Subject: [sfc] Dataplane Metadata vs. Shared Metadata

From: Guanxiaoran <[email-masked]>
Date: Tue, 13 May 2014 08:32:14 +0000

Hi,
I found there're different usage definitions of the metadata. I've copied these below for your convenience.
Could anyone explain what's the difference between them? Or is there any possible new explanation of the metadata?
Thanks,
Ran

From: draft-quinn-sfc-arch-05.txt
4.7.  Shared Metadata

   Sharing metadata allows the network to provide network-derived
   information to the SFs, SF-to-SF information exchange and the sharing
   of service-derived information to the network.  This component is
   optional.  SFC infrastructure enables the exchange of this shared
   data along the SFP.  The shared metadata serves several possible
   roles within the SFC architecture:

   o  Allows elements that typically operate as ships-in-the-night to
      exchange information.

   o  Encodes information about the network and/or data for post-
      service forwarding.

   o  Creates an identifier used for policy binding by SFs.

   o  Context information can be derived in several ways:

      *  External sources

      *  Network node classification

      *  Service function classification

From: draft-ietf-sfc-problem-statement-05.txt
3.4.  Dataplane Metadata

   Data plane metadata provides the ability to exchange information
   between logical classification points and service functions (and vice
   versa) and between service functions.  As such metadata is not used
   as forwarding information to deliver packets along the service
   overlay.

   Metadata can include the result of antecedent classification and/or
   information from external sources.  Service functions utilize
   metadata, as required, for localized policy decisions.

   In addition to sharing of information, the use of metadata addresses
   several of the issues raised in section 2, most notably the de-
   coupling of policy from the topology, and the need for per-service
   classification (and re-classification).

   A common approach to service metadata creates a common foundation for
   interoperability between service functions, regardless of vendor.