An Abstract API for Multicast Address Allocation
RFC 2771

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Network Working Group                                     R. Finlayson
Request for Comments: 2771                                    LIVE.COM
Category: Informational                                  February 2000

            An Abstract API for Multicast Address Allocation

Status of this Memo

   This memo provides information for the Internet community.  It does
   not specify an Internet standard of any kind.  Distribution of this
   memo is unlimited.

Copyright Notice

   Copyright (C) The Internet Society (2000).  All Rights Reserved.

Abstract

   This document describes the "abstract service interface" for the
   dynamic multicast address allocation service, as seen by
   applications.  While it does not describe a concrete API (i.e., for a
   specific programming language), it describes - in abstract terms -
   the semantics of this service, including the guarantees that it makes
   to applications.

   Additional documents (not necessarily products of the IETF) would
   describe concrete APIs for this service.

1. Introduction

   Applications are the customers of a multicast address allocation
   service, so a definition of this service should include not only the
   inter-node network protocols that are used to implement it, but also
   the 'protocol' that applications use to access the service.  While
   APIs ("application programming interfaces") for specific programming
   languages (or operating systems) are outside the domain of the IETF,
   it is appropriate for us to define - in abstract terms - the semantic
   interface that this service presents to applications.  Specific APIs
   would then be based upon this abstract service interface.

   Note that it is possible to implement the multicast address
   allocation service in at least two different ways.  The first (and
   perhaps most common) way is for end nodes to allocate addresses by
   communicating with a separate "Address Allocation Server" node, using
   the "Host to Address Allocation Server" network protocol (MADCAP)
   [1][7].  Alternatively, an "Address Allocation Server" implementation

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RFC 2771     Abstract API for Multicast Address Allocation February 2000

   might be co-located (along with one or more applications) on an end
   node, in which case some other, internal, mechanism might be used to
   access the server.  In either case, however, the abstract service
   interface (and, presumably, any specific APIs) would remain the same.

   The remainder of this document describes the abstract interface.

   Note that this interface is intended only for the allocation of
   dynamic multicast addresses, as used by the traditional multicast
   service model [2].  Future multicast service models might allocate or
   assign multicast addresses in other ways, but this is outside the
   scope of this document.

2. Abstract Data Types

   The interface described below uses the following abstract data types:

   -  AddressFamily: e.g., IPv4 or IPv6

   -  MulticastAddress: An actual multicast address (i.e., that could
      subsequently be used as the destination of a datagram)

   -  MulticastAddressSet: A set of "MulticastAddress"es

   -  LanguageTag: The code for a (human) language, as defined in [4]

   -  Scope: An "administrative scope" [3] from which multicast
             addresses are to be allocated.  Each scope is a
             "MulticastAddressSet", with an associated set of
             (character-string) names - indexed by "LanguageTag".  (Each
             language tag has at most one corresponding name, per
             scope.)  For each scope, a (language tag, name) pair may be
             defined to be the 'default' name for this scope. (See the
             section "Querying the name of a scope" below.)

             (An implementation of this abstract data type might also
             include other information, such as a default TTL for the
             scope.)

   -  Time: An (absolute) event time.  This is used for specifying the
            "lifetime" of multicast addresses: the period of time during
            which allocated multicast addresses are guaranteed to be
            available.  (It is also used to specify the desired start
            time for an "advance allocation".)

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RFC 2771     Abstract API for Multicast Address Allocation February 2000

            Note that a concrete API might prefer to specify some of
            these times as relative times (i.e., relative to the current
            time-of-day), rather than absolute time.  (Relative times
            have the advantage of not requiring clock synchronization.)

   -  Lease: A compound data type that describes the result of a
             (successful) multicast address allocation.  It consists of:

             -  [MulticastAddressSet] The set of addresses that were