| Internet-Draft | ALTO-PV | November 2020 |
| Gao, et al. | Expires 6 May 2021 | [Page] |
This document is an extension to the base Application-Layer Traffic Optimization protocol [RFC7285]. While the current ALTO Cost Services only allow applications to obtain numerical/ordinal cost values on an end-to-end path defined by its source and destination, the present extension enables the provision of abstracted information on particular Abstract Network Elements on the path. These Abstract Network Elements, or simply Elements, are components of the network which handle data packets, and their properties may have an impact on the end-to-end performance of the applications' traffic. Examples of such Elements include physical devices such as routers, cables and interfaces, and aggregations of devices such as subnetworks and data centers. Such information is useful for applications whose performance is impacted by particular Abstract Network Elements they traverse or by their properties. Applications having the choice among several connection paths may use this information to select paths accordingly and improve their performance. In particular, they may infer that several paths share common links and prevent traffic bottlenecks by avoiding such paths. This document introduces a new cost type called Path Vector. A Path Vector is an array of entities that each identifies an Abstract Network Element (ANE). Each ANE is associated with a set of properties. ANE properties are conveyed by an ALTO information resource called "Property Map", that can be packed together with the Path Vectors in a multipart response. They can also be obtained via a separate ALTO request to a Property Map. An ALTO Property Map is an extension to the ALTO protocol, that is specified in another document entitled "Unified Properties for the ALTO Protocol" [I-D.ietf-alto-unified-props-new].¶
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Network performance metrics are crucial to the Quality of Experience (QoE) of today's applications. The ALTO protocol allows Internet Service Providers (ISPs) to provide guidance, such as topological distance between different end hosts, to overlay applications. Thus, the overlay applications can potentially improve the QoE by better orchestrating their traffic to utilize the resources in the underlying network infrastructure.¶
Existing ALTO Cost Map and Endpoint Cost Service provide only cost information on 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 [I-D.ietf-alto-performance-metrics], to query multiple costs simultaneously [RFC8189], and to obtain the time-varying values [I-D.ietf-alto-cost-calendar].¶
While the existing extensions are sufficient for many overlay applications, however, the QoE of some overlay applications depends not only on the cost information of end-to-end paths, but also on particular components of a network on the paths and their properties. For example, job completion time, which is an important QoE metric for a large-scale data analytics application, is impacted by shared bottleneck links inside the carrier network. We refer to such components of a network as Abstract Network Elements (ANE).¶
Predicting such information can be very complex without the help of the ISP [AAAI2019]. 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 benefits, ISPs are not likely to expose details on their network paths: first for the sake of confidentiality, second because it may result in a huge volume and overhead, and last because it is difficult for ISPs to figure out what information and what details an application needs. Likewise, applications do not necessarily need all the network path details and are likely not able to understand them.¶
Therefore, it is beneficial for both parties if an ALTO server provides ALTO clients with an "abstract network state" that provides the necessary details to applications, while hiding the network complexity and confidential information. An "abstract network state" is a selected set of abstract representations of Abstract Network Elements traversed by the paths between <source, destination> pairs combined with properties of these Abstract Network Elements 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 Abstract Network Elements. The pressure on the server scalability can also be reduced by combining Abstract Network Elements and their properties in a single response.¶
This document extends [RFC7285] to allow an ALTO server convey "abstract network state", for paths defined by their <source, destination> pairs. To this end, it introduces a new cost type called "Path Vector". A Path Vector is an array of identifiers that each identifies an Abstract Network Element, which can be associated with various properties. The associations between ANEs and their properties are encoded in an ALTO information resource called Unified Property Map, which is specified in [I-D.ietf-alto-unified-props-new].¶
For better confidentiality, this document aims to minimize information exposure.
In particular, this document enables and recommends that first ANEs are
constructed on demand, and second an ANE is only associated with properties that
are requested by an ALTO client. A Path Vector response involves two ALTO Maps:
the Cost Map that contains the Path Vector results and the up-to-date Unified
Property Map that contains the properties requested for these ANEs. To enforce
consistency and improve server scalability, this document uses the
multipart/related message defined in [RFC2387] to return the two maps in a
single response.¶
The rest of the document is organized as follows. Section 3 introduces the extra terminologies that are used in this document. Section 4 uses an illustrative example to introduce the additional requirements of the ALTO framework, and discusses potential use cases. Section 5 gives an overview of the protocol design. Section 6 and Section 7 specify the Path Vector extension to the ALTO IRD and the information resources, with some concrete examples presented in Section 8. Section 9 discusses the backward compatibility with the base protocol and existing extensions. Security and IANA considerations are discussed in Section 11 and Section 12 respectively.¶
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.¶
When the words appear in lower case, they are to be interpreted with their natural language meanings.¶
NOTE: This document depends on the Unified Property Map extension [I-D.ietf-alto-unified-props-new] and should be processed after the Unified Property Map document.¶
This document extends the ALTO base protocol [RFC7285] and the Unified Property Map extension [I-D.ietf-alto-unified-props-new]. In addition to the terms defined in these documents, this document also uses the following additional terms:¶
Abstract Network Element (ANE): An Abstract Network Element is an abstract representation for a component in a network that handle 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 Abstract Network Element is similar to Network Element defined in [RFC2216] in the sense that they both provide an abstract representation of particular components of a network. However, they have different criteria on how these particular components are selected. Specifically, Network Element requires the components to be potentially capable of exercising QoS control, while Abstract Network Element only requires the components to have an impact on the end-to-end performance.¶
This section gives an illustrative example of how an overlay application can benefit from the Path Vector extension.¶
Assume that an application has control over a set of flows, which may go through shared links or switches and share a bottleneck. The application hopes to schedule the traffic among multiple flows to get better performance. The capacity region information for those flows will benefit the scheduling. However, existing cost maps can not reveal such information.¶
Specifically, consider a network as shown in Figure 1. The network has 7 switches (sw1 to sw7) forming a dumb-bell topology. Switches sw1/sw3 provide access on one side, sw2/sw4 provide access on the other side, and sw5-sw7 form the backbone. Endhosts eh1 to eh4 are connected to access switches sw1 to sw4 respectively. Assume that the bandwidth of link eh1 -> sw1 and link sw1 -> sw5 are 150 Mbps, and the bandwidth of the rest links are 100 Mbps.¶
+------+
| |
--+ sw6 +--
/ | | \
PID1 +-----+ / +------+ \ +-----+ PID2
eh1__| |_ / \ ____| |__eh2
1.2.3.4 | sw1 | \ +--|---+ +---|--+ / | sw2 | 2.3.4.5
+-----+ \ | | | |/ +-----+
\_| sw5 +---------+ sw7 |
PID3 +-----+ / | | | |\ +-----+ PID4
eh3__| |__/ +------+ +------+ \____| |__eh4
3.4.5.6 | sw3 | | sw4 | 4.5.6.7
+-----+ +-----+
The single-node ALTO topology abstraction of the network is shown in Figure 2.¶
+----------------------+
{eh1} | | {eh2}
PID1 | | PID2
+------+ +------+
| |
| |
{eh3} | | {eh4}
PID3 | | PID4
+------+ +------+
| |
+----------------------+
Consider an application overlay (e.g., a large-scale data analytics system) which wants to optimize the total throughput of the traffic among a set of end host <source, destination> pairs, say eh1 -> eh2 and eh1 -> eh4. The application can request a cost map providing end-to-end available bandwidth, using "availbw" as cost-metric and "numerical" as cost-mode.¶
The application will receive from the ALTO server that the bandwidth of eh1 -> eh2 and eh1 -> eh4 are both 100 Mbps. But this information is not enough to determine the optimal total throughput. Consider the following two cases:¶
To allow applications to distinguish the two aforementioned cases, the network needs to provide more details. In particular:¶
In general, we can conclude that to support the multiple flow scheduling use case, the ALTO framework must be extended to satisfy the following additional requirements:¶
The Path Vector extension defined in this document propose a solution to provide these details.¶
While the multiple flow scheduling problem is used to help identify the additional requirements, the Path Vector extension can be applied to a wide range of applications. This section highlights some real use cases that are reported.¶
One potential use case of the Path Vector extension is for large-scale data analytics such as [SENSE] and [LHC], where data of Gigabytes, Terabytes and even Petabytes are transferred. For these applications, the QoE is usually measured as the job completion time, which is related to the completion time of the slowest data transfer. With the Path Vector extension, an ALTO client can identify bottlenecks inside the network. Therefore, the overlay application can make optimal traffic distribution or resource reservation (i.e., proportional to the size of the transferred data), leading to optimal job completion time and network resource utilization.¶
It is getting important to know the capabilities of various ANEs between two end hosts, especially in the mobile environment. With the Path Vector extension, an ALTO client may query the "network context" information, i.e., whether the two hosts are connected to the access network through a wireless link or a wire, and the capabilities of the access network. Thus, the client may use different data transfer mechanisms, or even deploy different 5G User Plane Functions (UPF) [I-D.ietf-dmm-5g-uplane-analysis] to optimize the data transfer.¶
A growing trend in today's applications is to bring storage and computation closer to the end user for better QoE, such as Content Delivery Network (CDN), AR/VR, and cloud gaming, as reported in various documents ([I-D.contreras-alto-service-edge], [I-D.huang-alto-mowie-for-network-aware-app], and [I-D.yang-alto-deliver-functions-over-networks]).¶
With the Path Vector extension, an ALTO server can selectively reveal the CDNs and service edges that reside along the paths between different end hosts, together with their properties such as available Service Level Agreement (SLA) plans. Otherwise, the ALTO client may have to make multiple queries and potentially with the complete list of CDNs and/or service edges. While both approaches offer the same information, making multiple queries introduces larger delay and more overhead on both the ALTO server and the ALTO client.¶
This section gives a non-normative overview of the Path Vector extension. It is assumed that readers are familiar with both the base protocol [RFC7285] and the Unified Property Map extension [I-D.ietf-alto-unified-props-new].¶
To satisfies the additional requirements, this extension:¶
Thus, an ALTO client can learn about the ANEs that are critical to the QoE of a <source, destination> pair by investigating the corresponding Path Vector value (AR1), identify common ANEs if an ANE appears in the Path Vectors of multiple <source, destination> pairs (AR2), and retrieve the properties of the ANEs by searching the Unified Property Map (AR3).¶
This extension introduces Abstract Network Element (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 the end-to-end performance for traffic between a source and a destination.¶
When an ANE is defined by the ALTO server, it MUST be assigned an identifier, i.e., string of type ANEName as specified in Section 6.1, and a set of associated properties.¶
In this extension, the associations between ANE and the properties are conveyed in a Unified Property Map. Thus, they must follow the mechanisms specified in the [I-D.ietf-alto-unified-props-new].¶
Specifically, this document defines a new entity domain called ane as
specified in Section 6.2 and defines two initial properties for the ane
domain.¶
For different requests, there can be different ways of grouping components of a network and assigning ANEs. For example, an ALTO server may define an ANE for each aggregated bottleneck link between the sources and destinations specified in the request. As the aggregated bottleneck links vary for different combinations of sources and destinations, the ANEs are ephemeral and are no longer valid after the request completes. Thus, the scope of ephemeral ANEs are limited to the corresponding Path Vector response.¶
While ephemeral ANEs returned by a Path Vector response do not exist beyond that response, some of them may represent entities that are persistent and defined in a standalone Property Map. Indeed, it may be useful for clients to occasionally query properties on persistent entities, without caring about the path that traverses them. Persistent entities have a persistent ID that is registered in a Property Map, together with their properties.¶
Resource-constrained ALTO clients 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 as a new capability called ane-property-names.
The selected properties are specified in a filter called ane-property-names in
the request body, and the response MUST only return the selected properties for
the ANEs in the response.¶
The ane-property-names capability for Cost Map and for Endpoint Cost Service
are specified in Section 7.1.4 and Section 7.2.4 respectively. The
ane-property-names filter for Cost Map and Endpoint Cost Service are specified
in Section 7.1.3 and Section 7.2.3 accordingly.¶
For an ALTO client to correctly interpret the Path Vector, this extension specifies a new cost type called the Path Vector cost type, which must be included both in the Information Resource Directory and the ALTO Cost Map or Endpoint Cost Map so that an ALTO client can correctly interpret the cost values.¶
The Path Vector cost type must convey both the interpretation and semantics in the "cost-mode" and "cost-metric" respectively. Unfortunately, a single "cost-mode" value cannot fully specify the interpretation of a Path Vector, which is a compound data type. For example, in programming languages such as Java, a Path Vector will have the type of JSONArray[ANEName].¶
Instead of extending the "type system" of ALTO, this document takes a simple and backward compatible approach. Specifically, the "cost-mode" of the Path Vector cost type is "array", which indicates the value is a JSON array. Then, an ALTO client must check the value of the "cost-metric". If the value is "ane-path", meaning the JSON array should be further interpreted as a path of ANENames.¶
The Path Vector cost type is specified in Section 6.5.¶
For a basic ALTO information resource, a response contains only one type of ALTO resources, e.g., Network Map, Cost Map, or Property Map. Thus, only one round of communication is required: An ALTO client sends a request to an ALTO server, and the ALTO server returns a response, as shown in Figure 3.¶
ALTO client ALTO server
|-------------- Request ---------------->|
|<------------- Response ----------------|
The Path Vector extension, on the other hand, involves two types of information resources: Path Vectors conveyed in a Cost Map or an Endpoint Cost Map, and ANE properties conveyed in a Unified Property Map. Instead of two consecutive message exchanges, the Path Vector extension enforces one round of communication. Specifically, the ALTO client must include the source and destination pairs and the requested ANE properties in a single request, and the ALTO server must encapsulate both Path Vectors and properties associated with the ANEs in a single response, as shown in Figure 4. Since the two parts are bundled together in one response message, their orders are interchangeable. See Section 7.1.6 and Section 7.2.6 for details.¶
ALTO client ALTO server
|------------- PV Request -------------->|
|<----- PV Response (Cost Map Part) -----|
|<--- PV Response (Property Map Part) ---|
This design is based on the following considerations:¶
One approach to realize the one-round communication is to define a new media
type to contain both objects, but this violates modular design. This document
follows the standard-conforming usage of multipart/related media type defined
in [RFC2387] to elegantly combine the objects. Path Vectors are encoded as a
Cost Map or an Endpoint Cost Map, and the Property Map is encoded as a Unified
Propert Map. They are encapsulated as parts of a multipart message. The modular
composition allows ALTO servers and clients to reuse the data models of the
existing information resources. Specifically, this document addresses the
following practical issues using multipart/related.¶
ALTO uses media type to indicate the type of an entry in the Information
Resource Directory (IRD) (e.g., application/alto-costmap+json for Cost Map
and application/alto-endpointcost+json for Endpoint Cost Map). Simply
putting multipart/related as the media type, however, makes it impossible
for an ALTO client to identify the type of service provided by related
entries.¶
To address this issue, this document uses the type parameter to indicate the
root object of a multipart/related message. For a Cost Map resource, the
media-type in the IRD entry must be multipart/related with the parameter
type=application/alto-costmap+json; for an Endpoint Cost Service, the
parameter must be type=application/alto-endpointcost+json.¶
The ALTO SSE extension (see [I-D.ietf-alto-incr-update-sse]) uses
client-id to demultiplex push updates. However, client-id is provided
for each request, which introduces ambiguity when applying SSE to a Path Vector
resource.¶
To address this issue, an ALTO server must assign a unique identifier to each
part of the multipart/related response message. This identifier, referred to
as a Part Resource ID (See Section 6.6 for details), must be present in
the part message's Resource-Id header. The MIME part header must also contain
the Content-Type header, whose value is the media type of the part (e.g.,
application/alto-costmap+json, application/alto-endpointcost+json, or
application/alto-propmap+json).¶
If an ALTO server provides incremental updates for this Path Vector resource, it must generate incremental updates for each part separately. The client-id must have the following format:¶
pv-client-id '.' part-resource-id¶
where pv-client-id is the client-id assigned to the Path Vector request, and
part-resource-id is the Resource-Id header value of the part. The media-type
must match the Content-Type of the part.¶
The same problem applies to the part messages as well. The two parts must contain a version tag, which SHOULD contain a unique Resource ID. This document requires the resource-id in a Version Tag to have the following format:¶
pv-resource-id '.' part-resource-id¶
where pv-resource-id is the resource ID of the Path Vector resource in the IRD
entry, and the part-resource-id has the same value as the Resource-Id header
of the part.¶
According to [RFC2387], the Path Vector part, whose media type is
the same as the type parameter of the multipart response message, is the root
object. Thus, it is the element the application processes first. Even though the
start parameter allows it to be placed anywhere in the part sequence, it is
RECOMMENDED that the parts arrive in the same order as they are processed, i.e.,
the Path Vector part is always put as the first part, followed by the property
map part. It is also RECOMMENDED that when doing so, an ALTO server SHOULD NOT
set the start parameter, which implies the first part is the root object.¶
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.¶
The ANE domain associates property values with the Abstract Network Elements in a Property Map. Accordingly, the ANE domain always depends on a Property Map.¶
The entity identifiers are the ANE Names in the associated Property Map.¶
There is no hierarchy or inheritance for properties associated with ANEs.¶
When resource specific domains are defined with entities of domain type ane,
the defining resource for entity domain type pid MUST be a Property Map. The
media type of defining resources for the ane domain is:¶
application/alto-propmap+json¶
Specifically, for ephemeral ANEs that appear in a Path Vector response, their entity domain names MUST be ".ane" and the defining resource of these ANEs is the Property Map part of the multipart response. Meanwhile, for persistent ANEs whose entity domain name has the format of "PROPMAP.ane" where PROPMAP is the name of a Property Map resource, PROPMAP is the defining resource of these ANEs.¶
For example, the defining resource of ".ane:NET1" is the Property Map part that contains this identifier, i.e., the ANE entity ".ane:NET1" is self-defined. The defining resource of "dc-props.ane:DC1" is the Property Map with the resource ID "dc-props".¶
An ANE Property Name is encoded as a JSON string with the same format as that of Entity Property Name (Section 5.2.2 of [I-D.ietf-alto-unified-props-new]).¶
In this document, two initial ANE property types are specified,
max-reservable-bandwidth and persistent-entity-id.¶
Note that the two property types defined in this document do not depend on any information resource, so their ResourceID part must be empty.¶
----- L1
/
PID1 +---------------+ 10 Gbps +----------+ PID3
1.2.3.0/24+---+ +-----------+ +---------+ +---+3.4.5.0/24
| | MEC1 | | | |
| +-----------+ | +-----+ |
PID2 | | | +----------+
2.3.4.0/24+---+ | | NET3
| | | 15 Gbps
| | | \
+---------------+ | -------- L2
NET1 |
+---------------+
| +-----------+ | PID4
| | MEC2 | +---+4.5.6.0/24
| +-----------+ |
+---------------+
NET2
In this document, Figure 5 is used to illustrate the use of the two initial ANE property types. There are 3 sub-networks (NET1, NET2 and NET3) and two interconnection links (L1 and L2). It is assumed that each sub-network has sufficiently large bandwidth to be reserved.¶
max-reservable-bandwidth¶
To illustrate the use of max-reservable-bandwidth, consider the network in
Figure 5. An ALTO server can create an ANE for each interconnection link,
where the initial value for max-reservable-bandwidth is the link capacity.¶
persistent-entity-id¶
The persistent entity ID property is the entity identifier of the persistent ANE which an ephemeral ANE presents (See Section 5.1.2 for details). The value of this property is encoded with the format defined in Section 5.1.3 of [I-D.ietf-alto-unified-props-new]. In this format, the entity ID combines:¶
With this format, the client has all the needed information for further standalone query properties on the persistent ANE.¶
To illustrate the use of persistent-entity-id, consider the network in
Figure 5. Assume the ALTO server has a Property Map resource called
"mec-props" that defines persistent ANEs "MEC1" and "MEC2" that represent the
corresponding mobile edge computing (MEC) clusters. Since MEC1 is associated
with NET1, the persistent-entity-id of the ephemeral ANE .ane:NET1 is the
persistent entity id mec-props.ane:MEC1.¶
This document defines a new cost type, which is referred to as the Path Vector
cost type. An ALTO server MUST offer this cost type if it supports the Path
Vector extension.¶
The cost metric "ane-path" indicates 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. However, under certain scenarios where the traversal order is not crucial, an ALTO server implementation may choose to not follow strictly the physical traversal order and may even obfuscate the order intentionally, for security and performance considerations. For example, in the multi-flow bandwidth reservation use case as introduced in Section 4, only the available bandwidth of the shared bottleneck link is crucial, and the ALTO server may change the order of links appearing in the Path Vector response.¶
The cost mode "array" indicates that every cost value in a Cost Map or an Endpoint Cost Map MUST be interpreted as a JSON array object.¶
Note that this cost mode only requires the cost value to be a JSON array of JSONValue. However, an ALTO server that enables this extension MUST return a JSON array of ANEName (Section 6.1) when the cost metric is "ane-path".¶
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 resource ID and client ID related to a Path Vector resource to 31 characters.¶
This document introduces a new ALTO resource called multipart filtered cost map resource, which allows an ALTO server to provide other ALTO resources associated to the cost map resource in the same response.¶
The media type of the multipart filtered cost map resource is
multipart/related;type=application/alto-costmap+json.¶
The multipart filtered cost map is requested using the HTTP POST method.¶
The input parameters of the multipart filtered cost map are supplied in the body
of an HTTP POST request. This document extends the input parameters to a
filtered cost map with a data format indicated by the media type
application/alto-costmapfilter+json, which is a JSON object of type
PVReqFilteredCostMap, where:¶
object {
[EntityPropertyName ane-property-names<0..*>;]
} PVReqFilteredCostMap : ReqFilteredCostMap;
¶
with fields:¶
ane-property-names capability. If the field is NOT present, it
MUST be interpreted as an empty list, indicating that the ALTO server MUST NOT
return any property in the Unified Property part.¶
Example: Consider the network in Figure 1. If an ALTO client wants to
query the max-reservable-bandwidth 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: [TBD]
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" ]
}
¶
The multipart filtered cost map resource extends the capabilities defined in Section 11.3.2.4 of [RFC7285]. The capabilities are defined by a JSON object of type PVFilteredCostMapCapabilities:¶
object {
[EntityPropertyName ane-property-names<0..*>;]
} PVFilteredCostMapCapabilities : FilteredCostMapCapabilities;
¶
with fields:¶
cost-type-names field MUST only include the Path Vector cost type,
unless explicitly documented by a future extension. This also implies that the
Path Vector cost type MUST be defined in the cost-types of the Information
Resource Directory's meta field.¶
cost-type-names field includes the Path Vector cost type,
cost-constraints field MUST be false or not present unless specifically
instructed by a future document.¶
cost-type-names field includes the Path Vector cost type, the Path
Vector cost type MUST NOT be included in the testable-cost-type-names field
unless specifically instructed by a future document.¶
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.¶
The response MUST indicate an error, using ALTO protocol error handling, as defined in Section 8.5 of [RFC7285], if the request is invalid.¶
The "Content-Type" header of the response MUST be multipart/related as defined
by [RFC2387] with the following parameters:¶
Resource-Id header of the Path Vector part.¶
The body of the response MUST consist of two parts:¶
The Path Vector part MUST include Resource-Id and Content-Type in its
header. The value of Resource-Id MUST has the format of a Part Resource ID.
The Content-Type MUST be application/alto-costmap+json.¶
The body of the Path Vector part MUST be a JSON object with the same format as
defined in Section 11.2.3.6 of [RFC7285]. The JSON object MUST include the
vtag field in the meta field, which provides the version tag of the
returned cost map. The resource ID of the version tag MUST follow the format in
Section 5.3.2. The meta field MUST also include the dependent-vtags
field, whose value is a single-element array to indicate the version tag of the
network map used, where the network map is specified in the uses attribute of
the multipart filtered cost map resource in IRD.¶
The Unified Property Map part MUST also include Resource-Id and
Content-Type in its header. The value of Resource-Id has the format of a
Part Resource ID. The Content-Type MUST be application/alto-propmap+json.¶
The body of the Unified Property Map part MUST be a JSON object with the same
format as defined in Section 4.6 of [I-D.ietf-alto-unified-props-new]. The
JSON object MUST include the dependent-vtags field in the meta field. The
value of the dependent-vtags field MUST be an array of VersionTag objects as
defined by Section 10.3 of [RFC7285]. The vtag of the Path Vector part MUST
be included in the dependent-vtags. 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 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 [I-D.ietf-alto-unified-props-new]. The EntityProps has one member
for each property requested by an ALTO client if applicable.¶
If the start parameter is not present, the Path Vector part MUST be the first
part in the multipart response. If any part is NOT present, the client MUST
discard the received information and send another request if necessary.¶
Example: Consider the network in Figure 1. The response of the example
request in Section 7.1.3 is as follows, where ANE1 represents the
aggregation of all the switches in the network.¶
HTTP/1.1 200 OK
Content-Length: [TBD]
Content-Type: multipart/related; boundary=example-1;
type=application/alto-costmap+json
--example-1
Resource-Id: costmap
Content-Type: application/alto-costmap+json
{
"meta": {
"vtag": {
"resource-id": "filtered-cost-map-pv.costmap",
"tag": "d827f484cb66ce6df6b5077cb8562b0a"
},
"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
Resource-Id: propmap
Content-Type: application/alto-propmap+json
{
"meta": {
"dependent-vtags": [
{
"resource-id": "filtered-cost-map-pv.costmap",
"tag": "d827f484cb66ce6df6b5077cb8562b0a"
}
]
},
"property-map": {
".ane:ANE1": { "max-reservable-bandwidth": 100000000 }
}
}
¶
This document introduces a new ALTO resource called multipart endpoint cost resource, which allows an ALTO server to provide other ALTO resources associated to the endpoint cost resource in the same response.¶
The media type of the multipart endpoint cost resource is
multipart/related;type=application/alto-endpointcost+json.¶
The multipart endpoint cost resource is requested using the HTTP POST method.¶
The input parameters of the multipart endpoint cost resource are supplied in the
body of an HTTP POST request. This document extends the input parameters to an
endpoint cost map with a data format indicated by the media type
application/alto-endpointcostparams+json, which is a JSON object of type
PVEndpointCostParams, where¶
object {
[EntityPropertyName ane-property-names<0..*>;]
} PVReqEndpointcost : ReqEndpointcost;
¶
with fields:¶
ane-property-names in PVReqEndpointcost as the
same as in PVReqFilteredCostMap. See Section 7.1.3.¶
Example: Consider the network in Figure 1. If an ALTO client wants to
query the max-reservable-bandwidth 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: [TBD]
Content-Type: application/alto-endpointcostparams+json
{
"cost-type": {
"cost-mode": "array",
"cost-metric": "ane-path"
},
"endpoints": {
"srcs": [ "ipv4:1.2.3.4" ],
"dsts": [ "ipv4:2.3.4.5" ]
},
"ane-property-names": [ "max-reservable-bandwidth" ]
}
¶
The capabilities of the multipart endpoint cost resource are defined by a JSON object of type PVEndpointcostCapabilities, which is defined as the same as PVFilteredCostMapCapabilities. See Section 7.1.4.¶
If this resource supports persistent-entity-id, it MUST also include the
defining resources of persistent ANEs that may appear in the response.¶
The response MUST indicate an error, using ALTO protocol error handling, as defined in Section 8.5 of [RFC7285], if the request is invalid.¶
The "Content-Type" header of the response MUST be multipart/related as defined
by [RFC7285] with the following parameters:¶
The body MUST consist of two parts:¶
The Path Vector part MUST include Resource-Id and Content-Type in its
header. The value of Resource-Id MUST has the format of a Part Resource ID.
The Content-Type MUST be application/alto-endpointcost+json.¶
The body of the Path Vector part MUST be a JSON object with the same format as
defined in Section 11.5.1.6 of [RFC7285]. The JSON object MUST include the
vtag field in the meta field, which provides the version tag of the returned
endpoint cost map. The resource ID of the version tag MUST follow the format in
Section 5.3.2.¶
The Unified Property Map part MUST also include Resource-Id and
Content-Type in its header. The value of Resource-Id MUST has the format
of a Part Resource ID. The Content-Type MUST be
application/alto-propmap+json.¶
The body of the Unified Property Map part MUST be a JSON object with the same
format as defined in Section 4.6 of [I-D.ietf-alto-unified-props-new]. The
JSON object MUST include the dependent-vtags field in the meta field. The
value of the dependent-vtags field MUST be an array of VersionTag objects as
defined by Section 10.3 of [RFC7285]. The vtag of the Path Vector part MUST
be included in the dependent-vtags. 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 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
[I-D.ietf-alto-unified-props-new]. The EntityProps has one member for each
property requested by the ALTO client if applicable.¶
If the start parameter is not present, the Path Vector part MUST be the first
part in the multipart response. If any part is NOT present, the client MUST
discard the received information and send another request if necessary.¶
Example: Consider the network in Figure 1. The response of the example request in Section 7.2.3 is as follows.¶
HTTP/1.1 200 OK
Content-Length: [TBD]
Content-Type: multipart/related; boundary=example-1;
type=application/alto-endpointcost+json
--example-1
Resource-Id: ecs
Content-Type: application/alto-endpointcost+json
{
"meta": {
"vtag": {
"resource-id": "ecs-pv.costmap",
"tag": "d827f484cb66ce6df6b5077cb8562b0a"
},
"dependent-vtags": [
{
"resource-id": "my-default-networkmap",
"tag": "75ed013b3cb58f896e839582504f6228"
}
],
"cost-type": { "cost-mode": "array", "cost-metric": "ane-path" }
},
"cost-map": {
"ipv4:1.2.3.4": { "ipv4:2.3.4.5": ["ANE1"] }
}
}
--example-1
Resource-Id: propmap
Content-Type: application/alto-propmap+json
{
"meta": {
"dependent-vtags": [
{
"resource-id": "ecs-pv.costmap",
"tag": "d827f484cb66ce6df6b5077cb8562b0a"
}
]
},
"property-map": {
".ane:ANE1": { "max-reservable-bandwidth": 100000000 }
}
}
¶
This section lists some examples of Path Vector queries and the corresponding responses. Some long lines are truncated for better readability.¶
To give a comprehensive example of the Path Vector extension, we consider the network in Figure 5. The example ALTO server provides the following information resources:¶
my-default-networkmap: A Network Map resource which contains the PIDs in the
network.¶
filtered-cost-map-pv: A Multipart Filtered Cost Map resource for Path Vector,
which exposes the max-reservable-bandwidth property for the PIDs in
my-default-networkmap.¶
ane-props: A filtered Unified Property resource that exposes the
information for persistent ANEs in the network.¶
endpoint-cost-pv: A Multipart Endpoint Cost Service for Path Vector, which
exposes the max-reservable-bandwidth and the persistent-entity-id properties.¶
update-pv: An Update Stream service, which provides the incremental update
service for the endpoint-cost-pv service.¶
Below is the Information Resource Directory of the example ALTO server. To
enable the Path Vector extension, the path-vector cost type
(Section 6.5) is defined in the cost-types of the meta field, and is
included in the cost-type-names of resources filetered-cost-map-pv and
endpoint-cost-pv.¶
{
"meta": {
"cost-types": {
"path-vector": {
"cost-mode": "array",
"cost-metric": "ane-path"
}
}
},
"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
}
}
}
}
¶
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
for the Path Vector but not the ANE properties.¶
The response consists of two parts. The first part returns the array of ANEName
for each source and destination pair. There are two ANEs, where L1 represents
the interconnection link L1, and L2 represents the interconnection link L2.¶
The second part returns an empty Property Map. Note that the ANE entries are omitted since they have no properties (See Section 3.1 of [I-D.ietf-alto-unified-props-new]).¶
POST /costmap/pv HTTP/1.1
Host: alto.example.com
Accept: multipart/related;type=application/alto-costmap+json,
application/alto-error+json
Content-Length: [TBD]
Content-Type: application/alto-costmapfilter+json
{
"cost-type": {
"cost-mode": "array",
"cost-metric": "ane-path"
},
"pids": {
"srcs": [ "PID1" ],
"dsts": [ "PID3", "PID4" ]
}
}
¶
HTTP/1.1 200 OK
Content-Length: [TBD]
Content-Type: multipart/related; boundary=example-1;
type=application/alto-costmap+json
--example-1
Resource-Id: costmap
Content-Type: application/alto-costmap+json
{
"meta": {
"vtag": {
"resource-id": "filtered-cost-map-pv.costmap",
"tag": "d827f484cb66ce6df6b5077cb8562b0a"
},
"dependent-vtags": [
{
"resource-id": "my-default-networkmap",
"tag": "75ed013b3cb58f896e839582504f6228"
}
],
"cost-type": {
"cost-mode": "array",
"cost-metric": "ane-path"
}
},
"cost-map": {
"PID1": {
"PID3": [ "L1" ],
"PID4": [ "L1", "L2" ]
}
}
}
--example-1
Resource-Id: propmap
Content-Type: application/alto-propmap+json
{
"meta": {
"dependent-vtags": [
{
"resource-id": "filtered-cost-map-pv.costmap",
"tag": "d827f484cb66ce6df6b5077cb8562b0a"
}
]
},
"property-map": {
}
}
¶
The following examples demonstrate the request to the endpoint-cost-pv
resource and the corresponding response.¶
The request uses the path vector cost type in the cost-type field, and
queries the Maximum Reservable Bandwidth ANE property and the Persistent Entity
property.¶
The response consists of two parts. The first part returns the array of ANEName
for each valid source and destination pair, where NET1 represent sub-network
NET1, and AGGR is the aggregation of L1 and NET3.¶
The second part returns the requested properties of ANEs. Since NET1 has
sufficient bandwidth, it sets the max-reservable-bandwidth to a sufficiently
large number. It also represents a persistent ANE defined in the ane-props
resource, identified by ane-props.ane:datacenter1. The aggregated
max-reservable-bandwidth of ane:AGGR is constrained by the link capacity of
L1. The persistent-entity-id property is omitted as both L1 and NET3 do not
represent any persistent entity.¶
POST /endpointcost/pv HTTP/1.1
Host: alto.example.com
Accept: multipart/related;
type=application/alto-endpointcost+json,
application/alto-error+json
Content-Length: [TBD]
Content-Type: application/alto-endpointcostparams+json
{
"cost-type": {
"cost-mode": "array",
"cost-metric": "ane-path"
},
"endpoints": {
"srcs": [ "ipv4:1.2.3.4", "ipv4:2.3.4.5" ],
"dsts": [ "ipv4:3.4.5.6" ]
},
"ane-property-names": [
"max-reservable-bandwidth",
"persistent-entity-id"
]
}
¶
HTTP/1.1 200 OK
Content-Length: [TBD]
Content-Type: multipart/related; boundary=example-2;
type=application/alto-endpointcost+json
--example-2
Resource-Id: ecs
Content-Type: application/alto-endpointcost+json
{
"meta": {
"vtags": {
"resource-id": "endpoint-cost-pv.ecs",
"tag": "bb6bb72eafe8f9bdc4f335c7ed3b10822a391cef"
},
"cost-type": {
"cost-mode": "array",
"cost-metric": "ane-path"
}
},
"endpoint-cost-map": {
"ipv4:1.2.3.4": {
"ipv4:3.4.5.6": [ "NET1", "AGGR" ]
},
"ipv4:2.3.4.5": {
"ipv4:3.4.5.6": [ "NET1", "AGGR" ]
}
}
}
--example-2
Resource-Id: propmap
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:datacenter1",
},
".ane:AGGR": {
"max-reservable-bandwidth": 10000000000
}
}
}
¶
After the client obtains ane-props.ane:datacenter1, it can query the
ane-props resource to get the properties of the persistent ANE.¶
In this example, an ALTO client subscribes to the incremental update for the
multipart endpoint cost resource endpoint-cost-pv.¶
POST /updates/pv HTTP/1.1
Host: alto.example.com
Accept: text/event-stream
Content-Type: application/alto-updatestreamparams+json
Content-Length: [TBD]
{
"add": {
"ecspvsub1": {
"resource-id": "endpoint-cost-pv",
"input": <ecs-input>
}
}
}
¶
Based on the server-side process defined in [I-D.ietf-alto-incr-update-sse],
the ALTO server will send the control-uri first using Server-Sent Event (SSE),
followed by the full response of the multipart message.¶
HTTP/1.1 200 OK
Connection: keep-alive
Content-Type: text/event-stream
event: application/alto-updatestreamcontrol+json
data: {"control-uri": "https://alto.example.com/updates/streams/123"}
event: multipart/related;boundary=example-3;
type=application/alto-endpointcost+json,ecspvsub1
data: --example-3
data: Resource-ID: ecsmap
data: Content-Type: application/alto-endpointcost+json
data:
data: <endpoint-cost-map-entry>
data: --example-3
data: Resource-ID: propmap
data: Content-Type: application/alto-propmap+json
data:
data: <property-map-entry>
data: --example-3--
¶
When the contents change, the ALTO server will publish the updates for each node in this tree separately.¶
event: application/merge-patch+json, ecspvsub1.ecsmap data: <Merge patch for endpoint-cost-map-update> event: application/merge-patch+json, ecspvsub1.propmap data: <Merge patch for property-map-update>¶
The multipart filtered cost map resource and the multipart endpoint cost resource has no backward compatibility issue with legacy ALTO clients and servers. Although these two types of resources reuse the media types defined in the base ALTO protocol for the accept input parameters, they have different media types for responses. If the ALTO server provides these two types of resources, but the ALTO client does not support them, the ALTO client will ignore the resources without conducting any incompatibility.¶
This document does not specify how to integrate the Path Vector cost type with the multi-cost extension [RFC8189]. While it is not RECOMMENDED to put the Path Vector cost type with other cost types in a single query, there is no compatibility issue.¶
The extension specified in this document is NOT compatible with the original incremental update extension [I-D.ietf-alto-incr-update-sse]. A legacy ALTO client CANNOT recognize the compound client-id, and a legacy ALTO server MAY use the same client-id for updates of both parts.¶
ALTO clients and servers MUST follow the specifications given in this document to support incremental updates for a Path Vector resource.¶
The extension specified in this document is compatible with the Cost Calendar extension [I-D.ietf-alto-cost-calendar]. When used together with the Cost Calendar extension, the cost value between a source and a destination is an array of path vectors, where the k-th path vector refers to the abstract network paths traversed in the k-th time interval by traffic from the source to the destination.¶
When used with time-varying properties, e.g., maximum reservable bandwidth (maxresbw), a property of a single 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 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).¶
The constraint test is a simple approach to query the data. It allows users to
filter the query result by specifying some boolean tests. This approach is
already used in the ALTO protocol. [RFC7285] and [RFC8189] allow ALTO
clients to specify the constraints and or-constraints tests to better
filter the result.¶
However, the current 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 language for general-purpose boolean tests can be complex and is likely to be a duplicated work. Thus, it is worth looking into the direction of integrating existing well-developed query languages, e.g., XQuery and JSONiq, or their subset with ALTO.¶
Filtering the Path Vector results or developing a more sophisticated filtering mechanism is beyond the scope of this document.¶
Querying multiple ALTO information resources continuously MAY be a general requirement. And the coming issues like inefficiency and inconsistency are also general. There is no standard solving these issues yet. So we need some approach to make the ALTO client request the compound ALTO information resources in a single query.¶
This document is an extension of the base ALTO protocol, so the Security Considerations [RFC7285] of the base ALTO protocol fully apply when this extension is provided by an ALTO server.¶
The Path Vector extension requires additional considerations on two security considerations discussed in the base protocol: confidentiality of ALTO information (Section 15.3 of [RFC7285]) and availability of ALTO service (Section 15.5 of [RFC7285]).¶
For confidentiality of ALTO information, a network operator should be aware of that this extension may introduce a new risk: the Path Vector information may make network attacks easier. For example, as the Path Vector information may reveal more fine-grained internal network structures than the base protocol, an ALTO client may detect the bottleneck link and start a distributed denial-of-service (DDoS) attack involving minimal flows to conduct the in-network congestion.¶
To mitigate this risk, the ALTO server should consider protection mechanisms to reduce information exposure or obfuscate the real information, in particular, in settings where the network and the application do not belong to the same trust domain. But the implementation of Path Vector extension involving reduction or obfuscation should guarantee the requested properties are still accurate, for example, by using minimal feasible region compression algorithms [TON2019] or obfuscation protocols [SC2018][JSAC2019].¶
For availability of ALTO service, an ALTO server should be cognizant that using Path Vector extension might have a new risk: frequent requesting for Path Vectors might conduct intolerable increment of the server-side storage and break the ALTO server, for example, if an ALTO server implementation dynamically computes the Path Vectors for each requests. Hence, the service providing Path Vectors may become an entry point for denial-of-service attacks on the availability of an ALTO server. To avoid this risk, authenticity and authorization of this ALTO service may need to be better protected. Also, an ALTO server may consider using optimizations such as precomputation-and-projection mechanisms [JSAC2019].¶
This document registers a new entry to the ALTO Domain Entity Type Registry, as instructed by Section 12.2 of [I-D.ietf-alto-unified-props-new]. The new entry is as shown below in Table 1.¶
| Identifier | Entity Address Encoding | Hierarchy & Inheritance |
|---|---|---|
| ane | See Section 6.2.2 | None |
Two initial entries are registered to the ALTO Domain ane in the ALTO Entity
Property Type Registry, as instructed by Section 12.3 of
[I-D.ietf-alto-unified-props-new]. The two new entries are shown below in
Table 2.¶
| Identifier | Intended Semantics |
|---|---|
| max-reservable-bandwidth | See Section 6.4.1 |
| persistent-entity-id | See Section 6.4.2 |
The authors would like to thank discussions with Andreas Voellmy, Erran Li, Haibin Song, Haizhou Du, Jiayuan Hu, Qiao Xiang, Tianyuan Liu, Xiao Shi, Xin Wang, and Yan Luo. The authors thank Greg Bernstein (Grotto Networks), Dawn Chen (Tongji University), Wendy Roome, and Michael Scharf for their contributions to earlier drafts.¶
Revision -12¶
Revision -11¶
persistent-entities to persistent-entity-id;¶
application/alto-propmap+json as the media type of defining resources
for the ane domain;¶
Revision -10¶
revises the introduction which¶
This revision¶
We emphasize the importance of the path vector extension in two aspects:¶