Network Working Group S. Randriamasy Internet-Draft W. Roome Intended status: Standards Track Nokia Bell Labs Expires: March 16, 2017 N. Schwan Thales Deutschland September 12, 2016 Multi-Cost ALTO draft-ietf-alto-multi-cost-04 Abstract The ALTO (Application Layer-Traffic Optimization) Protocol ([RFC7285]) defines several services that return various metrics describing the costs between network endpoints. 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. For example, when downloading a file that is mirrored on several sites, a user application may consider more than one metric, perhaps trading bandwidth for latency to determine the most efficient mirror site. While the base ALTO Protocol allows an ALTO 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/. Internet-Drafts are draft documents valid for a maximum of six months and may be updated, replaced, or obsoleted by other documents at any Randriamasy, et al. Expires March 16, 2017 [Page 1] Internet-Draft Multi-Cost ALTO September 2016 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 March 16, 2017. Copyright Notice Copyright (c) 2016 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. Randriamasy, et al. Expires March 16, 2017 [Page 2] Internet-Draft Multi-Cost ALTO September 2016 Table of Contents 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 4 2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 5 3. Overview Of Approach . . . . . . . . . . . . . . . . . . . . . 6 3.1. Multi-Cost Data Format . . . . . . . . . . . . . . . . . . 6 3.2. Compatibility With Legacy ALTO Clients . . . . . . . . . . 7 3.3. Filtered Multi Cost Map Resources . . . . . . . . . . . . 7 3.4. Endpoint Cost Service Resources . . . . . . . . . . . . . 8 3.5. Full Cost Map Resources . . . . . . . . . . . . . . . . . 8 3.6. Extended Constraint Tests . . . . . . . . . . . . . . . . 9 3.6.1. Extended constraint predicates . . . . . . . . . . . . 9 3.6.2. Extended logical combination of predicates . . . . . . 9 3.6.3. Testable Cost Types in constraints . . . . . . . . . . 10 3.6.4. Testable Cost Type Names in IRD capabilities . . . . . 10 3.6.5. Legacy ALTO Client issues . . . . . . . . . . . . . . 11 4. Protocol Extensions for Multi-Cost ALTO Transactions . . . . . 12 4.1. Filtered Cost Map Extensions . . . . . . . . . . . . . . . 12 4.1.1. Capabilities . . . . . . . . . . . . . . . . . . . . . 12 4.1.2. Accept Input Parameters . . . . . . . . . . . . . . . 13 4.1.3. Response . . . . . . . . . . . . . . . . . . . . . . . 16 4.2. Endpoint Cost Service Extensions . . . . . . . . . . . . . 17 4.2.1. Capabilities . . . . . . . . . . . . . . . . . . . . . 17 4.2.2. Accept Input Parameters . . . . . . . . . . . . . . . 17 4.2.3. Response . . . . . . . . . . . . . . . . . . . . . . . 18 5. Examples . . . . . . . . . . . . . . . . . . . . . . . . . . . 19 5.1. Information Resource Directory . . . . . . . . . . . . . . 19 5.2. Multi-Cost Filtered Cost Map: Example #1 . . . . . . . . . 21 5.3. Multi-Cost Filtered Cost Map: Example #2 . . . . . . . . . 22 5.4. Multi-Cost Filtered Cost Map: Example #3 . . . . . . . . . 24 5.5. Multi-Cost Filtered Cost Map: Example #4 . . . . . . . . . 25 5.6. Endpoint Cost Service . . . . . . . . . . . . . . . . . . 27 6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 28 7. Privacy And Security Considerations . . . . . . . . . . . . . 28 8. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 29 9. References . . . . . . . . . . . . . . . . . . . . . . . . . . 29 9.1. Normative References . . . . . . . . . . . . . . . . . . . 29 9.2. Informative References . . . . . . . . . . . . . . . . . . 29 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 29 Randriamasy, et al. Expires March 16, 2017 [Page 3] Internet-Draft Multi-Cost ALTO September 2016 1. Introduction IETF has defined ALTO services in [RFC7285] to provide 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 as 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 Cost Maps and their modes provide values 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 (CDN), 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. Handling multiple costs, however, can add more complexities, such as overheads and consistency. In particular, cost values that change more frequently than previously assumed may require more frequent ALTO requests. Moreover, to make sure to have up to date values, applications using several frequently changing metrics will tend to refresh their values simultaneously. The ALTO protocol [RFC7285], which this document refers to as the base protocol, 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 Round Trip Time (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 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 for their transmission. Additionally, Randriamasy, et al. Expires March 16, 2017 [Page 4] Internet-Draft Multi-Cost ALTO September 2016 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: providing values for several Cost Types in one single batch is useful for ALTO 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 an ALTO 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 extends 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, only the Filtered Cost Map and Endpoint Cost Map services are extended to return Multi-Cost values. Full Cost Map services remain unchanged, and are restricted to returning single cost values. 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 definitions. Section 5 gives several complete examples. The remaining sections describe the IANA and privacy considerations. 2. Terminology o {1.2.3}: References with curly brackets are to sections in the ALTO protocol specification [RFC7285]. 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, or any application client that can choose between several connection points for data or resource exchange. Randriamasy, et al. Expires March 16, 2017 [Page 5] Internet-Draft Multi-Cost ALTO September 2016 o Client: This term refers to an ALTO client, when used with a capital "C". o Endpoint (EP): An endpoint is defined as in {2.1} of [RFC7285]. It can be for example a peer, a CDN storage location, a physical server involved in a virtual server-supported application, a party 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 CDNs who care for the dissemination, persistent storage and possibly identification of the best/closest content copy. o Server: This term refers to an ALTO server, when used with a capital "S". 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 March 16, 2017 [Page 6] Internet-Draft Multi-Cost ALTO September 2016 { "meta" : { "dependent-vtags" : [ ... ], "cost-type" : {}, "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 ALTO Clients The multi-cost extensions defined in this document must not break legacy implementations (that is, ALTO 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 Multi Cost Map resources. This relies on the requirement that ALTO Clients MUST ignore unknown fields ({8.3.7}). 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 March 16, 2017 [Page 7] Internet-Draft Multi-Cost ALTO September 2016 "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 ALTO 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 ALTO 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 ALTO 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 ALTO 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. Therefore unless we create a new media type for array-valued Cost Maps, it is not possible to define a Multi-Cost Full Cost Map resource so that multi- cost-aware ALTO Clients can recognize it and legacy ALTO 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 ALTO 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. Randriamasy, et al. Expires March 16, 2017 [Page 8] Internet-Draft Multi-Cost ALTO September 2016 However {11.3.2.3} of [RFC7285] requires a Filtered Cost Map to return the entire Cost Map if the ALTO Client omits the source and destination PIDs. Hence an ALTO 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 ALTO Client. For example, if the ALTO 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. 3.6.1. Extended constraint predicates 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. 3.6.2. Extended logical combination of predicates Second, once multiple cost metrics are involved, the "AND" of simple predicates is no longer 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: Randriamasy, et al. Expires March 16, 2017 [Page 9] Internet-Draft Multi-Cost ALTO September 2016 { "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": {...} } 3.6.3. Testable Cost Types in constraints Finally, a Client may want to test a cost type whose actual value is irrelevant, as long as it satisfies the tests. For example, a Client may want the value of the cost metric "routingcost" for all PID pairs that satisfy constraints on the metric "hopcount", without needing the actual value of "hopcount". For example, the 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. (If "testable-cost-types" is omitted, it is assumed to be the same as "multi-cost-types".) 3.6.4. Testable Cost Type Names in IRD capabilities In [RFC7285], when a resource's capability "constraints" is true, the Server accepts constraints on all the cost types listed in the "cost- type-names" capability. However, some ALTO Servers may not be willing to allow constraint tests on all available cost metrics. Therefore the Multi-Cost ALTO protocol extension defines the Randriamasy, et al. Expires March 16, 2017 [Page 10] Internet-Draft Multi-Cost ALTO September 2016 capability field "testable-cost-type-names". Like "cost-type-names", it is an array of cost type names. If present, that resource only allows constraint tests on the cost types in that list. "testable- cost-type-names" MUST be a subset of "cost-type-names". 3.6.5. Legacy ALTO Client issues While a multi-cost-aware Client will recognize the "testable-cost- type-names" field, and will honor those restrictions, a legacy Client will not. Hence a legacy may send a request with a constraint test on any of the cost types listed in "cost-type-names". To avoid that problem, the "testable-cost-type-names" and "cost- constraints" fields are mutually exclusive: a resource may define one or the other capability, but MUST NOT define both. Thus a resource that does not allow constraint tests on all cost metrics will set "testable-cost-type-names" to the testable metrics, and will set "cost-constraints" to "false". A multi-cost-aware Client will recognize the "testable-cost-type-names" field, and will realize that its existence means the resource does allow (limited) constraint tests, while a legacy Client will think that resource does not allow constraint tests at all. To allow legacy Clients to use constraint tests, the ALTO Server MAY define an additional resource with "cost- constraints" set to "true" and "cost-type-names" set to the metrics which can be tested. In the IRD example below, the resource "filtered-cost-map-extended" provides values for three metrics: "num-routingcost", "num-hopcount" and "num-bwscore". The capability "testable-cost-type-names" indicates that the Server only allows constraints on "routingcost" and "hopcount". A multi-cost capable Client will see this capability, and will limit its constraint tests to those metrics. Because capability "cost-constraints" is false (by default), a legacy Client will not use constraint tests on this resource at all. The second resource, "filtered-multicost-map", is similar to the first, except that all the metrics it returns are testable. Therefore it sets "cost-constraints" to "true", and does not set the "testable-cost-type-names" field. A legacy Client that needs a constraint test will use this resource rather than the first. A multi-cost-aware Client that does not need to retrieve the "num- bwscore" metric may use either resource. Randriamasy, et al. Expires March 16, 2017 [Page 11] Internet-Draft Multi-Cost ALTO September 2016 "filtered-cost-map-extended" : { "uri" : "http://alto.example.com/multi/extn/costmap/filtered", "media-types" : [ "application/alto-costmap+json" ], "accepts" : [ "application/alto-costmapfilter+json" ], "uses" : [ "my-default-network-map" ], "capabilities" : { "max-cost-types" : 3, "cost-type-names" : [ "num-routingcost", "num-hopcount", "num-bwscore"], "testable-cost-type-names" : [ "num-routingcost", "num-hopcount" ] } }, "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"], } } 4. Protocol Extensions for Multi-Cost ALTO Transactions This section formally specifies the 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. Capabilities The filtered cost map capabilities are extended with two new members: Randriamasy, et al. Expires March 16, 2017 [Page 12] Internet-Draft Multi-Cost ALTO September 2016 o max-cost-types, o testable-cost-type-names The capability "max-cost-types" indicates whether this resource supports the Multi-Cost ALTO extensions, and the capability "testable-cost-type-names" allows the resource to restrict constraint tests to a subset of the available cost types. 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<1..*>;] } FilteredCostMapCapabilities; cost-type-names and cost-constraints: As defined in {11.3.2.4} of [RFC7285]. 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, the resource allows constraint tests, but only on the cost type names in this array. Each name in "testable-cost-type-names" MUST also be in "cost-type-names". If "testable-cost-type-names" is present, the "cost-constraints" capability MUST NOT be "true", and if "cost-constraints" is "true", "testable-cost-type-names" MUST NOT be present. Thus if "cost-constraints" is "true", the resource MUST accept constraint tests on any cost type in "cost-type-names". As discussed in Section 3.6.4, this capability is useful when a Server is unable or unwilling to implement constraint tests on all cost types. As discussed in Section 3.6.5, "testable-cost-type- names" and "cost-constraints" are mutually exclusive to prevent legacy Clients from issuing constraint tests on untestable cost types. 4.1.2. Accept Input Parameters The ReqFilteredCostMap object in {11.3.2.3} of [RFC7285] is extended as follows: Randriamasy, et al. Expires March 16, 2017 [Page 13] Internet-Draft Multi-Cost ALTO September 2016 object { [CostType cost-type;] [CostType multi-cost-types<1..*>;] [CostType testable-cost-types<1..*>;] [JSONString constraints<0..*>;] [JSONString or-constraints<1..*><1..*>;] PIDFilter pids; } ReqFilteredCostMap; object { PIDName srcs<0..*>; PIDName dsts<0..*>; } PIDFilter; cost-type: As defined in {11.3.2.3} of [RFC7285], with the additional requirement that the Client MUST specify either "cost- type" or "multi-cost-types", but MUST NOT specify 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 member "cost-type-names" of this resource's "capabilities" field (Section 4.1.1). The Client MUST NOT use this field unless this resource's "max-cost-types" capability exists and has a value greater than 0. This field MUST NOT have more than "max-cost-types" cost types. The Client MUST specify either "cost-type" or "multi-cost-types", but MUST NOT specify both. Note that if "multi-cost-types" has one cost type, the values in the cost map will be arrays with one value. testable-cost-types: A list of cost types used for extended constraint tests, as described for the "constraints" and "or- constraints" parameters. These cost types must either be a subset of the cost types in the resource's "testable-cost-type-names" capability (Section 4.1.1), or else, if the resource's capability "cost-constraints" is true, a subset of the cost types in the resource's "cost-type-names" capability. If "testable-cost-types" is omitted, it is assumed to have the cost types in "multi-cost-types" or "cost-type". This feature is useful when a Client wants to test a cost type whose actual value is irrelevant, as long as it satisfies the tests. For example, a Client may want the cost metric "routingcost" for those PID pairs whose "hopcount" is less than Randriamasy, et al. Expires March 16, 2017 [Page 14] Internet-Draft Multi-Cost ALTO September 2016 10. The exact hopcount does not matter. constraints: If this resource's "max-cost-types" capability (Section 4.1.1) has the value 0 (or is not defined), this parameter is as defined in {11.3.2.3} of [RFC7285]: an array of constraint tests related to each other by a logical AND. In this case it MUST NOT be specified unless the resource's "cost- constraints" capability is "true". If this resource's "max-cost-types" capability has a value greater than 0, then this parameter is an array of extended constraint predicates as defined below and related to each other by a logical AND. In this case, it MAY be specified if the resource allows constraint tests (the resource's "cost-constraints" capability is "true" or its "testable-cost-type-names" capability is not empty). This parameter MUST NOT be specified if the "or-constraints" parameter is specified. An extended constraint predicate 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, i, specifies the cost type to test. If the "testable-cost-type" parameter is present, 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 that array. If neither parameters are present, the test applies to the cost type in the "cost-type" parameter, in which case the index MUST be 0. Regardless of how the tested cost type is selected, it MUST be in the resource's "testable-cost- type-names" capability, or, if not present, in the "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 and provide routingcost WHERE hopcount <= 5". Note that the index is optional, so a constraint test as defined in {11.3.2.3}, such as "le 10", is equivalent to "[0] le 10". Thus legacy constraint tests are also legal extended constraint tests. Randriamasy, et al. Expires March 16, 2017 [Page 15] Internet-Draft Multi-Cost ALTO September 2016 Note that a "constraints" parameter with the array of extended predicates [P1, P2, ...] is equivalent to an "or-constraints" parameter as defined below, with the value [[P1, P2, ...]]. or-constraints: A JSONArray of JSONArrays of JSONStrings, where each string is an extended constraint predicate as defined above. The "or-constraint" tests are interpreted as the logical OR of ANDs of predicates. 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 MAY be specified if this resource's "max-cost- types" capability is defined with a value greater than 0 (Section 4.1.1), and if the resource allows constraint tests (the resource's "cost-constraints" capability is "true" or its "testable-cost-type-names" capability is not empty). Otherwise this parameter MUST NOT be specified. This parameter MUST NOT be specified if the "constraints" parameter is specified. This parameter MUST NOT contain any empty array of AND predicates. An empty array would be equivalent to a constraint that is always "true". An OR combination including such a constraint would be always "true" and thus useless. As an example, suppose "multi-cost-types" has the two elements "routingcost" and "bandwidthscore", and "testable-cost-types" has the two elements "routingcost" and "hopcount", and "or- constraints" has the two elements ["[0] le 100", "[1] le 2"] and ["[0] le 10", "[1] le 6"]. This is equivalent to the database query: "SELECT and provide routingcost and bandwidthscore WHERE ("routingcost" <= 100 AND "hopcount" <= 2) OR ("routingcost" <= 10 AND "hopcount" <= 6)". Note that if the "max-cost-types" capability has a value greater than 0, a Client MAY use the "or-constraints" parameter together 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]. 4.1.3. 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: Randriamasy, et al. Expires March 16, 2017 [Page 16] Internet-Draft Multi-Cost ALTO September 2016 o In "meta", the field "cost-type" is provided with a dummy value. Instead, the field "multi-cost-types" is added 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. 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. Capabilities The extensions to the Endpoint Cost Service capabilities are identical to the extensions to the Filtered Cost Map (see Section 4.1.1). 4.2.2. 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<1..*><1..*>;] EndpointFilter endpoints; } ReqFilteredCostMap; object { [TypedEndpointAddr srcs<0..*>;] [TypedEndpointAddr dsts<0..*>;] } EndpointFilter; Randriamasy, et al. Expires March 16, 2017 [Page 17] Internet-Draft Multi-Cost ALTO September 2016 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 MUST NOT specify 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 4.2.1). The Client MUST NOT use this field unless this resource's "max-cost-types" capability exists and has a value greater than 0. This field MUST NOT have more than "max-cost- types" cost types. The Client MUST specify either "cost-type" or "multi-cost-types", but MUST NOT specify both. Note that if "multi-cost-types" has one cost type, the values in the cost map will be arrays with one value. testable-cost-types, constraints, or-constraints: Defined equivalently to the corresponding input parameters for an extended Filtered Cost Map (Section 4.1.2). endpoints, srcs, dsts: As defined in {11.5.1.3} of [RFC7285]. 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 provided with a dummy value. Instead, the field "multi-cost-types" is added 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. Randriamasy, et al. Expires March 16, 2017 [Page 18] Internet-Draft Multi-Cost ALTO September 2016 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 two Filtered Cost Map and an Endpoint Cost Service, which all understand the multi-cost extensions. GET /directory HTTP/1.1 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" }, "num-bwscore" : { "cost-mode" : "numerical", "cost-metric" : "bandwidthscore" }, ..... Other ALTO cost types as described in RFC7285 ..... } }, "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" ], Randriamasy, et al. Expires March 16, 2017 [Page 19] Internet-Draft Multi-Cost ALTO September 2016 "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" ] } }, ......... Other 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" ] } }, "filtered-cost-map-extended" : { "uri" : "http://alto.example.com/multi/extn/costmap/filtered", "media-types" : [ "application/alto-costmap+json" ], "accepts" : [ "application/alto-costmapfilter+json" ], "uses" : [ "my-default-network-map" ], "capabilities" : { "max-cost-types" : 3, "cost-type-names" : [ "num-routingcost", "num-hopcount", "num-bwscore"], "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, Randriamasy, et al. Expires March 16, 2017 [Page 20] Internet-Draft Multi-Cost ALTO September 2016 "max-cost-types" : 2, "cost-type-names" : [ "num-routingcost", "num-hopcount" ] } } } } 5.2. Multi-Cost Filtered Cost Map: Example #1 This example illustrates a simple multi-cost ALTO transaction. The ALTO Server provides two Cost Types, "routingcost" and "hopcount", both in "numerical" mode. The ALTO Server does not know the value of the "routingcost" between PID2 and PID3, and hence uses "null" for those costs. POST /multi/costmap/filtered" HTTP/1.1 Host: alto.example.com Accept: application/alto-costmap+json,application/alto-error+json Content-Type: application/alto-costmapfilter+json Content-Length: ### { "multi-cost-types": [ {"cost-mode": "numerical", "cost-metric": "routingcost"}, {"cost-mode": "numerical", "cost-metric": "hopcount"} ], "pids" : { "srcs" : [ ], "dsts" : [ ] } } Randriamasy, et al. Expires March 16, 2017 [Page 21] Internet-Draft Multi-Cost ALTO September 2016 HTTP/1.1 200 OK Content-Type: application/alto-costmap+json Content-Length: ### { "meta" : { "dependent-vtags" : [ {"resource-id": "my-default-network-map", "tag": "3ee2cb7e8d63d9fab71b9b34cbf764436315542e" } ], "cost-type" : {}, "multi-cost-types" : [ {"cost-mode": "numerical", "cost-metric": "routingcost"}, {"cost-mode": "numerical", "cost-metric": "hopcount"} ] } } "cost-map" : { "PID1": { "PID1":[1,0], "PID2":[4,3], "PID3":[10,2] }, "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 example uses 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 March 16, 2017 [Page 22] Internet-Draft Multi-Cost ALTO September 2016 POST /multi/costmap/filtered HTTP/1.1 Host: alto.example.com Accept: application/alto-costmap+json,application/alto-error+json Content-Type: application/alto-costmapfilter+json Content-Length: ### { "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 Content-Length: ### { "meta" : { "dependent-vtags" : [ {"resource-id": "my-default-network-map", "tag": "3ee2cb7e8d63d9fab71b9b34cbf764436315542e" } ], "cost-type" : {}, "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] } } } Randriamasy, et al. Expires March 16, 2017 [Page 23] Internet-Draft Multi-Cost ALTO September 2016 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" <= 3 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- types" to tell the Server to return scalar costs instead of array costs: POST /multi/multicostmap/filtered HTTP/1.1 Host: alto.example.com Accept: application/alto-costmap+json,application/alto-error+json Content-Type: application/alto-costmapfilter+json Content-Length: ### { "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" : [ ] } } Randriamasy, et al. Expires March 16, 2017 [Page 24] Internet-Draft Multi-Cost ALTO September 2016 HTTP/1.1 200 OK Content-Type: application/alto-costmap+json Content-Length: ### { "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 } } } 5.5. Multi-Cost Filtered Cost Map: Example #4 This example uses extended constraints to limit the response to cost points with ("routingcost" <= 10 and "hopcount" <= 2), or else ("routingcost" <= 3 and "hopcount" <= 6). In this example, the Client is interested in the "routingcost" and "bandwidthscore" cost metrics, but not in the "hopcount" metric: Randriamasy, et al. Expires March 16, 2017 [Page 25] Internet-Draft Multi-Cost ALTO September 2016 POST /multi/extn/costmap/filtered HTTP/1.1 Host: alto.example.com Accept: application/alto-costmap+json,application/alto-error+json Content-Type: application/alto-costmapfilter+json Content-Length: ### { "multi-cost-types" : [ {"cost-mode": "numerical", "cost-metric": "routingcost"}, {"cost-mode": "numerical", "cost-metric": "bandwidthscore"} ], "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" : [ ] } } Randriamasy, et al. Expires March 16, 2017 [Page 26] Internet-Draft Multi-Cost ALTO September 2016 HTTP/1.1 200 OK Content-Type: application/alto-costmap+json Content-Length: ### { "meta" : { "dependent-vtags" : [ {"resource-id": "my-default-network-map", "tag": "3ee2cb7e8d63d9fab71b9b34cbf764436315542e" } ], "cost-type" : {}, "multi-cost-types" : [ {"cost-mode": "numerical", "cost-metric": "routingcost"}, {"cost-mode": "numerical", "cost-metric": "bandwidthscore"} ] } "cost-map" : { "PID1": { "PID1": [1,16] "PID3": [10,19] }, "PID2": { "PID2": [1,8] }, "PID3": { "PID3": [1,19] } } } 5.6. 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). POST /multi/endpointcost/lookup HTTP/1.1 Host: alto.example.com Accept: application/alto-endpointcost+json, application/alto-error+json Content-Type: application/alto-endpoincostparams+json Content-Length: ### { "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"] ], Randriamasy, et al. Expires March 16, 2017 [Page 27] Internet-Draft Multi-Cost ALTO September 2016 "endpoints" : { "srcs": [ "ipv4:192.0.2.2", "ipv6:2001:db8::1:0 ], "dsts": [ "ipv4:192.0.2.89", "ipv4:198.51.100.34", "ipv4:203.0.113.45", "ipv6:2001:db8::10" ] } } HTTP/1.1 200 OK Content-Length: ### 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] } "ipv6:2001:db8::1:0": { "ipv4:198.51.100.34": [16, 5], "ipv6:2001:db8::10": [10, 2] } } } 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. Randriamasy, et al. Expires March 16, 2017 [Page 28] Internet-Draft Multi-Cost ALTO September 2016 8. Acknowledgements The authors would like to thank Richard Alimi, Fred Baker, Dhruv Dhodi, Vijay Gurbani, Dave Mac Dysan, Young Lee, Richard Yang, for fruitful discussions and feedback on this document and previous versions. Gao Kai, Hans Seidel, Richard Yang, Qiao Xiang and Wang Xin provided substantial review feedback and suggestions to the protocol design. 9. References 9.1. Normative References [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", RFC 2119, BCP 14, 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 Nokia Bell Labs Route de Villejust NOZAY 91460 FRANCE Email: Sabine.Randriamasy@nokia-bell-labs.com Randriamasy, et al. Expires March 16, 2017 [Page 29] Internet-Draft Multi-Cost ALTO September 2016 Wendy Roome Nokia Bell Labs 600 Mountain Ave, Rm 3B-324 Murray Hill, NJ 07974 USA Phone: +1-908-582-7974 Email: w.roome@nokia-bell-labs.com Nico Schwan Thales Deutschland Lorenzstrasse 10 Stuttgart 70435 Germany Email: nico.schwan@thalesgroup.com Randriamasy, et al. Expires March 16, 2017 [Page 30]