieeexplore.ieee.org/document/8665783>.
[RFC2216] Shenker, S. and J. Wroclawski, "Network Element Service
Specification Template", RFC 2216, DOI 10.17487/RFC2216,
September 1997, <https://www.rfc-editor.org/info/rfc2216>.
[RFC4271] Rekhter, Y., Ed., Li, T., Ed., and S. Hares, Ed., "A
Border Gateway Protocol 4 (BGP-4)", RFC 4271,
DOI 10.17487/RFC4271, January 2006,
<https://www.rfc-editor.org/info/rfc4271>.
[RFC9113] Thomson, M., Ed. and C. Benfield, Ed., "HTTP/2", RFC 9113,
DOI 10.17487/RFC9113, June 2022,
<https://www.rfc-editor.org/info/rfc9113>.
[RFC9114] Bishop, M., Ed., "HTTP/3", RFC 9114, DOI 10.17487/RFC9114,
June 2022, <https://www.rfc-editor.org/info/rfc9114>.
[SENSE] ESnet, "Software Defined Networking (SDN) for End-to-End
Networked Science at the Exascale", 2019,
<https://www.es.net/network-r-and-d/sense/>.
[SEREDGE] Contreras, L., Baliosian, J., Martínez-Julia, P., and J.
Serrat, "Computing at the Edge: But, what Edge?",
Proceedings of NOMS 2020 - 2020 IEEE/IFIP Network
Operations and Management Symposium, pp. 1-9,
DOI 10.1109/NOMS47738.2020.9110342, April 2020,
<https://ieeexplore.ieee.org/document/9110342>.
[SWAN] Hong, C., Kandula, S., Mahajan, R., Zhang, M., Gill, V.,
Nanduri, M., and R. Wattenhofer, "Achieving high
utilization with software-driven WAN", Proceedings of the
ACM SIGCOMM 2013 conference on SIGCOMM (SIGCOMM '13), New
York, NY, pp. 15-26, DOI 10.1145/2486001.2486012, August
2013, <https://dl.acm.org/doi/10.1145/2486001.2486012>.
[UNICORN] Xiang, Q., Wang, T., Zhang, J., Newman, H., Yang, Y.R.,
and Y. Liu, "Unicorn: Unified resource orchestration for
multi-domain, geo-distributed data analytics", Future
Generation Computer Systems, Volume 93, pp. 188-197,
DOI 10.1016/j.future.2018.09.048, April 2019,
<https://www.sciencedirect.com/science/article/abs/pii/
S0167739X18302413?via%3Dihub>.
[XQuery] Robie, J., Ed., Dyck, M., Ed., and J. Spiegel, Ed.,
"XQuery 3.1: An XML Query Language", W3C Recommendation,
March 2017, <https://www.w3.org/TR/xquery-31/>.
Acknowledgments
The authors would like to thank Andreas Voellmy, Erran Li, Haibin
Song, Haizhou Du, Jiayuan Hu, Tianyuan Liu, Xiao Shi, Xin Wang, and
Yan Luo for fruitful discussions. The authors thank Greg Bernstein,
Dawn Chen, Wendy Roome, and Michael Scharf for their contributions to
earlier draft versions of this document.
The authors would also like to thank Tim Chown, Luis Contreras, Roman
Danyliw, Benjamin Kaduk, Erik Kline, Suresh Krishnan, Murray
Kucherawy, Warren Kumari, Danny Lachos, Francesca Palombini, Éric
Vyncke, Samuel Weiler, and Qiao Xiang, whose feedback and suggestions
were invaluable for improving the practicability and conciseness of
this document; and Mohamed Boucadair, Martin Duke, Vijay Gurbani, Jan
Seedorf, and Qin Wu, who provided great support and guidance.
Authors' Addresses
Kai Gao
Sichuan University
No.24 South Section 1, Yihuan Road
Chengdu
610000
China
Email: kaigao@scu.edu.cn
Young Lee
Samsung
Republic of Korea
Email: younglee.tx@gmail.com
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 06511
United States of America
Email: yry@cs.yale.edu
Jingxuan Jensen Zhang
Tongji University
4800 Caoan Road
Shanghai
201804
China
Email: jingxuan.n.zhang@gmail.com
ERRATA
