A SLR (Service Level Requirements) based footprint for CDNI
draft-song-cdni-slr-based-footprint-01

CDNI                                                             H. Song
Internet-Draft                                                    Huawei
Intended status: Standards Track                                Y. Zhang
Expires: January 17, 2013                                   China Mobile
                                                           July 16, 2012

      A SLR (Service Level Requirements) based footprint for CDNI
                 draft-song-cdni-slr-based-footprint-01

Abstract

   Footprint advertisement is a very important step for CDN
   interconnection and generates a lot of discussion.  Actually, each
   CDN can serve the whole world if its surrogates are publicly
   reachable by IP addresses.  But if a CDN does that, it can not
   satisfy the requirements from the applications.  So CDNs deliver
   contents for applications, and the basic requirements should be from
   the applications, but there is rare discussion on service level
   requirements based footprint.  This document is used to generate the
   discussion on this aspect.

Status of this Memo

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   This Internet-Draft will expire on January 17, 2013.

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Table of Contents

   1.  Terminology . . . . . . . . . . . . . . . . . . . . . . . . . . 3
   2.  Why SLR Based Footprint . . . . . . . . . . . . . . . . . . . . 3
   3.  What are the Parameters for SLR . . . . . . . . . . . . . . . . 4
     3.1.  Average Response Time . . . . . . . . . . . . . . . . . . . 4
     3.2.  Throughput  . . . . . . . . . . . . . . . . . . . . . . . . 4
     3.3.  Startup Delay . . . . . . . . . . . . . . . . . . . . . . . 4
     3.4.  Average downloading rate  . . . . . . . . . . . . . . . . . 4
     3.5.  Hit Ratio . . . . . . . . . . . . . . . . . . . . . . . . . 5
     3.6.  Capability  . . . . . . . . . . . . . . . . . . . . . . . . 5
     3.7.  Up-time . . . . . . . . . . . . . . . . . . . . . . . . . . 5
     3.8.  Discussion  . . . . . . . . . . . . . . . . . . . . . . . . 5
   4.  Dynamic Mapping for Footprint . . . . . . . . . . . . . . . . . 5
   5.  Message Flows . . . . . . . . . . . . . . . . . . . . . . . . . 6
   6.  Security Considerations . . . . . . . . . . . . . . . . . . . . 6
   7.  IANA Considerations . . . . . . . . . . . . . . . . . . . . . . 6
   8.  Normative References  . . . . . . . . . . . . . . . . . . . . . 6
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . . . 7

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1.  Terminology

   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 [RFC2119].

2.  Why SLR Based Footprint

   Each CDN's footprint can be worldwide, if its surrogates' IP
   addresses are publicly reachable.  However, not every CDN can serve
   the applications for worldwide distribution because it can not
   satisfy the serverice level required by those applications.  So what
   an application basically needs is a CDN to satisfy its service level,
   and distribute the contents to certain areas.  If a CDN or together
   with its downstream CDNs, cannot meet the SLR (service level
   requirements) in an area from an application, then we can say this
   upstream CDN is not competent for this content distribution task.
   This document specifies how the parameters of SLR impact a CDN's
   footprint.  There is other draft [I-D.he-cdni-cap-info-advertising]
   mentioned capability advertisement, please note that capability
   advertisement is also very important and footprint is impacted by
   capability of a CDN.  While each CDN serve many tasks concurrently,
   the dynamic resources that it can allocate is also variable at
   different time.

   The physical deployment area of a CDN might be small, but it can have
   larger footprint area where it can satisfy an application's SLR.  The
   footprint area might be even larger than a CDN that has larger
   physical deployment area.  Choosing SLR as the basis for footprint
   can avoid some CDN magnifying its service level and service area on
   purpose, and also make some other "small" but powerful CDN be treated
   with justness.

   We think that applications should participate in the CDN
   interconnection process implicitly, i.e. its requirements for service
   level should be transmitted between upstream and downstream CNDs
   (message protection is required due to the privacy).  A downstream
   CDN should notify its capability information to its upstream CDN as
   well when notifying its footprint that satisfies certain SLR, which
   will allow a upstream CDN to choose multiple downstream CDN to
   fullfill a task even in a same area.

   From the application's perspective, a file downloading application
   may not care about when the user receive the first bit, but more care
   about the average downloading rate.  While a streaming application
   may have different opinion.  So for a same CDN, it can serve the file
   downloading application well with one wide footprint and serve

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   streaming application well with another smaller footprint.

   In general, service level is the main driver for the definition of
   footprint, and applications do not care about the locations where a
   CDN's surrogates are deployed while it can satisfy its service
   requirements.  And topologically, ALTO [I-D.ietf-alto-protocol] is
   used for the appropriate surrogate selection after the footprints are
   defined.  And ALTO network map information can also be used for the
   footprint description to upstream CDN .

3.  What are the Parameters for SLR

   The general principal for SLR is fast, scalable, secure and reliable.
   But it needs detailed measurement metrics for it.  Here we put the
   capability requirements as one parameter for SLR, as one upstream CDN
   can choose multiple downstream CDNs to satisfy an customer
   application's requirements.  This section lists the possible
   parameters for SLR.  However, this document is not going to define
   the specifics for the measurement methods.

3.1.  Average Response Time

   This value is to refelct the average response time in normal network
   condition.  This value impacts the footprint a lot.

3.2.  Throughput

   This parameter will also impact the footprint.  If a CDN's available
   throughput is very big then it can serve more than its deployment
   area.

3.3.  Startup Delay

   This parameter is a very important metric for the streaming media
   delivery.  As a TCP connection throughput close to MTU/RTT.  Long
   distance transport maybe mean smaller MTU and longer RTT, as well as
   more packet lost rate, which will result in a low rate data
   transport, and in consequence long startup delay.

3.4.  Average downloading rate

   Application usually needs the CDN to gurantee a certain downloading
   rate for a certain service.  More discussion is needed on this
   parameter and how it impacts footprint.

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3.5.  Hit Ratio

   This parameter is about the content availability.  High hit ratio
   means more local service and low burden on original servers.  This
   parameter is more related to the CDN's optimization policies than to
   the footprint.

3.6.  Capability

   Please refer other documents for the CDN capability advertisement in
   CDNI WG.

3.7.  Up-time

   Uptime is a measure of the time a machine has been up without any
   downtime.  For a CDN system, it usually needs to guarantee a 100% up-
   time for system (not for each host).

3.8.  Discussion

   Not all parameters required for a certain service level are listed.
   More discussion is needed.  Some parameters might impact a CDN's
   footprint, and some will not.  Should all of them or just a portion
   that affect the footprint be conveyed in the same way among CDNs?

4.  Dynamic Mapping for Footprint

   Each CDN participate in the CDN interconnection network should
   maintain a map between the SLR parameters and its footprint.  There
   are choices to exchange the map information.

   (1) An application's SLR is directly sent from upstream CDN to the
   downstream CDN.  So that downstream CDN can report its footprint to
   upstream CDN accordingly.  The downstream CDN should guarantee it
   satisfies the SLR for users in its reported footprint.  Although this
   method requires message exchange for each application, but it is
   simple to implement.

   (2) Each CDN report its mapping between SLR parameters and footprint
   to upstream CDN.  And the upstream CDN will make the final decision
   on the downstream CDN's footprint according to a specific
   application's SLR.  This method reduces the messge exchanges but the
   map itself might be very complicated, due to various combination of
   these parameter values exist.

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5.  Message Flows

   TBD.

6.  Security Considerations

   These security issues are open for discussion:

   (1) Applications might take its service level requrements as a
   confidential?  Although it can be a confidential to users, but it can
   be protected without leaking to any third party that is not involved
   in the CDN interconnection?

   (2) CDNs might take its footprint according to SLR as confidential?

   (3) Footprint cheating.  A CDN may cheat with its footprint.  If the
   behavior is disovered, the application cannot get the service level
   in that announced footprint, punishment policies should be applied to
   the CDN provider.

7.  IANA Considerations

   There is no IANA consideration for this document.

8.  Normative References

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

   [I-D.he-cdni-cap-info-advertising]
              He, X., Dawkins, S., Chen, G., Zhang, Y., and W. Ni,
              "Capability Information Advertising for CDN
              Interconnection", draft-he-cdni-cap-info-advertising-01
              (work in progress), March 2012.

   [I-D.seedorf-cdni-request-routing-alto]
              Seedorf, J., "CDNI Request Routing with ALTO",
              draft-seedorf-cdni-request-routing-alto-01 (work in
              progress), March 2012.

   [I-D.ietf-alto-protocol]
              Alimi, R., Penno, R., and Y. Yang, "ALTO Protocol",
              draft-ietf-alto-protocol-12 (work in progress), July 2012.

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Authors' Addresses

   Haibin Song
   Huawei

   Email: haibin.song@huawei.com

   Yunfei Zhang
   China Mobile

   Email: zhangyunfei@chinamobile.com

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