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DECADE                                                          P. Zhang
Internet-Draft                                               Mar 5, 2012
Intended status: Informational
Expires: September 6, 2012


                     Comparison of DECADE with CDNi
                 draft-zhang-decade-cdni-comparison-00

Abstract

   This document gives a brief comparison of DECADE and CDNi, two
   working groups on content delivery.  CDNi aims at overcoming the
   limited resource and footprints of a single CDN by interconnecting
   multiple CDNs.  While DECADE is mainly concerned with reducing the
   last-mile bandwidth bottleneck and inter-domain traffics with in-
   network storage.  This in-network storage can also be utilized by
   Content Service Providers (CSPs) as a CDN, whose footprints be across
   multiple Internet Service Providers (CSPs).  In this sense, DECADE
   can also be a possible approach to overcome the limited footprints of
   a single CDN.  This document attempts to gain some understanding on
   the relationship of these two solutions.

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
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   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
   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 September 6, 2012.

Copyright Notice

   Copyright (c) 2012 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



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   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
     1.1.  Concepts  . . . . . . . . . . . . . . . . . . . . . . . . . 3
       1.1.1.  Content Service Provider (CSP)  . . . . . . . . . . . . 3
       1.1.2.  DECADE server . . . . . . . . . . . . . . . . . . . . . 3
       1.1.3.  DECADE portal . . . . . . . . . . . . . . . . . . . . . 3
   2.  DECADE as a CDN across mutliple ISPs  . . . . . . . . . . . . . 4
   3.  Comparison of DECADE with CDNi  . . . . . . . . . . . . . . . . 5
     3.1.  Deployment complexity and cost  . . . . . . . . . . . . . . 6
     3.2.  Support of individual users . . . . . . . . . . . . . . . . 6
     3.3.  Support of P2P mode . . . . . . . . . . . . . . . . . . . . 6
   4.  Security Considerations . . . . . . . . . . . . . . . . . . . . 7
   5.  IANA Considerations . . . . . . . . . . . . . . . . . . . . . . 7
   6.  Normative References  . . . . . . . . . . . . . . . . . . . . . 7
   Author's Address  . . . . . . . . . . . . . . . . . . . . . . . . . 7



























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1.  Introduction

   Content Delivery Networks (CDNs) are widely utilized to deliver
   videos, voices, and other content generated by Content Service
   Providers (CSPs) to end users.  However, a single CDN is mostly
   constrained in geographical coverage and resource volume, and the
   CDNi working group is aimed at interconnecting standalone CDNs so
   that their geographic coverage and resources can be aggregated.

   On the other hand, DECADE working group is aimed at introducing in-
   network storage to alleviate last-mile bandwidth bottleneck, as well
   as reduce inter-domain traffics.  Seemingly the goals of DECADE and
   CDNi are orthogonal, but actually the in-network storage of DECADE
   can be leveraged by CSPs to deliver their content in a similar way as
   using a CDN.  For example, after an ISP have deployed DECADE servers
   its network, a CSP can send their content to the DECADE Portal
   provided by the ISP, which will distribute the content to DECADE
   servers in multiple locations.  When a content request the content
   from CSP, it is directed to the DECADE portal, which then select a
   DECADE server that is optimal for them.  In this way, DECADE provides
   a similar service like CDN in a single ISP.  In the next section, we
   will show how DECADE can be used as a CDN across multiple ISPs.

   To this end, we are interested in comparing DECADE with CDNi as
   another possible approach to overcome the geographical coverage
   limitation of standalone CDNs.

1.1.  Concepts

1.1.1.  Content Service Provider (CSP)

   A content service provider leverages CDNs to delivery their content
   to content customers over Internet.

1.1.2.  DECADE server

   A DECADE server is implemented with DECADE protocols, management
   mechanism and storage strategies.  It is an important element to
   provide DECADE services.  In a DECADE server, we have a number of
   Data Lockers each of which is a virtual account and private STORAGE
   space for applications.

1.1.3.  DECADE portal

   A DECADE portal offers CSPs a portal site for file upload.  It also
   uses ALTO service to direct end users to an optimal DECADE Server to
   download files.




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2.  DECADE as a CDN across mutliple ISPs

   The DECADE integration example document illustrates how to construct
   a file distribution platform based on the DECADE+ALTO architecture.
   In that document, DECADE is deployed in a single ISP, and CSPs can
   use DECADE as a distribution platform or CDN in within this ISP.  In
   the following, we illustrate how this example can be extended to the
   multiple-ISP scenarios, in which DECADE servers owned by multiple
   ISPs can be leveraged to deliver content for CSPs.

   For simplicity of illustration, let us take two ISPs for example.  A
   CSP register at ISP-1 and upload the file to the DECADE portal of
   ISP-1, which then distributes the file to multiple DECADE servers.  A
   client in ISP-2 requests the file from the CSP, and is redirected to
   the DECADE portal in ISP-1, which recognizes that the request is from
   a client in ISP-2.  Then, it redirects the request to the optimal
   DECADE server (DECADE server B) at ISP-2 using information provided
   by ALTO service.  If server B has the file cached in its memory, then
   it sends the file directly to the user.  Otherwise, server B will
   send a request to the DECADE portal of ISP-1.  Recognizing this
   request is from a DECADE server, it is redirected to the optimal
   server DECADE server A in ISP-1.  Then A sends the file to B, which
   will cache the file and send it to the client that requested the
   file.

   The detailed communication diagram is as follow, and we omit the
   interaction of DECADE-1 portal with ALTO servers for limited space.
























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   _________     ____________     __________     __________     __________
  |         |   |Publisher's |   | DECADE-1 |   | DECADE   |   | DECADE   |
  | Client  |   |   Portal   |   | Portal   |   | Server A |   | Server B |
  |_________|   |____________|   |__________|   |__________|   |__________|
      |              |                |             |               |
      |Download Req  |                |             |               |
      |------------->|                |             |               |
      | URLs&Tokens  |                |             |               |
      |<-------------|                |             |               |
      |              |                |             |               |
      |    Download Require(Tokens)   |             |               |
      |------------------------------>|             |               |
      |              |                |             |               |
      | addree of the optimal server  |             |               |
      | in ISP-2                      |             |               |
      |<------------------------------|             |               |
      |              |                |             |               |
      |              |       Get Data (Tokens)      |               |
      |------------------------------------------------------------>|
      |              |                |             |               |
      |              |                |  Download Require(Tokens)   |
      |              |                |<----------------------------|
      |              |                |             |               |
      |              |                | addree of the optimal       |
      |              |                | server in ISP-1             |
      |              |                |---------------------------->|
      |              |                |             |   Get Data    |
      |              |                |             |   (Tokens)    |
      |              |                |             |<--------------|
      |              |                |             |   Send Data   |
      |              |                |             |-------------->|
      |              |    Send Data   |             |               |
      |<------------------------------------------------------------|





   An example of distribution platform of DECADE across two ISPs

                                 Figure 1


3.  Comparison of DECADE with CDNi

   In this section, we take DECADE as another possible solution to the
   limited coverage problem of standalone CDNs, and try to compare it to
   the CDNi solution.



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   Before comparisons, we should note the similarity and relation
   between DECADE and CDNi.  First, note that these two solutions can
   both benefit from using ALTO as a service to make decisions.  In
   DECADE, ALTO helps DECADE portal to decide which is the best server
   for a specific end users; In CDNi, a CDN can use ALTO to decide to
   which CDN it should redirect a client's requests.  Secondly, as
   outlined in the requirement document of CDNi, DECADE can be used by
   CDNi for control message exchanges, acquisition of content objects
   between different CDNs, and for content delivery within a given CDN.
   But the benefits of using DECADE in CDNi are rather limited.

3.1.  Deployment complexity and cost

   Since DECADE provides a open standard for in-network storage
   architecture, ISPs can easily deploy their own DECADE servers in
   their networks.  Moreover, it is more likely that ISP can deploy
   their storage servers more widely and closer to end users in their
   networks than third-party CDN providers can.  When multiple ISPs have
   deployed their DECADE storage systems, a CSP can just subscribe the
   DECADE service provided by one ISP, and can distribute its content to
   DECADE servers across these multiple ISPs, as shown in the example in
   the last section.  The possible requirement may be there should be a
   charging model so that ISPs can charge each other on the DECADE
   storage consumption incurred by delivering content generated by CSPs
   in other ISPs.  Since ISPs have already initiated contracts with each
   other, this model can be built just like traffic charging model.
   Moreover, no request routing interface is needed by DECADE.  The
   downside is that ISPs should deploy DECADE servers, and for ISPs that
   have no DECADE service, their users can be outside of coverage.
   While using CDNi, existing CDNs can be leveraged without the need to
   deploy new servers.  This implies a lower deployment cost.

3.2.  Support of individual users

   Apart from providing service to large CSPs, DECADE can also provide
   services to personal users.  For example, a user can register at a
   nearby DECADE server deployed by the ISP she subscribes to.  Using
   this DECADE server, it is possible for her to stream videos or voices
   to her friends, despite the uplink link bandwidth constraint.  On the
   other hand, most CDNs are CSP oriented and not practical for
   individual end users.  This will also be true for CDNi, which is a
   interconnection of CDNs.

3.3.  Support of P2P mode

   Since DECADE service can be open to end users, CSPs can also
   distribute their content using P2P. Under this mode, end users will
   upload and download chunks of a file to and from the DECADE server



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   they are connected to.  By using P2P, CSPs can reduce the cost of
   employing DECADE services provided by ISPs.  But it is more likely
   that CSPs still use DECADE services to distribute content, but can
   use P2P simultaneously to reduce cost.


4.  Security Considerations

   This document does not contain any security considerations.


5.  IANA Considerations

   This document does not have any IANA considerations.


6.  Normative References

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119, March 1997.


Author's Address

   Peng Zhang

   Email: pzhang.thu@gmail.com
























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