ALTO WG K. Gao Internet-Draft Sichuan University Intended status: Standards Track Y. Lee Expires: January 23, 2020 Huawei S. Randriamasy Nokia Bell Labs Y. Yang Yale University J. Zhang Tongji University July 22, 2019 ALTO Extension: Path Vector draft-ietf-alto-path-vector-08 Abstract This document defines an ALTO extension that allows a resource to provide not only preferences of network paths but also correlations of network paths, including aggregations of network components and their properties on the paths between different PIDs or endpoints. The extended information can be used to improve the robustness and performance for applications in some new usage scenarios, such as high-speed data transfers and traffic optimization using in-network storage and computation. This document introduces abstract network element (ANE) as an abstraction for aggregations of network components. It extends the base protocol and the Unified Property extension to enable the capability of encoding such information in a "path vector", i.e., an array of ANEs that are traversed by traffic from a source to a destination. Requirements Language The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in RFC 2119 [RFC2119]. Status of This Memo This Internet-Draft is submitted in full conformance with the provisions of BCP 78 and BCP 79. Internet-Drafts are working documents of the Internet Engineering Task Force (IETF). Note that other groups may also distribute working documents as Internet-Drafts. The list of current Internet- Drafts is at http://datatracker.ietf.org/drafts/current/. Gao, et al. Expires January 23, 2020 [Page 1] Internet-Draft ALTO Extension: Path Vector July 2019 Internet-Drafts are draft documents valid for a maximum of six months and may be updated, replaced, or obsoleted by other documents at any time. It is inappropriate to use Internet-Drafts as reference material or to cite them other than as "work in progress." This Internet-Draft will expire on January 23, 2020. Copyright Notice Copyright (c) 2019 IETF Trust and the persons identified as the document authors. All rights reserved. This document is subject to BCP 78 and the IETF Trust's Legal Provisions Relating to IETF Documents (http://trustee.ietf.org/license-info) in effect on the date of publication of this document. Please review these documents carefully, as they describe your rights and restrictions with respect to this document. Code Components extracted from this document must include Simplified BSD License text as described in Section 4.e of the Trust Legal Provisions and are provided without warranty as described in the Simplified BSD License. Table of Contents 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 4 2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 5 3. Use Cases . . . . . . . . . . . . . . . . . . . . . . . . . . 5 3.1. Shared Risk Resource Group . . . . . . . . . . . . . . . 6 3.2. Capacity Region . . . . . . . . . . . . . . . . . . . . . 7 3.3. In-Network Caching . . . . . . . . . . . . . . . . . . . 9 4. Overview . . . . . . . . . . . . . . . . . . . . . . . . . . 9 4.1. Workflow . . . . . . . . . . . . . . . . . . . . . . . . 10 4.2. Abstract Network Element . . . . . . . . . . . . . . . . 11 4.3. Protocol Extensions . . . . . . . . . . . . . . . . . . . 12 4.3.1. Path Vector Cost Type . . . . . . . . . . . . . . . . 12 4.3.2. Property Negotiation . . . . . . . . . . . . . . . . 12 4.3.3. Multipart/Related Message . . . . . . . . . . . . . . 13 5. Basic Data Types . . . . . . . . . . . . . . . . . . . . . . 14 5.1. ANE Identifier . . . . . . . . . . . . . . . . . . . . . 15 5.2. Path Vector Cost Type . . . . . . . . . . . . . . . . . . 15 5.2.1. Cost Metric: ane-path . . . . . . . . . . . . . . . . 15 5.2.2. Cost Mode: array . . . . . . . . . . . . . . . . . . 15 5.3. ANE Domain . . . . . . . . . . . . . . . . . . . . . . . 15 5.3.1. Entity Domain Type . . . . . . . . . . . . . . . . . 16 5.3.2. Domain-Specific Entity Identifier . . . . . . . . . . 16 5.3.3. Hierarchy and Inheritance . . . . . . . . . . . . . . 16 5.4. New Resource-Specific Entity Domain Exports . . . . . . . 16 5.4.1. ANE Domain of Cost Map Resource . . . . . . . . . . . 16 Gao, et al. Expires January 23, 2020 [Page 2] Internet-Draft ALTO Extension: Path Vector July 2019 5.4.2. ANE Domain of Endpoint Cost Resource . . . . . . . . 16 5.5. ANE Properties . . . . . . . . . . . . . . . . . . . . . 16 5.5.1. ANE Property: Maximum Reservable Bandwidth . . . . . 16 5.5.2. ANE Property: Persistent Entity . . . . . . . . . . . 17 5.6. Part Resource ID . . . . . . . . . . . . . . . . . . . . 17 6. Service Extensions . . . . . . . . . . . . . . . . . . . . . 17 6.1. Multipart Filtered Cost Map for Path Vector . . . . . . . 17 6.1.1. Media Type . . . . . . . . . . . . . . . . . . . . . 17 6.1.2. HTTP Method . . . . . . . . . . . . . . . . . . . . . 17 6.1.3. Accept Input Parameters . . . . . . . . . . . . . . . 18 6.1.4. Capabilities . . . . . . . . . . . . . . . . . . . . 18 6.1.5. Uses . . . . . . . . . . . . . . . . . . . . . . . . 19 6.1.6. Response . . . . . . . . . . . . . . . . . . . . . . 19 6.2. Multipart Endpoint Cost Service for Path Vector . . . . . 20 6.2.1. Media Type . . . . . . . . . . . . . . . . . . . . . 20 6.2.2. HTTP Method . . . . . . . . . . . . . . . . . . . . . 20 6.2.3. Accept Input Parameters . . . . . . . . . . . . . . . 20 6.2.4. Capabilities . . . . . . . . . . . . . . . . . . . . 21 6.2.5. Uses . . . . . . . . . . . . . . . . . . . . . . . . 21 6.2.6. Response . . . . . . . . . . . . . . . . . . . . . . 21 7. Examples . . . . . . . . . . . . . . . . . . . . . . . . . . 22 7.1. Example: Information Resource Directory . . . . . . . . . 22 7.2. Example: Multipart Filtered Cost Map . . . . . . . . . . 24 7.3. Example: Multipart Endpoint Cost Resource . . . . . . . . 26 7.4. Example: Incremental Updates . . . . . . . . . . . . . . 28 8. Compatibility . . . . . . . . . . . . . . . . . . . . . . . . 29 8.1. Compatibility with Legacy ALTO Clients/Servers . . . . . 29 8.2. Compatibility with Multi-Cost Extension . . . . . . . . . 29 8.3. Compatibility with Incremental Update . . . . . . . . . . 29 8.4. Compatibility with Cost Calendar . . . . . . . . . . . . 29 9. General Discussions . . . . . . . . . . . . . . . . . . . . . 30 9.1. Provide Calendar for Property Map . . . . . . . . . . . . 30 9.2. Constraint Tests for General Cost Types . . . . . . . . . 30 9.3. General Multipart Resources Query . . . . . . . . . . . . 31 10. Security Considerations . . . . . . . . . . . . . . . . . . . 31 11. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 32 11.1. ALTO Cost Mode Registry . . . . . . . . . . . . . . . . 32 11.2. ALTO Entity Domain Registry . . . . . . . . . . . . . . 32 11.3. ALTO Entity Property Type Registry . . . . . . . . . . . 32 11.4. ALTO Resource Entity Domain Export Registries . . . . . 32 11.4.1. costmap . . . . . . . . . . . . . . . . . . . . . . 33 11.4.2. endpointcost . . . . . . . . . . . . . . . . . . . . 33 12. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 33 13. References . . . . . . . . . . . . . . . . . . . . . . . . . 33 13.1. Normative References . . . . . . . . . . . . . . . . . . 33 13.2. Informative References . . . . . . . . . . . . . . . . . 34 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 34 Gao, et al. Expires January 23, 2020 [Page 3] Internet-Draft ALTO Extension: Path Vector July 2019 1. Introduction The ALTO protocol is aimed to provide applications with knowledge of the underlying network topologies from the point of views of ISPs. The base protocol [RFC7285] defines cost maps and endpoint cost services that expose the preferences of network paths for a set of source and destination pairs. While the preferences of network paths are already sufficient for a wide range of applications, new application traffic patterns and new network technologies are emerging that are well beyond the domain for which existing ALTO maps are engineered, including but not limited to: Very-high-speed data transfers: Applications, such as Content Distribution Network (CDN) overlays, geo-distributed data centers and large-scale data analytics, are foundations of many Internet services today and have very large traffic between a source and a destination. Thus, the interference between traffic of different source and destination pairs cannot be omitted, which cannot be provided by or inferred from existing ALTO base protocol and extensions. In-network storage and computation: Emerging networking technologies such as network function virtualization and mobile edge computing provide storage and computation inside the network. Applications can leverage these resources to further improve their performance, for example, using in-network caching to reduce latency and bandwidth from a given source to multiple clients. However, existing ALTO extensions provide no map resources to discover available in-network services, nor any information to help ALTO clients determine how to effectively and efficiently use these services. This document specifies a new extension to incorporate these newly emerged scenarios into the ALTO framework. The essence of this extension is that an ALTO server exposes correlations of network paths in additional to preferences of network paths. The correlations of network paths are represented by path vectors. Each element in a path vector, which is referred to as an abstract network element (ANE), is the aggregation of network components on the path, such as routers, switches, links and clusters of in-network servers. If an abstract network element appears in multiple network paths, the traffic along these paths will join at this abstract network element and are subject to the corresponding resource constraints. Gao, et al. Expires January 23, 2020 [Page 4] Internet-Draft ALTO Extension: Path Vector July 2019 The availability of the path correlations by itself can help ALTO clients conduct better traffic scheduling. For example, an ALTO client can use the path correlations to conduct more intelligent end- to-end measurement and identify traffic bottlenecks. By augmenting these abstract network elements with different properties, an ALTO server can provide a more fine-grained view of the network. ALTO clients can use this view to derive information such as shared risk resource groups, capacity regions and available in-network cache locations, which can be used to improve the robustness and performance of the application traffic. 2. Terminology This document extends the ALTO base protocol [RFC7285] and the Unified Property Map extension [I-D.ietf-alto-unified-props-new]. In additional to the ones defined in these documents, this document also uses the following additional terms: o Abstract network element (ANE): An abstract network element is an abstraction of network components. It can be a link, a middleboxes, a virtualized network function (VNF), etc., or their aggregations. In a response, each abstract network element has a unique ANE identifier. o Path vector: A path vector is an array of ANE identifiers. It presents an abstract network path between source/destination points such as PIDs or endpoints. o Path vector resource: A path vector resource refers to an ALTO resource which supports the extension defined in this document. o o Path vector response: A path vector response refers to the multipart/related message returned by a path vector resource. It consists of a path vector part, i.e., the (endpoint) cost map part which contains the path vector information, and a property map part. 3. Use Cases This section describes typical use cases of the path vector extension. These use cases provide new usage scenarios of the ALTO framework. Gao, et al. Expires January 23, 2020 [Page 5] Internet-Draft ALTO Extension: Path Vector July 2019 3.1. Shared Risk Resource Group Consider an application which controls 4 end hosts (eh1, eh2, eh3 and eh4), which are connected by an ISP network with 5 switches (sw1, sw2, sw3, sw4 and sw5) and 5 links (l1, l2, l3, l4 and l5), as shown in Figure 1. Assume the end hosts are running data storage services and some analytics tasks, which requires high data availability. In order to determine the replica placement, the application must know how the end hosts will be partitioned if certain network failures happen. +-----------------+ ------------->| |<--------- / ---------->| ALTO Client |<------ \ / / +-----------------+ \ \ | | ^ | | | | | | | | | v | | | | +-----------------+ | | | | ..........| |...... | | | | . | ALTO Server | . | | | | . +-----------------+ . | | | | . . | | | v . +-----+ +-----+ . v | | eh1 --| |- l3. -| |-- eh3 | | . | sw1 | \..l1 ../ | sw4 | . | | . +-----+ \ +-----+ / +-----+ . | | . --| |-- | . | | . | sw3 | l5..| . | | . --| |-- | . | | . +-----+ / +-----+ \ +-----+ . | | . | | /..l2 l4..\ | | . | -->eh2 --| sw2 |- -| sw5 |-- eh4<-- . +-----+ +-----+ . ................................... Figure 1: Topology for the Shared Risk Resource Group and the Capacity Region Use Cases For that purpose, the application uses an ALTO client, which communicates with an ALTO server provided by the ISP network. Since the Endpoint Cost Service with only scalar cost values cannot provide essential information for the application, thus, both the client and the server have the path vector extension enabled. Assume the ISP uses shortest path routing. For simplicity, consider the data availability on eh4. The network components on the paths from all other end hosts to eh4 are as follows: Gao, et al. Expires January 23, 2020 [Page 6] Internet-Draft ALTO Extension: Path Vector July 2019 eh1->eh4: sw1, l1, sw3, l4, sw5 eh2->eh4: sw2, l2, sw3, l4, sw5 eh3->eh4: sw4, l5, sw5 These network components can be categorized into 5 categories: 1. Failure will only disconnect eh1 to eh4: sw1, l1. 2. Failure will only disconnect eh2 to eh4: sw2, l2. 3. Failure will only disconnect eh3 to eh4: sw4, l5. 4. Failure will only disconnect eh1 and eh2 to eh4: sw3, l4. 5. Failure will disconnect eh1, eh2 and eh3 to eh4: sw5. The ALTO server can then aggregate sw1 and l1 as an abstract network element, ane1. By applying the aggregation to the categories, the response may be as follows: eh1->eh4: ane1, ane4, ane5 eh2->eh4: ane2, ane4, ane5 eh3->eh4: ane3, ane5 Thus, the application can still derive the potential network partitions for all possible network failures without knowing the exact network topology, which protects the privacy of the ISP. 3.2. Capacity Region This use case uses the same topology and application settings as in Section 3.1 as shown in Figure 1. Assume the capacity of each link is 10 Gbps, except l5 whose capacity is 5 Gbps . Assume the application is running a map-reduce task, where the optimal traffic scheduling is usually referred to the co-flow scheduling problem. Consider a simplified co-flow scheduling problem, e.g., the first stage of a map-reduce task which needs to transfer data from two data nodes (eh1 and eh3) to the mappers (eh2 and eh4). In order to optimize the job completion time, the application needs to determine the bottleneck of the transfers. If the ALTO server encodes the routing cost as bandwidth of the path, the client will obtain the following information: eh1->eh2: 10 Gbps, eh1->eh4: 10 Gbps, eh3->eh2: 10 Gbps, eh3->eh4: 5 Gbps. Gao, et al. Expires January 23, 2020 [Page 7] Internet-Draft ALTO Extension: Path Vector July 2019 However, it does not provide sufficient information to determine the bottleneck. With the path vector extension, the ALTO server will first return the correlations of network paths between eh1, eh3 and eh2, eh4, as follows: eh1->eh2: ane1 (l1), ane2 (l2), eh1->eh4: ane1 (l1), ane4 (l4), eh3->eh2: ane3 (l3), ane2 (l2), eh3->eh3: ane5 (l5). Meanwhile, the ALTO server can also return the capacity of each ANE: ane1.capacity = 10 Gbps, ane2.capacity = 10 Gbps, ane3.capacity = 10 Gbps, ane4.capacity = 10 Gbps, ane5.capacity = 5 Gbps. With the correlation of network paths and the link capacity property, the client is able to derive the capacity region of data transfer rates. Let x1 denote the transfer rate of eh1->eh2, x2 denote the rate of eh1->eh4, x3 denote the rate of eh3->eh2, and x4 denote the rate of eh3->eh4. The application can derive the following information from the responses: eh1->eh2 eh1->eh4 eh3->eh2 eh3->eh4 capaity ane1 1 1 0 0 | 10 Gbps ane2 1 0 1 0 | 10 Gbps ane3 0 0 1 0 | 10 Gbps ane4 0 1 0 0 | 10 Gbps ane5 0 0 0 1 | 5 Gbps Specifically, the coefficient matrix on the left hand side is the transposition of the matrix directly derived from the path vector part, and the right-hand-side vector is directly derived from the property map part. Thus, the bandwidth constraints of the data transfers are as follows: x1 + x2 <= 10 Gbps (ane1), x1 + x3 <= 10 Gbps (ane2), x2 + x3 <= 10 Gbps (ane3), x2 <= 10 Gbps (ane4), x4 <= 5 Gbps (ane5). Gao, et al. Expires January 23, 2020 [Page 8] Internet-Draft ALTO Extension: Path Vector July 2019 3.3. In-Network Caching Consider an application which controls 3 end hosts (eh1, eh2 and eh3), which are connected by an ISP network and the Internet, as shown in Figure 2. Assume two clients at end hosts eh2 and eh3 are downloading the same data from a data server at eh1. Meanwhile, the network provider offers an in-network caching service at the gateway. +-------------+ ------->| |<----------------------- / ----->| ALTO Client |<------- \ / / +-------------+ | \ / / v | / / +-------------+ | / / ........................| ALTO Server |...... | / / . +-------------+ . | / / . +---------+ . | | | . -+ Caching | . | | | . / | Proxy | . | | |S .+-------+ / +---------+ . | | -->eh1--| sub |_ | . | | .| net 1 | \ +------+ +----------+. | | .+-------+ ---| | | |. v C2 | . | Gate +---------+ Internet |--eh3 | C1 .+-------+ --| way | | |. ----->eh2--| sub |__/ +------+ +----------+. .| net 2 | . .+-------+ . ............................................. Figure 2: Topology for the In-Network Caching Use Case. With the path vector extension enabled, the ALTO server can expose two types of information Without the traffic correlation information, the ALTO client cannot know whether or how the traffic goes through the proxy. For example, if subnet1 and subnet2 are directly connected and the traffic from eh1 to eh2 bypasses the gateway, the in-network cache can only be used for traffic from C2 to S and is less effective. 4. Overview This section gives a top-down overview of approaches adopted by the path vector extension, with discussions to fully explore the design space. 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]. Gao, et al. Expires January 23, 2020 [Page 9] Internet-Draft ALTO Extension: Path Vector July 2019 4.1. Workflow The workflow of the base ALTO protocol consists of one round of communication: An ALTO client sends a request to an ALTO server, and the ALTO server returns a response, as shown in Figure 3. Each response contains only one type of ALTO resources, e.g., network maps, cost maps, or property maps. +-------------+ +-------------+ | ALTO Client | | ALTO Server | +-------------+ +-------------+ | Request | |--------------------------------------->| | | | Response | |<---------------------------------------| | | . . . . . . . . . | PV Request | |--------------------------------------->| | | | PV Response (Cost Map Part) | |<---------------------------------------| | | | PV Response (Property Map Part) | |<---------------------------------------| | | Figure 3: Information Exchange Process of the base ALTO Protocol and the Path Vector Extension The path vector extension, on the other hand, CAN be decomposed to two types of information resources. First, path vectors, which represent the correlations of network paths for all pairs in the requst, CAN be encoded as an (endpoint) cost map with an extended cost type. Second, properties associated with the ANEs CAN be encoded as a property map. Instead of making two consecutive queries, however, the path vector extension adopts a workflow which also consists of only one round of communication, based on the following reasons: 1. ANE Computation Flexibility. For better scalability, flexibility and privacy, Abstract Network Elements MAY be constructed on demand, and potentially based on the properties (See Section 4.2 for more details). If sources and destinations are not in the Gao, et al. Expires January 23, 2020 [Page 10] Internet-Draft ALTO Extension: Path Vector July 2019 same request as the properties, an ALTO server either CANNOT construct ANEs on-demand, or MUST wait until both requests are received. 2. Server Scalability. As ANEs are constructed on demand, mappings of each ANE to its underlying network devices and resources CAN be different in different queries. In order to respond to the second request correctly, an ALTO server MUST store the mapping of each path vector request until the client fully retrieves the property information, which CAN substantially harm the server scalability and potentially lead to Denial-of-Service attacks. Thus, the path vector extension encapsulates all essential information in one request, and returns both path vectors and properties associated with the ANEs in a single response. See Section 4.3 for more details. 4.2. Abstract Network Element A key design in the path vector extension is abstract network element. Abstract network elements can be statically generated, for example, based on geo-locations, OSPF areas, or simply the raw network topology. They CAN also be generated dynamically, based on a client's request. This on-demand ANE generation allows for better scalability, flexibility and privacy enhancement. Consider an extreme case where the client only queries the bandwidth between one source and one destination in the topology shown in Figure 4. Without knowing in prior the desired property, an ALTO server MAY need to include all network components on the paths for high accuracy. However, with the prior knowledge that the client only asks for the bandwidth information, an ALTO server CAN either 1) selectively pick the link with the smallest available bandwidth, or 2) dynamically generate a new ANE whose available bandwidth is the smallest value of the links' on the path. Thus, an ALTO server can provide accurate information with very little leak of its internal network topology. ANEs MAY also be constructed based on algebraic aggregations, please see [TON2019] for more details. +-----+ +-----+ +-----+ eh1 --| sw1 |--| sw2 |--...--| swN |-- eh2 +-----+ +-----+ +-----+ Figure 4: Topology for Dynamic ANE Example. An ANE is uniquely identified by an ANE identifier (see Section 5.1) in the same response. However, since ANEs CAN be generated dynamically, an ALTO client MUST NOT assume that ANEs with the same Gao, et al. Expires January 23, 2020 [Page 11] Internet-Draft ALTO Extension: Path Vector July 2019 identifier but from different queries refer to the same aggregation of network components. This approach simplifies the management of ANE identifiers at ALTO servers, and increases the difficulty to infer the real network topology with cross queries. It is RECOMMENDED that the identifiers of statically generated ANEs be anonymized in the path vector response, for example, by shuffling the ANEs and shrinking their identifier space to [1, N], where N is the number of ANEs etc. 4.3. Protocol Extensions Section 4.1 has well articulated the reasons to complete the information exchange in a single round of communication. This section introduces the three major extended components to the base ALTO protocol and the Unified Property Map extension, as shown in Table 1. +------------------------+-------+----------+-----------+ | Component | IRD | Request | Response | +------------------------+-------+----------+-----------+ | Path Vector Cost Type | Yes | Yes | Yes | | Property Negotiation | Yes | Yes | Yes | | Multipart Message | Yes | No | Yes | +------------------------+-------+----------+-----------+ Table 1: Extended Components and Where They Apply. 4.3.1. Path Vector Cost Type Existing cost modes defined in [RFC7285] allow only scalar cost values. However, the path vector extension MUST convey vector format information. To fulfill this requirement, this document defines a new cost mode named "array", which indicates that the cost value MUST be interpreted as an array of JSONValue. This document also introduces a new cost metric "ane-path" to convey an array of ANE identifiers. The combination of the "array" cost mode and the "ane-path" cost metric also complies best with the ALTO base protocol, where cost mode specifies the interpretation of a cost value, and cost metric conveys the meaning. 4.3.2. Property Negotiation Similar to cost types, an ALTO server MAY only support a given set of ANE properties in a path vector information resource. Meanwhile, an ALTO client MAY only require a subset of the available properties. Thus, a property negotiation process is required. Gao, et al. Expires January 23, 2020 [Page 12] Internet-Draft ALTO Extension: Path Vector July 2019 This document uses a similar approach as the negotiation process of cost types: the available properties for a given resource are announced in the Information Resource Directory and more specifically, in a new capability called "ane-properties"; the selected properties SHOULD be specified in a new filter called "ane- properties" in the request body; the response MUST return and only return the selected properties for the ANEs in the response, if applicable. 4.3.3. Multipart/Related Message Path vectors and the property map containing the ANEs are two different types of objects, but they need to be encoded in one message. One approach is to define a new media type to contain both objects, but this violates modular design. This document uses standard-conforming usage of "multipart/related" media type defined in [RFC2387] to elegantly combine the objects. Path vectors are encoded as a cost map or an endpoint cost map, and the property map is encoded as a Unified Propert Map. They are encapsulated as parts of a multipart message. The modular composition allows ALTO servers and clients to reuse the data models of the existing information resources. Specifically, this document addresses the following practical issues using "multipart/related". 4.3.3.1. Identifying the Media Type of the Root Object ALTO uses media type to indicate the type of an entry in the Information Resource Directory (IRD) (e.g., "application/alto- costmap+json" for cost map and "application/alto-endpointcost+json" for endpoint cost map). Simply putting "multipart/related" as the media type, however, makes it impossible for an ALTO client to identify the type of service provided by related entries. To address this issue, this document uses the "type" parameter to indicate the root object of a multipart/related message. For a cost 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". 4.3.3.2. References to Part Messages The ALTO SSE extension (see [I-D.ietf-alto-incr-update-sse]) uses "client-id" to demultiplex push updates. However, "client-id" is provided for each request, which introduces ambiguity when applying SSE to a path vector resource. Gao, et al. Expires January 23, 2020 [Page 13] Internet-Draft ALTO Extension: Path Vector July 2019 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 5.6 for details), MUST be present in the part message's "Resource-Id" header. The MIME part header MUST also contain the "Content-Type" header, whose value is the media type of the part (e.g., "application/alto- costmap+json", "application/alto-endpointcost+json", or "application/ alto-propmap+json"). If an ALTO server provides incremental updates for this path vector resource, it MUST generate incremental updates for each part separately. The client-id MUST have the following format: pv-client-id '.' part-resource-id where pv-client-id is the client-id assigned to the path vector request, and part-resource-id is the "Resource-Id" header value of the part. The media-type MUST match the "Content-Type" of the part. The same problem happens inside the part messages as well. The two parts MUST contain a version tag, which SHOULD contain a unique Resource ID. This document requires the resource-id in a Version Tag to have the following format: pv-resource-id '.' part-resource-id where pv-resource-id is the resource ID of the path vector resource in the IRD entry, and the part-resource-id has the same value as the "Resource-Id" header of the part. 4.3.3.3. Order of Part Messages According to RFC 2387 [RFC2387], the path vector part, whose media type is the same as the "type" parameter of the multipart response message, is the root object. Thus, it is the element the application processes first. Even though the "start" parameter allows it to be placed anywhere in the part sequence, it is RECOMMENDED that the parts arrive in the same order as they are processed, i.e., the path vector part is always put as the first part, followed by the property map part. It is also RECOMMENDED that when doing so, an ALTO server SHOULD NOT set the "start" parameter, which implies the first part is the root object. 5. Basic Data Types Gao, et al. Expires January 23, 2020 [Page 14] Internet-Draft ALTO Extension: Path Vector July 2019 5.1. ANE Identifier An ANE identifier is encoded as a JSON string. The string MUST be no more than 64 characters, and it MUST NOT contain characters other than US-ASCII alphanumeric characters (U+0030-U+0039, U+0041-U+005A, and U+0061-U+007A), the hyphen ("-", U+002D), the colon (":", U+003A), the at sign ("@", code point U+0040), the low line ("_", U+005F), or the "." separator (U+002E). The "." separator is reserved for future use and MUST NOT be used unless specifically indicated in this document, or an extension document. The type ANEIdentifier is used in this document to indicate a string of this format. 5.2. Path Vector Cost Type This document defines a new cost type, which is referred to as the "path vector" cost type. An ALTO server MUST offer this cost type if it supports the path vector extension. 5.2.1. Cost Metric: ane-path This cost metric conveys an array of ANE identifiers, where each identifier uniquely represents an ANE traversed by traffic from a source to a destination. 5.2.2. Cost Mode: array This cost mode indicates that every cost value in a cost map or an endpoint cost map MUST be interpreted as a JSON array object. Note that this cost mode only requires the cost value to be a JSON array of JSONValue. However, an ALTO server that enables this extension MUST return a JSON array of ANEIdentifier (Section 5.1) when the cost metric is "ane-path". 5.3. ANE Domain This document specifies a new ALTO entity domain called "ane" in addition to the ones in [I-D.ietf-alto-unified-props-new]. The ANE domain associates property values with the ANEs in a network. The entity in ANE domain is often used in the path vector by cost maps or endpoint cost resources. Accordingly, the ANE domain always depends on a cost map or an endpoint cost map. Gao, et al. Expires January 23, 2020 [Page 15] Internet-Draft ALTO Extension: Path Vector July 2019 5.3.1. Entity Domain Type ane 5.3.2. Domain-Specific Entity Identifier The entity identifier of ANE domain uses the same encoding as ANEIdentifier (Section 5.1). 5.3.3. Hierarchy and Inheritance There is no hierarchy or inheritance for properties associated with ANEs. 5.4. New Resource-Specific Entity Domain Exports 5.4.1. ANE Domain of Cost Map Resource If an ALTO cost map resource supports "ane-path" cost metric, it can export an "ane" typed entity domain defined by the union of all sets of ANE names, where each set of ANE names are an "ane-path" metric cost value in this ALTO cost map resource. 5.4.2. ANE Domain of Endpoint Cost Resource If an ALTO endpoint cost resource supports "ane-path" cost metric, it can export an "ane" typed entity domain defined by the union of all sets of ANE names, where each set of ANE names are an "ane-path" metric cost value in this ALTO endpoint cost resource. 5.5. ANE Properties 5.5.1. ANE Property: Maximum Reservable Bandwidth The maximum reservable bandwidth property conveys the maximum bandwidth that can be reserved for traffic from a source to a destination and is indicated by the property name "maxresbw". The value MUST be encoded as a numerical cost value as defined in Section 6.1.2.1 of [RFC7285] and the unit is bit per second. If this property is requested but is missing for a given ANE, it MUST be interpreted as that the ANE does not support bandwidth reservation but have sufficiently large bandwidth for all traffic that traverses it. Gao, et al. Expires January 23, 2020 [Page 16] Internet-Draft ALTO Extension: Path Vector July 2019 5.5.2. ANE Property: Persistent Entity The persistent entity property conveys the physical or logical network entities (e.g., links, in-network caching service) that are contained by an abstract network element. It is indicated by the property name "persistent-entity". The value is encoded as a JSON array of entity identifiers ([I-D.ietf-alto-unified-props-new]). These entity identifiers are persistent so that a client CAN further query their properties for future use. If this property is requested but is missing for a given ANE, it MUST be interpreted as that no such entities exist in this ANE. 5.6. Part Resource ID A Part Resource ID is encoded as a JSON string with the same format as that of the Resource ID (Section 10.2 of [RFC7285]). WARNING: Even though the client-id assigned to a path vector request and the Part Resource ID MAY contain up to 64 characters by their own definition. Their concatenation (see Section 4.3.3.2) MUST also conform to the same length constraint. The same requirement applies to the resource ID of the path vector resource, too. Thus, it is RECOMMENDED to limit the length of resource ID and client ID related to a path vector resource to 31 characters. 6. Service Extensions 6.1. Multipart Filtered Cost Map for Path Vector This document introduces a new ALTO resource called multipart filtered cost map resource, which allows an ALTO server to provide other ALTO resources associated to the cost map resource in the same response. 6.1.1. Media Type The media type of the multipart filtered cost map resource is "multipart/related;type=application/alto-costmap+json". 6.1.2. HTTP Method The multipart filtered cost map is requested using the HTTP POST method. Gao, et al. Expires January 23, 2020 [Page 17] Internet-Draft ALTO Extension: Path Vector July 2019 6.1.3. Accept Input Parameters The input parameters of the multipart filtered cost map are supplied in the body of an HTTP POST request. This document extends the input parameters to a filtered cost map with a data format indicated by the media type "application/alto-costmapfilter+json", which is a JSON object of type PVReqFilteredCostMap, where: object { [PropertyName ane-properties<0..*>;] } PVReqFilteredCostMap : ReqFilteredCostMap; with fields: ane-properties: A list of properties that are associated with the ANEs. Each property in this list MUST match one of the supported ANE properties indicated in the resource's "ane-properties" 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. 6.1.4. Capabilities The multipart filtered cost map resource extends the capabilities defined in Section 11.3.2.4 of [RFC7285]. The capabilities are defined by a JSON object of type PVFilteredCostMapCapabilities: object { [PropertyName ane-properties<0..*>;] } PVFilteredCostMapCapabilities : FilteredCostMapCapabilities; with fields: cost-type-names: The "cost-type-names" field MUST only include the path vector cost type, unless explicitly documented by a future extension. This also implies that the path vector cost type MUST be defined in the "cost-types" of the Information Resource Directory's "meta" field. ane-properties: Defines a list of ANE properties that can be returned. If the field is NOT present, it MUST be interpreted as an empty list, indicating the ALTO server CANNOT provide any ANE property. Gao, et al. Expires January 23, 2020 [Page 18] Internet-Draft ALTO Extension: Path Vector July 2019 6.1.5. Uses The resource ID of the network map based on which the PIDs in the returned cost map will be defined. If this resource supports "persistent-entities", it MUST also include ALL the resources that exposes the entities that MAY appear in the response. 6.1.6. Response The response MUST indicate an error, using ALTO protocol error handling, as defined in Section 8.5 of [RFC7285], if the request is invalid. The "Content-Type" header of the response MUST be "multipart/related" as defined by [RFC2387] with the following parameters: type: The type parameter MUST be "application/alto-costmap+json". Note that [RFC2387] permits both parameters with and without the double quotes. start: The start parameter MUST be a quoted string where the quoted part has the same value as the "Resource-ID" header in the first part. boundary: The boundary parameter is as defined in [RFC2387]. The body of the response consists of two parts. The first part MUST include "Resource-Id" and "Content-Type" in its header. The value of "Resource-Id" MUST has the format of a Part Resource ID. The "Content-Type" MUST be "application/alto- costmap+json". The body of the first part MUST be a JSON object with the same format as defined in Section 11.2.3.6 of [RFC7285]. The JSON object MUST include the "vtag" field in the "meta" field, which provides the version tag of the returned cost map. The resource ID of the version tag MUST follow the format in Section 4.3.3.2. The "meta" field MUST also include the "dependent-vtags" field, whose value is a single- element array to indicate the version tag of the network map used, where the network map is specified in the "uses" attribute of the multipart filtered cost map resource in IRD. The second part MUST also include "Resource-Id" and "Content-Type" in its header. The value of "Resource-Id" has the format of a Part Resource ID. The "Content-Type" MUST be "application/alto- propmap+json". Gao, et al. Expires January 23, 2020 [Page 19] Internet-Draft ALTO Extension: Path Vector July 2019 The body of the second part MUST be a JSON object with the same format as defined in Section 4.6 of [I-D.ietf-alto-unified-props-new]. The JSON object MUST include the "dependent-vtags" field in the "meta" field. The value of the "dependent-vtags" field MUST be an array of VersionTag objects as defined by Section 10.3 of [RFC7285]. The "vtag" of the first part MUST be included in the "dependent-vtags". If "persistent-entities" is requested, the version tags of the dependent resources that MAY expose the entities in the response MUST also be included. The PropertyMapData has one member for each ANE identifier that appears in the first part, where the EntityProps has one member for each property requested by the client if applicable. 6.2. Multipart Endpoint Cost Service for Path Vector This document introduces a new ALTO resource called multipart endpoint cost resource, which allows an ALTO server to provide other ALTO resources associated to the endpoint cost resource in the same response. 6.2.1. Media Type The media type of the multipart endpoint cost resource is "multipart/related;type=application/alto-endpointcost+json". 6.2.2. HTTP Method The multipart endpoint cost resource is requested using the HTTP POST method. 6.2.3. Accept Input Parameters The input parameters of the multipart endpoint cost resource are supplied in the body of an HTTP POST request. This document extends the input parameters to an endpoint cost map with a data format indicated by the media type "application/alto- endpointcostparams+json", which is a JSON object of type PVEndpointCostParams, where object { [PropertyName ane-properties<0..*>;] } PVReqEndpointcost : ReqEndpointcost; with fields: ane-properties: This document defines the "ane-properties" in PVReqEndpointcost as the same as in PVReqFilteredCostMap. See Section 6.1.3. Gao, et al. Expires January 23, 2020 [Page 20] Internet-Draft ALTO Extension: Path Vector July 2019 6.2.4. Capabilities The capabilities of the multipart endpoint cost resource are defined by a JSON object of type PVEndpointcostCapabilities, which is defined as the same as PVFilteredCostMapCapabilities. See Section 6.1.4. 6.2.5. Uses If a multipart endpoint cost resource supports "persistent-entities", the "uses" field in its IRD entry MUST include ALL the resources which exposes the entities that MAY appear in the response. 6.2.6. 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 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". start: The start parameter MUST be a quoted string where the quoted part has the same value as the "Resource-ID" header in the first part. boundary: The boundary parameter is as defined in [RFC2387]. The body consists of two parts: The first part MUST include "Resource-Id" and "Content-Type" in its header. The value of "Resource-Id" MUST has the format of a Part Resource ID. The "Content-Type" MUST be "application/alto- endpointcost+json". The body of the first part MUST be a JSON object with the same format as defined in Section 11.5.1.6 of [RFC7285]. The JSON object MUST include the "vtag" field in the "meta" field, which provides the version tag of the returned endpoint cost map. The resource ID of the version tag MUST follow the format in Section 4.3.3.2. The second part MUST also include "Resource-Id" and "Content-Type" in its header. The value of "Resource-Id" MUST has the format of a Part Resource ID. The "Content-Type" MUST be "application/alto- propmap+json". Gao, et al. Expires January 23, 2020 [Page 21] Internet-Draft ALTO Extension: Path Vector July 2019 The body of the second part MUST be a JSON object with the same format as defined in Section 4.6 of [I-D.ietf-alto-unified-props-new]. The JSON object MUST include the "dependent-vtags" field in the "meta" field. The value of the "dependent-vtags" field MUST be an array of VersionTag objects as defined by Section 10.3 of [RFC7285]. The "vtag" of the first part MUST be included in the "dependent-vtags". If "persistent-entities" is requested, the version tags of the dependent resources that MAY expose the entities in the response MUST also be included. The PropertyMapData has one member for each ANE identifier that appears in the first part, where the EntityProps has one member for each property requested by the client if applicable. 7. Examples This section lists some examples of path vector queries and the corresponding responses. Some long lines are truncated for better readability. 7.1. Example: Information Resource Directory Below is an example of an Information Resource Directory which enables the path vector extension. Some critical modifications include: o The "path-vector" cost type (Section 5.2) is defined in the "cost- types" of the "meta" field. o The "cost-map-pv" information resource provides a multipart filtered cost map resource, which exposes the Maximum Reservable Bandwidth ("maxresbw") property. o The "http-proxy-props" information resource provides a filtered unified property map resource, which exposes the HTTP proxy entity domain (encoded as "http-proxy") and the "price" property. Note that HTTP proxy is NOT a valid entity domain yet and is used here only for demonstration. o The "endpoint-cost-pv" information resource provides a multipart endpoint cost resource. It exposes the Maximum Reservable Bandwidth ("maxresbw") property and the Persistent Entity property ("persistent-entities"). The persistent entities MAY come from the "http-proxy-props" resource. o The "update-pv" information resource provides the incremental update ([I-D.ietf-alto-incr-update-sse]) service for the "endpoint-cost-pv" resource. Gao, et al. Expires January 23, 2020 [Page 22] Internet-Draft ALTO Extension: Path Vector July 2019 { "meta": { "cost-types": { "path-vector": { "cost-mode": "array", "cost-metric": "ane-path" } } }, "resources": { "my-default-networkmap": { "uri" : "http://alto.example.com/networkmap", "media-type" : "application/alto-networkmap+json" }, "cost-map-pv": { "uri": "http://alto.example.com/costmap/pv", "media-type": "multipart/related; type=application/alto-costmap+json", "accepts": "application/alto-costmapfilter+json", "capabilities": { "cost-type-names": [ "path-vector" ], "ane-properties": [ "maxresbw" ] }, "uses": [ "my-default-networkmap" ] }, "http-proxy-props": { "uri": "http://alto.example.com/proxy-props", "media-type": "application/alto-propmap+json", "accpets": "application/alto-propmapparams+json", "capabilities": { "mappings": { "http-proxy": [ "price" ] } } }, "endpoint-cost-pv": { "uri": "http://alto.exmaple.com/endpointcost/pv", "media-type": "multipart/related; type=application/alto-endpointcost+json", "accepts": "application/alto-endpointcostparams+json", "capabilities": { "cost-type-names": [ "path-vector" ], "ane-properties": [ "maxresbw", "persistent-entities" ] }, "uses": [ "http-proxy-props" ] }, "update-pv": { "uri": "http://alto.example.com/updates/pv", Gao, et al. Expires January 23, 2020 [Page 23] Internet-Draft ALTO Extension: Path Vector July 2019 "media-type": "text/event-stream", "uses": [ "endpoint-cost-pv" ], "accepts": "application/alto-updatestreamparams+json", "capabilities": { "support-stream-control": true } } } } 7.2. Example: Multipart Filtered Cost Map The following examples demonstrate the request to the "cost-map-pv" resource and the corresponding response. The request uses the path vector cost type in the "cost-type" field. The "ane-properties" 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 ANE identifiers for each source and destination pair. There are three ANEs, where "ane:L001" is shared by traffic from "PID1" to both "PID2" and "PID3". The second part returns an empty property map. Note that the ANE entries are omitted since they have no properties (See Section 3.1 of [I-D.ietf-alto-unified-props-new]). POST /costmap/pv HTTP/1.1 Host: alto.example.com Accept: multipart/related;type=application/alto-costmap+json, application/alto-error+json Content-Length: [TBD] Content-Type: application/alto-costmapfilter+json { "cost-type": { "cost-mode": "array", "cost-metric": "ane-path" }, "pids": { "srcs": [ "PID1" ], "dsts": [ "PID2", "PID3" ] } } HTTP/1.1 200 OK Content-Length: [TBD] Gao, et al. Expires January 23, 2020 [Page 24] Internet-Draft ALTO Extension: Path Vector July 2019 Content-Type: multipart/related; boundary=example-1; type=application/alto-costmap+json --example-1 Resource-Id: costmap Content-Type: application/alto-costmap+json { "meta": { "vtag": { "resource-id": "cost-map-pv.costmap", "tag": "d827f484cb66ce6df6b5077cb8562b0a" }, "dependent-vtags": [ { "resource-id": "my-default-networkmap", "tag": "75ed013b3cb58f896e839582504f6228" } ], "cost-type": { "cost-mode": "array", "cost-metric": "ane-path" } }, "cost-map": { "PID1": { "PID2": [ "ane:L001", "ane:L003" ], "PID3": [ "ane:L001", "ane:L004" ] } } } --example-1 Resource-Id: propmap Content-Type: application/alto-propmap+json { "meta": { "dependent-vtags": [ { "resource-id": "cost-map-pv.costmap", "tag": "d827f484cb66ce6df6b5077cb8562b0a" } ] }, "property-map": { } } Gao, et al. Expires January 23, 2020 [Page 25] Internet-Draft ALTO Extension: Path Vector July 2019 7.3. Example: Multipart Endpoint Cost Resource The following examples demonstrate the request to the "endpoint-cost- pv" resource and the corresponding response. The request uses the path vector cost type in the "cost-type" field, and queries the Maximum Reservable Bandwidth ANE property and the Persistent Entity property. The response consists of two parts. The first part returns the array of ANE identifiers for each valid source and destination pair. The second part returns the requested properties of ANEs in the first part. The "ane:NET001" element contains an HTTP proxy entity, which can be further used by the client. Since it does not contain a "maxresbw" property, the client SHOULD assume it does NOT support bandwidth reservation but will NOT become a traffic bottleneck, as specified in Section 5.5.1. POST /endpointcost/pv HTTP/1.1 Host: alto.example.com Accept: multipart/related; type=application/alto-endpointcost+json, application/alto-error+json Content-Length: [TBD] Content-Type: application/alto-endpointcostparams+json { "cost-type": { "cost-mode": "array", "cost-metric": "ane-path" }, "endpoints": { "srcs": [ "ipv4:192.0.2.2" ], "dsts": [ "ipv4:192.0.2.89", "ipv4:203.0.113.45", "ipv6:2001:db8::10" ] }, "ane-properties": [ "maxresbw", "persistent-entities" ] } HTTP/1.1 200 OK Content-Length: [TBD] Content-Type: multipart/related; boundary=example-2; type=application/alto-endpointcost+json --example-2 Resource-Id: ecs Gao, et al. Expires January 23, 2020 [Page 26] Internet-Draft ALTO Extension: Path Vector July 2019 Content-Type: application/alto-endpointcost+json { "meta": { "vtags": { "resource-id": "endpoint-cost-pv.ecs", "tag": "bb6bb72eafe8f9bdc4f335c7ed3b10822a391cef" }, "cost-type": { "cost-mode": "array", "cost-metric": "ane-path" } }, "endpoint-cost-map": { "ipv4:192.0.2.2": { "ipv4:192.0.2.89": [ "ane:NET001", "ane:L002" ], "ipv4:203.0.113.45": [ "ane:NET001", "ane:L003" ] } } } --example-2 Resource-Id: propmap Content-Type: application/alto-propmap+json { "meta": { "dependent-vtags": [ { "resource-id": "endpoint-cost-pv.ecs", "tag": "bb6bb72eafe8f9bdc4f335c7ed3b10822a391cef" }, { "resource-id": "http-proxy-props", "tag": "bf3c8c1819d2421c9a95a9d02af557a3" } ] }, "property-map": { "ane:NET001": { "persistent-entities": [ "http-proxy:192.0.2.1" ] }, "ane:L002": { "maxresbw": 48000000 }, "ane:L003": { "maxresbw": 35000000 } } } Gao, et al. Expires January 23, 2020 [Page 27] Internet-Draft ALTO Extension: Path Vector July 2019 7.4. Example: Incremental Updates In this example, an ALTO client subscribes to the incremental update for the multipart endpoint cost resource "endpoint-cost-pv". POST /updates/pv HTTP/1.1 Host: alto.example.com Accept: text/event-stream Content-Type: application/alto-updatestreamparams+json Content-Length: [TBD] { "add": { "ecspvsub1": { "resource-id": "endpoint-cost-pv", "input": } } } Based on the server-side process defined in [I-D.ietf-alto-incr-update-sse], the ALTO server will send the "control-uri" first using Server-Sent Event (SSE), followed by the full response of the multipart message. HTTP/1.1 200 OK Connection: keep-alive Content-Type: text/event-stream event: application/alto-updatestreamcontrol+json data: {"control-uri": "http://alto.example.com/updates/streams/1414"} event: multipart/related;boundary=example-3; type=application/alto-endpointcost+json,ecspvsub1 data: --example-3 data: Resource-ID: ecsmap data: Content-Type: application/alto-endpointcost+json data: data: data: --example-3 data: Resource-ID: propmap data: Content-Type: application/alto-propmap+json data: data: data: --example-3-- When the contents change, the ALTO server will publish the updates for each node in this tree separately. Gao, et al. Expires January 23, 2020 [Page 28] Internet-Draft ALTO Extension: Path Vector July 2019 event: application/merge-patch+json, ecspvsub1.ecsmap data: event: application/merge-patch+json, ecspvsub1.propmap data: 8. Compatibility 8.1. Compatibility with Legacy ALTO Clients/Servers The multipart filtered cost map resource and the multipart endpoint cost resource has no backward compatibility issue with legacy ALTO clients and servers. Although these two types of resources reuse the media types defined in the base ALTO protocol for the accept input parameters, they have different media types for responses. If the ALTO server provides these two types of resources, but the ALTO client does not support them, the ALTO client will ignore the resources without conducting any incompatibility. 8.2. Compatibility with Multi-Cost Extension This document does not specify how to integrate the "path-vector" cost mode with the multi-cost extension [RFC8189]. Although there is no reason why somebody has to compound the path vectors with other cost types in a single query, there is no compatible issue doing it without constraint tests. 8.3. Compatibility with Incremental Update The extension specified in this document is NOT compatible with the original incremental update extension [I-D.ietf-alto-incr-update-sse]. A legacy ALTO client CANNOT recognize the compound client-id, and a legacy ALTO server MAY use the same client-id for updates of both parts. ALTO clients and servers MUST follow the specifications given in this document to ensure compatibility with the incremental update extension. 8.4. Compatibility with Cost Calendar The extension specified in this document is compatible with the Cost Calendar extension [I-D.ietf-alto-cost-calendar]. When used together with the Cost Calendar extension, the cost value between a source and a destination is an array of path vectors, where the k-th path vector refers to the abstract network paths traversed in the k-th time interval by traffic from the source to the destination. Gao, et al. Expires January 23, 2020 [Page 29] Internet-Draft ALTO Extension: Path Vector July 2019 When used with time-varying properties, e.g., maximum reservable bandwidth (maxresbw), a property of a single entity may also have different values in different time intervals. In this case, an ANE with different property values MUST be considered as different ANEs. The two extensions combined together CAN provide the historical network correlation information for a set of source and destination pairs. A network broker or client MAY use this information to derive other resource requirements such as Time-Block-Maximum Bandwidth, Bandwidth-Sliding-Window, and Time-Bandwidth-Product (TBP) (See [SENSE] for details.) 9. General Discussions 9.1. Provide Calendar for Property Map Fetching the historical network information is useful for many traffic optimization problem. [I-D.ietf-alto-cost-calendar] already proposes an ALTO extension called Cost Calendar which provides the historical cost values using filtered cost map and endpoint cost service. However, the calendar for only path costs is not enough. For example, as the properties of ANEs (e.g., available bandwidth and link delay) are usually the real-time network states, they change frequently in the real network. It is very helpful to get the historical value of these properties. Applications may predicate the network status using these information to better optimize their performance. So the coming requirement may be a general calendar service for the ALTO information resources. 9.2. Constraint Tests for General Cost Types The constraint test is a simple approach to query the data. It allows users to filter the query result by specifying some boolean tests. This approach is already used in the ALTO protocol. [RFC7285] and [RFC8189] allow ALTO clients to specify the "constraints" and "or-constraints" tests to better filter the result. However, the current defined syntax is too simple and can only be used to test the scalar cost value. For more complex cost types, like the "array" mode defined in this document, it does not work well. It will be helpful to propose more general constraint tests to better perform the query. In practice, it is too complex to customize a language for the general-purpose boolean tests, and can be a duplicated work. So it Gao, et al. Expires January 23, 2020 [Page 30] Internet-Draft ALTO Extension: Path Vector July 2019 may be a good idea to integrate some already defined and widely used query languages (or their subset) to solve this problem. The candidates can be XQuery and JSONiq. 9.3. General Multipart Resources Query Querying multiple ALTO information resources continuously MAY be a general requirement. And the coming issues like inefficiency and inconsistency are also general. There is no standard solving these issues yet. So we need some approach to make the ALTO client request the compound ALTO information resources in a single query. 10. Security Considerations This document is an extension of the base ALTO protocol, so the Security Considerations [RFC7285] of the base ALTO protocol fully apply when this extension is provided by an ALTO server. The path vector extension requires additional considerations on two security considerations discussed in the base protocol: confidentiality of ALTO information (Section 15.3 of [RFC7285]) and availability of ALTO service (Section 15.5 of [RFC7285]). For confidentiality of ALTO information, a network operator should be aware of that this extension may introduce a new risk: the path vector information may make network attacks easier. For example, as the path vector information may reveal more network internal 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 guarantees the constraints on the requested properties are still accurate. For availability of ALTO service, an ALTO server should be cognizant that using path vector extension might have a new risk: frequent requesting for path vectors might conduct intolerable increment of the server-side storage and break the ALTO server. It is known that the computation of path vectors is unlikely to be cacheable, in that the results will depend on the particular requests (e.g., where the flows are distributed). Hence, the service providing path vectors may become an entry point for denial-of-service attacks on the Gao, et al. Expires January 23, 2020 [Page 31] Internet-Draft ALTO Extension: Path Vector July 2019 availability of an ALTO server. To avoid this risk, authenticity and authorization of this ALTO service may need to be better protected. 11. IANA Considerations 11.1. ALTO Cost Mode Registry This document specifies a new cost mode "path-vector". However, the base ALTO protocol does not have a Cost Mode Registry where new cost mode can be registered. This new cost mode will be registered once the registry is defined either in a revised version of [RFC7285] or in another future extension. 11.2. ALTO Entity Domain Registry As proposed in Section 9.2 of [I-D.ietf-alto-unified-props-new], "ALTO Domain Entity Registry" is requested. Besides, a new domain is to be registered, listed in Table 2. +-------------+--------------------------+--------------------------+ | Identifier | Entity Address Encoding | Hierarchy & Inheritance | +-------------+--------------------------+--------------------------+ | ane | See Section 5.3.2 | None | +-------------+--------------------------+--------------------------+ Table 2: ALTO Entity Domain 11.3. ALTO Entity Property Type Registry The "ALTO Entity Property Type Registry" is required by the ALTO Domain "ane", listed in Table 3. +-------------------------+-----------------------------------------+ | Identifier | Intended Semantics | +-------------------------+-----------------------------------------+ | ane:maxresbw | The maximum reservable bandwidth for | | | the ANE | | ane:persistent-entities | An array of identifiers of persistent | | | entities that reside in an ANE | +-------------------------+-----------------------------------------+ Table 3: ALTO Entity Property Types 11.4. ALTO Resource Entity Domain Export Registries Gao, et al. Expires January 23, 2020 [Page 32] Internet-Draft ALTO Extension: Path Vector July 2019 11.4.1. costmap +---------------------+--------------------+ | Entity Domain Type | Export Function | +---------------------+--------------------+ | ane | See Section 5.4.1 | +---------------------+--------------------+ Table 4: ALTO Cost Map Entity Domain Export. 11.4.2. endpointcost +---------------------+--------------------+ | Entity Domain Type | Export Function | +---------------------+--------------------+ | ane | See Section 5.4.2 | +---------------------+--------------------+ Table 5: ALTO Endpoint Cost Entity Domain Export. 12. Acknowledgments The authors would like to thank discussions with Andreas Voellmy, Erran Li, Haibin Song, Haizhou Du, Jiayuan Hu, Qiao Xiang, Tianyuan Liu, Xiao Shi, Xin Wang, and Yan Luo. The authors thank Greg Bernstein (Grotto Networks), Dawn Chen (Tongji University), Wendy Roome, and Michael Scharf for their contributions to earlier drafts. 13. References 13.1. Normative References [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, DOI 10.17487/RFC2119, March 1997, . [RFC2387] Levinson, E., "The MIME Multipart/Related Content-type", RFC 2387, DOI 10.17487/RFC2387, August 1998, . [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, . Gao, et al. Expires January 23, 2020 [Page 33] Internet-Draft ALTO Extension: Path Vector July 2019 [RFC8189] Randriamasy, S., Roome, W., and N. Schwan, "Multi-Cost Application-Layer Traffic Optimization (ALTO)", RFC 8189, DOI 10.17487/RFC8189, October 2017, . 13.2. Informative References [I-D.bernstein-alto-topo] Bernstein, G., Yang, Y., and Y. Lee, "ALTO Topology Service: Uses Cases, Requirements, and Framework", draft- bernstein-alto-topo-00 (work in progress), October 2013. [I-D.ietf-alto-cost-calendar] Randriamasy, S., Yang, Y., Wu, Q., Lingli, D., and N. Schwan, "ALTO Cost Calendar", draft-ietf-alto-cost- calendar-01 (work in progress), February 2017. [I-D.ietf-alto-incr-update-sse] Roome, W. and Y. Yang, "ALTO Incremental Updates Using Server-Sent Events (SSE)", draft-ietf-alto-incr-update- sse-16 (work in progress), March 2019. [I-D.ietf-alto-performance-metrics] Wu, Q., Yang, Y., Lee, Y., Dhody, D., and S. Randriamasy, "ALTO Performance Cost Metrics", draft-ietf-alto- performance-metrics-06 (work in progress), November 2018. [I-D.ietf-alto-unified-props-new] Roome, W., Randriamasy, S., Yang, Y., and J. Zhang, "Unified Properties for the ALTO Protocol", draft-ietf- alto-unified-props-new-07 (work in progress), March 2019. [SENSE] "Services - SENSE", 2019, . [TON2019] Gao, K., Xiang, Q., Wang, X., Yang, Y., and J. Bi, "An objective-driven on-demand network abstraction for adaptive applications", IEEE/ACM Transactions on Networking (TON) 27, no. 2 (2019): 805-818., 2019. Authors' Addresses Kai Gao Sichuan University Chengdu 610000 China Email: kaigao@scu.edu.cn Gao, et al. Expires January 23, 2020 [Page 34] Internet-Draft ALTO Extension: Path Vector July 2019 Young Lee Huawei TX USA Email: leeyoung@huawei.com Sabine Randriamasy Nokia Bell Labs Route de Villejust NOZAY 91460 FRANCE Email: Sabine.Randriamasy@nokia-bell-labs.com Y. Richard Yang Yale University 51 Prospect St New Haven CT USA Email: yry@cs.yale.edu Jingxuan Jensen Zhang Tongji University 4800 Caoan Road Shanghai 201804 China Email: jingxuan.n.zhang@gmail.com Gao, et al. Expires January 23, 2020 [Page 35]