RFC 1241 (rfc1241) - Page 2 of 17

Scheme for an internet encapsulation protocol: Version 1

RFC 1241                 Internet Encapsulation                July 1991


     to a Decapsulator.

   Encapsulation Header -
     The header for the Encapsulation Protocol prepended to the
     Clear Datagram during Encapsulation.  This header consists
     of an IP header followed by an Encapsulation Protocol
     Header.

   Encapsulation Protocol Header -
     The Encapsulation Protocol specific portion of the
     Encapsulation Header.

   Encapsulation Space -
     The address and routing space within which the
     Encapsulators and Decapsulators reside.  Routing within
     this space is accomplished via Flows.  Encapsulation
     Spaces do not overlap, that is, the address of any
     Encapsulator or Decapsulator is unique for all
     Encapsulation Spaces.

   Encapsulator -
     The entity responsible for mapping a given User Space
     datagram to the Encapsulation Space, encapsulating the
     datagram, and forwarding the Encapsulated Datagram to a
     Decapsulator.  An Encapsulator may be a host or a gateway.

   Flow -
     Also called a "tunnel."  A flow is the end-to-end path in
     the Encapsulation Space over which Encapsulated Datagrams
     travel.  There may be several Encapsulator/Decapsulator
     pairs along a given flow.  Note that a Flow does not
     denote what User Space gateways are traversed along the
     path.

   Flow ID -
     A 32-bit identifier which uniquely distinguishes a flow in
     a given Encapsulator or Decapsulator.  Flow IDs are
     specific to a single Encapsulator/Decapsulator Entity and
     are not global quantities.

   Mapping Function -
     This is the function of mapping a Clear Header to a
     particular Flow.  All encapsulators along a given Flow are
     required to map a given Clear Header to the same Flow.

   User Address -
     The address or identifier uniquely identifying an entity
     within a User Space.



Woodburn & Mills