Internet-Draft CDNI Capacity Capability Advertisement E May 2024
Ryan, et al. Expires 27 November 2024 [Page]
Content Delivery Networks Interconnection
Intended Status:
Standards Track
A. Ryan
Disney Streaming
B. Rosenblum
N. Sopher

CDNI Capacity Capability Advertisement Extensions


The CDNI Capacity Capability Advertisement Extensions define a set of additional Capability Objects that provide information about current dCDN utilization and specified usage limits to the delegating uCDN in order to inform traffic delegation decisions.

This document supplements the CDNI Capability Objects defined in RFC 8008 with two additional Capability Objects: FCI.CapacityLimits and FCI.Telemetry.

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

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 27 November 2024.

Table of Contents

1. Introduction

The Streaming Video Technology Alliance [SVTA] is a global association that works to solve streaming video challenges in an effort to improve end-user experience and adoption. The Open Caching Working Group [OCWG] of the Streaming Video Technology Alliance [SVTA] is focused on the delegation of video delivery requests from commercial CDNs to a caching layer at the ISP's network. Open Caching architecture is a specific use case of CDNI where the commercial CDN is the upstream CDN (uCDN) and the ISP caching layer is the downstream CDN (dCDN).

While delegating traffic from one CDN to the other, it is important to ensure that an appropriate amount of traffic is delegated. To achieve that, the SVTA Open Caching Capacity Insight Specification [OC-CII] defines a feedback mechanism to inform the delegator how much traffic may be delegated. The traffic level information provided by that interface will be consumed by services, such as the Open Caching Request router [OC-RR], to inform that service's traffic delegation decisions.

The provided information is advisory and does not represent a guarantee, commitment, or reservation of capacity. This document defines and registers CDNI Payload Types (as defined at section 7.1 of [RFC8006]). These Payload types are used for Capability Objects added to those defined at section 4 of [RFC8008], which are required for the Open Caching Capacity Insights Interface [OC-CII].

For consistency with other CDNI documents this document follows the CDNI convention of uCDN (upstream CDN) and dCDN (downstream CDN) to represent the commercial CDN and ISP caching layer respectively.

1.1. Terminology

The following terms are used throughout this document:

  • CDN - Content Delivery Network

Additionally, this document reuses the terminology defined in [RFC6707]. Specifically, we use the following CDNI acronyms:

  • uCDN, dCDN - Upstream CDN and Downstream CDN, respectively

1.2. Requirements Language

The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in BCP 14 [RFC2119] [RFC8174] when, and only when, they appear in all capitals, as shown here.

1.3. Objectives

To enable information exchange between a uCDN and a dCDN regarding acceptable levels of traffic delegation, the following process has been defined:

In normal operation a uCDN will communicate with a dCDN, via an interface, to collect and understand any limits that a dCDN has set forth for traffic delegation from a uCDN. These limits will come in the form of metrics such as bits per second, requests per second, etc. These limits can be thought of as Not to Exceed (NTE) limits.

The dCDN should provide access to a telemetry source of near real-time metrics that the uCDN can use to track current usage. The uCDN should compare its current usage to the limits the dCDN has put forth and adjust traffic delegation decisions accordingly to keep current usage under the specified limits.

In summary, the dCDN will inform the uCDN of the amount of traffic may be delegated. Additionally, it will provide a telemetry source aligned with this limit, allowing the uCDN to monitor its current usage against the advertised value. Having a limit and a corresponding telemetry source creates an unambiguous definition understood by both parties.

Limits that are communicated from the dCDN to the uCDN should be considered valid based on the TTL (Time To Live) provided by a mechanism of the underlying transport, e.g., an HTTP Cache-Control header. The intention is that the limits would have a long lived TTL and would represent a reasonable peak utilization limit that the uCDN should target.

2. CDNI Additional Capability Objects

Section 5 of [RFC8008] describes the FCI Capability Advertisement Object, which contains a CDNI Capability Object as well as the capability object type (a CDNI Payload Type). The section also defines the Capability Objects per such type. Below, we define two additional Capability Objects.

Note: In the following sections, the term "mandatory-to-specify" is used to convey which properties MUST be included when serializing a given capability object. When mandatory-to-specify is defined as a "Yes" for an individual property, it means that if the object containing that property is included in an FCI message, then the mandatory-to-specify property MUST be included.

2.1. Telemetry Capability Object

The Telemetry Capability Object advertises a list of telemetry sources made available to the uCDN by the dCDN. In this document, Telemetry data is being defined as near real-time aggregated metrics of dCDN utilization, such as bits per second egress, and is specific to the uCDN and dCDN traffic delegation relationship.

Telemetry data is uniquely defined by a source ID, a metric name, and the footprints that are associated with an FCI.Capability advertisement. When defining a CapacityLimit, the meaning of a limit might be ambiguous if the uCDN and dCDN are observing telemetry via different data sources. A dCDN provided telemetry source that both parties reference serves as a non-ambiguous metric for use when comparing current usage to a limit.

Telemetry data is important for making informed traffic delegation decisions. Additionally, it is essential in providing visibility of traffic that has been delegated. In situations where there are multiple CDN delegations, a uCDN will need to aggregate the usage information from any dCDNs to which it delegated when asked to provide usage information, otherwise the traffic may seem unaccounted for.

Example: A Content Provider delegates traffic directly to a uCDN, and that uCDN delegates that traffic to a dCDN. When the Content Provider polls the uCDN Telemetry interface, any of the traffic the uCDN delegated to the dCDN would become invisible to the Content Provider unless the uCDN aggregates the dCDN Telemetry with its own metrics.

  • Property: sources

    • Description: Telemetry sources made available to the uCDN.

    • Type: A JSON array of Telemetry Source objects (see Section 2.1.1).

    • Mandatory-to-Specify: Yes.

2.1.1. Telemetry Source Object

The Telemetry Source Object is built of an associated type, a list of exposed metrics, and type-specific configuration data.

  • Property: id

    • Description: An identifier of a telemetry source. The ID string assigned to this Telemetry Source MUST be unique across all Telemetry Source objects in the advertisement. The ID string SHOULD remain consistent for the same source reference across advertisements.

    • Type: String.

    • Mandatory-to-Specify: Yes.

  • Property: type

    • Description: A valid telemetry source type. See Section

    • Type: String.

    • Mandatory-to-Specify: Yes.

  • Property: metrics

    • Description: The metrics exposed by this source.

    • Type: A JSON array of Telemetry Source Metric objects (see Section

    • Mandatory-to-Specify: Yes.

  • Property: configuration

    • Description: a source-specific representation of the Telemetry source configuration. For the generic source type, this configuration format is defined out-of-band. For other types, the configuration format will be specified in a yet to be defined Telemetry Interface specification. The goal of this element is to allow for forward compatibility with a formal Telemetry interface.

    • Type: A JSON object, the structure of which is specific to the Telemetry source and outside the scope of this document.

    • Mandatory-to-Specify: No. Telemetry Source Types

At the time of this draft, the registry of valid Telemetry Source Object types is limited to a single type: Generic. The intention of this type registry is to allow for to reference a to another specification, e.g. a future CDNI Telemetry interface, which would standardize the definition and format of Telemetry data between participants of a CDNI workflow.

Table 1
Source Type Description
generic An object which allows for advertisement of generic datasources Telemetry Source Metric Object

The Telemetry Source Metric Object describes the metric to be exposed.

  • Property: name

    • Description: An identifier for this metric. This ID string MUST be unique among metric objects within the containing Telemetry Source. The ID string SHOULD remain consistent for the same source reference across advertisements.

    • Type: String.

    • Mandatory-to-Specify: Yes.

  • Property: time-granularity

    • Description: Represents the time frame that the data represents in seconds. e.g., is this a data set over 300 seconds (i.e., 5 minutes), 3600 seconds (i.e., one hour), etc.

    • Type: Integer.

    • Mandatory-to-Specify: No.

  • Property: data-percentile

    • Description: The percentile calculation the data represents, i.e., 50 percentile would equate to the median over the time-granularity. Lack of a data-percentile will mean that the data is the average over the time representation.

    • Type: Integer.

    • Mandatory-to-Specify: No.

  • Property: latency

    • Description: Time in seconds that the data is behind real-time. This is important to specify to help the uCDN understand how long it might take to reflect traffic adjustments in the metrics.

    • Type: Integer.

    • Mandatory-to-Specify: No.

2.1.2. Telemetry Capability Object Serialization

The following shows an example of Telemetry Capability including two metrics for a source, that is scoped to a footprint.

"capabilities": [
    "capability-type": "FCI.Telemetry",
    "capability-value": {
      "sources": [
          "id": "capacity_metrics_region1",
          "type": "generic",
          "metrics": [
              "name": "egress_5m",
              "time-granularity": 300,
              "data-percentile": 50,
              "latency": 1500
              "name": "requests_5m",
    "footprints": [
      <footprint objects>

2.2. CapacityLimits Capability Object

The CapacityLimits Capability Object enables the dCDN to specify traffic delegation limits to a uCDN within an FCI.Capabilities advertisement. The limits specified by the dCDN will inform the uCDN on how much traffic may be delegated to the dCDN. The limits specified by the dCDN should be considered Not To Exceed (NTE) limits. The limits should be based on near real-time telemetry data that the dCDN provides to the uCDN. In other words, for each limit that is advertised, there should also exist a telemetry source which provides current utilization data against the particular advertised limit.

  • Property: limits

    • Description: A collection of CapacityLimit objects.

    • Type: A JSON array of CapacityLimit objects (see Section 2.2.1).

    • Mandatory-to-Specify: Yes.

2.2.1. CapacityLimit Object

A CapacityLimit object is used to represent traffic limits for delegation from the uCDN towards the dCDN. The limit object is scoped to the footprint associated with the FCI capability advertisement encompassing this object. Limits will be considered using a logical "AND": a uCDN will need to ensure that all limits are considered rather than choosing only the most specific.

  • Property: limit-type

    • Description: The units of maximum-hard and maximum-soft.

    • Type: String. One of the values listed in Section

    • Mandatory-to-Specify: Yes.

  • Property: id

    • Description: Specifies an identifier associated with a limit. This MAY be used as a relational identifier to a specific CapacityLimit Object. If specified, this identifier MUST be unique among specified identifiers associated with any other CapacityLimit objects in the advertisement.

    • Type: String.

    • Mandatory-to-Specify: No.

  • Property: maximum-hard

    • Description: The maximum unit of capacity that is available for use.

    • Type: Integer.

    • Mandatory-to-Specify: Yes.

  • Property: maximum-soft

    • Description: A soft limit at which a uCDN SHOULD reduce traffic before hitting the hard limit. This value SHOULD be less than the value of maximum-hard. If this value is not specified, it is equal to the value of maximum-hard.

    • Type: Integer.

    • Mandatory-to-Specify: No.

  • Property: current

    • Description: Specifies the current usage value of the limit. It is NOT RECOMMENDED to specify the current usage value inline with the FCI.CapacityLimits advertisements as it will reduce the ability to cache the response, but this mechanism exists for simple use cases where an external telemetry source cannot be feasibly implemented. The intended method for providing telemetry data is to reference a Telemetry Source object Section to poll for the current usage.

    • Type: Integer.

    • Mandatory-to-Specify: No.

  • Property: telemetry-source

    • Description: Mapping of each particular limit to a specific metric with relevant real-time data provided by a telemetry source.

    • Type: CapacityLimitTelemetrySource object (see Section

    • Mandatory-to-Specify: No. CapacityLimit Types

Below are listed the valid capacity limit types. Additional limits would need to be specified and extended into this list. The values specified here represent the types that were identified as being the most relevant metrics for the purposes of traffic delegation between CDNs.

Table 2
Limit Type Units
egress Bits per second
requests Requests per second
storage-size Total bytes
storage-objects Count
sessions Count
cache-size Total bytes CapacityLimitTelemetrySource Object

The CapacityLimitTelemetrySource Object refers to a specific metric within a Telemetry Source.

  • Property: id

    • Description: Reference to the "id" of a telemetry source defined by a Telemetry Capability object as defined in Section 2.1.

    • Type: String.

    • Mandatory-to-Specify: Yes.

  • Property: metric

    • Description: Reference to the "name" property of a metric defined within a telemetry source of an Telemetry Capability object.

    • Type: String.

    • Mandatory-to-Specify: Yes.

2.2.2. CapacityLimit Object Serialization

The following shows an example of an FCI.CapacityLimits object.

      "<footprint objects>"

3. IANA Considerations

3.1. CDNI Payload Types

This document requests the registration of the two additional payload types:

Table 3
Payload Type Specification
FCI.Telemetry RFCthis
FCI.CapacityLimits RFCthis

[RFC Editor: Please replace RFCthis with the published RFC number for this document.]

3.1.1. CDNI FCI Telemetry Payload Type

  • Purpose: The purpose of this Payload Type is to list the supported telemetry sources and the metrics made available by each source.

  • Interface: FCI.

  • Encoding: See section Section 2.1.

3.1.2. CDNI FCI Capacity Limits Payload Type

  • Purpose: The purpose of this Payload Type is to define Capacity Limits based on a utilization metrics corresponding to telemetry sources provided by the dCDN.

  • Interface: FCI.

  • Encoding: See section Section 2.2.

4. Security Considerations

This specification is in accordance with the CDNI Request Routing: Footprint and Capabilities Semantics. As such, it is subject to the security and privacy considerations as defined in Section 7 of [RFC8008].

5. Acknowledgements

The authors would like to express their gratitude to the members of the Streaming Video Technology Alliance [SVTA] Open Caching Working Group for their guidance, contribution, and review.

6. References

6.1. Normative References

Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, DOI 10.17487/RFC2119, , <>.
Seedorf, J., Peterson, J., Previdi, S., van Brandenburg, R., and K. Ma, "Content Delivery Network Interconnection (CDNI) Request Routing: Footprint and Capabilities Semantics", RFC 8008, DOI 10.17487/RFC8008, , <>.
Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC 2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174, , <>.

6.2. Informative References

Ryan, A., Ed., Rosenblum, B., Goldstein, G., Roskin, R., and G. Bichot, "Open Caching Capacity Insights - Functional Specification (Placeholder before publication)", <>.
Finkelman, O., Ed., Hofmann, J., Klein, E., Mishra, S., Ma, K., Sahar, D., and B. Zurat, "Open Caching Request Routing - Functional Specification", Version 1.1, , <>.
"Open Caching Home Page", <>.
Niven-Jenkins, B., Le Faucheur, F., and N. Bitar, "Content Distribution Network Interconnection (CDNI) Problem Statement", RFC 6707, DOI 10.17487/RFC6707, , <>.
Peterson, L., Davie, B., and R. van Brandenburg, Ed., "Framework for Content Distribution Network Interconnection (CDNI)", RFC 7336, DOI 10.17487/RFC7336, , <>.
Niven-Jenkins, B., Murray, R., Caulfield, M., and K. Ma, "Content Delivery Network Interconnection (CDNI) Metadata", RFC 8006, DOI 10.17487/RFC8006, , <>.
Murray, R. and B. Niven-Jenkins, "Content Delivery Network Interconnection (CDNI) Control Interface / Triggers", RFC 8007, DOI 10.17487/RFC8007, , <>.
Finkelman, O. and S. Mishra, "Content Delivery Network Interconnection (CDNI) Request Routing Extensions", RFC 8804, DOI 10.17487/RFC8804, , <>.
"Streaming Video Technology Alliance Home Page", <>.

Authors' Addresses

Andrew Ryan
Disney Streaming
1211 Avenue of the Americas
New York , NY 10036
United States of America
Ben Rosenblum
4375 River Green Pkwy #100
Duluth , GA 30096
United States of America
Nir B. Sopher
6, Ha'harash
Hod HaSharon 4524079