Separating Abstraction from Implementation
                 in Communication Network Design


                          Ramon Caceres
                    Computer Science Division
                    University of California
                       Berkeley, CA 94720


                            ABSTRACT

Datagrams and virtual circuits are not disjoint conceptual models
for  data  communication, but rather inhabitants of a wide design
space containing many other viable  networking  solutions.   Many
design choices often closely associated with these two communica-
tion styles can be decoupled from the datagram and  virtual  cir-
cuit abstractions, and combined to form new and effective network
implementations.  This paper examines  several  key  elements  of
network  architecture.   For  each  element, it shows how certain
characteristics often thought to differentiate datagrams and vir-
tual  circuits  are  independent of these two concepts and form a
multi-valued spectrum of  design  choices.   This  discussion  is
motivated  by  the  current  drive  to design a new generation of
high-speed wide-area networks, and the observation that this  ef-
fort  would benefit from a more systematic evaluation of existing
and future network design.