Network Working Group S. Randriamasy, Ed. Internet-Draft W. Roome, Ed. Intended status: Standards Track Alcatel-Lucent Expires: April 21, 2016 N. Schwan Thales Deutschland October 19, 2015 Multi-Cost ALTO draft-ietf-alto-multi-cost-01 Abstract The ALTO (Application Layer-Traffic Optimization) Protocol ([RFC7285]) defines several services that return various metrics describing the costs between network endpoints. For example, when downloading a file that is mirrored on several sites, a user application may use these ALTO cost metrics to determine the most efficient mirror site. An ALTO Server may offer a variety of cost metrics, based on latency, bandwidth, hop count, jitter, or whatever else the ALTO Server deems useful. When selecting a mirror site, a client may consider more than one metric, perhaps trading bandwidth for latency. While the base ALTO Protocol allows a client to use more than one cost metric, to do so, the client must request each metric separately. This document defines a new service that allows a client to retrieve several cost metrics with one request, which is considerably more efficient. In addition, this document extends the ALTO constraint tests to allow a user to specify an arbitrary logical combination of tests on several cost metrics. 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/. Randriamasy, et al. Expires April 21, 2016 [Page 1] Internet-Draft Multi-Cost ALTO October 2015 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 April 21, 2016. Copyright Notice Copyright (c) 2015 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 . . . . . . . . . . . . . . . . . . . . . . . . 3 2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 4 3. Overview Of Approach . . . . . . . . . . . . . . . . . . . . 5 3.1. Multi-Cost Data Format . . . . . . . . . . . . . . . . . 5 3.2. Compatibility With Legacy Clients . . . . . . . . . . . . 6 3.3. Filtered Multi Cost Map Resources . . . . . . . . . . . . 6 3.4. Endpoint Cost Service Resources . . . . . . . . . . . . . 7 3.5. Full Cost Map Resources . . . . . . . . . . . . . . . . . 7 3.6. Extended Constraint Tests . . . . . . . . . . . . . . . . 8 4. Protocol Extensions for Multi-Cost ALTO Transactions . . . . 9 4.1. Filtered Cost Map Extensions . . . . . . . . . . . . . . 9 4.1.1. Accept Input Parameters . . . . . . . . . . . . . . . 9 4.1.2. Capabilities . . . . . . . . . . . . . . . . . . . . 12 4.1.3. Response . . . . . . . . . . . . . . . . . . . . . . 12 4.2. Endpoint Cost Service Extensions . . . . . . . . . . . . 13 4.2.1. Accept Input Parameters . . . . . . . . . . . . . . . 13 4.2.2. Capabilities . . . . . . . . . . . . . . . . . . . . 14 4.2.3. Response . . . . . . . . . . . . . . . . . . . . . . 14 5. Examples . . . . . . . . . . . . . . . . . . . . . . . . . . 14 5.1. Information Resource Directory . . . . . . . . . . . . . 14 5.2. Multi-Cost Filtered Cost Map: Example #1 . . . . . . . . 16 5.3. Multi-Cost Filtered Cost Map: Example #2 . . . . . . . . 17 5.4. Multi-Cost Filtered Cost Map: Example #3 . . . . . . . . 18 5.5. Endpoint Cost Service . . . . . . . . . . . . . . . . . . 20 Randriamasy, et al. Expires April 21, 2016 [Page 2] Internet-Draft Multi-Cost ALTO October 2015 6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 22 7. Privacy And Security Considerations . . . . . . . . . . . . . 22 8. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 22 9. References . . . . . . . . . . . . . . . . . . . . . . . . . 22 9.1. Normative References . . . . . . . . . . . . . . . . . . 22 9.2. Informative References . . . . . . . . . . . . . . . . . 22 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 22 1. Introduction IETF has designed a new service called ALTO that provides guidance to overlay applications, which have to select one or several hosts from a set of candidates that are able to provide a desired resource. This guidance is based on parameters such the topological distance, that affect performance and efficiency of the data transmission between the hosts. The purpose of ALTO is to improve Quality of Experience (QoE) in the application while reducing resource consumption in the underlying network infrastructure. The ALTO protocol conveys the Internet View from the perspective of a Provider Network region that spans from a region to one or more Autonomous System (AS) and is called a Network Map. ALTO may also provide the Provider determined Cost Map between locations of the Network Map or Endpoint Cost Map between groups of individual endpoints. Last, these costs are provided as numerical or ordinal values. Current ALTO Costs and their modes provide values that are seen to be stable over a longer period of time, such as hopcount and administrative routing cost to reflect ISP routing preferences. Recently, new use cases have extended the usage scope of ALTO to Content Delivery Networks, Data Centers and applications that need additional information to select their Endpoints or handle their PIDs. Thus a multitude of new Cost Types that better reflect the requirements of these applications are expected to be specified, in particular cost values that change more frequently than previously assumed. The ALTO protocol [RFC7285] restricts ALTO Cost Maps and Endpoint Cost services to only one Cost Type and Cost Mode per ALTO request. To retrieve information for several Cost Types, an ALTO client must send several separate requests to the server. It would be far more efficient, in terms of RTT, traffic, and processing load on the ALTO client and server, to get all costs with a single query/response transaction. Vector costs provide a robust and natural input to multi-variate path computation as well as robust multi-variate selection of multiple Endpoints. In particular, one Randriamasy, et al. Expires April 21, 2016 [Page 3] Internet-Draft Multi-Cost ALTO October 2015 Cost Map reporting on N Cost Types is less bulky than N Cost Maps containing one Cost Type each. This is valuable for both the storage of these maps and their transmission. Additionally, for many emerging applications that need information on several Cost Types, having them gathered in one map will save time. Another potential advantage is consistency: provide values on several Cost Types in one single batch is useful for Clients needing synchronized ALTO information updates. Along with multi-cost values queries, the filtering capabilities need to be extended to allow constraints on multiple metrics. The base protocol allows a client to provide optional constraint tests for a Filtered Cost Map or the Endpoint Cost Service. In the base protocol, the constraint tests are limited to the AND-combination of simple comparison tests on the value of the (single) requested Cost Type. It is therefore necessary to allow constraints on multiple metrics. Beyond that, applications that are sensitive to several metrics and struggle with complicated network conditions may need to arbitrate between conflicting objectives such as routing cost and network performance. To address this issue, this document proposes to extend the base protocol by extending constraints to test multiple metrics, and by allowing these constraints to be combined with logical 'ORs' as well as logical 'ANDs'. This allows an application to make requests such as: "select solutions with either (moderate "hopcount" AND high "routingcost") OR (higher "hopcount" AND moderate "routingcost")". To ensure compatibility with legacy ALTO Clients, Multi-Cost extensions are specified for the Filtered Cost Map service and the Endpoint Cost Map service only, while enabling to provide full Cost maps as well. This document is organized as follows: Section 2 defines terminology used in this document. Section 3 gives a non-normative overview of the multi-cost extensions, and Section 4 gives their formal definition. Section 5 gives several complete examples. The remaining sections describe the IANA and privacy considerations. 2. Terminology This document uses terms defined as follows: o {1.2.3}: References of this form are to sections in the ALTO protocol specification [RFC7285]. o When refering to a section of this document, the format 1.2.3, without brackets, will be used. o Endpoint (EP): can be a Peer, a CDN storage location, a physical server involved in a virtual server-supported application, a Party Randriamasy, et al. Expires April 21, 2016 [Page 4] Internet-Draft Multi-Cost ALTO October 2015 in a resource sharing swarm such as a computation Grid or an online multi-party game. o Endpoint Discovery (EP Discovery) : this term covers the different types of processes used to discover the eligible endpoints. o Network Service Provider (NSP): includes both ISPs, who provide means to transport the data, and Content Delivery Networks (CDNs) who care for the dissemination, persistent storage and possibly identification of the best/closest content copy. o ALTO transaction: a request/response exchange between an ALTO Client and an ALTO Server. o Application Client (AC): this term generalizes the case of a P2P client to include the case of a CDN client, a client of an application running on a virtual server, a Grid application client and any Client having the choice in several connection points for data or resource exchange. 3. Overview Of Approach The following is a non-normative overview of the multi-cost extensions defined in this document. It assumes the reader is familiar with Cost Map resources in the ALTO Protocol ([RFC7285]). 3.1. Multi-Cost Data Format Formally, the cost entries in an ALTO Cost Map can be any type of JSON value (see the DstCosts object in {11.2.3.6}). However, that section also says that an implementation may assume costs are JSON numbers, unless the implementation is using an extension which signals a different data type. Therefore this document extends the definition of a Cost Map to allow a cost to be an array of costs, one per metric, instead of just one number. For example, here is a Cost Map with the "routingcost" and "hopcount" metrics. Note that this is identical to a regular ALTO Cost Map, except that the values are arrays instead of numbers. Randriamasy, et al. Expires April 21, 2016 [Page 5] Internet-Draft Multi-Cost ALTO October 2015 { "meta" : { "dependent-vtags" : [ ... ], "multi-cost-types" : [ {"cost-mode": "numerical", "cost-metric": "routingcost"}, {"cost-mode": "numerical", "cost-metric": "hopcount"} ] } "cost-map" : { "PID1": { "PID1":[1,0], "PID2":[5,23], "PID3":[10,5] }, ... } } 3.2. Compatibility With Legacy Clients The multi-cost extensions defined in this document should not break legacy implementations (that is, clients and servers which are not aware of these extensions). One way to achieve that would be to define a new media type for an array-valued Multi Cost Map. However, as indicated above, an array-valued Multi Cost Map is almost identical to a single-valued Cost Map, so it should be simple to write a parser which handles either type of cost map. Hence defining a new media type could result in a lot of wasteful duplication. Therefore this document does not define any new media types. Instead, as described below, it extends the specifications in the ALTO Server's Information Resource Directory (IRD) so that legacy clients will not request array-valued Cost Map resources. This relies on the requirement that implementations MUST ignore unknown fields ({8.3.7} in [RFC7285]). 3.3. Filtered Multi Cost Map Resources This document extends the Filtered Cost Map service to allow the same resource to return either a single-valued Cost Map, as defined in [RFC7285], or an array-valued Multi Cost Map, as defined in this document. An extended Filtered Cost Map resource has a new capability, "max-cost-types". The value is the maximum number of cost types this resource can return for one request. The existence of this capability means the resource understands the extensions in this document. For example, the following fragment from an IRD defines an extended Filtered Cost Map resource: Randriamasy, et al. Expires April 21, 2016 [Page 6] Internet-Draft Multi-Cost ALTO October 2015 "filtered-multicost-map" : { "uri" : "http://alto.example.com/multi/costmap/filtered", "media-types" : [ "application/alto-costmap+json" ], "accepts" : [ "application/alto-costmapfilter+json" ], "uses" : [ "my-default-network-map" ], "capabilities" : { "max-cost-types" : 2, "cost-type-names" : [ "num-routingcost", "num-hopcount" ], ... } A legacy client will ignore the "max-cost-types" capability, and will send a request with the input parameter "cost-type" describing the desired cost metric, as defined in [RFC7285]. The ALTO Server will return a single-valued legacy Cost Map. However, a multi-cost-aware client will realize that this resource supports the multi-cost extensions, and can send a POST request with the new input parameter "multi-cost-types", whose value is an array of cost types. Because the request has the "multi-cost-types" parameter (rather than the "cost-type" parameter defined in the base protocol), the server realizes that the client also supports the extensions in this document, and hence responds with a Multi Cost Map, with the costs in the order listed in "multi-cost-types". 3.4. Endpoint Cost Service Resources This document uses the technique described in Section 3.3 to extend the Endpoint Cost Service to return array-valued costs to clients who also are aware of these extensions. 3.5. Full Cost Map Resources Full Cost Map resources are GET-mode requests, with no capabilities other than the name of the cost type they return. It is therefore not possible to define an array-valued Full Cost Map resource so that multi-cost-aware clients can recognize it and legacy clients will ignore it. Indeed, the response for a Full Cost Map conveying multiple cost types would include a "meta" field that would itself include a "cost-type" field, that would list several values corresponding to the cost types of the cost map. A legacy client would not be able to understand this list. It would not know what the cost type of the map is and neither would it be able to interpret the cost values array provided by a Multi-Cost full maps. However {11.3.2.3} of [RFC7285] requires a Filtered Cost Map to return the entire Cost Map if the client omits the source and Randriamasy, et al. Expires April 21, 2016 [Page 7] Internet-Draft Multi-Cost ALTO October 2015 destination PIDs. Hence a client can use an extended Filtered Cost Map resource to get a full Multi Cost Map. 3.6. Extended Constraint Tests [RFC7285] defines a simple constraint test capability for Filtered Cost Maps and Endpoint Cost Services. If a resource supports constraints, the server restricts the response to costs that satisfy a list of simple predicates provided by the client. For example, if the client gives the constraints "constraints": ["ge 10", "le 20"] Then the server only returns costs in the range [10,20]. To be useful with multi-cost requests, the constraint tests require several extensions. First, because a multi-cost request involves more than one cost metric, the simple predicates must be extended to specify the metric to test. Therefore we extend the predicate syntax to "[##] op value", where "##" is the index of a cost metric in this multi cost request. Second, if the client for example wants values either greater than 10 or smaller than 20, the "AND" of simple predicates is not sufficient; to be useful, clients must be able to express "OR" tests. Hence we add a new field, "or-constraints", to the client request. The value is an array of arrays of simple predicates, and represents the OR of ANDs of those predicates. Thus the following request tells the server to limit its response to cost points with "routingcost" <= 100 AND "hopcount" <= 2, OR else "routingcost" <= 10 AND "hopcount" <= 6: { "multi-cost-types": [ {"cost-metric": "routingcost", "cost-mode": "numerical"}, {"cost-metric": "hopcount", "cost-mode": "numerical"} ], "or-constraints": [ ["[0] le 100", "[1] le 2"], ["[0] le 10", "[1] le 6"] ], "pids": {...} } Finally, a client might want to test a cost type whose actual value is irrelevant, as long as it satisfies the tests. For example, the Randriamasy, et al. Expires April 21, 2016 [Page 8] Internet-Draft Multi-Cost ALTO October 2015 following request tells the server to return just "routingcost" for those source and destination pairs for which "hopcount" is <= 6: { "multi-cost-types": [ {"cost-metric": "routingcost", "cost-mode": "numerical"}, ], "testable-cost-types": [ {"cost-metric": "hopcount", "cost-mode": "numerical"}, ], "constraints": ["[0] le 6"], "pids": {...} } In this example, "[0]" means the constraint applies to "hopcount" because that is the first cost type in the "testable-cost-types" parameter. 4. Protocol Extensions for Multi-Cost ALTO Transactions This section provides the formal specifications of extensions to RFC7285 to support Multi-Cost ALTO transactions. 4.1. Filtered Cost Map Extensions This document extends Filtered Cost Maps, as defined in {11.3.2} of [RFC7285], by adding new input parameters and capabilities, and by returning JSONArrays instead of JSONNumbers as the cost values. The media type (11.3.2.1}, HTTP method (11.3.2.2} and "uses" specifications (11.3.2.5} are unchanged. 4.1.1. Accept Input Parameters The ReqFilteredCostMap object in {11.3.2.3} of [RFC7285] is extended as follows: Randriamasy, et al. Expires April 21, 2016 [Page 9] Internet-Draft Multi-Cost ALTO October 2015 object { [CostType cost-type;] [CostType multi-cost-types<1..*>;] [CostType testable-cost-types<1..*>;] [JSONString constraints<0..*>;] [JSONString or-constraints<0..*>;] PIDFilter pids; } ReqFilteredCostMap; object { PIDName srcs<0..*>; PIDName dsts<0..*>; } PIDFilter; cost-type: If present, as defined in {11.3.2.3} of [RFC7285], with the additional requirement that the client MUST provide either "cost-type" or "multi-cost-types", but MUST NOT provide both. multi-cost-types: If present, the ALTO Server MUST return array- valued costs for the cost types in thlis list. For each entry, the "cost-metric" and "cost-mode" fields MUST match one of the supported cost types indicated in this resource's "capabilities" field (Section 4.1.2). The client MUST NOT use this field unless this resource's "max-cost-types" capability exists and has a value greater than 0. The client MUST specify either "cost-type" or "multi-cost-types", but MUST NOT specify both. testable-cost-types: A list of cost types for extended constraint tests, as described for the "constraints" parameter. If present, the cost types must be a subset of the cost types in the resource's "testable-cost-type-names" capability (Section 4.1.2). This feature allows a client to test a cost type whose actual value is irrelevant, as long as it satisfies the tests. For example, a client may want a Filtered Cost Map for cost metric "routingcost" that is restricted to those PID pairs that satisfy constraints on metric "hopcount". This feature is also useful for a server that does not allow constraints on all the cost types indicated in this resource's capabilities. constraints: Unless this resource's "max-cost-types" capability (Section 4.1.2) is defined with a value greater than 0, this parameter is an array of constraint tests where each test is formulated as defined in {11.3.2.3} of [RFC7285]. Randriamasy, et al. Expires April 21, 2016 [Page 10] Internet-Draft Multi-Cost ALTO October 2015 This parameter MUST NOT be specified if the "or-constraints" parameter is specified, or if the resource's "cost-constraints" capability is false. If this resource's "max-cost-types" capability is greater than 0, then this parameter MUST be an array of extended constraint tests, where each test consists of two or three entities separated by white space: (1) an optional cost type index, of the form "[#]", with default value "[0]", (2) a required operator, and (3) a required target value. The operator and target value are as defined in {11.3.2.3} of [RFC7285]. The cost type index specifies the cost type to test. If the "testable-cost-types" parameter is present, assuming the index is "i", the test applies to the i'th cost type in "testable-cost-types" (starting with index 0). Otherwise, if the "multi-cost-types" parameter is present, the test applies to the i'th cost type in "multi-cost-types". If neither of those parameters is present, the test applies to the cost type in the "cost-type" parameter. In this case, the index MUST be 0. Regardless of how the tested cost type is selected, it MUST be a cost type in the resource's "testable-cost-type-names" capability, or, if omitted, the resource's "cost-type-names" capability. As an example: suppose "multi-cost-types" has the single element "routingcost", "testable-cost-types" has the single element "hopcount", and "constraints" has the single element "[0] le 5". This is equivalent to the database query "SELECT routingcost WHERE hopcount <= 5". Note that as long as this resource's "max-cost-types" capability is greater than 0, a client may use the extended constraint tests even on single-valued cost map requests, that is, requests with the "cost-type" parameter rather than "multi-cost-types". or-constraints: A JSONArray of JSONArrays of JSONStrings, where each string is a constraint test as defined for the "constraints" parameter. The constraint tests are interpreted as the logical OR of ANDs. That is, the ALTO Server should return a cost point only if it satisfies all constraints in any one of the sub-arrays. This parameter MUST NOT be specified unless this resource's "cost- constraints" capability is "true" and its "max-cost-types" capability is defined with a value greater than 0 (Section 4.1.2). This parameter MUST NOT be specified if the "constraints" parameter is specified. Note that if the "max-cost-types" capability has a value greater than 0, a client MAY use the "or-constraints" parameter together Randriamasy, et al. Expires April 21, 2016 [Page 11] Internet-Draft Multi-Cost ALTO October 2015 with the "cost-type" parameter. That is, if the client and server are both aware of the extensions in this document, a client MAY use an "OR" test for a single-valued cost request. pids, srcs, dsts: As defined in {11.3.2.3} of [RFC7285]. 4.1.2. Capabilities The FilteredCostMapCapabilities object in {11.3.2.4} is extended as follows: object { JSONString cost-type-names<1..*>; [JSONBool cost-constraints;] [JSONNumber max-cost-types;] [JSONString testable-cost-type-names<0..*>;] } FilteredCostMapCapabilities; max-cost-types: If present with value N greater than 0, this resource understands the multi-cost extensions in this document, and can return a Multi Cost Map with any combination of N or fewer cost types in the "cost-type-names" list. If omitted, the default value is 0. testable-cost-type-names: If present, and if "cost-constraints" is true, the resource only allows constraint tests on the cost type names in this array. Each name in "testable-cost-type-names" MUST be in "cost-type-names". If omitted or empty, the default is the value of the "cost-type-names" capability. cost-type-names and cost-constraints: As defined in {11.3.2.4} of [RFC7285]. Note that "testable-cost-type-names" allows an ALTO Server to provide constraint tests on some, but not all, cost types. 4.1.3. Response If the client specifies the "cost-type" input parameter, the response is exactly as defined in {11.2.3.6} of [RFC7285]. If the client provides the "multi-cost-types" instead, then the response is changed as follows: o In "meta", the field "cost-type" is replaced with the field "multi-cost-types", with the same value as the "multi-cost-types" input parameter. Randriamasy, et al. Expires April 21, 2016 [Page 12] Internet-Draft Multi-Cost ALTO October 2015 o The costs are JSONArrays, instead of JSONNumbers. All arrays have the same cardinality as the "multi-cost-types" input parameter, and contain the cost type values in that order. If a cost type is not available for a particular source and destination, the ALTO Server MUST use the JSON null value for that array element. If none of the cost types are available for a particular source and destination, the ALTO Server MAY omit the entry for that source and destination. 4.2. Endpoint Cost Service Extensions This document extends the Endpoint Cost Service, as defined in {11.5.1} of [RFC7285], by adding new input parameters and capabilities, and by returning JSONArrays instead of JSONNumbers as the cost values. The media type (11.5.1.1}, HTTP method (11.5.1.2} and "uses" specifications (11.5.1.5} are unchanged. 4.2.1. Accept Input Parameters The ReqEndpointCostMap object in {11.5.1.3} of [RFC7285] is extended as follows: object { [CostType cost-type;] [CostType multi-cost-types<1..*>;] [CostType testable-cost-types<1..*>;] [JSONString constraints<0..*>;] [JSONString or-constraints<0..*>;] EndpointFilter endpoints; } ReqFilteredCostMap; object { [TypedEndpointAddr srcs<0..*>;] [TypedEndpointAddr dsts<0..*>;] } EndpointFilter; cost-type: As defined in {11.5.1.3} of [RFC7285], with the additional requirement that the client MUST specify either "cost- type" or "multi-cost-types", but not both. multi-cost-types: If present, the ALTO Server MUST return array- valued costs for the cost types in this list. For each entry, the "cost-metric" and "cost-mode" fields MUST match one of the supported cost types indicated in this resource's "capabilities" field (Section 4.2.2). The client MUST NOT use this field unless this resource's "max-cost-types" capability exists and has a value Randriamasy, et al. Expires April 21, 2016 [Page 13] Internet-Draft Multi-Cost ALTO October 2015 greater than 0. Although optional, the client MUST specify either "cost-type" or "multi-cost-types". The client MUST NOT specify both. testable-cost-types, constraints, or-constraints: Defined equivalently to the corresponding input parameters for an extended Filtered Cost Map (Section 4.1.1). endpoints, srcs, dsts: As defined in {11.5.1.3} of [RFC7285]. 4.2.2. Capabilities The extensions to the Endpoint Cost Service capabilities are identical to the extensions to the Filtered Cost Map (see Section 4.1.2). 4.2.3. Response The extensions to the Endpoint Cost Service response are similar to the extensions to the Filtered Cost Map response (Section 4.1.3). Specifically, if the client specifies the "cost-type" input parameter, the response is exactly as defined in {11.5.1.6} of [RFC7285]. If the client provides the "multi-cost-types" instead, then the response is changed as follows: o In "meta", the field "cost-type" is replaced with the field "multi-cost-types", with the same value as the "multi-cost-types" input parameter. o The costs are JSONArrays, instead of JSONNumbers. All arrays have the same cardinality as the "multi-cost-types" input parameter, and contain the cost type values in that order. If a cost type is not available for a particular source and destination, the ALTO Server MUST use the JSON null value for that array element. If none of the cost types are available for a particular source and destination, the ALTO Server MAY omit the entry for that source and destination. 5. Examples 5.1. Information Resource Directory The following is an example of an ALTO Server's Information Resource Directory. In addition to Network and Cost Map resources, it defines a Filtered Cost Map and an Endpoint Cost Service, both which understand the multi-cost extensions. GET /directory HTTP/1.1 Randriamasy, et al. Expires April 21, 2016 [Page 14] Internet-Draft Multi-Cost ALTO October 2015 Host: alto.example.com Accept: application/alto-directory+json,application/alto-error+json HTTP/1.1 200 OK Content-Length: [TODO] Content-Type: application/alto-directory+json { "meta" : { "default-alto-network-map" : "my-default-network-map", "cost-types" : { "num-routing" : { "cost-mode" : "numerical", "cost-metric" : "routingcost" }, "num-hopcount" : { "cost-mode" : "numerical", "cost-metric" : "hopcount" }, ..... Other ALTO cost types as described in current ALTO Protocol ..... } }, "resources" : { "my-default-network-map" : { "uri" : "http://alto.example.com/networkmap", "media-type" : "application/alto-networkmap+json" }, "numerical-routing-cost-map" : { "uri" : "http://alto.example.com/costmap/num-routing", "media-types" : [ "application/alto-costmap+json" ], "uses" : [ "my-default-network-map" ], "capabilities" : { "cost-type-names" : [ "num-routing" ] } }, "numerical-hopcount-cost-map" : { "uri" : "http://alto.example.com/costmap/num-hopcount", "media-types" : [ "application/alto-costmap+json" ], "uses" : [ "my-default-network-map" ], "capabilities" : { "cost-type-names" : [ "num-hopcount" ] } }, ......... Randriamasy, et al. Expires April 21, 2016 [Page 15] Internet-Draft Multi-Cost ALTO October 2015 And other information resources as described in RFC7285 ......... "filtered-multicost-map" : { "uri" : "http://alto.example.com/multi/costmap/filtered", "media-types" : [ "application/alto-costmap+json" ], "accepts" : [ "application/alto-costmapfilter+json" ], "uses" : [ "my-default-network-map" ], "capabilities" : { "cost-constraints" : true, "max-cost-types" : 2, "cost-type-names" : [ "num-routingcost", "num-hopcount" ], "testable-cost-type-names" : [ "num-routingcost", "num-hopcount" ] } }, "endpoint-multicost-map" : { "uri" : "http://alto.example.com/multi/endpointcost/lookup", "media-types" : [ "application/alto-endpointcost+json" ], "accepts" : [ "application/alto-endpointcostparams+json" ], "uses" : [ "my-default-network-map" ], "capabilities" : { "cost-constraints" : true, "max-cost-types" : 2, "cost-type-names" : [ "num-routingcost", "num-hopcount" ], "testable-cost-type-names" : [ "num-routingcost", "num-hopcount" ] } } } } 5.2. Multi-Cost Filtered Cost Map: Example #1 This example illustrates a static multi-cost ALTO transaction, where the utilized Cost Types all have static values. We assume that the Cost Types available at the ALTO Server are "routingcost" and "hopcount" and the "numerical" mode is available for both of them. The "routingcost" may be based on monetary considerations where as the "hopcount" is used to report on the path delay. We also assume that ALTO server does not know the value of the "routingcost" between PID2 and PID3, and hence uses 'null' for those costs. Randriamasy, et al. Expires April 21, 2016 [Page 16] Internet-Draft Multi-Cost ALTO October 2015 POST /multi/costmap/filtered" HTTP/1.1 Host: alto.example.com Accept: application/alto-costmap+json,application/alto-error+json { "multi-cost-types": [ {"cost-mode": "numerical", "cost-metric": "routingcost"}, {"cost-mode": "numerical", "cost-metric": "hopcount"} ], "pids" : { "srcs" : [ ], "dsts" : [ ] } } HTTP/1.1 200 OK Content-Length: [TODO] Content-Type: application/alto-costmap+json { "meta" : { "dependent-vtags" : [ {"resource-id": "my-default-network-map", "tag": "3ee2cb7e8d63d9fab71b9b34cbf764436315542e" } ], "multi-cost-types" : [ {"cost-mode": "numerical", "cost-metric": "routingcost"}, {"cost-mode": "numerical", "cost-metric": "hopcount"} ] } } "cost-map" : { "PID1": { "PID1":[1,0], "PID2":[4,23], "PID3":[10,5] }, "PID2": { "PID1":[15,5], "PID2":[1,0], "PID3":[null,9] }, "PID3": { "PID1":[20,12], "PID2":[null,1], "PID3":[1,0] } } } 5.3. Multi-Cost Filtered Cost Map: Example #2 This is an example of using constraints to restrict the returned source/destination PID pairs to those with "routingcost" between 5 and 10, or "hopcount" equal to 0. Randriamasy, et al. Expires April 21, 2016 [Page 17] Internet-Draft Multi-Cost ALTO October 2015 POST multi/multicostmap/filtered HTTP/1.1 Host: alto.example.com Content-Type: application/alto-costmapfilter+json Accept: application/alto-costmap+json,application/alto-error+json { "multi-cost-types" : [ {"cost-mode": "numerical", "cost-metric": "routingcost"}, {"cost-mode": "numerical", "cost-metric": "hopcount"} ], "or-constraints" : [ ["[0] ge 5", "[0] le 10"], ["[1] eq 0"] ] "pids" : { "srcs" : [ "PID1", "PID2" ], "dsts" : [ "PID1", "PID2", "PID3" ] } } HTTP/1.1 200 OK Content-Type: application/alto-costmap+json { "meta" : { "dependent-vtags" : [ {"resource-id": "my-default-network-map", "tag": "3ee2cb7e8d63d9fab71b9b34cbf764436315542e" } ], "multi-cost-types" : [ {"cost-mode": "numerical", "cost-metric": "routingcost"}, {"cost-mode": "numerical", "cost-metric": "hopcount"} ] } "cost-map" : { "PID1": { "PID1": [1,0], "PID3": [10,5] }, "PID2": { "PID2": [1,0] } } } 5.4. Multi-Cost Filtered Cost Map: Example #3 This example uses extended constraints to limit the response to cost points with ("routingcost" <= 10 and "hopcount" <= 2), or else ("routingcost" <= 2 and "hopcount" <= 6). Unlike the previous example, the client is only interested in the "routingcost" cost type, and uses the "cost-type" parameter instead of "multi-cost- Randriamasy, et al. Expires April 21, 2016 [Page 18] Internet-Draft Multi-Cost ALTO October 2015 types" to tell the server to return scalar costs instead of array costs: POST multi/multicostmap/filtered HTTP/1.1 Host: alto.example.com Content-Type: application/alto-costmapfilter+json Accept: application/alto-costmap+json,application/alto-error+json { "cost-type" : { "cost-mode": "numerical", "cost-metric": "routingcost" }, "testable-cost-types" : [ {"cost-mode": "numerical", "cost-metric": "routingcost"}, {"cost-mode": "numerical", "cost-metric": "hopcount"} ], "or-constraints": [ ["[0] le 10", "[1] le 2"], ["[0] le 3", "[1] le 6"] ], "pids" : { "srcs" : [ ], "dsts" : [ ] } } HTTP/1.1 200 OK Content-Type: application/alto-costmap+json { "meta" : { "dependent-vtags" : [ {"resource-id": "my-default-network-map", "tag": "3ee2cb7e8d63d9fab71b9b34cbf764436315542e" } ], "cost-type" : { "cost-mode": "numerical", "cost-metric": "routingcost" } } "cost-map" : { "PID1": { "PID1": 1, "PID3": 10 }, "PID2": { "PID2": 1 }, "PID3": { "PID3": 1 } } } Randriamasy, et al. Expires April 21, 2016 [Page 19] Internet-Draft Multi-Cost ALTO October 2015 5.5. Endpoint Cost Service This example uses the Endpoint Cost Service to retrieve the "routingcost" and "hopcount" for selected endpoints, limiting the response to costs with either low hopcount and reasonable routingcost (hopcount <= 2 and routingcost <= 10), or else low routingcost and reasonable hopcount (routingcost <= 3 and hopcount <= 6). Randriamasy, et al. Expires April 21, 2016 [Page 20] Internet-Draft Multi-Cost ALTO October 2015 POST /multi/endpointcost/lookup HTTP/1.1 Host: alto.example.com Content-Length: [TODO] Content-Type: application/alto-endpoincostparams+json Accept: application/alto-endpointcost+json, application/alto-error+json { "multi-cost-types" : [ {"cost-mode": "numerical", "cost-metric": "routingcost"}, {"cost-mode": "numerical", "cost-metric": "hopcount"} ], "or-constraints": [ ["[0] le 10", "[1] le 2"], ["[0] le 3", "[1] le 6"] ], "endpoints" : { "srcs": [ "ipv4:192.0.2.2" ], "dsts": [ "ipv4:192.0.2.89", "ipv4:198.51.100.34", "ipv4:203.0.113.45" ] } } HTTP/1.1 200 OK Content-Length: [TODO] Content-Type: application/alto-endpointcost+json { "meta" : { "multi-cost-types" : [ {"cost-mode": "numerical", "cost-metric": "routingcost"}, {"cost-mode": "numerical", "cost-metric": "hopcount"} ] } "endpoint-cost-map" : { "ipv4:192.0.2.2": { "ipv4:192.0.2.89": [15, 5], "ipv4:203.0.113.45": [4, 23] } } } Randriamasy, et al. Expires April 21, 2016 [Page 21] Internet-Draft Multi-Cost ALTO October 2015 6. IANA Considerations This document does define any new media types or introduce any new IANA considerations. 7. Privacy And Security Considerations This document does introduce any privacy or security issues not already present in the ALTO protocol. 8. Acknowledgements The authors would like to thank Richard Alimi, Vijay Gurbani, Dave Mac Dysan, Dhruv Dhodi, Young Lee, Richard Yang and Wang Xin for fruitful discussions and feedback on this document and previous versions. 9. References 9.1. 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, . [RFC5693] "Application Layer Traffic Optimization (ALTO) Problem Statement", October 2009. [RFC7285] Almi, R., Penno, R., Yang, Y., Kiesel, S., Previdi, S., Roome, W., Shalunov, S., and R. Woundy, "Application-Layer Traffic Optimization (ALTO) Protocol", RFC 7285, September 2014. 9.2. Informative References [RFC6708] "Application-Layer Traffic Optimization (ALTO) Requirements", February 2012. Authors' Addresses Sabine Randriamasy (editor) Alcatel-Lucent/Bell Labs Route de Villejust NOZAY 91460 FRANCE Email: Sabine.Randriamasy@alcatel-lucent.com Randriamasy, et al. Expires April 21, 2016 [Page 22] Internet-Draft Multi-Cost ALTO October 2015 Wendy Roome (editor) Alcatel-Lucent/Bell Labs 600 Mountain Ave, Rm 3B-324 Murray Hill, NJ 07974 USA Phone: +1-908-582-7974 Email: w.roome@alcatel-lucent.com Nico Schwan Thales Deutschland Lorenzstrasse 10 Stuttgart 70435 Germany Email: nico.schwan@thalesgroup.com Randriamasy, et al. Expires April 21, 2016 [Page 23]