RFC 2269 (rfc2269) - Page 2 of 6

Using the MARS Model in non-ATM NBMA Networks

RFC 2269          MARS Model in non-ATM NBMA Networks       January 1998


2.  RFC 2022's basic assumptions.

   Section 3 of [2] describes the basic assumptions that the MARS model
   makes about the services available from the link layer network (using
   ATM as the specific case).  In summary these are:

      The ATM model broadly describes an 'AAL User' as any entity that
      establishes and manages VCs and underlying AAL services to
      exchange data.  An IP over ATM interface is a form of 'AAL User'

      The most fundamental limitations of UNI 3.0/3.1's multicast
      support are:

         Only point to multipoint, unidirectional VCs may be
         established.

         Only the root (source) node of a given VC may add or remove
         leaf nodes.

      Leaf nodes are identified by their unicast ATM addresses.

   Given this point to multipoint call service, the MARS document goes
   on to describe two architectures for emulating multipoint to
   multipoint IP multicasting - the VC Mesh, and the Multicast Server.
   In either case it was assumed that IP/ATM interfaces (whether in
   routers or hosts) are allowed to originate and manage outgoing point
   to multipoint calls without network operator intervention or manual
   provisioning.

   The MARS document also specifies that AAL5 be used for all SVCs,
   implying a requirement that the underlying link service supports the
   atomic exchange of PDUs.

3.  Generalising the MARS model.

   Any NBMA service that offers an equivalent to (or superset of) the
   ATM point to multipoint call service can use the MARS model directly.
   It must be possible to transmit atomic data units bi-directionally
   with point to point calls, and unidirectionally (from root to leaves)
   on point to multipoint calls.

   A MARS is an entity known by its NBMA address.

   A MARS Client is an entity known by its NBMA address.

   An MCS (where needed) is an entity known by its NBMA address.





Armitage                     Informational