CDNI                                                          J. Seedorf
Internet-Draft                 HFT Stuttgart - Univ. of Applied Sciences
Intended status: Standards Track                                 Y. Yang
Expires: January 21, 2018                                    Tongji/Yale
                                                                   K. Ma
                                                             J. Peterson
                                                           July 20, 2017

 Content Delivery Network Interconnection (CDNI) Request Routing: CDNI
          Footprint and Capabilities Advertisement using ALTO


   The Content Delivery Networks Interconnection (CDNI) WG is defining a
   set of protocols to inter-connect CDNs, to achieve multiple goals
   such as extending the reach of a given CDN to areas that are not
   covered by that particular CDN.  One componet that is needed to
   achieve the goal of CDNI is the CDNI Request Routing Footprint &
   Capabilities Advertisement interface (FCI) [RFC7336].  [RFC8008] has
   defined precisely the semantics of FCI and provided guidelines on the
   FCI protocol, but the exact protocol is explicitly outside the scope
   of that document.  In this document, we define an FCI protocol using
   the Application Layer Traffic Optimization (ALTO) protocol.

Status of This Memo

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   This Internet-Draft will expire on January 21, 2018.

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Copyright Notice

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   described in the Simplified BSD License.

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
   2.  Background  . . . . . . . . . . . . . . . . . . . . . . . . .   4
     2.1.  Semantics of FCI Advertisment . . . . . . . . . . . . . .   4
     2.2.  ALTO Background and Benefits  . . . . . . . . . . . . . .   5
   3.  CDNI FCI ALTO Service . . . . . . . . . . . . . . . . . . . .   7
     3.1.  Server Response Encoding  . . . . . . . . . . . . . . . .   8
       3.1.1.  Media Type  . . . . . . . . . . . . . . . . . . . . .   8
       3.1.2.  Meta Information  . . . . . . . . . . . . . . . . . .   8
       3.1.3.  Data Information  . . . . . . . . . . . . . . . . . .   8
     3.2.  Protocol Errors . . . . . . . . . . . . . . . . . . . . .   8
     3.3.  Examples  . . . . . . . . . . . . . . . . . . . . . . . .   8
       3.3.1.  Basic Example . . . . . . . . . . . . . . . . . . . .   8
       3.3.2.  Incremental FCI Update Example  . . . . . . . . . . .   9
       3.3.3.  FCI Using ALTO Network Map Example  . . . . . . . . .   9
   4.  Security Considerations . . . . . . . . . . . . . . . . . . .   9
   5.  Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .  10
   6.  References  . . . . . . . . . . . . . . . . . . . . . . . . .  10
     6.1.  Normative References  . . . . . . . . . . . . . . . . . .  10
     6.2.  Informative References  . . . . . . . . . . . . . . . . .  11
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  11

1.  Introduction

   Many Network Service Providers (NSPs) are currently considering or
   have already started to deploy Content Delivery Networks (CDNs)
   within their networks.  As a consequence of this development, there
   is a need for interconnecting these local CDNs.  Content Delivery
   Networks Interconnection (CDNI) has the goal of standardizing
   protocols to enable such interconnection of CDNs [RFC6707].

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   The CDNI problem statement [RFC6707] defines four interfaces to be
   standardized within the IETF for CDN interconnection:

   o  CDNI Request Routing Interface

   o  CDNI Metadata Interface

   o  CDNI Logging Interface

   o  CDNI Control Interface

   The main purpose of the CDNI Request Routing Interface is described
   in [RFC6707] as follows: "The CDNI Request Routing interface enables
   a Request Routing function in an Upstream CDN to query a Request
   Routing function in a Downstream CDN to determine if the Downstream
   CDN is able (and willing) to accept the delegated Content Request.
   It also allows the Downstream CDN to control what should be returned
   to the User Agent in the redirection message by the upstream Request
   Routing function."  On a high level, the scope of the CDNI Request
   Routing Interface therefore contains two main tasks:

   o  determining if the downstream CDN is willing to accept a delegated
      content request;

   o  redirecting the content request coming from an upstream CDN to the
      proper entry point or entity in the downstream CDN.

   Correspondingly, the request routing interface is broadly divided
   into two functionalities:

   o  CDNI FCI: the advertisement from a dCDN to a uCDN or a query from
      a uCDN to a dCDN for the uCDN to decide whether to redirect
      particular user requests to that dCDN;

   o  CDNI RI: the synchronous operation of actually redirecting a user

   This document focuses solely on CDNI FCI, with a goal to specify a
   new Application Layer Traffic Optimization (ALTO) [RFC7285] service
   called 'CDNI/FCI Service', to transport and update CDNI FCI JSON
   objects, which are defined in a separate document in [RFC8008].

   Throughout this document, we use the terminology for CDNI defined in
   [RFC6707] and [RFC8008].

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2.  Background

   The design of CDNI FCI transport using ALTO depends on understanding
   of both FCI semantics and ALTO.  Hence, we start with a review of

2.1.  Semantics of FCI Advertisment

   The CDNI document on "Footprint and Capabilities Semantics" [RFC8008]
   defines the semantics for the CDNI FCI.  It thus provides guidance on
   what Footprint and Capabilities mean in a CDNI context and how a
   protocol solution should in principle look like.  The definitions in
   [RFC8008] depend on [RFC8006].  Here we briefly summarize key related
   points of [RFC8008] and [RFC8006].  For a detailed discussion, the
   reader is referred to the RFCs.

   o  Footprint and capabilities are tied together and cannot be
      interpreted independently from each other.  In such cases, i.e.
      where capabilities must be expressed on a per footprint basis, it
      may be beneficial to combine footprint and capabilities
      advertisement.  [RFC8008] integrates footprint and capabilities
      with an approach of "capabilities with footprint restrictions".

   o  Given that a large part of Footprint and Capabilities
      Advertisement will actually happen in contractual agreements, the
      semantics of CDNI Footprint and Capabilities advertisement refer
      to answering the following question: what exactly still needs to
      be advertised by the CDNI FCI?  For instance, updates about
      temporal failures of part of a footprint can be useful information
      to convey via the CDNI request routing interface.  Such
      information would provide updates on information previously agreed
      in contracts between the participating CDNs.  In other words, the
      CDNI FCI is a means for a dCDN to provide changes/updates
      regarding a footprint and/or capabilities it has prior agreed to
      serve in a contract with a uCDN.  Hence, server push and
      incremental encoding will be necessary techniques.

   o  Multiple types of footprints are defined in [RFC8006]:

      *  List of ISO Country Codes

      *  List of AS numbers

      *  Set of IP-prefixes

      A 'set of IP-prefixes' must be able to contain full IP addresses,
      i.e., a /32 for IPv4 and a /128 for IPv6, and also IP prefixes
      with an arbitrary prefix length.  There must also be support for

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      multiple IP address versions, i.e., IPv4 and IPv6, in such a

   o  For all of these mandatory-to-implement footprint types,
      footprints can be viewed as constraints for delegating requests to
      a dCDN: A dCDN footprint advertisement tells the uCDN the
      limitations for delegating a request to the dCDN.  For IP prefixes
      or ASN(s), the footprint signals to the uCDN that it should
      consider the dCDN a candidate only if the IP address of the
      request routing source falls within the prefix set (or ASN,
      respectively).  The CDNI specifications do not define how a given
      uCDN determines what address ranges are in a particular ASN.
      Similarly, for country codes a uCDN should only consider the dCDN
      a candidate if it covers the country of the request routing
      source.  The CDNI specifications do not define how a given uCDN
      determines the country of the request routing source.  Multiple
      footprint constraints are additive, i.e. the advertisement of
      different types of footprint narrows the dCDN candidacy

   o  The following capabilities are defined as 'base' capabilities,
      i.e. ones that are needed in any case and therefore constitute
      mandatory capabilities to be supported by the CDNI FCI:

      *  Delivery Protocol (e.g., HTTP vs. RTMP)

      *  Acquisition Protocol (for acquiring content from a uCDN)

      *  Redirection Mode (e.g., DNS Redirection vs. HTTP Redirection as
         discussed in [RFC7336])

      *  Capabilities related to CDNI Logging (e.g., supported logging

      *  Capabilities related to CDNI Metadata (e.g., authorization
         algorithms or support for proprietary vendor metadata)

2.2.  ALTO Background and Benefits

   Application Layer Traffic Optimization (ALTO) [RFC7285] is an
   approach for guiding the resource provider selection process in
   distributed applications that can choose among several candidate
   resources providers to retrieve a given resource.  By conveying
   network layer (topology) information, an ALTO server can provide
   important information to "guide" the resource provider selection
   process in distributed applications.  Usually, it is assumed that an
   ALTO server conveys information these applications cannot measure
   themselves [RFC5693].

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   Originally, ALTO was motivated by the huge amount of cross-ISP
   traffic generated by P2P applications [RFC5693].  Recently, however,
   ALTO is also being considered for improving the request routing in
   CDNs [I-D.jenkins-alto-cdn-use-cases].  In this context, it has also
   been proposed to use ALTO for selecting an entry-point in a
   downstream NSP's network (see section 3.4 "CDN delivering Over-The-
   Top of a NSP's network" in [I-D.jenkins-alto-cdn-use-cases]).  Also,
   the CDNI problem statement explicitly mentions ALTO as a candidate
   protocol for "algorithms for selection of CDN or Surrogate by
   Request-Routing systems" [RFC6707].

   The following reasons make ALTO a suitable candidate protocol for
   downstream CDN selection as part of CDNI request routing and in
   particular for an FCI protocol:

   o  CDN request routing is done at the application layer.  ALTO is a
      protocol specifically designed to improve application layer
      traffic (and application layer connections among hosts on the
      Internet) by providing additional information to applications that
      these applications could not easily retrieve themselves.  For
      CDNI, this is exactly the case: a uCDN wants to improve
      application layer CDN request routing by using dedicated
      information (provided by a dCDN) that the uCDN could not easily
      obtain otherwise.

   o  The semantics of an ALTO network map are an exact match for the
      needed information to convey a footprint by a downstream CDN, in
      particular if such a footprint is being expressed by IP-prefix

   o  Security: ALTO maps can be signed and hence provide inherent
      integrity protection (see Section 4)

   o  RESTful-Design: The ALTO protocol has undergone extensive
      revisions in order to provide a RESTful design regarding the
      client-server interaction specified by the protocol.  A CDNI FCI
      interface based on ALTO would inherit this RESTful design.

   o  Error-handling: The ALTO protocol has undergone extensive
      revisions in order to provide sophisticated error-handling, in
      particular regarding unexpected cases.  A CDNI FCI interface based
      on ALTO would inherit this thought-through and mature error-

   o  Filtered network map: The ALTO Map Filtering Service (see
      [RFC7285] for details) would allow a uCDN to query only for parts
      of an ALTO map.

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   o  Server-initiated Notifications and Incremental Updates: In case
      the footprint or the capabilities of a downstream CDN change
      abruptly (i.e. unexpectedly from the perspective of an upstream
      CDN), server initiated notifications would enable a dCDN to
      directly inform an upstream CDN about such changes.  Consider the
      case where - due to failure - part of the footprint of the dCDN is
      not functioning, i.e. the CDN cannot serve content to such clients
      with reasonable QoS.  Without server-initiated notifications, the
      uCDN might still use a very recent network and cost map from dCDN,
      and therefore redirect request to dCDN which it cannot serve.
      Similarly, the possibility for incremental updates would enable
      efficient conveyance of the aforementioned (or similar) status
      changes by the dCDN to the uCDN.  The newest design of ALTO
      supports server pushed incremental updates

   o  Content Availability on Hosts: A dCDN might want to express CDN
      capabilities in terms of certain content types (e.g. codecs/
      formats, or content from certain content providers).  The new
      endpoint property for ALTO would enable a dCDN to make available
      such information to an upstream CDN.  This would enable a uCDN to
      determine if a given dCDN actually has the capabilities for a
      given request with respect to the type of content requested.

   o  Resource Availability on Hosts or Links: The capabilities on links
      (e.g. maximum bandwidth) or caches (e.g. average load) might be
      useful information for an upstream CDN for optimized downstream
      CDN selection.  For instance, if a uCDN receives a streaming
      request for content with a certain bitrate, it needs to know if it
      is likely that a dCDN can fulfill such stringent application-level
      requirements (i.e. can be expected to have enough consistent
      bandwidth) before it redirects the request.  In general, if ALTO
      could convey such information via new endpoint properties, it
      would enable more sophisticated means for downstream CDN selection
      with ALTO.

3.  CDNI FCI ALTO Service

   The ALTO protocol is based on an ALTO Information Service Framework
   which consists of several services, where all ALTO services are
   'provided through a common transport protocol, messaging structure
   and encoding, and transaction model' [RFC7285].  The ALTO protocol
   specification [RFC7285] defines several such services, e.g. the ALTO
   map service.

   This document defines a new ALTO Service called 'CDNI Footprint &
   Capabilities Advertisement Service' which conveys JSON objects of
   media type 'application/cdni'.  This media type and JSON object

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   format is defined in [RFC8006] and [RFC8008]; this document specifies
   how to transport such JSON objects via the ALTO protocol with the
   ALTO 'CDNI Footprint & Capabilities Advertisement Service'.

3.1.  Server Response Encoding

3.1.1.  Media Type

   The media type of the CDNI FCI Map is 'application/cdni'.

3.1.2.  Meta Information

   The 'meta' field of a FCI response MUST include 'vtag', which is an
   ALTO Version Tag of the retrieved FCIMapData according to [RFC7285]
   (Section 10.3.).  It thus contains a 'resource-id' attribute, and a
   'tag' is an identifier string.

3.1.3.  Data Information

   The data component of a CDNI FCI resource is named 'cdni-fcimap'
   which is a JSON object defined by [RFC8008].  This JSON object is
   derived from ResponseEntityBase as specified in the ALTO protocol
   [RFC7285] (Section 8.4.).

3.2.  Protocol Errors

   Protocol errors are handled as specified in the ALTO protocol
   [RFC7285] (Section 8.5.).

3.3.  Examples

3.3.1.  Basic Example

   The following example shows an CDNI FCI response as in [RFC8008],
   however with meta-information as defined in Section 3.1.2 of this

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      GET /fcimap HTTP/1.1
      Accept: application/cdni,application/alto-error+json

      HTTP/1.1 200 OK
      Content-Length: 439
      Content-Type: application/cdni
        "meta" : {
          "vtag": {
            "resource-id": "my-default-fcimap",
             "tag": "da65eca2eb7a10ce8b059740b0b2e3f8eb1d4785"
        "cdni-fcimap": {
          "capabilities": [
              "capability-type": "FCI.DeliveryProtocol",
              "capability-value": {
                "delivery-protocols": [
              "footprints": [
                <Footprint objects>

3.3.2.  Incremental FCI Update Example

3.3.3.  FCI Using ALTO Network Map Example

4.  Security Considerations

   One important security consideration is the proper authentication of
   advertisement information provided by a downstream CDN.  The ALTO
   protocol provides a specification for a signature of ALTO information
   (see 8.2.2. of [RFC7285].  ALTO thus provides a proper means for
   protecting the integrity of FCI information.

   More Security Considerations will be discussed in a future version of
   this document.

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5.  Acknowledgements

   The authors would like to thank Kevin Ma, Daryl Malas, and Matt
   Caulfield for their timely reviews and invaluable comments.

   Jan Seedorf is partially supported by the GreenICN project (GreenICN:
   Architecture and Applications of Green Information Centric
   Networking), a research project supported jointly by the European
   Commission under its 7th Framework Program (contract no. 608518) and
   the National Institute of Information and Communications Technology
   (NICT) in Japan (contract no. 167).  The views and conclusions
   contained herein are those of the authors and should not be
   interpreted as necessarily representing the official policies or
   endorsements, either expressed or implied, of the GreenICN project,
   the European Commission, or NICT.

6.  References

6.1.  Normative References

   [RFC5693]  Seedorf, J. and E. Burger, "Application-Layer Traffic
              Optimization (ALTO) Problem Statement", RFC 5693,
              DOI 10.17487/RFC5693, October 2009,

   [RFC6707]  Niven-Jenkins, B., Le Faucheur, F., and N. Bitar, "Content
              Distribution Network Interconnection (CDNI) Problem
              Statement", RFC 6707, DOI 10.17487/RFC6707, September
              2012, <>.

   [RFC6770]  Bertrand, G., Ed., Stephan, E., Burbridge, T., Eardley,
              P., Ma, K., and G. Watson, "Use Cases for Content Delivery
              Network Interconnection", RFC 6770, DOI 10.17487/RFC6770,
              November 2012, <>.

   [RFC7285]  Alimi, R., Ed., Penno, R., Ed., Yang, Y., Ed., Kiesel, S.,
              Previdi, S., Roome, W., Shalunov, S., and R. Woundy,
              "Application-Layer Traffic Optimization (ALTO) Protocol",
              RFC 7285, DOI 10.17487/RFC7285, September 2014,

   [RFC7336]  Peterson, L., Davie, B., and R. van Brandenburg, Ed.,
              "Framework for Content Distribution Network
              Interconnection (CDNI)", RFC 7336, DOI 10.17487/RFC7336,
              August 2014, <>.

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   [RFC7337]  Leung, K., Ed. and Y. Lee, Ed., "Content Distribution
              Network Interconnection (CDNI) Requirements", RFC 7337,
              DOI 10.17487/RFC7337, August 2014,

   [RFC8006]  Niven-Jenkins, B., Murray, R., Caulfield, M., and K. Ma,
              "Content Delivery Network Interconnection (CDNI)
              Metadata", RFC 8006, DOI 10.17487/RFC8006, December 2016,

   [RFC8008]  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, December 2016,

6.2.  Informative References

              Roome, W. and Y. Yang, "ALTO Incremental Updates Using
              Server-Sent Events (SSE)", draft-ietf-alto-incr-update-
              sse-07 (work in progress), July 2017.

              Niven-Jenkins, B., Watson, G., Bitar, N., Medved, J., and
              S. Previdi, "Use Cases for ALTO within CDNs", draft-
              jenkins-alto-cdn-use-cases-03 (work in progress), June

              Ma, K. and J. Seedorf, "CDNI Footprint & Capabilities
              Advertisement Interface", draft-ma-cdni-capabilities-09
              (work in progress), April 2016.

Authors' Addresses

   Jan Seedorf
   HFT Stuttgart - Univ. of Applied Sciences
   Schellingstrasse 24
   Stuttgart  70174

   Phone: +49-0711-8926-2801

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   Y.R. Yang
   Tongji/Yale University
   51 Prospect Street
   New Haven, CT  06511
   United States of America


   Kevin J. Ma
   43 Nagog Park
   Acton, MA  01720
   United States of America

   Phone: +1-978-844-5100

   Jon Peterson
   1800 Sutter St Suite 570
   Concord, CA  94520
   United States of America


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